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Sample records for cdse colloidal quantum

  1. Enhanced random lasing from a colloidal CdSe quantum dot-Rh6G system

    NASA Astrophysics Data System (ADS)

    Augustine, Anju K.; Radhakrishnan, P.; Nampoori, V. P. N.; Kailasnath, M.

    2015-02-01

    In this letter, we report random laser action in a system where optical amplification is provided by colloidal CdSe quantum dots (CQDs) triggered by the emission from Rhodamine 6G. The laser emission from CdSe QDs is optically excited by Rh-6G which in turn is photo-pumped by a frequency-doubled Q-switched Nd : YAG laser system at an excitation wavelength of 532 nm. At intensities greater than the threshold value, laser emission is characterized by narrowing peaks.

  2. Selenium Redox Reactivity on Colloidal CdSe Quantum Dot Surfaces

    PubMed Central

    2016-01-01

    Understanding the structural and compositional origins of midgap states in semiconductor nanocrystals is a longstanding challenge in nanoscience. Here, we report a broad variety of reagents useful for photochemical reduction of colloidal CdSe quantum dots, and we establish that these reactions proceed via a dark surface prereduction step prior to photoexcitation. Mechanistic studies relying on the specific properties of various reductants lead to the proposal that this surface prereduction occurs at oxidized surface selenium sites. These results demonstrate the use of small-molecule inorganic chemistries to control the physical properties of colloidal QDs and provide microscopic insights into the identities and reactivities of their localized surface species. PMID:27518320

  3. Selenium Redox Reactivity on Colloidal CdSe Quantum Dot Surfaces.

    PubMed

    Tsui, Emily Y; Hartstein, Kimberly H; Gamelin, Daniel R

    2016-09-01

    Understanding the structural and compositional origins of midgap states in semiconductor nanocrystals is a longstanding challenge in nanoscience. Here, we report a broad variety of reagents useful for photochemical reduction of colloidal CdSe quantum dots, and we establish that these reactions proceed via a dark surface prereduction step prior to photoexcitation. Mechanistic studies relying on the specific properties of various reductants lead to the proposal that this surface prereduction occurs at oxidized surface selenium sites. These results demonstrate the use of small-molecule inorganic chemistries to control the physical properties of colloidal QDs and provide microscopic insights into the identities and reactivities of their localized surface species. PMID:27518320

  4. Charge carrier transport in thin films of colloidal CdSe quantum rods

    NASA Astrophysics Data System (ADS)

    Persano, A.; Leo, G.; Manna, L.; Cola, A.

    2008-10-01

    Phototransport properties of organically capped colloidal CdSe quantum rod thin films deposited by spin coating are studied in air at room temperature in planar electrode configuration. Under optical excitation, the observed current-voltage characteristics and current transients are well described by a resonant tunneling model. A significant and irreversible current quenching of the photoresponse occurs with either the aging of the samples or the flowing of the current itself when above few picoamperes. The process, which is still interpreted in the frame of the model, can be attributed to the charge trapping by the defect states at the barrier between rods with a consequent increase in the barrier height.

  5. Mid-Infrared Photoluminescence of CdS and CdSe Colloidal Quantum Dots.

    PubMed

    Jeong, Kwang Seob; Guyot-Sionnest, Philippe

    2016-02-23

    Mid-infrared intraband photoluminescence is observed from CdSe and CdS colloidal quantum dots (CQDs) and core/shell systems when excited by a visible laser. The CQDs show more intraband photoluminescence with dodecanethiol than with other ligands. Core/shells show an increase of the intraband photoluminescence with increasing shell thickness. The detected emission is restricted to below 2900 cm(-1), bounded by the C-H vibrational modes of the organic ligands. Upon photoexcitation in air for all dodecanethiol ligands capped CQD systems studied, the intraband photoluminescence is quenched over time, and emission at lower frequency is observed, which is assigned to laser heating and thermal emission from oxides. PMID:26799582

  6. Measuring photoluminescence spectra of self-assembly array nanowire of colloidal CdSe quantum dots using scanning near-field optics microscopy

    NASA Astrophysics Data System (ADS)

    Bai, Zhongchen; Hao, Licai; Zhang, Zhengping; Qin, Shuijie

    2016-05-01

    A novel periodic array CdSe nanowire is prepared on a substrate of the porous titanium dioxide by using a self-assembly method of the colloidal CdSe quantum dots (QDs). The experimental results show that the colloidal CdSe QDs have renewedly assembled on its space scale and direction in process of losing background solvent and form the periodic array nanowire. The main peak wavelength of Photoluminescence (PL) spectra, which is measured by using a 100-nm aperture laser beam spot on a scanning near-field optics microscopy, has shifted 60 nm with compared to the colloidal CdSe QDs. Furthermore, we have measured smaller ordered nanometer structure in thin QDs area as well, a 343-nm periodic nanowire in thick QDs area and the colloidal QDs in edge of well-ordered nanowire.

  7. A mirage study of CdSe colloidal quantum dot films, Urbach tail, and surface states

    NASA Astrophysics Data System (ADS)

    Guyot-Sionnest, Philippe; Lhuillier, Emmanuel; Liu, Heng

    2012-10-01

    Thermal deflection spectroscopy allows to measure very small absorption and uncovers absorption tails extending well below the bulk bandgap energy for CdSe quantum dots films after ligand exchange by sulfide. In this monodispersed system, the redshift, the broadening, and the absorption tails cannot be solely attributed to electronic coupling between the dots. Instead, mixing of hole states from the quantum dot and surface is proposed to dominate the changes of the interband spectra at the absorption edge.

  8. A mirage study of CdSe colloidal quantum dot films, Urbach tail, and surface states.

    PubMed

    Guyot-Sionnest, Philippe; Lhuillier, Emmanuel; Liu, Heng

    2012-10-21

    Thermal deflection spectroscopy allows to measure very small absorption and uncovers absorption tails extending well below the bulk bandgap energy for CdSe quantum dots films after ligand exchange by sulfide. In this monodispersed system, the redshift, the broadening, and the absorption tails cannot be solely attributed to electronic coupling between the dots. Instead, mixing of hole states from the quantum dot and surface is proposed to dominate the changes of the interband spectra at the absorption edge. PMID:23083181

  9. Direct Observation of sp-d Exchange Interactions in Colloidal Mn2+- and Co2+-Doped CdSe Quantum Dots

    SciTech Connect

    Archer, Paul I.; Santangelo, Steven A.; Gamelin, Daniel R.

    2007-03-23

    The defining attribute of a diluted magnetic semiconductor (DMS) is the existence of dopant-carrier magnetic exchange interactions. In this letter, we report the first direct observation of such exchange interactions in colloidal doped CdSe nanocrystals. Doped CdSe quantum dots were synthesized by thermal decomposition of (Me4N)2[Cd4(SePh)10] in the presence of TMCl2 (TM2+ ) Mn2+ or Co2+) in hexadecylamine and were characterized by several analytical and spectroscopic techniques. Using magnetic circular dichroism spectroscopy, successful doping and the existence of giant excitonic Zeeman splittings in both Mn2+- and Co2+-doped wurtzite CdSe quantum dots are demonstrated unambiguously.

  10. Photochemical electronic doping of colloidal CdSe nanocrystals.

    PubMed

    Rinehart, Jeffrey D; Schimpf, Alina M; Weaver, Amanda L; Cohn, Alicia W; Gamelin, Daniel R

    2013-12-18

    A method for electronic doping of colloidal CdSe nanocrystals (NCs) is reported. Anaerobic photoexcitation of CdSe NCs in the presence of a borohydride hole quencher, Li[Et3BH], yields colloidal n-type CdSe NCs possessing extra conduction-band electrons compensated by cations deposited by the hydride hole quencher. The photodoped NCs possess excellent optical quality and display the key spectroscopic signatures associated with NC n-doping, including a bleach at the absorption edge, appearance of a new IR absorption band, and Auger quenching of the excitonic photoluminescence. Although stable under anaerobic conditions, these spectroscopic changes are all reversed completely upon exposure of the n-doped NCs to air. Chemical titration of the added electrons confirms previous correlations between absorption bleach and electron accumulation and provides a means of quantifying the extent of electron trapping in some NCs. The generality of this photodoping method is demonstrated by initial results on colloidal CdE (E = S, Te) NCs as well as on CdSe quantum dot films. PMID:24289732

  11. Self-assembly of CdSe quantum dots and colloidal titanium dioxide on copolymer microspheres (PS) for CdSe/PS and TiO2/CdSe/PS sub-microspheres with yolk-shell structure

    NASA Astrophysics Data System (ADS)

    Zhao, Qingchun

    2015-07-01

    Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, chemical/biological sensors, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in nanostructures. In this paper, relying on the interaction including van der Waals forces and hydrogen bond, CdSe/PS sub-microspheres composite and TiO2/CdSe/PS sub-microspheres with yolk-shell structure were prepared via self-assembly of CdSe quantum dots and colloidal titanium dioxide on modified PS surface. The morphology, structure and composition obtained products were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy disperse X-ray spectroscopy (EDX). Transmission electron microscopy (TEM) investigations show the CdSe quantum dots and colloidal titanate were assembled on the surface of PS sub-microspheres. CdSe QD-polymer sub-microspheres composites in which the QDs retain their original emission efficiency can be obtained. TiO2/CdSe/PS sub-microspheres with yolk-shell structure can improve the efficiency of charge separation.

  12. Spontaneous emission enhancement of colloidal CdSe nanoplatelets

    NASA Astrophysics Data System (ADS)

    Yang, Zhili; Pelton, Matthew; Waks, Edo

    Colloidal CdS /CdSe/CdS nanoplatelets synthesized recently are high efficient nano-emitters and gain media for nanoscale lasers and other nonlinear optical devices. They are characterized as quantum well structure due to energy gap difference between core CdSe and shell CdS, of which the luminescent wavelength could be tuned precisely by their thickness of growth. However, the influence of environment on the material's optical properties and further enhancement of the emission to implement nanoscale systems remains to be investigated. Here we demonstrate spontaneous emission rate enhancement of these CdSe nanoplatelets coupled to a photonic crystal cavity. We show clearly the photoluminescent spectrum modification of the nanoplatelets emission and an averaged Purcell enhancement factor of 3.1 is achieved when they are coupled to carefully-designed nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our experiment of lifetime measurement. Also the phenomenon of cavity quality factor increasing is observed when increasing intensity of pumping, which attributes to saturable absorption of the nanoplatelets. Our success in enhancement of emission from these nanoplatelets here paves the road to realize actual nanoscale integrated systems such as ultra-low threshold micro-cavity lasers.

  13. Red, Yellow, Green, and Blue Amplified Spontaneous Emission and Lasing Using Colloidal CdSe Nanoplatelets.

    PubMed

    She, Chunxing; Fedin, Igor; Dolzhnikov, Dmitriy S; Dahlberg, Peter D; Engel, Gregory S; Schaller, Richard D; Talapin, Dmitri V

    2015-10-27

    There have been multiple demonstrations of amplified spontaneous emission (ASE) and lasing using colloidal semiconductor nanocrystals. However, it has been proven difficult to achieve low thresholds suitable for practical use of nanocrystals as gain media. Low-threshold blue ASE and lasing from nanocrystals is an even more challenging task. Here, we show that colloidal nanoplatelets (NPLs) with electronic structure of quantum wells can produce ASE in the red, yellow, green, and blue regions of the visible spectrum with low thresholds and high gains. In particular, for blue-emitting NPLs, the ASE threshold is 50 μJ/cm(2), lower than any reported value for nanocrystals. We then demonstrate red, yellow, green, and blue lasing using NPLs with different thicknesses. We find that the lateral size of NPLs does not show any strong effect on the Auger recombination rates and, correspondingly, on the ASE threshold or gain saturation. This observation highlights the qualitative difference of multiexciton dynamics in CdSe NPLs and other quantum-confined CdSe materials, such as quantum dots and rods. Our measurements of the gain bandwidth and gain lifetime further support the prospects of colloidal NPLs as solution-processed optical gain materials. PMID:26302368

  14. Fluorescence relaxation dynamics of CdSe and CdSe/CdS core/shell quantum dots

    SciTech Connect

    Kaur, Gurvir; Kaur, Harmandeep; Tripathi, S. K.

    2014-04-24

    Time-resolved fluorescence spectra for colloidal CdSe and CdSe/CdS core/shell quantum dots have been investigated to know their electron relaxation dynamics at the maximum steady state fluorescence intensity. CdSe core and CdSe/CdS type I core-shell materials with different shell (CdS) thicknesses have been synthesized using mercaptoacetic acid as a capping agent. Steady state absorption and emission studies confirmed successful synthesis of CdSe and CdSe/CdS core-shell quantum dots. The fluorescence shows a tri-exponential decay with lifetimes 57.39, 7.82 and 0.96 ns for CdSe quantum dots. The lifetime of each recombination decreased with growth of CdS shell over the CdSe core, with maximum contribution to fluorescence by the fastest transition.

  15. Temporary Charge Carrier Separation Dominates the Photoluminescence Decay Dynamics of Colloidal CdSe Nanoplatelets.

    PubMed

    Rabouw, Freddy T; van der Bok, Johanna C; Spinicelli, Piernicola; Mahler, Benoît; Nasilowski, Michel; Pedetti, Silvia; Dubertret, Benoît; Vanmaekelbergh, Daniël

    2016-03-01

    Luminescent colloidal CdSe nanoplatelets with atomically defined thicknesses have recently been developed, and their potential for various applications has been shown. To understand their special properties, experiments have until now focused on the relatively short time scales of at most a few nanoseconds. Here, we measure the photoluminescence decay dynamics of colloidal nanoplatelets on time scales up to tens of microseconds. The excited state dynamics are found to be dominated by the slow (∼μs) dynamics of temporary exciton storage in a charge-separated state, previously overlooked. We study the processes of charge carrier separation and exciton recovery in pure CdSe nanoplatelets as well as in core-crown and core-shell CdSe/CdS nanoplatelets with high ensemble quantum yields of 50%, and discuss the implications. Our work highlights the importance of reversible charge carrier trapping and experiments over a wide range of time scales for the understanding of colloidal nanoemitters in general and nanoplatelets in particular. PMID:26863992

  16. Photoluminescence of patterned CdSe quantum dot for anti-counterfeiting label on paper

    NASA Astrophysics Data System (ADS)

    Isnaeni, Yulianto, Nursidik; Suliyanti, Maria Margaretha

    2016-03-01

    We successfully developed a method utilizing colloidal CdSe nanocrystalline quantum dot for anti-counterfeiting label on a piece of glossy paper. We deposited numbers and lines patterns of toluene soluble CdSe quantum dot using rubber stamper on a glossy paper. The width of line pattern was about 1-2 mm with 1-2 mm separation between lines. It required less than one minute for deposited CdSe quantum dot on glossy paper to dry and become invisible by naked eyes. However, patterned quantum dot become visible using long-pass filter glasses upon excitation of UV lamp or blue laser. We characterized photoluminescence of line patterns of quantum dot, and we found that emission boundaries of line patterns were clearly observed. The error of line size and shape were mainly due to defect of the original stamper. The emission peak wavelength of CdSe quantum dot was 629 nm. The emission spectrum of deposited quantum dot has full width at half maximum (FWHM) of 30-40 nm. The spectra similarity between deposited quantum dot and the original quantum dot in solution proved that our stamping method can be simply applied on glossy paper without changing basic optical property of the quantum dot. Further development of this technique is potential for anti-counterfeiting label on very important documents or objects.

  17. Multielectron ionization of CdSe quantum dots in intense femtosecond ultraviolet light

    SciTech Connect

    Son, D.H.; Wittenberg, Joshua S.; Alivisatos, A. Paul

    2004-03-26

    Multielectron ionization of colloidal CdSe quantum dots under intense femtosecond UV excitation has been studied. By directly probing the absorption from the ionized electron, quantitative measurements of the yield and dynamics of the ionization have been made as a function of excitation fluence and variations of size and potential structure of quantum dots. The results have been explained by an ionization mechanism involving resonant two-photon absorption.

  18. Detection of CdSe quantum dot photoluminescence for security label on paper

    NASA Astrophysics Data System (ADS)

    Isnaeni, Sugiarto, Iyon Titok; Bilqis, Ratu; Suseno, Jatmiko Endro

    2016-02-01

    CdSe quantum dot has great potential in various applications especially for emitting devices. One example potential application of CdSe quantum dot is security label for anti-counterfeiting. In this work, we present a practical approach of security label on paper using one and two colors of colloidal CdSe quantum dot, which is used as stamping ink on various types of paper. Under ambient condition, quantum dot is almost invisible. The quantum dot security label can be revealed by detecting emission of quantum dot using photoluminescence and cnc machine. The recorded quantum dot emission intensity is then analyzed using home-made program to reveal quantum dot pattern stamp having the word 'RAHASIA'. We found that security label using quantum dot works well on several types of paper. The quantum dot patterns can survive several days and further treatment is required to protect the quantum dot. Oxidation of quantum dot that occurred during this experiment reduced the emission intensity of quantum dot patterns.

  19. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    SciTech Connect

    Xu, Xingsheng

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  20. Chiroptical activity in colloidal quantum dots coated with achiral ligands.

    PubMed

    Melnikau, Dzmitry; Savateeva, Diana; Gaponik, Nikolai; Govorov, Alexander O; Rakovich, Yury P

    2016-01-25

    We studied the chiroptical properties of colloidal solution of CdSe and CdSe/ZnS quantum dots (QDs) with a cubic lattice structure which were initially prepared without use of any chiral molecules and coated with achiral ligands. We demonstrate circular dichroism (CD) activity around first and second excitonic transition of these CdSe based nanocrystals. We consider that this chiroptical activity is caused by imbalance in racemic mixtures of QDs between the left and right handed nanoparticles, which appears as a result of the formation of various defects or incorporation of impurities into crystallographic structure during their synthesis. We demonstrate that optical activity of colloidal solution of CdSe QDs with achiral ligands weakly depends on the QDs size and number of ZnS monolayers, but does not depend on the nature of achiral ligands or polarity of the solution. PMID:26832599

  1. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  2. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  3. Quantum chemistry of the minimal CdSe clusters

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Tretiak, Sergei; Masunov, Artëm E.; Ivanov, Sergei

    2008-08-01

    Colloidal quantum dots are semiconductor nanocrystals (NCs) which have stimulated a great deal of research and have attracted technical interest in recent years due to their chemical stability and the tunability of photophysical properties. While internal structure of large quantum dots is similar to bulk, their surface structure and passivating role of capping ligands (surfactants) are not fully understood to date. We apply ab initio wavefunction methods, density functional theory, and semiempirical approaches to study the passivation effects of substituted phosphine and amine ligands on the minimal cluster Cd2Se2, which is also used to benchmark different computational methods versus high level ab initio techniques. Full geometry optimization of Cd2Se2 at different theory levels and ligand coverage is used to understand the affinities of various ligands and the impact of ligands on cluster structure. Most possible bonding patterns between ligands and surface Cd/Se atoms are considered, including a ligand coordinated to Se atoms. The degree of passivation of Cd and Se atoms (one or two ligands attached to one atom) is also studied. The results suggest that B3LYP/LANL2DZ level of theory is appropriate for the system modeling, whereas frequently used semiempirical methods (such as AM1 and PM3) produce unphysical results. The use of hydrogen atom for modeling of the cluster passivating ligands is found to yield unphysical results as well. Hence, the surface termination of II-VI semiconductor NCs with hydrogen atoms often used in computational models should probably be avoided. Basis set superposition error, zero-point energy, and thermal corrections, as well as solvent effects simulated with polarized continuum model are found to produce minor variations on the ligand binding energies. The effects of Cd-Se complex structure on both the electronic band gap (highest occupied molecular orbital-lowest unoccupied molecular orbital energy difference) and ligand binding

  4. How quickly does a hole relax into an engineered defect state in CdSe quantum dots.

    PubMed

    Avidan, Assaf; Pinkas, Iddo; Oron, Dan

    2012-04-24

    Intraband hole relaxation of colloidal Te-doped CdSe quantum dots is studied using state-selective transient absorption spectroscopy. The dots are excited at the band edge, and the defect band bleach caused by state filling of the hole is probed. Close to the defect energy, the hole relaxation is substantially slowed down, indicating a gap separating the defect state from the CdSe band edge. A clear dependence of the relaxation time with the QD's size is presented, implying that the hole relaxation is mediated by longitudinal optical (LO) phonon modes of the CdSe host. In addition, we find that overcoating the quantum dots by two monolayers of a ZnS shell extends the hole relaxation time by a factor of 2, suggesting a combined effect of LO phonons and surface effects governing intraband hole relaxation. PMID:22439798

  5. Anisotropy in CdSe quantum rods

    SciTech Connect

    Li, Liang-shi

    2003-09-01

    The size-dependent optical and electronic properties of semiconductor nanocrystals have drawn much attention in the past decade, and have been very well understood for spherical ones. The advent of the synthetic methods to make rod-like CdSe nanocrystals with wurtzite structure has offered us a new opportunity to study their properties as functions of their shape. This dissertation includes three main parts: synthesis of CdSe nanorods with tightly controlled widths and lengths, their optical and dielectric properties, and their large-scale assembly, all of which are either directly or indirectly caused by the uniaxial crystallographic structure of wurtzite CdSe. The hexagonal wurtzite structure is believed to be the primary reason for the growth of CdSe nanorods. It represents itself in the kinetic stabilization of the rod-like particles over the spherical ones in the presence of phosphonic acids. By varying the composition of the surfactant mixture used for synthesis we have achieved tight control of the widths and lengths of the nanorods. The synthesis of monodisperse CdSe nanorods enables us to systematically study their size-dependent properties. For example, room temperature single particle fluorescence spectroscopy has shown that nanorods emit linearly polarized photoluminescence. Theoretical calculations have shown that it is due to the crossing between the two highest occupied electronic levels with increasing aspect ratio. We also measured the permanent electric dipole moment of the nanorods with transient electric birefringence technique. Experimental results on nanorods with different sizes show that the dipole moment is linear to the particle volume, indicating that it originates from the non-centrosymmetric hexagonal lattice. The elongation of the nanocrystals also results in the anisotropic inter-particle interaction. One of the consequences is the formation of liquid crystalline phases when the nanorods are dispersed in solvent to a high enough

  6. Femtosecond cooling of hot electrons in CdSe quantum-well platelets.

    PubMed

    Sippel, Philipp; Albrecht, Wiebke; van der Bok, Johanna C; Van Dijk-Moes, Relinde J A; Hannappel, Thomas; Eichberger, Rainer; Vanmaekelbergh, Daniel

    2015-04-01

    Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well nanoplatelets using ultrafast two-photon photoemission spectroscopy at low excitation intensities, resulting typically in 1-5 hot electrons per platelet. We observe initial electron cooling in the femtosecond time domain that slows down with decreasing electron energy and is finished within 2 ps. The cooling is considerably faster at cryogenic temperatures than at room temperature, and at least for the systems that we studied, independent of the thickness of the platelets (here 3-5 CdSe units) and the presence of a CdS shell. The cooling rates that we observe are orders of magnitude faster than reported for similar CdSe platelets under strong excitation. Our results are understood by a classic cooling mechanism with emission of longitudinal optical phonons without a significant influence of the surface. PMID:25764379

  7. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    SciTech Connect

    Singh, Neetu Kapoor, Avinashi; Kumar, Vinod; Mehra, R. M.

    2014-04-24

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  8. New transient absorption observed in the spectrum of colloidal CdSe nanoparticles pumped with high-power femtosecond pulses

    SciTech Connect

    Burda, C.; Link, S.; Green, T.C.; El-Sayed, M.A.

    1999-12-09

    The power dependence of the transient absorption spectrum of CdSe nanoparticle colloids with size distribution of 4.0 {+-} 0.4 nm diameter is studied with femtosecond pump-probe techniques. At the lowest pump laser power, the absorption bleaching (negative spectrum) characteristic of the exciton spectrum is observed with maxima at 560 and 480 nm. As the pump laser power increases, two new transient absorptions at 510 and 590 nm with unresolved fast rise (<100 fs) and long decay times ({much{underscore}gt}150 ps) are observed. The energy of each of the positive absorption is red shifted from that of the bleach bands by {approximately}120 MeV. The origin of this shift is discussed in terms of the effect of the internal electric field of the many electron-hole pairs formed within the quantum dot at the high pump intensity, absorption from a metastable excited state or the formation of biexcitons.

  9. Experimental Observation of Quantum Confinement in the Conduction Band of CdSe Quantum Dots

    SciTech Connect

    Lee, J I; Meulenberg, R W; Hanif, K M; Mattoussi, H; Klepeis, J E; Terminello, L J; van Buuren, T

    2006-12-15

    Recent theoretical descriptions as to the magnitude of effect that quantum confinement has on he conduction band (CB) of CdSe quantum dots (QD) have been conflicting. In this manuscript, we experimentally identify quantum confinement effects in the CB of CdSe QDs for the first time. Using X-ray absorption spectroscopy, we have unambiguously witnessed the CB minimum shift to higher energy with decreasing particle size and have been able to compare these results to recent theories. Our experiments have been able to identify which theories correctly describe the CB states in CdSe QDs. In particular, our experiments suggest that multiple theories describe the shifts in the CB of CdSe QDs and are not mutually exclusive.

  10. Chemically synthesized CdSe quantum dots inhibit growth of human lung carcinoma cells via ROS generation

    PubMed Central

    Jigyasu, Aditya Kumar; Siddiqui, Sahabjada; Lohani, Mohatashim; Khan, Irfan Ali; Arshad, Md

    2016-01-01

    Quantum dots (QDs), semiconducting materials have potential applications in the field of electronic and biomedical applications including cancer therapy. In present study, cadmium selenide (CdSe) QDs were synthesized by chemical method. Octadecene was used as non-coordinating solvent which facilitated the formation of colloidal solutions of nanoparticles. CdSe QDs were characterized by UV-vis spectrometer and transmission electron microscope (TEM). The size measured by TEM was varied between 2-5 nm depending upon temperature. The cytotoxic activity of QDs was monitored by MTT assay, nuclear condensation, ROS activity and DNA fragmentation assay on human lung epithelial A549 cell line. Cells were treated with different concentrations of varying size of CdSe QDs for 24 h. CdSe QDs induced significant (p < 0.05) dose dependent cytotoxicity and this was comparable to the sizes of particles. Smaller particles were more cytotoxic to the large particles. Fluorescence microscopic analysis revealed that QDs induced oxidative stress generating significant ROS level and consequently, induced nuclear condensation and DNA fragmentation. Study suggested the cytotoxicity of CdSe QDs via ROS generation and DNA fragmentation depending upon particles size. PMID:27047318

  11. Electroluminescence from colloidal semiconductor CdSe nanoplatelets in hybrid organic-inorganic light emitting diode

    NASA Astrophysics Data System (ADS)

    Vitukhnovsky, A. G.; Lebedev, V. S.; Selyukov, A. S.; Vashchenko, A. A.; Vasiliev, R. B.; Sokolikova, M. S.

    2015-01-01

    We report on the fabrication of a hybrid light-emitting-diode based on colloidal semiconductor CdSe nanoplatelets as emitters and organic TAZ [3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole] and TPD [N, N‧-bis (3-methylphenyl)-N, N‧-bis (phenyl)-benzidine] materials as the electron and hole transporting layers. Electroluminescent and current-voltage characteristics of the developed hybrid device with the turn-on voltage of 5.5 V and the radiation wavelength of 515 nm have been obtained. Semiconductor nanoplatelets like CdSe are attractive for the fabrication of hybrid LEDs with low operating voltages, spectrally pure color and short-wavelength electroluminescence, which is required for RGB devices.

  12. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    PubMed Central

    Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

  13. Thermal Recovery of Colloidal Quantum Dot Ensembles Following Photoinduced Dimming.

    PubMed

    Jensen, Russell A; Coropceanu, Igor; Chen, Yue; Bawendi, Moungi G

    2015-08-01

    Colloidal CdSe quantum dot (QD) core ensembles were photodimmed and allowed to recover in the dark using ambient thermal energy at a range of temperatures. Nonlinear thermal recovery is well described by a stretched exponential function, and further analysis yields an underlying probability distribution of rate constants. Casting the rate constants as a collection of first-order activated processes provides an activation barrier probability distribution with significant density at room-temperature thermal energy that peaks at 200 meV before decaying to zero. This treatment for the recovery transition intuitively describes the distributed kinetics observed and complements commonly proposed blinking mechanisms. PMID:26267184

  14. Optical enhancement of photoluminescence with colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Abraham, Gabrielle; French, David A.; Bajwa, Pooja; Heyes, Colin D.; Herzog, Joseph B.

    2015-08-01

    This work investigates colloidal, semiconductor Cadmium Selenide (CdSe) QDs with optical spectroscopy measurements. A custom-built microscope has been used for photoluminescence spectroscopy and has collected images, videos, and spectra of samples to study the effects of substrates, sample density, uniformity, and QD aging with time. This set up will be used to detect single to a few molecules, shown by fluorescent intermittency, or QD blinking. Differences in the spectrum will be noted as related to the age of samples, the density of the quantum dots, and the concentration of samples. Further experiments include the potential plasmonic enhancement of QD photoluminescence by gold nanoparticles or nanostructures.

  15. Influence of Surfactants and Charges on CdSe Quantum Dots

    SciTech Connect

    Yang, Ping; Tretiak, Sergei; Ivanov, Sergei

    2011-07-11

    The chemistry between CdSe quantum dots and common surface capping ligands is invested using density functional theory. We will discuss the electronic structures and optical properties of CdSe QDs controlled by the size of particle, self-organization, capping ligands, and positive charges. Charges on quantum dots have profound effects on their structures, binding energies, and optical properties.

  16. A Safer, Easier, Faster Synthesis for CdSe Quantum Dot Nanocrystals

    ERIC Educational Resources Information Center

    Boatman, Elizabeth M.; Lisensky, George C.; Nordell, Karen J.

    2005-01-01

    The synthesis for CdSe quantum dot nanocrystals that vary in color and are a visually engaging way to demonstrate quantum effects in chemistry is presented. CdSe nanocrystals are synthesized from CdO and elemental Se using a kinetic growth method where particle size depends on reaction time.

  17. CdSe quantum dot internalization by Bacillus subtilis and Escherichia coli

    NASA Technical Reports Server (NTRS)

    Kloepfer, Jeremiah A.; Mielke, Randall E.; Nadeau, Jay L.

    2004-01-01

    Biological labeling has been demonstrated with CdSe quantum dots in a variety of animal cells, but bacteria are harder to label because of their cell walls. We discuss the challenges of using minimally coated, bare CdSe quantum dots as luminescent internal labels for bacteria.

  18. Luminescent gelatin nanospheres by encapsulating CdSe quantum dots.

    PubMed

    Chen, Longyan; Willoughby, Adrienne; Zhang, Jin

    2014-02-01

    Quantum dots (QDs) have been encapsulated within gelatin nanoparticles (GNPs), which gives GNPs fluorescent properties and improves the biocompatibility of QDs. Hydrophilic CdSe QDs were produced through thermodecomposition following the ligand-exchange method, and were then encapsulated in GNPs. The results of high-resolution transmission electron microscopy and transmission electron microscopy show that CdSe QDs and QDs-encapsulated GNPs (QDs-GNPs) have average diameters of 5 ± 1 and 150 ± 10 nm, respectively. Results of both high-resolution transmission electron microscopy and confocal laser scanning microscopy indicate that CdSe QDs are successfully encapsulated within GNPs. The QDs-GNPs have distinctive fluorescent properties with maximum emission at 654 nm, with a 24 nm red-shift compared with hydrophilic mercaptoundecanoic acid (MUA)-modified QDs. In addition, an in vitro cytotoxicity test shows that QDs-GNPs do not have any toxic effect on cells. It is expected that QDs-GNPs might be an excellent candidate as a contrast agent in bio-imaging. PMID:23533134

  19. Radial Electron Momentum Densities of Colloidal CdSe Nanocrystals Determined by Positron Beam Analysis

    SciTech Connect

    Denison, A B; Meulenberg, R; Eijt, S W H; Van Veen, A; Mijnarends, P E; Barbiellini, B; Bansil, A; Fischer, C; Weber, M H; Lynn, K G

    2003-07-31

    We present depth-resolved positron 2D angular correlation of annihilation radiation (2DACAR) experiments on CdSe quantum dots in the diameter range from 2.5 to 6 nm, deposited as micrometer thin layers. The average radial distribution of the valence electron momentum density (EMD) of CdSe quantum dots has been extracted, which reveals a systematic dependence upon particle size. The quantum confinement related changes and their size scaling observable at the Jones zone momentum of {approx}0.8 a.u. seem to agree with the previous coincidence Doppler study. In addition, the average radial EMD shows an increase in the low-momentum range (<0.6 a.u.) and a reduction in the high-momentum range (>1.6 a.u.) with respect to that measured on a bulk CdSe single crystal. Possible origins of these are described. First-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method were performed to gain a better insight.

  20. Macroscopic Superlattices of CdSe Colloidal Nanocrystals: Appearance and Optical Properties

    SciTech Connect

    Zaitseva, N; Manna, L; Leon, F; Gerion, D; Saw, C; Galli, G

    2004-03-25

    distribution of sizes and shapes that always exist in NCs one more reason to prevent faceting. At the same time, formation of faceted SLs from colloidal solutions has been reported in a number of works [1, 6, 8, 11]. Two recent publications in this journal [12,13] were devoted to the case of CdSe that, for its well-known properties, can be considered as a model NC material. These publications stated that perfectly shaped hexagonal platelets obtained from a toluene solution of CdSe NCs were faceted SLs. The size of the crystals (up to 200 {micro}m) was large enough to observe them in an optical microscope, but apparently too small for the separation and characterization by macroscopic techniques. Therefore no optical characterization was presented, and the conclusion was made on the basis of TEM images of small fragments that did not show any visible faceting. It is important to say here that, despite the fact that the authors used a special triple-solvent ''controlled oversaturation technique'', formation of these hexagonal platelets is not rare in CdSe NC solutions and had been discussed previously in the connection with SL formation [1]. In our experiments with CdSe NCs, we frequently observed them to form spontaneously in relatively large number and size. Such common and easy formation of these crystals stimulated us to take a closer look at their nature. Here we present the results of our investigations, together with new attempts to obtain micron-scale SLs of CdSe NCs suitable for direct characterization by combination of electron microscopy with macroscopic techniques, such as optical polarization microscopy, x-ray diffraction, and photoluminescence spectroscopy.

  1. A Closer Look into the Traditional Purification Process of CdSe Semiconductor Quantum Dots.

    PubMed

    Shakeri, Behtash; Meulenberg, Robert W

    2015-12-15

    This paper describes how the postprocessing procedure for wurtzite CdSe quantum dots (QDs) 4.8 and 6.7 nm in diameter is affected by both the choice of nonsolvent and the number of processing steps. Using a host of analytical techniques (ultraviolet-visible, photoluminescence, nuclear magnetic, X-ray photoelectron, and infrared spectroscopy, as well as thermogravimetric analysis), we find that control over the ligand type and surface density can be achieved simply by the number of washing steps used during the postprocessing procedure. Using multiple washing steps we can achieve colloidally stable solutions of QDs with organic mass fractions as low as 13% by mass. For CdSe QDs passivated with trioctylphosphine oxide (TOPO) and stearic acid (SA), essentially no TOPO is bound to the particle surface after three or four washing steps, with a plateau in the amount of SA being removed. The results can be explained using the L- and X-type ligand classification system for QDs, with L-type ligands (TOPO) removed in the early processing steps but the removal of X-type (SA) ligand stalling at a large number of washing steps due to charging of the QDs. Importantly, very little change is observed in the photoluminescence (PL) properties, suggesting that the choice of nonsolvent during postprocessing will allow the production of QD materials with very low organic content by mass but with good PL quantum yields. PMID:26625188

  2. Importance of Polaronic Effects for Charge Transport in CdSe Quantum Dot Solids.

    PubMed

    Prodanović, Nikola; Vukmirović, Nenad; Ikonić, Zoran; Harrison, Paul; Indjin, Dragan

    2014-04-17

    We developed an accurate model accounting for electron-phonon interaction in colloidal quantum dot supercrystals that allowed us to identify the nature of charge carriers and the electrical transport regime. We find that in experimentally analyzed CdSe nanocrystal solids, the electron-phonon interaction is sufficiently strong that small polarons localized to single dots are formed. Charge-carrier transport occurs by small polaron hopping between the dots, with mobility that decreases with increasing temperature. While such a temperature dependence of mobility is usually considered as a proof of band transport, we show that the same type of dependence occurs in the system where transport is dominated by small polaron hopping. PMID:26269977

  3. Experimental Observation of Quantum Confinement in the Conduction Band of CdSe Quantum Dots

    SciTech Connect

    Lee, Jonathan R. I.; Meulenberg, Robert W.; Klepeis, John E.; Terminello, Louis J.; Buuren, Tony van; Hanif, Khalid M.; Mattoussi, Hedi

    2007-04-06

    X-ray absorption spectroscopy has been used to characterize the evolution in the conduction band (CB) density of states of CdSe quantum dots (QDs) as a function of particle size. We have unambiguously witnessed the CdSe QD CB minimum (CBM) shift to higher energy with decreasing particle size, consistent with quantum confinement effects, and have directly compared our results with recent theoretical calculations. At the smallest particle size, evidence for a pinning of the CBM is presented. Our observations can be explained by considering a size-dependent change in the angular-momentum-resolved states at the CBM.

  4. Direct Patterning of CdSe Quantum Dots into Sub-100 nm Structures

    SciTech Connect

    Hampton, Meredith J.; Templeton, Joseph L.; DeSimone, Joseph M.

    2010-03-02

    Ordered, two-dimensional cadmium selenide (CdSe) arrays have been fabricated on indium-doped tin oxide (ITO) electrodes using the pattern replication in nonwetting templates (PRINT) process. CdSe quantum dots (QDs) with an average diameter of 2.7 nm and a pyridine surface ligand were used for patterning. The PRINT technique utilizes a perfluoropolyether (PFPE) elastomeric mold that is tolerant of most organic solvents, thus allowing solutions of CdSe QDs in 4-picoline to be used for patterning without significant deformation of the mold. Nanometer-scale diffraction gratings have been successfully replicated with CdSe QDs.

  5. Photophysical properties of biologically compatible CdSe quantum dot structures.

    PubMed

    Kloepfer, Jeremiah A; Bradforth, Stephen E; Nadeau, Jay L

    2005-05-26

    The photophysical properties of CdSe and ZnS(CdSe) semiconductor quantum dots in nonpolar and aqueous solutions were examined with steady-state (absorption and emission) and time-resolved (time-correlated single-photon-counting) spectroscopy. The CdSe structures were prepared from a single CdSe synthesis, a portion of which were ZnS-capped, thus any differences observed in the spectral behavior between the two preparations were due to changes in the molecular shell. Quantum dots in nonpolar solvents were surrounded with a trioctylphosphine oxide (TOPO) coating from the initial synthesis solution. ZnS-capped CdSe were initially brighter than bare uncapped CdSe and had overall faster emission decays. The dynamics did not vary when the solvent was changed from hexane to dichloromethane; however, replacement of the TOPO cap by pyridine affected CdSe but not ZnS(CdSe). CdSe was then solubilized in water with mercapto-acetic acid or dihydrolipoic acid, whereas ZnS(CdSe) could be solubilized only with dihydrolipoic acid. Both solubilization agents quenched the nanocrystal emission, though with CdSe the quenching was nearly complete. Additional quenching of the remaining emission was observed when the redox-active molecule adenine was conjugated to the water-soluble CdSe but was not seen with ZnS(CdSe). The emission of aqueous CdSe could be enhanced under prolonged exposure to room light and resulted in a substantial increase of the emission lifetimes; however, the enhancement occurred concurrently with precipitation of the nanocrystals, which was possibly caused by photocatalytic destruction of the mercaptoacetic acid coating. These results are the first presented on aqueous CdSe quantum dot structures and are presented in the context of designing better, more stable biological probes. PMID:16852208

  6. CdSe colloidal nanocrystals monolithically integrated in a pseudomorphic semiconductor epilayer

    SciTech Connect

    Larramendi, Erick M.; Schoeps, Oliver; Woggon, Ulrike; Artemyev, Mikhail V.; Schikora, Detlef; Lischka, Klaus

    2013-01-14

    As optically active emitters in a semiconductor matrix, core/shell and bare CdSe colloidal nanocrystals (CNCs) were monolithically incorporated in ZnSe pseudomorphic epilayers by molecular beam epitaxy (MBE). A suspension of wet chemically synthesized CNCs was sprayed ex-situ over a pseudomorphic ZnSe/GaAs(001) heterostructure using a nebulizer. Subsequently, the matrix material growth was resumed to form a capping layer by a slow MBE growth mode. Structural investigations show high crystalline quality and pseudomorphic epitaxial character of the whole hybrid CNC-matrix structure. The core/shell CNCs remain optically active following the embedding process. Their emission is blue shifted without a significant change on the spectral shape, and shows the same temperature dependence as that of the free exciton peak energy in zinc-blende CdSe at temperatures above 80 K. Our optical characterization of the samples showed that the embedded CNCs were stable and that the structure of the host was preserved. These results are encouraging for the fabrication of more complex optoelectronic devices based on CNCs.

  7. Preparation of highly luminescent CdSe quantum dots by reverse micelles

    NASA Astrophysics Data System (ADS)

    Liu, Kang; Park, Sang Joon

    2014-08-01

    CdSe quantum dots (QDs) with relatively high photoluminescence (PL) quantum yield (QY) (about 30%) were prepared by a safe, low-cost, and simple synthesis method, utilizing a sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/cyclohexane microemulsion system. Cadmium chloride (CdCl2) and selenium powder were used as the cadmium and selenium sources, respectively. Size-tunable CdSe nanoparticles were obtained at various water-to-surfactant ratios, W ([H2O]/[surfactant]). The size of the CdSe nanoparticles increased, and the UV-vis absorption and PL peaks shifted towards the red region as W increased. Interestingly, the redshift also occurred when the ratio of Cd to Se increased. The highest PL efficiency was obtained at W of 5 and a Cd/Se ratio of 2:1. In addition, the CdSe nanoparticles with higher Cd to Se molar ratio (3/1) showed a higher stability against photooxidation.

  8. Direct determination of absorption anisotropy in colloidal quantum rods

    NASA Astrophysics Data System (ADS)

    Kamal, John Sundar; Gomes, Raquel; Hens, Zeger; Karvar, Masoumeh; Neyts, Kristiaan; Compernolle, Sien; Vanhaecke, Frank

    2012-01-01

    We propose a direct method to determine absorption anisotropy of colloidal quantum rods. In this method, the rods are aligned in solution by using an alternating electric field and we measure simultaneously the resulting average change in absorption. We show that a frequency window for the electric field exists in which the change in absorbance as a function of field strength can be analyzed in terms of the quantum-rod dipole moment and the absorption coefficient for light that is polarized parallel or perpendicular to the long axis of the rod. The approach is verified by measuring the absorbance change of CdSe rods at 400 nm as a function of field strength, where we demonstrate excellent agreement between experiment and theory. This enables us to propose improved values for the CdSe quantum-rod extinction coefficient. Next, we analyze CdSe/CdS dot-in-rods and find that the absorption of the first exciton transition is fully anisotropic, with a vanishing absorption coefficient for light that is polarized perpendicularly to the long axis of the rods.

  9. Fluorescence quenching of CdSe quantum dots on graphene

    SciTech Connect

    Guo, Xi Tao; Hua Ni, Zhen Yan Nan, Hai; Hui Wang, Wen; Yan Liao, Chun; Zhang, Yan; Wei Zhao, Wei

    2013-11-11

    We studied systematically the fluorescence quenching of CdSe quantum dots (QDs) on graphene and its multilayers, as well as graphene oxide (GO) and reduced graphene oxide (rGO). Raman intensity of QDs was used as a quantitatively measurement of its concentration in order to achieve a reliable quenching factor (QF). It was found that the QF of graphene (∼13.1) and its multilayers is much larger than rGO (∼4.4), while GO (∼1.5) has the lowest quenching efficiency, which suggests that the graphitic structure is an important factor for quenching the fluorescence of QDs. It was also revealed that the QF of graphene is not strongly dependent on its thicknesses.

  10. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  11. Evaluation of all-inorganic CdSe quantum dot thin films for optoelectronic applications.

    PubMed

    Zhang, Y Q; Cao, X A

    2012-07-11

    Exchanging the original organic ligands of colloidal CdSe quantum dots (QDs) with inorganic metal chalcogenide SnS(4) ligands resulted in absorption peak redshifts and complete photoluminescence (PL) quenching in QD solids. The SnS(4)-capped QDs, meanwhile, were able to retain strong excitonic absorption. After the ligand exchange, the ITO/QDs/Al structure showed much higher electrical conductivity and reduced space-charge limited current. Its photocurrent spectral response increased by over two orders of magnitude and closely resembled the absorption spectrum of the QDs. However, it was found that mild thermal treatment above 200 °C transformed the SnS(4)-capped QD film into to a more conductive assembly, degrading its absorption and photocurrent generation. These results suggest that the inorganic ligands considerably enhanced the inter-dot electronic coupling in QD solids, leading to facile charge separation and transport. Our study thus demonstrates the potential applicability of colloidal QDs with metal chalcogenide ligands processed at low temperatures for efficient photodetection and solar energy conversion. PMID:22705470

  12. High-conjugation-efficiency aqueous CdSe quantum dots.

    PubMed

    Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng

    2013-11-12

    Quantum dots (QDs) are photoluminescent nanoparticles that can be directly or indirectly coupled with a receptor such as an antibody to specifically image a target biomolecule such as an antigen. Recent studies have shown that QDs can be directly made at room temperature and in an aqueous environment (AQDs) with 3-mercaptopropionic acid (MPA) as the capping ligand without solvent and ligand exchange typically required by QDs made by the organic solvent routes (OQDs). In this study, we have synthesized CdSe AQDs and compared their conjugation efficiency and imaging efficacy with commercial carboxylated OQDs in HT29 colon cancer cells using a primary antibody-biotinylated secondary antibody-streptavidin (SA) sandwich. We showed that the best imaging condition for AQDs occurred when one AQD was bound with 3 ± 0.3 SA with a nominal SA/AQD ratio of 4 corresponding to an SA conjugation efficiency of 75 ± 7.5%. In comparison, for commercial CdSe-ZnS OQDs to achieve 2.7 ± 0.4 bound SAs per OQD for comparable imaging efficacy a nominal SA/OQD ratio of 80 was needed corresponding to an SA conjugation efficiency of 3.4 ± 0.5% for CdSe-ZnS OQDs. The more than 10 times better SA conjugation efficiency of the CdSe AQDs as compared to that of the CdSe-ZnS OQDs was attributed to more capping molecules on the AQD surface as a result of the direct aqueous synthesis. More capping molecules on the AQD surface also allowed the SA-AQD conjugate to be stable in cell culture medium for more than three days without losing their staining capability in a flowing cell culture medium. In contrast, SA-OQD conjugates aggregated in cell culture medium and in phosphate buffer saline solution over time. PMID:24151632

  13. Telegraphic noise in transport through colloidal quantum dots.

    PubMed

    Lachance-Quirion, Dany; Tremblay, Samuel; Lamarre, Sébastien A; Méthot, Vincent; Gingras, Daniel; Camirand Lemyre, Julien; Pioro-Ladrière, Michel; Allen, Claudine Nì

    2014-02-12

    We report measurements of electrical transport through single CdSe/CdS core/shell colloidal quantum dots (cQDs) connected to source and drain contacts. We observe telegraphic switching noise showing few plateaus at room temperature. We model and interpret these results as charge trapping of individual trap states, and therefore we resolve individual charge defects in these high-quality low-strain cQDs. The small number of observed defects quantitatively validates the passivation method based on thick CdS shells nearly lattice-matched to CdSe cores first developed to suppress photoluminescence blinking. Finally, we introduce a figure of merit useful to efficiently distinguish telegraphic noise from noise with a Gaussian distribution. PMID:24437447

  14. Hydrophilic colloidal quantum dots with long peptide chain coats.

    PubMed

    Dąbrowska, Anna; Nyk, Marcin; Worch, Remigiusz; Grzyb, Joanna

    2016-09-01

    Here, the transition of colloidal CdSe quantum dots (QDs) from hydrophobic to hydrophilic environments after coating the surface with long peptide chains of membrane scaffold proteins (MSP) is reported. The intermediate step included the solubilization of QDs with detergents, where n-octyl glucoside was the most promising ligand. Furthermore, size analysis by fluorescence correlation spectroscopy, gel filtration and atomic force microscopy suggested that the obtained QD-MSP conjugates were primarily discoidal and were likely formed from single QDs tightly encircled by helix belts. In addition, Fourier-transformed infrared spectroscopy analysis confirmed the preservation of the secondary structure of most proteins during conjugate formation, with no signs of denaturation. The obtained QD-MSP conjugates were optimal in terms of stability in water environments, suggesting that it is possible to obtain QDs with single peptide coats and providing the first guidelines for future research in this direction. PMID:27289307

  15. Controlled growth of CdSe quantum dots on silica spheres

    NASA Astrophysics Data System (ADS)

    Kim, Byoung-Ju; Jo, Dong-Hyun; Lim, Se-Han; Kim, Do-Kyoon; Park, Jin-Young; Kang, Kwang-Sun

    2015-08-01

    Various sizes of CdSe quantum dots have been fabricated on the surface of the monodisperse silica spheres and five diffe rent photoluminescence (PL) peaks are observed from the CdSe quantum dots. The monodisperse silica spheres were syn thesized with Stöber synthetic method. The surface of the spheres was modified with 100:1 ratio of phenylpropyltrimeth oxysilane (PTMS) and mercaptopropyltrimethoxysilane (MPTMS). The MPTMS works as a covalent bond formation wi th CdSe quantum dots, and the PTMS acts as a separating quantum dots to prevent PL quenching by neighboring quantu m dots. The Fourier transform infrared (FTIR) spectrum of the surface modified spheres (SMSiO2) shows strong absorpti on peak at 2852 and 2953 cm-1 representing the characteristic absorption of -CH or -CH2. The FTIR absorption peak at 1 741 cm-1 represents the characteristic absorption of CdSe quantum dots. The field emission scanning electron microscope image shows the average diameter of the spheres ranging approximately 418 nm. The ultraviolet-visible transmittance s pectrum shows stop band at 880 nm. The PL spectrum shows five different emission bands at 434, 451, 468, 492 and 545 nm, which indicates the formation of several different sizes of CdSe quantum dots.

  16. Effect of Chemicals on Morphology and Luminescence of CdSe Quantum Dots.

    PubMed

    Zhang, Xiao; Li, Xiaoyu; Zhang, Ruili; Yang, Ping

    2015-04-01

    CdSe quantum dots (QDs) with several morphologies were fabricated using various reaction sys- tems. In a trioctylamine (TOA) and octadecylphosphonic acid (ODPA) system, yellow-emitting (a photoluminescence (PL) peak wavelength of 583 nm) CdSe QDs revealed rod morphology and nar- row size distribution. When ODPA was replaced by tetradecylphosphonic acid (TDPA), red-emitting CdSe rods (a PL peak wavelength of 653 nm) with broad size distribution were fabricated. This is ascribed that the short carbon chain accelerated the growth of CdSe QDs. As a result, the use of ODPA resulted in CdSe QDs with high PL efficiency (3.1%). Furthermore, cubic-like CdSe QDs were created in a stearic acid (SA) and octadecene (ODE) reaction system. The PL efficiency of the QDs is low (0.2%). When hexadecylamine (HDA) was added in such SA and ODE reaction system, spherical CdSe QDs with narrow size distribution and high PL efficiency (3.4%) were prepared. PMID:26353513

  17. Sulforaphane Protects the Liver against CdSe Quantum Dot-Induced Cytotoxicity

    PubMed Central

    Wang, Wei; He, Yan; Yu, Guodong; Li, Baolong; Sexton, Darren W.; Wileman, Thomas; Roberts, Alexandra A.; Hamilton, Chris J.; Liu, Ruoxi; Chao, Yimin; Shan, Yujuan; Bao, Yongping

    2015-01-01

    The potential cytotoxicity of cadmium selenide (CdSe) quantum dots (QDs) presents a barrier to their use in biomedical imaging or as diagnostic and therapeutic agents. Sulforaphane (SFN) is a chemoprotective compound derived from cruciferous vegetables which can up-regulate antioxidant enzymes and induce apoptosis and autophagy. This study reports the effects of SFN on CdSe QD-induced cytotoxicity in immortalised human hepatocytes and in the livers of mice. CdSe QDs induced dose-dependent cell death in hepatocytes with an IC50 = 20.4 μM. Pre-treatment with SFN (5 μM) increased cell viability in response to CdSe QDs (20 μM) from 49.5 to 89.3%. SFN induced a pro-oxidant effect characterized by depletion of intracellular reduced glutathione during short term exposure (3–6 h), followed by up-regulation of antioxidant enzymes and glutathione levels at 24 h. SFN also caused Nrf2 translocation into the nucleus, up-regulation of antioxidant enzymes and autophagy. siRNA knockdown of Nrf2 suggests that the Nrf2 pathway plays a role in the protection against CdSe QD-induced cell death. Wortmannin inhibition of SFN-induced autophagy significantly suppressed the protective effect of SFN on CdSe QD-induced cell death. Moreover, the role of autophagy in SFN protection against CdSe QD-induced cell death was confirmed using mouse embryonic fibroblasts lacking ATG5. CdSe QDs caused significant liver damage in mice, and this was decreased by SFN treatment. In conclusion, SFN attenuated the cytotoxicity of CdSe QDs in both human hepatocytes and in the mouse liver, and this protection was associated with the induction of Nrf2 pathway and autophagy. PMID:26402917

  18. Enchanced methods of hydrophilized CdSe quantum dots synthesis

    NASA Astrophysics Data System (ADS)

    Potapkin, D. V.; Zharkova, I. S.; Goryacheva, I. Y.

    2015-03-01

    Quantum dots are bright and stable fluorescence signal sources, but for most of applications they need an additional hydrophilization step. Unfortunately, most of existing approaches lead to QD's fluorescence quenching, so there is a need for additional enhancing of hydrophilized QD's brightness like UV irradiation, which can be used both on water insoluble QD's with oleic acid ligands (in toluene) and on hydrophilized QD's covered with UV-stable polymer (in aqueous solution). For synthesis of bright water-soluble fluorescent labels CdSe/CdS/ZnS colloidal quantum dots were covered with PAMAM dendrimer and irradiated with UV lamp in quartz cuvettes for 3 hours at the room temperature and then compared with control sample.

  19. Tuning luminescence and reducing reabsorption of CdSe quantum disks for luminescent solar concentrators

    NASA Astrophysics Data System (ADS)

    Lin, Huichuan; Xie, Peng; Liu, Yong; Zhou, Xiang; Li, Baojun

    2015-08-01

    Cadmium selenide (CdSe) quantum disks (QDs) have been synthesized for application in luminescent solar concentrators (LSCs). Luminescence tuning and reabsorption reduction of the QDs were achieved by controlling their size using a hot injection method. The overlap of the absorption and photoluminescence spectra of the as-prepared CdSe QDs was negligible. The as-prepared CdSe QDs were incorporated into polymethylmethacrylate without aggregation and luminescence quenching. The obtained highly transparent composites with non-affecting light-emitting properties were used as LSCs. The placement of a CdSe QDs doped LSC prototype (10 × 1 × 0.1 cm) on a Si-cell resulted in a 201% increase in the electrical power output of the Si-cell compared with that of the bare Si-cell.

  20. Electron Transfer Reactions in Colloidal Quantum Dot-Ligand Complexes

    NASA Astrophysics Data System (ADS)

    Morris-Cohen, Adam Joshua

    This thesis describes a quantitative analysis of the chemical composition of colloidal II-VI quantum dot (QD)-ligand complexes and transient absorption experiments analyzing the rates of electron transfer reactions in these complexes functionalized with redox active ligands. Chemical analysis reveals that phosphonate impurities in the surfactants used to synthesize CdSe QDs are the dominant ligands on the surface of the QDs, and these phosphonate impurities cause size-dependent Cd-enrichment of the QD surface. A study of the adsorption equilibrium of solution-phase CdS quantum dots and acid-derivatized viologen ligands (V2+) reveals that the structure of the surfaces of the QDs depends on the concentration of the QDs. A new model based on the Langmuir isotherm that treats both the number of adsorbed ligands per QD and the number of available binding sites per QD as binomially-distributed quantities is described. Transient absorption spectroscopy of solution-phase mixtures of colloidal CdS QDs and V2+ indicates electron transfer occurs from the conduction band of the QD to the LUMO of V2+. The rate constant for photoinduced electron transfer (PET) is independent of the number of methylene groups in the alkyl chain on the acid-derivatized viologen. The insensitivity of the electron transfer rate constant to the length of the functional groups on the viologen suggests a van der Waals (vdW) pathway for PET, where the electron bypasses the alkylcarboxylate and tunnels through the orbitals of the QD and of the bipyridinium core. The rate of PET from colloidal CdSe quantum dots (QDs) to oxo-centered triruthenium clusters (Ru 3O) depends on the structure of the chemical headgroup by which the Ru3O clusters adsorb to the QDs. Complexes comprising QDs and Ru 3O clusters adsorbed through a pyridine-4-carboxylic acid ligand have a PET rate constant of (4.9 ± 0.9)×109 s -1 whereas complexes comprising QDs and Ru3O clusters adsorbed through a 4-mercaptopyridine ligand have an

  1. CdSe Nanoplatelets: Living Polymers.

    PubMed

    Jana, Santanu; Davidson, Patrick; Abécassis, Benjamin

    2016-08-01

    Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a "living polymer" character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends. PMID:27329047

  2. In-situ material state monitoring using embedded CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Brubaker, Cole D.; Frecker, Talitha M.; Njoroge, Ian; Shane, Dylan O.; Smudde, Christine M.; Rosenthal, Sandra J.; Jennings, G. Kane; Adams, Douglas E.

    2016-04-01

    The development of new, smart materials capable of intrinsically detecting and communicating the occurrence of external loads and resultant damage present in a material will be crucial in the advancement of future structural health monitoring (SHM) and nondestructive evaluation (NDE) technologies. Traditionally, many SHM and NDE approaches have relied on the use of physical sensors to monitor a structure for damage, but are often hindered by their requirements for power consumption and large-scale data collection. In this work, we seek to evaluate the effectiveness of ultrasmall, white-light emitting Cadmium Selenide quantum dots (CdSe QDs) as an alternative to providing in-situ material state monitoring capabilities, while also aiming to reduce reliance on data collection and power consumption to effectively monitor a material and structure for damage. To achieve this goal, CdSe QDs are embedded in an optically clear epoxy composite matrix and exposed to external mechanical loadings. Initial results show a corresponding relationship between the shifts in observed emission spectra and external load for samples containing CdSe QDs. The effectiveness of CdSe QDs as a surface strain gauge on aluminum and fiberglass are also investigated in this paper. By monitoring changes in the emission spectra for materials containing CdSe QDs before, during and after the application of external loads, the effectiveness of CdSe QDs for communicating the occurrence of external loads acting on a material and detecting changes in material state is evaluated.

  3. Microwave-assisted synthesis of CdSe quantum dots: can the electromagnetic field influence the formation and quality of the resulting nanocrystals?

    PubMed

    Moghaddam, Mojtaba Mirhosseini; Baghbanzadeh, Mostafa; Keilbach, Andreas; Kappe, C Oliver

    2012-12-01

    Microwave-assisted syntheses of colloidal nanocrystals (NCs), in particular CdSe quantum dots (QDs), have gained considerable attention due to unique opportunities provided by microwave dielectric heating. The extensive use of microwave heating and the frequently suggested specific microwave effects, however, pose questions about the role of the electromagnetic field in both the formation and quality of the produced QDs. In this work a one-pot protocol for the tunable synthesis of monodisperse colloidal CdSe NCs using microwave dielectric heating under carefully controlled conditions is introduced. CdSe QDs are fabricated using selenium dioxide as a selenium precursor, 1-octadecene as a solvent and reducing agent, cadmium alkyl carboxylates or alkyl phosphonates as cadmium sources, 1,2-hexadecanediol to stabilize the cadmium complex and oleic acid to stabilize the resulting CdSe QDs. Utilizing the possibilities of microwave heating technology in combination with accurate online temperature control the influence of different reaction parameters such as reaction temperature, ramp and hold times, and the timing and duration of oleic acid addition have been carefully investigated. Optimum results were obtained by performing the reaction at 240 °C applying a 5 min ramp time, 2 min hold time before oleic acid addition, 90 s for oleic acid addition, and a 5 min hold time after oleic acid addition (8.5 min overall holding at 240 °C). By using different cadmium complexes in the microwave protocol CdSe QDs with a narrow size distribution can be obtained in different sizes ranging from 0.5-4 nm by simply changing the cadmium source. The QDs were characterized by TEM, HRTEM, UV-Vis, and photoluminescence methods and the size distribution was monitored by SAXS. Control experiments involving conventional conductive heating under otherwise identical conditions ensuring the same heating and cooling profiles, stirring rates, and reactor geometries demonstrate that the

  4. Pulsed laser deposition of Mn doped CdSe quantum dots for improved solar cell performance

    SciTech Connect

    Dai, Qilin; Wang, Wenyong E-mail: jtang2@uwyo.edu; Tang, Jinke E-mail: jtang2@uwyo.edu; Sabio, Erwin M.

    2014-05-05

    In this work, we demonstrate (1) a facile method to prepare Mn doped CdSe quantum dots (QDs) on Zn{sub 2}SnO{sub 4} photoanodes by pulsed laser deposition and (2) improved device performance of quantum dot sensitized solar cells of the Mn doped QDs (CdSe:Mn) compared to the undoped QDs (CdSe). The band diagram of photoanode Zn{sub 2}SnO{sub 4} and sensitizer CdSe:Mn QD is proposed based on the incident-photon-to-electron conversion efficiency (IPCE) data. Mn-modified band structure leads to absorption at longer wavelengths than the undoped CdSe QDs, which is due to the exchange splitting of the CdSe:Mn conduction band by the Mn dopant. Three-fold increase in the IPCE efficiency has also been observed for the Mn doped samples.

  5. Surface-enhanced Raman scattering by colloidal CdSe nanocrystal submonolayers fabricated by the Langmuir–Blodgett technique

    PubMed Central

    Sveshnikova, Larisa L; Duda, Tatyana A; Rodyakina, Ekaterina E; Dzhagan, Volodymyr M; Gordan, Ovidiu D; Veber, Sergey L; Himcinschi, Cameliu; Latyshev, Alexander V; Zahn, Dietrich R T

    2015-01-01

    Summary We present the results of an investigation of surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR) energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm), confirming the formation of SERS “hot spots”. PMID:26734529

  6. Blue and green electroluminescence from CdSe nanocrystal quantum-dot-quantum-wells

    SciTech Connect

    Lu, Y. F.; Cao, X. A.

    2014-11-17

    CdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique, and their optical properties were tuned by bandgap and strain engineering. 3-monolayer (ML) CdSe QWs emitted blue photoluminescence at 467 nm with a spectral full-width-at-half-maximum of ∼30 nm. With a 3 ML ZnS cladding layer, which also acts as a passivating and strain-compensating layer, the QDQWs acquired a ∼35% quantum yield of the QW emission. Blue and green electroluminescence (EL) was obtained from QDQW light-emitting devices with 3–4.5 ML CdSe QWs. It was found that as the peak blueshifted, the overall EL was increasingly dominated by defect state emission due to poor hole injection into the QDQWs. The weak EL was also attributed to strong field-induced charge separation resulting from the unique QDQW geometry, weakening the oscillator strength of optical transitions.

