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Sample records for cdse obtenidas por

  1. Ab Initio Study on Atomic Structures and Physical Properties of CdSe Quantum Nanodots

    DTIC Science & Technology

    2009-11-25

    CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ). Effects of organic ligand binding on the stability of CdSe as well...calculations of optical absorption spectra for CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ), have been calculated in...1 AOARD-08-4037 Title of Proposed Project: Ab initio study on atomic structures and physical

  2. Amphoteric CdSe nanocrystalline quantum dots.

    PubMed

    Islam, Mohammad A

    2008-06-25

    The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.

  3. Shell deposition of CdSe nano dots and rods

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Chen, Hsueh Shin; Zhang, Qiang; Shi, Ruixia; Wang, Junpeng; Che, Quande

    2014-08-01

    To investigate the shell deposited kinetics, CdSe quantum dots (QDs) and nanorods (NRs) with a maximum length of 17 nm were fabricated via organic synthesis routes. CdSe with a hexagonal crystal structure (wurtzite) favors epitaxial growth on the {002} surfaces when well-controlled conditions were used. The morphologies and sizes of CdSe samples depended strongly on chemicals and temperature. In the case of 320 °C, CdSe NRs with adjusted length of 7-17 nm were obtained from trioctylphosphine oxide (TOPO) and tetradecylphosphonic acid (TDPA). In contrast, short CdSe NRs (less than 10 nm) were created from octadecylphosphonic acid (ODPA) and trioctylamine (TOA). Spherical CdSe QDs were further fabricated using stearic acid (SA) and TOPO at 300 °C. CdSe cores were coated with Cd0.5Zn0.5S and CdTe shells. Anisotropic growth occurred during shell deposition because CdS shells grown preferentially on the {001} facet of the CdSe core. In the case of CdSe core prepared from TOPO and TDPA, CdSe/Cd0.5Zn0.5S core/shell samples prepared from long CdSe NRs (more than 10 nm) revealed a peanut morphology while the core/shell samples created from short ones (less than 10 nm) exhibited a spherical morphology. All of the CdSe/Cd0.5Zn0.5S core/shell samples revealed a similar length to that of the CdSe cores. This phenomenon was also observed for the core/shell samples fabricated using CdSe NRs prepared by ODPA and TOA. This is ascribed to the well-developed crystal structure of CdSe NRs fabricated using an organic synthesis at high temperature. In contrast, this anisotropic growth did not occur when spherical CdSe QDs prepared from SA and TOPO and the shell (Cd0.5Zn0.5S) coating carried out using SA and TOA. To indicate the shell depositing process, CdSe NRs fabricated using TDPA and TOPO were coated with a CdTe shell. CdTe monomers were deposited on the middle and tip parts of the CdSe NRs to form a tetrapod-like morphology at 220 °C. This is ascribed to the large difference of

  4. Anisotropy in CdSe quantum rods

    SciTech Connect

    Li, Liang-shi

    2003-01-01

    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

  5. Phonons in bulk CdSe and CdSe nanowires.

    PubMed

    Mohr, Marcel; Thomsen, Christian

    2009-03-18

    We present first-principles calculations for bulk CdSe and CdSe nanowires with diameters of up to 22 A. Their electronic and structural properties are presented and discussed. The vibrational properties of bulk CdSe and the zone-center vibrations of the nanowires are calculated and analyzed. An iterative, symmetry-based relaxation method is used that yields improved results for phonon frequencies. We find that the band gap varies with the surface termination and that strongly size-dependent and nearly constant vibrational modes exist in the nanowires, depending on the displacement directions. A strong shift in frequency for specific modes is found, stemming from surface contributions to the polarization, similar to that reported for thin slabs. A comparison with experimental data from Raman measurements is given.

  6. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum.

    PubMed

    Yamaguchi, Takaaki; Tsuruda, Yoshijiro; Furukawa, Tomohiro; Negishi, Lumi; Imura, Yuki; Sakuda, Shohei; Yoshimura, Etsuro; Suzuki, Michio

    2016-10-20

    CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results suggested that the amount of superoxide dismutase (SOD) decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se(4+) to Se(2-) and inhibit the aggregation of CdSe to make nanoparticles.

  7. Biomolecular recognition in DNA tagged CdSe nanowires.

    PubMed

    Sarangi, S N; Goswami, K; Sahu, S N

    2007-06-15

    DNA template driven CdSe nanobeads (NBs) and nanowires (NWs) have been synthesized by an electrodeposition technique. The synthesis protocol has yielded randomly oriented cubic CdSe NBs with mean size approximately 3.0 nm in presence of single stranded DNA, poly G(30). Monocrystalline cubic CdSe NWs of width approximately 4.0 nm with string-like morphology have been achieved when synthesized in presence of both poly G(30) and its conjugate, poly C(30). Optical absorption of CdSe NBs show a blue shift of 0.8 eV and long wavelength tailing where as NWs show steep increase of absorption in shorter wavelength regime accompanied by a further blue shift. DNA tags to the NBs or NWs have been confirmed from Fourier transform infrared spectroscopy measurements. Biomolecular recognition with CdSe NWs have been established by photoluminescence measurements.