  7. Application of CdSe quantum dots for the direct detection of TNT.

    PubMed

    Yi, Kui-Yu

    2016-02-01

    CdSe quantum dots were synthesized through a simple, green organic-phase method. Paraffin was used as the reaction solvent and a reducing agent, oleic acid was the reaction ligand, and oleyl amine was the stabilizer. Based on the phenomenon of TNT quenched oil-soluble CdSe quantum dot fluorescence, a simple, fast, and direct method of TNT detection was established. Under optimum conditions, the degree of fluorescence quenching of oil-soluble CdSe quantum dots had a good linear correlation with TNT concentration in the 1.0×10(-7)-5.0×10(-5) mol/L range, and the correlation coefficient was 0.9990. TNT detection limit was 2.1×10(-8)mol/L. The method was successfully used to determine TNT-explosion dust samples, results were satisfactory. The fluorescence quenching mechanism of oil-soluble CdSe quantum dots by TNT was also discussed. PMID:26773219

  8. The effect of Pb addition on the morphology of CdSe quantum dot

    NASA Astrophysics Data System (ADS)

    Kim, Young-Kuk; Cho, Young-Sang; Chung, Kookchae; Choi, Chul-Jin

    2010-08-01

    CdSe quantum dots had been synthesized with a hot injection method. It was shown that the addition of Pb ions in the initial precursor solution changed the morphology of CdSe nanocrystals from slightly prolate ellipsoid to branched rod. Photoluminescence (PL) of the branched nanocrystals showed rapid depression of emission intensity due to the morphological development to the branched nanocrystal induced by Pb addition. Low temperature PL spectrum indicated that the surface recombination of charge carrier resulted in the large depression of emission from the branched nanocrystal.

  9. An oleic acid-capped CdSe quantum-dot sensitized solar cell

    SciTech Connect

    Chen Jing; Song, J. L.; Deng, W. Q.; Sun, X. W.; Jiang, C. Y.; Lei, W.; Huang, J. H.; Liu, R. S.

    2009-04-13

    In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO{sub 2}/OA-CdSe photoanode in a two-electrode device exhibited a photon-to-current conversion efficiency of 17.5% at 400 nm. At AM1.5G irradiation with 100 mW/cm{sup 2} light intensity, the QDSSCs based on OA-capped CdSe showed a power conversion efficiency of about 1%. The function of OA was to increase QD loading, extend the absorption range and possibly suppress the surface recombination.

  10. The direct observation of charge separation dynamics in CdSe quantum dots/cobaloxime hybrids.

    PubMed

    Huang, J; Tang, Y; Mulfort, K L; Zhang, X

    2016-02-14

    In this work, we investigated photoinduced charge separation dynamics in a CdSe quantum dot/cobaloxime molecular catalyst hybrid using the combination of transient optical (OTA) and X-ray absorption (XTA) spectroscopy. We show that ultrafast charge separation occurs through electron transfer (ET) from CdSe QDs to cobaloxime. In addition to the enhanced 1S exciton bleach recovery in CdSe QDs due to the presence of cobaloxime, the direct evidence for ET process, i.e. the formation of the transient charge separated state, is captured by XTA. These results not only demonstrate the capability of XTA to capture the transient species during the photoinduced reactions in hybrid nanostructures but also enhance our understanding of charge separation dynamics in semiconductor nanocrystal/molecular catalyst hybrid. PMID:26805707

  11. The Optical Properties of CdSe Quantum Dots by Using Spray-Atomization Method

    NASA Astrophysics Data System (ADS)

    Rosmani, C. H.; Abdullah, S.; Rusop, M.

    2013-06-01

    Cadmium Selenide (CdSe) quantum dots (QDs) is inorganic material by using spray-atomization method which is the novelty to find out the optical properties for the CdSe QDs. The Selenium (Se) precursor and Cadmium (Cd) precursor were prepared first. Se precursor by using sodium sulfite aqueous was mixed with selenium (Se) powder. For Cd precursor was used cadmium chloride (CdCI) as the Cd precursor. From previous research, CdSe QDs was obtained by using capping agent such as tri-n-octylphosphine oxide (TOPO) and trioctylphosphine (TOP). These capping agent are hazardous to environment and human. By using spray-atomization method it is more safe and economically. The photoluminescence (PL) was used to investigate the optical properties and to investigate the energy band gap from PL result. The field emission scanning electron microscopy (FESEM) was used to know the surface morphology of CdSe QDs. By PL result, the energy band gap was calculate and the comparison was investigate between the size of particle and the energy band gap. This important in this paper is to investigate the optical properties of CdSe QDs by using sprays-atomization method and to relate with the particle size.

  12. Enhanced photorefractive performance in CdSe quantum-dot-dispersed poly(styrene-co-acrylonitrile) polymers

    SciTech Connect

    Li Xiangping; Embden, Joel van; Chon, James W. M.; Gu Min; Evans, Richard A.

    2010-06-21

    This paper reports on the enhanced photorefractive behavior of a CdSe quantum-dot-dispersed less expensive polymer of poly(styrene-co-acrylonitrile). The capability of CdSe quantum dots used as photosensitizers and the associated photorefractive performance are characterized through a photocurrent experiment and a two-beam coupling experiment, respectively. An enhanced two-beam coupling gain coefficient of 12.2 cm{sup -1} at 46 V/mum was observed owning to the reduced potential barrier. The photorefractive performance per CdSe quantum dot is three orders of magnitude higher than that in the sample sensitized by trinitrofluorenone in poly(styrene-co-acrylonitrile), and almost ten times higher than that in the CdSe quantum-dot-sensitized poly(N-vinylcarbazole) polymers.

  13. Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots

    SciTech Connect

    Sharma, Madhulika; Sharma, A.B.; Mishra, N.; Pandey, R.K.

    2011-03-15

    Research highlights: {yields} CdSe q-dots have been synthesized using simple chemical synthesis route. {yields} Thin film of CdSe quantum dots exhibited self-organized growth. {yields} Size dependent blue shift observed in the absorption edge of CdSe nanocrystallites. {yields} PL emission band corresponds to band edge luminescence and defect luminescence. {yields} Organized growth led to enhancement in luminescence yield of smaller size Q-dots. -- Abstract: Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.

  14. Wavefunction engineering: From quantum wells to near-infrared type-II colloidal quantum dots synthesized by layer-by-layer colloidal epitaxy.

    PubMed

    Li, J Jack; Tsay, James M; Michalet, Xavier; Weiss, Shimon

    2005-11-15

    We review the concept and the evolution of bandgap and wavefunction engineering, the seminal contributions of Dr. Chemla to the understanding of the rich phenomena displayed in epitaxially grown quantum confined systems, and demonstrate the application of these concepts to the colloidal synthesis of high quality type-II CdTe/CdSe quantum dots using successive ion layer adsorption and reaction chemistry. Transmission electron microscopy reveals that CdTe/CdSe can be synthesized layer by layer, yielding particles of narrow size distribution. Photoluminescence emission and excitation spectra reveal discrete type-II transitions, which correspond to energy lower than the type-I bandgap. The increase in the spatial separation between photoexcited electrons and holes as a function of successive addition of CdSe monolayers was monitored by photoluminescence lifetime measurements. Systematic increase in lifetimes demonstrates the high level of wavefunction engineering and control in these systems. PMID:22865949

  15. Enhanced chemiluminescence CdSe quantum dots by histidine and tryptophan

    NASA Astrophysics Data System (ADS)

    Hosseini, Morteza; Ganjali, Mohammad Reza; Jarrahi, Afsaneh; Vaezi, Zahra; Mizani, Farhang; Faridbod, Farnoush

    2014-11-01

    The enhancing effect of histidine and tryptophan on chemiluminescence (CL) of CdSe quantum dots (QDs)-H2O2 system was studied. This reaction is based on the catalytic effect of amino acids, causing a significant increase in the light emission, as a result of the reaction of quantum dots (QDs) with hydrogen peroxide. In the optimum conditions, this method was satisfactorily described by linear calibration curve in the range of 0.66-35.5 μM and 0.83-35.1 μM for histidine and tryptophan, respectively. The effect of various parameters such as concentration of CdSe QDs, concentration of H2O2 and concentration of imidazole on the intensity of CL system were studied. The main experimental advantage of the proposed method is it's selective to two amino acids compared with other amino acids.

  16. Electro-absorption of an ensemble of close-packed CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Gurinovich, Leonid I.; Artemyev, Mikhail V.

    2002-05-01

    Highly monodisperse CdSe quantum dots 1.8 nm in size were synthesized capped with surface monolayer of 1-thioglycerol. The optical absorption of thin films of matrix free close- packed and isolated in PMMA matrix quantum dots was studied at various electric field biases. The broadening and red shift of optical transitions in close-packed ensemble against isolated is attributed to the formation of collective electronic submini-bands between interacting nanocrystals. The reversible collapse of collective electronic subminibands has been achieved by applying of strong electric field to the thin film of close-packed quantum dots.

  17. Photostability of CdSe quantum dots functionalized with aromatic dithiocarbamate ligands.

    PubMed

    Tan, Yizheng; Jin, Song; Hamers, Robert J

    2013-12-26

    Organic ligands are widely used to enhance the ability of CdSe quantum dots (QDs) to resist photodegradation processes such as photo-oxidation. Because long alkyl chains may adversely affect the performance of QD devices that require fast and efficient charge transfer, shorter aromatic ligands are of increasing interest. In this work, we characterize the formation of phenyl dithiocarbamate (DTC) adducts on CdSe surfaces and the relative effectiveness of different para-substituted phenyl dithiocarbamates to enhance the aqueous photostability of CdSe QDs on TiO2. Optical absorption and photoluminescence measurements show that phenyl DTC ligands can be highly effective at reducing QD photocorrosion in water, and that ligands bearing electron-donating substituents are the most effective. A comparison of the QD photostability resulting from use of ligands bearing DTC versus thiol surface-binding groups shows that the DTC group provides greater QD photostability. Density functional calculations with natural bond order analysis show that the effectiveness of substituted phenyl DTC results from the ability of these ligands to remove positive charge away from the CdSe and to delocalize positive charge on the ligand. PMID:24256318

  18. Magnetoconductance of CdSe in the hopping regime: The effect of quantum interference

    SciTech Connect

    Zhang, Y.; Dai, P.; Sarachik, M.P. )

    1992-04-15

    A magnetoconductance is observed for weakly insulating {ital n}-type CdSe, which, depending on the temperature of the measurement, is quadratic or approximately linear with field in small magnetic fields, and exhibits saturation as the field is increased. The crossovers from quadratic to linear behavior and to saturation occur at magnetic fields which are consistent with theoretical expectations for the effect of quantum interference in the hopping regime.

  19. Influence of Surfactants and Charges on CdSe Quantum Dots

    SciTech Connect

    Yang, Ping; Tretiak, Sergei; Ivanov, Sergei

    2011-01-01

    Surface effects significantly influence the functionality of semiconductor nanocrystals. High quality nanocrystals can be achieved with good control of surface passivation by various hydrophobic ligands. In this work, the chemistry between CdSe quantum dots and common surface capping ligands is investigated using density functional theory (DFT). We discuss the electronic structures and optical properties of small CdSe clusters controlled by their size of particle, self-organization, capping ligands, and positive charges. The chosen model ligands reproduce good structural and energetic description of the interactions between the ligands and quantum dots. In order to capture the chemical nature and energetics of the interactions between the capping ligands and CdSe quantum dots, we found that PMe3 is needed to adequately model trioctylphosphine (TOP), NH3 is sufficient for amines, while OPH2Me could be used to model trioctylphosphine oxide. The relative binding interaction strength between ligands was found to decrease in order Cd–O > Cd–N > Cd–P with average binding energy per ligand being -25 kcal/mol for OPH₂Me, -20 kcal/mol for NH₃ and -10 kcal/mol for PMe₃. Charges on studied stoichiometric clusters were found to have a significant effect on their structures, binding energies, and optical properties.

  20. CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

    NASA Astrophysics Data System (ADS)

    Dieu Thuy Ung, Thi; Tran, Thi Kim Chi; Nga Pham, Thu; Nghia Nguyen, Duc; Khang Dinh, Duy; Liem Nguyen, Quang

    2012-12-01

    This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ∼500 and 700 nm with the luminescence quantum yield (LQY) of 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml‑1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng μl‑1 with a detection limit of 3 ng μL‑1 has been performed based on the antibody-antigen recognition.

  1. Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Gao, Bing; Shen, Chao; Zhang, Bo; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia; Chen, Guorong

    2014-05-01

    Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30 nm, and absorption peak from 475 nm to 510 nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO2 electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO2's to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO2. The resulting green synthesized CdSe QDSCs with Cu2S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

  2. Templating growth of gold nanostructures with a CdSe quantum dot array.

    PubMed

    Paul, Neelima; Metwalli, Ezzeldin; Yao, Yuan; Schwartzkopf, Matthias; Yu, Shun; Roth, Stephan V; Müller-Buschbaum, Peter; Paul, Amitesh

    2015-06-01

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing incidence small-angle X-ray scattering (GISAXS) during gold sputter deposition. Gold is sputtered on a CdSe quantum dot array with a characteristic quantum dot spacing of ≈7 nm. In the initial stages of gold nanostructure growth, a preferential deposition of gold on top of quantum dots occurs. Thus, the quantum dots act as nucleation sites for gold growth. In later stages, the gold nanoparticles surrounding the quantum dots undergo a coarsening to form a complete layer comprised of gold-dot clusters. Next, growth proceeds dominantly via vertical growth of gold on these gold-dot clusters to form an gold capping layer. In this capping layer, a shift of the cluster boundaries due to ripening is found. Thus, a templating of gold on a CdSe quantum dot array is feasible at low gold coverage. PMID:25960066

  3. Templating growth of gold nanostructures with a CdSe quantum dot array

    NASA Astrophysics Data System (ADS)

    Paul, Neelima; Metwalli, Ezzeldin; Yao, Yuan; Schwartzkopf, Matthias; Yu, Shun; Roth, Stephan V.; Müller-Buschbaum, Peter; Paul, Amitesh

    2015-05-01

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing incidence small-angle X-ray scattering (GISAXS) during gold sputter deposition. Gold is sputtered on a CdSe quantum dot array with a characteristic quantum dot spacing of ~7 nm. In the initial stages of gold nanostructure growth, a preferential deposition of gold on top of quantum dots occurs. Thus, the quantum dots act as nucleation sites for gold growth. In later stages, the gold nanoparticles surrounding the quantum dots undergo a coarsening to form a complete layer comprised of gold-dot clusters. Next, growth proceeds dominantly via vertical growth of gold on these gold-dot clusters to form an gold capping layer. In this capping layer, a shift of the cluster boundaries due to ripening is found. Thus, a templating of gold on a CdSe quantum dot array is feasible at low gold coverage.

  4. Optical properties of water soluble CdSe quantum dots modified by a novel biopolymer based on sodium alginate

    NASA Astrophysics Data System (ADS)

    Bardajee, Ghasem Rezanejade; Hooshyar, Zari

    2013-10-01

    Water soluble CdSe quantum dots (QDs) were modified using a novel biopolymer based on the graft copolymerization of poly (acrylic acid) as a monomer onto sodium alginate as a backbone at room temperature. The obtained CdSe QDs were characterized by Fourier transform infrared spectrometer, thermo-gravimetry analysis, transmission electron microscopy, and dynamic light scattering. Optical properties of the prepared CdSe QDs were investigated by absorption and fluorescence spectra. It was found that the resultant QDs incredibly exhibited high fluorescence intensity and quantum yields. Lastly, the influence of the aging time on the fluorescence intensity of the modified CdSe QDs was studied by their fluorescence spectra. Due to the optical behavior of this modified QDs; it could be of potential interest in biological systems.

  5. Size control by rate control in colloidal PbSe quantum dot synthesis

    NASA Astrophysics Data System (ADS)

    Čapek, Richard Karel; Yanover, Dianna; Lifshitz, Efrat

    2015-03-01

    A recently demonstrated approach to control the size of colloidal nanoparticles, ``size control by rate control'', which was validated on the examples of colloidal CdSe- and CdS-quantum dot (CQD) synthesis, appears to be a general strategy for designing technically applicable CQD-syntheses. The ``size control by rate control'' concept allows full-yield syntheses of ensembles of CQDs with different sizes by tuning the solute formation rate. In this work, we extended this strategy to dialkylphosphine enhanced hot-injection synthesis of PbSe-CQDs. Furthermore, we provide new insight into the reaction mechanism of dialkylphosphine enhancement in TOPSe based CQD-syntheses.A recently demonstrated approach to control the size of colloidal nanoparticles, ``size control by rate control'', which was validated on the examples of colloidal CdSe- and CdS-quantum dot (CQD) synthesis, appears to be a general strategy for designing technically applicable CQD-syntheses. The ``size control by rate control'' concept allows full-yield syntheses of ensembles of CQDs with different sizes by tuning the solute formation rate. In this work, we extended this strategy to dialkylphosphine enhanced hot-injection synthesis of PbSe-CQDs. Furthermore, we provide new insight into the reaction mechanism of dialkylphosphine enhancement in TOPSe based CQD-syntheses. Electronic supplementary information (ESI) available: Additional data about the reaction and growth kinetics, NMR-data and exemplary TEM images of PbSe-CQDs prepared by the procedure described in this publication. See DOI: 10.1039/c5nr00028a

  6. Exploring size and state dynamics in CdSe quantum dots using two-dimensional electronic spectroscopy

    SciTech Connect

    Caram, Justin R.; Zheng, Haibin; Rolczynski, Brian S.; Griffin, Graham B.; Engel, Gregory S.; Dahlberg, Peter D.; Dolzhnikov, Dmitriy S.; Talapin, Dmitri V.

    2014-02-28

    Development of optoelectronic technologies based on quantum dots depends on measuring, optimizing, and ultimately predicting charge carrier dynamics in the nanocrystal. In such systems, size inhomogeneity and the photoexcited population distribution among various excitonic states have distinct effects on electron and hole relaxation, which are difficult to distinguish spectroscopically. Two-dimensional electronic spectroscopy can help to untangle these effects by resolving excitation energy and subsequent nonlinear response in a single experiment. Using a filament-generated continuum as a pump and probe source, we collect two-dimensional spectra with sufficient spectral bandwidth to follow dynamics upon excitation of the lowest three optical transitions in a polydisperse ensemble of colloidal CdSe quantum dots. We first compare to prior transient absorption studies to confirm excitation-state-dependent dynamics such as increased surface-trapping upon excitation of hot electrons. Second, we demonstrate fast band-edge electron-hole pair solvation by ligand and phonon modes, as the ensemble relaxes to the photoluminescent state on a sub-picosecond time-scale. Third, we find that static disorder due to size polydispersity dominates the nonlinear response upon excitation into the hot electron manifold; this broadening mechanism stands in contrast to that of the band-edge exciton. Finally, we demonstrate excitation-energy dependent hot-carrier relaxation rates, and we describe how two-dimensional electronic spectroscopy can complement other transient nonlinear techniques.

  7. Exploring size and state dynamics in CdSe quantum dots using two-dimensional electronic spectroscopy

    PubMed Central

    Caram, Justin R.; Zheng, Haibin; Dahlberg, Peter D.; Rolczynski, Brian S.; Griffin, Graham B.; Dolzhnikov, Dmitriy S.; Talapin, Dmitri V.; Engel, Gregory S.

    2014-01-01

    Development of optoelectronic technologies based on quantum dots depends on measuring, optimizing, and ultimately predicting charge carrier dynamics in the nanocrystal. In such systems, size inhomogeneity and the photoexcited population distribution among various excitonic states have distinct effects on electron and hole relaxation, which are difficult to distinguish spectroscopically. Two-dimensional electronic spectroscopy can help to untangle these effects by resolving excitation energy and subsequent nonlinear response in a single experiment. Using a filament-generated continuum as a pump and probe source, we collect two-dimensional spectra with sufficient spectral bandwidth to follow dynamics upon excitation of the lowest three optical transitions in a polydisperse ensemble of colloidal CdSe quantum dots. We first compare to prior transient absorption studies to confirm excitation-state-dependent dynamics such as increased surface-trapping upon excitation of hot electrons. Second, we demonstrate fast band-edge electron-hole pair solvation by ligand and phonon modes, as the ensemble relaxes to the photoluminescent state on a sub-picosecond time-scale. Third, we find that static disorder due to size polydispersity dominates the nonlinear response upon excitation into the hot electron manifold; this broadening mechanism stands in contrast to that of the band-edge exciton. Finally, we demonstrate excitation-energy dependent hot-carrier relaxation rates, and we describe how two-dimensional electronic spectroscopy can complement other transient nonlinear techniques. PMID:24588185

  8. Facile and green synthesis of CdSe quantum dots in protein matrix: tuning of morphology and optical properties.

    PubMed

    Ahmed, M; Guleria, A; Rath, M C; Singh, A K; Adhikari, S; Sarkar, S K

    2014-08-01

    Herein, we have demonstrated a facile and green approach for the synthesis of Cadmium selenide (CdSe) quantum dots (QDs). The process was mediated by bovine serum albumin (BSA) and it was found that BSA plays the dual role of reducing agent as well as a stabilizing agent. The QDs exhibited sharp excitonic absorption features at ~500 nm and subsequently showed reasonably good photoluminescence (PL) at room temperature. The PL is seen to be strongly dependent on the concentration of the precursors and hence, the luminescence of these QDs could be conveniently tuned across the visible spectrum simply by varying molar ratio of the precursors. It can be envisaged from the fact that a red-shift of about 100 nm in the PL peak position was observed when the molar ratio of the precursors ([Cd2+]:[Se2-], in mM) was varied from 10:5 to 10:40. Subsequently, the charge carrier relaxation dynamics associated with the different molar ratio of precursors has been investigated and very interesting information regarding the energy level structures of these QDs were revealed. Most importantly, in conjunction with the optical tuning, the nanomorphology of these nanoparticles was found to vary with the change in molar ratios of Se and Cd precursors. This aspect can provide a new direction of controlling the shape of CdSe nanoparticles. The possible mechanism of the formation as well as for the shape variation of these nanoparticles with the molar ratios of precursors has been proposed, taking into account the role of amino acid residues (present in BSA). Moreover, the QDs were water soluble and possessed fairly good colloidal stability therefore, can have potential applications in catalysis and bio-labeling. On the whole, the present methodology of protein assisted synthesis is relatively new especially for semiconducting nanomaterials and may provide some unique and interesting aspects to control and fine tune the morphology vis-à-vis, their optical properties. PMID:25935997

  9. Multicolored silica coated CdSe core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Goftman, Valentina V.; Markin, Alexey V.; De Saeger, Sarah; Goryacheva, Irina Y.

    2016-04-01

    Silanization is a convenient route to provide water-solubility to the quantum dots (QDs) with different structure. Green, orange and red emitting CdSe-based QDs were synthesized by varying of number and material of wider-band gap shells and fluorescent properties of QDs were characterized before and after silanization. It was shown that structure of the QD influences on the quantum yield of the silanized QDs: the better CdSe core is protected with wider-band gap semiconductor shells, the more fluorescence properties remain after silica coated QD possess. Hence silica coated QDs have a great perspectives for the multiplex analysis.

  10. Observation of an Excitonic Quantum Coherence in CdSe Nanocrystals.

    PubMed

    Dong, Shuo; Trivedi, Dhara; Chakrabortty, Sabyasachi; Kobayashi, Takayoshi; Chan, Yinthai; Prezhdo, Oleg V; Loh, Zhi-Heng

    2015-10-14

    Recent observations of excitonic coherences within photosynthetic complexes suggest that quantum coherences could enhance biological light harvesting efficiencies. Here, we employ optical pump-probe spectroscopy with few-femtosecond pulses to observe an excitonic quantum coherence in CdSe nanocrystals, a prototypical artificial light harvesting system. This coherence, which encodes the high-speed migration of charge over nanometer length scales, is also found to markedly alter the displacement amplitudes of phonons, signaling dynamics in the non-Born-Oppenheimer regime. PMID:26359970

  11. CdSe Quantum-Dot-Sensitized Solar Cell with ~100% Internal Quantum Efficiency

    SciTech Connect

    Fuke, Nobuhiro; Hoch, Laura B.; Koposov, Alexey Y.; Manner, Virginia W.; Werder, Donald J.; Fukui, Atsushi; Koide, Naoki; Katayama, Hiroyuki; Sykora, Milan

    2010-10-20

    We have constructed and studied photoelectrochemical solar cells (PECs) consisting of a photoanode prepared by direct deposition of independently synthesized CdSe nanocrystal quantum dots (NQDs) onto a nanocrystalline TiO2 film (NQD/TiO2), aqueous Na2S or Li2S electrolyte, and a Pt counter electrode. We show that light harvesting efficiency (LHE) of the NQD/TiO2 photoanode is significantly enhanced when the NQD surface passivation is changed from tri-n-octylphosphine oxide (TOPO) to 4-butylamine (BA). In the PEC the use of NQDs with a shorter passivating ligand, BA, leads to a significant enhancement in both the electron injection efficiency at the NQD/TiO2 interface and charge collection efficiency at the NQD/electrolyte interface, with the latter attributed mostly to a more efficient diffusion of the electrolyte through the pores of the photoanode. We show that by utilizing BA-capped NQDs and aqueous Li2S as an electrolyte, it is possible to achieve ~100% internal quantum efficiency of photon-to-electron conversion, matching the performance of dye-sensitized solar cells.

  12. Electroluminescence of colloidal quasi-two-dimensional semiconducting CdSe nanostructures in a hybrid light-emitting diode

    SciTech Connect

    Selyukov, A. S. Vitukhnovskii, A. G.; Lebedev, V. S.; Vashchenko, A. A.; Vasiliev, R. B.; Sokolikova, M. S.

    2015-04-15

    We report on the results of studying quasi-two-dimensional nanostructures synthesized here in the form of semiconducting CdSe nanoplatelets with a characteristic longitudinal size of 20–70 nm and a thick-ness of a few atomic layers. Their morphology is studied using TEM and AFM and X-ray diffraction analysis; the crystal structure and sizes are determined. At room and cryogenic temperatures, the spectra and kinetics of the photoluminescence of such structures (quantum wells) are investigated. A hybrid light-emitting diode operating on the basis of CdSe nanoplatelets as a plane active element (emitter) is developed using the organic materials TAZ and TPD to form electron and hole transport layers, respectively. The spectral and current-voltage characteristics of the constructed device with a radiation wavelength λ = 515 nm are obtained. The device triggering voltage is 5.5 V (visible glow). The use of quasi-two-dimensional structures of this type is promising for hybrid light-emitting diodes with pure color and low operating voltages.

  13. Reversed oxygen sensing using colloidal quantum wells towards highly emissive photoresponsive varnishes.

    PubMed

    Lorenzon, Monica; Christodoulou, Sotirios; Vaccaro, Gianfranco; Pedrini, Jacopo; Meinardi, Francesco; Moreels, Iwan; Brovelli, Sergio

    2015-01-01

    Colloidal quantum wells combine the advantages of size-tunable electronic properties with vast reactive surfaces that could allow one to realize highly emissive luminescent-sensing varnishes capable of detecting chemical agents through their reversible emission response, with great potential impact on life sciences, environmental monitoring, defence and aerospace engineering. Here we combine spectroelectrochemical measurements and spectroscopic studies in a controlled atmosphere to demonstrate the 'reversed oxygen-sensing' capability of CdSe colloidal quantum wells, that is, the exposure to oxygen reversibly increases their luminescence efficiency. Spectroelectrochemical experiments allow us to directly relate the sensing response to the occupancy of surface states. Magneto-optical measurements demonstrate that, under vacuum, heterostructured CdSe/CdS colloidal quantum wells stabilize in their negative trion state. The high starting emission efficiency provides a possible means to enhance the oxygen sensitivity by partially de-passivating the particle surfaces, thereby enhancing the density of unsaturated sites with a minimal cost in term of luminescence losses. PMID:25910499

  14. Reversed oxygen sensing using colloidal quantum wells towards highly emissive photoresponsive varnishes

    NASA Astrophysics Data System (ADS)

    Lorenzon, Monica; Christodoulou, Sotirios; Vaccaro, Gianfranco; Pedrini, Jacopo; Meinardi, Francesco; Moreels, Iwan; Brovelli, Sergio

    2015-03-01

    Colloidal quantum wells combine the advantages of size-tunable electronic properties with vast reactive surfaces that could allow one to realize highly emissive luminescent-sensing varnishes capable of detecting chemical agents through their reversible emission response, with great potential impact on life sciences, environmental monitoring, defence and aerospace engineering. Here we combine spectroelectrochemical measurements and spectroscopic studies in a controlled atmosphere to demonstrate the ‘reversed oxygen-sensing’ capability of CdSe colloidal quantum wells, that is, the exposure to oxygen reversibly increases their luminescence efficiency. Spectroelectrochemical experiments allow us to directly relate the sensing response to the occupancy of surface states. Magneto-optical measurements demonstrate that, under vacuum, heterostructured CdSe/CdS colloidal quantum wells stabilize in their negative trion state. The high starting emission efficiency provides a possible means to enhance the oxygen sensitivity by partially de-passivating the particle surfaces, thereby enhancing the density of unsaturated sites with a minimal cost in term of luminescence losses.

  15. Reversed oxygen sensing using colloidal quantum wells towards highly emissive photoresponsive varnishes

    PubMed Central

    Lorenzon, Monica; Christodoulou, Sotirios; Vaccaro, Gianfranco; Pedrini, Jacopo; Meinardi, Francesco; Moreels, Iwan; Brovelli, Sergio

    2015-01-01

    Colloidal quantum wells combine the advantages of size-tunable electronic properties with vast reactive surfaces that could allow one to realize highly emissive luminescent-sensing varnishes capable of detecting chemical agents through their reversible emission response, with great potential impact on life sciences, environmental monitoring, defence and aerospace engineering. Here we combine spectroelectrochemical measurements and spectroscopic studies in a controlled atmosphere to demonstrate the ‘reversed oxygen-sensing’ capability of CdSe colloidal quantum wells, that is, the exposure to oxygen reversibly increases their luminescence efficiency. Spectroelectrochemical experiments allow us to directly relate the sensing response to the occupancy of surface states. Magneto-optical measurements demonstrate that, under vacuum, heterostructured CdSe/CdS colloidal quantum wells stabilize in their negative trion state. The high starting emission efficiency provides a possible means to enhance the oxygen sensitivity by partially de-passivating the particle surfaces, thereby enhancing the density of unsaturated sites with a minimal cost in term of luminescence losses. PMID:25910499

  16. Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

    SciTech Connect

    Bera, Susnata; Singh, Shashi B.; Ray, S.K.

    2012-05-15

    Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage ({approx}2.2 V) .The EL peak intensity was found to increase by increasing the operating current. - Graphical abstract: Light emitting diode was fabricated using CdSe quantum dots using olive oil as the capping agent, instead of toxic phosphine. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting device shows strong electroluminescence in the range 630-661 nm. Highlights: Black-Right-Pointing-Pointer CdSe Quantum dots were synthesized using olive oil as the capping agent. Black-Right-Pointing-Pointer Light emitting device was fabricated using CdSe QDs/P3HT polymer heterojunction. Black-Right-Pointing-Pointer The I-V characteristics study showed low turn on voltage at {approx}2.2 V. Black-Right-Pointing-Pointer The EL peak intensity increases with increasing the operating current.

  17. Quantum dot sensitized solar cells. A tale of two semiconductor nanocrystals: CdSe and CdTe.

    PubMed

    Bang, Jin Ho; Kamat, Prashant V

    2009-06-23

    CdSe and CdTe nanocrystals are linked to nanostructured TiO2 films using 3-mercaptopropionic acid as a linker molecule for establishing the mechanistic aspects of interfacial charge transfer processes. Both these quantum dots are energetically capable of sensitizing TiO2 films and generating photocurrents in quantum dot solar cells. These two semiconductor nanocrystals exhibit markedly different external quantum efficiencies ( approximately 70% for CdSe and approximately 0.1% for CdTe at 555 nm). Although CdTe with a more favorable conduction band energy (E(CB) = -1.0 V vs NHE) is capable of injecting electrons into TiO2 faster than CdSe (E(CB) = -0.6 V vs NHE), hole scavenging by a sulfide redox couple remains a major bottleneck. The sulfide ions dissolved in aqueous solutions are capable of scavenging photogenerated holes in photoirradiated CdSe system but not in CdTe. The anodic corrosion and exchange of Te with S dominate the charge transfer at the CdTe interface. Factors that dictate the efficiency and photostability of CdSe and CdTe quantum dots are discussed. PMID:19435373

  18. Spin Selective Charge Transport through Cysteine Capped CdSe Quantum Dots.

    PubMed

    Bloom, Brian P; Kiran, Vankayala; Varade, Vaibhav; Naaman, Ron; Waldeck, David H

    2016-07-13

    This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport. The spin filtering properties of chiral nanoparticles were investigated by magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements and magnetoresistance measurements. The mCP-AFM measurements show that the chirality of the quantum dots and the magnetic orientation of the tip affect the current-voltage curves. Similarly, magnetoresistance measurements demonstrate that the electrical transport through films of chiral quantum dots correlates with the chiroptical properties of the QD. The spin filtering properties of chiral quantum dots may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices. PMID:27336320

  19. Photo-gated charge transfer of organized assemblies of CdSe quantum dots.

    PubMed

    Pradhan, Sulolit; Chen, Shaowei; Wang, Shizhong; Zou, Jing; Kauzlarich, Susan M; Louie, Angelique Y

    2006-01-17

    The electronic conductivity of tri-n-octylphosphineoxide (TOPO)-protected CdSe quantum dots (QDs) was studied at the air-water interface using the Langmuir technique within the context of photochemical and photophysical excitation. It was found that, upon photoirradiation with photon energies higher than that of the absorption threshold, the voltammetric currents increased rather substantially with a pair of voltammetric peaks at positive potentials. However, the photoconductivity profiles exhibited a dynamic transition, which was ascribed to the strong affinity of oxygen onto the CdSe surface and the consequent trapping of the photogenerated electrons. The resulting excess of holes led to photocorrosion of the particle cores. The oxygen adsorption and photoetching processes were found to be reversible upon cessation of the photoexcitation. In contrast, only featureless voltammetric responses were observed when the particle monolayers were deposited onto the electrode surface and the film conductance was measured in a vacuum (the overall profiles were analogous to that of a Coulomb blockade). A comparative study was also carried out with a CdSe dropcast thick film immersed in acetonitrile, where the photoconductivity profiles were reversible and almost linear. The latter was attributed to the separation of photogenerated electrons and holes which were subsequently collected at the electrodes under voltammetric control. In the dropcast system, the oxygen effects were minimal which was ascribed to the acetontrile medium that limited the access to oxygen and thus the particles were chemically intact. These studies suggest that chemical environment plays an important role in the determination of the chemical stability and electronic conductivity of CdSe QD thin films. PMID:16401132

  20. Study of colloidal quantum dot surfaces using an innovative thin-film positron 2D-ACAR method

    NASA Astrophysics Data System (ADS)

    Barbiellini, B.; Bansil, A.; Eijt, S. W. H.; Schut, H.; Mijnarends, P. E.; Denison, A. B.

    2006-03-01

    Despite a wealth of information, many fundamental questions regarding the nature of the surface of nanosized inorganic particles and its relationship with the electronic structure remain unsolved. We have investigated the electron momentum density (EMD) of colloidal CdSe quantum-dots via depth-resolved positron 2D angular correlation of annihilation (2D-ACAR) spectroscopy at the Delft intense variable-energy positron beam. This method, in combination with first-principles calculations of the EMD, shows that implanted positrons are trapped at the surface of CdSe nanocrystals. They annihilate mostly with the Se electrons and monitor changes in composition and structure of the surface while hardly sensing the ligand molecules. We thus unambiguously confirm [1] the strong surface relaxation predicted by first-principles calculations [2]. Work supported by the USDOE.[1] S.W.H. Eijt et al., Nature Materials (in press).[2] A. Puzder, et al., Phys. Rev. Lett. 92, 217401 (2004).

  1. Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

    NASA Astrophysics Data System (ADS)

    Bera, Susnata; Singh, Shashi B.; Ray, S. K.

    2012-05-01

    Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage (˜2.2 V) .The EL peak intensity was found to increase by increasing the operating current.

  2. Determination of the Exciton Binding Energy in CdSe Quantum Dots

    SciTech Connect

    Meulenberg, R; Lee, J; Wolcott, A; Zhang, J; Terminello, L; van Buuren, T

    2009-10-27

    The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been determined using x-ray spectroscopy. Using x-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been determined and combined to obtain the true band gap of the QDs (i.e. without and exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to determine the EBE. The experimental EBE results are compared with theoretical calculations on the EBE and show excellent agreement.

  3. Electrooptical properties of hybrid liquid crystalline systems containing CdSe quantum dots

    SciTech Connect

    Dradrach, K. Bartkiewicz, S.; Miniewicz, A.

    2014-12-08

    In this paper, we present electrooptical properties of hybrid liquid crystalline systems, which contained CdSe quantum dots (QDs). We have shown by experiments of degenerated two-wave mixing and transverse conductivity measurements that liquid crystal cells filled with nematic and doped with semiconductor nanoparticles exhibit photorefractive effect associated with photoconductivity appearing in the system. We also present the mathematical model, which explains the relationship between the photoconductivity of the layer on which the QDs reside and the generation of holographic gratings. Our research may help to develop better understanding of processes observed in such systems and create more efficient materials for holographic data storage.

  4. Electrooptical properties of hybrid liquid crystalline systems containing CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Dradrach, K.; Bartkiewicz, S.; Miniewicz, A.

    2014-12-01

    In this paper, we present electrooptical properties of hybrid liquid crystalline systems, which contained CdSe quantum dots (QDs). We have shown by experiments of degenerated two-wave mixing and transverse conductivity measurements that liquid crystal cells filled with nematic and doped with semiconductor nanoparticles exhibit photorefractive effect associated with photoconductivity appearing in the system. We also present the mathematical model, which explains the relationship between the photoconductivity of the layer on which the QDs reside and the generation of holographic gratings. Our research may help to develop better understanding of processes observed in such systems and create more efficient materials for holographic data storage.

  5. A novel strategy towards designing a CdSe quantum dot-metallohydrogel composite material.

    PubMed

    Chatterjee, Sayantan; Maitra, Uday

    2016-08-11

    We have described here an efficient method to disperse hydrophobic CdSe quantum dots (QDs) in an aqueous phase using cetyltrimethylammonium bromide (CTAB) micelles without any surface ligand exchange. The water soluble QDs were then embedded in 3D self assembled fibrillar networks (SAFINs) of a hydrogel showing homogeneous dispersibility as evidenced from optical and electron microscopic techniques. The photophysical studies of the hydrogel-QD composite are reported for the first time. These composite materials may have potential applications in biology, optoelectronics, sensors, non-linear optics and materials science. PMID:27465805

  6. Luminescence upconversion in colloidal double quantum dots.

    PubMed

    Deutsch, Zvicka; Neeman, Lior; Oron, Dan

    2013-09-01

    Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved. PMID:23912060

  7. Synthesis of CdSe quantum dots using selenium dioxide as selenium source and its interaction with pepsin

    NASA Astrophysics Data System (ADS)

    Wang, Yilin; Mo, Yunchuan; Zhou, Liya

    2011-09-01

    A novel method has been developed for the synthesis of thioglycolic acid (TGA)-capped CdSe quantum dots (QDs) in an aqueous medium when selenium dioxide worked as a selenium source and sodium borohydride acted as a reductant. The interaction between CdSe QDs and pepsin was investigated by fluorescence spectroscopy. It was proved that the fluorescence quenching of pepsin by CdSe QDs was mainly a result of the formation of CdSe-pepsin complex. Based on the fluorescence quenching results, the Stern-Volmer quenching constant ( Ksv), binding constant ( KA) and binding sites ( n) were calculated. According to the Foster's non-radiative energy transfer theory, the binding distance ( r) between pepsin and CdSe QDs was obtained. The influence of CdSe QDs on the conformation of pepsin has been analyzed by synchronous fluorescence spectra, which provided that the secondary structure of pepsin has been changed by the interaction of CdSe QDs with pepsin.

  8. Energy relaxation in CdSe nanocrystals: the effects of morphology and film preparation.

    PubMed

    Spann, Bryan T; Chen, Liangliang; Ruan, Xiulin; Xu, Xianfan

    2013-01-14

    Ultrafast time-resolved absorption spectroscopy is used to investigate exciton dynamics in CdSe nanocrystal films. The effects of morphology, quantum-dot versus quantum-rod, and preparation of nanocrystals in a thin film form are investigated. The measurements revealed longer intraband exciton relaxation in quantum-rods than in quantum-dots. The slowed relaxation in quantum-rods is due to mitigation of the Auger-relaxation mechanism from elongating the nanocrystal. In addition, the nanocrystal thin film showed long-lived confined acoustic phonons corresponding to the ellipsoidal breathing mode, contrary to others work on colloidal systems of CdSe nanocrystals. PMID:23389266

  9. Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Kelley, Anne Myers

    2016-06-01

    Three empirical interatomic force fields are parametrized using structural, elastic, and phonon dispersion data for bulk CdSe and their predictions are then compared for the structures and phonons of CdSe quantum dots having average diameters of ˜2.8 and ˜5.2 nm (˜410 and ˜2630 atoms, respectively). The three force fields include one that contains only two-body interactions (Lennard-Jones plus Coulomb), a Tersoff-type force field that contains both two-body and three-body interactions but no Coulombic terms, and a Stillinger-Weber type force field that contains Coulombic interactions plus two-body and three-body terms. While all three force fields predict nearly identical peak frequencies for the strongly Raman-active "longitudinal optical" phonon in the quantum dots, the predictions for the width of the Raman peak, the peak frequency and width of the infrared absorption peak, and the degree of disorder in the structure are very different. The three force fields also give very different predictions for the variation in phonon frequency with radial position (core versus surface). The Stillinger-Weber plus Coulomb type force field gives the best overall agreement with available experimental data.

  10. Efficient intranuclear gene delivery by CdSe aqueous quantum dots electrostatically-coated with polyethyleneimine

    NASA Astrophysics Data System (ADS)

    Au, Giang H. T.; Y Shih, Wan; Shih, Wei-Heng

    2015-01-01

    Quantum dots (QDs) are semiconducting nanoparticles with photoluminescence properties that do not photobleach. Due to these advantages, using QDs for non-viral gene delivery has the additional benefit of being able to track the delivery of the genes in real time as it happens. We investigate the efficacy of mercaptopropionic acid (MPA)-capped CdSe aqueous quantum dots (AQDs) electrostatically complexed with branched polyethyleneimine (PEI) both as a non-viral gene delivery vector and as a fluorescent probe for tracking the delivery of genes into nuclei. The MPA-capped CdSe AQDs that were completely synthesized in water were the model AQDs. A nominal MPA:Cd:Se = 4:3:1 was chosen for optimal photoluminescence and zeta potential. The gene delivery study was carried out in vitro using a human colon cancer cell line, HT29 (ATCC). The model gene was a plasmid DNA (pDNA) that can express red fluorescent protein (RFP). Positively charged branched PEI was employed to provide a proton buffer to the AQDs to allow for endosomal escape. It is shown that by using a PEI-AQD complex with a PEI/AQD molar ratio of 300 and a nominal pDNA/PEI-AQD ratio of 6, we can achieve 75 ± 2.6% RFP expression efficiency with cell vitality remaining at 78 ± 4% of the control.

  11. Interaction of Globular Plasma Proteins with Water-Soluble CdSe Quantum Dots.

    PubMed

    Pathak, Jyotsana; Rawat, Kamla; Sanwlani, Shilpa; Bohidar, H B

    2015-06-01

    The interactions between water-soluble semiconductor quantum dots [hydrophilic 3-mercaptopropionic acid (MPA)-coated CdSe] and three globular plasma proteins, namely, bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and human serum albumin (HSA), are investigated. Acidic residues of protein molecules form electrostatic interactions with these quantum dots (QDs). To determine the stoichiometry of proteins bound to QDs, we used dynamic light scattering (DLS) and zeta potential techniques. Fluorescence resonance energy transfer (FRET) experiments revealed energy transfer from tryptophan residues in the proteins to the QD particles. Quenching of the intrinsic fluorescence of protein molecules was noticed during this binding process (hierarchy HSA<β-Lg

  12. Quantum-confined emission and fluorescence blinking of individual exciton complexes in CdSe nanowires.

    PubMed

    Franz, Dennis; Reich, Aina; Strelow, Christian; Wang, Zhe; Kornowski, Andreas; Kipp, Tobias; Mews, Alf

    2014-11-12

    One-dimensional semiconductor nanostructures combine electron mobility in length direction with the possibility of tailoring the physical properties by confinement effects in radial direction. Here we show that thin CdSe quantum nanowires exhibit low-temperature fluorescence spectra with a specific universal structure of several sharp lines. The structure strongly resembles the pattern of bulk spectra but show a diameter-dependent shift due to confinement effects. Also the fluorescence shows a pronounced complex blinking behavior with very different blinking dynamics of different emission lines in one and the same spectrum. Time- and space-resolved optical spectroscopy are combined with high-resolution transmission electron microscopy of the very same quantum nanowires to establish a detailed structure-property relationship. Extensive numerical simulations strongly suggest that excitonic complexes involving donor and acceptor sites are the origin of the feature-rich spectra. PMID:25343231

  13. Building devices from colloidal quantum dots.

    PubMed

    Kagan, Cherie R; Lifshitz, Efrat; Sargent, Edward H; Talapin, Dmitri V

    2016-08-26

    The continued growth of mobile and interactive computing requires devices manufactured with low-cost processes, compatible with large-area and flexible form factors, and with additional functionality. We review recent advances in the design of electronic and optoelectronic devices that use colloidal semiconductor quantum dots (QDs). The properties of materials assembled of QDs may be tailored not only by the atomic composition but also by the size, shape, and surface functionalization of the individual QDs and by the communication among these QDs. The chemical and physical properties of QD surfaces and the interfaces in QD devices are of particular importance, and these enable the solution-based fabrication of low-cost, large-area, flexible, and functional devices. We discuss challenges that must be addressed in the move to solution-processed functional optoelectronic nanomaterials. PMID:27563099

  14. Bacterial Interactions with CdSe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Holden, P.; Nadeau, J. L.; Kumar, A.; Clarke, S.; Priester, J. H.; Stucky, G. D.

    2007-12-01

    Cadmium selenide quantum dots (QDs) are semiconductor nanoparticles that are manufactured for biomedical imaging, photovoltaics, and other applications. While metallic nanoparticles can be made biotically by bacteria and fungi, and thus occur in nature, the fate of either natural or engineered QDs and relationships to nanoparticle size, conjugate and biotic conditions are mostly unknown. Working with several different bacterial strains and QDs of different sizes and conjugate chemistries, including QDs synthesized by a Fusarium fungal strain, we show that QDs can enter cells through specfic receptor-mediated processes, that QDs are broken down by bacteria during cell association, and that toxicity to cells is much like that imposed by Cd(II) ions. The mechanisms of entry and toxicity are not fully understood, but preliminary evidence suggests that electron transfer between cells and QDs occurs. Also, cell membranes are compromised, indicating oxidative stress is occurring. Results with planktonic and biofilm bacteria are similar, but differently, biofilms tend to accumulate Cd(II) associated with QD treatments.

  15. Comparative behavior of CdS and CdSe quantum dots in poly(3-hexylthiophene) based nanocomposites

    SciTech Connect

    Sonar, Prashant . E-mail: sonar@mat.ethz.ch; Sreenivasan, K.P.; Madddanimath, Trupti; Vijayamohanan, K. . E-mail: viji@ems.ncl.res.in

    2006-01-05

    CdS and CdSe nanoparticles have been prepared using conducting poly(3-hexylthiophene) (P3HT) matrix with an objective to understand the effect of nanoparticles on the polymer matrix using electrochemical and spectroscopic techniques. The spectroscopic results reveal that the electronic structure of polymer is strongly influenced by the characteristics of embedded semiconducting nanoparticles. SEM and TEM images show the ordered morphology of the CdS and CdSe nanoparticles in presence of the polymer matrix. Cyclic voltammetry performed both in the presence and absence of light enables us to understand the redox changes in P3HT due to CdS and CdSe quantum dots such as the generation of free radical in the excited state and their electrochemical band gaps.

  16. Internal field switching in CdSe quantum dot films on Si.

    PubMed

    Sarkar, Shaibal K; Cohen, Hagai; Hodes, Gary

    2005-01-13

    If a thin film (tens of nm) of CdSe quantum dots (4 nm diameter) is deposited by chemical bath deposition onto various substrates, the films, although essentially intrinsic, behave as if they were n-type with respect to charge separation. However, films deposited under certain deposition conditions on Si (both n(+)- and p(+)-type) behave as if they were p-type. In this case, we show that it is possible to switch this p-type photoresponse by either light illumination intensity or injection of electrons from an external filament. Using both surface photovoltage spectroscopy and a novel adaptation of X-ray photoelectron spectroscopy, we show how this behavior results from a Cd(OH)(2) layer adsorbed at the Si surface at the beginning of the deposition. This response is explained by a competition between a high concentration of relatively shallow hole traps in the CdSe and a lower concentration of deeper electron traps in the Cd(OH)(2). The relative occupancies of these traps determine the fields in the film and their response to external parameters. PMID:16851002

  17. Photocurrent enhancement of SiNW-FETs by integrating protein-shelled CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Moh, Sang Hyun; Kulkarni, Atul; San, Boi Hoa; Lee, Jeong Hun; Kim, Doyoun; Park, Kwang Su; Lee, Min Ho; Kim, Taesung; Kim, Kyeong Kyu

    2016-01-01

    We proposed a new strategy to increase the photoresponsivity of silicon NW field-effect transistors (FETs) by integrating CdSe quantum dots (QDs) using protein shells (PSs). CdSe QDs were synthesized using ClpP, a bacterial protease, as protein shells to control the size and stability of QD and to facilitate the mounting of QDs on SiNWs. The photocurrent of SiNW-FETs in response to light at a wavelength of 480 nm was enhanced by a factor of 6.5 after integrating CdSe QDs because of the coupling of the optical properties of SiNWs and QDs. As a result, the photoresponsivity to 480 nm light reached up to 3.1 × 106, the highest value compared to other SiNW-based devices in the visible light range.We proposed a new strategy to increase the photoresponsivity of silicon NW field-effect transistors (FETs) by integrating CdSe quantum dots (QDs) using protein shells (PSs). CdSe QDs were synthesized using ClpP, a bacterial protease, as protein shells to control the size and stability of QD and to facilitate the mounting of QDs on SiNWs. The photocurrent of SiNW-FETs in response to light at a wavelength of 480 nm was enhanced by a factor of 6.5 after integrating CdSe QDs because of the coupling of the optical properties of SiNWs and QDs. As a result, the photoresponsivity to 480 nm light reached up to 3.1 × 106, the highest value compared to other SiNW-based devices in the visible light range. Electronic supplementary information (ESI) available: Materials and methods. See DOI: 10.1039/c5nr07901b

  18. Small bright charged colloidal quantum dots.

    PubMed

    Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

    2014-01-28

    Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (∼4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (∼4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices. PMID:24350673

  19. Colloidal quantum dot light-emitting devices.

    PubMed

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Förster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs. PMID:22110863

  20. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

  1. A Quantitative Description of the Binding Equilibria of para-Substituted Aniline Ligands and CdSe Quantum Dots

    SciTech Connect

    Donakowski, Martin D.; Godbe, Jacqueline M.; Sknepnek, Rastko; Knowles, Kathryn E.; Olvera de la Cruz, Monica; Weiss, Emily A.

    2010-01-01

    This paper describes the use of ¹H NMR spectroscopy to measure the equilibrium constants for the solution-phase binding of two para-substituted aniline molecules (R-An), p-methoxyaniline (MeO-An) and p-bromoaniline (Br-An), to colloidal 4.1 nm CdSe quantum dots (QDs). Changes in the chemical shifts of the aromatic protons located ortho to the amine group on R-An were used to construct a binding isotherm for each R-An/QD system. These isotherms fit to a Langmuir function to yield K{sub a}, the equilibrium constant for binding of the R-An ligands to the QDs; Ka ≈ 150 M-1 and ΔGads ≈ -19 kJ/mol for both R = MeO and R = Br. ³¹P NMR indicates that the native octylphosphonate ligands, which, by inductively coupled plasma atomic emission spectroscopy, cover 90% of the QD surface, are not displaced upon binding of R-An. The MeO-An ligand quenches the photoluminescence of the QDs at much lower concentrations than does Br-An; the observation, therefore, that Ka,MeO-An ≈ Ka,Br-An shows that this difference in quenching efficiencies is due solely to differences in the nature of the electronic interactions of the bound R-An with the excitonic state of the QD.

  2. Electronic structure of cobalt doped CdSe quantum dots using soft X-ray spectroscopy

    SciTech Connect

    Joshua T. Wright; Su, Dong; van Buuren, Tony; Meulenberg, Robert W.

    2014-08-21

    The electronic structure and magnetic properties of cobalt doped CdSe quantum dots (QDs) are studied using electron microscopy, soft X-ray spectroscopy, and magnetometry. Magnetometry measurements suggest these QDs are superparamagnetic, contrary to a spin-glass state observed in the bulk analogue. Moreover, the electron microscopy shows well formed QDs, but with cobalt existing as doped into the QD and as unreacted species not contained in the QD. X-ray absorption measurements at the Co L3-edge suggest that changes in spectra features as a function of particle size can be described considering combination of a cobalt ion in a tetrahedral crystal field and an octahedrally coordinated (impurity) phase. With decreasing particle sizes, the impurity phase increases, suggesting that small QDs can be difficult to dope.

  3. Photoconductivity of composites based on CdSe quantum dots and low-band-gap polymers

    NASA Astrophysics Data System (ADS)

    Dayneko, Sergey; Linkov, Pavel; Martynov, Igor; Tameev, Alexey; Tedoradze, Marine; Samokhvalov, Pavel; Nabiev, Igor; Chistyakov, Alexander

    2016-05-01

    Photoconductivity of thin layers prepared by spin coating of blends of CdSe quantum dots (QDs) and a low-band-gap polymer PCDTBT or PTB7 has been studied. It has been found that photocurrent in the composites containing QDs of 10-nm in size is significantly higher than in those of containing 5-nm QDs. Analysis of the results showed that the photoresponse of the thin layers is mainly determined by the relative positions of the frontier energy levels of the materials used, organic semiconductors and QDs. Therefore, the ability to tune the relative positions of these levels by varying the QD size is of special importance, thus allowing the optimization of photodetectors and photovoltaic cells.

  4. Radiative rate modification in CdSe quantum dot-coated microcavity

    NASA Astrophysics Data System (ADS)

    Veluthandath, Aneesh V.; Bisht, Prem B.

    2015-12-01

    Whispering gallery modes (WGMs) of the microparticles with spherical or cylindrical symmetry have exceptionally high quality factors and small mode volume. Quantum dots (QDs) are zero dimensional systems with variable band gap as well as luminescent properties with applications in photonics. In this paper, the WGMs have been observed in the luminescence spectra of CdSe QD-coated single silica microspheres. Theoretical estimations of variation of resonance frequency, electric field, and Q-values have been done for a multilayer coating of QDs on silica microspheres. Observed WGMs have been identified for their mode number and polarization using Mie theory. Broadening of modes due to material absorption has been observed. Splitting of WGMs has also been observed due to coherent coupling of counter propagating waves in the microcavity due to the presence of QDs. At room temperature, the time-resolved study indicates the modification of the radiative rate due to coupling of WGMs of the microcavity-QD hybrid system.

  5. Silver nanowires-based signal amplification for CdSe quantum dots electrochemiluminescence immunoassay.

    PubMed

    Huang, Tingyu; Meng, Qingmin; Jie, Guifen

    2015-04-15

    A novel silver-cysteine hybrid nanowires (SCNWs) with many reactive carboxyl and amine groups were prepared, which enable them to be used as idea signal amplifying labels in bioassays. A large number of CdSe quantum dots (QDs) were loaded on the SCNWs to develop amplified SCNWs-QDs electrochemiluminescence (ECL) signal probe. The PAMAM dendrimer-SCNWs nanohybrids covered on the electrode constructed an effective antibody immobilization matrix and made the immobilized biomolecules hold high stability and bioactivity. Based on the specific sandwich immunoreaction strategy, the detection antibody (Ab2)-SCNWs-QDs ECL signal probe was applied to the sensitive signal-on ECL immunoassay of human IgG. The SCNWs-QDs ECL not only opens promising new ECL emitting species, but also promotes the development of novel ECL signal-transition platforms for biosensing devices. PMID:25460886

  6. Radiative rate modification in CdSe quantum dot-coated microcavity

    SciTech Connect

    Veluthandath, Aneesh V.; Bisht, Prem B.

    2015-12-21

    Whispering gallery modes (WGMs) of the microparticles with spherical or cylindrical symmetry have exceptionally high quality factors and small mode volume. Quantum dots (QDs) are zero dimensional systems with variable band gap as well as luminescent properties with applications in photonics. In this paper, the WGMs have been observed in the luminescence spectra of CdSe QD-coated single silica microspheres. Theoretical estimations of variation of resonance frequency, electric field, and Q-values have been done for a multilayer coating of QDs on silica microspheres. Observed WGMs have been identified for their mode number and polarization using Mie theory. Broadening of modes due to material absorption has been observed. Splitting of WGMs has also been observed due to coherent coupling of counter propagating waves in the microcavity due to the presence of QDs. At room temperature, the time-resolved study indicates the modification of the radiative rate due to coupling of WGMs of the microcavity-QD hybrid system.

  7. Optical and Phonon Characterization of Ternary CdSe x S1- x Alloy Quantum Dots

    NASA Astrophysics Data System (ADS)

    Thi, L. A.; Cong, N. D.; Dang, N. T.; Nghia, N. X.; Quang, V. X.

    2016-05-01

    Ternary CdSe x S1- x alloy quantum dots (QDs) were synthesized using a wet chemical method. Their morphology, particle size, structural, optical, and vibrational properties were investigated using transmission electron microscopy, x-ray diffraction, UV-Vis, fluorescence and Raman spectroscopy, respectively. The optical and vibrational properties of the QDs can be controlled by adjusting the Se/S molar ratio. The absorption and emission peaks shift to a longer wavelength range when increasing the Se content. The presence of two CdSe-like and CdS-like longitudinal optical phonon modes was observed. The dependencies of the optical and phonon modes on the Se content are discussed in detail.

  8. Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid

    NASA Astrophysics Data System (ADS)

    Dickerson, B. D.; Irving, D. M.; Herz, E.; Claus, R. O.; Spillman, W. B.; Meissner, K. E.

    2005-04-01

    A diffusion-barrier model described the early evolution of size-dependent photoluminescence emission from CdSe quantum dots formed by organometallic synthesis. Emission peak widths, emission redshift rates, and nanocrystal growth rates all decreased to a minimum at a reaction completion time. Growth after the completion time by Ostwald ripening was marked by a doubling of the activation energy. The temperature dependence of both reaction completion rates and photoluminescence redshift rates followed Arrhenius behavior governed by activation energies that increased with solvent molecular weight, in this limited case. In stearic acid and in trioctylphosphine oxide, the typical activation energies were 0.6±0.1 and 0.92±0.26eV/molecule, respectively.

  9. Mn2+-Doped CdSe/CdS Core/Multishell Colloidal Quantum Wells Enabling Tunable Carrier-Dopant Exchange Interactions

    NASA Astrophysics Data System (ADS)

    Delikanli, Savas; Scrace, Thomas; Murphy, Joseph; Barman, Biblop; Tsai, Yutsung; Zhang, Peiyao; Hernandez-Martinez, Pedro Ludwig; Christodoulides, Joseph; Cartwright, Alexander N.; Petrou, Athos; Demir, Hilmi Volkan

    We report the manifestations of carrier-dopant exchange interactions in colloidal Mn2+-doped CdSe/CdS core/multishell quantum wells. In our solution-processed quantum well heterostructures, Mn2+ was incorporated by growing a Cd0.985Mn0:015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. The carrier-magnetic ion exchange interaction effects are tunable through wave function engineering. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions through adjusting the location, composition, and number of the CdSe, Cd1-xMnxS, and CdS layers. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices. H.V.D. acknowledges support from EU-FP7 Nanophotonics4Energy NoE, TUBITAK, NRF-CRP-6-2010-02 and A*STAR of Singapore. Work at the University at Buffalo was supported by NSF DMR 1305770.

  10. Size-Dependent Exciton Formation Dynamics in Colloidal Silicon Quantum Dots.

    PubMed

    Bergren, Matthew R; Palomaki, Peter K B; Neale, Nathan R; Furtak, Thomas E; Beard, Matthew C

    2016-02-23

    We report size-dependent exciton formation dynamics within colloidal silicon quantum dots (Si QDs) using time-resolved terahertz (THz) spectroscopy measurements. THz photoconductivity measurements are used to distinguish the initially created hot carriers from excitons that form at later times. At early pump/probe delays, the exciton formation dynamics are revealed by the temporal evolution of the THz transmission. We find an increase in the exciton formation time, from ∼500 to ∼900 fs, as the Si QD diameter is reduced from 7.3 to 3.4 nm and all sizes exhibit slower hot-carrier relaxation times compared to bulk Si. In addition, we determine the THz absorption cross section at early delay times is proportional to the carrier mobility while at later delays is proportional to the exciton polarizability, αX. We extract a size-dependent αX and find an ∼r(4) dependence, consistent with previous reports for quantum-confined excitons in CdSe, InAs, and PbSe QDs. The observed slowing in exciton formation time for smaller Si QDs is attributed to decreased electron-phonon coupling due to increased quantum confinement. These results experimentally verify the modification of hot-carrier relaxation rates by quantum confinement in Si QDs, which likely plays a significant role in the high carrier multiplication efficiency observed in these nanomaterials. PMID:26811876

  11. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

  12. Synthesis and characterization of CdSe quantum dots dispersed in PVA matrix by chemical route

    NASA Astrophysics Data System (ADS)

    Khan, Zubair M. S. H.; Ganaie, Mohsin; Khan, Shamshad A.; Husain, M.; Zulfequar, M.

    2016-05-01

    CdSe quantum dots using polyvinyl alcohol as a capping agent have been synthesized via a simple heat induced thermolysis technique. The structural analysis of CdSe/PVA thin film was studied by X-ray diffraction, which confirms crystalline nature of the prepared film. The surface morphology and particle size of the prepared sample was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The SEM studies of CdSe/PVA thin film shows the average size of particles in the form of clusters of several quantum dots in the range of 10-20 nm. The morphology of CdSe/PVA thin film was further examined by TEM. The TEM image shows the fringes of tiny dots with average sizes of 4-7 nm. The optical properties of CdSe/PVA thin film were studied by UV-VIS absorption spectroscopy. The CdSe/PVA quantum dots follow the role of direct transition and the optical band gap is found to be 4.03 eV. From dc conductivity measurement, the observed value of activation energy was found to be 0.71 eV.