  8. Medición de placas astrométricas obtenidas con el telescopio Astrográfico de La Plata

    NASA Astrophysics Data System (ADS)

    di Sisto, R. P.; Orellana, R.

    El Observatorio de La Plata cuenta con un gran número de placas de asteroides y cometas obtenidas con el telescopio astrográfico, que cubren gran parte del cielo del hemisferio sur. En 1996 se recopilaron y clasificaron 2187 placas (Beca para estudiantes de la AAA 1996) de las cuales 2031 corresponden a asteroides. Los datos de cada placa se volcaron en una base de datos creada para facilitar su manejo y preservar la información. A partir de este trabajo se revisaron los MPC electrónicos y se identificaron aquellas placas de asteroides pertenecientes a nuestra base de datos cuyos resultados no fueron publicados en los mismos. De un total de 400 placas que no aparecían publicadas sobresalía un paquete constituído por 40 placas obtenidas en 1977. Estas últimas fueron reducidas utilizando las posiciones y movimientos propios de las estrellas de referencia obtenidas del catálogo SAO 2000 dadas para el sistema FK5. Las posiciones calculadas fueron enviadas y publicadas en los Minor Planet Circulars (MPC).

  9. Novel mechanical behaviors of wurtzite CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Fu, Bing; Chen, Li; Xie, Yiqun; Feng, Jie; Ye, Xiang

    2015-09-01

    As an important semiconducting nanomaterial, CdSe nanowires have attracted much attention. Although many studies have been conducted in the electronic and optical properties of CdSe NWs, the mechanical properties of Wurtzite (WZ) CdSe nanowires remain unclear. Using molecular dynamics simulations, we have studied the tensile mechanical properties and behaviors of [0001]-oriented Wurtzite CdSe nanowires. By monitoring the stretching processes of CdSe nanowires, three distinct structures are found: the WZ wire, a body-centered tetragonal structure with four-atom rings (denoted as BCT-4), and a structure that consists of ten-atom rings with two four-atom rings (denoted as TAR-4) which is observed for the first time. Not only the elastic tensile characteristics are highly reversible under unloading, but a reverse transition between TAR-4 and BCT-4 is also observed. The stretching processes also have a strong dependence on temperature. A tubular structure similar to carbon nanotubes is observed at 150 K, a single-atom chain is formed at 300, 350 and 450 K, and a double-atom chain is found at 600 K. Our findings on tensile mechanical properties of WZ CdSe nanowires does not only provide inspiration to future study on other properties of CdSe nanomaterials but also help design and build efficient nanoscale devices.

  10. Synthesis and characterization of Cr doped CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Majid, Abdul; Arshad, Humaira; Murtaza, Shahzad

    2015-09-01

    Chromium doped cadmium selenide (CdSe) nanoparticles were prepared via Chemical Co-precipitation Method. The effects of doping and doping concentration on structural and optical properties of the materials were studied. The structural characterization of samples carried out by using X-ray diffraction (XRD) indicated the formation of CdSe nanoparticles of zinc blend (cubic) polytype. It was also noted that lattice parameter decreases with increase in doping concentration. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the samples shows the presence of several modes of vibration related to CdSe nanoparticles and the dopant.

  11. Magnetic study of Fe-doped CdSe nanomaterials

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Banerjee, Sourish; Sinha, T. P.

    2016-05-01

    Nanoparticles of pure and iron (50 %) doped cadmium selenide (CdSe) have been synthesized by soft chemical route. EDAX analysis supports the inclusion of Fe into CdSe nanoparticles. The average particle size of pure and doped CdSe is found to be ˜50 nm from scanning electron microscopy (SEM). Magnetization of the samples are measured under the field cooled (FC) and zero field cooled (ZFC) modes in the temperature range from 5K to 300K applying a magnetic field of 500Oe. Field dependent magnetization (M-H) measurement indicates presence of room temperature (RT) paramagnetism and low temperature (5K) ferromagnetism of the sample.

  12. Magnetic study of Fe-doped CdSe nanomaterials

    SciTech Connect

    Das, Sayantani Banerjee, Sourish; Sinha, T. P.