  13. Computational insights into CdSe quantum dots' interactions with acetate ligands.

    PubMed

    Tamukong, Patrick K; Peiris, Wadumesthrige D N; Kilina, Svetlana

    2016-07-27

    Using density functional theory (DFT) and time-dependent DFT (TDDFT), we investigate the effects of carboxylate groups on the electronic and optical properties of CdSe quantum dots (QDs). We specifically focus on the mechanisms of the binding of the acetate anion to the QD surface with and without excess of Cd(2+) cations. Our calculations show that the most stable ligated conformations are those where an acetate is attached to extra Cd(2+) ion forming a [Cd(2+)(CH3COO(-))] at the QD's surface, while also accompanied by an acetate attached nearby at the surface balancing the overall neutral charge of the system. In contrast, formation of a neutral metal-acetate complex [Cd(2+)(CH3COO(-))2] at the QD surface is found to be the least energetically preferable. A strength of the QD-ligand interaction depends on the solvent, the facet of the QD to which the ligands are attached, and the binding mode - with the bridging mode found to be the most stable conformation for both acetate and cadmium acetate ligands. The cadmium acetate ligands introduce electron trap states at the edge of the conduction band - unoccupied orbitals predominately localized on Cd(2+) ion - that are extremely sensitive to the ligand position and the solvent polarity. Polar solvents like acetonitrile delocalize the electronic density over the entire system and, thus, eliminate trap states. As a result, mixed passivation of the CdSe QDs by pairs of cadmium acetate and acetate ligands provides optimal optical properties with minimal contributions of the ligand-related trap states and optically bright lowest energy transitions. PMID:27406268

  14. Anomalous photoluminescence in CdSe quantum-dot solids at high pressure due to nonuniform stress.

    PubMed

    Grant, Christian D; Crowhurst, Jonathan C; Hamel, Sebastien; Williamson, Andrew J; Zaitseva, Natalia

    2008-06-01

    The application of static high pressure provides a means to precisely control and investigate many fundamental and unique properties of nanoparticles. CdSe is a model quantum-dot system, the behavior of which under high pressure has been extensively studied; however, the effect of nonuniform stresses on this system has not been fully appreciated. Photoluminescence data obtained from CdSe quantum-dot solids in different stress environments varying from purely uniform to highly nonuniform are presented. Small deviations from a uniform stress distribution profoundly affect the electronic properties of this system. In nonuniform stress environments, a pronounced flattening of the photoluminescence enegy is observed above 3 GPa. The observations are validated with theoretical calculations obtained using an all-atom semiempirical pseudopotential technique. This effect must be considered when investigating other potentially pressure-mediated phenomena. PMID:18481798

  15. Epitaxial growth and photoluminescence excitation spectroscopy of CdSe quantum dots in (Zn,Cd)Se barrier

    NASA Astrophysics Data System (ADS)

    Piwowar, J.; Pacuski, W.; Smoleński, T.; Goryca, M.; Bogucki, A.; Golnik, A.; Nawrocki, M.; Kossacki, P.; Suffczyński, J.

    2016-05-01

    Design, epitaxial growth, and resonant spectroscopy of CdSe Quantum Dots (QDs) embedded in an innovative (Zn,Cd)Se barrier are presented. The (Zn,Cd)Se barrier enables shifting of QDs energy emission down to 1.87 eV, that is below the energy of Mn$^{2+}$ ions internal transition (2.1 eV). This opens a perspective for implementation of epitaxial CdSe QDs doped with several Mn ions as, e. g., the light sources in high quantum yield magnetooptical devices. Polarization resolved Photoluminescence Excitation measurements of individual QDs reveal sharp ($\\Gamma <$ 150 $\\mu$eV) maxima and transfer of optical polarization to QD confining charged exciton state with efficiency attaining 26 %. The QD doping with single Mn$^{2+}$ ions is achieved.

  16. Controlled synthesis and optical properties of tunable CdSe quantum dots and effect of pH

    SciTech Connect

    Ratnesh, R. K.; Mehata, Mohan Singh

    2015-09-15

    Cadmium selenide (CdSe) quantum dots (Q-dots) were prepared by using non-coordinating solvent octadecene instead of coordinating agent trioctylphosphine oxide (TOPO). Reaction processes were carried out at various temperatures of 240°, 260°, 280° and 300° C under nitrogen atmosphere. The prepared CdSe Q-dots which are highly stable show uniform size distribution and tunable optical absorption and photoluminescence (PL). The growth temperature significantly influenced the particle size; spectral behavior, energy band gap and PL intensity and the full width at half maxima (FWHM). Three different methods were employed to determine the particle size and the average particle size of the CdSe Q-dots is 3.2 - 4.3 nm, grown at different temperatures. In addition, stable and mono-dispersed water soluble CdSe Q-dots were prepared by the ligand exchange technique. Thus, the water soluble Q-dots, which are sensitive to the basic pH may be important for biological applications.

  17. Quantum confinement effect in multilayer structure of alternate CdSe and SiOx insulator matrix thinfilms

    NASA Astrophysics Data System (ADS)

    Melvin David Kumar, M.; Devadason, Suganthi

    2013-06-01

    Multilayer (ML) structure of layer-by-layer deposited CdSe/SiOx thin films and their monolayers were prepared using sequential thermal evaporation technique. X-ray diffraction study confirmed the (002) plane of CdSe with wurtzite structure. It is noticed that the microstrain, developed in ML thin films, increased with decreasing particle size. Experimentally measured band gap energies confirmed the splitting of valence band energy levels which rise due to hole confinement in CdSe. Crystallite sizes (5-7 nm) were calculated using the effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites was smaller than the Bohr exciton diameter (11.2 nm) of CdSe. The main band in the emission spectra of ML samples gradually shifted to longer wavelength side when particle size was increased from 5 to 7 nm. This is characteristic of quantum size effect. It is inferred that disorderliness in CdSe/SiOx ML thin films would increase when the thickness of CdSe sublayer is greater than that of SiOx matrix layer.

  18. Controlled synthesis and optical properties of tunable CdSe quantum dots and effect of pH

    NASA Astrophysics Data System (ADS)

    Ratnesh, R. K.; Mehata, Mohan Singh

    2015-09-01

    Cadmium selenide (CdSe) quantum dots (Q-dots) were prepared by using non-coordinating solvent octadecene instead of coordinating agent trioctylphosphine oxide (TOPO). Reaction processes were carried out at various temperatures of 240°, 260°, 280° and 300° C under nitrogen atmosphere. The prepared CdSe Q-dots which are highly stable show uniform size distribution and tunable optical absorption and photoluminescence (PL). The growth temperature significantly influenced the particle size; spectral behavior, energy band gap and PL intensity and the full width at half maxima (FWHM). Three different methods were employed to determine the particle size and the average particle size of the CdSe Q-dots is 3.2 - 4.3 nm, grown at different temperatures. In addition, stable and mono-dispersed water soluble CdSe Q-dots were prepared by the ligand exchange technique. Thus, the water soluble Q-dots, which are sensitive to the basic pH may be important for biological applications.

  19. Decay and Dissociation of Excitons in Colloidal Semiconductor Quantum Dots in the Presence of Small Molecules

    NASA Astrophysics Data System (ADS)

    Knowles, Kathryn Eileen

    This dissertation describes interactions between colloidal semiconductor quantum dots (QDs) and small organic molecules that affect the electronic structure of the surfaces of the QDs and influence the decay and dissociation pathways available to excitonic charge carriers (electrons and holes) in the QDs. Pathways by which electrons and holes in QDs leave conduction and valence band-edge states, respectively, include charge trapping to a state localized in the QD core or on the surface, charge transfer to a redox partner, and radiative recombination. Analysis of transient absorption and time-resolved photoluminescence (PL) spectroscopies enabled the construction of a time-resolved, charge carrier-resolved map of decay from the first excitonic state of colloidal CdSe QDs. This map reveals three different populations of CdSe QDs that differ in the timescales of available hole and electron-trapping processes. The mechanism by which a p-substituted aniline quenches the PL of CdSe QDs upon displacing native hexadecylamine ligands depends on the electronic nature of its para substituent. Anilines with electron withdrawing substituents quench PL through incomplete passivation of Cd2+ surface sites, and anilines with electron donating substituents quench PL through photoinduced hole transfer. Transient absorption measurements on both the picosecond and microsecond timescales reveal that a series of alkyl-substituted p-benzoquinone (s-BQ) molecules participate in both static and collisional photoinduced electron transfer (PET) with PbS QDs. The efficiencies of both static and collisional PET are limited by the presence of the oleate ligand shell, and depend on the size and shape of the (s-BQ) molecule. A model for the dependence of the collisional quenching efficiency on the volume of the s-BQ molecule produces a parameter that provides a quantitative measure of the permeability of the organic ligand shell of the QDs. Thermodynamically spontaneous electron transfer occurs

  20. Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

    PubMed

    Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

    2016-06-15

    Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs. PMID:27224958

  1. Spectroscopic properties of colloidal indium phosphide quantum wires

    SciTech Connect

    Wang, Lin-Wang; Wang, Fudong; Yu, Heng; Li, Jingbo; Hang, Qingling; Zemlyanov, Dmitry; Gibbons, Patrick C.; Wang, Lin-Wang; Janes, David B.; Buhro, William E.

    2008-07-11

    Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photo-oxidation, without a significant influence on quantum-wire photoluminescence. However, photo-oxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation, and that colloidal quantum wires have intrinsically low photoluminescence efficiencies.

  2. Size dependence of the multiple exciton generation rate in CdSe quantum dots.

    PubMed

    Lin, Zhibin; Franceschetti, Alberto; Lusk, Mark T

    2011-04-26

    The multiplication rates of hot carriers in CdSe quantum dots are quantified using an atomistic pseudopotential approach and first-order perturbation theory. We consider both the case of an individual carrier (electron or hole) decaying into a trion and the case of an electron-hole pair decaying into a biexciton. The dependence on quantum dot volume of multiplication rate, density of final states, and effective Coulomb interaction are determined. We show that the multiplication rate of a photogenerated electron-hole pair decreases with dot size for a given absolute photon energy. However, if the photon energy is rescaled by the volume-dependent optical gap, then smaller dots exhibit an enhancement in carrier multiplication rate for a given relative photon energy. We find that holes have much higher multiplication rates than electrons of the same excess energy due to the larger density of final states (positive trions). When electron-hole pairs are generated by photon absorption, however, the net carrier multiplication rate is dominated by electrons because they have much higher excess energy on average. We also find, contrary to earlier studies, that the effective Coulomb coupling governing carrier multiplication is energy-dependent. PMID:21355556

  3. Low Pressure Phase Transitions in Wurtzite CdSe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Meulenberg, Robert W.; Strouse, Geoffrey F.

    2001-03-01

    Over the last several years, significant efforts in understanding the effects of high pressures on quantum dots (QDs) have been reported. It has been shown that the high-pressure phase transition from wurtzite (WZ) to rock-salt for CdSe QDs is doubled (3 - 6 GPa), but the energy dependence of the absorption edge is near that of the bulk value (partialE/partialP 45 meV/GPa). Upon release of pressure, mixtures of both hexagonal and cubic (WZ and zinc blende (ZB), respectively) structures are seen, due to the low energy of interconversion of the lattice. Surprisingly, ZB is rarely observed for II-VI nanomaterials although it is thermodynamically preferred and moderate to low pressures should induce a WZ -> ZB phase transition. Experiments with pressures in lower pressure ranges (< 1 GPa) have been ignored and may give insight into these types of low energy phase transitions. We report findings of QD size dependent pressure coefficients and postulate that changes in the band structure of quantum confined semiconductors (which lead to these changes in the pressure coefficient) are a function of the compressibility and defect nature of the material, which induce surface reconstruction events. We present optical absorption and photoluminescence data, as well as time-resolved luminescence data to infer to the mechanism of the pressure dependence.

  4. Achiral CdSe quantum dots exhibit optical activity in the visible region upon post-synthetic ligand exchange with D- or L-cysteine.

    PubMed

    Tohgha, Urice; Varga, Krisztina; Balaz, Milan

    2013-03-01

    Semiconductor cadmium selenide (CdSe) quantum dots (QDs) exhibited mirror-image circular dichroism (CD) spectra in the visible region (350-570 nm) after replacing the trioctylphosphine oxide/oleic acid ligands on achiral nanocrystals with D- and L-cysteines. Chiroptical properties of cysteine-capped CdSe QDs depend on their size and can be fine-tuned by changing the radius of QDs. PMID:23361413

  5. Two-photon photoemission study of competing Auger and surface-mediated relaxation of hot electrons in CdSe quantum dot solids.

    PubMed

    Sippel, Philipp; Albrecht, Wiebke; Mitoraj, Dariusz; Eichberger, Rainer; Hannappel, Thomas; Vanmaekelbergh, Daniel

    2013-04-10

    Solids composed of colloidal quantum dots hold promise for third generation highly efficient thin-film photovoltaic cells. The presence of well-separated conduction electron states opens the possibility for an energy-selective collection of hot and equilibrated carriers, pushing the efficiency above the one-band gap limit. However, in order to reach this goal the decay of hot carriers within a band must be better understood and prevented, eventually. Here, we present a two-photon photoemission study of the 1Pe→1Se intraband relaxation dynamics in a CdSe quantum dot solid that mimics the active layer in a photovoltaic cell. We observe fast hot electron relaxation from the 1Pe to the 1Se state on a femtosecond-scale by Auger-type energy donation to the hole. However, if the oleic acid capping is exchanged for hexanedithiol capping, fast deep hole trapping competes efficiently with this relaxation pathway, blocking the Auger-type electron-hole energy exchange. A slower decay becomes then visible; we provide evidence that this is a multistep process involving the surface. PMID:23506122

  6. Optical and Surface Characterization Studies of CdSe Quantum Dots Undergoing Photooxidation

    NASA Astrophysics Data System (ADS)

    Powell, Lauren C. J.

    Realization of the potential of Quantum Dots (QDs) for biological, energy-efficient lighting and energy harvesting applications requires that their long-term photostability be improved, especially with regards to protection from photooxidation. The overarching objective of this project was the determination of the chemical and physical mechanisms of photooxidation of CdSe QDs. Pittsburgh-based Crystalplex, Inc. provided CdSe QDs with different organic ligands for this research. Three integrated in situ and ex situ characterization techniques were used to observe changes in optical behavior, QD morphology, and surface chemistry during photooxidation conditions. Single-molecule fluorescence microscopy experiments were used to observe real-time changes in the photoluminescence (PL) behavior of single QDs with oleic and lauric acid ligands. The QDs are exposed to 1 atm of pure O2, dry Ar, Ar bubbled through DI water, or air in an environmental chamber and excited with a 488 nm light. Changes in PL intensities were analyzed with respect to the periods of exposure to controlled atmospheres and light. Samples illuminated continuously exhibited strong photoenhancement effects, while those kept in the dark showed atmospheric-dependent PL loss. Microstructural and chemical identification was performed with aberration-corrected transmission electron microscopy (TEM). Ex situ exposures of QD samples to air, dry O2, and dry Ar revealed changes in surface oxide growth with respect to exposure length, illumination, and column vacuum pressure. Samples exposed to air and light exhibited the most extensive photooxidation. Quantum dots with oleic acid ligands were treated with UV/ozone plasma, and extensive degradation of QDs was observed. X-ray photoemission spectroscopy (XPS) measurements at CMU were used to identify the chemical and bonding states of the surface species before and after photooxidation. Analysis of the acquired spectra showed that exposure to below-bandgap light

  7. Photonic Enhancement of Colloidal Quantum Dot Photovoltaics

    NASA Astrophysics Data System (ADS)

    Labelle, Andre Jean-Romeo Richard

    Colloidal quantum dots, nanocrystal semiconductors that can be cross-linked and assembled into absorbing thin films, are an attractive material for third-generation photovoltaic applications due to low-cost fabrication and bandgap tunability. As a result of their limited charge transport, these solution-processed thin films suffer from a mismatch in absorption length and charge extraction length. Concepts based on the interdigitation of n- and p-doped layers, approaches that reduce the distance photogenerated carriers must travel before extraction, offer promise on overcoming this limitation. In this thesis, I explore and develop techniques to address the absorption-extraction compromise in CQD materials by implementing nano- and micro-structuring techniques to enhance light absorption in the active film. First, I focus on the development of nanomaterials for light guiding/scattering enhancement in CQD films. For this, I develop a nanostructured gold reflector that, when suitably designed, guides light and traps it within the active film. I show that this yields enhanced broadband absorption with more than 4-fold improvement at the most improved wavelength, which translated into a 34% improvement in photocurrent in a working solar cell. I also show that periodic nanostructures employed for absorption enhancement can lead to improvements in solar cell performance. Limitations in device architecture and film formation, however, prevented significant performance advances for these nano-scale approaches. Regardless, these early results pointed me to a new and more impactful strategy. I focus in on realizing micron-scale structured electrodes to enhance absorption, which I show to be considerably more useful in view of the need to extract charge carriers with high efficiency. I discover that conformal film formation atop these structured electrodes is an absolute prerequisite to enhancing performance. These devices, which I term micro-pyramid CQD cells, provide a 24

  8. Enhanced electrochemiluminescence of CdSe quantum dots composited with graphene oxide and chitosan for sensitive sensor.

    PubMed

    Wang, Teng; Zhang, Shengyi; Mao, Changjie; Song, Jiming; Niu, Helin; Jin, Baokang; Tian, Yupeng

    2012-01-15

    A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdSe quantum dots (QDs) with graphene oxide-chitosan (GO-CHIT). The ECL sensor fabricated with CdSe QDs/GO-CHIT composite exhibited high ECL intensity, good biocompatibility and long-term stability, and was used to detect of cytochrome C (Cyt C). The results show that the ECL sensor has high sensitivity for Cyt C with the linear range from 4.0 to 324 μM and the detection limit of 1.5 μM. Furthermore, the ECL sensor can selectively sense Cyt C from glucose and bovine serum albumin (BSA). PMID:22099955

  9. SU-E-T-526: On the Linearity, Stability and Beam Energy Dependence of CdSe Quantum Dots as Scintillating Probes

    SciTech Connect

    Delage, M-E; Lecavalier, M-E; Lariviere, D; Allen, C; Beaulieu, L

    2014-06-01

    Purpose: Structure and energy transfer mechanisms confer colloidal quantum dots (cQDs) interesting properties, among them their potential as scintillators. CdSe multi-shell cQDs in powder were investigated under photons irradiation. The purpose of this work is to characterize signal to dose linearity, stability with time and to quantify the dependence of their light output with beam energy. Methods: The cQDs are placed at the extremity of a non-scintillating plastic collecting fiber, with the other extremity connected to an Apogee U2000C CCD camera. The CCD camera collects the fluorescence light from irradiated cQDs from which the delivered dose is extracted. This signal is corrected for Cerenkov contamination at MV energies using the chromatic technique. The detector was irradiated with two devices: Xstrahl 200 orthovoltage unit for 120, 180 and 220 kVp and a Varian Clinac iX for 6 and 23 MV. Results: Linear output response with varying dose is observed for all beam energies with R2 factors > 0,999. Reproducibility measurements were performed at 120 kVp: the same set-up was irradiated at different time intervals (one week and three months). The results showed only a small relative decrease of light output of 3,2 % after a combine deposited dose of approximately 95 Gy. CdSe nanocrystals response has been studied as a function of beam energy. The output increases with decreasing energy from 120 kVp to 6 MV and increase again for 23 MV. This behavior could be explained in part by the cQDs high-Z composition. Conclusion: The fluorescence light output of CdSe cQDs was found to be linear as a function of dose. The results suggest stability of the scintillation output of cQDs over time. The specific composition of cQDs is the main cause of the observed energy dependence. We will further look into particle beam dependence of the cQDs. Bourse d'excellence aux etudes graduees du CRC (Centre de Recherche sur le Cancer, Universite Laval) Bourse d'excellence aux etudes

  10. Enhancement in the photorefractive performance of organic composites photosensitized with functionalized CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Liang, Yichen; Wang, Wei; Moon, Jong-Sik; Winiarz, Jeffrey G.

    2016-08-01

    Enhancement in the photorefractive (PR) performance of organic composites photosensitized by CdSe quantum dots (QCdSe) passivated with the charge-transport ligands, sulfonated triphenyldiamine (STPD), is reported. This enhancement is primarily attributed to the ability of the passivating ligand, STPD, to facilitate the charge-transfer process between the QCdSe and the triphenyldiamine (TPD) charge-transport matrix. The PR composites exhibited a maximum photocharge-generation efficiency of 0.9% and two-beam coupling gain coefficient of 110 cm-1. These figures of merit represent a significant improvement over similar composites photosensitized with more conventional trioctylphosphine oxide-passivated QCdSe (TQCdSe). Moreover, composites photosensitized with SQCdSe had a faster response time of τ = 128 ms at an electric field of 60 V/μm compared with τ = 982 ms for those containing TQCdSe. Because of the molecular similarity between the STPD passivating groups and the TPD-based charge-transport matrix, concentrations of up to 1.4 wt% of SQCdSe are achieved in PR composites without any detectable phase separation, a considerable improvement over the 0.7 wt% for TQCdSe.

  11. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy

    SciTech Connect

    Doughty, Benjamin L.; Ma, Yingzhong; Shaw, Robert W

    2015-01-07

    Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in the SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.

  12. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy

    DOE PAGESBeta

    Doughty, Benjamin L.; Ma, Yingzhong; Shaw, Robert W

    2015-01-07

    Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in themore » SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.« less

  13. Folded-Light-Path Colloidal Quantum Dot Solar Cells

    PubMed Central

    Koleilat, Ghada I.; Kramer, Illan J.; Wong, Chris T. O.; Thon, Susanna M.; Labelle, André J.; Hoogland, Sjoerd; Sargent, Edward H.

    2013-01-01

    Colloidal quantum dot photovoltaics combine low-cost solution processing with quantum size-effect tuning to match absorption to the solar spectrum. Rapid advances have led to certified solar power conversion efficiencies of over 7%. Nevertheless, these devices remain held back by a compromise in the choice of quantum dot film thickness, balancing on the one hand the need to maximize photon absorption, mandating a thicker film, and, on the other, the need for efficient carrier extraction, a consideration that limits film thickness. Here we report an architecture that breaks this compromise by folding the path of light propagating in the colloidal quantum dot solid. Using this method, we achieve a substantial increase in short-circuit current, ultimately leading to improved power conversion efficiency. PMID:23835564

  14. Colloidal crystal formation in a semiconductor quantum plasma

    SciTech Connect

    Zeba, I.; Uzma, Ch.; Jamil, M.; Salimullah, M.; Shukla, P. K.

    2010-03-15

    The static shielding and the far-field dynamical oscillatory wake potentials in an ion-implanted piezoelectric semiconductor with colloid ions as test particles have been investigated in detail. The dielectric response function of the semiconductor is contributed by the quantum effect of electrons through the Bohm potential and lattice electron-phonon coupling effects. It is found that the quantum effect causes tighter binding of the electrons reducing the quantum Debye shielding length and the effective length of the wake potential to several angstroms. Hence, a quasiquantum lattice of colloid ions can be formed in the semiconductor in the quantum scales giving rise to drastic modifications of the ion-implanted semiconductor properties.

  15. Colloidal quantum dots entrained in microstructured optical fibers

    NASA Astrophysics Data System (ADS)

    Holton, Carvel E.; Meissner, Kenith E.; Herz, Erik; Kominsky, Daniel; Pickrell, Gary R.

    2004-06-01

    We present the initial results of entraining colloidal quantum dots emitting at wavelengths from 0.5um through 1.2um, in various micro-structured optical fibers. Conventional and non-conventional, micro-structured optical fibers fabricated at Virginia Tech"s Fiber & ElectroOptics Research Center (FEORC) have been combined with semiconductor, colloidal quantum dots fabricated by the VT Advanced Biomedical Center (VTabc). The results are presented primarily in the form of visual verification and analysis of entrainment phenomena, for a cross-section of colloidal dot and micro-structured fiber forms. Unique optical, electro-optical and material properties resulting from the combinations are visibly suggested in the results. Core/clad/free space propagation properties and effects of emitted and absorbed light fields are observed to be dependent on the structure, aspect ratio and materials of the fibers as well as the properties of the colloidal quantum dots. Basic spectral data on representative free-space materials will be presented in the current paper. The presentation will explore in passing, the research options available to such quantum dot-fiber combinations, including advanced sensors, sources and filters.

  16. Tandem structured quantum dot/rod sensitized solar cell based on solvothermal synthesized CdSe quantum dots and rods

    NASA Astrophysics Data System (ADS)

    Golobostanfard, Mohammad Reza; Abdizadeh, Hossein

    2014-06-01

    The quantum dots (QD) and quantum rods (QR) of different sizes, shapes, and crystalline phases are synthesized by modified solvothermal method spontaneously employed stirring system and controlled internal applied pressure. The tandem structure of QDs and QRs as well as tetrapods is formed on hierarchical porous titania photoanode by means of electrophoretic deposition. A tremendous enhancement in efficiency of the cell is obtained in samples synthesized at 220 °C for 24 h due to the formation of tandem structure, utilization of Cu2S/CNT composite cathode, co-sensitization of CdS and CdSe, and beneficial role of QRs in electron lifetime. Smaller size QDs with higher band gaps penetrate deeper through the macro-channels of the hierarchical porous structure, while the QRs and tetrapods with lower band gaps are placed on upper layers. Although the charge injection is improved in smaller QDs, the electron lifetime in QRs is longer mainly due to the higher absorption cross section, proper charge separation, introduction of quasi-one dimensional route for charge transport through QRs, and higher surface area available for regeneration with electrolyte. The cell shows the efficiency of 1.05% with JSC of 4.48 mA cm-2, VOC of 0.45 V, and fill factor of 0.52.

  17. Aqueous-phase linker-assisted attachment of cysteinate(2-)-capped cdse quantum dots to TiO2 for quantum dot-sensitized solar cells.

    PubMed

    Coughlin, Kathleen M; Nevins, Jeremy S; Watson, David F

    2013-09-11

    We have synthesized water-dispersible cysteinate(2-)-capped CdSe nanocrystals and attached them to TiO2 using one-step linker-assisted assembly. Room-temperature syntheses yielded CdSe magic-sized clusters (MSCs) exhibiting a narrow and intense first excitonic absorption band centered at 422 nm. Syntheses at 80 °C yielded regular CdSe quantum dots (RQDs) with broader and red-shifted first excitonic absorption bands. Cysteinate(2-)-capped CdSe MSCs and RQDs adsorbed to bare nanocrystalline TiO2 films from aqueous dispersions. CdSe-functionalized TiO2 films were incorporated into working electrodes of quantum dot-sensitized solar cells (QDSSCs). Short-circuit photocurrent action spectra of QDSSCs corresponded closely to absorptance spectra of CdSe-functionalized TiO2 films. Power-conversion efficiencies were (0.43±0.04)% for MSC-functionalized TiO2 and (0.83±0.11)% for RQD-functionalized TiO2. Absorbed photon-to-current efficiencies under white-light illumination were approximately 0.3 for both MSC- and RQD-based QDSSCs, despite the significant differences in the electronic properties of MSCs and RQDs. Cysteinate(2-) is an attractive capping group and ligand, as it engenders water-dispersibility of CdSe nanocrystals with a range of photophysical properties, enables facile all-aqueous linker-assisted attachment of nanocrystals to TiO2, and promotes efficient interfacial charge transfer. PMID:23937323

  18. Electroluminescence from isolated CdSe /ZnS quantum dots in multilayered light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhao, Jialong; Zhang, Jingying; Jiang, Chaoyang; Bohnenberger, Jolanta; Basché, Thomas; Mews, Alf

    2004-09-01

    Electro- and photoluminescence spectra of the CdSe /ZnS core-shell quantum dots (QDs) covered by various organic ligands and incorporated into multilayered light-emitting diodes (LEDs) were recorded by a confocal optical microscope. The QDs were dispersed in a hole transporting material, N,N'-Diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), to investigate the LED performance at different QD concentrations and the effect of different surface modifications on the isolated QDs. No wavelength shift was observed in the electroluminescence spectra from the QD LEDs with or without the TPD. The peak energies of the electro- and photoluminescence showed only small spectral shifts (several nanometer) for the diluted QDs and no dependence on the QD-concentration, surface ligands, or conductive polymers that were used. This suggests that the relative peak shifts are related to the different filling processes in the CdSe QDs under photo excitation and electric injection, rather than to the "chemical" effects on the surface of the CdSe /ZnS QDs.

  19. Observed Shifts in Unoccupied States for Cu Doped CdSe Quantum Dots Observed via Synchrotron Techniques

    NASA Astrophysics Data System (ADS)

    Joshua, Joshua; Meulenberg, Robert

    2012-02-01

    Recent work has been targeted on examining the optical properties of guest ions in quantum dot (QD) lattice; however, very few studies have attempted to understand the effect the dopant has on the host electronic structure. In this talk, we will present data that suggests copper doping of CdSe QDs leads to trapped states below the conduction band (CB) minimum of the host CdSe particle. We propose that one possible reason for this could be hybridization between copper and cadmium, lowering the energy for the cadmium 5s states below the CB minimum of bulk CdSe. X-ray absorption near edge structure spectroscopy measurements at the Cd M3-edge for bulk, undoped, and doped QDs are compared and an unexpected lowering in the CB minimum is observed. We also present a first order theoretical model, for describing our results considering the effects caused by confinement, doping, and hybridization. Numerical approximations for atomic interactions suggest the hybridization parameter can lead to a lowering of the CB minimum by as much as 1.5 eV, as observed experimentally. Future work will include more in depth modelling of hybridization starting from tight binding calculations, developing a predictive model, applicable to more than existing data.

  20. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films.

    PubMed

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates. PMID:25483981

  1. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films

    NASA Astrophysics Data System (ADS)

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  2. A differential dielectric spectroscopy setup to measure the electric dipole moment and net charge of colloidal quantum dots

    SciTech Connect

    Kortschot, R. J.; Bakelaar, I. A.; Erné, B. H.; Kuipers, B. W. M.

    2014-03-15

    A sensitive dielectric spectroscopy setup is built to measure the response of nanoparticles dispersed in a liquid to an alternating electric field over a frequency range from 10{sup −2} to 10{sup 7} Hz. The measured complex permittivity spectrum records both the rotational dynamics due to a permanent electric dipole moment and the translational dynamics due to net charges. The setup consists of a half-transparent capacitor connected in a bridge circuit, which is balanced on pure solvent only, using a software-controlled compensating voltage. In this way, the measured signal is dominated by the contributions of the nanoparticles rather than by the solvent. We demonstrate the performance of the setup with measurements on a dispersion of colloidal CdSe quantum dots in the apolar liquid decalin.

  3. Colloidal quantum dot solids for solution-processed solar cells

    NASA Astrophysics Data System (ADS)

    Yuan, Mingjian; Liu, Mengxia; Sargent, Edward H.

    2016-03-01

    Solution-processed photovoltaic technologies represent a promising way to reduce the cost and increase the efficiency of solar energy harvesting. Among these, colloidal semiconductor quantum dot photovoltaics have the advantage of a spectrally tuneable infrared bandgap, which enables use in multi-junction cells, as well as the benefit of generating and harvesting multiple charge carrier pairs per absorbed photon. Here we review recent progress in colloidal quantum dot photovoltaics, focusing on three fronts. First, we examine strategies to manage the abundant surfaces of quantum dots, strategies that have led to progress in the removal of electronic trap states. Second, we consider new device architectures that have improved device performance to certified efficiencies of 10.6%. Third, we focus on progress in solution-phase chemical processing, such as spray-coating and centrifugal casting, which has led to the demonstration of manufacturing-ready process technologies.

  4. Temperature-dependent photovoltaic behavior of CdSe quantum dots/P3HT hybrid thinfilm

    NASA Astrophysics Data System (ADS)

    Zhang, Hui-chao; Du, Xiao-wei; Wang, Yu-qiao; Guan, Qiu-mei; Sun, Yue-ming; Cui, Yi-ping; Zhang, Jia-yu

    2013-03-01

    An organic-inorganic hybrid solar cell based on CdSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) was fabricated. Its temperature-dependent photovoltaic behaviors, such as I-V characteristic curves and open circuit voltage (Voc) transient response, were measured. The photovoltaic behavior of this hybrid thin film device was similar with that of organic thin film solar cells, according to analysis results based on the equivalent circuit method. The exact carrier lifetime was remarkably different between under low-temperature region and under temperature above 197 K.

  5. Raman analysis of chemical substitution of Cd atoms by Hg in CdSe quantum dots and rods

    NASA Astrophysics Data System (ADS)

    Cherevkov, Sergei A.; Baranov, Alexander V.; Ushakova, Elena V.; Litvin, Alexander P.; Fedorov, Anatoly V.; Prudnikau, Anatol V.; Artemyev, Mikhail V.

    2016-01-01

    We investigate nanocrystals of ternary compounds CdXHg1-XSe with 0CdSe NCs used for Cd/Hg substitution, either zinc blende or wurtzite, strongly affects the structural properties of the resultant CdXHg1-XSe quantum dots and rods.

  6. CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds.

    PubMed

    Algarra, M; Campos, B B; Miranda, M S; da Silva, Joaquim C G Esteves

    2011-02-15

    The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G(4) dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K(SV)=65(5)×10(4) M(-1); ACNB, K(SV)=19(2)×10(4) M(-1); and, MNP, K(SV)=33(1)×10(2) M(-1). These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L(-1) for MNB and ACNB and about 0.1 mg L(-1) for MNP. No interferences or small interferences are observed for trinitrotoluene [K(SV)=10(2)×10(2)×M(-1)], 2,4-dinitrotoluene [K(SV)=20(3)×10 M(-1)], 2,6-dinitrotoluene [K(SV)=11(4)×10 M(-1)] and nitrobenzene [K(SV)=2(1)×10(3)×M(-1)]. PMID:21238718

  7. Hybrid solar cells of micro/mesoporous Zn( and its graphite composites sensitized by CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Islam, SM Z.; Gayen, Taposh; Tint, Naing; Shi, Lingyan; Ebrahim, Amani M.; Seredych, Mykola; Bandosz, Teresa J.; Alfano, Robert

    2014-01-01

    Quantum efficiencies (QEs) of innovative hybrid solar cells fabricated using micro/mesoporous zinc (hydr)oxide and its graphite-based composites sensitized by semiconductor quantum dots (SQDs) are reported. High absorption coefficient of CdSe SQDs and the wide band gap of zinc (hydr)oxide and its composites with graphite oxide (GO) are essential to achieve solar cells of higher QEs. Hybrid solar cells are fabricated from zinc (hydr)oxide and its composites (with 2 and 5 wt.% of graphite oxides, termed as, ZnGO-2 and ZnGO-5, respectively) while using potassium iodide or perovskite as an electrolyte. A two-photon fluorescence (TPF) imaging technique was used to determine the internal structure of the solar cell device. The photocurrent and current-voltage measurements were used to measure short-circuit current and open-circuit voltage to calculate the fill factor and QE of these solar cells. The highest QE (up to ˜10.62%) is realized for a ZnGO-2-based solar cell using potassium iodide as its electrolyte and the CdSe quantum dot as its sensitizer.

  8. Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

    NASA Technical Reports Server (NTRS)

    Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

    1995-01-01

    One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

  9. Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties

    NASA Astrophysics Data System (ADS)

    Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher

    1995-08-01

    One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.

  10. Structure of Colloidal Quantum Dots from Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy.

    PubMed

    Piveteau, Laura; Ong, Ta-Chung; Rossini, Aaron J; Emsley, Lyndon; Copéret, Christophe; Kovalenko, Maksym V

    2015-11-01

    Understanding the chemistry of colloidal quantum dots (QDs) is primarily hampered by the lack of analytical methods to selectively and discriminately probe the QD core, QD surface and capping ligands. Here, we present a general concept for studying a broad range of QDs such as CdSe, CdTe, InP, PbSe, PbTe, CsPbBr3, etc., capped with both organic and inorganic surface capping ligands, through dynamic nuclear polarization (DNP) surface enhanced NMR spectroscopy. DNP can enhance NMR signals by factors of 10-100, thereby reducing the measurement times by 2-4 orders of magnitude. 1D DNP enhanced spectra acquired in this way are shown to clearly distinguish QD surface atoms from those of the QD core, and environmental effects such as oxidation. Furthermore, 2D NMR correlation experiments, which were previously inconceivable for QD surfaces, are demonstrated to be readily performed with DNP and provide the bonding motifs between the QD surfaces and the capping ligands. PMID:26473384

  11. Microsecond-sustained lasing from colloidal quantum dot solids

    NASA Astrophysics Data System (ADS)

    Adachi, Michael M.; Fan, Fengjia; Sellan, Daniel P.; Hoogland, Sjoerd; Voznyy, Oleksandr; Houtepen, Arjan J.; Parrish, Kevin D.; Kanjanaboos, Pongsakorn; Malen, Jonathan A.; Sargent, Edward H.

    2015-10-01

    Colloidal quantum dots have grown in interest as materials for light amplification and lasing in view of their bright photoluminescence, convenient solution processing and size-controlled spectral tunability. To date, lasing in colloidal quantum dot solids has been limited to the nanosecond temporal regime, curtailing their application in systems that require more sustained emission. Here we find that the chief cause of nanosecond-only operation has been thermal runaway: the combination of rapid heat injection from the pump source, poor heat removal and a highly temperature-dependent threshold. We show microsecond-sustained lasing, achieved by placing ultra-compact colloidal quantum dot films on a thermally conductive substrate, the combination of which minimizes heat accumulation. Specifically, we employ inorganic-halide-capped quantum dots that exhibit high modal gain (1,200 cm-1) and an ultralow amplified spontaneous emission threshold (average peak power of ~50 kW cm-2) and rely on an optical structure that dissipates heat while offering minimal modal loss.

  12. Microsecond-sustained lasing from colloidal quantum dot solids

    PubMed Central

    Adachi, Michael M.; Fan, Fengjia; Sellan, Daniel P.; Hoogland, Sjoerd; Voznyy, Oleksandr; Houtepen, Arjan J.; Parrish, Kevin D.; Kanjanaboos, Pongsakorn; Malen, Jonathan A.; Sargent, Edward H.

    2015-01-01

    Colloidal quantum dots have grown in interest as materials for light amplification and lasing in view of their bright photoluminescence, convenient solution processing and size-controlled spectral tunability. To date, lasing in colloidal quantum dot solids has been limited to the nanosecond temporal regime, curtailing their application in systems that require more sustained emission. Here we find that the chief cause of nanosecond-only operation has been thermal runaway: the combination of rapid heat injection from the pump source, poor heat removal and a highly temperature-dependent threshold. We show microsecond-sustained lasing, achieved by placing ultra-compact colloidal quantum dot films on a thermally conductive substrate, the combination of which minimizes heat accumulation. Specifically, we employ inorganic-halide-capped quantum dots that exhibit high modal gain (1,200 cm−1) and an ultralow amplified spontaneous emission threshold (average peak power of ∼50 kW cm−2) and rely on an optical structure that dissipates heat while offering minimal modal loss. PMID:26493282

  13. Momentum Transfer Studies and Studies of Linear and Nonlinear Optical Properties of Metal Colloids and Semiconductor Quantum Dots

    NASA Technical Reports Server (NTRS)

    Collins, W. E.; Burger, A.; Dyer, K.; George, M.; Henderson, D.; Morgan, S.; Mu, R.; Shi, D.; Conner, D; Thompson, E.; Collins, L.; Curry, L.; Mattox, S.; Williams, G.

    1996-01-01

    Phase 1 of this work involved design work on a momentum transfer device. The progress on design and testing will be presented. Phase 2 involved the systematic study of the MPD thruster for dual uses. Though it was designed as a thruster for space vehicles, the characteristics of the plasma make it an excellent candidate for industrial applications. This project sought to characterize the system for use in materials processing and characterization. The surface modification on ZnCdTe, CdTe, and ZnTe will be presented. Phase 3 involved metal colloids and semiconductor quantum dots. One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantation for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga, and As. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb, and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. The results of some of this work will also be reported.

  14. Study of optical nonlinearity of CdSe and CdSe@ZnO core-shell quantum dots in nanosecond regime

    NASA Astrophysics Data System (ADS)

    Deepika; Dhar, Rakesh; Mohan, Devendra

    2015-12-01

    Thioglycolic acid capped cadmium selenide (CdSe) and CdSe@ZnO core-shell quantum dots have been synthesized in aqueous phase. The sample was characterized by UV-vis spectrophotometer, TEM and Z-scan technique. The nonlinear optical parameters viz. nonlinear absorption coefficient (β), nonlinear refractive index (n2) and third-order nonlinear susceptibilities (χ3) of quantum dots have been estimated using second harmonic of Nd:YAG laser. The study predicts that CdSe@ZnO quantum dots exhibits strong nonlinearity as compared to core CdSe quantum dots. The nonlinearity in quantum dots is attributed to the presence of resonant excitation and free optical processes. The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.

  15. Photoluminescence limiting of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Ullrich, B.; Xi, H.; Wang, J. S.

    2016-02-01

    The exposure of colloidal 2 nm PbS quantum dots to growing continuous wave laser excitation at 532 nm increases the photoluminescence intensity with the square root of the optical stimulus. The results herein in conjunction with previous findings [B. Ullrich and H. Xi, Opt. Lett. 38, 4698 (2013)] advocate the square root trend to be the general limiting function for photo-carrier transport and emission of optically excited nano-sized materials. We further show that the excitation of one electron-hole pair per quantum dot defines the saturation threshold for photoluminescence intensity and dynamic band filling.

  16. Description of the Adsorption and Exciton Delocalizing Properties of p-Substituted Thiophenols on CdSe Quantum Dots.

    PubMed

    Aruda, Kenneth O; Amin, Victor A; Thompson, Christopher M; Lau, Bryan; Nepomnyashchii, Alexander B; Weiss, Emily A

    2016-04-12

    This work describes the quantitative characterization of the interfacial chemical and electronic structure of CdSe quantum dots (QDs) coated in one of five p-substituted thiophenolates (X-TP, X = NH2, CH3O, CH3, Cl, or NO2), and the dependence of this structure on the p-substituent X. (1)H NMR spectra of mixtures of CdSe QDs and X-TPs yield the number of X-TPs bound to the surface of each QD. The binding data, in combination with the shift in the energy of the first excitonic peak of the QDs as a function of the surface coverage of X-TP and Raman and NMR analysis of the mixtures, indicate that X-TP binds to CdSe QDs in at least three modes, two modes that are responsible for exciton delocalization and a third mode that does not affect the excitonic energy. The first two modes involve displacement of OPA from the QD core, whereas the third mode forms cadmium-thiophenolate complexes that are not electronically coupled to the QD core. Fits to the data using the dual-mode binding model also yield the values of Δr1, the average radius of exciton delocalization due to binding of the X-TP in modes 1 and 2. A 3D parametrized particle-in-a-sphere model enables the conversion of the measured value of Δr1 for each X-TP to the height of the potential barrier that the ligand presents for tunneling of excitonic hole into the interfacial region. The height of this barrier increases from 0.3 to 0.9 eV as the substituent, X, becomes more electron-withdrawing. PMID:27002248

  17. Inverted colloidal quantum dot solar cells.

    PubMed

    Kim, Gi-Hwan; Walker, Bright; Kim, Hak-Beom; Kim, Jin Young; Sargent, Edward H; Park, Jongnam; Kim, Jin Young

    2014-05-28

    An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage. PMID:24677118

  18. Enhancing the conversion efficiency of red emission by spin-coating CdSe quantum dots on the green nanorod light-emitting diode.

    PubMed

    Lee, Ya-Ju; Lee, Chia-Jung; Cheng, Chun-Mao

    2010-11-01

    A hybrid structure of CdSe quantum dots (QDs) (λ = 640 nm) spin-coated on the indium gallium nitride (InGaN) nanorod light-emitting diode (LED, λ = 525 nm) is successfully fabricated. Experimental results indicate that the randomness and the minuteness of nanorods scatter the upcoming green light into the surrounding CdSe QDs efficiently, subsequently alleviating the likelihood of the emitted photons of red emission being recaptured by the CdSe QDs (self-absorption effect), and that increases the coupling probability of emission lights and the overall conversion efficiency. Moreover, the revealed structure with high color stability provides an alternative solution for general lighting applications of next generation. PMID:21165088

  19. Coverage control of CdSe quantum dots in the photodeposition on TiO2 for the photoelectrochemical solar hydrogen generation.

    PubMed

    Yoshii, Mari; Murata, Yusuke; Nakabayashi, Yasunari; Ikeda, Takuya; Fujishima, Musashi; Tada, Hiroaki

    2016-07-15

    CdSe quantum dots (QDs) have successfully been formed on the TiO2 surface by the photodeposition of Se QDs and their subsequent transformation into CdSe QDs (CdSe/TiO2) (Fujishima et al., 2014). The addition of mercaptoacetic acid (MAA) in the second step of the two-step photodeposition process significantly decreases the CdSe particle size and the contact angle against the TiO2 surface to increase the TiO2-surface coverage by CdSe QDs with the particle size distribution sharpened. X-ray photoelectron and Raman spectroscopy measurements indicated that MAA is densely chemisorbed on the surface of CdSe QDs through CdS bond, whereas sparsely adsorbed on the TiO2 surface. Photoelectrochemical (PEC) cells using CdSe/TiO2 as the photoanode for hydrogen (H2) generation from aqueous sulfide solution were fabricated. The rate of H2 generation strongly depends on the concentration of MAA (C) added in the photoanode preparation, and the photoanode prepared at C=0.04mM affords a maximum solar-to-hydrogen conversion efficiency of 0.028%. PMID:27100903

  20. Effects of morphology, diameter and periodic distance of the Ag nanoparticle periodic arrays on the enhancement of the plasmonic field absorption in the CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Kohnehpoushi, Saman; Eskandari, Mehdi; Ahmadi, Vahid; Yousefirad, Mansooreh; Nabavi, Elham

    2016-09-01

    In this work, the numerical calculations of plasmonic field absorption of Ag nanoparticles (Ag NPs) periodic arrays in the CdSe quantum dot (QD) film are investigated by the three-dimensional finite difference time domain (FDTD). Diameter (D), periodic distance (P), and morphology effects of Ag NPs are investigated on the improvement of the plasmonic field absorption in CdSe QD film. Results show that plasmonic field absorption in CdSe QD film is enhanced with reduction of D of Ag NPs until 5 nm and reduces thereafter. It is observed that with raising D of Ag NPs, optimum plasmonic field absorption in CdSe QD film is shifted toward the higher P. Moreover, with varying morphology of Ag NPs from spherical to cylindrical, cubic, ringing and pyramid, the plasmonic field absorption is considerably enhanced in CdSe QD film and position of quadrupole plasmon mode (QPPM) is shifted toward further wavelength. For cylindrical Ag NPs, the QPPM intensity increased with raising height (H) until 15 nm and reduces thereafter.

  1. Fabrication of fluorescence-based biosensors from functionalized CdSe and CdTe quantum dots for pesticide detection

    NASA Astrophysics Data System (ADS)

    Tran, Thi Kim Chi; Chinh Vu, Duc; Dieu Thuy Ung, Thi; Yen Nguyen, Hai; Hai Nguyen, Ngoc; Cao Dao, Tran; Nga Pham, Thu; Liem Nguyen, Quang

    2012-09-01

    This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of ATCh catalyzed by the enzyme AChE, whose activity is specifically inhibited by pesticides. Two kinds of QDs were used to fabricate our biosensors: (i) CdSe QDs synthesized in high-boiling non-polar organic solvent and then functionalized by shelling with two monolayers (2-ML) of ZnSe and eight monolayers (8-ML) of ZnS and finally capped with 3-mercaptopropionic acid (MPA) to become water soluble; and (ii) CdTe QDs synthesized in aqueous phase then shelled with CdS. For normal checks the fabricated biosensors could detect parathion methyl (PM) pesticide at very low contents of ppm with the threshold as low as 0.05 ppm. The dynamic range from 0.05 ppm to 1 ppm for the pesticide detection could be expandable by increasing the AChE amount in the biosensor.

  2. Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry.

    PubMed

    Humbert, Christophe; Dahi, Abdellatif; Dalstein, Laetitia; Busson, Bertrand; Lismont, Marjorie; Colson, Pierre; Dreesen, Laurent

    2015-05-01

    We develop an innovative manufacturing process, based on radio-frequency magnetron sputtering (RFMS), to prepare neat CdSe quantum dots (QDs) on glass and silicon substrates and further chemically functionalize them. In order to validate the fabrication protocol, their optical properties are compared with those of QDs obtained from commercial solutions and deposited by wet chemistry on the substrates. Firstly, AFM measurements attest that nano-objects with a mean diameter around 13 nm are located on the substrate after RFMS treatment. Secondly, the UV-Vis absorption study of this deposited layer shows a specific optical absorption band, located at 550 nm, which is related to a discrete energy level of QDs. Thirdly, by using two-color sum-frequency generation (2C-SFG) nonlinear optical spectroscopy, we show experimentally the functionalization efficiency of the RFMS CdSe QDs layer with thiol derived molecules, which is not possible on the QDs layer prepared by wet chemistry due to the surfactant molecules from the native solution. Finally, 2C-SFG spectroscopy, performed at different visible wavelengths, highlights modifications of the vibration mode shape whatever the QDs deposition method, which is correlated to the discrete energy level of the QDs. PMID:25596370

  3. Parametric interactions in presence of different size colloids in semiconductor quantum plasmas

    SciTech Connect

    Vanshpal, R. Sharma, Uttam; Dubey, Swati

    2015-07-31

    Present work is an attempt to investigate the effect of different size colloids on parametric interaction in semiconductor quantum plasma. Inclusion of quantum effect is being done in this analysis through quantum correction term in classical hydrodynamic model of homogeneous semiconductor plasma. The effect is associated with purely quantum origin using quantum Bohm potential and quantum statistics. Colloidal size and quantum correction term modify the parametric dispersion characteristics of ion implanted semiconductor plasma medium. It is found that quantum effect on colloids is inversely proportional to their size. Moreover critical size of implanted colloids for the effective quantum correction is determined which is found to be equal to the lattice spacing of the crystal.

  4. Genotoxic capacity of Cd/Se semiconductor quantum dots with differing surface chemistries

    PubMed Central

    Manshian, Bella B.; Soenen, Stefaan J.; Brown, Andy; Hondow, Nicole; Wills, John; Jenkins, Gareth J. S.; Doak, Shareen H.

    2016-01-01

    Quantum dots (QD) have unique electronic and optical properties promoting biotechnological advances. However, our understanding of the toxicological structure–activity relationships remains limited. This study aimed to determine the biological impact of varying nanomaterial surface chemistry by assessing the interaction of QD with either a negative (carboxyl), neutral (hexadecylamine; HDA) or positive (amine) polymer coating with human lymphoblastoid TK6 cells. Following QD physico-chemical characterisation, cellular uptake was quantified by optical and electron microscopy. Cytotoxicity was evaluated and genotoxicity was characterised using the micronucleus assay (gross chromosomal damage) and the HPRT forward mutation assay (point mutagenicity). Cellular damage mechanisms were also explored, focusing on oxidative stress and mitochondrial damage. Cell uptake, cytotoxicity and genotoxicity were found to be dependent on QD surface chemistry. Carboxyl-QD demonstrated the smallest agglomerate size and greatest cellular uptake, which correlated with a dose dependent increase in cytotoxicity and genotoxicity. Amine-QD induced minimal cellular damage, while HDA-QD promoted substantial induction of cell death and genotoxicity. However, HDA-QD were not internalised by the cells and the damage they caused was most likely due to free cadmium release caused by QD dissolution. Oxidative stress and induced mitochondrial reactive oxygen species were only partially associated with cytotoxicity and genotoxicity induced by the QD, hence were not the only mechanisms of importance. Colloidal stability, nanoparticle (NP) surface chemistry, cellular uptake levels and the intrinsic characteristics of the NPs are therefore critical parameters impacting genotoxicity induced by QD. PMID:26275419

  5. High Efficiency Colloidal Quantum Dot Phosphors

    SciTech Connect

    Kahen, Keith

    2013-12-31

    The project showed that non-Cd containing, InP-based nanocrystals (semiconductor materials with dimensions of ~6 nm) have high potential for enabling next-generation, nanocrystal-based, on chip phosphors for solid state lighting. Typical nanocrystals fall short of the requirements for on chip phosphors due to their loss of quantum efficiency under the operating conditions of LEDs, such as, high temperature (up to 150 °C) and high optical flux (up to 200 W/cm2). The InP-based nanocrystals invented during this project maintain high quantum efficiency (>80%) in polymer-based films under these operating conditions for emission wavelengths ranging from ~530 to 620 nm. These nanocrystals also show other desirable attributes, such as, lack of blinking (a common problem with nanocrystals which limits their performance) and no increase in the emission spectral width from room to 150 °C (emitters with narrower spectral widths enable higher efficiency LEDs). Prior to these nanocrystals, no nanocrystal system (regardless of nanocrystal type) showed this collection of properties; in fact, other nanocrystal systems are typically limited to showing only one desirable trait (such as high temperature stability) but being deficient in other properties (such as high flux stability). The project showed that one can reproducibly obtain these properties by generating a novel compositional structure inside of the nanomaterials; in addition, the project formulated an initial theoretical framework linking the compositional structure to the list of high performance optical properties. Over the course of the project, the synthetic methodology for producing the novel composition was evolved to enable the synthesis of these nanomaterials at a cost approximately equal to that required for forming typical conventional nanocrystals. Given the above results, the last major remaining step prior to scale up of the nanomaterials is to limit the oxidation of these materials during the tens of

  6. High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays

    NASA Astrophysics Data System (ADS)

    Hou, Juan; Zhao, Haifeng; Huang, Fei; Jing, Qun; Cao, Haibin; Wu, Qiang; Peng, Shanglong; Cao, Guozhong

    2016-09-01

    Doping transition metal ions Mn2+ to semiconductor quantum dots (QDs) are extremely interesting for the development of photovoltaic devices. Quantum dot sensitized solar cells (QDSCs) are able to show promising power conversion efficiencies (PCE) by employing Mn2+ doped QDs. Herein we achieve effective CdS/Mnsbnd CdSe/ZnS QDs co-sensitized vertical ZnO nanorod arrays film that provides an appreciable enhancement in photovoltaic performance. The measured PCE of the solar cells with Mn2+ doped CdSe QDs is 4.14%, which is higher than the efficiency of 2.91% for the solar cells without Mn2+ or a ∼42% increase. The improvement in PCE is ascribed to a higher open-circuit voltage (Voc = 0.74 V) and a superior short-circuit current density (Jsc = 12.6 mA cm-2) with the introduction of Mn2+ into CdSe QDs. The enhancement seen with Mn2+ doped CdSe QDs are investigated and explained by the fact that the enhanced light absorption and reduced charge recombination by the formation of Mnsbnd CdSe passivation layer covering the QDs.

  7. HgTe colloidal quantum dot LWIR infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Pimpinella, R. E.; Ciani, A.; Guyot-Sionnest, P.; Grein, C.

    2015-08-01

    The majority of modern infrared photon imaging devices are based on epitaxially grown bulk semiconductor materials. Colloidal quantum dot (CQD)-based infrared devices provide great promise for significantly reducing cost as well as significantly increased operating temperatures of infrared imaging systems. In addition, CQD-based infrared devices greatly benefit from band gap tuning by controlling the CQD size rather than the composition. In this work, we investigate the absorption coefficient of HgTe CQD films as a function of temperature and cutoff wavelength. The optical absorption properties are predicted for defect-free HgTe films as well as films which vary from ideal.

  8. Colloidal semiconductor quantum dots with tunable surface composition.

    PubMed

    Wei, Helen Hsiu-Ying; Evans, Christopher M; Swartz, Brett D; Neukirch, Amanda J; Young, Jeremy; Prezhdo, Oleg V; Krauss, Todd D

    2012-09-12

    Colloidal CdS quantum dots (QDs) were synthesized with tunable surface composition. Surface stoichiometry was controlled by applying reactive secondary phosphine sulfide precursors in a layer-by-layer approach. The surface composition was observed to greatly affect photoluminescence properties. Band edge emission was quenched in sulfur terminated CdS QDs and fully recovered when QDs were cadmium terminated. Calculations suggest that electronic states inside the band gap arising from surface sulfur atoms could trap charges, thus inhibiting radiative recombination and facilitating nonradiative relaxation. PMID:22924603

  9. Observation of quantum-size effects in the electronic structure of CdSe quantum dots by high resolution positron spectroscopy

    NASA Astrophysics Data System (ADS)

    Denison, A. B.; Eijt, S. W.; van Veen, A.; Falub, C. V.; Mijnarends, P. E.; Schut, H.; Barbiellini, B.; Bansil, A.

    2003-03-01

    The electron momentum density (EMD) of CdSe quantum dots deposited as micrometer thin layers is investigated in the diameter range from 2.5 to 6 nm. For this purpose, we have carried out depth-resolved positron 2D angular correlation of annihilation radiation (2D-ACAR) experiments at the TU-Delft intense variable-energy positron beam, together with extensive first-principles simulations of the EMD, including the case of the bulk CdSe single crystal. The EMD shows a smearing at the Jones zone boundary, which is inversely proportional to the square of the quantum dot diameter. A reduction in the Cd(4d) electron contribution is revealed and tentatively ascribed to annihilation at incomplete TOPO-covered Se-rich surfaces. We compare and contrast our results to earlier Doppler measurements [1] and recently proposed models [1,2]. [1] M. Weber, K. Lynn, B. Barbiellini, P. Sterne and A. Denison, Phys. Rev. B 66 (2002) 41305 [2] R. Saniz, B. Barbiellini and A. Denison, Phys. Rev. B 65 (2002) 245310

  10. Hot spot assisted blinking suppression of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Lu, Liu; Tong, Xuan; Zhang, Xu; Ren, Naifei; Jiang, Bo; Lu, Haifei

    2016-05-01

    This work compares the blinking of CdSe QDs on glass, single silver nanowire, and double aligned nanowires. The corresponding on-time fractions of these three cases are 50%, 70% and 85% respectively, which indicates that aligned double nanowires shows more efficient suppression than that of single nanowire. This phenomenon is attributed to the higher concentration of hot electron from hot spot between nanowires. Occupation of the non-radiative recombination centers by hot electrons from silver nanowires can be explained for the suppressed blinking behavior. The result has provided a novel pathway of suppressing the blinking behavior of QDs through plasmonic hot spot.

  11. Colloidal quantum dot solar cells on curved and flexible substrates

    SciTech Connect

    Kramer, Illan J.; Moreno-Bautista, Gabriel; Minor, James C.; Kopilovic, Damir; Sargent, Edward H.

    2014-10-20

    Colloidal quantum dots (CQDs) are semiconductor nanocrystals synthesized with, processed in, and deposited from the solution phase, potentially enabling low-cost, facile manufacture of solar cells. Unfortunately, CQD solar cell reports, until now, have only explored batch-processing methods—such as spin-coating—that offer limited capacity for scaling. Spray-coating could offer a means of producing uniform colloidal quantum dot films that yield high-quality devices. Here, we explore the versatility of the spray-coating method by producing CQD solar cells in a variety of previously unexplored substrate arrangements. The potential transferability of the spray-coating method to a roll-to-roll manufacturing process was tested by spray-coating the CQD active layer onto six substrates mounted on a rapidly rotating drum, yielding devices with an average power conversion efficiency of 6.7%. We further tested the manufacturability of the process by endeavoring to spray onto flexible substrates, only to find that spraying while the substrate was flexed was crucial to achieving champion performance of 7.2% without compromise to open-circuit voltage. Having deposited onto a substrate with one axis of curvature, we then built our CQD solar cells onto a spherical lens substrate having two axes of curvature resulting in a 5% efficient device. These results show that CQDs deposited using our spraying method can be integrated to large-area manufacturing processes and can be used to make solar cells on unconventional shapes.

  12. Structural characterization and observation of variable range hopping conduction mechanism at high temperature in CdSe quantum dot solids

    NASA Astrophysics Data System (ADS)

    Sinha, Subhojyoti; Kumar Chatterjee, Sanat; Ghosh, Jiten; Kumar Meikap, Ajit

    2013-03-01

    We have used Rietveld refinement technique to extract the microstructural parameters of thioglycolic acid capped CdSe quantum dots. The quantum dot formation and its efficient capping are further confirmed by HR-TEM, UV-visible and FT-IR spectroscopy. Comparative study of the variation of dc conductivity with temperature (298 K ≤ T ≤ 460 K) is given considering Arrhenius formalism, small polaron hopping and Schnakenberg model. We observe that only Schnakenberg model provides good fit to the non-linear region of the variation of dc conductivity with temperature. Experimental variation of ac conductivity and dielectric parameters with temperature (298 K ≤ T ≤ 460 K) and frequency (80 Hz ≤ f ≤ 2 MHz) are discussed in the light of hopping theory and quantum confinement effect. We have elucidated the observed non-linearity in the I-V curves (measured within ±50 V), at dark and at ambient light, in view of tunneling mechanism. Tunnel exponents and non-linearity weight factors have also been evaluated in this regard.

  13. Mechanism for strong binding of CdSe quantum dots to multiwall carbon nanotubes for solar energy harvesting

    NASA Astrophysics Data System (ADS)

    Azoz, Seyla; Jiang, Jie; Keskar, Gayatri; McEnally, Charles; Alkas, Alp; Ren, Fang; Marinkovic, Nebojsa; Haller, Gary L.; Ismail-Beigi, Sohrab; Pfefferle, Lisa D.

    2013-07-01

    As hybrid nanomaterials have myriad of applications in modern technology, different functionalization strategies are being intensely sought for preparing nanocomposites with tunable properties and structures. Multi-Walled Carbon Nanotube (MWNT)/CdSe Quantum Dot (QD) heterostructures serve as an important example for an active component of solar cells. The attachment mechanism of CdSe QDs and MWNTs is known to affect the charge transfer between them and consequently to alter the efficiency of solar cell devices. In this study, we present a novel method that enables the exchange of some of the organic capping agents on the QDs with carboxyl functionalized MWNTs upon ultrasonication. This produces a ligand-free covalent attachment of the QDs to the MWNTs. EXAFS characterization reveals direct bond formation between the CdSe QDs and the MWNTs. The amount of oleic acid exchanged is quantified by temperature-programmed decomposition; the results indicate that roughly half of the oleic acid is removed from the QDs upon functionalized MWNT addition. Additionally, we characterize the optical and structural properties of the QD-MWNT heterostructures and investigate how these properties are affected by the attachment. The steady state photoluminescence response of QDs is completely quenched. The lifetime of the PL of the QDs measured with time resolved photoluminescence shows a significant decrease after they are covalently bonded to functionalized MWNTs, suggesting a fast charge transfer between QDs and MWNTs. Our theoretical calculations are consistent with and support these experimental findings and provide microscopic models for the QD binding mechanisms.As hybrid nanomaterials have myriad of applications in modern technology, different functionalization strategies are being intensely sought for preparing nanocomposites with tunable properties and structures. Multi-Walled Carbon Nanotube (MWNT)/CdSe Quantum Dot (QD) heterostructures serve as an important example for an

  14. Red shift in the photoluminescence of colloidal carbon quantum dots induced by photon reabsorption

    SciTech Connect

    Zhang, Wenxia; Dai, Dejian; Chen, Xifang; Guo, Xiaoxiao; Fan, Jiyang

    2014-03-03

    We synthesize the colloidal carbon/graphene quantum dots 1–9 nm in diameter and study their photoluminescence properties. Surprisingly, the luminescence properties of a fixed collection of colloidal carbon quantum dots can be systematically changed as the concentration varies. A model based on photon reabsorption is proposed which explains well the experiment. Infrared spectral study indicates that the surfaces of the carbon quantum dots are substantially terminated by oxygen atoms, which causes their ultra-high hydrophilicity. Our result clarifies the mystery of distinct emission colors in carbon quantum dots and indicates that photon reabsorption can strongly affect the luminescence properties of colloidal nanocrystals.

  15. Investigation of CdSe quantum dots in MgS barriers as active region in light emitting diodes

    NASA Astrophysics Data System (ADS)

    Gust, A.; Kruse, C.; Hommel, D.

    2007-04-01

    On the way towards a quantum dot (QD) based single photon emitting device operating at room temperature (RT) we investigated the electrical and optical properties of light emitting diodes (LEDs) containing single CdSe quantum dot sheets surrounded by different types of barriers. The barriers consist either of MgS layers or a combination of MgS and ZnSSe layers in order to improve the luminescence stability of the QDs at elevated temperatures. The turn-on voltages of the LEDs at RT are in the range of 4-7 V while electro-luminescence (EL) spectra show distinct QD-related emission in the green spectral region. The LEDs containing the barriers show a factor of five lower intensity compared to the reference sample without barriers due to the tunneling process of the carriers through the barriers. However, the sample with the MgS/ZnSSe barrier has a significantly higher device lifetime under constant current driving conditions compared to the samples without the ZnSSe layer.

  16. Seed-mediated synthesis, properties and application of γ-Fe 2O 3-CdSe magnetic quantum dots

    NASA Astrophysics Data System (ADS)

    Lin, Alex W. H.; Yen Ang, Chung; Patra, Pranab K.; Han, Yu; Gu, Hongwei; Le Breton, Jean-Marie; Juraszek, Jean; Chiron, Hubert; Papaefthymiou, Georgia C.; Tamil Selvan, Subramanian; Ying, Jackie Y.

    2011-08-01

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around γ-Fe 2O 3 magnetic cores was performed at high temperature (300 °C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells.

  17. Vectorial electron transfer for improved hydrogen evolution by mercaptopropionic-acid-regulated CdSe quantum-dots-TiO2 -Ni(OH)2 assembly.

    PubMed

    Yu, Shan; Li, Zhi-Jun; Fan, Xiang-Bing; Li, Jia-Xin; Zhan, Fei; Li, Xu-Bing; Tao, Ye; Tung, Chen-Ho; Wu, Li-Zhu

    2015-02-01

    A visible-light-induced hydrogen evolution system based on a CdSe quantum dots (QDs)-TiO2 -Ni(OH)2 ternary assembly has been constructed under an ambient environment, and a bifunctional molecular linker, mercaptopropionic acid, is used to facilitate the interaction between CdSe QDs and TiO2 . This hydrogen evolution system works effectively in a basic aqueous solution (pH 11.0) to achieve a hydrogen evolution rate of 10.1 mmol g(-1)  h(-1) for the assembly and a turnover frequency of 5140 h(-1) with respect to CdSe QDs (10 h); the latter is comparable with the highest value reported for QD systems in an acidic environment. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and control experiments demonstrate that Ni(OH)2 is an efficient hydrogen evolution catalyst. In addition, inductively coupled plasma optical emission spectroscopy and the emission decay of the assembly combined with the hydrogen evolution experiments show that TiO2 functions mainly as the electron mediator; the vectorial electron transfer from CdSe QDs to TiO2 and then from TiO2 to Ni(OH)2 enhances the efficiency for hydrogen evolution. The assembly comprises light antenna CdSe QDs, electron mediator TiO2 , and catalytic Ni(OH)2 , which mimics the strategy of photosynthesis exploited in nature and takes us a step further towards artificial photosynthesis. PMID:25470751

  18. Air-stable n-type colloidal quantum dot solids.

    PubMed

    Ning, Zhijun; Voznyy, Oleksandr; Pan, Jun; Hoogland, Sjoerd; Adinolfi, Valerio; Xu, Jixian; Li, Min; Kirmani, Ahmad R; Sun, Jon-Paul; Minor, James; Kemp, Kyle W; Dong, Haopeng; Rollny, Lisa; Labelle, André; Carey, Graham; Sutherland, Brandon; Hill, Ian; Amassian, Aram; Liu, Huan; Tang, Jiang; Bakr, Osman M; Sargent, Edward H

    2014-08-01

    Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO2. This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials. PMID:24907929

  19. Colloidal quantum dots for low-cost MWIR imaging

    NASA Astrophysics Data System (ADS)

    Ciani, Anthony J.; Pimpinella, Richard E.; Grein, Christoph H.; Guyot-Sionnest, Philippe

    2016-05-01

    Monodisperse suspensions of HgTe colloidal quantum dots (CQD) are readily synthesized with infrared energy gaps between 3 and 12 microns. Infrared photodetection using dried films of these CQDs has been demonstrated up to a wavelength of 12 microns, and HgTe CQD single-elemnet devices with 3.6 micron cutoff have bee nreported nad show ogod absorption <(10^4 cm^-1), response time and detectivity (2*10^10 Jones) at at emperature of 175 K; with the potential fo uncooled imaging. The synthesis of CQDs and fabrication of detector devices employ bench-top chemistry techniques, leading to the potential for rapid, wafer-scale manufacture of MWIR imaging devices with low production costs and overhead. The photoconductive, photovoltaic and optical properties of HgTe CQD films will be discussed relative to infrared imaging, along with recent achievements in integrating CQD films with readout integrated circuits to produce CQD-based MWIR focal plane arrays.

  20. Exciton Dynamics in InSb Colloidal Quantum Dots.

    PubMed

    Sills, Andrew; Harrison, Paul; Califano, Marco

    2016-01-01

    Extraordinarily fast biexciton decay times and unexpectedly large optical gaps are two striking features observed in InSb colloidal quantum dots that have remained so far unexplained. The former, should its origin be identified as an Auger recombination process, would have important implications regarding carrier multiplication efficiency, suggesting these nanostructures as potentially ideal active materials in photovoltaic devices. The latter could offer new insights into the factors that influence the electronic structure and consequently the optical properties of systems with reduced dimensionality and provide additional means to fine-tune them. Using the state-of-the-art atomistic semiempirical pseudopotential method we unveil the surprising origins of these features and show that a comprehensive explanation for these properties requires delving deep into the atomistic detail of these nanostructures and is, therefore, outside the reach of less sophisticated, albeit more popular, theoretical approaches. PMID:26650516

  1. Coexpression of CdSe and CdSe/CdS quantum dots in live cells using molecular hyperspectral imaging technology

    NASA Astrophysics Data System (ADS)

    Li, Qingli; Peng, Hui; Wang, Jing; Wang, Yiting; Guo, Fangmin

    2015-11-01

    A direct spatial and spectral observation of CdSe and CdSe/CdS quantum dots (QDs) as probes in live cells is performed by using a custom molecular hyperspectral imaging (MHI) system. Water-soluble CdSe and CdSe/CdS QDs are synthesized in aqueous solution under the assistance of high-intensity ultrasonic irradiation and incubated with colon cancer cells for bioimaging. Unlike the traditional fluorescence microscopy methods, MHI technology can identify QD probes according to their spectral signatures and generate coexpression and stain titer maps by a clustering method. The experimental results show that the MHI method has potential to unmix biomarkers by their spectral information, which opens up a pathway of optical multiplexing with many different QD probes.

  2. A Two-Step Synthetic Strategy toward Monodisperse Colloidal CdSe and CdSe/CdS Core/Shell Nanocrystals.

    PubMed

    Zhou, Jianhai; Pu, Chaodan; Jiao, Tianyu; Hou, Xiaoqi; Peng, Xiaogang

    2016-05-25

    CdSe magic-size clusters with close-shell surface and fixed molecular formula are well-known in the size range between ∼1 and 3 nm. By applying high concentration of cadmium alkanoates as ligands, a conventional synthetic system for CdSe nanocrystals was tuned to discriminate completion from initiation of atomic flat facets. This resulted in ∼4-13 nm CdSe nanocrystals with hexahedral shape terminated with low-index facets, namely three (100), one (110), and two (111) facets. These low-symmetry (Cs group with single mirror plane) yet monodisperse hexahedra were found to be persistent not only in a broad size range but also under typical synthetic temperatures for growth of both CdSe and CdS. Atomic motion on the surface of the nanocrystals under enhanced ligand dynamics initiated intraparticle ripening without activating interparticle ripening, which converted the hexahedral nanocrystals to monodisperse spherical ones. This new synthetic strategy rendered optimal color purity of photoluminescence (PL) of the CdSe and CdSe/CdS core/shell nanocrystals, with the ensemble PL peak width comparable with that of a corresponding single dot. PMID:27144923

  3. Colloidal CdTe/HgTe quantum dots with high photoluminescence quantum efficiency at room temperature

    NASA Astrophysics Data System (ADS)

    Kershaw, Stephen V.; Burt, Mike; Harrison, Mike; Rogach, Andrey; Weller, Horst; Eychmüller, Alex

    1999-09-01

    We have used an aqueous colloidal growth technique to form hybrid CdTe/HgTe quantum dots with a broad, strong fluorescence in the infrared (800-1200 nm). The quantum efficiency is high, around 44%, when pumped in the visible (488 nm), and the excited state lifetime is around 130 ns, making the material interesting as an optical amplifier medium. Using a pump-probe experiment, we have demonstrated weak optical amplification in a dilute aqueous suspension of CdTe/HgTe dots in the short wavelength wing of the emission spectrum at 808 nm.

  4. Electron - acoustic phonon coupling in colloidal lead sulfide quantum dots

    NASA Astrophysics Data System (ADS)

    Cho, Byungmoon; Tiwari, Vivek; Spencer, Austin; Baranov, Dmitry; Park, Samuel; Jonas, David

    2014-03-01

    Lead chalcogenide quantum dots (QDs) with bandgaps in the shortwave infrared are candidate materials for next generation photovoltaics exceeding the Shockley-Queisser limit. Despite ongoing controversy, multiple exciton generation (MEG) in QDs offers potential for improved photovoltaic efficiency. Hot carriers from high energy photoexcitation dissipate excess energy via coupled phonons; this is detrimental to MEG. The electron-phonon coupling (EPC) magnitude, partitioning among modes and dependence on the size/shape are poorly understood. We performed degenerate femtosecond pump-probe spectroscopy to investigate Auger recombination dynamics, a reverse process of MEG. We observe a quantum beat due to coherent acoustic phonons in femtosecond pump-probe signals from oleate capped colloidal lead sulfide QDs in toluene. A 3.4 ps period oscillation decays with 4.6 ps damping constant in 8 nm diameter dots; the amplitude increases linearly with pump energy and modulation is weaker than reported in smaller dots. An elastic continuum model for acoustic phonon frequency vs. dot diameter suggests a not yet understood quantitative discrepancy with prior work. These relaxation processes have important implications for QD photovoltaics.

  5. Quantitative assessment of Tn antigen in breast tissue micro-arrays using CdSe aqueous quantum dots.

    PubMed

    Au, Giang H T; Mejias, Linette; Swami, Vanlila K; Brooks, Ari D; Shih, Wan Y; Shih, Wei-Heng

    2014-03-01

    In this study, we examined the use of CdSe aqueous quantum dots (AQDs) each conjugated to three streptavidin as a fluorescent label to image Tn antigen expression in various breast tissues via a sandwich staining procedure where the primary monoclonal anti-Tn antibody was bound to the Tn antigen on the tissue, a biotin-labeled secondary antibody was bound to the primary anti-Tn antibody, and finally the streptavidin-conjugated AQDs were bound to the biotin on the secondary antibody. We evaluated the AQD staining of Tn antigen on tissue microarrays consisting of 395 cores from 115 cases including three tumor cores and one normal-tissue core from each breast cancer case and three tumor cores from each benign case. The results indicated AQD-Tn staining was positive in more than 90% of the cells in the cancer cores but not the cells in the normal-tissue cores and the benign tumor cores. As a result, AQD-Tn staining exhibited 95% sensitivity and 90% specificity in differentiating breast cancer against normal breast tissues and benign breast conditions. These results were better than the 90% sensitivity and 80% specificity exhibited by the corresponding horse radish peroxidase (HRP) staining using the same antibodies on the same tissues and those of previous studies that used different fluorescent labels to image Tn antigen. In addition to sensitivity and specificity, the current AQD-Tn staining with a definitive threshold was quantitative. PMID:24411673

  6. Lifetime and Polarization of the Radiative Decay of Excitons, Biexcitons, and Trions in CdSe Nanocrystal Quantum Dots

    SciTech Connect

    Califano, M.; Franceschetti, A.; Zunger, A.

    2007-01-01

    Using the pseudopotential configuration-interaction method, we calculate the intrinsic lifetime and polarization of the radiative decay of single excitons (X), positive and negative trions (X{sup +} and X{sup -}), and biexcitons (XX) in CdSe nanocrystal quantum dots. We investigate the effects of the inclusion of increasingly more complex many-body treatments, starting from the single-particle approach and culminating with the configuration-interaction scheme. Our configuration-interaction results for the size dependence of the single-exciton radiative lifetime at room temperature are in excellent agreement with recent experimental data. We also find the following. (i) Whereas the polarization of the bright exciton emission is always perpendicular to the hexagonal c axis, the polarization of the dark exciton switches from perpendicular to parallel to the hexagonal c axis in large dots, in agreement with experiment. (ii) The ratio of the radiative lifetimes of mono- and biexcitons (X):(XX) is {approx}1:1 in large dots (R=19.2 {angstrom}). This ratio increases with decreasing nanocrystal size, approaching 2 in small dots (R=10.3 {angstrom}). (iii) The calculated ratio (X{sup +}):(X{sup -}) between positive and negative trion lifetimes is close to 2 for all dot sizes considered.

  7. Size and Temperature Dependence of Electron Transfer between CdSe Quantum Dots and a TiO 2 Nanobelt

    DOE PAGESBeta

    Tafen, De Nyago; Prezhdo, Oleg V.

    2015-02-24

    Understanding charge transfer reactions between quantum dots (QD) and metal oxides is fundamental for improving photocatalytic, photovoltaic and electronic devices. The complexity of these processes makes it difficult to find an optimum QD size with rapid charge injection and low recombination. We combine time-domain density functional theory with nonadiabatic molecular dynamics to investigate the size and temperature dependence of the experimentally studied electron transfer and charge recombination at CdSe QD-TiO2 nanobelt (NB) interfaces. The electron injection rate shows strong dependence on the QD size, increasing for small QDs. The rate exhibits Arrhenius temperature dependence, with the activation energy of themore » order of millielectronvolts. The charge recombination process occurs due to coupling of the electronic subsystem to vibrational modes of the TiO2 NB. Inelastic electron-phonon scattering happens on a picosecond time scale, with strong dependence on the QD size. Our simulations demonstrate that the electron-hole recombination rate decreases significantly as the QD size increases, in excellent agreement with experiments. The temperature dependence of the charge recombination rates can be successfully modeled within the framework of the Marcus theory through optimization of the electronic coupling and the reorganization energy. Our simulations indicate that by varying the QD size, one can modulate the photoinduced charge separation and charge recombination, fundamental aspects of the design principles for high efficiency devices.« less

  8. Electron relaxation in the CdSe quantum dot--ZnO composite: prospects for photovoltaic applications.

    PubMed

    Zídek, Karel; Abdellah, Mohamed; Zheng, Kaibo; Pullerits, Tõnu

    2014-01-01

    Quantum dot (QD)-metal oxide composite forms a "heart" of the QD-sensitized solar cells. It maintains light absorption and electron-hole separation in the system and has been therefore extensively studied. The interest is largely driven by a vision of harvesting the hot carrier energy before it is lost via relaxation. Despite of importance of the process, very little is known about the carrier relaxation in the QD-metal oxide composites. In order to fill this gap of knowledge we carry out a systematic study of initial electron dynamics in different CdSe QD systems. Our data reveal that QD attachment to ZnO induces a speeding-up of transient absorption onset. Detailed analysis of the onset proves that the changes are caused by an additional relaxation channel dependent on the identity of the QD-ZnO linker molecule. The faster relaxation represents an important factor for hot carrier energy harvesting, whose efficiency can be influenced by almost 50%. PMID:25430684

  9. Conditions for Directional Charge Transfer in CdSe Quantum Dots Functionalized by Ru(II) Polypyridine Complexes.

    PubMed

    Kilina, Svetlana; Cui, Peng; Fischer, Sean A; Tretiak, Sergei

    2014-10-16

    Thermodynamic conditions governing the charge transfer direction in CdSe quantum dots (QD) functionalized by either Ru(II)-trisbipyridine or black dye are studied using density functional theory (DFT) and time-dependent DFT (TDDFT). Compared to the energy offsets of the isolated QD and the dye, QD-dye interactions strongly stabilize dye orbitals with respect to the QD states, while the surface chemistry of the QD has a minor effect on the energy offsets. In all considered QD/dye composites, the dyes always introduce unoccupied states close to the edge of the conduction band and control the electron transfer. Negatively charged ligands and less polar solvents significantly destabilize the dye's occupied orbitals shifting them toward the very edge of the valence band, thus, providing favorite conditions for the hole transfer. Overall, variations in the dye's ligands and solvent polarity can progressively adjust the electronic structure of QD/dye composites to modify conditions for the directed charge transfer. PMID:26278611

  10. All-Inorganic Colloidal Perovskite Quantum Dots: A New Class of Lasing Materials with Favorable Characteristics.

    PubMed

    Wang, Yue; Li, Xiaoming; Song, Jizhong; Xiao, Lian; Zeng, Haibo; Sun, Handong

    2015-11-25

    All-inorganic colloidal cesium lead halide perovskite quantum dots (CsPbX3 , X = Cl, Br, I) are revealed to be a new class of favorable optical-gain materials, which show -combined merits of both colloidal quantum dots and halide perovskites. Low-threshold and -ultrastable stimulated emission is -demonstrated under atmospheric conditions with wavelength tunability across the whole -visible spectrum via either size or composition control. PMID:26448638

  11. Nanoscale connectivity in a TiO2/CdSe quantum dots/functionalized graphene oxide nanosheets/Au nanoparticles composite for enhanced photoelectrochemical solar cell performance.

    PubMed

    Narayanan, Remya; Deepa, Melepurath; Srivastava, Avanish Kumar

    2012-01-14

    Electron transfer dynamics in a photoactive coating made of CdSe quantum dots (QDs) and Au nanoparticles (NPs) tethered to a framework of ionic liquid functionalized graphene oxide (FGO) nanosheets and mesoporous titania (TiO(2)) was studied. High resolution transmission electron microscopy analyses on TiO(2)/CdSe/FGO/Au not only revealed the linker mediated binding of CdSe QDs with TiO(2) but also, surprisingly, revealed a nanoscale connectivity between CdSe QDs, Au NPs and TiO(2) with FGO nanosheets, achieved by a simple solution processing method. Time resolved fluorescence decay experiments coupled with the systematic quenching of CdSe emission by Au NPs or FGO nanosheets or by a combination of the latter two provide concrete evidences favoring the most likely pathway of ultrafast decay of excited CdSe in the composite to be a relay mechanism. A balance between energetics and kinetics of the system is realized by alignment of conduction band edges, whereby, CdSe QDs inject photogenerated electrons into the conduction band of TiO(2), from where, electrons are promptly transferred to FGO nanosheets and then through Au NPs to the current collector. Conductive-atomic force microscopy also provided a direct correlation between the local nanostructure and the enhanced ability of composite to conduct electrons. Point contact I-V measurements and average photoconductivity results demonstrated the current distribution as well as the population of conducting domains to be uniform across the TiO(2)/CdSe/FGO/Au composite, thus validating the higher photocurrent generation. A six-fold enhancement in photocurrent and a 100 mV increment in photovoltage combined with an incident photon to current conversion efficiency of 27%, achieved in the composite, compared to the inferior performance of the TiO(2)/CdSe/Au composite imply that FGO nanosheets and Au NPs work in tandem to promote charge separation and furnish less impeded pathways for electron transfer and transport. Such a

  12. Nanoscale patterning of colloidal quantum dots on transparent and metallic planar surfaces.

    PubMed

    Park, Yeonsang; Roh, Young-Geun; Kim, Un Jeong; Chung, Dae-Young; Suh, Hwansoo; Kim, Jineun; Cheon, Sangmo; Lee, Jaesoong; Kim, Tae-Ho; Cho, Kyung-Sang; Lee, Chang-Won

    2012-09-01

    The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing and microcontact printing of quantum dots have been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10 nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum. PMID:22895055

  13. Anodic Electrogenerated Chemiluminescence of Ru(bpy)32+ with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA

    NASA Astrophysics Data System (ADS)

    Dong, Yong-Ping; Gao, Ting-Ting; Zhou, Ying; Jiang, Li-Ping; Zhu, Jun-Jie

    2015-10-01

    In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)32+ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)32+. Ru(bpy)32+ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)32+ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)32+, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

  14. Nondestructive chemical functionalization of MWNTs by poly(2-dimethylaminoethyl methacrylate) and their conjugation with CdSe quantum dots: Synthesis, properties, and cytotoxicity studies

    NASA Astrophysics Data System (ADS)

    Islam, Md. Rafiqul; Bach, Long Giang; Vo, Thanh-Sang; Tran, Thi-Nga; Lim, Kwon Taek

    2013-12-01

    Multi-walled carbon nanotubes (MWNTs) were functionalized with poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) in a nondestructive manner by UV-driven surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization. The RAFT agent having benzophenone groups was initially synthesized, and anchored to MWNTs through UV-triggered photoreaction. The subsequent RAFT polymerization of DMAEMA from the surface of MWNTs afforded PDMAEMA grafted MWNTs (MWNTs-g-PDMAEMA). The successful grafting of PDMAEMA on MWNTs via chemical linkage was confirmed by FT-IR, 1H NMR, XPS, EDX, TGA, TEM, and SEM analyses. A reversible dispersion phenomenon was observed in an aqueous solution of MWNTs-g-PDMAEMA as induced either by temperature or pH. The CdSe quantum dots (CdSe QDs) were attached to quaternized MWNTs-g-PDMAEMA to produce MWNTs-g-PDMAEMA-MeI/CdSe nanohybrids via electrostatic self-assembly. The formation of the nanohybrids was elucidated by EDS, TEM, and XRD. The cell viability assessment of the nanohybrids suggested their biocompatible character. The photoluminescence spectra of the nanohybrids indicated that the CdSe QDs significantly preserved its optical property after conjugation with MWNTs-g-PDMAEMA.

  15. Anodic Electrogenerated Chemiluminescence of Ru(bpy)32+ with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA

    PubMed Central

    Dong, Yong-Ping; Gao, Ting-Ting; Zhou, Ying; Jiang, Li-Ping; Zhu, Jun-Jie

    2015-01-01

    In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)32+ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)32+. Ru(bpy)32+ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)32+ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)32+, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit. PMID:26472243

  16. Understanding the electronic structure of CdSe quantum dot-fullerene (C{sub 60}) hybrid nanostructure for photovoltaic applications

    SciTech Connect

    Sarkar, Sunandan; Rajbanshi, Biplab; Sarkar, Pranab

    2014-09-21

    By using the density-functional tight binding method, we studied the electronic structure of CdSe quantum dot(QD)-buckminsterfullerene (C{sub 60}) hybrid systems as a function of both the size of the QD and concentration of the fullerene molecule. Our calculation reveals that the lowest unoccupied molecular orbital energy level of the hybrid CdSeQD-C{sub 60} systems lies on the fullerene moiety, whereas the highest occupied molecular orbital (HOMO) energy level lies either on the QD or the fullerene depending on size of the CdSe QD. We explored the possibility of engineering the energy level alignment by varying the size of the CdSe QD. With increase in size of the QD, the HOMO level is shifted upward and crosses the HOMO level of the C{sub 60}-thiol molecule resulting transition from the type-I to type-II band energy alignment. The density of states and charge density plot support these types of band gap engineering of the CdSe-C{sub 60} hybrid systems. This type II band alignment indicates the possibility of application of this nanohybrid for photovoltaic purpose.

  17. A CdSe thin film: a versatile buffer layer for improving the performance of TiO2 nanorod array:PbS quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Tan, Furui; Wang, Zhijie; Qu, Shengchun; Cao, Dawei; Liu, Kong; Jiang, Qiwei; Yang, Ying; Pang, Shan; Zhang, Weifeng; Lei, Yong; Wang, Zhanguo

    2016-05-01

    To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells.To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady

  18. CdSe magic-sized quantum dots incorporated in biomembrane models at the air-water interface composed of components of tumorigenic and non-tumorigenic cells.

    PubMed

    Goto, Thiago E; Lopes, Carla C; Nader, Helena B; Silva, Anielle C A; Dantas, Noelio O; Siqueira, José R; Caseli, Luciano

    2016-07-01

    Cadmium selenide (CdSe) magic-sized quantum dots (MSQDs) are semiconductor nanocrystals with stable luminescence that are feasible for biomedical applications, especially for in vivo and in vitro imaging of tumor cells. In this work, we investigated the specific interaction of CdSe MSQDs with tumorigenic and non-tumorigenic cells using Langmuir monolayers and Langmuir-Blodgett (LB) films of lipids as membrane models for diagnosis of cancerous cells. Surface pressure-area isotherms and polarization modulation reflection-absorption spectroscopy (PM-IRRAS) showed an intrinsic interaction between the quantum dots, inserted in the aqueous subphase, and Langmuir monolayers constituted either of selected lipids or of tumorigenic and non-tumorigenic cell extracts. The films were transferred to solid supports to obtain microscopic images, providing information on their morphology. Similarity between films with different compositions representing cell membranes, with or without the quantum dots, was evaluated by atomic force microscopy (AFM) and confocal microscopy. This study demonstrates that the affinity of quantum dots for models representing cancer cells permits the use of these systems as devices for cancer diagnosis. PMID:27107554

  19. Fast current blinking in individual PbS and CdSe quantum dots.

    PubMed

    Maturova, Klara; Nanayakkara, Sanjini U; Luther, Joseph M; van de Lagemaat, Jao

    2013-06-12

    Fast current intermittency of the tunneling current through single semiconductor quantum dots was observed through time-resolved intermittent contact conductive atomic force microscopy in the dark and under illumination at room temperature. The current through a single dot switches on and off at time scales ranging from microseconds to seconds with power-law distributions for both the on and off times. On states are attributed to the resonant tunneling of charges from the electrically conductive AFM tip to the quantum dot, followed by transfer to the substrate, whereas off states are attributed to a Coulomb blockade effect in the quantum dots that shifts the energy levels out of resonance conditions due to the presence of the trapped charge, while at the same bias. The observation of current intermittency due to Coulomb blockade effects has important implications for the understanding of carrier transport through arrays of quantum dots. PMID:23472703

  20. Green biosynthesis of biocompatible CdSe quantum dots in living Escherichia coli cells

    NASA Astrophysics Data System (ADS)

    Yan, Zhengyu; Qian, Jing; Gu, Yueqing; Su, Yilong; Ai, Xiaoxia; Wu, Shengmei

    2014-03-01

    A green and efficient biosynthesis method to prepare fluorescence-tunable biocompatible cadmium selenide quantum dots using Escherichia coli cells as biological matrix was proposed. Decisive factors in biosynthesis of cadmium selenide quantum dots in a designed route in Escherichia coli cells were elaborately investigated, including the influence of the biological matrix growth stage, the working concentration of inorganic reactants, and the co-incubation duration of inorganic metals to biomatrix. Ultraviolet-visible, photoluminescence, and inverted fluorescence microscope analysis confirmed the unique optical properties of the biosynthesized cadmium selenide quantum dots. The size distribution of the nanocrystals extracted from cells and the location of nanocrystals foci in vivo were also detected seriously by transmission electron microscopy. A surface protein capping layer outside the nanocrystals was confirmed by Fourier transform infrared spectroscopy measurements, which were supposed to contribute to reducing cytotoxicity and maintain a high viability of cells when incubating with quantum dots at concentrations as high as 2 μM. Cell morphology observation indicated an effective labeling of living cells by the biosynthesized quantum dots after a 48 h co-incubation. The present work demonstrated an economical and environmentally friendly approach to fabricating highly fluorescent quantum dots which were expected to be an excellent fluorescent dye for broad bio-imaging and labeling.

  1. Synthesis of a CdSe-graphene hybrid composed of CdSe quantum dot arrays directly grown on CVD-graphene and its ultrafast carrier dynamics.

    PubMed

    Kim, Yong-Tae; Shin, Hee-Won; Ko, Young-Seon; Ahn, Tae Kyu; Kwon, Young-Uk

    2013-02-21

    We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices. PMID:23334263

  2. Enhanced performance of branched TiO{sub 2} nanorod based Mn-doped CdS and Mn-doped CdSe quantum dot-sensitized solar cell

    SciTech Connect

    Kim, Soo-Kyoung; Gopi, Chandu V. V. M.; Lee, Jae-Cheol; Kim, Hee-Je

    2015-04-28

    TiO{sub 2} branched nanostructures could be efficient as photoanodes for quantum dot-sensitized solar cells (QDSCs) due to their large surface area for QD deposition. In this study, Mn-doped CdS/Mn-doped CdSe deposited branched TiO{sub 2} nanorods were fabricated to enhance the photovoltaic performance of QDSCs. Mn doping in CdS and CdSe retards the recombination losses of electrons, while branched TiO{sub 2} nanorods facilitate effective electron transport and compensate for the low surface area of the nanorod structure. As a result, the charge-transfer resistance (R{sub CT}), electron lifetime (τ{sub e}), and the amount of QD deposition were significantly improved with branched TiO{sub 2} nanorod based Mn-doped CdS/Mn-doped CdSe quantum dot-sensitized solar cell.

  3. Enhancement of multiphoton emission from single CdSe quantum dots coupled to gold films.

    PubMed

    LeBlanc, Sharonda J; McClanahan, Mason R; Jones, Marcus; Moyer, Patrick J

    2013-04-10

    Single molecule time-resolved fluorescence spectroscopy of CdSe/ZnS core-shell quantum dots (QDs) localized near a rough gold thin film demonstrates significant enhancement of multiphoton emission while at the same time showing a decrease in single photon emission. A rigorous analysis of time-resolved photon correlation spectroscopy and fluorescence lifetime data on single quantum dots at room temperature reveals an increase in radiative recombination rate of multiexcitons that is much higher than expected and, perhaps more significantly, is not correlated with concomitant increases in single exciton recombination rates. We believe that these results confirm a stronger coupling of multiexcitons to plasmon modes via a coupling to plasmon multipole modes. PMID:23510412

  4. XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

    2013-04-01

    The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

  5. Photo- and electroluminescence from semiconductor colloidal quantum dots in organic matrices: QD-OLED

    SciTech Connect

    Vitukhnovskii, A. G. Vaschenko, A. A.; Bychkovskii, D. N.; Dirin, D. N.; Tananaev, P. N.; Vakshtein, M. S.; Korzhonov, D. A.

    2013-12-15

    The results are reported of an experimental study of samples of organic light-emitting diodes (OLEDs) with luminescent layers fabricated on the basis of two types of CdSe/CdS/ZnS semiconductor quantum dots (QDs) with average CdSe core diameters of 3.2 and 4.1 nm and the same overall diameters of 6.5 nm. The dependences of the LED efficiency on the applied voltage are determined. Assumptions are made about ways of optimizing the design of high-efficiency LEDs.

  6. Molecularly imprinted optosensing material based on hydrophobic CdSe quantum dots via a reverse microemulsion for specific recognition of ractopamine.

    PubMed

    Liu, Huilin; Fang, Guozhen; Wang, Shuo

    2014-05-15

    A novel molecularly imprinted polymer (MIP) based on hydrophobic CdSe quantum dots (QDs) was synthesized using a one-pot room-temperature reverse microemulsion polymerization, and this polymer was applied as a molecular recognition element to construct a ractopamine (RAC) optosensor. Here, hydrophobic CdSe QDs were first introduced to the hydrophilic analyte-imprinted polymer for highly selective and sensitive detection of RAC via the change in fluorescence intensity, because of the high-quality hydrophobic QDs with high quantum yield, sharp photoluminescence spectra and chemical and fluorescent stability. Under optimal conditions, the relative fluorescence intensity of MIP based on hydrophobic QDs decreased linearly with the increasing concentration of RAC in the range of 1.21 × 10(-9) -3.03 × 10(-6)mol L(-1) with a detection limit of 7.57 × 10(-10)mol L(-1), and the precision for five replicate detections of 1.51 × 10(-8)mol L(-1) RAC was 2.09% (relative standard deviation). The proposed method was successfully applied for the determination of trace RAC in pork samples, with good recoveries ranging from 82.79% to 97.23%. PMID:24370883

  7. Extracellular bio-production and characterization of small monodispersed CdSe quantum dot nanocrystallites.

    PubMed

    Suresh, Anil K

    2014-09-15

    Engineered nanoparticles of diverse forms are being profoundly used for various applications and demand ecologically benign synthesis processes. Conventional chemical methods employed for the syntheses of nanoparticles are environmentally unfriendly and energy intensive. Biologically inspired biofabrication approaches that utilize naturally existing microorganisms or plant extracts or biomaterials might overcome these issues. The present investigation for the first time shows the synthesis of small and monodispersed cadmium selenide nanoparticles utilizing the plant pathogenic fungus, Helminthosporum solani upon incubating with an aqueous solution of CdCl2 and SeCl4 under ambient conditions. Multiple physical characterizations involving ultraviolet-visible and photoluminescence spectroscopy, transmission electron microscopy, selected area electron diffraction and X-ray photoelectron spectroscopy confirmed the production, purity, optical and surface characteristics, crystalline nature, size and shape distributions, and elemental composition of the nanoparticles. Pluralities of the particles are monodisperse spheres with a mean diameter of 5.5±2 nm, are hydrophilic, highly stable with a broad photoluminescence and 1% quantum yield. This approach provides an alternative facile route for the biofabrication of quantum dot that is reliable, environmentally friendly, and lends itself directly for the creation of fluorescent biological labels. PMID:24802719

  8. Extracellular bio-production and characterization of small monodispersed CdSe quantum dot nanocrystallites

    NASA Astrophysics Data System (ADS)

    Suresh, Anil K.

    2014-09-01

    Engineered nanoparticles of diverse forms are being profoundly used for various applications and demand ecologically benign synthesis processes. Conventional chemical methods employed for the syntheses of nanoparticles are environmentally unfriendly and energy intensive. Biologically inspired biofabrication approaches that utilize naturally existing microorganisms or plant extracts or biomaterials might overcome these issues. The present investigation for the first time shows the synthesis of small and monodispersed cadmium selenide nanoparticles utilizing the plant pathogenic fungus, Helminthosporum solani upon incubating with an aqueous solution of CdCl2 and SeCl4 under ambient conditions. Multiple physical characterizations involving ultraviolet-visible and photoluminescence spectroscopy, transmission electron microscopy, selected area electron diffraction and X-ray photoelectron spectroscopy confirmed the production, purity, optical and surface characteristics, crystalline nature, size and shape distributions, and elemental composition of the nanoparticles. Pluralities of the particles are monodisperse spheres with a mean diameter of 5.5 ± 2 nm, are hydrophilic, highly stable with a broad photoluminescence and 1% quantum yield. This approach provides an alternative facile route for the biofabrication of quantum dot that is reliable, environmentally friendly, and lends itself directly for the creation of fluorescent biological labels.

  9. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films

    NASA Astrophysics Data System (ADS)

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R.; Voznyy, Oleksandr; Kwon, S. Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H.

    2015-07-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector.

  10. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films.

    PubMed

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R; Voznyy, Oleksandr; Kwon, S Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H

    2015-01-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector. PMID:26165185

  11. Red shift in the photoluminescence of colloidal carbon quantum dots induced by photon reabsorption

    NASA Astrophysics Data System (ADS)

    Zhang, Wenxia; Fan, Jiyang; Department of Physics, Southeast University, Nanjing 211189, People's Republic of China Team

    We synthesize the colloidal carbon/graphene quantum dots 1-9 nm in diameter through a novel alkaline-assisted method and deeply studied their photoluminescence properties. Surprisingly, the luminescence properties of a fixed collection of carbon dots can be systematically changed as the concentration varies. A model based on photon reabsorption is proposed which explains well the experiment. Infrared spectral study indicates that the surfaces of the carbon dots are totally terminated by three bonding-types of oxygen atoms, which result in their ultra-high hydrophilicity. Our result clarifies the mystery of distinct emission colors in carbon dots and indicates that photon reabsorption can strongly affect the luminescence properties of colloidal nanocrystals.This mechanism can be generalized to help understand the complex luminescence properties of other colloidal quantum dots. and should be seriously considered,otherwise, distinct conclusions may be drawn if different concentrations of quantum dots have been utilized in studying their luminescence properies.

  12. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films

    PubMed Central

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R.; Voznyy, Oleksandr; Kwon, S. Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H.

    2015-01-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles—yet size–effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector. PMID:26165185

  13. Fluorescence modulation in single CdSe quantum dots by moderate applied electric fields

    SciTech Connect

    LeBlanc, Sharonda J.; McClanahan, Mason R.; Moyer, Tully; Moyer, Patrick J.; Jones, Marcus

    2014-01-21

    Single molecule time-resolved fluorescence spectroscopy of CdSe/ZnS core-shell quantum dots (QDs) under the influence of moderate applied electric fields reveals distributed emission from states which are neither fully on nor off and pronounced changes in the excited state decay. The data suggest that a 54 kV/cm applied electric field causes small perturbations to the QD surface charge distribution, effectively increasing the surface trapping probability and resulting in the appearance of gray states. We present simultaneous blinking and fluorescence decay results for two sets of QDs, with and without an applied electric field. Further kinetic modeling analysis suggests that a single trapped charged cannot be responsible for a blinking off event.

  14. Study of optical and structural properties of CdSe quantum dot embedded in PVA polymer matrix

    SciTech Connect

    Tyagi, Chetna Sharma, Ambika

    2015-08-28

    To enhance the properties and applicability of devices it is essential to incorporate semiconductor nanoparticles into polymer matrix. This introduces a new branch of science which includes device fabrications such as gas sensors, nonlinear optics, catalysis etc. Herein, we have synthesized CdSe/PVA nanocomposite (NC) material using wet chemical synthesis technique. The XRD studies revealed the formation of crystalline structure of CdSe nanoparticles (NP’s) and PVA NC’s with an average size of 100 nm and 5 nm respectively. Energy band gap is determined using UV-VIS Spectroscopy. A red shift in the absorption edge of CdSe/PVA NC is observed with respect to CdSe Np’s, The photoluminescence spectra also show red shift for CdSe/PVA NC as compared to CdSe NP’s Thus the use of CdSe/PVA for solar cell application would be more preferable than CdSe NP’s.

  15. Self assembly and optical properties of CdSe nanoplatelet superlattice

    NASA Astrophysics Data System (ADS)

    Gao, Yunan; Tisdale, William; Tisdale Lab MIT Team

    Colloidal CdSe nanoplatelets (NPs) are 1-D confined materials with atomic uniform thickness, and only have homogeneous broadening in energy level distributions and very narrow emission spectrum. Additionally, NPs have a giant oscillator strength that leads to a faster emission rate compared to quantum dots and rods. Due to these properties, NPs have shown promising potential applications in light-emitting diodes, colloidal lasers, and harvesting multiple exciton generation in photovoltaic cells.Self-assembly of superlattice has been studied broadly for many nano-particles, but not yet for CdSe NPs. We will show for the first time a selective control of CdSe NP superlattice self-assembly, i.e., self-assembled into columnar or lamellar superlattice. Moreover, we will present that the assembly morphology of superlattice has direct effects on their optical properties, like polarization, absorption efficiency and emission rate, etc., and also on their Forster energy transfer properties. The self-assembly is based on liquid interfacial self-assembly and transfer technique. The structure and propertied of the superlattice are characterized by transmission electron microscopy, and time-, polarization- and space-resolved photo-luminescent micro-spectroscopy.

  16. Role of ZnS shell on stability, cytotoxicity, and photocytotoxicity of water-soluble CdSe semiconductor quantum dots surface modified with glutathione

    NASA Astrophysics Data System (ADS)

    Ibrahim, Salwa Ali; Ahmed, Wafaa; Youssef, Tareq

    2014-09-01

    Biomedical applications of quantum dots (QDs) have become a subject of a considerable concern in the past few decades. The present study examines the stability and cytotoxicity of two QDs systems in cell culture medium in the presence and absence of a thin layer of ZnS shell. The two systems were built from core, CdSe QDs, surface modified with glutathione (GSH), named CdSe˜GSH and CdSe/ZnS˜GSH. Our results demonstrated that 0.7 nm layer of ZnS shell played a significant role in the stability of CdSe/ZnS~GSH QDs in supplemented cell culture medium (RPMI). Also, a significant improvement in the physicochemical properties of the core CdSe QDs was shown by maintaining their spectroscopic characteristics in RPMI medium due to the wide band gap of ZnS shell. Both systems showed insignificant reduction in cell viability of HFB-4 or MCF-7 cell lines in the dark which was attributed to the effective GSH coating. Following photoirradiation with low laser power (irradiance 10 mW cm-2), CdSe~GSH QDs showed a significant decrease in cell viability after 60 min irradiation which may result from detachment of GSH molecules. Under the same irradiation condition, CdSe/ZnS~GSH QDs showed insignificant decrease in cell viability or after 2 h incubation from laser irradiation which was attributed to the strong binding between ZnS and GSH coatings. It can be concluded that the stability of CdSe core QDs was significantly improved in cell culture medium by encapsulation with a thin layer of ZnS shell whereas their cytotoxicity and photo-cytotoxicity are highly dependent on surface modification.

  17. Comparison of Toxicity of CdSe: ZnS Quantum Dots on Male Reproductive System in Different Stages of Development in Mice

    PubMed Central

    Amiri, Gholamreza; Valipoor, Akram; Parivar, Kazem; Modaresi, Mehrdad; Noori, Ali; Gharamaleki, Hamideh; Taheri, Jafar; Kazemi, Ali

    2016-01-01

    Background Quantum dots (QDs) are new types of fluorescent materials for biological labeling. QDs toxicity study is an essential requirement for future clinical applications. Therefore, this study aimed to evaluate cytotoxic effects of CdSe: ZnS QDs on male reproductive system. Materials and Methods In this experimental study, the different concentrations of CdSe: ZnS QDs (10, 20 and 40 mg/kg) were injected to 32 male mice (adult group) and 24 pregnant mice (embryo group) on day 8 of gestation. The histological changes of testis and epididymis were studied by a light microscopy, and the number of seminiferous tubules between two groups was compared. One-way analysis of variance (one-way Anova) using the Statistical Package for the Social Sciences (SPSS, SPSS Inc., USA) version 16 were performed for statistical analysis. Results In adult group, histological studies of testis tissues showed a high toxicity of CdSe: ZnS in 40 mg/kg dose followed by a decrease in lamina propria; destruction in interstitial tissue; deformation of seminiferous tubules; and a reduction in number of spermatogonia, spermatocytes, and spermatids. However, there was an interesting result in fetal testis development, meaning there was no significant effect on morphology and structure of the seminiferous tubules and number of sperm stem cells. Also histological study of epididymis tissues in both groups (adult and embryo groups) showed no significant effect on morphology and structure of tubule and epithelial cells, but there was a considerable reduction in number of spermatozoa in the lumen of the epididymal duct in 40 mg/kg dose of adult group. Conclusion The toxicity of QDs on testicular tissue of the mice embryo and adult are different before and after puberty. Due to lack of research in this field, this study can be an introduction to evaluate the toxicity of QDs on male reproduction system in different stages of development. PMID:26985339

  18. Interband optical transition energy and oscillator strength in a lead based CdSe quantum dot quantum well heterostructure

    SciTech Connect

    Saravanamoorthy, S. N.; Peter, A. John

    2015-06-24

    Binding energies of the exciton and the interband optical transition energies are studied in a CdSe/Pb{sub 1-x}Cd{sub x}Se/CdSe spherical quantum dot-quantum well nanostructure taking into account the geometrical confinement effect. The core and shell are taken as the same material. The initial and final states of energy and the overlap integrals of electron and hole wave functions are determined by the oscillator strength. The oscillator strength and the radiative transition life time with the dot radius are investigated for various Cd alloy content in the core and shell materials.

  19. Quantum funneling in blended multi-band gap core/shell colloidal quantum dot solar cells

    SciTech Connect

    Neo, Darren C. J.; Assender, Hazel E.; Watt, Andrew A. R.; Stranks, Samuel D.; Eperon, Giles E.; Snaith, Henry J.

    2015-09-07

    Multi-band gap heterojunction solar cells fabricated from a blend of 1.2 eV and 1.4 eV PbS colloidal quantum dots (CQDs) show poor device performance due to non-radiative recombination. To overcome this, a CdS shell is epitaxially formed around the PbS core using cation exchange. From steady state and transient photoluminescence measurements, we understand the nature of charge transfer between these quantum dots. Photoluminescence decay lifetimes are much longer in the PbS/CdS core/shell blend compared to PbS only, explained by a reduction in non-radiative recombination resulting from CdS surface passivation. PbS/CdS heterojunction devices sustain a higher open-circuit voltage and lower reverse saturation current as compared to PbS-only devices, implying lower recombination rates. Further device performance enhancement is attained by modifying the composition profile of the CQD species in the absorbing layer resulting in a three dimensional quantum cascade structure.

  20. Performances of some low-cost counter electrode materials in CdS and CdSe quantum dot-sensitized solar cells

    PubMed Central

    2014-01-01

    Different counter electrode (CE) materials based on carbon and Cu2S were prepared for the application in CdS and CdSe quantum dot-sensitized solar cells (QDSSCs). The CEs were prepared using low-cost and facile methods. Platinum was used as the reference CE material to compare the performances of the other materials. While carbon-based materials produced the best solar cell performance in CdS QDSSCs, platinum and Cu2S were superior in CdSe QDSSCs. Different CE materials have different performance in the two types of QDSSCs employed due to the different type of sensitizers and composition of polysulfide electrolytes used. The poor performance of QDSSCs with some CE materials is largely due to the lower photocurrent density and open-circuit voltage. The electrochemical impedance spectroscopy performed on the cells showed that the poor-performing QDSSCs had higher charge-transfer resistances and CPE values at their CE/electrolyte interfaces. PMID:24512605

  1. The Dynamic Organic/Inorganic Interface of Colloidal PbS Quantum Dots.

    PubMed

    Grisorio, Roberto; Debellis, Doriana; Suranna, Gian Paolo; Gigli, Giuseppe; Giansante, Carlo

    2016-06-01

    Colloidal quantum dots are composed of nanometer-sized crystallites of inorganic semiconductor materials bearing organic molecules at their surface. The organic/inorganic interface markedly affects forms and functions of the quantum dots, therefore its description and control are important for effective application. Herein we demonstrate that archetypal colloidal PbS quantum dots adapt their interface to the surroundings, thus existing in solution phase as equilibrium mixtures with their (metal-)organic ligand and inorganic core components. The interfacial equilibria are dictated by solvent polarity and concentration, show striking size dependence (leading to more stable ligand/core adducts for larger quantum dots), and selectively involve nanocrystal facets. This notion of ligand/core dynamic equilibrium may open novel synthetic paths and refined nanocrystal surface-chemistry strategies. PMID:27038221

  2. A CdSe thin film: a versatile buffer layer for improving the performance of TiO2 nanorod array:PbS quantum dot solar cells.

    PubMed

    Tan, Furui; Wang, Zhijie; Qu, Shengchun; Cao, Dawei; Liu, Kong; Jiang, Qiwei; Yang, Ying; Pang, Shan; Zhang, Weifeng; Lei, Yong; Wang, Zhanguo

    2016-05-21

    To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells. PMID:27124650

  3. Background limited mid-infrared photodetection with photovoltaic HgTe colloidal quantum dots

    SciTech Connect

    Guyot-Sionnest, Philippe Roberts, John Andris

    2015-12-21

    The photovoltaic response of thin films of HgTe colloidal quantum dots in the 3–5 μm range is observed. With no applied bias, internal quantum efficiency exceeding 40%, specific detectivity above 10{sup 10} Jones and microseconds response times are obtained at 140 K. The cooled devices detect the ambient thermal radiation. A detector with 5.25 μm cut-off achieves Background Limited Infrared Photodetection at 90 K.

  4. On the crystal structure of colloidally prepared CsPbBr3 quantum dots.

    PubMed

    Cottingham, Patrick; Brutchey, Richard L

    2016-04-18

    Colloidally synthesized quantum dots of CsPbBr3 are highly promising for light-emitting applications. Previous reports based on benchtop diffraction conflict as to the crystal structure of CsPbBr3 quantum dots. We present X-ray diffraction and PDF analysis of X-ray total scattering data that indicate that the crystal structure is unequivocally orthorhombic (Pnma). PMID:26975247

  5. Red, green, and blue lasing enabled by single-exciton gain in colloidal quantum dot films

    DOEpatents

    Nurmikko, Arto V.; Dang, Cuong

    2016-06-21

    The methods and materials described herein contemplate the use films of colloidal quantum dots as a gain medium in a vertical-cavity surface-emitting laser. The present disclosure demonstrates a laser with single-exciton gain in the red, green, and blue wavelengths. Leveraging this nanocomposite gain, the results realize a significant step toward full-color single-material lasers.

  6. Investigations into photo-excited state dynamics in colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Singh, Gaurav

    Colloidal Quantum dots (QDs) have garnered considerable scientific and technological interest as a promising material for next generation solar cells, photo-detectors, lasers, bright light-emitting diodes (LEDs), and reliable biomarkers. However, for practical realization of these applications, it is crucial to understand the complex photo-physics of QDs that are very sensitive to surface chemistry and chemical surroundings. Depending on the excitation density, QDs can support single or multiple excitations. The first part of this talk addresses evolution of QD excited state dynamics in the regime of low excitation intensity. We use temperature-resolved time-resolved fluorescence spectroscopy to study exciton dynamics from picoseconds to microseconds and use kinetic modeling based on classical electron transfer to show the effect of surface trap states on dynamics of ground-state exciton manifold in core-shell CdSe/CdS QDs. We show that the thickness of CdS shell plays an important role in interaction of CdSe core exciton states with nanocrystal environment, and find that a thicker shell can minimize the mixing of QD exciton states with surface trap states. I will then present an investigation into the dynamics of multiply-excited states in QDs. One of the key challenges in QD spectroscopy is to reliably distinguish multi- from single-excited states that have similar lifetime components and spectroscopic signatures. I will describe the development of a novel multi-pulse fluorescence technique to selectively probe multi-excited states in ensemble QD samples and determine the nature of the multi-excited state contributing to the total fluorescence even in the limit of low fluorescent yields. We find that in our sample of CdSe/CdS core/shell QDs the multi-excited emission is dominated by emissive trion states rather than biexcitons. Next, I will discuss the application of this technique to probe exciton-plasmon coupling in layered hybrid films of QD/gold nanoparticles

  7. Assessing potential harmful effects of CdSe quantum dots by using Drosophila melanogaster as in vivo model.

    PubMed

    Alaraby, Mohamed; Demir, Esref; Hernández, Alba; Marcos, Ricard

    2015-10-15

    Since CdSe QDs are increasingly used in medical and pharmaceutical sciences careful and systematic studies to determine their biosafety are needed. Since in vivo studies produce relevant information complementing in vitro data, we promote the use of Drosophila melanogaster as a suitable in vivo model to detect toxic and genotoxic effects associated with CdSe QD exposure. Taking into account the potential release of cadmium ions, QD effects were compared with those obtained with CdCl2. Results showed that CdSe QDs penetrate the intestinal barrier of the larvae reaching the hemolymph, interacting with hemocytes, and inducing dose/time dependent significant genotoxic effects, as determined by the comet assay. Elevated ROS production, QD biodegradation, and significant disturbance in the conserved Hsps, antioxidant and p53 genes were also observed. Overall, QD effects were milder than those induced by CdCl2 suggesting the role of Cd released ions in the observed harmful effects of Cd based QDs. To reduce the observed side-effects of Cd based QDs biocompatible coats would be required to avoid cadmium's undesirable effects. PMID:26026410

  8. Electronic Properties and Structure of Assemblies of CdSe Nanocrystal Quantum Dots and Ru-Polypyridine Complexes Probed by Steady State and Time-Resolved Photoluminescence

    SciTech Connect

    Koposov, Alexey Y.; Szymanski, Paul; Cardolaccia, Thomas; Meyer, Thomas J.; Klimov, Victor I.; Sykora, Milan

    2011-06-20

    Chemical and electronic interactions between CdSe nanocrystal quantum dots (NQDs) and Ru-polypyridine complexes are studied in solution. It is shown that photoluminescence (PL) can be used to effectively monitor the formation of NQD-complex assemblies in real time. It is also shown that with the aid of Langmuir isotherm modeling, the PL studies can be used to quantitatively characterize the composition of the assemblies and the strength of electronic interactions between their components. The approach demonstrated here is general and can be applied to other systems that combine semiconductor NQDs and appropriately functionalized organometallic or organic molecules interacting with NQDs via energy transfer, charge transfer, or other mechanisms leading to quenching of NQD emission.

  9. Electrical and thermal properties of a carbon nanotube/polycrystalline BiFeO3/Pt photovoltaic heterojunction with CdSe quantum dots sensitization.

    PubMed

    Zang, Yongyuan; Xie, Dan; Chen, Yu; Wu, Xiao; Ren, Tianling; Wei, Jinquan; Zhu, Hongwei; Plant, David

    2012-04-28

    Electrical and thermal properties of a carbon nanotube (CNT)/multiferroic BiFeO(3) (BFO)/Pt photovoltaic heterojunction are investigated for the first time. Enhanced photovoltaic properties (J(sc)≈ 2.1 μA cm(-2) and V(oc)≈ 0.47 V), as compared to the traditional polycrystalline BFO with indium tin oxide (ITO) as the top electrode, are observed due to the unique properties of CNT. An equivalent electrical and thermal model is constructed based on the energy band diagram of the CNT/BFO/Pt heterojunction for the first time and the carriers' transportation behavior is depicted theoretically. The influence of CdSe quantum dots (QDs) sensitization on the photovoltaic properties is presented, and a clear improvement of ~4 fold in photocurrent density is observed. PMID:22456599

  10. Electrical and thermal properties of a carbon nanotube/polycrystalline BiFeO3/Pt photovoltaic heterojunction with CdSe quantum dots sensitization

    NASA Astrophysics Data System (ADS)

    Zang, Yongyuan; Xie, Dan; Chen, Yu; Wu, Xiao; Ren, Tianling; Wei, Jinquan; Zhu, Hongwei; Plant, David

    2012-04-01

    Electrical and thermal properties of a carbon nanotube (CNT)/multiferroic BiFeO3 (BFO)/Pt photovoltaic heterojunction are investigated for the first time. Enhanced photovoltaic properties (Jsc ~ 2.1 μA cm-2 and Voc ~ 0.47 V), as compared to the traditional polycrystalline BFO with indium tin oxide (ITO) as the top electrode, are observed due to the unique properties of CNT. An equivalent electrical and thermal model is constructed based on the energy band diagram of the CNT/BFO/Pt heterojunction for the first time and the carriers' transportation behavior is depicted theoretically. The influence of CdSe quantum dots (QDs) sensitization on the photovoltaic properties is presented, and a clear improvement of ~4 fold in photocurrent density is observed.

  11. Synthesis of a CdSe-graphene hybrid composed of CdSe quantum dot arrays directly grown on CVD-graphene and its ultrafast carrier dynamics

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Tae; Shin, Hee-Won; Ko, Young-Seon; Ahn, Tae Kyu; Kwon, Young-Uk

    2013-01-01

    We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices.We report the original fabrication and performance of a photocurrent device that uses directly grown CdSe quantum dots (QDs) on a graphene basal plane. The direct junction between the QDs and graphene and the high quality of the graphene grown by chemical vapor deposition enables highly efficient electron transfer from the QDs to the graphene. Therefore, the hybrids show large photocurrent effects with a fast response time and shortened photoluminescence (PL) lifetime. The PL lifetime quenching can be explained as being due to the efficient electron transfer as evidenced by femtosecond transient absorption spectroscopy. These hybrids are expected to find applications in flexible electronics and optoelectronic devices. Electronic supplementary information (ESI) available: TEM data of MSTF, AFM data of T-QD-G samples, PL decay fitting results to the multiexponential decay equation, photoconductivity data of T-QD-2LG with two different illumination wavelengths, photocurrent efficiencies of QD-G hybrids prepared in various ways, photoconductivity and photoresponse data of T-QD-2LG and T-QD-3LG, and the bending stress on a PET film. See DOI: 10.1039/c2nr33294a

  12. CdSe quantum dot-functionalized TiO2 nanohybrids as a visible light induced photoelectrochemical platform for the detection of proprotein convertase subtilisin/kexin type 6.

    PubMed

    Pang, Xuehui; Pan, Jihong; Wang, Lin; Ren, Wei; Gao, Picheng; Wei, Qin; Du, Bin

    2015-09-15

    Proprotein convertase subtilisin/kexin type 6 (PCSK6) plays a major role in promoting the progression of rheumatoid arthritis to a higher aggressive status. A novel highly sensitive photoelectrochemical platform was developed for the detection of PCSK6 by using CdSe quantum dots (QDs)-functionalized TiO2 nanoparticles (NPs) nanohybrids (TiO2@CdSe) as the photo-to-electron conversion medium. TiO2@CdSe showed excellent visible-light absorbency, and much higher photoelectrochemical activity than both CdSe QDs and TiO2 NPs. The 5' and 3' primers of PCSK6 ssDNA acted as capture probes to realize the detection of PCSK6 ssDNA by the specific recognition. The capture probes can be fixed by poly-l-lysine (PLL) through positively strong electrostatic attraction and the carboxyl group of TiO2@CdSe nanohybrids. PLL was electropolymerized on ITO electrode by cyclic voltammetry (CV). Simultaneously, the amino group of PLL can interact with the carboxyl group of TiO2@CdSe nanohybrids to enhance the stability of the photoelectrochemical signal. The fabricated aptsensor exhibited excellent performance towards PCSK6 with a wide linear range (0.5 pg/mL to 80.0 ng/mL) and a detection limit of 0.1 fg/mL. This work opens up a new detection platform for PCSK6 with good sensitivity, reproducibility and stability. PMID:25889349

  13. Enhancement of Luminescence of Colloidal Ag2S Quantum Dots by Thionine Molecules

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, O. V.; Grevtseva, I. G.; Kondratenko, T. S.; Smirnov, M. S.; Evtukhova, A. V.

    2016-07-01

    Enhancement of IR luminescence (1205 nm) of colloidal Ag2S quantum dots (QDs) with an average size of 2.5 ± 0.3 nm was detected upon excitation in the absorption band of thionine dye molecules (530-610 nm). It is found that the observed effect occurs during a hybrid association of Ag2S QDs with monomers of the cationic thionine (Th + ) molecule. It is concluded that the photosensitization of IR luminescence of colloidal Ag2S QDs is realized due to a resonance nonradiative transfer of electronic excitation energy directly to the centers of radiative recombination from the excited Th + molecules.

  14. Fabrication and characterization of on-chip silicon nitride microdisk integrated with colloidal quantum dots.

    PubMed

    Xie, Weiqiang; Zhu, Yunpeng; Aubert, Tangi; Hens, Zeger; Brainis, Edouard; Van Thourhout, Dries

    2016-01-25

    We designed and fabricated free-standing, waveguide-coupled silicon nitride microdisks hybridly integrated with embedded colloidal quantum dots. An efficient coupling of quantum dot emission to resonant disk modes and eventually to the access waveguides is demonstrated. The amount of light coupled out to the access waveguide can be tuned by controlling its dimensions and offset with the disk edge. These devices open up new opportunities for both on-chip silicon nitride integrated photonics and novel optoelectronic devices with quantum dots. PMID:26832565

  15. Macrocrystals of Colloidal Quantum Dots in Anthracene: Exciton Transfer and Polarized Emission

    NASA Astrophysics Data System (ADS)

    Soran-Erdem, Zeliha; Erdem, Talha; Hernandez-Martinez, Pedro Ludwig; Akgul, Mehmet Zafer; Gaponik, Nikolai; Demir, Hilmi Volkan

    We systematically investigate the exciton energy transfer from anthracene host (donor) to quantum dots (acceptor) in a centimeter-scale macrocrystal of nonpolar colloidal quantum dots incorporated into anthracene. The decrease in photoluminescence lifetime of the donor anthracene indicate a strong energy transfer with increasing quantum dot concentration in the macrocrystals. In addition, anisotropic emission from the isotropic quantum dots in anthracene macrocrystals was observed. The quantum dots inside the anthracene host acquired a polarization ratio of ~1.5 at 0 degree collection angle, and this increases to ~2.5 at the collection angle of 60 degree. Finally, a proof-of-concept application of these excitonic macrocrystals as tunable color converters was employed in light-emitting diodes. Bilkent University.

  16. Modification of hybrid active bilayer for enhanced efficiency and stability in planar heterojunction colloidal quantum dot photovoltaics

    PubMed Central

    2013-01-01

    Solution-processed planar heterojunction colloidal quantum dot photovoltaics with a hybrid active bilayer is demonstrated. A power conversion efficiency of 1.24% under simulated air mass 1.5 illumination conditions is reported. This was achieved through solid-state treatment with cetyltrimethylammonium bromide of PbS colloidal quantum dot solid films. That treatment was used to passivate Br atomic ligands as well as to engineer the interface within the hybrid active bilayer. PMID:24252664

  17. Application of colloidal semiconductor quantum dots as fluorescent labels for diagnosis of brain glial cancer

    NASA Astrophysics Data System (ADS)

    Farias, Patrícia M. A.; Santos, Beate S.; Menezes, Frederico D.; Ferreira, Ricardo; Oliveira, Fernando J. M., Jr.; Carvalho, Hernandes F.; Romão, Luciana; Moura-Neto, Vivaldo; Amaral, Jane C. O. F.; Fontes, Adriana; Cesar, Carlos L.

    2006-02-01

    In this work we present the preparation, characterization and conjugation of colloidal core shell CdS-Cd(OH) II quantum dots to health and cancer glial rats living cells in culture media. The particles were obtained via colloidal synthesis in aqueous medium, with final pH=7.3-7.4. Laser Scan Confocal Microscopy (LSCM) and Fluorescence Microscopy were used to evaluate fluorescence intensities and patterns of health and cancer (glioblastoma) glial cells labeled with the quantum dots in different time intervals. Health and cancer glial cells clearly differ in their fluorescence intensities and patterns. These different fluorescence intensities and patterns may be associated to differences concerning cellular membrane and metabolic features of health and cancer cells. The results obtained indicate the potential of the methodology for fast and precise cancer diagnostics.

  18. Photoluminescence quantum yield of PbS nanocrystals in colloidal suspensions

    SciTech Connect

    Greben, M.; Fucikova, A.; Valenta, J.

    2015-04-14

    The absolute photoluminescence (PL) quantum yield (QY) of oleic acid-capped colloidal PbS quantum dots (QDs) in toluene is thoroughly investigated as function of QD size, concentration, excitation photon energy, and conditions of storage. We observed anomalous decrease of QY with decreasing concentration for highly diluted suspensions. The ligand desorption and QD-oxidation are demonstrated to be responsible for this phenomenon. Excess of oleic acid in suspensions makes the QY values concentration-independent over the entire reabsorption-free range. The PL emission is shown to be dominated by surface-related recombinations with some contribution from QD-core transitions. We demonstrate that QD colloidal suspension stability improves with increasing the concentration and size of PbS QDs.

  19. Detection of viral infections using colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Bentzen, Elizabeth L.; House, Frances S.; Utley, Thomas J.; Crowe, James E., Jr.; Wright, David W.

    2006-02-01

    Fluorescence is a tool widely employed in biological assays. Fluorescent semiconducting nanocrystals, quantum dots (QDs), are beginning to find their way into the tool box of many biologist, chemist and biochemist. These quantum dots are an attractive alternative to the traditional organic dyes due to their broad excitation spectra, narrow emission spectra and photostability. Quantum dots were used to detect and monitor the progession of viral glycoproteins, F (fusion) and G (attachment), from Respiratory Syncytial Virus (RSV) in HEp-2 cells. Additionally, oligo-Qdot RNA probes have been developed for identification and detection of mRNA of the N(nucleocapsid) protein for RSV. The use of quantum dot-FISH probes provides another confirmatory route to diagnostics as well as a new class of probes for monitoring the flux and fate of viral RNA RSV is the most common cause of lower respiratory tract infection in children worldwide and the most common cause of hospitalization of infants in the US. Antiviral therapy is available for treatment of RSV but is only effective if given within the first 48 hours of infection. Existing test methods require a virus level of at least 1000-fold of the amount needed for infection of most children and require several days to weeks to obtain results. The use of quantum dots may provide an early, rapid method for detection and provide insight into the trafficking of viral proteins during the course of infection.

  20. Physically flexible, rapid-response gas sensor based on colloidal quantum dot solids.

    PubMed

    Liu, Huan; Li, Min; Voznyy, Oleksandr; Hu, Long; Fu, Qiuyun; Zhou, Dongxiang; Xia, Zhe; Sargent, Edward H; Tang, Jiang

    2014-05-01

    A gas sensor based on PbS colloidal quantum dots (CQDs) is constructed on a paper substrate, yielding flexible, rapid-response NO₂ gas sensors, fabricated from the solution phase. The devices are highly sensitive and fully recoverable at room temperature, which is attributed to the excellent access of gas molecules to the CQD surface, realized by surface ligand removal, combined with the desirable binding energy of NO₂ with the PbS CQDs. PMID:24452852

  1. Infrared detection with colloidal quantum dots based on interband and intraband transitions

    NASA Astrophysics Data System (ADS)

    Guyot-Sionnest, Philippe

    2015-03-01

    While much research on colloidal quantum dots is focused on their potential as visible emitter or light harvester, this talk will cover our investigations of the mercury chalcogenide colloidal quantum dots in the thermal mid-infrared ranges of 3-5 microns and 8-12 microns where the atmosphere is transparent. HgTe is a zero-gap semiconductor. As a result, colloidal quantum dots (CQD) of sizes between 10 and 20 nm readily lead to infrared gaps tuning between 3 and 12 microns respectively. It is also very promising that infrared photodetection using dried films of these CQDs has now been demonstrated up to 12 microns. Further improvement through chemistry are likely and will be required to raise the detectivity to the level required to transform thermal infrared detection technology. In contrast to HgTe CQDs which tend to be intrinsic, beta-HgS and HgSe CQDs are naturally n-doped, in the first such instance with CQDs. Furthermore, the doping is modulated by modifying the surface composition, and this effect is attributed to the tuning of the energy level with respect to the environment, via the surface electrostatics. With controlled doping, both HgSe and HgS CQDs have now led to the first operation of mid-infrared CQD photodetector based on the intraband absorption. This is a breakthrough in the field of colloidal quantum dots where interband transitions had been exclusively used for the past 30 years. One challenge with both interband and intraband infrared CQDs will be to reduce the nonradiative recombination, which will improve the detectivity as well as allow to use their infrared luminescence.

  2. Double-Sided Junctions Enable High-Performance Colloidal-Quantum-Dot Photovoltaics.

    PubMed

    Liu, Mengxia; de Arquer, F Pelayo García; Li, Yiying; Lan, Xinzheng; Kim, Gi-Hwan; Voznyy, Oleksandr; Jagadamma, Lethy Krishnan; Abbas, Abdullah Saud; Hoogland, Sjoerd; Lu, Zhenghong; Kim, Jin Young; Amassian, Aram; Sargent, Edward H

    2016-06-01

    The latest advances in colloidal-quantum-dot material processing are combined with a double-sided junction architecture, which is done by efficiently incorporating indium ions in the ZnO eletrode. This platform allows the collection of all photogenerated carriers even at the maximum power point. The increased depletion width in the device facilitates full carrier collection, leading to a record 10.8% power conversion efficiency. PMID:27038256

  3. Water-dispersable colloidal quantum dots for the detection of ionizing radiation.

    PubMed

    Lecavalier, Marie-Eve; Goulet, Mathieu; Allen, Claudine Nì; Beaulieu, Luc; Larivière, Dominic

    2013-12-25

    Fluorescent CdSe-CdS-Cd0.5Zn0.5S-ZnS core-shell colloidal quantum dots (cQDs) dispersed in aqueous and organic solvents have been prepared and used as scintillators for detecting ionizing radiation. Results demonstrate a linear relationship between emitted luminescence and dose-activity. These results suggest that cQDs alone could be used as liquid scintillators for specific environmental and medical applications. PMID:24177415

  4. Spectroscopy of colloidal semiconductor core/shell nanoplatelets with high quantum yield.

    PubMed

    Tessier, M D; Mahler, B; Nadal, B; Heuclin, H; Pedetti, S; Dubertret, B

    2013-07-10

    Free standing two-dimensional materials appear as a novel class of structures. Recently, the first colloidal two-dimensional heterostructures have been synthesized. These core/shell nanoplatelets are the first step toward colloidal quantum wells. Here, we study in detail the spectroscopic properties of this novel generation of colloidal nanoparticles. We show that core/shell CdSe/CdZnS nanoplatelets with 80% quantum yield can be obtained. The emission time trace of single core/shell nanoplatelets exhibits reduced blinking compared to core nanoplatelets with a two level emission time trace. At cryogenic temperatures, these nanoplatelets have a quantum yield close to 100% and a stable emission time trace. A solution of core/shell nanoplatelets has emission spectra with a full width half-maximum close to 20 nm, a value much lower than corresponding spherical or rod-shaped heterostructures. Using single particle spectroscopy, we show that the broadening of the emission spectra upon the shell deposition is not due to dispersity between particles but is related to an intrinsic increased exciton-phonon coupling in the shell. We also demonstrate that optical spectroscopy is a relevant tool to investigate the presence of traps induced by shell deposition. The spectroscopic properties of the core/shell nanoplatelets presented here strongly suggest that this new generation of objects will be an interesting alternative to spherical or rod-shaped nanocrystals. PMID:23731211

  5. Study of optically trapped living Trypanosoma cruzi/Trypanosoma rangeli - Rhodnius prolixus interactions by real time confocal images using CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    de Thomaz, A. A.; Almeida, D. B.; Faustino, W. M.; Jacob, G. J.; Fontes, A.; Barbosa, L. C.; Cesar, C. L.; Stahl, C. V.; Santos-Mallet, J. R.; Gomes, S. A. O.; Feder, D.

    2008-08-01

    One of the fundamental goals in biology is to understand the interplay between biomolecules of different cells. This happen, for example, in the first moments of the infection of a vector by a parasite that results in the adherence to the cell walls. To observe this kind of event we used an integrated Optical Tweezers and Confocal Microscopy tool. This tool allow us to use the Optical Tweezers to trigger the adhesion of the Trypanosoma cruzi and Trypanosoma rangeli parasite to the intestine wall cells and salivary gland of the Rhodnius prolixus vector and to, subsequently observe the sequence of events by confocal fluorescence microscopy under optical forces stresses. We kept the microorganism and vector cells alive using CdSe quantum dot staining. Besides the fact that Quantum Dots are bright vital fluorescent markers, the absence of photobleaching allow us to follow the events in time for an extended period. By zooming to the region of interested we have been able to acquire confocal images at the 2 to 3 frames per second rate.

  6. Multi-photon microscopy based on resonant four-wave mixing of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Masia, F.; Langbein, W.; Borri, P.

    2009-02-01

    We demonstrate a novel multi-photon imaging modality based on the detection of four-wave mixing (FWM) from colloidal nanoparticles. Four-wave mixing is a third-order signal which can be excited and detected in resonance with the ground-state excitonic transition of CdSe/ZnS quantum dots. The coherent FWM signal is detected interferometrically to reject incoherent backgrounds for improved image contrast compared to fluorescence methods. We measure transversal and axial resolutions of 140nm and 590nm respectively, significantly beating the one-photon diffraction limit. We also demonstrate optical imaging of quantum-dot-labeled Golgi structures of HepG2 cells.

  7. Optimization schemes for efficient multiple exciton generation and extraction in colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Damtie, Fikeraddis A.; Karki, Khadga J.; Pullerits, Tõnu; Wacker, Andreas

    2016-08-01

    Multiple exciton generation (MEG) is a process in which more than one electron hole pair is generated per absorbed photon. It allows us to increase the efficiency of solar energy harvesting. Experimental studies have shown the multiple exciton generation yield of 1.2 in isolated colloidal quantum dots. However real photoelectric devices require the extraction of electron hole pairs to electric contacts. We provide a systematic study of the corresponding quantum coherent processes including extraction and injection and show that a proper design of extraction and injection rates enhances the yield significantly up to values around 1.6.

  8. Use of Surface Photovoltage Spectroscopy to Measure Built-in Voltage, Space Charge Layer Width, and Effective Band Gap in CdSe Quantum Dot Films.

    PubMed

    Zhao, Jing; Nail, Benjamin A; Holmes, Michael A; Osterloh, Frank E

    2016-09-01

    Surface photovoltage spectroscopy (SPS) was used to study the photochemistry of mercaptoethanol-ligated CdSe quantum dot (2.0-4.2 nm diameter) films on indium doped tin oxide (ITO) in the absence of an external bias or electrolyte. The n-type films generate negative voltages under super band gap illumination (0.1-0.5 mW cm(-2)) by majority carrier injection into the ITO substrate. The photovoltage onset energies track the optical band gaps of the samples and are assigned as effective band gaps of the films. The photovoltage values (-125 to -750 mV) vary with quantum dot sizes and are modulated by the built-in potential of the CdSe-ITO Schottky type contacts. Deviations from the ideal Schottky model are attributed to Fermi level pinning in states approximately 1.1 V negative of the ITO conduction band edge. Positive photovoltage signals of +80 to +125 mV in films of >4.0 nm nanocrystals and in thin (70 nm) nanocrystal films are attributed to electron-hole (polaron) pairs that are polarized by a space charge layer at the CdSe-ITO boundary. The space charge layer is 70-150 nm wide, based on thickness-dependent photovoltage measurements. The ability of SPS to directly measure built-in voltages, space charge layer thickness, sub-band gap states, and effective band gaps in drop-cast quantum dot films aids the understanding of photochemical charge transport in quantum dot solar cells. PMID:27505130

  9. A Highly Efficient Hybrid GaAs Solar Cell Based on Colloidal-Quantum-Dot-Sensitization

    PubMed Central

    Han, Hau-Vei; Lin, Chien-Chung; Tsai, Yu-Lin; Chen, Hsin-Chu; Chen, Kuo-Ju; Yeh, Yun-Ling; Lin, Wen-Yi; Kuo, Hao-Chung; Yu, Peichen

    2014-01-01

    This paper presents a hybrid design, featuring a traditional GaAs-based solar cell combined with various colloidal quantum dots. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. The merits of using highly efficient semiconductor solar cells and colloidal quantum dots were seamlessly combined to increase overall power conversion efficiency. Several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency, were measured and analyzed to investigate the performance of this hybrid device. Offering antireflective features at long wavelengths and luminescent downshifting for high-energy photons, the quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65% compared with traditional GaAs-based devices. The evolution of weighted reflectance as a function of the dilution factor of QDs was investigated. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6% of the entire enhancement of photogenerated current. PMID:25034623

  10. CdS quantum dots in colloids and polymer matrices: electronic structure and photochemical properties

    NASA Astrophysics Data System (ADS)

    Gurin, V. S.; Artemyev, M. V.

    1994-04-01

    We have studied the optical properties and electronic structures of quantum-confined CdS particles (Q-particles, quantum dots) prepared as CdS colloids in different solvents, CdS particles embedded in polymer matrices and vacuum evaporated island films of CdS. Due to the quantum-confined effect, the optical spectra of these systems exhibit the explicit blue shift of fundamental interband absorption and the appearance of well-pronounced exciton peaks at room temperature. The electronic structure of CdS quantum dots was examined by X-ray photoeletron spectroscopy and semi-empirical quantum-chemical calculations were performed. Both XRS data and results of calculations reveal the clear difference in valence band density of states for CdS Q-particles with respect to bulk CdS. Semiconductor-like electronic structure, especially for d-band, appears for CdS clusters containing more than 100 atoms. We also compare the relative stability of CdS clusters of different structure. Additionally, we studied the photochemical properties of CdS Q-particles and observed the effect of spectral hole burning in the absorption spectra of CdS colloids in 2-propanol during UV laser irradiation. This phenomenon results probably from selective photo-oxidation of CdS Q-particles, whose exciton absorption bands are close to irradiation wavelength.

  11. Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor

    PubMed Central

    Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos

    2016-01-01

    The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics. PMID:27311710

  12. Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor.

    PubMed

    Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H L; Konstantatos, Gerasimos

    2016-01-01

    The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 10(5) and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics. PMID:27311710

  13. Colloidal QDs-polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Gordillo, H.; Suárez, I.; Rodríguez-Cantó, P.; Abargues, R.; García-Calzada, R.; Chyrvony, V.; Albert, S.; Martínez-Pastor, J.

    2012-04-01

    Nanometer-size colloidal semiconductor nanocrystals, or Quantum Dots (NQD), are very prospective active centers because their light emission is highly efficient and temperature-independent. Nanocomposites based on the incorporation of QDs inside a polymer matrix are very promising materials for application in future photonic devices because they combine the properties of QDs with the technological feasibility of polymers. In the present work some basic applications of these new materials have been studied. Firstly, the fabrication of planar and linear waveguides based on the incorporation of CdS, CdSe and CdTe in PMMA and SU-8 are demonstrated. As a result, photoluminescence (PL) of the QDs are coupled to a waveguide mode, being it able to obtain multicolor waveguiding. Secondly, nanocomposite films have been evaluated as photon energy down-shifting converters to improve the efficiency of solar cells.

  14. The micropatterning of layers of colloidal quantum dots with inorganic ligands using selective wet etching.

    PubMed

    Hu, Chen; Aubert, Tangi; Justo, Yolanda; Flamee, Stijn; Cirillo, Marco; Gassenq, Alban; Drobchak, Oksana; Beunis, Filip; Roelkens, Günther; Hens, Zeger

    2014-05-01

    The micropatterning of layers of colloidal quantum dots (QDs) stabilized by inorganic ligands is demonstrated using PbS core and CdSe/CdS core/shell QDs. A layer-by-layer approach is used to assemble the QD films, where each cycle involves the deposition of a QD layer by dip-coating, and the replacement of the native organic ligands by inorganic moieties, such as OH(-) and S(2-), followed by a thorough cleaning of the resulting film. This results in a smooth and crack-free QD film on which a photoresist can be spun. The micropatterns are defined by a positive photoresist, followed by the removal of uncovered QDs by selective wet etching with an HCl/H3PO4 mixture. The resulting patterns can have submicron feature dimensions, limited by the resolution of the lithographic process, and can be formed on planar and 3D substrates. It is shown that the photolithography and wet etching steps have little effect on the photoluminescence quantum yield of CdSe/CdS QDs. Compared with the unpatterned CdSe/CdS QD film, only a 10% degradation in the quantum yield is observed. These results demonstrate the feasibility of the proposed micropatterning method to implement the large-scale device integration of colloidal quantum dots. PMID:24722007

  15. Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots.

    PubMed

    Swarnkar, Abhishek; Chulliyil, Ramya; Ravi, Vikash Kumar; Irfanullah, Mir; Chowdhury, Arindam; Nag, Angshuman

    2015-12-14

    Traditional CdSe-based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single-nanocrystal PL of colloidal CsPbBr3 nanocrystals (NCs) over the traditional cQDs. An ensemble of colloidal CsPbBr3 NCs (11 nm) exhibits ca. 90 % PL quantum yield with narrow (FWHM=86 meV) spectral width. Interestingly, the spectral width of a single-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Eliminating this problem leads to a negligible influence of self-absorption and Förster resonance energy transfer, along with batch-to-batch reproducibility of NCs exhibiting PL peaks within ±1 nm. Also, PL peak positions do not alter with measurement temperature in the range of 25 to 100 °C. Importantly, CsPbBr3 NCs exhibit suppressed PL blinking with ca. 90 % of the individual NCs remain mostly emissive (on-time >85 %), without much influence of excitation power. PMID:26546495

  16. Colloidal nanoplatelets with two-dimensional electronic structure.

    PubMed

    Ithurria, S; Tessier, M D; Mahler, B; Lobo, R P S M; Dubertret, B; Efros, Al L

    2011-12-01

    The syntheses of strongly anisotropic nanocrystals with one dimension much smaller than the two others, such as nanoplatelets, are still greatly underdeveloped. Here, we demonstrate the formation of atomically flat quasi-two-dimensional colloidal CdSe, CdS and CdTe nanoplatelets with well-defined thicknesses ranging from 4 to 11 monolayers. These nanoplatelets have the electronic properties of two-dimensional quantum wells formed by molecular beam epitaxy, and their thickness-dependent absorption and emission spectra are described very well within an eight-band Pidgeon-Brown model. They present an extremely narrow emission spectrum with full-width at half-maximum less than 40 meV at room temperature. The radiative fluorescent lifetime measured in CdSe nanoplatelets decreases with temperature, reaching 1 ns at 6 K, two orders of magnitude less than for spherical CdSe nanoparticles. This makes the nanoplatelets the fastest colloidal fluorescent emitters and strongly suggests that they show a giant oscillator strength transition. PMID:22019946

  17. Characterization of primary amine capped CdSe, ZnSe, and ZnS quantum dots by FT-IR: determination of surface bonding interaction and identification of selective desorption.

    PubMed

    Cooper, Jason K; Franco, Alexandra M; Gul, Sheraz; Corrado, Carley; Zhang, Jin Z

    2011-07-01

    Surface ligands of semiconductor quantum dots (QDs) critically influence their properties and functionalities. It is of strong interest to understand the structural characteristics of surface ligands and how they interact with the QDs. Three quantum dot (QD) systems (CdSe, ZnSe, and ZnS) with primary aliphatic amine capping ligands were characterized primarily by FT-IR spectroscopy as well as NMR, UV-vis, and fluorescence spectroscopy, and by transmission electron microscopy (TEM). Representative primary amines ranging from 8 to 16 carbons were examined in the vapor phase, KBr pellet, and neat and were compared to the QD samples. The strongest hydrogen-bonding effects of the adsorbed ligands were observed in CdSe QDs with the weakest observed in ZnS QDs. There was an observed splitting of the N-H scissoring mode from 1610 cm(-1) in the neat sample to 1544 and 1635 cm(-1) when bound to CdSe QDs, which had the largest splitting of this type. The splitting is attributed to amine ligands bound to either Cd or Se surface sites, respectively. The effect of exposure of the QDs dispersed in nonpolar medium to methanol as a crashing agent was also examined. In the CdSe system, the Cd-bound scissoring mode disappeared, possibly due to methanol replacing surface cadmium sites. The opposite was observed for ZnSe QDs, in which the Se-bound scissoring mode disappeared. It was concluded that surface coverage and ligand bonding partners could be characterized by FT-IR and that selective removal of surface ligands could be achieved through introduction of competitive binding interactions at the surface. PMID:21631120

  18. Amplified spontaneous emission and lasing in colloidal nanoplatelets.

    PubMed

    Guzelturk, Burak; Kelestemur, Yusuf; Olutas, Murat; Delikanli, Savas; Demir, Hilmi Volkan

    2014-07-22

    Colloidal nanoplatelets (NPLs) have recently emerged as favorable light-emitting materials, which also show great potential as optical gain media due to their remarkable optical properties. In this work, we systematically investigate the optical gain performance of CdSe core and CdSe/CdS core/crown NPLs having different CdS crown size with one- and two-photon absorption pumping. The core/crown NPLs exhibit enhanced gain performance as compared to the core-only NPLs due to increased absorption cross section and the efficient interexciton funneling, which is from the CdS crown to the CdSe core. One- and two-photon absorption pumped amplified spontaneous emission thresholds are found as low as 41 μJ/cm(2) and 4.48 mJ/cm(2), respectively. These thresholds surpass the best reported optical gain performance of the state-of-the-art colloidal nanocrystals (i.e., quantum dots, nanorods, etc.) emitting in the same spectral range as the NPLs. Moreover, gain coefficient of the NPLs is measured as high as 650 cm(-1), which is 4-fold larger than the best reported gain coefficient of the colloidal quantum dots. Finally, we demonstrate a two-photon absorption pumped vertical cavity surface emitting laser of the NPLs with a lasing threshold as low as 2.49 mJ/cm(2). These excellent results are attributed to the superior properties of the NPLs as optical gain media. PMID:24882737

  19. Optical power limiting in ensembles of colloidal Ag2S quantum dots

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, O. V.; Smirnov, M. S.; Perepelitsa, A. S.; Shatskikh, T. S.; Shapiro, B. I.

    2015-12-01

    The effect of power limiting for optical radiation at a wavelength of 660 nm with a pulse duration of 10 ms and operation threshold of 2.2 - 3.1 mJ cm-2 is observed in ensembles of colloidal Ag2S quantum dots (QDs). Using the z-scanning method in an open-aperture scheme it is found that the power is limited mainly due to reverse saturable absorption caused by two-photon optical transitions that involve energy levels of Ag2S photoluminescence centres, related to structural impurity defects in colloidal Ag2S QDs. At the same time, the z-scanning in a closed-aperture scheme demonstrates the formation of a thermal dynamic lens.

  20. Role of ZnS shell on stability, cytotoxicity, and photocytotoxicity of water-soluble CdSe semiconductor quantum dots surface modified with glutathione

    NASA Astrophysics Data System (ADS)

    Ibrahim, Salwa Ali; Ahmed, Wafaa; Youssef, Tareq

    2015-01-01

    The present study examines the stability and cytotoxicity of two quantum dots (QDs) systems in cell culture medium in the presence and absence of a thin layer of a ZnS shell. The two systems were built from a core, CdSe, and surface modified with glutathione (GSH), named CdSe˜GSH and CdSe/ZnS˜GSH. CdSe/ZnS˜GSH QDs exhibited a high photostability with a pronounced enhancement in photoluminescence in cell culture medium. Both systems showed insignificant reduction in cell viability of HFB-4 and MCF-7 cell lines in the dark. Following 60 min of low laser power exposure (irradiance of 10 mW cm-2), CdSe˜GSH QDs showed a remarkable decrease in cell viability, which may result from the detachment of GSH molecules, whereas CdSe/ZnS˜GSH QDs showed an insignificant decrease either immediately after irradiation or even 2 h post-exposure, which can be attributed to the high affinity between ZnS and GSH coatings. This study demonstrated that a thin layer of ZnS shell played a crucial role in the stability of CdSe/ZnS˜GSH QDs in cell culture medium with an improvement in luminescence efficiency, whereas surface modification with GSH molecules in the presence of ZnS showed no significant cytotoxic effects before or after photoirradiation, which makes this system attractive for several biomedical applications.

  1. A highly sensitive differential pulse anodic stripping voltammetry for determination of 17β-estradiol (E2) using CdSe quantum dots based on indirect competitive immunoassay.

    PubMed

    Chaisuwan, Nuanapa; Xu, He; Wu, Genying; Liu, Jianshe

    2013-08-15

    In this study a new and fast procedure was developed to determine trace 17β-estradiol (E2) concentrations using CdSe quantum dots (QDs) conjugation with bovine serum albumin (BSA)-E2. To increase the high efficiency of the method, the immunoassay design was restricted to an indirect competitive format. The E2 antigen and bioconjugate were incubated in a microtiter plate with an anti-E2 antibody and competition for antibody binding sites was established. The in situ bismuth-coated carbon electrodes were used for detecting the cadmium ions (Cd(2+)) released during the acid dissolution step. After optimization, the well-defined sharp anodic stripping voltammograms curves of the E2 concentration ranging from 50 to 1000 pg/mL was recorded, and the lowest detection limit was 50 pg/mL with 6% reproducibility and 7% repeatability. Finally, the assay was applied to tap water and wastewater samples. The detection limits were 52.56 ± 0.125 pg/mL for tap water and 51.42 ± 0.453 pg/mL for wastewater. These results show that the assay exhibited sensitive analytical performance in E2 detection with high sensitivity and accuracy with satisfactory results. PMID:23542084

  2. Size and Temperature Dependence of Electron Transfer between CdSe Quantum Dots and a TiO 2 Nanobelt

    SciTech Connect

    Tafen, De Nyago; Prezhdo, Oleg V.

    2015-02-24

    Understanding charge transfer reactions between quantum dots (QD) and metal oxides is fundamental for improving photocatalytic, photovoltaic and electronic devices. The complexity of these processes makes it difficult to find an optimum QD size with rapid charge injection and low recombination. We combine time-domain density functional theory with nonadiabatic molecular dynamics to investigate the size and temperature dependence of the experimentally studied electron transfer and charge recombination at CdSe QD-TiO2 nanobelt (NB) interfaces. The electron injection rate shows strong dependence on the QD size, increasing for small QDs. The rate exhibits Arrhenius temperature dependence, with the activation energy of the order of millielectronvolts. The charge recombination process occurs due to coupling of the electronic subsystem to vibrational modes of the TiO2 NB. Inelastic electron-phonon scattering happens on a picosecond time scale, with strong dependence on the QD size. Our simulations demonstrate that the electron-hole recombination rate decreases significantly as the QD size increases, in excellent agreement with experiments. The temperature dependence of the charge recombination rates can be successfully modeled within the framework of the Marcus theory through optimization of the electronic coupling and the reorganization energy. Our simulations indicate that by varying the QD size, one can modulate the photoinduced charge separation and charge recombination, fundamental aspects of the design principles for high efficiency devices.

  3. Gamma-radiation synthesis of silk fibroin coated CdSe quantum dots and their biocompatibility and photostability in living cells.

    PubMed

    Chang, Shu-Quan; Dai, Yao-Dong; Kang, Bin; Han, Wei; Chen, Da

    2009-10-01

    Silk fibroin coated CdSe quantum dots (SF-CdSe QDs) were successfully synthesized via a one-step gamma-radiation route in an aqueous system at room temperature. The as prepared products were characterized by transmission electron microscope (TEM), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis) and photoluminescence spectrum (PL). The SF-CdSe QDs were about 5 nm in diameter and exhibited excellent water-solubility and photoluminescence properties. The cellular distribution, photostability and cytotoxicity of SF-CdSe QDs with different amount of SF coatings were also investigated by laser scanning confocal microscope (LSCM) and MTT assays in human pancreatic carcinoma (PANC-1) cells. All the results reveal that these QDs could be easily internalized by cells and localized in cytoplasm around nuclei. Moreover, SF-CdSe QDs were proved to be low cytotoxicity (the concentration of QDs < 5 microg mL(-1)) and high photostability (the illumination energy density < 2 x 10(-5) W microm(-2)) within PANC-1 cells, which was mainly due to the biocompatible silk fibroin. The resulted SF-CdSe QDs might have many potential applications in tumor imaging and therapy. And the synthesis strategy could be easily extended to fabrication of other nanoparticles coated with silk fibroin. PMID:19908440

  4. Magnesium effects on CdSe self-assembled quantum dot formation on Zn xCd yMg 1-x-ySe layers

    NASA Astrophysics Data System (ADS)

    Noemi Perez-Paz, M.; Lu, Hong; Shen, Aidong; Jean Mary, F.; Akins, Daniel; Tamargo, Maria C.

    2006-09-01

    Optical and morphological studies are used to investigate the effects of chemical composition and, in particular, the magnesium content of the Zn xCd yMg 1-x-ySe barrier layers on the size, density and uniformity of CdSe self-assembled quantum dots (QDs). A reduction of the uncapped QD size, as well as a blue shift of the capped QD photoluminescence peak position by increasing Mg concentration in the Zn xCd yMg 1-x-ySe barrier has been demonstrated by changing the Mg cell temperature during growth. In addition, a more uniform and more densely packed QD layer has been observed with an increase of the MgSe fraction in the Zn xCd yMg 1-x-ySe barrier layer using three-dimensional topographic atomic force microscopy images of the surface of uncapped QDs. Results point to Mg as a chemical factor that induces QD formation, either by increasing the density of atomic steps or/and by changing the energy of the Zn xCd yMg 1-x-ySe surface.

  5. Synthesis of 2-Mercaptonicotinic Acid-Capped CdSe Quantum Dots and its Application to Spectrofluorometric Determination of Cr(VI) in Water Samples.

    PubMed

    Hosseini, Mohammad Saeid; Khorashahi, Somayeh; Hosseini, Navid

    2016-05-01

    The CdSe quantum dots (QDs) capped with 2-mercaptonicotinic acid (H2MN) were prepared through a controllable process at 80 °C. The prepared QDs were characterized by XRD, TEM, IR, UV-Vis and fluorescence (FL) techniques. It was found that the QDs were nearly mono-disperse with the diameters in the range of 8-10 nm. These QDs are capable to exhibit strong FL even in concentrated acidic media. They exhibit an enhanced fluorescence in the presence of Cr(VI), which was used for the determination of Cr(VI) in water samples. The linear range was found to be 1 × 10(-7)-6.0 × 10(-6) M with the RSD and DL of 0.92 % and 5 × 10(-8) M, respectively. Except that Ca(2+) and Fe(3+) which can be eliminated through a simple precipitation process, the other co-existent ions present in natural water were not interfered. The recoveries obtained for the added amounts of Cr(VI) were in the range of 96.9-103.2 %, which denote on application of the method, satisfactorily. PMID:26825078

  6. Comparison of magneto-optical properties of various excitonic complexes in CdTe and CdSe self-assembled quantum dots.

    PubMed

    Kobak, J; Smoleński, T; Goryca, M; Rousset, J-G; Pacuski, W; Bogucki, A; Oreszczuk, K; Kossacki, P; Nawrocki, M; Golnik, A; Płachta, J; Wojnar, P; Kruse, C; Hommel, D; Potemski, M; Kazimierczuk, T

    2016-07-01

    We present a comparative study of two self-assembled quantum dot (QD) systems based on II-VI compounds: CdTe/ZnTe and CdSe/ZnSe. Using magneto-optical techniques we investigated a large population of individual QDs. The systematic photoluminescence studies of emission lines related to the recombination of neutral exciton X, biexciton XX, and singly charged excitons (X(+), X(-)) allowed us to determine average parameters describing CdTe QDs (CdSe QDs): X-XX transition energy difference 12 meV (24 meV); fine-structure splitting δ1=0.14 meV (δ1=0.47 meV); g-factor g  =  2.12 (g  =  1.71); diamagnetic shift γ=2.5 μeV T(-2) (γ =1.3 μeV T(-2)). We find also statistically significant correlations between various parameters describing internal structure of excitonic complexes. PMID:27173643

  7. Comparison of magneto-optical properties of various excitonic complexes in CdTe and CdSe self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Kobak, J.; Smoleński, T.; Goryca, M.; Rousset, J.-G.; Pacuski, W.; Bogucki, A.; Oreszczuk, K.; Kossacki, P.; Nawrocki, M.; Golnik, A.; Płachta, J.; Wojnar, P.; Kruse, C.; Hommel, D.; Potemski, M.; Kazimierczuk, T.

    2016-07-01

    We present a comparative study of two self-assembled quantum dot (QD) systems based on II–VI compounds: CdTe/ZnTe and CdSe/ZnSe. Using magneto-optical techniques we investigated a large population of individual QDs. The systematic photoluminescence studies of emission lines related to the recombination of neutral exciton X, biexciton XX, and singly charged excitons (X+, X‑) allowed us to determine average parameters describing CdTe QDs (CdSe QDs): X–XX transition energy difference 12 meV (24 meV); fine-structure splitting δ1=0.14 meV (δ1=0.47 meV); g-factor g  =  2.12 (g  =  1.71) diamagnetic shift γ=2.5 μeV T‑2 (γ =1.3 μeV T‑2). We find also statistically significant correlations between various parameters describing internal structure of excitonic complexes.

  8. Picosecond Lifetimes with High Quantum Yields from Single-Photon-Emitting Colloidal Nanostructures at Room Temperature.

    PubMed

    Bidault, Sébastien; Devilez, Alexis; Maillard, Vincent; Lermusiaux, Laurent; Guigner, Jean-Michel; Bonod, Nicolas; Wenger, Jérôme

    2016-04-26

    Minimizing the luminescence lifetime while maintaining a high emission quantum yield is paramount in optimizing the excitation cross-section, radiative decay rate, and brightness of quantum solid-state light sources, particularly at room temperature, where nonradiative processes can dominate. We demonstrate here that DNA-templated 60 and 80 nm diameter gold nanoparticle dimers, featuring one fluorescent molecule, provide single-photon emission with lifetimes that can fall below 10 ps and typical quantum yields in a 45-70% range. Since these colloidal nanostructures are obtained as a purified aqueous suspension, fluorescence spectroscopy can be performed on both fixed and freely diffusing nanostructures to quantitatively estimate the distributions of decay rate and fluorescence intensity enhancements. These data are in excellent agreement with theoretical calculations and demonstrate that millions of bright fluorescent nanostructures, with radiative lifetimes below 100 ps, can be produced in parallel. PMID:26972678

  9. Phonon induced pure dephasing process of excitonic state in colloidal semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Huang, Tongyun; Han, Peng; Wang, Xinke; Feng, Shengfei; Sun, Wenfeng; Ye, Jiasheng; Zhang, Yan

    2016-04-01

    We present a theoretical study on the pure dephasing process of colloidal semiconductor quantum dots induced by lattice vibrations using continuum model calculations. By solving the time dependent Liouville-von Neumann equation, we present the ultrafast Rabi oscillations between excitonic state and virtual state via exciton-phonon interaction and obtain the pure dephasing time from the fast decayed envelope of the Rabi oscillations. The interaction between exciton and longitudinal optical phonon vibration is found to dominate the pure dephasing process and the dephasing time increases nonlinearly with the reduction of exciton-phonon coupling strength. We further find that the pure dephasing time of large quantum dots is more sensitive to temperature than small quantum dots.

  10. Determination of carrier lifetime and mobility in colloidal quantum dot films via impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Rath, Arup K.; Lasanta, Tania; Bernechea, Maria; Diedenhofen, Silke L.; Konstantatos, Gerasimos

    2014-02-01

    Impedance Spectroscopy (IS) proves to be a powerful tool for the determination of carrier lifetime and majority carrier mobility in colloidal quantum dot films. We employ IS to determine the carrier lifetime in PbS quantum dot Schottky solar cells with Al and we verify the validity of the technique via transient photovoltage. We also present a simple approach based on an RC model that allows the determination of carrier mobility in PbS quantum dot films and we corroborate the results via comparison with space charge limited measurements. In summary, we demonstrate the potential of IS to characterize key-to-photovoltaics optoelectronic properties, carrier lifetime, and mobility, in a facile way.

  11. Determination of carrier lifetime and mobility in colloidal quantum dot films via impedance spectroscopy

    SciTech Connect

    Rath, Arup K.; Lasanta, Tania; Bernechea, Maria; Diedenhofen, Silke L.; Konstantatos, Gerasimos

    2014-02-10

    Impedance Spectroscopy (IS) proves to be a powerful tool for the determination of carrier lifetime and majority carrier mobility in colloidal quantum dot films. We employ IS to determine the carrier lifetime in PbS quantum dot Schottky solar cells with Al and we verify the validity of the technique via transient photovoltage. We also present a simple approach based on an RC model that allows the determination of carrier mobility in PbS quantum dot films and we corroborate the results via comparison with space charge limited measurements. In summary, we demonstrate the potential of IS to characterize key-to-photovoltaics optoelectronic properties, carrier lifetime, and mobility, in a facile way.

  12. Quantum confined colloidal nanorod heterostructures for solar-to-fuel conversion.

    PubMed

    Wu, Kaifeng; Lian, Tianquan

    2016-07-11

    Solar energy conversion, particularly solar-driven chemical fuel formation, has been intensely studied in the past decades as a potential approach for renewable energy generation. Efficient solar-to-fuel conversion requires artificial photosynthetic systems with strong light absorption, long-lived charge separation and efficient catalysis. Colloidal quantum confined nanoheterostructures have emerged as promising materials for this application because of the ability to tailor their properties through size, shape and composition. In particular, colloidal one-dimensional (1D) semiconductor nanorods (NRs) offer the opportunity to simultaneously maintain quantum confinement in radial dimensions for tunable light absorptions and bulk like carrier transport in the axial direction for long-distance charge separations. In addition, the versatile chemistry of colloidal NRs enables the formation of semiconductor heterojunctions (such as CdSe/CdS dot-in-rod NRs) to separate photogenerated electron-hole pairs and deposition of metallic domains to accept charges and catalyze redox reactions. In this review, we summarize research progress on colloidal NR heterostructures and their applications for solar energy conversion, emphasizing mechanistic insights into the working principle of these systems gained from spectroscopic studies. Following a brief overview of synthesis of various NRs and heterostructures, we introduce their electronic structures and dynamics of exciton and carrier transport and interfacial transfer. We discuss how these exciton and carrier dynamics are controlled by their structures and provide key mechanistic understanding on their photocatalytic performance, including the photo-reduction of a redox mediator (methyl viologen) and light driven H2 generation. We discuss the solar-driven H2 generation mechanism, key efficiency limiting steps, and potential approaches for rational improvement in semiconductor NR/metal heterostructures (such as Pt tipped Cd

  13. A donor-supply electrode (DSE) for colloidal quantum dot photovoltaics.

    PubMed

    Koleilat, Ghada I; Wang, Xihua; Labelle, Andre J; Ip, Alexander H; Carey, Graham H; Fischer, Armin; Levina, Larissa; Brzozowski, Lukasz; Sargent, Edward H

    2011-12-14

    The highest-performing colloidal quantum dot (CQD) photovoltaics (PV) reported to date have relied on high-temperature (>500°C) annealing of electron-accepting TiO2. Room-temperature processing reduces energy payback time and manufacturing cost, enables flexible substrates, and permits tandem solar cells that integrate a small-bandgap back cell atop a low-thermal-budget larger-bandgap front cell. Here we report an electrode strategy that enables a depleted-heterojunction CQD PV device to be fabricated entirely at room temperature. We find that simply replacing the high-temperature-processed TiO2 with a sputtered version of the same material leads to poor performance due to the low mobility of the sputtered oxide. We develop instead a two-layer donor-supply electrode (DSE) in which a highly doped, shallow work function layer supplies a high density of free electrons to an ultrathin TiO2 layer via charge-transfer doping. Using the DSE we build all-room-temperature-processed small-bandgap (1 eV) colloidal quantum dot solar cells having 4% solar power conversion efficiency and high fill factor. These 1 eV bandgap cells are suitable for use as the back junction in tandem solar cells. The DSE concept, combined with control over TiO2 stoichiometry in sputtering, provides a much-needed tunable electrode to pair with quantum-size-effect CQD films. PMID:22084839

  14. Size-dependent optical properties of colloidal PbS quantum dots.

    PubMed

    Moreels, Iwan; Lambert, Karel; Smeets, Dries; De Muynck, David; Nollet, Tom; Martins, José C; Vanhaecke, Frank; Vantomme, André; Delerue, Christophe; Allan, Guy; Hens, Zeger

    2009-10-27

    We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots), by combining the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases with the Qdot volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on epsilon in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mus, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems. PMID:19780530

  15. Seed-mediated synthesis, properties and application of {gamma}-Fe{sub 2}O{sub 3}-CdSe magnetic quantum dots

    SciTech Connect

    Lin, Alex W.H.; Ang, Chung Yen; Patra, Pranab K.; Han Yu; Gu Hongwei; Le Breton, Jean-Marie; Juraszek, Jean; Chiron, Hubert; Papaefthymiou, Georgia C.; Tamil Selvan, Subramanian; Ying, Jackie Y.

    2011-08-15

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around {gamma}-Fe{sub 2}O{sub 3} magnetic cores was performed at high temperature (300 deg. C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells. - Graphical abstract: (a) HRTEM image of oleic acid capped MPs. The size of MPs ranges from 8 to 10 nm. (b) XRD pattern of {gamma}-Fe{sub 2}O{sub 3} MPs. Highlights: > The fabrication of MQDs through a seed-mediated approach has been demonstrated. > The formation and assembly of these bi-functional nanocomposites have been elucidated. > The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components. > MQDs with thin silica coating were successfully employed in the labeling of cancer cell membranes.

  16. Electron beam induced and microemulsion templated synthesis of CdSe quantum dots: tunable broadband emission and charge carrier recombination dynamics

    NASA Astrophysics Data System (ADS)

    Guleria, Apurav; Singh, Ajay K.; Rath, Madhab C.; Adhikari, Soumyakanti

    2015-04-01

    CdSe quantum dots (QDs) were synthesized by a rapid and one step templated approach inside the water pool of AOT (sodium bis(2-ethylhexyl) sulfosuccinate) based water-in-oil microemulsions (MEs) via electron beam (EB) irradiation technique with high dose rate, which favours high nucleation rate. The interplay of different experimental parameters such as precursor concentration, absorbed dose and {{W}0} values (aqueous phase to surfactant molar ratio) of MEs were found to have interesting consequences on the morphology, photoluminescence (PL), surface composition and carrier recombination dynamics of as-grown QDs. For instance, highly stable ultrasmall (∼1.7 nm) bluish-white light emitting QDs were obtained with quantum efficiency (η) of ∼9%. Furthermore, QDs were found to exhibit tunable broadband light emission extending from 450 to 750 nm (maximum FWHM ∼180 nm). This could be realized from the CIE (Commission Internationale d’Eclairage) chromaticity co-ordinates, which varied across the blue region to the orange region thereby, conferring their potential application in white light emitting diodes. Additionally, the average PL lifetime ≤ft( ≤ft< τ \\right> \\right) values could be varied from 18 ns to as high as 74 ns, which reflect the role of surface states in terms of their density and distribution. Another interesting revelation was the self-assembling of the initially formed QDs into nanorods with high aspect ratios ranging from 7 to 20, in correspondence with the {{W}0} values. Besides, the fundamental roles of the chemical nature of water pool and the interfacial fluidity of AOT MEs in influencing the photophysical properties of QDs were investigated by carrying out a similar study in CTAB (cetyltrimethylammonium bromide; cationic surfactant) based MEs. Surprisingly, very profound and contrasting results were observed wherein ≤ft< τ \\right> and η of the QDs in case of CTAB MEs were found to be at least three times lower as compared to

  17. Bias-induced photoluminescence quenching of single colloidal quantum dots embedded in organic semiconductors.

    PubMed

    Huang, Hao; Dorn, August; Nair, Gautham P; Bulović, Vladimir; Bawendi, Moungi G

    2007-12-01

    We demonstrate reversible quenching of the photoluminescence from single CdSe/ZnS colloidal quantum dots embedded in thin films of the molecular organic semiconductor N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) in a layered device structure. Our analysis, based on current and charge carrier density, points toward field ionization as the dominant photoluminescence quenching mechanism. Blinking traces from individual quantum dots reveal that the photoluminescence amplitude decreases continuously as a function of increasing forward bias even at the single quantum dot level. In addition, we show that quantum dot photoluminescence is quenched by aluminum tris(8-hydroxyquinoline) (Alq3) in chloroform solutions as well as in thin solid films of Alq3 whereas TPD has little effect. This highlights the importance of chemical compatibility between semiconductor nanocrystals and surrounding organic semiconductors. Our study helps elucidate elementary interactions between quantum dots and organic semiconductors, knowledge needed for designing efficient quantum dot organic optoelectronic devices. PMID:18034504

  18. Controlling the influence of Auger recombination on emission from colloidal quantum dots by photonic crystal.

    PubMed

    Xu, Xingsheng

    2014-07-01

    By investigating the time-resolved spectra of colloidal quantum dots (QDs) on silicon nitride (SiN) photonic crystals (PhCs), it is found that the ratio of charged-exciton (trion) emission and the multiexciton emission to the total emission can be controlled by two-dimensional PhCs. Even by conservative estimates, the ratios of trion to total emission from QDs on PCs reaches 10%, which is much larger than that of the dark state seen in the blinking phenomenon of single QDs. Therefore Auger recombination could be controlled by SiN PhCs. PMID:24978742

  19. Laser-induced wavelength-controlled self-assembly of colloidal quasi-resonant quantum dots.

    PubMed

    Tsipotan, Aleksey S; Gerasimova, Marina A; Slabko, Vitaliy V; Aleksandrovsky, Aleksandr S

    2016-05-16

    Self-assembly of colloidal semiconductor quantum dots controlled solely by laser-induced interaction is demonstrated for the first time. Pairs of CdTe nanoparticles are formed under irradiation with nanosecond pulses at wavelengths 555 or 560 nm. Formation of pairs is justified by corresponding changes of absorption spectra. Conditions of the experiment are in excellent agreement with those predicted by the theory of laser-induced dipole-dipole interaction of QDs. The fraction of QDs assembled into pairs is up to 47%. PMID:27409936

  20. Colloidal quantum dot lasers built on a passive two-dimensional photonic crystal backbone.

    PubMed

    Chang, Hojun; Min, Kyungtaek; Lee, Myungjae; Kang, Minsu; Park, Yeonsang; Cho, Kyung-Sang; Roh, Young-Geun; Woo Hwang, Sung; Jeon, Heonsu

    2016-03-17

    We report the room-temperature lasing action from two-dimensional photonic crystal (PC) structures composed of a passive Si3N4 backbone with an over-coat of CdSe/CdS/ZnS colloidal quantum dots (CQDs) for optical gain. When optically excited, devices lased in dual PC band-edge modes, with the modal dominance governed by the thickness of the CQD over-layer. The demonstrated laser platform should have an impact on future photonic integrated circuits as the on-chip coupling between active and passive components is readily achievable. PMID:26935411

  1. Secondary treatment of films of colloidal quantum dots for optoelectronics and devices produced thereby

    DOEpatents

    Semonin, Octavi Escala; Luther, Joseph M; Beard, Matthew C; Chen, Hsiang-Yu

    2014-04-01

    A method of forming an optoelectronic device. The method includes providing a deposition surface and contacting the deposition surface with a ligand exchange chemical and contacting the deposition surface with a quantum dot (QD) colloid. This initial process is repeated over one or more cycles to form an initial QD film on the deposition surface. The method further includes subsequently contacting the QD film with a secondary treatment chemical and optionally contacting the surface with additional QDs to form an enhanced QD layer exhibiting multiple exciton generation (MEG) upon absorption of high energy photons by the QD active layer. Devices having an enhanced QD active layer as described above are also disclosed.

  2. Effect of solvent environment on colloidal-quantum-dot solar-cell manufacturability and performance.

    PubMed

    Kirmani, Ahmad R; Carey, Graham H; Abdelsamie, Maged; Yan, Buyi; Cha, Dongkyu; Rollny, Lisa R; Cui, Xiaoyu; Sargent, Edward H; Amassian, Aram

    2014-07-16

    The absorbing layer in state-of-the-art colloidal quantum-dot solar cells is fabricated using a tedious layer-by-layer process repeated ten times. It is now shown that methanol, a common exchange solvent, is the main culprit, as extended exposure leaches off the surface halide passivant, creating carrier trap states. Use of a high-dipole-moment aprotic solvent eliminates this problem and is shown to produce state-of-the-art devices in far fewer steps. PMID:24894800

  3. A Surface Chemistry Approach to Enhancing Colloidal Quantum Dot Solids for Photovoltaics

    NASA Astrophysics Data System (ADS)

    Carey, Graham Hamilton

    Colloidal quantum dot (CQD) photovoltaic devices have improved rapidly over the past decade of research. By taking advantage of the quantum confinement effect, solar cells constructed using films of infrared-bandgap nanoparticles are able to capture previously untapped ranges of the solar energy spectrum. Additionally, films are fabricated using simple, cheap, reproducible solution processing techniques, enabling the creation of low-cost, flexible photovoltaic devices. A key factor limiting the creation of high efficiency CQD solar cells is the short charge carrier diffusion length in films. Driven by a combination of limited carrier mobility, poor nanoparticle surface passivation, and the presence of unexamined electrically active impurities throughout the film, the poor diffusion length limits the active layer thickness in CQD solar cells, leading to lower-than-desired light absorption, and curtailing the photocurrent generated by such devices. This thesis seeks to address poor diffusion length by addressing each of the limiting factors in turn. Electrical transport in quantum dot solids is examined in the context of improved quantum dot packing; methods are developed to improve packing by using actively densifying components, or by dramatically lowering the volume change required between quantum dots in solution and in solid state. Quantum dot surface passivation is improved by introducing a crucial secondary, small halide ligand source, and by surveying the impact of the processing environment on the final quality of the quantum dot surface. A heretofore unidentified impurity present in quantum dot solids is identified, characterized, and chemically eliminated. Finally, lessons learned through these experiments are combined into a single, novel materials system, leading to quantum dot devices with a significantly improved diffusion length (enhanced from 70 to 230 nm). This enabled thick, high current density (30 mA cm -2, compared to typical values in the 20

  4. Aqueous Synthesis of PEGylated Quantum Dots with Increased Colloidal Stability and Reduced Cytotoxicity.

    PubMed

    Ulusoy, Mehriban; Jonczyk, Rebecca; Walter, Johanna-Gabriela; Springer, Sergej; Lavrentieva, Antonina; Stahl, Frank; Green, Mark; Scheper, Thomas

    2016-02-17

    Ligands used on the surface of colloidal nanoparticles (NPs) have a significant impact on physiochemical properties of NPs and their interaction in biological environments. In this study, we report a one-pot aqueous synthesis of 3-mercaptopropionic acid (MPA)-functionalized CdTe/CdS/ZnS quantum dots (Qdots) in the presence of thiol-terminated methoxy polyethylene glycol (mPEG) molecules as a surface coordinating ligand. The resulting mPEG-Qdots were characterized by using ζ potential, FTIR, thermogravimetric (TG) analysis, and microscale thermophoresis (MST) studies. We investigated the effect of mPEG molecules and their grafting density on the Qdots photophysical properties, colloidal stability, protein binding affinity, and in vitro cellular toxicity. Moreover, cellular binding features of the resulting Qdots were examined by using three-dimensional (3D) tumor-like spheroids, and the results were discussed in detail. Promisingly, mPEG ligands were found to increase colloidal stability of Qdots, reduce adsorption of proteins to the Qdot surface, and mitigate Qdot-induced side effects to a great extent. Flow cytometry and confocal microscopy studies revealed that PEGylated Qdots exhibited distinctive cellular interactions with respect to their mPEG grafting density. As a result, mPEG molecules demonstrated a minimal effect on the ZnS shell deposition and the Qdot fluorescence efficiency at a low mPEG density, whereas they showed pronounced effect on Qdot colloidal stability, protein binding affinity, cytotoxicity, and nonspecific binding at a higher mPEG grafting amount. PMID:26567697

  5. Carrier dynamics in highly quantum-confined, colloidal indium antimonide nanocrystals.

    PubMed

    Chang, Angela Y; Liu, Wenyong; Talapin, Dmitri V; Schaller, Richard D

    2014-08-26

    Nanometer-sized particles of indium antimonide (InSb) offer opportunities in areas such as solar energy conversion and single photon sources. Here, we measure electron-hole pair dynamics, spectra, and absorption cross sections of strongly quantum-confined colloidal InSb nanocrystal quantum dots using femtosecond transient absorption. For all samples, we observe a bleach feature that develops on ultrafast time scales, which notably moves to lower energy during the first several picoseconds following excitation. We associate this unusual red shift, which becomes larger for larger particles and more distinct at lower sample temperatures, with hot exciton cooling through states that we suggest arise from energetically proximal conduction band levels. From controlled optical excitation intensities, we determine biexciton lifetimes, which range from 2 to 20 ps for the studied 3-6 nm diameter particle sizes. PMID:25106893

  6. Modeling photovoltaic performance in periodic patterned colloidal quantum dot solar cells.

    PubMed

    Fu, Yulan; Dinku, Abay G; Hara, Yukihiro; Miller, Christopher W; Vrouwenvelder, Kristina T; Lopez, Rene

    2015-07-27

    Colloidal quantum dot (CQD) solar cells have attracted tremendous attention mostly due to their wide absorption spectrum window and potentially low processability cost. The ultimate efficiency of CQD solar cells is highly limited by their high trap state density. Here we show that the overall device power conversion efficiency could be improved by employing photonic structures that enhance both charge generation and collection efficiencies. By employing a two-dimensional numerical model, we have calculated the characteristics of patterned CQD solar cells based of a simple grating structure. Our calculation predicts a power conversion efficiency as high as 11.2%, with a short circuit current density of 35.2 mA/cm2, a value nearly 1.5 times larger than the conventional flat design, showing the great potential value of patterned quantum dot solar cells. PMID:26367680

  7. All-Optical Wavelength Conversion by Picosecond Burst Absorption in Colloidal PbS Quantum Dots.

    PubMed

    Geiregat, Pieter; Houtepen, Arjan J; Van Thourhout, Dries; Hens, Zeger

    2016-01-26

    All-optical approaches to change the wavelength of a data signal are considered more energy- and cost-effective than current wavelength conversion schemes that rely on back and forth switching between the electrical and optical domains. However, the lack of cost-effective materials with sufficiently adequate optoelectronic properties hampers the development of this so-called all-optical wavelength conversion. Here, we show that the interplay between intraband and band gap absorption in colloidal quantum dots leads to a very strong and ultrafast modulation of the light absorption after photoexcitation in which slow components linked to exciton recombination are eliminated. This approach enables all-optical wavelength conversion at rates matching state-of-the-art convertors in speed, yet with cost-effective solution-processable materials. Moreover, the stronger light-matter interaction allows for implementation in small-footprint devices with low switching energies. Being a generic property, the demonstrated effect opens a pathway toward low-power integrated photonics based on colloidal quantum dots as the enabling material. PMID:26692112

  8. Colloidal quantum dot lasers built on a passive two-dimensional photonic crystal backbone

    NASA Astrophysics Data System (ADS)

    Chang, Hojun; Min, Kyungtaek; Lee, Myungjae; Kang, Minsu; Park, Yeonsang; Cho, Kyung-Sang; Roh, Young-Geun; Woo Hwang, Sung; Jeon, Heonsu

    2016-03-01

    We report the room-temperature lasing action from two-dimensional photonic crystal (PC) structures composed of a passive Si3N4 backbone with an over-coat of CdSe/CdS/ZnS colloidal quantum dots (CQDs) for optical gain. When optically excited, devices lased in dual PC band-edge modes, with the modal dominance governed by the thickness of the CQD over-layer. The demonstrated laser platform should have an impact on future photonic integrated circuits as the on-chip coupling between active and passive components is readily achievable.We report the room-temperature lasing action from two-dimensional photonic crystal (PC) structures composed of a passive Si3N4 backbone with an over-coat of CdSe/CdS/ZnS colloidal quantum dots (CQDs) for optical gain. When optically excited, devices lased in dual PC band-edge modes, with the modal dominance governed by the thickness of the CQD over-layer. The demonstrated laser platform should have an impact on future photonic integrated circuits as the on-chip coupling between active and passive components is readily achievable. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08544f

  9. Self-organized colloidal quantum dots and metal nanoparticles for plasmon-enhanced intermediate-band solar cells.

    PubMed

    Mendes, Manuel J; Hernández, Estela; López, Esther; García-Linares, Pablo; Ramiro, Iñigo; Artacho, Irene; Antolín, Elisa; Tobías, Ignacio; Martí, Antonio; Luque, Antonio

    2013-08-30

    A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude.In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance.The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells. PMID:23912379

  10. Towards bulk based preconditioning for quantum dotcomputations

    SciTech Connect

    Dongarra, Jack; Langou, Julien; Tomov, Stanimire; Channing,Andrew; Marques, Osni; Vomel, Christof; Wang, Lin-Wang

    2006-05-25

    This article describes how to accelerate the convergence of Preconditioned Conjugate Gradient (PCG) type eigensolvers for the computation of several states around the band gap of colloidal quantum dots. Our new approach uses the Hamiltonian from the bulk materials constituent for the quantum dot to design an efficient preconditioner for the folded spectrum PCG method. The technique described shows promising results when applied to CdSe quantum dot model problems. We show a decrease in the number of iteration steps by at least a factor of 4 compared to the previously used diagonal preconditioner.

  11. Functionalization-dependent induction of cellular survival pathways by CdSe quantum dots in primary normal human bronchial epithelial cells.

    PubMed

    Nagy, Amber; Hollingsworth, Jennifer A; Hu, Bin; Steinbrück, Andrea; Stark, Peter C; Rios Valdez, Cristina; Vuyisich, Momchilo; Stewart, Michael H; Atha, Donald H; Nelson, Bryant C; Iyer, Rashi

    2013-10-22

    Quantum dots (QDs) are semiconductor nanocrystals exhibiting unique optical properties that can be exploited for many practical applications ranging from photovoltaics to biomedical imaging and drug delivery. A significant number of studies have alluded to the cytotoxic potential of these materials, implicating Cd-leaching as the causal factor. Here, we investigated the role of heavy metals in biological responses and the potential of CdSe-induced genotoxicity. Our results indicate that, while negatively charged QDs are relatively noncytotoxic compared to positively charged QDs, the same does not hold true for their genotoxic potential. Keeping QD core composition and size constant, 3 nm CdSe QD cores were functionalized with mercaptopropionic acid (MPA) or cysteamine (CYST), resulting in negatively or positively charged surfaces, respectively. CYST-QDs were found to induce significant cytotoxicity accompanied by DNA strand breakage. However, MPA-QDs, even in the absence of cytotoxicity and reactive oxygen species formation, also induced a high number of DNA strand breaks. QD-induced DNA damage was confirmed by identifying the presence of p53 binding protein 1 (53BP1) in the nuclei of exposed cells and subsequent diminishment of p53 from cytoplasmic cellular extracts. Further, high-throughput real-time PCR analyses revealed upregulation of DNA damage and response genes and several proinflammatory cytokine genes. Most importantly, transcriptome sequencing revealed upregulation of the metallothionein family of genes in cells exposed to MPA-QDs but not CYST-QDs. These data indicate that cytotoxic assays must be supplemented with genotoxic analyses to better understand cellular responses and the full impact of nanoparticle exposure when making recommendations with regard to risk assessment. PMID:24007210

  12. White/blue-emitting, water-dispersible CdSe quantum dots prepared by counter ion-induced polymer collapse

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Goh, Jane Betty; Goh, M. Cynthia; Giri, Neeraj Kumar; Paige, Matthew F.

    2015-09-01

    The synthesis and characterization of water-dispersible, luminescent CdSe/ZnS semiconductor quantum dots that exhibit nominal "white" fluorescence emission and have potential applications in solid-state lighting is described. The nanomaterials, prepared through counter ion-induced collapse and UV cross-linking of high-molecular weight polyacrylic acid in the presence of appropriate aqueous inorganic ions, were of ∼2-3 nm diameter and could be prepared in gram quantities. The quantum dots exhibited strong luminescence emission in two bands, the first in the blue-region (band edge) of the optical spectrum and the second, a broad emission in the red-region (attributed to deep trap states) of the optical spectrum. Because of the relative strength of emission of the band edge and deep trap state luminescence, it was possible to achieve visible white luminescence from the quantum dots in aqueous solution and in dried, solid films. The optical spectroscopic properties of the nanomaterials, including ensemble and single-molecule spectroscopy, was performed, with results compared to other white-emitting quantum dot systems described previously in the literature.

  13. Nanoscale Interfaces in Colloidal Quantum Dot Solar Cells: Physical Insights and Materials Engineering Strategies

    NASA Astrophysics Data System (ADS)

    Kemp, Kyle Wayne

    With growing global energy demand there will be an increased need for sources of renewable energy such as solar cells. To make these photovoltaic technologies more competitive with conventional energy sources such as coal and natural gas requires further reduction in manufacturing costs that can be realized by solution processing and roll-to-roll printing. Colloidal quantum dots are a bandgap tunable, solution processible, semiconductor material which may offer a path forward to efficient, inexpensive photovoltaics. Despite impressive progress in performance with these materials, there remain limitations in photocarrier collection that must be overcome. This dissertation focuses on the characterization of charge recombination and transport in colloidal quantum dot photovoltaics, and the application of this knowledge to the development of new and better materials. Core-shell, PbS-CdS, quantum dots were investigated in an attempt to achieve better surface passivation and reduce electronic defects which can limit performance. Optimization of this material led to improved open circuit voltage, exceeding 0.6 V for the first time, and record published performance of 6% efficiency. Using temperature-dependent and transient photovoltage measurements we explored the significance of interface recombination on the operation of these devices. Careful engineering of the electrode using atomic layer deposition of ZnO helped lead to better TiO2 substrate materials and allowed us to realize a nearly two-fold reduction in recombination rate and an enhancement upwards of 50 mV in open circuit voltage. Carrier extraction efficiency was studied in these devices using intensity dependent current-voltage data of an operational solar cell. By developing an analytical model to describe recombination loss within the active layer of the device we were able to accurately determine transport lengths ranging up to 90 nm. Transient absorption and photoconductivity techniques were used to study

  14. Infrared Colloidal Quantum Dot Photovoltaics via Coupling Enhancement and Agglomeration Suppression.

    PubMed

    Ip, Alexander H; Kiani, Amirreza; Kramer, Illan J; Voznyy, Oleksandr; Movahed, Hamidreza F; Levina, Larissa; Adachi, Michael M; Hoogland, Sjoerd; Sargent, Edward H

    2015-09-22

    Materials optimized for single-junction solar spectral harvesting, such as silicon, perovskites, and large-band-gap colloidal quantum dot solids, fail to absorb the considerable infrared spectral energy that lies below their respective band gap. Here we explore through modeling and experiment the potential for colloidal quantum dots (CQDs) to augment the performance of solar cells by harnessing transmitted light in the infrared. Through detailed balance modeling, we identify the CQD band gap that is best able to augment wafer-based, thin-film, and also solution-processed photovoltaic (PV) materials. The required quantum dots, with an excitonic peak at 1.3 μm, have not previously been studied in depth for solar performance. Using computational studies we find that a new ligand scheme distinct from that employed in better-explored 0.95 μm band gap PbS CQDs is necessary; only via the solution-phase application of a short bromothiol can we prevent dot fusion during ensuing solid-state film treatments and simultaneously offer a high valence band-edge density of states to enhance hole transport. Photoluminescence spectra and transient studies confirm the desired narrowed emission peaks and reduced surface-trap-associated decay. Electronic characterization reveals that only through the use of the bromothiol ligands is strong hole transport retained. The films, when used to make PV devices, achieve the highest AM1.5 power conversion efficiency yet reported in a solution-processed material having a sub-1 eV band gap. PMID:26266671

  15. Organic/inorganic hybrid pn-junction between copper phthalocyanine and CdSe quantum dot layers as solar cells

    NASA Astrophysics Data System (ADS)

    Saha, Sudip K.; Guchhait, Asim; Pal, Amlan J.

    2012-08-01

    We have introduced an organic/inorganic hybrid pn-junction for solar cell applications. Layers of II-VI quantum dots and a metal-phthalocyanine in sequence have been used as n- and p-type materials, respectively, to form a junction. The film of quantum dots has been formed through a layer-by-layer process by replacing the long-chain ligands of the nanoparticles in each ultrathin layer or a monolayer with short-chain ones so that interparticle distance becomes small leading to a decrease in resistance of the quantum dot layer. With indium tin oxide and Au as electrodes, we have formed an inverted sandwiched structure. These electrodes formed ohmic contacts with the neighboring materials. From the current-voltage characteristics of the hybrid heterostructure, we have inferred formation of a depletion region at the pn-junction that played a key role in charge separation and correspondingly a photocurrent in the external circuit. For comparison, we have also formed and characterized Schottky devices based on components of the pn-junction keeping the electrode combination same. From capacitance-voltage characteristics, we have observed that the depletion region of the hybrid pn-junction was much wider as compared to that in Schottky devices based on components of the junction.

  16. Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells.

    PubMed

    Sauvage, Frédéric; Davoisne, Carine; Philippe, Laetitia; Elias, Jamil

    2012-10-01

    We investigated CdSe-sensitized TiO(2) solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO(2) gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO(2) nanoparticles. This technique has the advantage of providing not only a fast method for sensitization ( < 5 min) but also being easily scalable to the sensitization of large-area panels. XRD together with SAED analysis highlight that the deposit of CdSe is exclusively constituted of the hexagonal polymorph. In addition, hierarchical growth has also been shown, starting from the formation of a TiO(2)-CdSe core-shell structure followed by the growth of an assembly of CdSe nanoparticles resembling cauliflowers. This assembly exhibits at its core a mosaic texture with crystallites of about 3 nm in size, in contrast to a shell composed of well-crystallized single crystals between 5 and 10 nm in size. Preliminary results on the photovoltaic performance of such a nanostructured composite of TiO(2) and CdSe show 0.8% power conversion efficiency under A.M.1.5 G conditions-100 mW cm(-2) in association with a new regenerative redox couple based on cobalt(+III/+II) polypyridil complex (V(oc ) = 485 mV, J(sc ) = 4.26 mA cm (-2), ff=0.37). PMID:22972037

  17. Narrow bandgap colloidal metal chalcogenide quantum dots: synthetic methods, heterostructures, assemblies, electronic and infrared optical properties.

    PubMed

    Kershaw, Stephen V; Susha, Andrei S; Rogach, Andrey L

    2013-04-01

    The chemistry, material processing and fundamental understanding of colloidal semiconductor nanocrystals (quantum dots) are advancing at an astounding rate, bringing the prospects of widespread commercialization of these novel and exciting materials ever closer. Interest in narrow bandgap nanocrystals in particular has intensified in recent years, and the results of research worldwide point to the realistic prospects of applications for these materials in solar cells, infrared optoelectronics (e.g. lasers, optical modulators, photodetectors and photoimaging devices), low cost/large format microelectronics, and in biological imaging and biosensor systems to name only some technologies. Improvements in fundamental understanding and material quality are built on a vast body of experience spread over many different methods of colloidal synthetic growth, each with their own strengths and weaknesses for different materials and sometimes with regard to particular applications. The nanocrystal growth expertise is matched by a rapidly expanding, and highly interdisciplinary, understanding of how best to assemble these materials into films or hybrid composites and thereby into useful devices, and again there are many different strategies that can be adopted. In this review we have attempted to survey and compare the recent work on colloidal synthesis, film and nanocrystal composite material fabrication, concentrating on narrow bandgap chalcogenide materials and some of their topical applications in the solar energy and biological fields. Since these applications are attracting rising interest across a wide range of disciplines, from the biological sciences, device engineering, and materials processing fields as well as the physics and synthetic chemistry communities, we have endeavoured to make the review of these narrow bandgap nanomaterials both comprehensive and accessible to newcomers to the area. PMID:23361653

  18. Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

    SciTech Connect

    Singh, U. B.; Pandey, M. B.; Dhar, R; Pandey, A. S.; Kumar, S.; Dabrowski, R.

    2014-11-15

    We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.

  19. Study of colloidal quantum-dot surfaces using an innovative thin-film positron 2D-ACAR method

    NASA Astrophysics Data System (ADS)

    Eijt, Stephan W. H.; van Veen, Anton (Tom); Schut, Henk; Mijnarends, Peter E.; Denison, Art B.; Barbiellini, Bernardo; Bansil, Arun

    2006-01-01

    Nanosized inorganic particles are of great interest because their electronic properties can be easily tailored, providing a tremendous potential for applications in optoelectronic devices, light-emitting diodes, solar cells and hydrogen storage. Confinement of electrons and holes to dimensions comparable to their wavelength leads to quantum-well states with modified wavefunctions and density of states. Surface phenomena are crucial in determining nanoparticle properties in view of their large surface-to-volume ratio. Despite a wealth of information, many fundamental questions about the nature of the surface and its relationship with the electronic structure remain unsolved. Ab initio calculations on CdSe nanocrystals suggest that passivating the ligands does not produce the ideal wurtzite structure and that Se atoms relax outwards irrespective of passivation. Here we show that implanted positrons are trapped at the surface of CdSe nanocrystals. They annihilate mostly with the Se electrons, monitor changes in composition and structure of the surface while hardly sensing the ligand molecules, and we thus unambiguously confirm the predicted strong surface relaxation.

  20. Study of colloidal quantum-dot surfaces using an innovative thin-film positron 2D-ACAR method.

    PubMed

    Eijt, Stephan W H; van Veen, Anton Tom; Schut, Henk; Mijnarends, Peter E; Denison, Art B; Barbiellini, Bernardo; Bansil, Arun

    2006-01-01

    Nanosized inorganic particles are of great interest because their electronic properties can be easily tailored, providing a tremendous potential for applications in optoelectronic devices, light-emitting diodes, solar cells and hydrogen storage. Confinement of electrons and holes to dimensions comparable to their wavelength leads to quantum-well states with modified wavefunctions and density of states. Surface phenomena are crucial in determining nanoparticle properties in view of their large surface-to-volume ratio. Despite a wealth of information, many fundamental questions about the nature of the surface and its relationship with the electronic structure remain unsolved. Ab initio calculations on CdSe nanocrystals suggest that passivating the ligands does not produce the ideal wurtzite structure and that Se atoms relax outwards irrespective of passivation. Here we show that implanted positrons are trapped at the surface of CdSe nanocrystals. They annihilate mostly with the Se electrons, monitor changes in composition and structure of the surface while hardly sensing the ligand molecules, and we thus unambiguously confirm the predicted strong surface relaxation. PMID:16380729

  1. Hybrid zinc oxide/graphene electrodes for depleted heterojunction colloidal quantum-dot solar cells.

    PubMed

    Tavakoli, Mohammad Mahdi; Aashuri, Hossein; Simchi, Abdolreza; Fan, Zhiyong

    2015-10-01

    Recently, hybrid nanocomposites consisting of graphene/nanomaterial heterostructures have emerged as promising candidates for the fabrication of optoelectronic devices. In this work, we have employed a facile and in situ solution-based process to prepare zinc oxide/graphene quantum dots (ZnO/G QDs) in a hybrid structure. The prepared hybrid dots are composed of a ZnO core, with an average size of 5 nm, warped with graphene nanosheets. Spectroscopic studies show that the graphene shell quenches the photoluminescence intensity of the ZnO nanocrystals by about 72%, primarily due to charge transfer reactions and static quenching. A red shift in the absorption peak is also observed. Raman spectroscopy determines G-band splitting of the graphene shell into two separated sub-bands (G(+), G(-)) caused by the strain induced symmetry breaking. It is shown that the hybrid ZnO/G QDs can be used as a counter-electrode for heterojunction colloidal quantum-dot solar cells for efficient charge-carrier collection, as evidenced by the external quantum efficiency measurement. Under the solar simulated spectrum (AM 1.5G), we report enhanced power conversion efficiency (35%) with higher short current circuit (80%) for lead sulfide-based solar cells as compared to devices prepared by pristine ZnO nanocrystals. PMID:26339693

  2. Wavelength-tunable colloidal quantum dot laser on ultra-thin flexible glass

    SciTech Connect

    Foucher, C.; Guilhabert, B.; Laurand, N.; Dawson, M. D.

    2014-04-07

    A mechanically flexible and wavelength-tunable laser with an ultra-thin glass membrane as substrate is demonstrated. The optically pumped hybrid device has a distributed feedback cavity that combines a colloidal quantum dot gain film with a grating-patterned polymeric underlayer, all on a 30-μm thick glass sheet. The total thickness of the structure is only 75 μm. The hybrid laser has an average threshold fluence of 450 ± 80 μJ/cm{sup 2} (for 5-ns excitation pulses) at an emitting wavelength of 607 nm. Mechanically bending the thin-glass substrate enables continuous tuning of the laser emission wavelength over an 18-nm range, from 600 nm to 618 nm. The correlation between the wavelength tunability and the mechanical properties of the thin laser structure is verified theoretically and experimentally.

  3. 10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation.

    PubMed

    Lan, Xinzheng; Voznyy, Oleksandr; García de Arquer, F Pelayo; Liu, Mengxia; Xu, Jixian; Proppe, Andrew H; Walters, Grant; Fan, Fengjia; Tan, Hairen; Liu, Min; Yang, Zhenyu; Hoogland, Sjoerd; Sargent, Edward H

    2016-07-13

    Colloidal quantum dot (CQD) solar cells are solution-processed photovoltaics with broad spectral absorption tunability. Major advances in their efficiency have been made via improved CQD surface passivation and device architectures with enhanced charge carrier collection. Herein, we demonstrate a new strategy to improve further the passivation of CQDs starting from the solution phase. A cosolvent system is employed to tune the solvent polarity in order to achieve the solvation of methylammonium iodide (MAI) and the dispersion of hydrophobic PbS CQDs simultaneously in a homogeneous phase, otherwise not achieved in a single solvent. This process enables MAI to access the CQDs to confer improved passivation. This, in turn, allows for efficient charge extraction from a thicker photoactive layer device, leading to a certified solar cell power conversion efficiency of 10.6%, a new certified record in CQD photovoltaics. PMID:27351104

  4. Resonance-induced absorption enhancement in colloidal quantum dot solar cells using nanostructured electrodes.

    PubMed

    Mahpeykar, Seyed Milad; Xiong, Qiuyang; Wang, Xihua

    2014-10-20

    The application of nanostructured indium-doped tin oxide (ITO) electrodes as diffraction gratings for light absorption enhancement in colloidal quantum dot solar cells is numerically investigated using finite-difference time-domain (FDTD) simulation. Resonant coupling of the incident diffracted light with supported waveguide modes in light absorbing layer at particular wavelengths predicted by grating far-field projection analysis is shown to provide superior near-infrared light trapping for nanostructured devices as compared to the planar structure. Among various technologically feasible nanostructures, the two-dimensional nano-branch array is demonstrated as the most promising polarization-independent structure and proved to be able to maintain its performance despite structural imperfections common in fabrication. PMID:25607315

  5. Lasing and magnetic microbeads loaded with colloidal quantum dots and iron oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Minxu; You, Guanjun; Wang, Andrew Y.; Hu, Wenjia; Wang, Jingkang; Sun, Fengqing; Zhu, Yiming; Henderson, Ron; Xu, Jian

    2013-09-01

    This study investigates the feasibility of loading nanostructured lasing medium and magnetic nanocrystals in the same microbead for potential applications in bio- and chemical sensing. A sequential infiltration process is proposed and tested for the preparation of magnetic and lasing microbeads by incorporating, respectively, iron oxide nanocrystals in the inner cores and colloidal quantum dots (CQDs) in the periphery regions of mesoporous silica microbeads. The co-doped bead structure was confirmed by electron microscopy and energy dispersive spectroscopy. The lasing action of the CQD gain medium in the mesoporous beads was characterized with micro-photoluminescence, revealing sharp whispering gallery mode lasing signatures, whereas the distinguishing superparamagnetic property was measured from the co-doped microbeads with vibrating sample magnetometry.

  6. Statistical interpretation of transient current power-law decay in colloidal quantum dot arrays

    NASA Astrophysics Data System (ADS)

    Sibatov, R. T.

    2011-08-01

    A new statistical model of the charge transport in colloidal quantum dot arrays is proposed. It takes into account Coulomb blockade forbidding multiple occupancy of nanocrystals and the influence of energetic disorder of interdot space. The model explains power-law current transients and the presence of the memory effect. The fractional differential analogue of the Ohm law is found phenomenologically for nanocrystal arrays. The model combines ideas that were considered as conflicting by other authors: the Scher-Montroll idea about the power-law distribution of waiting times in localized states for disordered semiconductors is applied taking into account Coulomb blockade; Novikov's condition about the asymptotic power-law distribution of time intervals between successful current pulses in conduction channels is fulfilled; and the carrier injection blocking predicted by Ginger and Greenham (2000 J. Appl. Phys. 87 1361) takes place.

  7. High-performance SWIR sensing from colloidal quantum dot photodiode arrays

    NASA Astrophysics Data System (ADS)

    Klem, Ethan; Lewis, Jay; Gregory, Chris; Cunningham, Garry; Temple, Dorota; D'Souza, Arvind; Robinson, Ernest; Wijewarnasuriya, P. S.; Dhar, Nibir

    2013-09-01

    RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome the high cost, limited spectral response, and challenges in the reduction in pixel size associated with InGaAs focal plane arrays. The most significant advantage of the CQD technology is ease of fabrication. The devices can be fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. Further, device performance is not expected to degrade significantly with reduced pixel size. We present results for upward-looking detectors fabricated on Si substrates with sensitivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

  8. PbS colloidal quantum dot photodiodes for low-cost SWIR sensing

    NASA Astrophysics Data System (ADS)

    Klem, Ethan J. D.; Gregory, Chris; Temple, Dorota; Lewis, Jay

    2015-06-01

    RTI has developed a photodiode technology based on solution-processed PbS colloidal quantum dots (CQD). These devices are capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. At the core of this technology is a heterojunction diode structure fabricated using techniques well suited to wafer-scale fabrication, such as spin coating and thermal evaporation. This enables RTI's CQD diodes to be processed at room temperature directly on top of read-out integrated circuits (ROIC), without the need for the hybridization step required by traditional SWIR detectors. Additionally, the CQD diodes can be fabricated on ROICs designed for other detector material systems, effectively allowing rapid prototype demonstrations of CQD focal plane arrays at low cost and on a wide range of pixel pitches and array sizes.

  9. Random lasing in a colloidal quantum dot-doped disordered polymer.

    PubMed

    Cao, Mingxuan; Zhang, Yating; Song, Xiaoxian; Che, Yongli; Zhang, Haiting; Dai, Haitao; Zhang, Guizhong; Yao, Jianquan

    2016-05-01

    We report random lasing in colloidal quantum dots (CQDs) doped disordered polymer. The CdSe/ZnS core-shell CQDs are dispersed in hybrid polymer including two types of monomers with different rates of polymerization. After UV curing, spatially localized random resonators are formed owing to long range refractive-index fluctuations in inhomogeneous polymer with gain. Upon the optical excitation, random lasing action is triggered above the threshold of 7mJ/cm2. Through the investigation on the spectral characteristics of random laser, the wavelengths of random lasers strongly depend on pump position, which confirms that random laser modes originate from spatially localized resnonators. According to power Fourier transform of emission spectrum, the average size of equivalent micro resonators is attributed to be 50 μm. The proposed method provides a facile route to develop random lasers based on CQDs, showing potential applications on random fiber laser and laser displays. PMID:27137548

  10. Gain high-quality colloidal quantum dots directly from natural minerals.

    PubMed

    Wu, Wen-Tian; Liu, Hui; Dong, Chao; Zheng, Wen-Jing; Han, Li-Li; Li, Lan; Qiao, Shi-Zhang; Yang, Jing; Du, Xi-Wen

    2015-03-01

    Green and simple synthesis of high-quality colloidal quantum dots (CQDs) is of great importance and highly anticipated yet not fully implemented. Herein, we achieve the direct conversion of natural minerals to highly uniform, crystalline lead sulfide CQDs based on laser irradiation in liquid. The trivial fragmentation of mineral particles by an intense nanosecond laser was found to create a localized high degree of monomer supersaturation in oleic acid, initiating the LaMer growth of uniform CQDs. The photoconductive device made of these CQDs exhibits a competitive temporal response of photocurrent with those highly sensitive photodetectors based on PbS CQDs reported in the literature. Our synthesis strategy paves the way for the most environmentally friendly and convenient mass production of high-quality uniform CQDs. PMID:25689447

  11. Solution-processed high-performance colloidal quantum dot tandem photodetectors on flexible substrates

    SciTech Connect

    Jiang, Zhenyu; You, Guanjun; Wang, Li; Liu, Jie; Xu, Jian; Hu, Wenjia; Zhang, Yu

    2014-08-28

    We report a high-performance colloidal quantum dot (CQD)-based near-infrared tandem photodetector fabricated on flexible substrates via solution-processed method. The tandem photodetector on poly(ethylene terephthalate) substrates exhibited low dark current and high detectivities over ∼8.8 × 10{sup 11} Jones at near infrared range at −0.5 V bias and over ∼10{sup 13} Jones near 0 bias. The critical bend radii of ∼8 mm and ∼3 mm have been demonstrated for tensile and compressive bending, respectively. The performance of photodetectors remains stable under mechanical stress, making PbSe CQD material a promise candidate for flexible infrared sensing applications.

  12. Negative differential resistance phenomena in colloidal quantum dots-based organic light-emitting diodes

    SciTech Connect

    Yang, Shengyi Zhang, Li; Yang, Dan; Zou, Bingsuo; Liu, Peng; Jiang, Yurong; Guo, Sanwei

    2014-01-20

    The influence of ligands on the electrical behavior of CdSe/ZnS core-shell colloidal quantum dots (CQDs)-based organic light-emitting diodes is presented. Negative differential resistance (NDR) phenomena at room temperature are observed from single-layer device ITO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/CQDs/Al in which the original capping ligand tri-n-octylphosphine oxide (TOPO) of CQDs is exchanged with oleylamine, as well as in both bilayer device ITO/PEDOT:PSS/CQDs/BCP(10 nm)/Al and trilayer device ITO/PEDOT:PSS/CQDs/BCP(10 nm)/Alq{sub 3}(10 nm)/Al. However, such a kind of NDR phenomenon disappears if TOPO is exchanged with hexadecylamine. Therefore, NDR phenomenon depends greatly on the ligands of the CQDs, and the origin of NDR from these devices is discussed.

  13. Surface-emitting red, green, and blue colloidal quantum dot distributed feedback lasers.

    PubMed

    Roh, Kwangdong; Dang, Cuong; Lee, Joonhee; Chen, Songtao; Steckel, Jonathan S; Coe-Sullivan, Seth; Nurmikko, Arto

    2014-07-28

    We demonstrate surface emitting distributed feedback (DFB) lasers across the red, green, and blue from densely packed colloidal quantum dot (CQD) films. The solid CQD films were deposited on periodic grating patterns to enable 2nd-order DFB lasing action at mere 120, 280, and 330 μJ/cm2 of optical pumping energy densities for red, green, and blue DFB lasers, respectively. The lasers operated in single mode operation with less than 1 nm of full-width-half-maximum. We measured far-field patterns showing high degree of spatial beam coherence. Specifically, by taking advantage of single exciton optical gain regime from our engineered CQDs, we can significantly suppress the Auger recombination to reduce lasing threshold and achieve quasi-steady state, optically pumped operation. PMID:25089497

  14. Optical Properties of CdSe Nanoparticle Assemblies

    SciTech Connect

    Huser, T; Gerion, D; Zaitseva, N; Krol, D M; Leon, F R

    2003-11-24

    We report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals were grown by slow evaporation from toluene solutions of CdSe nanocrystals in the range of 3-6 nm, produced by traditional wet-chemistry techniques. By using a confocal microscope with laser illumination, three-dimensional raster-scanning and synchronized hyper-spectral detection, we have generated spatial profiles of the fluorescence emission intensity and spectrum. The fluorescence data of the micro-crystals were compared with spectra of individual nanocrystals obtained from the same solution. The results do not support the assertion that these microcrystals consist of CdSe superlattices.

  15. Non-blinking single-photon generation with anisotropic colloidal nanocrystals: towards room-temperature, efficient, colloidal quantum sources.

    PubMed

    Pisanello, Ferruccio; Leménager, Godefroy; Martiradonna, Luigi; Carbone, Luigi; Vezzoli, Stefano; Desfonds, Pascal; Cozzoli, Pantaleo Davide; Hermier, Jean-Pierre; Giacobino, Elisabeth; Cingolani, Roberto; De Vittorio, Massimo; Bramati, Alberto

    2013-04-11

    Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability. PMID:23334905

  16. Silanization of Low-Temperature-Plasma Synthesized Silicon Quantum Dots for Production of a Tunable, Stable, Colloidal Solution

    SciTech Connect

    Anderson, I. E.; Shircliff, R. A.; Macauley, C.; Smith, D. K.; Lee, B. G.; Agrawal, S.; Stradins, P.; Collins, R. T.

    2012-02-16

    We present a method for grafting silanes onto low-temperature-plasma synthesized silicon quantum dots. The resulting solution of dots is characterized with Fourier transform infrared spectroscopy and transmission electron microscopy, and determined to be a colloidal suspension. The silane is attached at a single point on the quantum dot surface to avoid cross-linking and multilayer formation, and photoluminescence spectroscopy shows the colloidal suspension of dots is stable for over two months in air. The hydroxyl-terminated surfaces required for silanization are created by wet chemical etch, which can be used to tune the luminescence of the silicon dots in the green- to red-wavelength range. We find, however, that the wet etch cannot move the emission into the blue-wavelength range and discuss this observation in terms of the nature of etching process and origin of the emission. In addition, we discuss the photoluminescence quantum yield in the context of other passivation and synthetic techniques.

  17. Light quenching and dark states in colloidal solutions of semiconductor CdSe/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Danilov, V. V.; Panfutova, A. S.; Shilov, V. B.; Belousova, I. M.; Ermolaeva, G. M.; Khrebtov, A. I.

    2014-06-01

    The photodynamics of optical limiting in colloidal solutions of different-size CdSe/ZnS quantum dots is studied. The behavior of the dependences points to a multistage process that includes the bleaching and optical limiting stages. The limiting photodynamics is compared with luminescence dynamics of quantum dots under conditions of high-power excitation. It is shown that the optical limiting efficiency in such media is determined by the position of exciting radiation with respect to the main exciton absorption band of the quantum dot. The roles played by so-called dark states and light quenching in limiting photodynamics are discussed.

  18. Composition-dependent trap distributions in CdSe and InP quantum dots probed using photoluminescence blinking dynamics.

    PubMed

    Chung, Heejae; Cho, Kyung-Sang; Koh, Weon-Kyu; Kim, Dongho; Kim, Jiwon

    2016-07-21

    Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices. PMID:27272126

  19. Uptake of CdSe and CdSe/ZnS quantum dots into bacteria via purine-dependent mechanisms.

    PubMed

    Kloepfer, J A; Mielke, R E; Nadeau, J L

    2005-05-01

    Quantum dots (QDs) rendered water soluble for biological applications are usually passivated by several inorganic and/or organic layers in order to increase fluorescence yield. However, these coatings greatly increase the size of the particle, making uptake by microorganisms impossible. We find that adenine- and AMP-conjugated QDs are able to label bacteria only if the particles are <5 nm in diameter. Labeling is dependent upon purine-processing mechanisms, as mutants lacking single enzymes demonstrate a qualitatively different signal than do wild-type strains. This is shown for two example species, one gram negative and one gram positive. Wild-type Bacillus subtilis incubated with QDs conjugated to adenine are strongly fluorescent; very weak signal is seen in mutant cells lacking either adenine deaminase or adenosine phosphoribosyltransferase. Conversely, QD-AMP conjugates label mutant strains more efficiently than the wild type. In Escherichia coli, QD conjugates are taken up most strongly by adenine auxotrophs and are extruded from the cells over a time course of hours. No fluorescent labeling is seen in killed bacteria or in the presence of EDTA or an excess of unlabeled adenine, AMP, or hypoxanthine. Spectroscopy and electron microscopy suggest that QDs of <5 nm can enter the cells whole, probably by means of oxidative damage to the cell membrane which is aided by light. PMID:15870345

  20. Composition-dependent trap distributions in CdSe and InP quantum dots probed using photoluminescence blinking dynamics

    NASA Astrophysics Data System (ADS)

    Chung, Heejae; Cho, Kyung-Sang; Koh, Weon-Kyu; Kim, Dongho; Kim, Jiwon

    2016-07-01

    Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices.Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization

  1. Surface Induced Magnetism in Quantum Dots

    SciTech Connect

    Meulenberg, R W; Lee, J I

    2009-08-20

    The study of nanometer sized semiconductor crystallites, also known as quantum dots (QDs), has seen rapid advancements in recent years in scientific disciplines ranging from chemistry, physics, biology, materials science, and engineering. QD materials of CdSe, ZnSe, InP, as well as many others, can be prepared in the size range of 1-10 nm producing uniform, nearly monodisperse materials that are typically coated with organic molecules [1-3]. The strength of charge carrier confinement, which dictates the size-dependent properties, in these QDs depends on the nature of the material and can be correlated to the Bohr radius for the system of interest. For instance, the Bohr radius for CdSe is {approx} 5 nm, while in the more covalent structure of InP, the Bohr radius approaches {approx} 10 nm. The study of CdSe QDs has been particularly extensive during the last decade because they exhibit unique and tunable optical properties and are readily synthesized with high-crystallinity and narrow size dispersions. Although the core electronic properties of CdSe are explained in terms of the quantum confinement model, experimental efforts to elucidate the surface structure of these materials have been limited. Typically, colloidal CdSe QDs are coated with an organic surfactant, which typically consists of an organo-phosphine, -thiol, or -amine, that has the function of energetically relaxing defect states via coordination to partially coordinated surface atoms. The organic surfactant also acts to enhance carrier confinement and prevent agglomeration of the particles. Chemically, it has been shown that the bonding of the surfactant to the CdSe QD occurs through Cd atoms resulting cleavage of the Se atoms and formation of a Cd-rich (i.e. non-stoichiometric) particle [5].

  2. High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers.

    PubMed

    Kim, Gi-Hwan; García de Arquer, F Pelayo; Yoon, Yung Jin; Lan, Xinzheng; Liu, Mengxia; Voznyy, Oleksandr; Jagadamma, Lethy Krishnan; Abbas, Abdullah Saud; Yang, Zhenyu; Fan, Fengjia; Ip, Alexander H; Kanjanaboos, Pongsakorn; Hoogland, Sjoerd; Kim, Jin Young; Sargent, Edward H

    2015-11-11

    The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls. PMID:26509283

  3. Conformal fabrication of colloidal quantum dot solids for optically enhanced photovoltaics.

    PubMed

    Labelle, André J; Thon, Susanna M; Kim, Jin Young; Lan, Xinzheng; Zhitomirsky, David; Kemp, Kyle W; Sargent, Edward H

    2015-05-26

    Colloidal quantum dots (CQD) are an attractive thin-film material for photovoltaic applications due to low material costs, ease of fabrication, and size-tunable band gap. Unfortunately, today they suffer from a compromise between light absorption and photocarrier extraction, a fact that currently prevents the complete harvest of incoming above-band-gap solar photons. We have investigated the use of structured substrates and/or electrodes to increase the effective light path through the active material and found that these designs require highly conformal application of the light-absorbing films to achieve the greatest enhancement. This conformality requirement derives from the need for maximal absorption enhancement combined with shortest-distance charge transport. Here we report on a means of processing highly conformal layer-by-layer deposited CQD absorber films onto microstructured, light-recycling electrodes. Specifically, we engineer surface hydrophilicity to achieve conformal deposition of upper layers atop underlying ones. We show that only with the application of conformal coating can we achieve optimal quantum efficiency and enhanced power conversion efficiency in structured-electrode CQD cells. PMID:25880708

  4. Counterion-Mediated Ligand Exchange for PbS Colloidal Quantum Dot Superlattices

    PubMed Central

    2015-01-01

    In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing. PMID:26512884

  5. Solution-processed colloidal quantum dot photodiodes for low-cost SWIR imaging

    NASA Astrophysics Data System (ADS)

    Klem, Ethan J. D.; Lewis, Jay; Gregory, Christopher; Cunningham, Garry; Temple, Dorota

    2012-06-01

    While InGaAs-based focal plane arrays (FPAs) provide excellent detectivity and low noise for SWIR imaging applications, wider scale adoption of systems capable of working in this spectral range is limited by high costs, limited spectral response, and costly integration with Si ROIC devices. RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome these limitations of InGaAs FPAs. We have fabricated devices with quantum efficiencies exceeding 50%, and detectivities that are competitive with that of InGaAs. Dark currents of ~2 nA/cm2 were measured at temperatures compatible with solid state coolers. Additionally, by processing these devices entirely at room temperature we find them to be compatible with monolithic integration onto readout ICs, thereby removing any limitation on device size. We will show early efforts towards demonstrating a direct integration of this sensor technology onto a Si ROIC IC and describe a path towards fabricating sensors sensitive from the visible to 2200 nm at a cost comparable to that of CMOS based devices. This combination of high performance, dramatic cost reduction, and multispectral sensitivity is ideally suited to expand the use of SWIR imaging in current applications, as well as to address applications which require a multispectral sensitivity not met by existing technologies.

  6. Counterion-Mediated Ligand Exchange for PbS Colloidal Quantum Dot Superlattices.

    PubMed

    Balazs, Daniel M; Dirin, Dmitry N; Fang, Hong-Hua; Protesescu, Loredana; ten Brink, Gert H; Kooi, Bart J; Kovalenko, Maksym V; Loi, Maria Antonietta

    2015-12-22

    In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing. PMID:26512884

  7. Automated synthesis of photovoltaic-quality colloidal quantum dots using separate nucleation and growth stages.

    PubMed

    Pan, Jun; El-Ballouli, Ala'a O; Rollny, Lisa; Voznyy, Oleksandr; Burlakov, Victor M; Goriely, Alain; Sargent, Edward H; Bakr, Osman M

    2013-11-26

    As colloidal quantum dot (CQD) optoelectronic devices continue to improve, interest grows in the scaled-up and automated synthesis of high-quality materials. Unfortunately, all reports of record-performance CQD photovoltaics have been based on small-scale batch syntheses. Here we report a strategy for flow reactor synthesis of PbS CQDs and prove that it leads to solar cells having performance similar to that of comparable batch-synthesized nanoparticles. Specifically, we find that, only when using a dual-temperature-stage flow reactor synthesis reported herein, are the CQDs of sufficient quality to achieve high performance. We use a kinetic model to explain and optimize the nucleation and growth processes in the reactor. Compared to conventional single-stage flow-synthesized CQDs, we achieve superior quality nanocrystals via the optimized dual-stage reactor, with high photoluminescence quantum yield (50%) and narrow full width-half-maximum. The dual-stage flow reactor approach, with its versatility and rapid screening of multiple parameters, combined with its efficient materials utilization, offers an attractive path to automated synthesis of CQDs for photovoltaics and, more broadly, active optoelectronics. PMID:24131473

  8. Multiple exciton generation and ultrafast exciton dynamics in HgTe colloidal quantum dots.

    PubMed

    Al-Otaify, Ali; Kershaw, Stephen V; Gupta, Shuchi; Rogach, Andrey L; Allan, Guy; Delerue, Christophe; Binks, David J

    2013-10-21

    The investigation of sub-nanosecond exciton dynamics in HgTe colloidal quantum dots using ultrafast transient absorption spectroscopy is reported. The transmittance change spectrum acquired immediately after pumping is dominated by a bleach blue-shifted by ~200-300 nm from the photoluminescent emission band. Comparison with a tight-binding model of the electronic structure allows this feature to be attributed to the filling of band edge states. The form of the pump-induced transmittance transients is dependent on the excitation rate and the rate of sample stirring. For moderate pumping of stirred samples, the transmittance transients are well-described by a mono-exponential decay associated with biexciton recombination, with a lifetime of 49 ± 2 ps. For samples that are strongly-pumped or unstirred, the decay becomes bi-exponential in form, indicating that trap-related recombination has become significant. We also present a new analysis that enables fractional transmittance changes to be related to band edge occupation for samples with arbitrary optical density at the pump wavelength. This allows us to identify the occurrence of multiple exciton generation, which results in a quantum yield of 1.36 ± 0.04 for a photon energy equivalent to 3.1 times the band gap, in good agreement with the results of the model. PMID:23999734

  9. Novel Colloidal MoS2 Quantum Dot Heterojunctions on Silicon Platforms for Multifunctional Optoelectronic Devices.

    PubMed

    Mukherjee, Subhrajit; Maiti, Rishi; Katiyar, Ajit K; Das, Soumen; Ray, Samit K

    2016-01-01

    Silicon compatible wafer scale MoS2 heterojunctions are reported for the first time using colloidal quantum dots. Size dependent direct band gap emission of MoS2 dots are presented at room temperature. The temporal stability and decay dynamics of excited charge carriers in MoS2 quantum dots have been studied using time correlated single photon counting spectroscopy technique. Fabricated n-MoS2/p-Si 0D/3D heterojunctions exhibiting excellent rectification behavior have been studied for light emission in the forward bias and photodetection in the reverse bias. The electroluminescences with white light emission spectra in the range of 450-800 nm are found to be stable in the temperature range of 10-350 K. Size dependent spectral responsivity and detectivity of the heterojunction devices have been studied. The peak responsivity and detectivity of the fabricated heterojunction detector are estimated to be ~0.85 A/W and ~8 × 10(11) Jones, respectively at an applied bias of -2 V for MoS2 QDs of 2 nm mean diameter. The above values are found to be superior to the reported results on large area photodetector devices fabricated using two dimensional materials. PMID:27357596

  10. Novel Colloidal MoS2 Quantum Dot Heterojunctions on Silicon Platforms for Multifunctional Optoelectronic Devices

    PubMed Central

    Mukherjee, Subhrajit; Maiti, Rishi; Katiyar, Ajit K.; Das, Soumen; Ray, Samit K.

    2016-01-01

    Silicon compatible wafer scale MoS2 heterojunctions are reported for the first time using colloidal quantum dots. Size dependent direct band gap emission of MoS2 dots are presented at room temperature. The temporal stability and decay dynamics of excited charge carriers in MoS2 quantum dots have been studied using time correlated single photon counting spectroscopy technique. Fabricated n-MoS2/p-Si 0D/3D heterojunctions exhibiting excellent rectification behavior have been studied for light emission in the forward bias and photodetection in the reverse bias. The electroluminescences with white light emission spectra in the range of 450–800 nm are found to be stable in the temperature range of 10–350 K. Size dependent spectral responsivity and detectivity of the heterojunction devices have been studied. The peak responsivity and detectivity of the fabricated heterojunction detector are estimated to be ~0.85 A/W and ~8 × 1011 Jones, respectively at an applied bias of −2 V for MoS2 QDs of 2 nm mean diameter. The above values are found to be superior to the reported results on large area photodetector devices fabricated using two dimensional materials. PMID:27357596

  11. Chemistry of the colloidal group II-VI nanocrystal synthesis

    NASA Astrophysics Data System (ADS)

    Liu, Haitao

    In the last two decades, the field of nanoscience and nanotechnology has witnessed tremendous advancement in the synthesis and application of group II-VI colloidal nanocrystals. The synthesis based on high temperature decomposition of organometallic precursors has become one of the most successful methods of making group II-VI colloidal nanocrystals. This method is first demonstrated by Bawendi and coworkers in 1993 to prepare cadmium chalcogenide colloidal quantum dots and later extended by others to prepare other group II-VI quantum dots as well as anisotropic shaped colloidal nanocrystals, such as nanorod and tetrapod. This dissertation focuses on the chemistry of this type of nanocrystal synthesis. The synthesis of group II-VI nanocrystals was studied by characterizing the molecular structures of the precursors and products and following their time evolution in the synthesis. Based on these results, a mechanism was proposed to account for the reaction between the precursors that presumably produces monomer for the growth of nanocrystals. Theoretical study based on density functional theory calculations revealed the detailed free energy landscape of the precursor decomposition and monomer formation pathway. Based on the proposed reaction mechanism, a new synthetic method was designed that uses water as a novel reagent to control the diameter and the aspect ratio of CdSe and US nanorods.

  12. The Colloidal Stabilization of Quantum Dots: Towards Manufacturable, Efficient Solution-Processed Solar Cells

    NASA Astrophysics Data System (ADS)

    Rollny, Lisa

    Understanding colloidal stabilization can influence the design of optoelectronic devices and enable improvements to their performance and stability. For photovoltaics, important characteristics of the active layer material are high conductivity along with a minimum of recombination centers. In order to capitalize on the benefits of solution-processed materials, it is important to minimize the number of processing steps: ideally, to achieve a low-cost solution, materials would be deposited using a single process step compatible with roll-to-roll manufacturing. Prior to this work, the highest-performing colloidal quantum dots (CQD) solar cells have relied on several deposition steps that are repeated in a layer-by-layer (LBL) fashion. The purpose of these process steps has been to remove the long insulating ligands used in synthesis and replace them with short ligands that allow electrical conduction. The large number of steps combined, typically implemented via spin coating, leads to inefficient materials utilization and fails to show a path to a manufacturable solution. In this work, the first CQD solar cells were designed, built, and characterized combining state-of-art performance with scalable manufacture. Firstly, I report the first automated CQD synthesis to result in CQDs that form high-performance CQD solar cells. I analyze the CQD synthesis and by separating it into two phases---nucleation and growth phase---my insights are used to create higher-quality CQDs exhibiting enhanced monodispersity. I then proceed to develop a CQD ink: a CQD solution ready for direct deposition to form a semiconducting film exhibiting low trap state density. In early trials the CQD ink showed only limited power conversion efficiencies of 2%. I designed a new ink strategy, which I term cleavable hemiketal ligands. This novel two-component ligand strategy enables the combination of colloidal stabilization (via this longer two-component ligand) and cleavability (enabling excellent

  13. Process-Dependent Properties in Colloidally Synthesized “Giant” Core/Shell Nanocrystal Quantum Dots

    SciTech Connect

    Hollingsworth, Jennifer A.; Ghosh, Yagnaseni; Dennis, Allison M.; Mangum, Benjamin D.; Park, Young-Shin; Kundu, Janardan; Htoon, Han

    2012-06-07

    Due to their characteristic bright and stable photoluminescence, semiconductor nanocrystal quantum dots (NQDs) have attracted much interest as efficient light emitters for applications from single-particle tracking to solid-state lighting. Despite their numerous enabling traits, however, NQD optical properties are frustratingly sensitive to their chemical environment, exhibit fluorescence intermittency ('blinking'), and are susceptible to Auger recombination, an efficient nonradiative decay process. Previously, we showed for the first time that colloidal CdSe/CdS core/shell nanocrystal quantum dots (NQDs) comprising ultrathick shells (number of shell monolayers, n, > 10) grown by protracted successive ionic layer adsorption and reaction (SILAR) leads to remarkable photostability and significantly suppressed blinking behavior as a function of increasing shell thickness. We have also shown that these so-called 'giant' NQDs (g-NQDs) afford nearly complete suppression of non-radiative Auger recombination, revealed in our studies as long biexciton lifetimes and efficient multiexciton emission. The unique behavior of this core/shell system prompted us to assess correlations between specific physicochemical properties - beyond shell thickness - and functionality. Here, we demonstrate the ability of particle shape/faceting, crystalline phase, and core size to determine ensemble and single-particle optical properties (quantum yield/brightness, blinking, radiative lifetimes). Significantly, we show how reaction process parameters (surface-stabilizing ligands, ligand:NQD ratio, choice of 'inert' solvent, and modifications to the SILAR method itself) can be tuned to modify these function-dictating NQD physical properties, ultimately leading to an optimized synthetic approach that results in the complete suppression of blinking. We find that the resulting 'guiding principles' can be applied to other NQD compositions, allowing us to achieve non-blinking behavior in the near

  14. Optical and structural properties of ensembles of colloidal Ag{sub 2}S quantum dots in gelatin

    SciTech Connect

    Ovchinnikov, O. V. Smirnov, M. S.; Shapiro, B. I.; Shatskikh, T. S.; Perepelitsa, A. S.; Korolev, N. V.

    2015-03-15

    The size dependences of the absorption and luminescence spectra of ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots produced by the sol-gel method and dispersed in gelatin are analyzed. By X-ray diffraction analysis and transmission electron microscopy, the formation of core/shell nanoparticles is detected. The characteristic feature of the nanoparticles is the formation of crystalline cores, 1.5–2.0 nm in dimensions, and shells of gelatin and its complexes with the components of synthesis. The observed slight size dependence of the position of infrared photoluminescence bands (in the range 1000–1400 nm) in the ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots is explained within the context of the model of the radiative recombination of electrons localized at structural and impurity defects with free holes.

  15. Remote trap passivation in colloidal quantum dot bulk nano-heterojunctions and its effect in solution-processed solar cells.

    PubMed

    Rath, Arup K; Pelayo Garcia de Arquer, F; Stavrinadis, Alexandros; Lasanta, Tania; Bernechea, Maria; Diedenhofen, Silke L; Konstantatos, Gerasimos

    2014-07-16

    More-efficient charge collection and suppressed trap recombination in colloidal quantum dot (CQD) solar cells is achieved by means of a bulk nano-heterojunction (BNH) structure, in which p-type and n-type materials are blended on the nanometer scale. The improved performance of the BNH devices, compared with that of bilayer devices, is displayed in higher photocurrents and higher open-circuit voltages (resulting from a trap passivation mechanism). PMID:24895324

  16. Colloidal Quantum Dots and J-Aggregating Cyanine Dyes for Infrared Photodetection

    NASA Astrophysics Data System (ADS)

    Osedach, Timothy Paul

    The emergence of nanostructured semiconducting materials enables new approaches toward the realization of photodetectors that operate in the technologically important near- and short-wave infrared (NIR and SWIR) spectral ranges. In particular, organic semiconductors and colloidal quantum dots (QDs) possess numerous advantages over conventional crystalline semiconductors including highly tunable optical and electronic characteristics, the prospect for low-temperature processing, and compatibility with inexpensive and flexible substrates. Photodetectors based on such materials may lead to low-cost IR focal plane arrays for night-vision imaging as well as a multitude of novel applications in biological and chemical sensing. This thesis describes the development and detailed characterization of several photodetectors that incorporate colloidal QD and organic semiconductor thin films as active layers. The electronic properties of PbS QDs are thoroughly investigated in a field effect transistor (FET) geometry and several QD-based photoconductive structures exhibiting SWIR photosensitivity are demonstrated. We describe a novel QD-sensitized lateral heterojunction photoconductor in which the functions of optical absorption and charge transport are dissociated into different physical layers that can be independently optimized. This structure is advantageous because it obviates the need for aggressive chemical treatments to the QD film that may compromise the quality of QD surface passivation. Photovoltaic device architectures are addressed, noting their advantages of being operable without an external applied bias and at fast response speeds. We present detailed experimental and theoretical characterization of a photovoltaic structure that is sensitized at NIR wavelengths by a J-aggregating cyanine dye. The high absorption coefficient of the J-aggregate film, combined with the use of a reflective anode and optical spacer layer, enables an external quantum efficiency (EQE

  17. Group velocity dispersion of CdSSe/ZnS core-shell colloidal quantum dots measured with white light interferometry

    NASA Astrophysics Data System (ADS)

    VanEngen Spivey, Amelia G.

    2016-03-01

    We measure the group velocity dispersion coefficient of CdSSe/ZnS core-shell colloidal quantum dots in liquid suspension in the ∼700-900 nm wavelength range using a white-light Michelson interferometer. Two different sizes of dots are investigated. In both cases, the group velocity dispersion coefficient decreases with increasing wavelength above the absorption edge in the dots. For quantum dots in which the linear absorption spectrum shows clear peaks, the absorption characteristics of the dots can be used to accurately model the wavelength-dependence of the group velocity dispersion coefficient.

  18. Synthesis of colloidal InAs/ZnSe quantum dots and their quantum dot sensitized solar cell (QDSSC) application

    NASA Astrophysics Data System (ADS)

    Lee, S. H.; Jung, C.; Jun, Y.; Kim, S.-W.

    2015-11-01

    We report the synthesis of colloidal InAs/ZnSe core/shell quantum dots (QDs) by the hot injection method. InAs nanocrystals have a narrow band gap of 0.38 eV, a high absorption coefficient, and multiple exciton generation; hence, they are promising candidates for application in solar cells. However, poor coverage of the titania layer causes a low solar efficiency of ∼1.74%. We synthesized type-I InAs/ZnSe core/shell QDs as an effective solution; they are expected to have enhanced solar cell efficiency because of the different wettability of the ZnSe shell and their superior stability as compared to that of the unstable InAs core. We characterized the QDs by powder X-ray diffraction, transmission electron microscopy, and absorption and emission spectroscopy. The particle size increased from 2.6 nm to 5 nm, whereas the absorption and emission spectra exhibited a slight red shift, which is typical of type-I structured core/shell QDs. We then fabricated QD-based solar cells and investigated the cell properties, obtaining an open-circuit voltage (VOC) of 0.51 V, a short-circuit current density (JSC) of 12.4 mA/cm2, and a fill factor (FF) of 44%; the efficiency of 2.7% shows an improvement of more than 50% as compared to the values in previous reports.

  19. High fluorescence quantum efficiency of CdSe/ZnS quantum dots embedded in GPTS/TEOS-derived organic/silica hybrid colloids

    NASA Astrophysics Data System (ADS)

    Alencar, Lorena D. S.; Pilla, Viviane; Andrade, Acácio A.; Donatti, Dario A.; Vollet, Dimas R.; De Vicente, Fábio S.

    2014-04-01

    The thermo-optical properties of CdSe/ZnS core-shell quantum dots (QDs) embedded in organic/silica hybrid colloids (organic/silica sols) were measured using the thermal lens (TL) technique. GPTS/TEOS-derived organic/silica hybrid colloids were prepared by a sol-gel method from the hydrolysis reaction of 3-glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) alkoxides. TL transient measurements were performed to study the effect of the CdSe/ZnS QDs (with three different sizes ∼ 2.4, 2.9 and 4.4 nm) embedded in GPTS/TEOS-derived organic/silica sols. The thermal diffusivity, the fraction thermal load and the radiative quantum efficiency (η) were determined. Fluorescence measurements corroborate the TL results and high η values were obtained.

  20. Tuning shades of white light with multi-color quantum-dot quantum-well emitters based on onion-like CdSe ZnS heteronanocrystals

    NASA Astrophysics Data System (ADS)

    Demir, Hilmi Volkan; Nizamoglu, Sedat; Mutlugun, Evren; Ozel, Tuncay; Sapra, Sameer; Gaponik, Nikolai; Eychmüller, Alexander

    2008-08-01

    We present white light generation controlled and tuned by multi-color quantum-dot-quantum-well emitters made of onion-like CdSe/ZnS/CdSe core/shell/shell heteronanocrystals integrated on InGaN/GaN light-emitting diodes (LEDs). We demonstrate hybrid white LEDs with (x, y) tristimulus coordinates tuned from (0.26, 0.33) to (0.37, 0.36) and correlated color temperatures from 27 413 to 4192 K by controlling the number of their integrated red-green-emitting heteronanocrystals. We investigate the modification of in-film emission from these multi-layered heteronanocrystals with respect to their in-solution emission, which plays a significant role in hybrid LED applications. Our proof-of-principle experiments indicate that these complex heteronanocrystals hold promise for use as nanoluminophors in future hybrid white LEDs.

  1. Engineering of Doping and Transport for Enhanced Colloidal Quantum Dot Photovoltaics

    NASA Astrophysics Data System (ADS)

    Zhitomirsky, David

    Colloidal Quantum Dots (CQDs) are nanoscale quantum-tuned semiconductor particles suspended in solution. When deployed as optoelectronic materials, CQDs are closely packed together into thin films enabling charge transport. This also enables the formation of semiconductor junctions and contacts with other bulk semiconductor materials and metals, respectively. However, limited attention has been given to understanding the fundamental electronic behavior of these materials as bulk-like films, gaining fine control over their semiconducting properties, and then leveraging these insights to make better semiconductor devices. In this thesis, I explore two of the most fundamental concepts to CQD semiconductor device physics: charge carrier doping density and charge carrier transport. With the aid of optoelectronic simulation, I show that these are the most important paths to pursue in order to improve the photovoltaic device performance. I develop a doping density theory that I then rigorously test for the PbS CQD materials system; this theory is also applicable to other types of CQD materials. I demonstrate doping densities on the order of 10 16 cm-3 to 1018 cm-3 for both p- and n-type films. My work enables a previously unavailable p-n homojunction within one CQD materials system, and furthermore allows to grade the doping within the active absorber layer to reach power conversion efficiencies (PCEs) exceeding 7%. I then study CQD size polydispersity, and use it to investigate the details of charge transport in the rough energetic landscapes inherent to these materials. Here, I find that midgap trap elimination is the most important concept in rapidly obtaining dramatic photovoltaic performance gains. By directly measuring the diffusion length in highly coupled CQD films, and combined with optoelectronic modeling, I was able to develop a new passivation strategy achieving a record 8.5% PCE. My research serves as a roadmap for future performance improvements in CQD

  2. Multi-color colloidal quantum dot based light emitting diodes micropatterned on silicon hole transporting layers

    NASA Astrophysics Data System (ADS)

    Gopal, Ashwini; Hoshino, Kazunori; Kim, Sunmin; Zhang, Xiaojing

    2009-06-01

    We present a colloidal quantum dot based light emitting diode (QD-LED) which utilizes the p-type silicon substrate as the hole transporting layer. A microcontact printing technique was introduced to pattern self-assembled CdSe/ZnS QD films, which allowed creation of an LED with well-defined geometry suitable for monolithic integration on silicon substrates. Our QD-LED consists of multi-layers of inorganic materials: a combination of Au (thickness: 5 nm) and Ag (12 nm) as the cathode, a ZnO:SnO2 mixture (ratio 3:1, 40 nm) as the electron transporting layer, CdSe/ZnS QDs as the light emission layer, 1 nm SiO2 as an energy barrier layer, and p-type silicon as the hole transporting layer. These printed QD-LEDs are capable of multi-color emission peaked at wavelengths of 576 nm, 598 nm, and 622 nm, corresponding to sizes of the embedded QDs with the diameters of 8.4 nm, 9.0 nm, and 9.8 nm respectively. The optimal thickness of the quantum dot layers needed for light emission is characterized using atomic force microscopy: for 8.4 nm QDs, the value is 33 nm (± 5 nm) or ~4 ML (monolayers). Larger turn on voltages were measured (2, 4 and 5 V) for the smaller average particle diameters (9.8 nm, 9.0 nm and 8.4 nm, respectively). The mixture ratio of Zn and Sn was optimized (40% Zn and 25% Sn) to maintain proper hole-electron recombination at the QD layer and avoid the yellowish-white emission from ZnO/SnO2.

  3. Dynamics of Intraband and Interband Auger Processes in Colloidal Core-Shell Quantum Dots.

    PubMed

    Rabouw, Freddy T; Vaxenburg, Roman; Bakulin, Artem A; van Dijk-Moes, Relinde J A; Bakker, Huib J; Rodina, Anna; Lifshitz, Efrat; L Efros, Alexander; Koenderink, A Femius; Vanmaekelbergh, Daniël

    2015-10-27

    Conventional colloidal quantum dots (QDs) suffer from rapid energy losses by nonradiative (Auger) processes, leading to sub-ns lifetimes in all excited states but the lowest-energy single exciton. Suppression of interband Auger decay, such as biexciton Auger recombination, has been achieved with the design of heterostructured core-shell QDs. Auger-like processes are also believed to be responsible for rapid intraband hot-electron cooling in QDs. However, the simultaneous effect of shell growth on interband Auger recombination and intraband hot-electron cooling has not been addressed. Here we investigate how the growth of a CdS shell affects these two relaxation processes in CdSe/CdS core-shell QDs. Using a combination of ultrafast pump-push-probe spectroscopy on the QD ensemble and analysis of the photon statistics from single QDs, we find that Auger losses in the biexciton state are suppressed with increasing shell thickness, while hot-electron cooling remains unaffected. Calculations conducted within an eight-band k·p model confirm the experimental dependence of the biexciton Auger decay on the shell thickness, and provide insights into the factors determining the cooling rate of hot carriers. PMID:26389562

  4. Enhanced trion emission from colloidal quantum dots with photonic crystals by two-photon excitation.

    PubMed

    Xu, Xingsheng

    2013-01-01

    For colloidal quantum dots, the ongoing biggest problem is their fluorescence blinking. Until now, there is no generally accepted model for this fluorescence blinking. Here, two-photon excited fluorescence from CdSe/ZnS nanocrystals on silicon nitride photonic crystals is studied using a femtosecond laser. From analysis of the spectra and decay processes, most of the relative trion efficiency is larger than 10%, and the largest relative trion efficiency reaches 46.7%. The photonic crystals enhance the trion emission of CdSe/ZnS nanocrystals, where the enhancement is due to the coupling of the trion emission to the leaky mode of the photonic crystal slab. Moreover, the photonic crystals enhance the Auger-assisted trapping efficiency of electrons/holes to surface states, and then enhance the efficiency of the generations of charge separation and DC electric field, which modifies the trion spectrum. Therefore, a model is present for explaining the mechanism of fluorescence blinking including the effect of the environment. PMID:24231669

  5. The Influence of Doping on the Optoelectronic Properties of PbS Colloidal Quantum Dot Solids

    PubMed Central

    Papagiorgis, P.; Stavrinadis, A.; Othonos, A.; Konstantatos, G.; Itskos, G.

    2016-01-01

    We report on an extensive spectroscopic investigation of the impact of substitutional doping on the optoelectronic properties of PbS colloidal quantum dot (CQD) solids. N-doping is provided by Bi incorporation during CQD synthesis as well as post-synthetically via cation exchange reactions. The spectroscopic data indicate a systematic quenching of the excitonic absorption and luminescence and the appearance of two dopant-induced contributions at lower energies to the CQD free exciton. Temperature-dependent photoluminescence indicates the presence of temperature-activated detrapping and trapping processes of photoexcitations for the films doped during and after synthesis, respectively. The data are consistent with a preferential incorporation of the dopants at the QDs surface in the case of the cation-exchange treated films versus a more uniform doping profile in the case of in-situ Bi incorporation during synthesis. Time-resolved experiments indicate the presence of fast dopant- and excitation-dependent recombination channels attributed to Auger recombination of negatively charged excitons, formed due to excess of dopant electrons. The data indicate that apart from dopant compensation and filling of dopant induced trap states, a fraction of the Bi ionized electrons feeds the QD core states resulting in n-doping of the semiconductor, confirming reported work on devices based on such doped CQD material. PMID:26743934

  6. Effect of Chloride Passivation on Recombination Dynamics in CdTe Colloidal Quantum Dots

    PubMed Central

    Espinobarro-Velazquez, Daniel; Leontiadou, Marina A; Page, Robert C; Califano, Marco; O'Brien, Paul; Binks, David J

    2015-01-01

    Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers to produce light-emitting diodes, solar cells and other devices. The efficacy of CQDs in these applications is reduced by the non-radiative recombination associated with surface traps. Here we investigate the effect on the recombination dynamics in CdTe CQDs of the passivation of these surface traps by chloride ions. Radiative recombination dominates in these passivated CQDs, with the radiative lifetime scaling linearly with CQD volume over τr=20–55 ns. Before chloride passivation or after exposure to air, two non-radiative components are also observed in the recombination transients, with sample-dependent lifetimes typically of less than 1 ns and a few ns. The non-radiative dynamics can be explained by Auger-mediated trapping of holes and the lifetimes of this process calculated by an atomistic model are in agreement with experimental values if assuming surface oxidation of the CQDs. PMID:25630838

  7. Energy Gap Tuning and Carrier Dynamics in Colloidal Ge1-xSnx Quantum Dots.

    PubMed

    Hafiz, Shopan A; Esteves, Richard J Alan; Demchenko, Denis O; Arachchige, Indika U; Özgür, Ümit

    2016-09-01

    Optical transition energies and carrier dynamics in colloidally synthesized 2.0 ± 0.8 nm Ge1-xSnx quantum dots (x = 0.055-0.236) having visible luminescence were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopy supported by first-principles calculations. By changing Sn content from x = 0.055 to 0.236, experimentally determined HOMO-LUMO gap at 15 K was tuned from 1.88 to 1.61 eV. Considering the size and compositional variations, these values were consistent with theoretically calculated ones. At 15 K, time-resolved PL revealed slow decay of luminescence (3-27 μs), likely due to the recombination of spin-forbidden dark excitons and recombination of carriers trapped at surface states. Increasing Sn concentration to 23.6% led to 1 order of magnitude faster recombination. At 295 K, PL decays were 3 orders of magnitude faster (9-28 ns) owing to the thermal activation of bright excitons and carrier detrapping from surface states. PMID:27513723

  8. Crystal symmetry breaking and vacancies in colloidal lead chalcogenide quantum dots.

    PubMed

    Bertolotti, Federica; Dirin, Dmitry N; Ibáñez, Maria; Krumeich, Frank; Cervellino, Antonio; Frison, Ruggero; Voznyy, Oleksandr; Sargent, Edward H; Kovalenko, Maksym V; Guagliardi, Antonietta; Masciocchi, Norberto

    2016-09-01

    Size and shape tunability and low-cost solution processability make colloidal lead chalcogenide quantum dots (QDs) an emerging class of building blocks for innovative photovoltaic, thermoelectric and optoelectronic devices. Lead chalcogenide QDs are known to crystallize in the rock-salt structure, although with very different atomic order and stoichiometry in the core and surface regions; however, there exists no convincing prior identification of how extreme downsizing and surface-induced ligand effects influence structural distortion. Using forefront X-ray scattering techniques and density functional theory calculations, here we have identified that, at sizes below 8 nm, PbS and PbSe QDs undergo a lattice distortion with displacement of the Pb sublattice, driven by ligand-induced tensile strain. The resulting permanent electric dipoles may have implications on the oriented attachment of these QDs. Evidence is found for a Pb-deficient core and, in the as-synthesized QDs, for a rhombic dodecahedral shape with nonpolar {110} facets. On varying the nature of the surface ligands, differences in lattice strains are found. PMID:27295101

  9. The Influence of Doping on the Optoelectronic Properties of PbS Colloidal Quantum Dot Solids.

    PubMed

    Papagiorgis, P; Stavrinadis, A; Othonos, A; Konstantatos, G; Itskos, G

    2016-01-01

    We report on an extensive spectroscopic investigation of the impact of substitutional doping on the optoelectronic properties of PbS colloidal quantum dot (CQD) solids. N-doping is provided by Bi incorporation during CQD synthesis as well as post-synthetically via cation exchange reactions. The spectroscopic data indicate a systematic quenching of the excitonic absorption and luminescence and the appearance of two dopant-induced contributions at lower energies to the CQD free exciton. Temperature-dependent photoluminescence indicates the presence of temperature-activated detrapping and trapping processes of photoexcitations for the films doped during and after synthesis, respectively. The data are consistent with a preferential incorporation of the dopants at the QDs surface in the case of the cation-exchange treated films versus a more uniform doping profile in the case of in-situ Bi incorporation during synthesis. Time-resolved experiments indicate the presence of fast dopant- and excitation-dependent recombination channels attributed to Auger recombination of negatively charged excitons, formed due to excess of dopant electrons. The data indicate that apart from dopant compensation and filling of dopant induced trap states, a fraction of the Bi ionized electrons feeds the QD core states resulting in n-doping of the semiconductor, confirming reported work on devices based on such doped CQD material. PMID:26743934

  10. The Influence of Doping on the Optoelectronic Properties of PbS Colloidal Quantum Dot Solids

    NASA Astrophysics Data System (ADS)

    Papagiorgis, P.; Stavrinadis, A.; Othonos, A.; Konstantatos, G.; Itskos, G.

    2016-01-01

    We report on an extensive spectroscopic investigation of the impact of substitutional doping on the optoelectronic properties of PbS colloidal quantum dot (CQD) solids. N-doping is provided by Bi incorporation during CQD synthesis as well as post-synthetically via cation exchange reactions. The spectroscopic data indicate a systematic quenching of the excitonic absorption and luminescence and the appearance of two dopant-induced contributions at lower energies to the CQD free exciton. Temperature-dependent photoluminescence indicates the presence of temperature-activated detrapping and trapping processes of photoexcitations for the films doped during and after synthesis, respectively. The data are consistent with a preferential incorporation of the dopants at the QDs surface in the case of the cation-exchange treated films versus a more uniform doping profile in the case of in-situ Bi incorporation during synthesis. Time-resolved experiments indicate the presence of fast dopant- and excitation-dependent recombination channels attributed to Auger recombination of negatively charged excitons, formed due to excess of dopant electrons. The data indicate that apart from dopant compensation and filling of dopant induced trap states, a fraction of the Bi ionized electrons feeds the QD core states resulting in n-doping of the semiconductor, confirming reported work on devices based on such doped CQD material.

  11. Energy-saving quality road lighting with colloidal quantum dot nanophosphors

    NASA Astrophysics Data System (ADS)

    Erdem, Talha; Kelestemur, Yusuf; Soran-Erdem, Zeliha; Ji, Yun; Demir, Hilmi Volkan

    2014-12-01

    Here the first photometric study of road-lighting white light-emitting diodes (WLEDs) integrated with semiconductor colloidal quantum dots (QDs) is reported enabling higher luminance than conventional light sources, specifically in mesopic vision regimes essential to street lighting. Investigating over 100 million designs uncovers that quality road-lighting QD-WLEDs, with a color quality scale and color rendering index ≥85, enables 13-35% higher mesopic luminance than the sources commonly used in street lighting. Furthermore, these QD-WLEDs were shown to be electrically more efficient than conventional sources with power conversion efficiencies ≥16-29%. Considering this fact, an experimental proof-of-concept QD-WLED was demonstrated, which is the first account of QD based color conversion custom designed for street lighting applications. The obtained white LED achieved the targeted mesopic luminance levels in accordance with the road lighting standards of the USA and the UK. These results indicate that road-lighting QD-WLEDs are strongly promising for energy-saving quality road lighting.

  12. Optical and Electronic Properties of Nonconcentric PbSe/CdSe Colloidal Quantum Dots.

    PubMed

    Zaiats, Gary; Shapiro, Arthur; Yanover, Diana; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2015-07-01

    Lead chalcogenide colloidal quantum dots are attractive candidates for applications operating in the near infrared spectral range. However, their function is forestalled by limited stability under ambient conditions. Prolonged temperature-activated cation-exchange of Cd(2+) for Pb(2+) forms PbSe/CdSe core/shell heterostructures, unveiling a promising surface passivation route and a method to modify the dots' electronic properties. Here, we follow early stages of an-exchange process, using spectroscopic and structural characterization tools, as well as numerical calculations. We illustrate that preliminary-exchange stages involve the formation of nonconcentric heterostructures, presumably due to a facet selective reaction, showing a pronounced change in the optical properties upon the increase of the degree of nonconcentricity or/and plausible creation of core/shell interfacial alloying. However, progressive-exchange stages lead to rearrangement of the shell segment into uniform coverage, providing tolerance to oxygen exposure with a spectral steadiness already on the formation of a monolayer shell. PMID:26266716

  13. The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot

    SciTech Connect

    Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.

    2006-05-10

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.

  14. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    SciTech Connect

    Patty, Kira; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Sadeghi, Seyed M.; Mao, Chuanbin

    2014-09-21

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  15. Visible-Light Photocatalyzed Cross-Linking of Diacetylene Ligands by Quantum Dots to Improve Their Aqueous Colloidal Stability

    PubMed Central

    2015-01-01

    Ligand cross-linking is known to improve the colloidal stability of nanoparticles, particularly in aqueous solutions. However, most cross-linking is performed chemically, in which it is difficult to limit interparticle cross-linking, unless performed at low concentrations. Photochemical cross-linking is a promising approach but usually requires ultraviolet (UV) light to initiate. Using such high-energy photons can be harmful to systems in which the ligand–nanoparticle bond is fairly weak, as is the case for the commonly used semiconductor quantum dots (QDs). Here, we introduce a novel approach to cross-link thiolated ligands on QDs by utilizing the photocatalytic activity of QDs upon absorbing visible light. We show that using visible light leads to better ligand cross-linking by avoiding the problem of ligand dissociation that occurs upon UV light exposure. Once cross-linked, the ligands significantly enhance the colloidal stability of those same QDs that facilitated cross-linking. PMID:25036275

  16. Synthesis of highly luminescent mercaptosuccinic acid-coated CdSe nanocrystals under atmospheric conditions.

    PubMed

    Dong, Meiting; Xu, Jingyi; Liu, Shuxian; Zhou, Ying; Huang, Chaobiao

    2014-11-01

    Here we report a facile one-pot method for the preparation of high-quality CdSe nanocrystals (NCs) in aqueous solution under an air atmosphere. Compared with the traditional use of NaHSe or H2 Se, the more stable sodium selenite is utilized as the Se source for preparing highly luminescent CdSe nanocrystals. By using mercaptosuccinic acid (MSA) as the capping agent and borate-citrate acid as the buffering solution, CdSe nanocrystals with high quantum yield (up to 70%) have been synthesized conveniently. The influence of different experimental parameters, such as the pH of the precursor solution, the molar ratio of Cd(2+) to Na2 SeO3 and Cd(2+) to MSA on the CdSe nanocrystals, has been systematically investigated. The prepared CdSe NCs were spherical with a size of ~ 5 nm. PMID:24639040

  17. Sensitive and selective determining ascorbic acid and activity of alkaline phosphatase based on electrochemiluminescence of dual-stabilizers-capped CdSe quantum dots in carbon nanotube-nafion composite.

    PubMed

    Ma, Xiaolong; Zhang, Xin; Guo, Xinli; Kang, Qi; Shen, Dazhong; Zou, Guizheng

    2016-07-01

    Sensitive and selective determining bio-related molecule and enzyme play an important role in designing novel procedure for biological sensing and clinical diagnosis. Herein, we found that dual-stabilizers-capped CdSe quantum dots (QDs) in composite film of multi-walled carbon nanotubes (CNTs) and Nafion, displaying eye-visible monochromatic electrochemiluminescence (ECL) with fwhm of 37nm, which offers promising ECL signal for detecting ascorbic acid (AA) as well as the activity of alkaline phosphatase (ALP) in biological samples. It was also shown that the dual-stabilizers-capped CdSe QDs can preserve their highly passivated surface states with prolonged lifetime of excited states in Nafion mixtures, and facilitate electron-transfer ability of Nafion film along with CNTs. Compared with the QDs/GCE, the ECL intensity is enhanced 1.8 times and triggering potential shifted to lower energy by 0.12V on the CdSe-CNTs-Nafion/GCE. The ECL quenching degree increases with increasing concentration of AA in the range of 0.01-30nM with a limit of detection (LOD) of 5pM. The activity of ALP was determined indirectly according to the concentration of AA, generated in the hydrolysis reaction of l-ascorbic acid 2-phosphate sesquimagnesium (AA-P) in the presence of ALP as a catalyst, with an LOD of 1μU/L. The proposed strategy is favorable for developing simple ECL sensor or device with high sensitivity, spectral resolution and less electrochemical interference. PMID:27154663

  18. Origins of photoluminescence decay kinetics in CdTe colloidal quantum dots.

    PubMed

    Califano, Marco

    2015-03-24

    Recent experimental studies have identified at least two nonradiative components in the fluorescence decay of solutions of CdTe colloidal quantum dots (CQDs). The lifetimes reported by different groups, however, differed by orders of magnitude, raising the question of whether different types of traps were at play in the different samples and experimental conditions and even whether different types of charge carriers were involved in the different trapping processes. Considering that the use of these nanomaterials in biology, optoelectronics, photonics, and photovoltaics is becoming widespread, such a gap in our understanding of carrier dynamics in these systems needs addressing. This is what we do here. Using the state-of-the-art atomistic semiempirical pseudopotential method, we calculate trapping times and nonradiative population decay curves for different CQD sizes considering up to 268 surface traps. We show that the seemingly discrepant experimental results are consistent with the trapping of the hole at unsaturated Te bonds on the dot surface in the presence of different dielectric environments. In particular, the observed increase in the trapping times following air exposure is attributed to the formation of an oxide shell on the dot surface, which increases the dielectric constant of the dot environment. Two types of traps are identified, depending on whether the unsaturated bond is single (type I) or part of a pair of dangling bonds on the same Te atom (type II). The energy landscape relative to transitions to these traps is found to be markedly different in the two cases. As a consequence, the trapping times associated with the different types of traps exhibit a strikingly contrasting sensitivity to variations in the dot environment. Based on these characteristics, we predict the presence of a sub-nanosecond component in all photoluminescence decay curves of CdTe CQDs in the size range considered here if both trap types are present. The absence of such a

  19. Size dependence of negative trion Auger recombination in photodoped CdSe nanocrystals.

    PubMed

    Cohn, Alicia W; Rinehart, Jeffrey D; Schimpf, Alina M; Weaver, Amanda L; Gamelin, Daniel R

    2014-01-01

    We report a systematic investigation of the size dependence of negative trion (T(-)) Auger recombination rates in free-standing colloidal CdSe nanocrystals. Colloidal n-type CdSe nanocrystals of various radii have been prepared photochemically, and their trion decay dynamics have been measured using time-resolved photoluminescence spectroscopy. Trion Auger time constants spanning 3 orders of magnitude are observed, ranging from 57 ps (radius R = 1.4 nm) to 2.2 ns (R = 3.2 nm). The data reveal a substantially stronger size dependence than found for bi- or multiexciton Auger recombination in CdSe or other semiconductor nanocrystals, scaling in proportion to R(4.3). PMID:24328385

  20. Electronic and excitonic processes in light-emitting devices based on organic materials and colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Anikeeva, P. O.; Madigan, C. F.; Halpert, J. E.; Bawendi, M. G.; Bulović, V.

    2008-08-01

    We investigate the mechanism of operation of hybrid organic/colloidal quantum dot light emitting devices (QD-LEDs). Novel quantum dot (QD) deposition methods allow us to change the location of an emissive QD monolayer within a QD-LED multilayer structure. We find that the quantum efficiency of devices improves by >50% upon imbedding QD monolayers into the hole transporting layer <10nm away from the interface between hole and electron transporting layers. We consider two possible mechanisms responsible for this improvement: one based on a charge injection model of the device operation and the other based on an exciton energy-transfer model. In order to differentiate between the two suggested mechanisms, we fabricate a set of structures that enable control over charge injection into colloidal QDs. We find that the dominant process limiting QD-LED efficiency is charging of the QDs by trapped electrons. We demonstrate that with the set of organic materials implemented in this study, device efficiency is increased by maximizing energy transfer from organics to QDs and by limiting direct charge injection that contributes to QD charging.

  1. Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots.

    PubMed

    Meinardi, Francesco; McDaniel, Hunter; Carulli, Francesco; Colombo, Annalisa; Velizhanin, Kirill A; Makarov, Nikolay S; Simonutti, Roberto; Klimov, Victor I; Brovelli, Sergio

    2015-10-01

    Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to colouring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymerized poly(lauryl methacrylate), we obtain freestanding, colourless slabs that introduce no distortion to perceived colours and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state associated with a native defect. PMID:26301902

  2. Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Meinardi, Francesco; McDaniel, Hunter; Carulli, Francesco; Colombo, Annalisa; Velizhanin, Kirill A.; Makarov, Nikolay S.; Simonutti, Roberto; Klimov, Victor I.; Brovelli, Sergio

    2015-10-01

    Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to colouring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymerized poly(lauryl methacrylate), we obtain freestanding, colourless slabs that introduce no distortion to perceived colours and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state associated with a native defect.

  3. Suppression of dark current through barrier engineer for solution-processed colloidal quantum-dots infrared photodetectors

    SciTech Connect

    Jiang, Zhenyu E-mail: jianxu@engr.psu.edu; Liu, Yan; Mo, Chen; Wang, Li; Atalla, Mahmoud R. M.; Liu, Jie; Kurhade, Kandhar K.; Xu, Jian E-mail: jianxu@engr.psu.edu; Hu, Wenjia; Zhang, Wenjun; You, Guanjun; Zhang, Yu

    2015-08-31

    In an attempt to suppress the dark current, the barrier layer engineer for solution-processed PbSe colloidal quantum-dot (CQD) photodetectors has been investigated in the present study. It was found that the dark current can be significantly suppressed by implementing two types of carrier blocking layers, namely, hole blocking layer and electron blocking layer, sandwiched in between two active PbSe CQD layers. Meanwhile no adverse impact has been observed for the photo current. Our study suggests that this improvement resides on the transport pathway created via carrier recombination at intermediate layer, which provides wide implications for the suppression of dark current for infrared photodetectors.

  4. Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier

    SciTech Connect

    Ip, Alexander H.; Labelle, André J.; Sargent, Edward H.

    2013-12-23

    Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells.

  5. Acid-free sol-gel fabrication of glass thin films embedded with II-VI colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Jani, Hemang; Duan, Lingze

    2015-01-01

    II-VI colloidal quantum dots (QDs) are ideal for optical sensors thanks to their high fluorescent brightness and good size uniformity. However, embedding colloidal QDs into a glass matrix with the standard sol-gel process leads to the QDs being damaged by the acid catalyst. Here, we report an acid-free sol-gel technique, which proves to be both simple and effective in fabricating silica glass thin films embedded with commercial II-VI colloidal QDs. Octadecylamine ligands are used as a bifunctional aid to not only stabilize the QDs in solution, but also assist the formation of the SiO2 gel. We demonstrate that high-quality QD-embedded glass thin films can be developed with this technique, and our fluorescent tests indicate that, except for a small blueshift in the emission spectrum, the QDs are very well preserved through the sol-gel process. This method offers a fast and low-cost path towards thin-film QD sensors with good mechanical and thermal stabilities, which are desirable for applications involving highly focused laser beams, such as ultrafast nanophotonics.

  6. Infrared Photodetection Based on Colloidal Quantum-Dot Films with High Mobility and Optical Absorption up to THz.

    PubMed

    Lhuillier, Emmanuel; Scarafagio, Marion; Hease, Patrick; Nadal, Brice; Aubin, Hervé; Xu, Xiang Zhen; Lequeux, Nicolas; Patriarche, Gilles; Ithurria, Sandrine; Dubertret, Benoit

    2016-02-10

    Infrared thermal imaging devices rely on narrow band gap semiconductors grown by physical methods such as molecular beam epitaxy and chemical vapor deposition. These technologies are expensive, and infrared detectors remain limited to defense and scientific applications. Colloidal quantum dots (QDs) offer a low cost alternative to infrared detector by combining inexpensive synthesis and an ease of processing, but their performances are so far limited, in terms of both wavelength and sensitivity. Herein we propose a new generation of colloidal QD-based photodetectors, which demonstrate detectivity improved by 2 orders of magnitude, and optical absorption that can be continuously tuned between 3 and 20 μm. These photodetectors are based on the novel synthesis of n-doped HgSe colloidal QDs whose size can be tuned continuously between 5 and 40 nm, and on their assembly into solid nanocrystal films with mobilities that can reach up to 100 cm(2) V(-1) s(-1). These devices can be operated at room temperature with the same level of performance as the previous generation of devices when operated at liquid nitrogen temperature. HgSe QDs can be synthesized in large scale (>10 g per batch), and we show that HgSe films can be processed to form a large scale array of pixels. Taken together, these results pave the way for the development of the next generation mid- and far-infrared low-cost detectors and camera. PMID:26753599

  7. "Darker-than-black" PbS quantum dots: enhancing optical absorption of colloidal semiconductor nanocrystals via short conjugated ligands.

    PubMed

    Giansante, Carlo; Infante, Ivan; Fabiano, Eduardo; Grisorio, Roberto; Suranna, Gian Paolo; Gigli, Giuseppe

    2015-02-11

    Colloidal quantum dots (QDs) stand among the most attractive light-harvesting materials to be exploited for solution-processed optoelectronic applications. To this aim, quantitative replacement of the bulky electrically insulating ligands at the QD surface coming from the synthetic procedure is mandatory. Here we present a conceptually novel approach to design light-harvesting nanomaterials demonstrating that QD surface modification with suitable short conjugated organic molecules permits us to drastically enhance light absorption of QDs, while preserving good long-term colloidal stability. Indeed, rational design of the pendant and anchoring moieties, which constitute the replacing ligand framework leads to a broadband increase of the optical absorbance larger than 300% for colloidal PbS QDs also at high energies (>3.1 eV), which could not be predicted by using formalisms derived from effective medium theory. We attribute such a drastic absorbance increase to ground-state ligand/QD orbital mixing, as inferred by density functional theory calculations; in addition, our findings suggest that the optical band gap reduction commonly observed for PbS QD solids treated with thiol-terminating ligands can be prevalently ascribed to 3p orbitals localized on anchoring sulfur atoms, which mix with the highest occupied states of the QDs. More broadly, we provide evidence that organic ligands and inorganic cores are inherently electronically coupled materials thus yielding peculiar chemical species (the colloidal QDs themselves), which display arising (opto)electronic properties that cannot be merely described as the sum of those of the ligand and core components. PMID:25574692

  8. Preparation of SnS2 colloidal quantum dots and their application in organic/inorganic hybrid solar cells

    PubMed Central

    2011-01-01

    Dispersive SnS2 colloidal quantum dots have been synthesized via hot-injection method. Hybrid photovoltaic devices based on blends of a conjugated polymer poly[2-methoxy-5-(3",7"dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and crystalline SnS2 quantum dots as electron acceptor have been studied. Photoluminescence measurement has been performed to study the surfactant effect on the excitons splitting process. The photocurrent of solar cells with the hybrid depends greatly on the ligands exchange as well as the device heat treatment. AFM characterization has demonstrated morphology changes happening upon surfactant replacement and annealing, which can explain the performance variation of hybrid solar cells. PMID:21711811

  9. Topological colloids.

    PubMed

    Senyuk, Bohdan; Liu, Qingkun; He, Sailing; Kamien, Randall D; Kusner, Robert B; Lubensky, Tom C; Smalyukh, Ivan I

    2013-01-10

    Smoke, fog, jelly, paints, milk and shaving cream are common everyday examples of colloids, a type of soft matter consisting of tiny particles dispersed in chemically distinct host media. Being abundant in nature, colloids also find increasingly important applications in science and technology, ranging from direct probing of kinetics in crystals and glasses to fabrication of third-generation quantum-dot solar cells. Because naturally occurring colloids have a shape that is typically determined by minimization of interfacial tension (for example, during phase separation) or faceted crystal growth, their surfaces tend to have minimum-area spherical or topologically equivalent shapes such as prisms and irregular grains (all continuously deformable--homeomorphic--to spheres). Although toroidal DNA condensates and vesicles with different numbers of handles can exist and soft matter defects can be shaped as rings and knots, the role of particle topology in colloidal systems remains unexplored. Here we fabricate and study colloidal particles with different numbers of handles and genus g ranging from 1 to 5. When introduced into a nematic liquid crystal--a fluid made of rod-like molecules that spontaneously align along the so-called 'director'--these particles induce three-dimensional director fields and topological defects dictated by colloidal topology. Whereas electric fields, photothermal melting and laser tweezing cause transformations between configurations of particle-induced structures, three-dimensional nonlinear optical imaging reveals that topological charge is conserved and that the total charge of particle-induced defects always obeys predictions of the Gauss-Bonnet and Poincaré-Hopf index theorems. This allows us to establish and experimentally test the procedure for assignment and summation of topological charges in three-dimensional director fields. Our findings lay the groundwork for new applications of colloids and liquid crystals that range from

  10. Cobalt-doped cadmium selenide colloidal nanowires.

    PubMed

    Li, Zhen; Du, Ai Jun; Sun, Qiao; Aljada, Muhsen; Cheng, Li Na; Riley, Mark J; Zhu, Zhong Hua; Cheng, Zhen Xiang; Wang, Xiao Lin; Hall, Jeremy; Krausz, Elmars; Qiao, Shi Zhang; Smith, Sean C; Lu, Gao Qing Max

    2011-11-21

    Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires. PMID:21975534

  11. Picosecond Dynamics of Excitonic Magnetic Polarons in Colloidal Diffusion-Doped Cd(1-x)Mn(x)Se Quantum Dots.

    PubMed

    Nelson, Heidi D; Bradshaw, Liam R; Barrows, Charles J; Vlaskin, Vladimir A; Gamelin, Daniel R

    2015-11-24

    Spontaneous magnetization is observed at zero magnetic field in photoexcited colloidal Cd(1-x)Mn(x)Se (x = 0.13) quantum dots (QDs) prepared by diffusion doping, reflecting strong Mn(2+)-exciton exchange coupling. The picosecond dynamics of this phenomenon, known as an excitonic magnetic polaron (EMP), are examined using a combination of time-resolved photoluminescence, magneto-photoluminescence, and Faraday rotation (TRFR) spectroscopies, in conjunction with continuous-wave absorption, magnetic circular dichroism (MCD), and magnetic circularly polarized photoluminescence (MCPL) spectroscopies. The data indicate that EMPs form with random magnetization orientations at zero external field, but their formation can be directed by an external magnetic field. After formation, however, external magnetic fields are unable to reorient the EMPs within the luminescence lifetime, implicating anisotropy in the EMP potential-energy surfaces. TRFR measurements in a transverse magnetic field reveal rapid (<5 ps) spin transfer from excitons to Mn(2+) followed by coherent EMP precession at the Mn(2+) Larmor frequency for over a nanosecond. A dynamical TRFR phase inversion is observed during EMP formation attributed to the large shifts in excitonic absorption energies during spontaneous magnetization. Partial optical orientation of the EMPs by resonant circularly polarized photoexcitation is also demonstrated. Collectively, these results highlight the extraordinary physical properties of colloidal diffusion-doped Cd(1-x)Mn(x)Se QDs that result from their unique combination of strong quantum confinement, large Mn(2+) concentrations, and relatively narrow size distributions. The insights gained from these measurements advance our understanding of spin dynamics and magnetic exchange in colloidal doped semiconductor nanostructures, with potential ramifications for future spin-based information technologies. PMID:26417918

  12. Degenerate four-wave mixing and two-photon induced gratings in colloidal quantum dots CdSe/ZnS

    NASA Astrophysics Data System (ADS)

    Smirnov, A. M.; Kozlova, M. V.; Dneprovskii, V. S.

    2015-05-01

    The features of nonlinear and electro-optical processes has been discovered in the case of two-photon resonant excitation of the excitons in colloidal CdSe/ZnS quantum dots. Self-diffraction arises for two laser beams intersecting in the cell with colloidal CdSe/ZnS quantum dots (QDs) due to the dynamic phase grating formatting. The calculated induced change in the refractive is sufficient to form a phase diffraction grating. Such a large value of χ(3) as compared to the third-order nonlinear susceptibility for the solvent (hexane) is due to the increase in χ(3) occurring when the intermediate resonance is attained in a medium transparent for laser radiation. In order to identify physical processes responsible for the induced grating formation and the diffraction efficiency self-diffracted pulse intensity dependences on the incident pulse intensity were measured for two samples of colloidal QD CdSe/ZnS, which frequency of the fundamental exciton transition is tuned to the high-frequency and low-frequency region from the double laser frequency. The discovered cubic dependence of the self-diffracted pulse intensity on the incident pulse intensity was explained by four-wave mixing process. Discovered above 5-th index of power dependence of the self-diffracted pulse intensity on the excitation pulses intensity we explained by the increasing magnitude of two-photon absorption (due to shifting of two photons energy of laser radiation to the exact exciton absorption resonance by red Stark shift of the exciton absorption), accompanied by the growth absorption by two-photon excited carriers that leads to the induced amplitude grating formation in addition to the phase grating.

  13. Low-cost photovoltaics: Luminescent solar concentrators and colloidal quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Leow, Shin Woei

    /emission spectra of an organic luminescent dye (LR305), the transmission coefficient and refractive index of acrylic as parameters that describe the system. Simulations suggest that for LR305, 8-10cm of luminescent material surrounding the PV cell yields the highest increase in power gain per unit area of LSC added, thereby determining the ideal spacing between PV cells in the panel. The model also predicts that for different PV cell dimensions, there exists an optimum waveguide thickness which efficiently transports photon collected by the waveguide to the PV cell with minimal loss, and maintains an even distribution of photons across the cell surface. For the case of the 12.5 by 1cm rectangular cells used in this work, the calculated waveguide thickness is 3mm. For larger cells, every 1cm increment in PV cell width should be accompanied by a 0.75mm increase in waveguide thickness to preserve peak performance. In line with the goal of pushing for cost competitive photovoltaics, the last part of this work shifts to the study of colloidal quantum dot solar cells. A combination of low temperature, highly scalable fabrication process and reduced material usage for thin films offers us a means to produce flexible and cheap solar cells. Tagging on to existing work already performed on germanium quantum dot solar cells, additional work was carried out to further characterize the material. The effect of film thickness, nano-particle surface conditions and thermal anneal were investigated. There is evidence to suggest that the quantum dot devices contain high levels of parasitic resistances. Short circuit current densities increase by up to two times with two spin-cast layers compared to four, leading to the conjecture that charge carrier life time is low with high levels of recombination. Annealing to improve carrier mobility produces devices with current densities up to 301microA, a fourfold increase, but output voltages saw a sharp decrease from 0.12V to 0.015V. In tandem with the work

  14. Low-cost photovoltaics: Luminescent solar concentrators and colloidal quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Leow, Shin Woei

    /emission spectra of an organic luminescent dye (LR305), the transmission coefficient and refractive index of acrylic as parameters that describe the system. Simulations suggest that for LR305, 8-10cm of luminescent material surrounding the PV cell yields the highest increase in power gain per unit area of LSC added, thereby determining the ideal spacing between PV cells in the panel. The model also predicts that for different PV cell dimensions, there exists an optimum waveguide thickness which efficiently transports photon collected by the waveguide to the PV cell with minimal loss, and maintains an even distribution of photons across the cell surface. For the case of the 12.5 by 1cm rectangular cells used in this work, the calculated waveguide thickness is 3mm. For larger cells, every 1cm increment in PV cell width should be accompanied by a 0.75mm increase in waveguide thickness to preserve peak performance. In line with the goal of pushing for cost competitive photovoltaics, the last part of this work shifts to the study of colloidal quantum dot solar cells. A combination of low temperature, highly scalable fabrication process and reduced material usage for thin films offers us a means to produce flexible and cheap solar cells. Tagging on to existing work already performed on germanium quantum dot solar cells, additional work was carried out to further characterize the material. The effect of film thickness, nano-particle surface conditions and thermal anneal were investigated. There is evidence to suggest that the quantum dot devices contain high levels of parasitic resistances. Short circuit current densities increase by up to two times with two spin-cast layers compared to four, leading to the conjecture that charge carrier life time is low with high levels of recombination. Annealing to improve carrier mobility produces devices with current densities up to 301microA, a fourfold increase, but output voltages saw a sharp decrease from 0.12V to 0.015V. In tandem with the work

  15. Efficient cw lasing in a Cr{sup 2+}:CdSe crystal

    SciTech Connect

    Akimov, V A; Kozlovskii, V I; Korostelin, Yu V; Landman, A I; Podmar'kov, Yu P; Skasyrsky, Ya K; Frolov, M P

    2007-11-30

    Continuous wave lasing in a Cr{sup 2+}:CdSe crystal is obtained for the first time. The Cr{sup 2+}:CdSe crystal pumped by a 1.908-{mu}m thulium fibre laser generated 1.07 W at 2.623 {mu}m with the quantum slope efficiency with respect to the absorbed power equal to 60%. (letters)

  16. Purification non-aqueous solution of quantum dots CdSe- CdS-ZnS from excess organic substance-stabilizer by use PE- HD membrane

    NASA Astrophysics Data System (ADS)

    Kosolapova, K.; Al-Alwani, A.; Gorbachev, I.; Glukhovskoy, E.

    2015-11-01

    Recently, a new simple method for the purification of CdSe-CdS-ZnS quantum dots by using membrane filtration, the filtration process, successfully separated the oleic acid from quantum dots through membranes purification after synthesis; purification of quantum dots is a very significant part of post synthetical treatment that determines the properties of the material. We explore the possibilities of the Langmuir-Blodgett technique to make such layers, using quantum dots as a model system. The Langmuir monolayer of quantum dots were then investigated the surface pressure-area isotherm. From isotherm, we found the surface pressure monolayer changed with time.

  17. Cl-capped CdSe nanocrystals via in situ generation of chloride anions

    NASA Astrophysics Data System (ADS)

    Palencia, Cristina; Lauwaet, Koen; de La Cueva, Leonor; Acebrón, María; Conde, Julio J.; Meyns, Michaela; Klinke, Christian; Gallego, José M.; Otero, Roberto; Juárez, Beatriz H.

    2014-05-01

    Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance (1H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio.Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim

  18. Colloidal PbSe quantum dot-solution-filled liquid-core optical fiber for 1.55 μm telecommunication wavelengths.

    PubMed

    Zhang, Lei; Zhang, Yu; Kershaw, Steve V; Zhao, Yanhui; Wang, Yu; Jiang, Yongheng; Zhang, Tieqiang; Yu, William W; Gu, Pengfei; Wang, Yiding; Zhang, Hanzhuang; Rogach, Andrey L

    2014-03-14

    We have studied the optical properties of PbSe colloidal quantum dot-solution filled hollow core multimode silica waveguides as a function of quantum dot-solution concentration, waveguide length, optical pump power and choice of organic solvent in order to establish the conditions to maximize near infrared spontaneous emission intensities. The optical performance was compared and showed good agreement with a simple three level system model for the quantum dots confined in an optical waveguide. Near infrared absorption-free solvent of tetrachlorethylene was confirmed to be a good candidate for the waveguide medium due to the enhancement of output intensity from the liquid-core fiber compared to the performance in toluene-based fiber. This approach demonstrates a useful method for early characterization of quantum dot materials in a waveguide test-bed with minimal material processing on the colloidal nanoparticles. PMID:24532174

  19. Colloidal PbSe quantum dot-solution-filled liquid-core optical fiber for 1.55 μm telecommunication wavelengths

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Zhang, Yu; Kershaw, Steve V.; Zhao, Yanhui; Wang, Yu; Jiang, Yongheng; Zhang, Tieqiang; Yu, William W.; Gu, Pengfei; Wang, Yiding; Zhang, Hanzhuang; Rogach, Andrey L.

    2014-03-01

    We have studied the optical properties of PbSe colloidal quantum dot-solution filled hollow core multimode silica waveguides as a function of quantum dot-solution concentration, waveguide length, optical pump power and choice of organic solvent in order to establish the conditions to maximize near infrared spontaneous emission intensities. The optical performance was compared and showed good agreement with a simple three level system model for the quantum dots confined in an optical waveguide. Near infrared absorption-free solvent of tetrachlorethylene was confirmed to be a good candidate for the waveguide medium due to the enhancement of output intensity from the liquid-core fiber compared to the performance in toluene-based fiber. This approach demonstrates a useful method for early characterization of quantum dot materials in a waveguide test-bed with minimal material processing on the colloidal nanoparticles.

  20. Intracellular Biosynthesis of Fluorescent CdSe Quantum Dots in Bacillus subtilis: A Strategy to Construct Signaling Bacterial Probes for Visually Detecting Interaction Between Bacillus subtilis and Staphylococcus aureus.

    PubMed

    Yan, Zheng-Yu; Ai, Xiao-Xia; Su, Yi-Long; Liu, Xin-Ying; Shan, Xiao-Hui; Wu, Sheng-Mei

    2016-02-01

    In this work, fluorescent Bacillus subtilis (B. subtilis) cells were developed as probes for imaging applications and to explore behaviorial interaction between B. subtilis and Staphylococcus aureus (S. aureus). A novel biological strategy of coupling intracellular biochemical reactions for controllable biosynthesis of CdSe quantum dots by living B. subtilis cells was demonstrated, through which highly luminant and photostable fluorescent B. subtilis cells were achieved with good uniformity. With the help of the obtained fluorescent B. subtilis cells probes, S. aureus cells responded to co-cultured B. subtilis and to aggregate. The degree of aggregation was calculated and nonlinearly fitted to a polynomial model. Systematic investigations of their interactions implied that B. subtilis cells inhibit the growth of neighboring S. aureus cells, and this inhibition was affected by both the growth stage and the amount of surrounding B. subtilis cells. Compared to traditional methods of studying bacterial interaction between two species, such as solid culture medium colony observation and imaging mass spectrometry detection, the procedures were more simple, vivid, and photostable due to the efficient fluorescence intralabeling with less influence on the cells' surface, which might provide a new paradigm for future visualization of microbial behavior. PMID:26687198

  1. Uniform Thin Films of CdSe and CdSe(ZnS) Core(shell) Quantum Dots by Sol-Gel Assembly: Enabling Photoelectrochemical Characterization and Electronic Applications

    PubMed Central

    Korala, Lasantha; Wang, Zhijie; Liu, Yi; Maldonado, Stephen; Brock, Stephanie L.

    2013-01-01

    Optoelectronic properties of quantum dot (QD) films are limited by (1) poor interfacial chemistry and (2) non-radiative recombination due to surface traps. To address these performance issues, sol-gel methods are applied to fabricate thin films of CdSe and core(shell) CdSe(ZnS) QDs. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with chemical analysis confirms that the surface of the QDs in the sol-gel thin films are chalcogen-rich, consistent with an oxidative-induced gelation mechanism in which connectivity is achieved by formation of dichalcogenide covalent linkages between particles. The ligand removal and assembly process is probed by thermogravimetric, spectroscopic and microscopic studies. Further enhancement of inter-particle coupling via mild thermal annealing, which removes residual ligands and reinforces QD connectivity, results in QD sol-gel thin films with superior charge transport properties, as shown by a dramatic enhancement of electrochemical photocurrent under white light illumination relative to thin films composed of ligand-capped QDs. A more than 2-fold enhancement in photocurrent, and a further increase in photovoltage can be achieved by passivation of surface defects via overcoating with a thin ZnS shell. The ability to tune interfacial and surface characteristics for the optimization of photophysical properties suggests that the sol-gel approach may enable formation of QD thin films suitable for a range of optoelectronic applications. PMID:23350924

  2. Controllable in situ photo-assisted chemical deposition of CdSe quantum dots on ZnO/CdS nanorod arrays and its photovoltaic application.

    PubMed

    Wang, Xinwei; Liu, Hong; Shen, Wenzhong

    2016-02-26

    Compound semiconductors have been widely applied in the energy field as light-harvesting materials, conducting substrates and other functional parts. Nevertheless, to effectively grow them in various forms toward objective applications, limitations have often been met to achieving high growth rate, simplicity of method and controllability of growing processes simultaneously. In this work, we have grown a uniform CdSe layer on ZnO/CdS nanorod arrays by a novel in situ photo-assisted chemical deposition method. The morphology and quality of the as-formed material could be significantly influenced by tuning the optical parameters of the injected light. Due to the effect of injected light on the key reactions during the growth, a modified natural light with removal of the UV and IR components seems to be more suitable than monochromic light. An efficiency of 3.59% was achieved without any additional treatment, significantly higher than the efficiency of 2.88% of the sample by conventional CBD method under similar conditions with growth rate one order of magnitude higher. In general, the result has suggested its potential importance for other compound materials and opto-electronic devices. PMID:26821250

  3. Controllable in situ photo-assisted chemical deposition of CdSe quantum dots on ZnO/CdS nanorod arrays and its photovoltaic application

    NASA Astrophysics Data System (ADS)

    Wang, Xinwei; Liu, Hong; Shen, Wenzhong

    2016-02-01

    Compound semiconductors have been widely applied in the energy field as light-harvesting materials, conducting substrates and other functional parts. Nevertheless, to effectively grow them in various forms toward objective applications, limitations have often been met to achieving high growth rate, simplicity of method and controllability of growing processes simultaneously. In this work, we have grown a uniform CdSe layer on ZnO/CdS nanorod arrays by a novel in situ photo-assisted chemical deposition method. The morphology and quality of the as-formed material could be significantly influenced by tuning the optical parameters of the injected light. Due to the effect of injected light on the key reactions during the growth, a modified natural light with removal of the UV and IR components seems to be more suitable than monochromic light. An efficiency of 3.59% was achieved without any additional treatment, significantly higher than the efficiency of 2.88% of the sample by conventional CBD method under similar conditions with growth rate one order of magnitude higher. In general, the result has suggested its potential importance for other compound materials and opto-electronic devices.

  4. Flexible, High-Speed CdSe Nanocrystal Integrated Circuits.

    PubMed

    Stinner, F Scott; Lai, Yuming; Straus, Daniel B; Diroll, Benjamin T; Kim, David K; Murray, Christopher B; Kagan, Cherie R

    2015-10-14

    We report large-area, flexible, high-speed analog and digital colloidal CdSe nanocrystal integrated circuits operating at low voltages. Using photolithography and a newly developed process to fabricate vertical interconnect access holes, we scale down device dimensions, reducing parasitic capacitances and increasing the frequency of circuit operation, and scale up device fabrication over 4 in. flexible substrates. We demonstrate amplifiers with ∼7 kHz bandwidth, ring oscillators with <10 μs stage delays, and NAND and NOR logic gates. PMID:26407206

  5. Low-cost SWIR sensors: advancing the performance of ROIC-integrated colloidal quantum dot photodiode arrays

    NASA Astrophysics Data System (ADS)

    Klem, Ethan J. D.; Lewis, Jay; Gregory, Chris; Temple, Dorota; Wijewarnasuriya, Priyalal S.; Dhar, Nibir

    2014-06-01

    RTI has developed a novel photodiode technology based on solution-processed PbS colloidal quantum dots (CQD) capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. The most significant advantages of the CQD technology are ease of fabrication, small pixel size, and extended wavelength range. The devices are fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. We will discuss recent advances in device architecture and processing that result in measured dark currents of 15 nA/cm2 at room temperature and enhanced SWIR responsivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

  6. Poly(3-hexylthiophene-2,5-diyl) as a Hole Transport Layer for Colloidal Quantum Dot Solar Cells.

    PubMed

    Neo, Darren C J; Zhang, Nanlin; Tazawa, Yujiro; Jiang, Haibo; Hughes, Gareth M; Grovenor, Chris R M; Assender, Hazel E; Watt, Andrew A R

    2016-05-18

    Lead sulfide colloidal quantum dot (CQD) solar cells demonstrate extremely high short-circuit currents (Jsc) and are making decent progress in power conversion efficiencies. However, the low fill factors (FF) and open-circuit voltages have to be addressed with urgency to prevent the stalling of efficiency improvements. This paper highlights the importance of improving hole extraction, which received much less attention as compared to the electron-accepting component of the device architecture (e.g., TiO2 or ZnO). Here, we show the use of semiconducting polymer poly(3-hexylthiophene-2,5-diyl) to create efficient CQD devices by improving hole transport, removing interfacial barriers, and minimizing shunt pathways, thus resulting in an overall improvement in device performance stemming from better Jsc and FF. PMID:27090378

  7. Trap State Effects in PbS Colloidal Quantum Dot Exciton Kinetics Using Photocarrier Radiometry Intensity and Temperature Measurements

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Mandelis, Andreas; Melnikov, Alexander; Sun, Qiming

    2016-06-01

    Colloidal quantum dots (CQDs) have attracted significant interest for applications in electronic and optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. However, a poor understanding of charge transport in these nanocrystalline films hinders their practical applications. The photocarrier radiometry (PCR) technique, a frequency-domain photoluminescence method spectrally gated for monitoring radiative recombination photon emissions while excluding thermal infrared photons due to non-radiative recombination, has been applied to PbS CQD thin films for the analysis of charge transport properties. Linear excitation intensity responses of PCR signals were found in the reported experimental conditions. The type and influence of trap states in the coupled PbS CQD thin film were analyzed with PCR temperature- and time-dependent results.

  8. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

    PubMed

    Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping

    2015-04-28

    Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn(4+) as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors. PMID:25824283

  9. Effective improvement in optical properties of colloidal CdTe@ZnS quantum dots synthesized from aqueous solution

    NASA Astrophysics Data System (ADS)

    Wang, Yongbo; Si, Boni; Lu, Siwu; Ma, Xuan; Liu, Enzhou; Fan, Jun; Li, Xinghua; Hu, Xiaoyun

    2016-09-01

    Efficient synthesis of high-quality quantum dots (QDs) with excellent optical properties by aqueous synthesis is still of great significance for extended optical applications. Herein we highlight the advantages in optical properties of colloidal CdTe@ZnS QDs prepared by a facile and highly effective aqueous synthesis method. These achievements were realized by delicate manipulation of the conditions involved in nucleation and the growth process. Transmission electron microscopy (TEM) images indicated the QDs were uniform size and well dispersible. The emission peaks of the as-prepared QDs could shift from 496 to 698 nm with narrow full width at half maximum (FWHM), and the corresponding fluorescent color changed from green to red. Moreover, the emission could even reach to the near-infrared (NIR) region (706–796 nm) by extending the reaction time. The highest photoluminescence (PL) quantum yield (QY) of the QDs could reach to 60%, and the average of FWHM was about 55 nm. To address the problem of wide size-distribution in PL QY decrease and FWHM broadening, the colloids of QDs prepared at long reaction time (above 3 h) were centrifuged (12 000 r min‑1). In addition, the assessment of QD cytotoxicity indicated the CdTe@ZnS QDs were much less cytotoxic and showed good biocompatibility. Compared with organic synthesis, our aqueous synthesis of QDs could be carried out efficiently on a large scale and showed good batch-to-batch reproducibility. The as-prepared CdTe@ZnS QDs exhibited excellent optical properties and hold a good potential to be applied in optoelectronic and biological applications.

  10. Surface structure of CdSe Nanorods revealed by combined X-rayabsorption fine structure measurements and ab-initio calculations

    SciTech Connect

    Aruguete, Deborah A.; Marcus, Matthew A.; Li, Liang-shi; Williamson, Andrew; Fakra, Sirine; Gygi, Francois; Galli, Giulia; Alivisatos, A. Paul

    2006-01-27

    We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.

  11. Optical properties of colloidal aqueous synthesized 3 mercaptopropionic acid stabilized CdS quantum dots

    NASA Astrophysics Data System (ADS)

    Sumanth Kumar, D.; Jai Kumar, B.; Mahesh H., M.

    2016-05-01

    We have explored an easiest and simplest aqueous route to synthesize bright green luminescent CdS QDs using 3-Mercaptopropionic acid (MPA) as a stabilizer in air ambient for solar cell applications. The CdS quantum dots showed a strong quantum confinement effect with good stability, size and excellent photoluminescence. MPA Capping on CdS QDs was confirmed through FTIR. The Optical absorption spectrum revealed the CdS quantum dots are highly transparent in the visible region with absorption peak at 380 nm, confirming the quantum confinement. Photoluminescence showed an emission peak at 525 nm wavelength. The optical band gap energy was found to be 3.19 eV and CdS quantum dots radius calculated using Brus equation is 1.5 nm. The results are presented and discussed in detail.

  12. The pH-dependent photoluminescence of colloidal CdSe/ZnS quantum dots with different organic coatings

    NASA Astrophysics Data System (ADS)

    Debruyne, David; Deschaume, Olivier; Coutiño-Gonzalez, Eduardo; Locquet, Jean-Pierre; Hofkens, Johan; Van Bael, Margriet J.; Bartic, Carmen

    2015-06-01

    The photoluminescence (PL) of colloidal quantum dots (QDs) is known to be sensitive to the solution pH. In this work we investigate the role played by the organic coating in determining the pH-dependent PL. We compare two types of CdSe/ZnS QDs equipped with different organic coatings, namely dihydrolipoic acid (DHLA)-capped QDs and phospholipid micelle-encapsulated QDs. Both QD types have their PL intensity quenched at acidic pH values, but they differ in terms of the reversibility of the quenching process. For DHLA-capped QDs, the quenching is nearly irreversible, with a small reversible component visible only on short time scales. For phospholipid micelle-encapsulated QDs the quenching is notably almost fully reversible. We suggest that the surface passivation by the organic ligands is reversible for the micelle-encapsulated QDs. Additionally, both coatings display pH-dependent spectral shifts. These shifts can be explained by a combination of irreversible processes, such as photo-oxidation and acid etching, and reversible charging of the QD surface, leading to the quantum-confined Stark effect (QCSE), the extent of each effect being coating-dependent. At high ionic strengths, the aggregation of QDs also leads to a spectral (red) shift, which is attributable to the QCSE and/or electronic energy transfer.

  13. Resonance energy transfer from PbS colloidal quantum dots to bulk silicon: the road to hybrid photovoltaics

    NASA Astrophysics Data System (ADS)

    Andreakou, P.; Brossard, M.; Bernechea, M.; Konstantatos, G.; Lagoudakis, P.

    2012-02-01

    Semiconductor Quantum Dots (QDs) are promising materials for photovoltaic applications because they can be engineered to absorb light from visible to near infrared and single absorbed photons can generate multiple excitons. However, these materials suffer from low carrier mobility, which severely limits the prospects of efficient charge extraction and carrier transport. We take advantage of the optical properties of QDs and overcome their drawback by using a hybrid photovoltaic device. This photovoltaic configuration exploits the absorption of solar photons in the QDs and the transfer of excitons from the QDs to a silicon p-n junction. We study the Resonance Energy Transfer (RET) mechanism to inject excitons from the QDs into the depletion layer of a silicon p-n junction. Lead sulphide (PbS) nanocrystals are deposited onto the silicon substrate and the efficiency of Resonance Energy Transfer (RET) from the PbS nanoparticles to bulk silicon is investigated. We study the efficiency of this transfer channel between the PbS nanocrystals and silicon by varying their separation distance. These results demonstrate RET from colloidal quantum dots to bulk silicon. Temperature measurements are also presented and show that the RET efficiency is as high as 44% at room temperature. Such a hybrid photovoltaic device makes a potentially inexpensive scheme for achieving highefficiency and low-cost solar-cell platforms.

  14. Fluorescence resonance energy transfer measured by spatial photon migration in CdSe-ZnS quantum dots colloidal systems as a function of concentration

    SciTech Connect

    Azevedo, G.; Monte, A. F. G.; Reis, A. F.; Messias, D. N.

    2014-11-17

    The study of the spatial photon migration as a function of the concentration brings into attention the problem of the energy transfer in quantum dot embedded systems. By measuring the photon propagation and its spatial dependence, it is possible to understand the whole dynamics in a quantum dot system, and also improve their concentration dependence to maximize energy propagation due to radiative and non-radiative processes. In this work, a confocal microscope was adapted to scan the spatial distribution of photoluminescence from CdSe-ZnS core-shell quantum dots in colloidal solutions. The energy migration between the quantum dots was monitored by the direct measurement of the photon diffusion length, according to the diffusion theory. We observed that the photon migration length decreases by increasing the quantum dot concentration, this kind of behavior has been regarded as a signature of Förster resonance energy transfer in the system.

  15. High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation

    NASA Astrophysics Data System (ADS)

    Chang, Jin; Kuga, Yuki; Mora-Seró, Iván; Toyoda, Taro; Ogomi, Yuhei; Hayase, Shuzi; Bisquert, Juan; Shen, Qing

    2015-03-01

    Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm2). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar

  16. Site-selective ion beam synthesis and optical properties of individual CdSe nanocrystal quantum dots in a SiO₂ matrix.

    PubMed

    Mangold, H Moritz; Karl, Helmut; Krenner, Hubert J

    2014-02-12

    Cadmium selenide nanocrystal quantum dots (NC-QDs) are site-selectively synthesized by sequential ion beam implantation of selenium and cadmium ions in a SiO2 matrix through submicrometer apertures followed by a rapid thermal annealing step. The structural and optical properties of the NC-QDs are controlled by the ion fluence during implantation and the diameter of the implantation aperture. For low fluences and small apertures the emission of these optically active emitters is blue-shifted compared to that of the bulk material by >100 meV due to quantum confinement. The emission exhibits spectral diffusion and blinking on a second time scales as established also for solution-synthesized NC-QDs. PMID:24450950

  17. Multiple Exciton Generation in Colloidal Silicon Nanocrystals

    SciTech Connect

    Beard, M. C.; Knutsen, K. P.; Yu, P.; Luther, J. M.; Song, Q.; Metzger, W. K.; Ellingson, R. J.; Nozik, A. M.

    2007-01-01

    Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a single photon in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junction photovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find the threshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap {identical_to} Eg = 1.20 eV) to be 2.4 {+-} 0.1E{sub g} and find an exciton-production quantum yield of 2.6 {+-} 0.2 excitons per absorbed photon at 3.4E{sub g}. While MEG has been previously reported in direct-gap semiconductor NCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEG is found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough to produce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Our findings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundance and accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.

  18. Plasmonic emission enhancement of colloidal quantum dots in the presence of bimetallic nanoparticles

    SciTech Connect

    Sadeghi, S. M.; Hatef, A.; Meunier, M.; Nejat, A.; Campbell, Q.

    2014-04-07

    We studied plasmonic features of bimetallic nanostructures consisting of gold nanoisland cores semi-coated with a chromium layer and explored how they influence emission of CdSe/ZnS quantum dots. We showed that, compared with chromium-covered glass substrates without the gold cores, the bimetallic nanostructures could significantly enhance the emission of the quantum dots. We studied the impact of the excitation intensity and thickness of the chromium layer on this process and utilized numerical means to identify the mechanisms behind it. Our results suggest that when the chromium layer is thin, the enhancement process is the result of the bimetallic plasmonic features of the nanostructures. As the chromium layer becomes thick, the impact of the gold cores is screened and the enhancement mostly happens mostly via the field enhancement of chromium nanoparticles in the absence of significant energy transfer from the quantum dots to these nanoparticles.

  19. Near-infrared electroluminescent devices based on colloidal HgTe quantum dot arrays

    NASA Astrophysics Data System (ADS)

    O'Connor, É.; O'Riordan, A.; Doyle, H.; Moynihan, S.; Cuddihy, A.; Redmond, G.

    2005-05-01

    Crystalline 4.6 nm HgTe quantum dots, stabilized by 1-thioglycerol ligands, were synthesized by wet chemical methods. Room-temperature photoluminescence spectra of the dots, both in solution and as solid arrays, exhibited near-infrared emission. Light-emitting devices were fabricated by deposition of quantum dot layers onto glass/indium tin oxide (ITO)/3,4-polyethylene-dioxythiophene-polystyrene sulfonate (PEDOT) substrates followed by top contacting with evaporated aluminum. Room-temperature near-infrared electroluminescence from 1mm2 ITO/PEDOT/HgTe/Al devices, centered at ˜1600nm, with an external quantum efficiency of 0.02% and brightness of 150nW/mm2 at 50 mA and 2.5 V was achieved.

  20. Photosensitized electron transfer processes in SiO/sub 2/ colloids and sodium lauryl sulfate micellar sytems: correlation of quantum yields with interfacial surface potentials

    SciTech Connect

    Laane, C.; Willner, I.; Otvos, J.W.; Calvin, M.

    1981-10-01

    The effectiveness of negatively charged colloidal SiO/sub 2/ particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO/sub 4/) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS/sup 0/) with tris(2,2'-bi-pyridinium)ruthenium(II) (Ru(bipy)/sub 3//sup 2 +/) as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS) in the SiO/sub 2/ colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO/sub 4/ micellar solution. The higher quantum yields obtained with the SiO/sub 2/ colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts - i.e., Ru(bipy)/sub 3//sup 3 +/ and PVS/sup -/ - by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO/sub 2/ particles and NaLauSO/sub 4/ micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO/sub 2/ interface is characterized by much higher surface potential than the micellar interface. The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated shows that the quantum yield is not affected by surface potentials smaller than approx. = -40 mV. At larger potentials, the quantum yield increases rapidly. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS/sup 0/ reduction.

  1. Hybrid light sensor based on ultrathin Si nanomembranes sensitized with CdSe/ZnS colloidal nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Peng, Weina; Sampat, Siddharth; Rupich, Sara M.; Anand, Benoy; Nguyen, Hue Minh; Taylor, David; Beardon, Brandon E.; Gartstein, Yuri N.; Chabal, Yves J.; Malko, Anton V.

    2015-04-01

    We report the observation of a large enhancement of the wavelength-dependent photocurrent in ultrathin silicon nanomembranes (SiNM) decorated with colloidal CdSe/ZnS nanocrystal quantum dots (NQDs). Back-gated, field-effect transistor structures based on 75 nm-thick SiNMs are functionalized with self-assembled monolayers (SAMs) preventing surface oxidation and minimizing the surface defect densities. NQDs are drop cast on the active region of the device and the photocurrent is measured as a function of the excitation wavelength across the NQD absorption region. Photocurrent enhancement on the order of several hundred nA's is observed for NQD/SAM/SiNM devices compared to reference SAM/SiNM structures, with the device peak response closely correlated to the NQD absorption peak. We propose light-induced gating of the surface electrostatic potential and forward self-biasing of the FET channel as the two key mechanisms leading to the large photocurrent increase. Our findings open the possibility of employing silicon-nanocrystal hybrid structures for light sensing applications.We report the observation of a large enhancement of the wavelength-dependent photocurrent in ultrathin silicon nanomembranes (SiNM) decorated with colloidal CdSe/ZnS nanocrystal quantum dots (NQDs). Back-gated, field-effect transistor structures based on 75 nm-thick SiNMs are functionalized with self-assembled monolayers (SAMs) preventing surface oxidation and minimizing the surface defect densities. NQDs are drop cast on the active region of the device and the photocurrent is measured as a function of the excitation wavelength across the NQD absorption region. Photocurrent enhancement on the order of several hundred nA's is observed for NQD/SAM/SiNM devices compared to reference SAM/SiNM structures, with the device peak response closely correlated to the NQD absorption peak. We propose light-induced gating of the surface electrostatic potential and forward self-biasing of the FET channel as the

  2. Evidence for a diffusion-controlled mechanism for fluorescence blinking of colloidal quantum dots.

    SciTech Connect

    Pelton, M.; Smith, G.; Scherer, N. F.; Marcus, R. A.; Univ. of Chicago; California Inst. of Tech.

    2007-09-04

    Fluorescence blinking in nanocrystal quantum dots is known to exhibit power-law dynamics, and several different mechanisms have been proposed to explain this behavior. We have extended the measurement of quantum-dot blinking by characterizing fluctuations in the fluorescence of single dots over time scales from microseconds to seconds. The power spectral density of these fluctuations indicates a change in the power-law statistics that occurs at a time scale of several milliseconds, providing an important constraint on possible mechanisms for the blinking. In particular, the observations are consistent with the predictions of models wherein blinking is controlled by diffusion of the energies of electron or hole trap states.

  3. Preparation of cadmium selenide colloidal quantum dots in non-coordinating solvent octadecene

    NASA Astrophysics Data System (ADS)

    Mazing, D. S.; Brovko, A. M.; Matyushkin, L. B.; Aleksandrova, O. A.; Moshnikov, V. A.

    2015-12-01

    Nearly monodisperse cadmium selenide quantum dots (QDs) were synthesized in non-coordinating solvent octadecene through phosphine-free method using oleic acid as surfactant. Selenium powder suspension in octadecene obtained by ultrasound processing was used as one of precursor solutions. Influence of multiple selenium precursor injections on nanocrystal growth process was investigated. Nanoparticles were characterized by means of absorption and photoluminescence spectroscopies.

  4. 'Giant' multishell CdSe nanocrystal quantum dots with supporessed blinking: novel fluorescent probes for real-time detection of single-molecule events

    SciTech Connect

    Hollingsworth, Jennifer A; Vela, Javier; Htoon, Han; Klimov, Victor I; Casson, Amy R; Chen, Yongfen

    2009-01-01

    We reported for the first time that key nanocrystal quantum dot (NQD) optical properties-quantum yield, photobleaching and blinking-can be rendered independent ofNQD surface chemistry and environment by growth of a very thick, defect-free inorganic shell. Here, we show the precise shell-thickness dependence of these effects. We demonstrate that 'giant-shell' NQDs can be largely non-blinking for observation times as long as 54 minutes and lhat on-time fractions are independent of experimental time-resolution from 1-200 ms. These effects are primarily demonstrated on (CdSe)CdS (core)shell NQDs, but we also show that alloyed shells comprising Cd.Znl.'S and terminated with a non-cytotoxic ZnS layer exhibit similar properties. The mechanism for suppressed blinking and dramatically enhanced stability is attributed to both effective isolation of the NQD core excitonic wavefunction from the NQD surface, as well as a quasi-Type II electronic structure. The unusual electronic structure provides for effective spatial separation of the electron and hole into the shell and core, respectively, and, thereby, for reduced efficiencies in non-radiative Auger recombination.

  5. Biodistribution and stability of CdSe core quantum dots in mouse digestive tract following per os administration: Advantages of double polymer/silica coated nanocrystals

    SciTech Connect

    Loginova, Y.F.; Dezhurov, S.V.; Zherdeva, V.V.; Kazachkina, N.I.; Wakstein, M.S.; Savitsky, A.P.

    2012-03-02

    Highlights: Black-Right-Pointing-Pointer New QDs coated with combination of polythiol ligands and silica shell were synthesized. Black-Right-Pointing-Pointer We examine the QDs stability in digestive tract of mice after per os administration. Black-Right-Pointing-Pointer The polymer/silica shell prevents QDs degradation and fluorescence quenching in vivo. -- Abstract: CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT-APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT-APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials - mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) - are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT-APS) are suitable for biological and biomedical applications in the gastrointestinal tract.

  6. Biodistribution and stability of CdSe core quantum dots in mouse digestive tract following per os administration: advantages of double polymer/silica coated nanocrystals.

    PubMed

    Loginova, Y F; Dezhurov, S V; Zherdeva, V V; Kazachkina, N I; Wakstein, M S; Savitsky, A P

    2012-03-01

    CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT-APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT-APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials - mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) - are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT-APS) are suitable for biological and biomedical applications in the gastrointestinal tract. PMID:22321397

  7. Conjugated assembly of colloidal zinc oxide quantum dots and multiwalled carbon nanotubes for an excellent photosensitive ultraviolet photodetector.

    PubMed

    Boruah, Buddha Deka; Misra, Abha

    2016-09-01

    Conjugation of highly dense colloidal zinc oxide quantum dots (ZnO QDs) on multiwalled carbon nanotubes (ZnO QDs@MWCNTs) is achieved for high performance ultraviolet (UV) photodetection. Significant improvement in the photoresponse of the ZnO QDs@MWCNTs photodetector (PD) is established as compared to a pristine ZnO QDs PD. The conjugation of two constituents allows the direct transfer of photoinduced charge carriers in ZnO QDs to MWCNTs for an efficient electrical path that considerably reduces charge recombination during UV exposure. Linearity in the response current with both the UV illumination intensity as well as external bias voltage reveals the photoelastic behavior of the ZnO QDs@MWCNTs PD. Moreover, the PD displays faster response and recovery times of 1.6 s and 1.9 s, respectively, than the most conventional PDs. In addition, spectral photoresponse analysis of the PD presents visible-blind behavior. Overall, conjugation of the hybrid heterostructure presented excellent photoelastic, high performance and visible-blind UV photodetection. PMID:27454746

  8. Quantum confinement and dielectric profiles of colloidal nanoplatelets of halide inorganic and hybrid organic-inorganic perovskites.

    PubMed

    Sapori, Daniel; Kepenekian, Mikaël; Pedesseau, Laurent; Katan, Claudine; Even, Jacky

    2016-03-28

    Quantum confinement as well as high frequency ε∞ and static εs dielectric profiles are described for nanoplatelets of halide inorganic perovskites CsPbX3 (X = I, Br, Cl) and hybrid organic-inorganic perovskites (HOP) in two-dimensional (2D) and three-dimensional (3D) structures. 3D HOP are currently being sought for their impressive photovoltaic ability. Prior to this sudden popularity, 2D HOP materials were driving intense activity in the field of optoelectronics. Such developments have been enriched by the recent ability to synthesize colloidal nanostructures of controlled sizes of 2D and 3D HOP. This raises the need to achieve a thorough description of the electronic structure and dielectric properties of these systems. In this work, we go beyond the abrupt dielectric interface model and reach the atomic scale description. We examine the influence of the nature of the halogen and of the cation on the band structure and dielectric constants. Similarly, we survey the effect of dimensionality and shape of the perovskite. In agreement with recent experimental results, we show an increase of the band gap and a decrease of ε∞ when the size of a nanoplatelet reduces. By inspecting 2D HOP, we find that it cannot be described as a simple superposition of independent inorganic and organic layers. Finally, the dramatic impact of ionic contributions on the dielectric constant εs is analysed. PMID:26705549

  9. Conjugated assembly of colloidal zinc oxide quantum dots and multiwalled carbon nanotubes for an excellent photosensitive ultraviolet photodetector

    NASA Astrophysics Data System (ADS)

    Deka Boruah, Buddha; Misra, Abha

    2016-09-01

    Conjugation of highly dense colloidal zinc oxide quantum dots (ZnO QDs) on multiwalled carbon nanotubes (ZnO QDs@MWCNTs) is achieved for high performance ultraviolet (UV) photodetection. Significant improvement in the photoresponse of the ZnO QDs@MWCNTs photodetector (PD) is established as compared to a pristine ZnO QDs PD. The conjugation of two constituents allows the direct transfer of photoinduced charge carriers in ZnO QDs to MWCNTs for an efficient electrical path that considerably reduces charge recombination during UV exposure. Linearity in the response current with both the UV illumination intensity as well as external bias voltage reveals the photoelastic behavior of the ZnO QDs@MWCNTs PD. Moreover, the PD displays faster response and recovery times of 1.6 s and 1.9 s, respectively, than the most conventional PDs. In addition, spectral photoresponse analysis of the PD presents visible-blind behavior. Overall, conjugation of the hybrid heterostructure presented excellent photoelastic, high performance and visible-blind UV photodetection.

  10. Investigations on the physical origin of lateral photovoltage in PbS-colloidal quantum dot/Si heterojunctions

    NASA Astrophysics Data System (ADS)

    Abhale, Atul Prakash; Koteswara Rao, K. S. R.; Pendyala, N. B.; Banerjee, A.

    2016-03-01

    Restricted area heterojunctions, an array of lead sulfide colloidal quantum dots (PbS-CQDs) and crystalline silicon, are studied with a non-destructive remote contact light beam induced current (RC-LBIC) technique. As well as getting good quality active area images we observed an anomalous unipolar signal response for the PbS-CQD/n-Si devices and a conventionally expected bipolar signal profile for the PbS-CQD/p-Si devices. Interestingly, our simulation results consistently yielded a unipolar and bipolar nature in the signals related to the PbS-CQD/n-Si and PbS-CQD/p-Si heterostructures, respectively. In order to explain the physical mechanism involved in the unipolar signal response of the PbS-CQD/n-Si devices, we propose a model based on the band alignment in the heterojunctions, in addition to the distribution of photo-induced excess majority carriers across the junction. Given that the RC-LBIC technique is well suited to this context, the presence of these two distinct mechanisms (the bipolar and unipolar nature of the signals) needs to be considered in order to have a better interpretation of the data in the characterization of an array of homo/heterojunctions.

  11. 3D Assembly of All-Inorganic Colloidal Nanocrystals into Gels and Aerogels.

    PubMed

    Sayevich, Vladimir; Cai, Bin; Benad, Albrecht; Haubold, Danny; Sonntag, Luisa; Gaponik, Nikolai; Lesnyak, Vladimir; Eychmüller, Alexander

    2016-05-17

    We report an efficient approach to assemble a variety of electrostatically stabilized all-inorganic semiconductor nanocrystals (NCs) by their linking with appropriate ions into multibranched gel networks. These all-inorganic non-ordered 3D assemblies benefit from strong interparticle coupling, which facilitates charge transport between the NCs with diverse morphologies, compositions, sizes, and functional capping ligands. Moreover, the resulting dry gels (aerogels) are highly porous monolithic structures, which preserve the quantum confinement of their building blocks. The inorganic semiconductor aerogel made of 4.5 nm CdSe colloidal NCs capped with I(-) ions and bridged with Cd(2+) ions had a large surface area of 146 m(2)  g(-1) . PMID:27100131

  12. Evidence for a diffusion-controlled mechanism for fluorescence blinking of colloidal quantum dots

    PubMed Central

    Pelton, Matthew; Smith, Glenna; Scherer, Norbert F.; Marcus, Rudolph A.

    2007-01-01

    Fluorescence blinking in nanocrystal quantum dots is known to exhibit power-law dynamics, and several different mechanisms have been proposed to explain this behavior. We have extended the measurement of quantum-dot blinking by characterizing fluctuations in the fluorescence of single dots over time scales from microseconds to seconds. The power spectral density of these fluctuations indicates a change in the power-law statistics that occurs at a time scale of several milliseconds, providing an important constraint on possible mechanisms for the blinking. In particular, the observations are consistent with the predictions of models wherein blinking is controlled by diffusion of the energies of electron or hole trap states. PMID:17720807

  13. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

    PubMed

    Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

    2014-07-22

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films. PMID:24883930

  14. Branched polyethylenimine improves hydrogen photoproduction from a CdSe quantum dot/[FeFe]-hydrogenase mimic system in neutral aqueous solutions.

    PubMed

    Liang, Wen-Jing; Wang, Feng; Wen, Min; Jian, Jing-Xin; Wang, Xu-Zhe; Chen, Bin; Tung, Chen-Ho; Wu, Li-Zhu

    2015-02-16

    Nature uses hydrogenase enzyme to catalyze proton reduction at pH 7 with overpotentials and catalytic efficiencies that rival platinum electrodes. Over the past several years, [FeFe]-hydrogenase ([FeFe]-H2 ase) mimics have been demonstrated to be effective catalysts for light-driven H2 evolution. However, it remains a significant challenge to realize H2 production by such an artificial photosynthetic system in neutral aqueous solution. Herein, we report a new system for photocatalytic H2 evolution working in a broad pH range, especially under neutral conditions. This unique system is consisted of branched polyethylenimine (PEI)-grafted [FeFe]-H2 ase mimic (PEI-g-Fe2 S2 ), MPA-CdSe quantum dots (MPA=mercaptopropionic acid), and ascorbic acid (H2 A) in water. Due to the secondary coordination sphere of PEI, which has high buffering capacity and stabilizing ability, the system is able to produce H2 under visible-light irradiation with turnover number of 10 600 based on the Fe2 S2 active site in PEI-g-Fe2 S2 . The stability and activity are much better than that of the same system under acidic or basic conditions and they are, to the best of our knowledge, the highest known to date for photocatalytic H2 evolution from a [FeFe]-H2 ase mimic in neutral aqueous solution. PMID:25572459

  15. Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles.

    PubMed

    Boyer, John-Christopher; van Veggel, Frank C J M

    2010-08-01

    In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF(4): 2% Er(3+), 20% Yb(3+) nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample. PMID:20820726

  16. Strong exciton-photon coupling with colloidal quantum dots in a high-Q bilayer microcavity

    SciTech Connect

    Giebink, Noel C; Wiederrecht, Gary P.; Wasielewski, Michael R

    2011-01-01

    We demonstrate evanescently coupled bilayer microcavities with Q -factors exceeding 250 fabricated by a simple spin-coating process. The cavity architecture consists of a slab waveguide lying upon a low refractive index spacer layer supported by a glass substrate. For a lossless guide layer, the cavity Q depends only on the thickness of the low index spacer and in principle can reach arbitrarily high values. We demonstrate the versatility of this approach by constructing cavities with a guide layer incorporating CdSe/ZnS core/shell quantum dots, where we observe strong coupling and hybridization between the 1S(e)-1S{sub 3/2} (h) and 1S(e)-2S{sub 3/2} (h) exciton states mediated by the cavity photon. This technique greatly simplifies the fabrication of high-Q planar microcavities for organic and inorganic quantum dot thin films and opens up new opportunities for the study of nonlinear optical phenomena in these materials.

  17. Multiplexed measurements by time resolved spectroscopy using colloidal CdSe/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Kaiser, U.; Jimenez de Aberasturi, D.; Malinowski, R.; Amin, F.; Parak, W. J.; Heimbrodt, W.

    2014-01-01

    Multiplexed measurements of analytes in parallel is a topical demand in bioanalysis and bioimaging. An interesting alternative to commonly performed spectral multiplexing is lifetime multiplexing. In this Letter, we present a proof of principle of single-color lifetime multiplexing by coupling the same fluorophore to different nanoparticles. The effective lifetime of the fluorophores can be tuned by more than one order of magnitude due to resonance energy transfer from donor states. Measurements have been done on a model systems consisting of ATTO-590 dye molecules linked to either gold particles or to CdSe/ZnS core shell quantum dots. Both systems show the same luminescence spectrum of ATTO-590 dye emission in continuous wave excitation, but can be distinguished by means of time resolved measurements. The dye molecules bound to gold particles exhibit a mono-exponential decay with a lifetime of 4.5 ns, whereas the dye molecules bound to CdSe/ZnS dots show a nonexponential decay with a slow component of about 135 ns due to the energy transfer from the quantum dots. We demonstrate the fundamental possibility to determine the mixing ratio for dyes with equal luminescence spectra but very different transients. This opens up a pathway independent of the standard optical multiplexing with many different fluorophores emitting from the near ultraviolet to the near infrared spectral region.

  18. Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles

    NASA Astrophysics Data System (ADS)

    Boyer, John-Christopher; van Veggel, Frank C. J. M.

    2010-08-01

    In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF4: 2% Er3+, 20% Yb3+ nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample.In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF4: 2% Er3+, 20% Yb3+ nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample. Electronic supplementary information (ESI) available: Experimental details, powder XRDs and TEM micrographs of the samples. See DOI: 10.1039/c0nr00253d

  19. Multiplexed measurements by time resolved spectroscopy using colloidal CdSe/ZnS quantum dots

    SciTech Connect

    Kaiser, U.; Jimenez de Aberasturi, D.; Malinowski, R.; Amin, F.; Parak, W. J.; Heimbrodt, W.

    2014-01-27

    Multiplexed measurements of analytes in parallel is a topical demand in bioanalysis and bioimaging. An interesting alternative to commonly performed spectral multiplexing is lifetime multiplexing. In this Letter, we present a proof of principle of single-color lifetime multiplexing by coupling the same fluorophore to different nanoparticles. The effective lifetime of the fluorophores can be tuned by more than one order of magnitude due to resonance energy transfer from donor states. Measurements have been done on a model systems consisting of ATTO-590 dye molecules linked to either gold particles or to CdSe/ZnS core shell quantum dots. Both systems show the same luminescence spectrum of ATTO-590 dye emission in continuous wave excitation, but can be distinguished by means of time resolved measurements. The dye molecules bound to gold particles exhibit a mono-exponential decay with a lifetime of 4.5 ns, whereas the dye molecules bound to CdSe/ZnS dots show a nonexponential decay with a slow component of about 135 ns due to the energy transfer from the quantum dots. We demonstrate the fundamental possibility to determine the mixing ratio for dyes with equal luminescence spectra but very different transients. This opens up a pathway independent of the standard optical multiplexing with many different fluorophores emitting from the near ultraviolet to the near infrared spectral region.

  20. Aminophosphines: A Double Role in the Synthesis of Colloidal Indium Phosphide Quantum Dots.

    PubMed

    Tessier, Mickael D; De Nolf, Kim; Dupont, Dorian; Sinnaeve, Davy; De Roo, Jonathan; Hens, Zeger

    2016-05-11

    Aminophosphines have recently emerged as economical, easy-to-implement precursors for making InP nanocrystals, which stand out as alternative Cd-free quantum dots for optoelectronic applications. Here, we present a complete investigation of the chemical reactions leading to InP formation starting from InCl3 and tris(dialkylamino)phosphines. Using nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction, we demonstrate that injection of the aminophosphine in the reaction mixture is followed by a transamination with oleylamine, the solvent of the reaction. In addition, mass spectrometry and NMR indicate that the formation of InP concurs with that of tetra(oleylamino)phosphonium chloride. The chemical yield of the InP formation agrees with this 4 P(+III) → P(-III) + 3 P(+V) disproportionation reaction occurring, since full conversion of the In precursor was only attained for a 4:1 P/In ratio. Hence it underlines the double role of the aminophosphine as both precursor and reducing agent. These new insights will guide further optimization of high quality InP quantum dots and might lead to the extension of synthetic protocols toward other pnictide nanocrystals. PMID:27111735

  1. Fabrication of micro/nano-composite porous TiO2 electrodes for quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Song, Xiaohui; Wang, Minqiang; Xing, Tiying; Deng, Jianping; Ding, Jijun; Yang, Zhi; Zhang, Xiangyu

    2014-05-01

    For colloidal quantum dots-sensitized solar cells (QDSSC), the penetration and distribution of quantum dots (QDs) within electrodes is very crucial for performance improvement. In view of much bigger size of colloidal QDs than that of dye molecules, a TiO2 electrode with open structure is helpful for the distribution of QDs. In this study, micro/nano-composite porous TiO2 electrodes are fabricated by incorporating polystyrene (PS) spheres into the TiO2 screen-printing paste. After sintering, the embedded PS spheres are burnt off, leaving randomly distributed submicrometer voids in the electrodes, which favor easy penetration of the colloidal CdSe QDs within the TiO2 electrodes, and thus avoiding the unfavorable clogging of pores by CdSe QDs. In addition, this kind of composite structure enhances the scattering properties of the electrodes and hence the light capture inside the device. In order to obtain optimized devices, we probe into the influence of the PS concentration on the photovoltaic performance. The result shows that a maximum conversion efficiency of 2.23% is obtained for the QDSSC made from the PS:TiO2 = 1:4 paste.

  2. Quantum confinement and dielectric profiles of colloidal nanoplatelets of halide inorganic and hybrid organic-inorganic perovskites

    NASA Astrophysics Data System (ADS)

    Sapori, Daniel; Kepenekian, Mikaël; Pedesseau, Laurent; Katan, Claudine; Even, Jacky

    2016-03-01

    Quantum confinement as well as high frequency ε∞ and static εs dielectric profiles are described for nanoplatelets of halide inorganic perovskites CsPbX3 (X = I, Br, Cl) and hybrid organic-inorganic perovskites (HOP) in two-dimensional (2D) and three-dimensional (3D) structures. 3D HOP are currently being sought for their impressive photovoltaic ability. Prior to this sudden popularity, 2D HOP materials were driving intense activity in the field of optoelectronics. Such developments have been enriched by the recent ability to synthesize colloidal nanostructures of controlled sizes of 2D and 3D HOP. This raises the need to achieve a thorough description of the electronic structure and dielectric properties of these systems. In this work, we go beyond the abrupt dielectric interface model and reach the atomic scale description. We examine the influence of the nature of the halogen and of the cation on the band structure and dielectric constants. Similarly, we survey the effect of dimensionality and shape of the perovskite. In agreement with recent experimental results, we show an increase of the band gap and a decrease of ε∞ when the size of a nanoplatelet reduces. By inspecting 2D HOP, we find that it cannot be described as a simple superposition of independent inorganic and organic layers. Finally, the dramatic impact of ionic contributions on the dielectric constant εs is analysed.Quantum confinement as well as high frequency ε∞ and static εs dielectric profiles are described for nanoplatelets of halide inorganic perovskites CsPbX3 (X = I, Br, Cl) and hybrid organic-inorganic perovskites (HOP) in two-dimensional (2D) and three-dimensional (3D) structures. 3D HOP are currently being sought for their impressive photovoltaic ability. Prior to this sudden popularity, 2D HOP materials were driving intense activity in the field of optoelectronics. Such developments have been enriched by the recent ability to synthesize colloidal nanostructures of controlled

  3. Inverted organic solar cells using a solution-processed TiO2/CdSe electron transport layer to improve performance

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoxiao; Xiong, Zhicheng; Wang, Wen; Zhang, Luming; Wu, Sujuan; Lu, Xubing; Gao, Xingsen; Shui, Lingling; Liu, Jun-Ming

    2016-04-01

    In the present work, cadmium selenide (CdSe) nanoparticles are deposited directly on TiO2 film to fabricate the TiO2/CdSe interlayer by a chemical bath deposition method. The inverted organic solar cells using poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) bulk heterojunction as an active layer and TiO2/CdSe interlayer as an electron transport layer (ETL) are fabricated in air. A series of microstructural, photo-electronic, and electrochemical characterizations on these cells are performed. The TiO2/CdSe structure with respect to either the TiO2 layer or the CdSe layer as the ETL exhibits significantly enhanced external quantum efficiency (EQE) in the visible region. The photoluminescence (PL) measurement shows that the exciton dissociation in the TiO2/CdSe structure is more effective than that in either the TiO2 or CdSe structure. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) implies that the charge recombination in the TiO2/CdSe structure can be suppressed with respect to that in either the CdSe or TiO2 structure. The photovoltaic performances of the cells with the TiO2/CdSe ETL are clearly improved compared with the reference cells only with the TiO2 layer or CdSe layer as the ETL.

  4. Efficient and bright colloidal quantum dot light-emitting diodes via controlling the shell thickness of quantum dots.

    PubMed

    Shen, Huaibin; Lin, Qinli; Wang, Hongzhe; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Zheng, Ying; Li, Lin Song

    2013-11-27

    In this paper, we use a simple device architecture based on solution-processed ZnO nanoparticles (NPs) as the electron injection/transport layer and bilayer structure of poly(ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as the hole injection/transport layer to assess the effect of shell thickness on the properties of quantum-dot-based light emitting diodes (QD-LEDs), comprising CdSe/CdS/ZnS core-shell QDs as the emitting layer. QDs with varying shell thickness were assessed to determine the best option of shell thickness, and the best improvement in device performance was observed when the shell thickness was 2.1 nm. Thereafter, different emissions of QDs, but with optimized same shell thickness (∼2.1 nm), were selected as emitters to be fabricated into same structured QD-LEDs. Highly bright orange-red and green QD-LEDs with peak luminances up to ∼30 000 and ∼52 000 cd m(-2), and power efficiencies of 16 and 19.7 lm W(-1), respectively, were demonstrated successfully. These results may demonstrate a striking basic prototype for the commercialization of QD-based displays and solid-state lightings. PMID:24191742

  5. Colloidal quantum dot Vis-SWIR imaging: demonstration of a focal plane array and camera prototype (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Klem, Ethan J. D.; Gregory, Christopher W.; Temple, Dorota S.; Lewis, Jay S.

    2015-08-01

    RTI has developed a photodiode technology based on solution-processed PbS colloidal quantum dots (CQD). These devices are capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. At the core of this technology is a heterojunction diode structure fabricated using techniques well suited to wafer-scale fabrication, such as spin coating and thermal evaporation. This enables RTI's CQD diodes to be processed at room temperature directly on top of read-out integrated circuits (ROIC), without the need for the hybridization step required by traditional SWIR detectors. Additionally, the CQD diodes can be fabricated on ROICs designed for other detector material systems, effectively allowing rapid prototype demonstrations of CQD focal plane arrays at low cost and on a wide range of pixel pitches and array sizes. We will show the results of fabricating CQD arrays directly on top of commercially available ROICs. Specifically, the ROICs are a 640 x 512 pixel format with 15 µm pitch, originally developed for InGaAs detectors. We will show that minor modifications to the surface of these ROICs make them suitable for use with our CQD detectors. Once completed, these FPAs are then assembled into a demonstration camera and their imaging performance is evaluated. In addition, we will discuss recent advances in device architecture and processing resulting in devices with room temperature dark currents of 2-5 nA/cm^2 and sensitivity from 350 nm to 1.7 μm. This combination of high performance, dramatic cost reduction, and multi-band sensitivity is ideally suited to expand the use of SWIR imaging in current applications, as well as to address applications which require a multispectral sensitivity not met by existing technologies.

  6. Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

    PubMed Central

    Das, Amit; Han, Zhiji; Haghighi, Mohsen Golbon; Eisenberg, Richard

    2013-01-01

    Unique tripodal S-donor capping agents with an attached carboxylate are found to bind tightly to the surface of CdSe nanocrystals (NCs), making the latter water soluble. Unlike that in similarly solubilized CdSe NCs with one-sulfur or two-sulfur capping agents, dissociation from the NC surface is greatly reduced. The impact of this behavior is seen in the photochemical generation of H2 in which the CdSe NCs function as the light absorber with metal complexes in aqueous solution as the H2-forming catalyst and ascorbic acid as the electron donor source. This precious-metal–free system for H2 generation from water using [Co(bdt)2]− (bdt, benzene-1,2-dithiolate) as the catalyst exhibits excellent activity with a quantum yield for H2 formation of 24% at 520 nm light and durability with >300,000 turnovers relative to catalyst in 60 h. PMID:24082134

  7. Nanostructured TiO2 Films Attached CdSe QDs Toward Enhanced Photoelectrochemical Performance.

    PubMed

    Du, Yingying; Yang, Ping; Liu, Yunshi; Zhao, Jie; He, Haiyan; Miao, Yanping

    2016-06-01

    TiO2 films consisted of small nanoparticles were fabricated via a spinning coating method on fluorine doped in tin oxide (FTO) slide glass. After calcination, the films were subsequently sensitized by CdSe quantum dots (QDs) using mercaptopropionic acid (MPA) as a bifunctional surface modifier. Upon UV light irradiation, CdSe QDs inject electrons into TiO2 nanoparticles, thus resulting in the generation of photocurrent in QD-sensitized solar cell. The results indicate that TiO2 films sensitized by CdSe QDs have achieved 1.5-fold enhancement in photocurrent compared with pure TiO2 films, indicating that CdSe QDs can improve the photocurrent by promoting the separation of photoinduced charge carriers. In addition, the photocurrent enhances as the thickness of TiO2 films increased. Such improved photoelectrochemical performance is ascribed to the basis of improved interfacial charge transport of the TiO2-CdSe composite films. Combining QDs on TiO2 thin films is a promising and effective way to enhance the photoelectrochemical performance, which is important in QD-sensitized solar cell application. PMID:27427714

  8. Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

    NASA Astrophysics Data System (ADS)

    Wawrzynczyk, Dominika; Szeremeta, Janusz; Samoc, Marek; Nyk, Marcin

    2015-11-01

    Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ2 for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ2Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.

  9. Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission

    SciTech Connect

    Wawrzynczyk, Dominika; Szeremeta, Janusz; Samoc, Marek; Nyk, Marcin

    2015-11-01

    Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ{sub 2} for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ{sub 2}Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.

  10. Photochemical properties and shape evolution of CdSe QDs in a non-injection reaction

    NASA Astrophysics Data System (ADS)

    Park, Eunjung; Ryu, Jiyoung; Choi, Youngseon; Hwang, Kwang-Jin; Song, Rita

    2013-04-01

    Highly monodispersed CdSe quantum dots (QDs) were prepared without an injection procedure. A series of Cd salts of long chain fatty acids, including Cd-myristate (C14), Cd-palmitate (C16) and Cd-stearate (C18) was prepared, and all metallic precursors and surfactants were mixed together followed by increasing the temperature in a controlled manner. The reaction resulted in highly monodisperse and bright zinc blende QDs. In addition, the effects of specific ligands which have been known to lead anisotropic growth of the nanocrystals in the injection method were investigated. The use of alkyl phosphonic acid and alkyl amine was found to produce extremely monodisperse CdSe QDs with a high quantum yield. This procedure was proven to be able to yield a large quantity of zinc blende CdSe QDs (2 g) in a one-pot reaction. The use of a controlled amount of tetradecylphosphonic acid and octadecylamine resulted in tetrapod- and match-shaped QDs, the first reported by a non-injection method. These results clearly demonstrate that appropriate combination of precursors can provide high quality of CdSe nanocrystals in terms of quantum yield, monodispersity and shape control by a non-injection method.

  11. Spectroscopic manifestations of hybrid association of CdS colloidal quantum dots with J-aggregates of a thiatrimethine cyanine dye

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, O. V.; Smirnov, M. S.; Shapiro, B. I.; Dedikova, A. O.; Shatskikh, T. S.

    2015-11-01

    We have found spectroscopic manifestations of hybrid association in mixtures of CdS colloidal quantum dots with an average size of 2.5-4.2 nm with J-aggregates of pyridinium salt of the 3,3'-di-(γ- sulfopropyl)-9-ethyl-4,5,4',5'-dibenzo-thiacarbocyanine betaine dye that were prepared by the sol-gel method in gelatin. Observed changes of the spectral properties of J-aggregates of dye molecules due to their hybrid association with CdS quantum dots are ensured by steric transformations of dye molecules, which lead to the formation of luminescent trans-J-aggregates. The hybrid association is accompanied by the quenching of the recombination luminescence band of CdS quantum dots (540-640 nm) and by an increase in the luminescence intensity of J-aggregates of dye molecules (670-680 nm). This regularity becomes enhanced with an increase in the ratio of the number of dye molecules to the number of quantum dots [ n dye]: [ n QD] and in the degree of overlap between the luminescence spectrum of quantum dots and the absorption spectrum of J-aggregates, which indicates that there is a resonant nonradiative transfer of the electronic excitation energy from recombination luminescence centers in CdS quantum dots to trans-J-aggregates of dye molecules conjugated to them.

  12. Experimental determination of the absorption cross-section and molar extinction coefficient of CdSe and CdTe nanowires.

    PubMed

    Protasenko, Vladimir; Bacinello, Daniel; Kuno, Masaru

    2006-12-21

    band edge, having order of magnitude values of 1.0 x 10(-11) cm2 at 488 nm. In all cases, experimental NW absorption cross-sections are 4-5 orders of magnitude larger than those for corresponding colloidal CdSe and CdTe quantum dots. Even when volume differences are accounted for, band edge NW cross-sections are larger by up to a factor of 8. When considered along with their intrinsic polarization sensitivity, obtained NW cross-sections illustrate fundamental and potentially exploitable differences between 0D and 1D materials. PMID:17165978

  13. Semiconductor nanoplatelets: a new colloidal system for low-threshold high-gain stimulated emission (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Pelton, Matthew A.; She, Chunxing; Fedin, Igor; Dolzhnikov, Dmitriy; Ithurria, Sandrine; Baghani, Erfan; O'Leary, Stephen K.; Demortiere, Arnaud; Schaller, Richard D.; Talapin, Dmitri V.

    2015-10-01

    Quantum wells (QWs) are thin semiconductor layers than confine electrons and holes in one dimension. They are widely used for optoelectronic devices, particularly semiconductor lasers, but have so far been produced using expensive epitaxial crystal-growth techniques. This has motivated research into the use of colloidal semiconductor nanocrystals, which can be synthesized chemically at low cost, and can be processed in the solution phase. However, initial demonstrations of optical gain from colloidal nanocrystals involved high thresholds. Recently, colloidal synthesis methods have been developed for the production of thin, atomically flat semiconductor nanocrystals, known as nanoplatelets (NPLs). We investigated relaxation of high-energy carriers in colloidal CdSe NPLs, and found that the relaxation is characteristic of a QW system. Carrier cooling and relaxation on time scales from picoseconds to hundreds of picoseconds are dominated by Auger-type exciton-exciton interactions. The picosecond-scale cooling of hot carriers is much faster than the exciton recombination rate, as required for use of these NPLs as optical gain and lasing materials. We therefore investigated amplified spontaneous emission using close-packed films of NPLs. We observed thresholds that were more than 4 times lower than the best reported value for colloidal nanocrystals. Moreover, gain in these films is 4 times higher than gain reported for other colloidal nanocrystals, and saturates at pump fluences more than two orders of magnitude above the ASE threshold. We attribute this exceptional performance to large optical cross-sections, relatively slow Auger recombination rates, and narrow ensemble emission linewidths.

  14. Colloidal Phenomena.

    ERIC Educational Resources Information Center

    Russel, William B.; And Others

    1979-01-01

    Described is a graduate level engineering course offered at Princeton University in colloidal phenomena stressing the physical and dynamical side of colloid science. The course outline, reading list, and requirements are presented. (BT)

  15. Final Report for DE-FG36-08GO18007 "All-Inorganic, Efficient Photovoltaic Solid State Devices Utilizing Semiconducting Colloidal Nanocrystal Quantum Dots"

    SciTech Connect

    Vladimir Bulovic and Moungi Bawendi

    2011-09-30

    We demonstrated robust colloidal quantum dot (QD) photovoltaics with high internal quantum efficiencies. In our structures, device durability is derived from use of all-inorganic atmospherically-stable semiconducting metal-oxide films together with QD photoreceptors. We have shown that both QD and metal-oxide semiconducting films and contacts are amenable to room temperature processing under minimal vacuum conditions, enabling large area processing of PV structures of high internal efficiency. We generated the state of the art devices with power conversion efficiency of more than 4%, and have shown that efficiencies as high as 9% are achievable in the near-term, and as high as 17% in the long-term.

  16. Trap-Assisted Transport and Non-Uniform Charge Distribution in Sulfur-Rich PbS Colloidal Quantum Dot-based Solar Cells with Selective Contacts.

    PubMed

    Malgras, Victor; Zhang, Guanran; Nattestad, Andrew; Clarke, Tracey M; Mozer, Attila J; Yamauchi, Yusuke; Kim, Jung Ho

    2015-12-01

    This study reports evidence of dispersive transport in planar PbS colloidal quantum dot heterojunction-based devices as well as the effect of incorporating a MoO3 hole selective layer on the charge extraction behavior. Steady state and transient characterization techniques are employed to determine the complex recombination processes involved in such devices. The addition of a selective contact drastically improves the device efficiency up to 3.15% (especially due to increased photocurrent and decreased series resistance) and extends the overall charge lifetime by suppressing the main first-order recombination pathway observed in device without MoO3. The lifetime and mobility calculated for our sulfur-rich PbS-based devices are similar to previously reported values in lead-rich quantum dots-based solar cells. Nevertheless, strong Shockley-Read-Hall mechanisms appear to keep restricting charge transport, as the equilibrium voltage takes more than 1 ms to be established. PMID:26541422

  17. Critical role of CdSe nanoplatelets in color-converting CdSe/ZnS nanocrystals for InGaN/GaN light-emitting diodes.

    PubMed

    Hasanov, Namig; Sharma, Vijay Kumar; Hernandez Martinez, Pedro Ludwig; Tan, Swee Tiam; Demir, Hilmi Volkan

    2016-06-15

    Here we report CdSe nanoplatelets that are incorporated into color-converting CdSe/ZnS nanocrystals for InGaN/GaN light-emitting diodes. The critical role of CdSe nanoplatelets as an exciton donor for the color conversion was experimentally investigated. The power conversion efficiency of the hybrid light-emitting diode was found to increase by 23% with the incorporation of the CdSe nanoplatelets. The performance enhancement is ascribed to efficient exciton transfer from the donor CdSe nanoplatelet quantum wells to the acceptor CdSe/ZnS nanocrystal quantum dots through Förster-type nonradiative resonance energy transfer. PMID:27304313

  18. Cl-capped CdSe nanocrystals via in situ generation of chloride anions.

    PubMed

    Palencia, Cristina; Lauwaet, Koen; de la Cueva, Leonor; Acebrón, María; Conde, Julio J; Meyns, Michaela; Klinke, Christian; Gallego, José M; Otero, Roberto; Juárez, Beatriz H

    2014-06-21

    Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance ((1)H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio. PMID:24827847

  19. Biopolymer-protected CdSe nanoparticles.

    PubMed

    Bozanić, D K; Djoković, V; Bibić, N; Sreekumari Nair, P; Georges, M K; Radhakrishnan, T

    2009-11-23

    A synthetic procedure for the encapsulation of cadmium selenide (CdSe) nanoparticles in a sago starch matrix is introduced. The nanocomposite was investigated using structural, spectroscopic, and thermal methods. TEM micrographs of the nanocomposite showed spherical CdSe particles of 4-5 nm in size coated with a biopolymer layer. The absorption edges of both the aqueous solution and the thin film of the CdSe-starch nanocomposite were shifted toward lower wavelengths in comparison to the value of the bulk semiconductor. Infrared measurements revealed that the interaction of CdSe nanoparticles and starch chains takes place via OH groups. Although the onset of the temperature of decomposition of CdSe-starch nanocomposite is lower than that of the pure matrix, thermogravimetric analysis also showed that introduction of CdSe nanoparticles significantly reduced starch degradation rate leading to high residual mass at the end of the degradation process. PMID:19772959

  20. Ligand-surface interactions and surface oxidation of colloidal PbSe quantum dots revealed by thin-film positron annihilation methods

    NASA Astrophysics Data System (ADS)

    Shi, Wenqin; Eijt, Stephan W. H.; Suchand Sandeep, C. S.; Siebbeles, Laurens D. A.; Houtepen, Arjan J.; Kinge, Sachin; Brück, Ekkes; Barbiellini, Bernardo; Bansil, Arun

    2016-02-01

    Positron Two Dimensional Angular Correlation of Annihilation Radiation (2D-ACAR) measurements reveal modifications of the electronic structure and composition at the surfaces of PbSe quantum dots (QDs), deposited as thin films, produced by various ligands containing either oxygen or nitrogen atoms. In particular, the 2D-ACAR measurements on thin films of colloidal PbSe QDs capped with oleic acid ligands yield an increased intensity in the electron momentum density (EMD) at high momenta compared to PbSe quantum dots capped with oleylamine. Moreover, the EMD of PbSe QDs is strongly affected by the small ethylenediamine ligands, since these molecules lead to small distances between QDs and favor neck formation between near neighbor QDs, inducing electronic coupling between neighboring QDs. The high sensitivity to the presence of oxygen atoms at the surface can be also exploited to monitor the surface oxidation of PbSe QDs upon exposure to air. Our study clearly demonstrates that positron annihilation spectroscopy applied to thin films can probe surface transformations of colloidal semiconductor QDs embedded in functional layers.

  1. Application of DNA Aptamers and Quantum Dots to Lateral Flow Test Strips for Detection of Foodborne Pathogens with Improved Sensitivity versus Colloidal Gold

    PubMed Central

    Bruno, John G.

    2014-01-01

    Preliminary studies aimed at improving the sensitivity of foodborne pathogen detection via lateral flow (LF) test strips by use of high affinity DNA aptamers for capture and reporter functions when coupled to red-emitting quantum dots (Qdot 655) are reported. A variety of DNA aptamers developed against Escherichia coli, Listeria monocytogenes, and Salmonella enterica were paired in capture and reporter combinations to determine which yielded the strongest detection of their cognate bacteria using a colloidal gold screening system. Several promising sandwich combinations were identified for each of the three bacterial LF strip systems. The best E. coli aptamer-LF system was further studied and yielded a visible limit of detection (LOD) of ~3,000 E. coli 8739 and ~6,000 E. coli O157:H7 in buffer. These LODs were reduced to ~300–600 bacterial cells per test respectively by switching to a Qdot 655 aptamer-LF system. Novel aspects of these assays such as the use of high levels of detergents to avoid quantum dot agglutination and enhance migration in analytical membranes, identification of optimal analytical membrane types, UV-immobilization of capture aptamers, and novel dual biotin/digoxigenin-end labeled aptamer streptavidin-colloidal gold or -Qdot 655 conjugates plus anti-digoxigenin antibody control lines are also discussed. In general, this work provides proof-of-principle for highly sensitive aptamer-Qdot LF strip assays for rapid foodborne pathogen detection. PMID:25437803

  2. Application of DNA Aptamers and Quantum Dots to Lateral Flow Test Strips for Detection of Foodborne Pathogens with Improved Sensitivity versus Colloidal Gold.

    PubMed

    Bruno, John G

    2014-01-01

    Preliminary studies aimed at improving the sensitivity of foodborne pathogen detection via lateral flow (LF) test strips by use of high affinity DNA aptamers for capture and reporter functions when coupled to red-emitting quantum dots (Qdot 655) are reported. A variety of DNA aptamers developed against Escherichia coli, Listeria monocytogenes, and Salmonella enterica were paired in capture and reporter combinations to determine which yielded the strongest detection of their cognate bacteria using a colloidal gold screening system. Several promising sandwich combinations were identified for each of the three bacterial LF strip systems. The best E. coli aptamer-LF system was further studied and yielded a visible limit of detection (LOD) of ~3,000 E. coli 8739 and ~6,000 E. coli O157:H7 in buffer. These LODs were reduced to ~300-600 bacterial cells per test respectively by switching to a Qdot 655 aptamer-LF system. Novel aspects of these assays such as the use of high levels of detergents to avoid quantum dot agglutination and enhance migration in analytical membranes, identification of optimal analytical membrane types, UV-immobilization of capture aptamers, and novel dual biotin/digoxigenin-end labeled aptamer streptavidin-colloidal gold or -Qdot 655 conjugates plus anti-digoxigenin antibody control lines are also discussed. In general, this work provides proof-of-principle for highly sensitive aptamer-Qdot LF strip assays for rapid foodborne pathogen detection. PMID:25437803

  3. Thermal activation of non-radiative Auger recombination in charged colloidal nanocrystals.

    PubMed

    Javaux, C; Mahler, B; Dubertret, B; Shabaev, A; Rodina, A V; Efros, Al L; Yakovlev, D R; Liu, F; Bayer, M; Camps, G; Biadala, L; Buil, S; Quelin, X; Hermier, J-P

    2013-03-01

    Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature. PMID:23396313

  4. Resonant surface-enhanced Raman scattering by optical phonons in a monolayer of CdSe nanocrystals on Au nanocluster arrays

    NASA Astrophysics Data System (ADS)

    Milekhin, Alexander G.; Sveshnikova, Larisa L.; Duda, Tatyana A.; Rodyakina, Ekaterina E.; Dzhagan, Volodymyr M.; Sheremet, Evgeniya; Gordan, Ovidiu D.; Himcinschi, Cameliu; Latyshev, Alexander V.; Zahn, Dietrich R. T.

    2016-05-01

    Here we present the results on an investigation of resonant Stokes and anti- Stokes surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on arrays of Au nanoclusters using the Langmuir-Blodgett technology. The thickness of deposited NCs, determined by transmission and scanning electron microscopy, amounts to approximately 1 monolayer. Special attention is paid to the determination of the localized surface plasmon resonance (LSPR) energy in the arrays of Au nanoclusters as a function of the nanocluster size by means of micro-ellipsometry. SERS by optical phonons in CdSe NCs shows a significant enhancement factor with a maximal value of 2 × 103 which depends resonantly on the Au nanocluster size and thus on the LSPR energy. The deposition of CdSe NCs on the arrays of Au nanocluster dimers enabled us to study the polarization dependence of SERS. It was found that a maximal SERS signal is observed for the light polarization along the dimer axis. Finally, SERS by optical phonons was observed for CdSe NCs deposited on the structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates quasi-single NC Raman spectra being obtained.

  5. Construction of dentate bonded TiO2-CdSe heterostructures with enhanced photoelectrochemical properties: versatile labels toward photoelectrochemical and electrochemical sensing.

    PubMed

    Gao, Picheng; Ma, Hongmin; Yan, Tao; Wu, Dan; Ren, Xiang; Yang, Jiaojiao; Du, Bin; Wei, Qin

    2015-01-14

    A facile synthetic route for TiO2-CdSe heterostructures was proposed based on dentate binding of TiO2 to carboxyl. Carboxyl functionalized CdSe quantum dots (CF-CdSe QDs) were successfully bonded onto TiO2 nanoparticles (NPs), which could significantly improve the photoelectrochemical (PEC) properties of TiO2 NPs. This is ascribed to the fact that CdSe QDs with a narrow band gap could be stimulated under visible light irradiation, and the energy levels of TiO2 NPs and CF-CdSe QDs are aligned with an electrolyte solution. High resolution transmission electron microscopy images revealed the heterostructures of the TiO2-CdSe composites. Ultraviolet visible spectroscopy, photoluminescence emission spectroscopy and electrochemical impedance spectroscopy analysis exhibited that the prepared TiO2-CdSe heterostructures have improved light absorption, charge separation efficiency and electron transfer ability in the visible light region. TiO2-CdSe heterostructures were used as versatile labels for fabrication of PEC and electrochemical immunosensors, and human immune globulin G (HIgG) was used as a model analyte. The immunosensor showed high sensitivity, a low detection limit and a wide linear range, which could be applied in practical serum sample analysis. The constructed TiO2-CdSe heterostructures would have potential applications in photocatalysis, aptasensors, cytosensors and other areas of nanotechnology. PMID:25408238

  6. Colloidal nanocrystals integrated in epitaxial nanostructures: structural and optical properties

    NASA Astrophysics Data System (ADS)

    Arens, Ch.; Roussau, N.; Schikora, D.; Lischka, K.; Schöps, O.; Herz, E.; Woggon, U.; Litvinov, D.; Gerthsen, D.; Artemyev, M. V.

    2006-03-01

    Using the well established MBE process, we introduced colloidal nanocrystals (NCs) into monocrystalline semiconductor layers. CdSe nanorods (NRs) and CdSe(ZnS) core-shell nanodots (NDs) with radii R between 2 and 4 nm on a ZnSe surface are capped by thin (d 2R ) and thick (d > 2R ) MBE-grown ZnSe layers of a thickness d . This new growth technique does not rely on strain like the Stranski-Krastanow growth of CdSe/ZnSe quantum dot layers, and thus offers additional degrees of freedom for choosing the NC composition, shape and size. In- and ex- situ characterisations of the samples are showing a ZnSe cap layer of high crystalline quality. After the growth of the cap layer the dots preserve their shape and emission spectrum. High-resolution transmission electron microscope images show the direct connection of the NCs crystal lattice to the crystal lattices of the ZnSe buffer and the epitaxially grown cap layer.

  7. Random Lasing with Systematic Threshold Behavior in Films of CdSe/CdS Core/Thick-Shell Colloidal Quantum Dots.

    PubMed

    Gollner, Claudia; Ziegler, Johannes; Protesescu, Loredana; Dirin, Dmitry N; Lechner, Rainer T; Fritz-Popovski, Gerhard; Sytnyk, Mykhailo; Yakunin, Sergii; Rotter, Stefan; Yousefi Amin, Amir Abbas; Vidal, Cynthia; Hrelescu, Calin; Klar, Thomas A; Kovalenko, Maksym V; Heiss, Wolfgang

    2015-10-27

    While over the past years the syntheses of colloidal quantum dots (CQDs) with core/shell structures were continuously improved to obtain highly efficient emission, it has remained a challenge to use them as active materials in laser devices. Here, we report random lasing at room temperature in films of CdSe/CdS CQDs with different core/shell band alignments and extra thick shells. Even though the lasing process is based on random scattering, we find systematic dependencies of the laser thresholds on morphology and laser spot size. To minimize laser thresholds, optimizing the film-forming properties of the CQDs, proven by small-angle X-ray scattering, was found to be more important than the optical parameters of the CQDs, such as biexciton lifetime and binding energy or fluorescence decay time. Furthermore, the observed systematic behavior turned out to be highly reproducible after storing the samples in air for more than 1 year. These highly reproducible systematic dependencies suggest that random lasing experiments are a valuable tool for testing nanocrystal materials, providing a direct and simple feedback for further development of colloidal gain materials toward lasing in continuous wave operation. PMID:26364796

  8. In situ investigation of energy transfer in hybrid organic/colloidal quantum dot light-emitting diodes via magneto-electroluminescence.

    PubMed

    Chen, Lixiang; Chen, Qiusong; Lei, Yanlian; Jia, Weiyao; Yuan, De; Xiong, Zuhong

    2016-08-10

    Energy transfer (ET) and charge injection (CI) in the hybrid organic/colloidal quantum dot light-emitting diodes (QD-LEDs) have been investigated by using magneto-electroluminescence (MEL) as an in situ tool. The feasibility and availability of MEL as an in situ tool were systematically demonstrated in the typical QD-LEDs based on CdSe-ZnS core-shell QDs. Our results suggest that the ET and CI processes can be well discerned by MEL measurements since these two processes exhibit distinct responses to the applied magnetic field. Through measurement of the MEL and current efficiency, we indicated that ET would be the main mechanism for light emission in the present hybrid QD-LEDs. This study strongly suggests that MEL could be a highly sensitive fingerprint for ET, which provides a facile and efficient method for the in situ investigation of fundamental processes in hybrid organic/colloidal QD-LEDs and other organic/inorganic composites. PMID:27461412

  9. Controlled waveguide coupling for photon emission from colloidal PbS quantum dot using tunable microcavity made of optical polymer and silicon

    NASA Astrophysics Data System (ADS)

    Nozaka, Takahiro; Mukai, Kohki

    2016-04-01

    A tunable microcavity device composed of optical polymer and Si with a colloidal quantum dot (QD) is proposed as a single-photon source for planar optical circuit. Cavity size is controlled by electrostatic micromachine behavior with the air bridge structure to tune timing of photon injection into optical waveguide from QD. Three-dimensional positioning of a QD in the cavity structure is available using a nanohole on Si processed by scanning probe microscope lithography. We fabricated the prototype microcavity with PbS-QD-mixed polymenthyl methacrylate on a SOI (semiconductor-on-insulator) substrate to show the tunability of cavity size as the shift of emission peak wavelength of QD ensemble.

  10. Colloidal Synthesis of Quantum Confined Single Crystal CsPbBr3 Nanosheets with Lateral Size Control up to the Micrometer Range

    PubMed Central

    2016-01-01

    We report the nontemplated colloidal synthesis of single crystal CsPbBr3 perovskite nanosheets with lateral sizes up to a few micrometers and with thickness of just a few unit cells (i.e., below 5 nm), hence in the strong quantum confinement regime, by introducing short ligands (octanoic acid and octylamine) in the synthesis together with longer ones (oleic acid and oleylamine). The lateral size is tunable by varying the ratio of shorter ligands over longer ligands, while the thickness is mainly unaffected by this parameter and stays practically constant at 3 nm in all the syntheses conducted at short-to-long ligands volumetric ratio below 0.67. Beyond this ratio, control over the thickness is lost and a multimodal thickness distribution is observed. PMID:27228475

  11. Colloidal Synthesis of Quantum Confined Single Crystal CsPbBr3 Nanosheets with Lateral Size Control up to the Micrometer Range.

    PubMed

    Shamsi, Javad; Dang, Zhiya; Bianchini, Paolo; Canale, Claudio; Stasio, Francesco Di; Brescia, Rosaria; Prato, Mirko; Manna, Liberato

    2016-06-15

    We report the nontemplated colloidal synthesis of single crystal CsPbBr3 perovskite nanosheets with lateral sizes up to a few micrometers and with thickness of just a few unit cells (i.e., below 5 nm), hence in the strong quantum confinement regime, by introducing short ligands (octanoic acid and octylamine) in the synthesis together with longer ones (oleic acid and oleylamine). The lateral size is tunable by varying the ratio of shorter ligands over longer ligands, while the thickness is mainly unaffected by this parameter and stays practically constant at 3 nm in all the syntheses conducted at short-to-long ligands volumetric ratio below 0.67. Beyond this ratio, control over the thickness is lost and a multimodal thickness distribution is observed. PMID:27228475

  12. White light emitting diode based on InGaN chip with core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Shen, Changyu; Hong, Yan; Ma, Jiandong; Ming, Jiangzhou

    2009-08-01

    Quantum dots have many applications in optoelectronic device such as LEDs for its many superior properties resulting from the three-dimensional confinement effect of its carrier. In this paper, single chip white light-emitting diodes (WLEDs) were fabricated by combining blue InGaN chip with luminescent colloidal quantum dots (QDs). Two kinds of QDs of core/shell CdSe /ZnS and core/shell/shell CdSe /ZnS /CdS nanocrystals were synthesized by thermal deposition using cadmium oxide and selenium as precursors in a hot lauric acid and hexadecylamine trioctylphosphine oxide hybrid. This two kinds of QDs exhibited high photoluminescence efficiency with a quantum yield more than 41%, and size-tunable emission wavelengths from 500 to 620 nm. The QDs LED mainly consists of flip luminescent InGaN chip, glass ceramic protective coating, glisten cup, QDs using as the photoluminescence material, pyroceram, gold line, electric layer, dielectric layer, silicon gel and bottom layer for welding. The WLEDs had the CIE coordinates of (0.319, 0.32). The InGaN chip white-light-emitting diodes with quantum dots as the emitting layer are potentially useful in illumination and display applications.

  13. The design and synthesis of heterostructured quantum dots with dual emission in the visible and infrared

    DOE PAGESBeta

    Lin, Qianglu; Makarov, Nikolay S.; Koh, Weon-kyu; Velizhanin, Kirill A.; Cirloganu, Claudiu M.; Luo, Hongmei; Klimov, Victor I.; Pietryga, Jeffrey M.

    2014-11-26

    The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR) -active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intra-band relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from themore » CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogenous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe as well as the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.« less

  14. The design and synthesis of heterostructured quantum dots with dual emission in the visible and infrared

    SciTech Connect

    Lin, Qianglu; Makarov, Nikolay S.; Koh, Weon-kyu; Velizhanin, Kirill A.; Cirloganu, Claudiu M.; Luo, Hongmei; Klimov, Victor I.; Pietryga, Jeffrey M.

    2014-11-26

    The unique optical properties exhibited by visible emitting core/shell quantum dots with especially thick shells are the focus of widespread study, but have yet to be realized in infrared (IR) -active nanostructures. We apply an effective-mass model to identify PbSe/CdSe core/shell quantum dots as a promising system for achieving this goal. We then synthesize colloidal PbSe/CdSe quantum dots with shell thicknesses of up to 4 nm that exhibit unusually slow hole intra-band relaxation from shell to core states, as evidenced by the emergence of dual emission, i.e., IR photoluminescence from the PbSe core observed simultaneously with visible emission from the CdSe shell. In addition to the large shell thickness, the development of slowed intraband relaxation is facilitated by the existence of a sharp core-shell interface without discernible alloying. Growth of thick shells without interfacial alloying or incidental formation of homogenous CdSe nanocrystals was accomplished using insights attained via a systematic study of the dynamics of the cation-exchange synthesis of both PbSe/CdSe as well as the related system PbS/CdS. Finally, we show that the efficiency of the visible photoluminescence can be greatly enhanced by inorganic passivation.

  15. Real-time in situ probing of high-temperature quantum dots solution synthesis.

    PubMed

    Abécassis, Benjamin; Bouet, Cécile; Garnero, Cyril; Constantin, Doru; Lequeux, Nicolas; Ithurria, Sandrine; Dubertret, Benoit; Pauw, Brian Richard; Pontoni, Diego

    2015-04-01

    Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium. PMID:25815414

  16. Photoluminescence study of the substitution of Cd by Zn during the growth by atomic layer epitaxy of alternate CdSe and ZnSe monolayers

    SciTech Connect

    Hernández-Calderón, I.; Salcedo-Reyes, J. C.

    2014-05-15

    We present a study of the substitution of Cd atoms by Zn atoms during the growth of alternate ZnSe and CdSe compound monolayers (ML) by atomic layer epitaxy (ALE) as a function of substrate temperature. Samples contained two quantum wells (QWs), each one made of alternate CdSe and ZnSe monolayers with total thickness of 12 ML but different growth parameters. The QWs were studied by low temperature photoluminescence (PL) spectroscopy. We show that the Cd content of underlying CdSe layers is affected by the exposure of the quantum well film to the Zn flux during the growth of ZnSe monolayers. The amount of Cd of the quantum well film decreases with higher exposures to the Zn flux. A brief discussion about the difficulties to grow the Zn{sub 0.5}Cd{sub 0.5}Se ordered alloy (CuAu-I type) by ALE is presented.

  17. Air-Stable, Near- to Mid-Infrared Emitting Solids of PbTe/CdTe Core-Shell Colloidal quantum dots.

    PubMed

    Protesescu, Loredana; Zünd, Tanja; Bodnarchuk, Maryna I; Kovalenko, Maksym V

    2016-03-01

    Light emitters and detectors operating in the near- and mid-infrared spectral regions are important to many applications, such as telecommunications, high-resolution gas analysis, atmospheric pollution monitoring, medical diagnostics, and night vision. Various lead chalcogenides (binary, ternary, and quaternary alloys) in the form of quantum dots (QDs) or quantum wells provide narrow bandgap energies that cover the broad infrared region corresponding to wavelengths of 1-30 μm. Here, we report an inexpensive, all-solution-based synthesis strategy to thin-film solids consisting of 5-16 nm PbTe QDs encapsulated by CdTe shells. Colloidally synthesized PbTe QDs were first converted into core-shell PbTe/CdTe QDs, and then deposited as thin films. The subsequent fusion of the CdTe shells is achieved by ligand removal and annealing in the presence of CdCl2 . Contrary to highly unstable bare PbTe QDs, PbTe/CdTe QD solids exhibit bright and stable near- to mid-infrared emission at wavelengths of 1-3 μm, which is also retained upon prolonged storage at ambient conditions for one year. PMID:26676076

  18. Hybrid nanostructures of well-organized arrays of colloidal quantum dots and a self-assembled monolayer of gold nanoparticles for enhanced fluorescence.

    PubMed

    Liu, Xiaoying; McBride, Sean P; Jaeger, Heinrich M; Nealey, Paul F

    2016-07-15

    Hybrid nanomaterials comprised of well-organized arrays of colloidal semiconductor quantum dots (QDs) in close proximity to metal nanoparticles (NPs) represent an appealing system for high-performance, spectrum-tunable photon sources with controlled photoluminescence. Experimental realization of such materials requires well-defined QD arrays and precisely controlled QD-metal interspacing. This long-standing challenge is tackled through a strategy that synergistically combines lateral confinement and vertical stacking. Lithographically generated nanoscale patterns with tailored surface chemistry confine the QDs into well-organized arrays with high selectivity through chemical pattern directed assembly, while subsequent coating with a monolayer of close-packed Au NPs introduces the plasmonic component for fluorescence enhancement. The results show uniform fluorescence emission in large-area ordered arrays for the fabricated QD structures and demonstrate five-fold fluorescence amplification for red, yellow, and green QDs in the presence of the Au NP monolayer. Encapsulation of QDs with a silica shell is shown to extend the design space for reliable QD/metal coupling with stronger enhancement of 11 times through the tuning of QD-metal spatial separation. This approach provides new opportunities for designing hybrid nanomaterials with tailored array structures and multiple functionalities for applications such as multiplexed optical coding, color display, and quantum transduction. PMID:27251019

  19. Optical and electrical characterizations of a single step ion beam milling mesa devices of chloride passivated PbS colloidal quantum dots based film

    NASA Astrophysics Data System (ADS)

    Hechster, Elad; Shapiro, Arthur; Lifshitz, Efrat; Sarusi, Gabby

    2016-07-01

    Colloidal Quantum Dots (CQDs) are of increasing interest, thanks to their quantum size effect that gives rise to their usage in various applications, such as biological tagging, solar cells and as the sensitizing layer of night vision devices. Here, we analyze the optical absorbance of chloride passivated PbS CQDs as well as revealing a correlation between their photoluminescence and sizes distribution, using theoretical models and experimental results from the literature. Next, we calculate the CQDs resistivity as a film. Although resistivity can be calculated from sheet resistance measurement using four point probes, such measurement is usually carried-out on the layer's surface that in most cases has dangling bonds and surface states, which might affect the charges flow and modify the resistivity. Therefore; our approach, which was applied in this work, is to extract the actual resistivity from measurements that are performed along the film's thickness (z-direction). For this intent, we fabricated gold capped PbS mesas devices using a single step Ion Beam Milling (IBM) process where we milled the gold and the PbS film continually, and then measured the vertical resistance. Knowing the mesas' dimensions, we calculate the resistivity. To the best of our knowledge, no previous work has extracted, vertically, the resistivity of chloride passivated PbS CQDs using the above method.

  20. Hybrid nanostructures of well-organized arrays of colloidal quantum dots and a self-assembled monolayer of gold nanoparticles for enhanced fluorescence

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoying; McBride, Sean P.; Jaeger, Heinrich M.; Nealey, Paul F.

    2016-07-01

    Hybrid nanomaterials comprised of well-organized arrays of colloidal semiconductor quantum dots (QDs) in close proximity to metal nanoparticles (NPs) represent an appealing system for high-performance, spectrum-tunable photon sources with controlled photoluminescence. Experimental realization of such materials requires well-defined QD arrays and precisely controlled QD–metal interspacing. This long-standing challenge is tackled through a strategy that synergistically combines lateral confinement and vertical stacking. Lithographically generated nanoscale patterns with tailored surface chemistry confine the QDs into well-organized arrays with high selectivity through chemical pattern directed assembly, while subsequent coating with a monolayer of close-packed Au NPs introduces the plasmonic component for fluorescence enhancement. The results show uniform fluorescence emission in large-area ordered arrays for the fabricated QD structures and demonstrate five-fold fluorescence amplification for red, yellow, and green QDs in the presence of the Au NP monolayer. Encapsulation of QDs with a silica shell is shown to extend the design space for reliable QD/metal coupling with stronger enhancement of 11 times through the tuning of QD–metal spatial separation. This approach provides new opportunities for designing hybrid nanomaterials with tailored array structures and multiple functionalities for applications such as multiplexed optical coding, color display, and quantum transduction.

  1. High resolution photoemission study of CdSe and CdSe/ZnS core-shell nanocrystals

    NASA Astrophysics Data System (ADS)

    Borchert, H.; Talapin, D. V.; McGinley, C.; Adam, S.; Lobo, A.; de Castro, A. R. B.; Möller, T.; Weller, H.

    2003-07-01

    Colloidally prepared CdSe and CdSe/ZnS core-shell nanocrystals passivated with trioctylphosphine/trioctylphosphine oxide and hexadecylamine have been studied by photoelectron spectroscopy with tuneable synchrotron radiation. High-resolution spectra of the Se 3d level in CdSe nanocrystals indicate the bonding of organic ligands not only to surface Cd but also to surface Se atoms. The investigation of the CdSe/ZnS core-shell nanocrystals allows us to determine the average thickness of the ZnS shell and to study the interface between the two semiconductor nanomaterials. The photoemission spectra indicate a rather well ordered interface. No evidence for interfacial bonds other than Cd-S and Se-Zn is found.

  2. Analysis of the effects of surface chemistry on the XAS spectra of CdSe nanomaterials

    NASA Astrophysics Data System (ADS)

    Whitley, Heather; Prendergast, David; Ogitsu, Tadashi; Schwegler, Eric

    2010-03-01

    X-ray absorption spectroscopy (XAS) is an element-specific probe of local electronic structure, and is an ideal method to analyze chemical bonding. We investigate the consistency of theoretically predicted structures of CdSe nanomaterials with recently measured XAS via ab initio calculations. Using plane-wave DFT, the x-ray absorption cross-section for the Cd L3-edge of small CdSe clusters with a variety of surface ligands is calculated. We also highlight the importance of including excitonic effects in our simulations of core excitation spectra. We compare our simulations to existing experimental data on the ligand dependence of XAS for ligated quantum dots up to ˜3nm in diameter. Based on the favorable comparison of our theoretical spectra with experimental measurements, we infer the validity of our DFT-derived structure and surface passivation for these quantum dots and its relevance to understanding optoelectronic properties of solution-synthesized CdSe nanocrystals. Prepared by LLNL under Contract DE-AC52-07NA27344.

  3. Hexadecapolar colloids

    PubMed Central

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  4. Colloidal polypyrrole

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  5. Hexadecapolar colloids

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of `colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  6. Hexadecapolar colloids.

    PubMed

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M; Chernyshuk, Stanislav B; Smalyukh, Ivan I

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of 'colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  7. Hexadecapolar Colloids

    DOE PAGESBeta

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

  8. Distance-Dependent Triplet Energy Transfer between CdSe Nanocrystals and Surface Bound Anthracene.

    PubMed

    Li, Xin; Huang, Zhiyuan; Zavala, Ramsha; Tang, Ming Lee

    2016-06-01

    We investigate triplet energy transfer (TET) across variable-length aromatic oligo-p-phenylene and aliphatic bridges in a covalently linked CdSe nanocrystal (NC)-bridge-anthracene hybrid system. Photon upconversion measurements in saturated 9,10-diphenylanthracene hexane solutions under air-free conditions at room temperature provided the steady-state rate of TET (ket) across this interface. For flexible transmitters, ket is similar for different lengths of aliphatic bridges, suggesting that the ligands bend backward. For the rigid phenylene spacer, triplet sensitization of anthracene transmitter molecules by CdSe NCs shows a strong distance dependence, with a Dexter damping coefficient of 0.43 ± 0.07 Å(-1). The anthracene transmitter bound closest to the NC surface gave the highest quantum yield of 14.3% for the conversion of green to violet light, the current record for a hybrid platform. PMID:27164056

  9. Coherent Acoustic Phonons in Colloidal Semiconductor Nanocrystal Superlattices.

    PubMed

    Poyser, Caroline L; Czerniuk, Thomas; Akimov, Andrey; Diroll, Benjamin T; Gaulding, E Ashley; Salasyuk, Alexey S; Kent, Anthony J; Yakovlev, Dmitri R; Bayer, Manfred; Murray, Christopher B

    2016-01-26

    The phonon properties of films fabricated from colloidal semiconductor nanocrystals play a major role in thermal conductance and electron scattering, which govern the principles for building colloidal-based electronics and optics including thermoelectric devices with a high ZT factor. The key point in understanding the phonon properties is to obtain the strength of the elastic bonds formed by organic ligands connecting the individual nanocrystallites. In the case of very weak bonding, the ligands become the bottleneck for phonon transport between infinitively rigid nanocrystals. In the opposite case of strong bonding, the colloids cannot be considered as infinitively rigid beads and the distortion of the superlattice caused by phonons includes the distortion of the colloids themselves. We use the picosecond acoustics technique to study the acoustic coherent phonons in superlattices of nanometer crystalline CdSe colloids. We observe the quantization of phonons with frequencies up to 30 GHz. The frequencies of quantized phonons depend on the thickness of the colloidal films and possess linear phonon dispersion. The measured speed of sound and corresponding wave modulus in the colloidal films point on the strong elastic coupling provided by organic ligands between colloidal nanocrystals. PMID:26696021

  10. A simple and facile synthesis of MPA capped CdSe and CdSe/CdS core/shell nanoparticles

    SciTech Connect

    Sukanya, D.; Sagayaraj, P.

    2015-06-24

    II-VI semiconductor nanostructures, in particular, CdSe quantum dots have drawn a lot of attention because of their promising potential applications in biological tagging, photovoltaic, display devices etc. due to their excellent optical properties, high emission quantum yield, size dependent emission wavelength and high photostability. In this paper, we describe the synthesis and properties of mercaptopropionic acid capped CdSe and CdSe/CdS nanoparticles through a simple and efficient co-precipitation method followed by hydrothermal treatment. The growth process, characterization and the optical absorption as a function of wavelength for the synthesized MPA capped CdSe and CdSe/CdS nanoparticles have been determined using X-ray diffraction study (XRD), Ultraviolet-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and High Resolution Transmission Electron Microscopy (HRTEM)

  11. Upconversion Nanoparticles for Security Printing and CdSe QDs for Drug Delivery Applications

    NASA Astrophysics Data System (ADS)

    Baride, Aravind

    demonstrated NIR light induced release of a target molecule, coumarin, from functionalized quantum dots. Coumarin, a model drug molecule, is released upon NIR two-photon excitation of cinnamate capped CdSe QDs. Electron transfer from the excited QD to the cinnamate ligand induces the release of coumarin. The electron transfer across the QD to the cinnamate ligand is confirmed by evaluation of uncaging activity in the cinnamate capped CdSe/ZnS core-shell QDs.

  12. Enhanced emission of charged-exciton polaritons from colloidal quantum dots on a SiN/SiO2 slab waveguide

    PubMed Central

    Xu, Xingsheng; Li, Xingyun

    2015-01-01

    We investigate the photoluminescence (PL) spectra and the time-resolved PL decay process from colloidal quantum dots on SiN/SiO2 wet etched via BOE (HF:NH4F:H2O). The spectrum displays multi-peak shapes that vary with irradiation time. The evolution of the spectral peaks with irradiation time and collection angle demonstrates that the strong coupling of the charged-exciton emission to the leaky modes of the SiN/SiO2 slab waveguide predominantly produces short-wavelength spectral peaks, resulting in multi-peak spectra. We conclude that BOE etching enhances the charged-exciton emission efficiency and its contribution to the total emission compared with the unetched case. BOE etching smoothes the electron confinement potential, thus decreasing the Auger recombination rate. Therefore, the charged-exciton emission efficiency is high, and the charged-exciton-polariton emission can be further enhanced through strong coupling to the leaky mode of the slab waveguide. PMID:25988709

  13. Ultralow Threshold One-Photon- and Two-Photon-Pumped Optical Gain Media of Blue-Emitting Colloidal Quantum Dot Films.

    PubMed

    Guzelturk, Burak; Kelestemur, Yusuf; Akgul, Mehmet Zafer; Sharma, Vijay Kumar; Demir, Hilmi Volkan

    2014-07-01

    Colloidal quantum dots (QDs) offer advantageous properties as an optical gain media for lasers. Optical gain in the QDs has been shown in the whole visible spectrum, yet it has been intrinsically challenging to realize efficient amplified spontaneous emission (ASE) and lasing in the blue region of the visible spectrum. Here, we synthesize large-sized core/gradient shell CdZnS/ZnS QDs as an efficient optical gain media in the blue spectral range. In this Letter, we demonstrate for the first time that two-photon-absorption-pumped ASE from the blue-emitting QD is achievable with a threshold as low as 6 mJ/cm(2). Utilizing these QDs, we also report one-photon-absorption-pumped ASE at an ultralow threshold of ∼60 μJ/cm(2), which is comparable to the state-of-the-art red-emitting QD-based gain media. This one-photon-pumped ASE threshold is an order of magnitude better than that of the previously reported best blue-emitting QD-based gain media. PMID:26279536

  14. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio

    2013-12-04

    The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured and reported. Two samples, consisting of thirty Ultra Thin Quantum Wells (UTQWs) of CdSe embedded in ZnSe, grown by Atomic Layer Epitaxy, are used for this study. The thicknesses of the UTQWs are one and three monolayers (MLs) in each sample, respectively. As expected, the sample with one ML UTQWs does not show any energy level in the UTQWs due to the small thickness of the UTQWs, while the thickness of the sample with 3 ML UTQWs is large enough to form an energy level inside the UTQWs. This energy level appears as a majority trap with an activation energy of 223.58 ± 9.54 meV. This corresponds to UTQWs with barrier heights (the conduction band offset) between 742 meV and 784 meV. These values suggest that the band gap misfit between strained CdSe and ZnSe is around 70.5 to 74 % in the conduction band.

  15. Electrogenerated chemiluminescence from a CdSe nanocrystal film and its sensing application in aqueous solution.

    PubMed

    Zou, Guizheng; Ju, Huangxian

    2004-12-01

    Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots in aqueous solutions and its first sensing application were studied by depositing CdSe nanocrystals (NCs) on a paraffin-impregnated graphite electrode (PIGE). The CdSe nanocrystal thin film exhibited two ECL peaks at -1.20 (ECL-1) and -1.50 V (ECL-2) in pH 9.3, 0.1 M PBS during the cyclic sweep between 0 and -1.8 V at 20 mV s(-1). The electron-transfer reaction between individual electrochemically reduced nanocrystal species and oxidant coreactants such as H(2)O(2) and reduced dissolved oxygen led to ECL-1. When mass NCs packed densely in the film were reduced electrochemically, assembly of reduced nanocrystal species could react with coreactants to produce another ECL signal, ECL-2. ECL-1 showed higher sensitivity to the concentration of oxidant coreactants than ECL-2 and thus was used for ECL detection of coreactant, H(2)O(2). A linear response of ECL-1 to H(2)O(2) was observed in the concentration range of 2.5 x 10(-7)-6 x 10(-5) M with a detection limit of 1.0 x10(-7) M. The fabrication of 10 CdSe nanocrystal thin-film modified PIGEs displayed an acceptable reproducibility with a RSD of 1.18% obtained at H(2)O(2) level of 10 microM. PMID:15571335

  16. Detection of bright trion states using the fine structure emission of single CdSe/ZnS colloidal quantum dots.

    PubMed

    Fernée, Mark J; Littleton, Bradley N; Rubinsztein-Dunlop, Halina

    2009-11-24

    We report direct observation of the lowest two states of the band-edge exciton fine structure in the photoluminescence from single CdSe/ZnS core/shell nanocrystals at cryogenic temperatures. The temperature dependence of this spectral fingerprint reveals exciton spin relaxation rates as low as 10 micros(-1). The fine structure is also dependent on the nanocrystal charge state facilitating the identification of a bright negatively charged trion state with a quantum yield comparable to that of neutral emission. PMID:19835398

  17. Colloidal polyaniline

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized amino-substituted aromatic monomer, a stabilizing effective amount of a random copolymer containing amino-benzene type moieties as side chain constituents, and dopant anions, and a method of preparing such polymer compositions are provided.

  18. Colloidal silicon quantum dots: synthesis and luminescence tuning from the near-UV to the near-IR range

    NASA Astrophysics Data System (ADS)

    Ghosh, Batu; Shirahata, Naoto

    2014-02-01

    This review describes a series of representative synthesis processes, which have been developed in the last two decades to prepare silicon quantum dots (QDs). The methods include both top-down and bottom-up approaches, and their methodological advantages and disadvantages are presented. Considerable efforts in surface functionalization of QDs have categorized it into (i) a two-step process and (ii) in situ surface derivatization. Photophysical properties of QDs are summarized to highlight the continuous tuning of photoluminescence color from the near-UV through visible to the near-IR range. The emission features strongly depend on the silicon nanostructures including QD surface configurations. Possible mechanisms of photoluminescence have been summarized to ascertain the future challenges toward industrial use of silicon-based light emitters.

  19. Influence of dielectric environment on exciton and bi-exciton properties in colloidal, type II quantum dots

    NASA Astrophysics Data System (ADS)

    Miloszewski, Jacek M.; Walsh, Thomas; Tomić, Stanko

    2015-05-01

    We present theoretical calculations of type II CdSe/CdTe quantum dots systems. We use an 8-band k.p Hamiltonian that includes spin-orbit interaction, strain, and first order piezoelectric effects. Exciton and bi-exciton states are found using the configuration interaction (CI) method that explicitly includes the effects of the Coulomb interaction, as well as exchange and correlation effects between many-electron configurations. We study convergence of the CI Hamiltonian with respect to the number of single particle states used in creation of the Hamiltonian. We show that there is a very strong correlation between the dielectric constant of the environment and exciton and bi-exciton energies.

  20. Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals.

    PubMed

    Rice, William D; Liu, Wenyong; Baker, Thomas A; Sinitsyn, Nikolai A; Klimov, Victor I; Crooker, Scott A

    2016-02-01

    Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn(2+), Co(2+) and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large Beff that exist in Mn(2+)-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ∼ 15 -30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn(2+) moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials. PMID:26595331