    2016-05-06

    Nanoparticles of pure and iron (50 %) doped cadmium selenide (CdSe) have been synthesized by soft chemical route. EDAX analysis supports the inclusion of Fe into CdSe nanoparticles. The average particle size of pure and doped CdSe is found to be ∼50 nm from scanning electron microscopy (SEM). Magnetization of the samples are measured under the field cooled (FC) and zero field cooled (ZFC) modes in the temperature range from 5K to 300K applying a magnetic field of 500Oe. Field dependent magnetization (M-H) measurement indicates presence of room temperature (RT) paramagnetism and low temperature (5K) ferromagnetism of the sample.

  13. Reversible ultrafast melting in bulk CdSe

    SciTech Connect

    Wu, Wenzhi; He, Feng; Wang, Yaguo

    2016-02-07

    In this work, transient reflectivity changes in bulk CdSe have been measured with two-color femtosecond pump-probe spectroscopy under a wide range of pump fluences. Three regions of reflectivity change with pump fluences have been consistently revealed for excited carrier density, coherent phonon amplitude, and lattice temperature. For laser fluences from 13 to 19.3 mJ/cm{sup 2}, ultrafast melting happens in first several picoseconds. This melting process is purely thermal and reversible. A complete phase transformation in bulk CdSe may be reached when the absorbed laser energy is localized long enough, as observed in nanocrystalline CdSe.

  14. Photoelectric processes in CdSe thin film solar cells

    SciTech Connect

    Rickus, E.

    1984-05-01

    Efficiencies exceeding 7 percent have been achieved with CdSe/ZnSe/Au thin film solar cells. The collection efficiency of carriers in highly oriented CdSe films is near unity, resulting in short circuit current densities comparable to values observed on single crystalline cells. Recombination of carriers at the CdSe/ZnSe interface plays a minor role. CdSe /SUB x/ Te /SUB 1-x/ cells show the potential of enhanced short circuit current densities. Crystallographic and chemical inhomogeneities have a major influence on their performance. The comparison of photoelectrochemical cells based on CdSe single crystals and on polycrystalline layers demonstrates the photovoltaic quality of our CdSe films.

  15. Upconversion luminescence from CdSe nanoparticles.

    PubMed

    Chen, Wei; Joly, Alan G; McCready, David E

    2005-06-08

    Efficient upconversion luminescence has been observed from CdSe nanoparticles ranging in size from 2.5 to 6 nm. The upconversion luminescence exhibits a near-quadratic laser power dependence. Emissions from both excitons and trap states are observed in the upconversion and photoluminescence spectra, and in the upconversion luminescence the emission from the trap states is enhanced relative to the trap-state emission in the photoluminescence. The upconversion decay lifetimes are slightly longer than the photoluminescence decay lifetimes. Time-resolved spectral measurements indicate that this is due to the involvement of long decay components from surface or trap states. Both the photoluminescence and upconversion luminescence decrease in intensity with increasing temperature due mainly to thermal quenching. All the observations indicate that trap states work as emitters rather than as intermediate states for upconversion luminescence and that two-photon absorption is the likely excitation mechanism.

  16. Dielectric relaxation of CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Dutta, Alo; Ghosh, Binita; Banerjee, Sourish; Sinha, T. P.

    2014-11-01

    Nanoparticles of cadmium selenide (CdSe) have been synthesized by soft chemical route using mercaptoethanol as a capping agent. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to sphalerite structure with the average particle size of 25 nm. The band gap of the material is found to be 2.1 eV. The photoluminescence (PL) emission spectra of the sample are measured at various excitation wavelengths. The PL spectra appear in the visible region, and the emission feature depends on the wavelength of the excitation. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 323 to 473 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). The dielectric relaxation of the sample is investigated in the electric modulus formalism. The temperature dependent relaxation times obey the Arrhenius law. The Havriliak-Negami model is used to investigate the dielectric relaxation mechanism in the sample. The frequency dependent conductivity spectra are found to obey the power law.

  17. Optics of colloidal quantum-confined CdSe nanoscrolls

    SciTech Connect

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

    2015-09-30

    Nanostructures in the form of 1.2-nm-thick colloidal CdSe nanoplatelets rolled into scrolls are investigated. The morphology of these scrolls is analysed and their basic geometric parameters are determined (diameter 29 nm, longitudinal size 100 – 150 nm) by TEM microscopy. Absorption and photoluminescence spectra of these objects are recorded, and the luminescence decay kinetics is studied. It is shown that the optical properties of CdSe nanoscrolls differ significantly from the properties of CdSe quantum dots and that these nanoscrolls are attractive for nanophotonic devices due to large oscillator strengths of the transition, small widths of excitonic peaks and short luminescence decay times. Nanoscrolls can be used to design hybrid organic–inorganic pure-color LEDs with a high luminescence quantum yield and low operating voltages. (optics and technology of nanostructures)

  18. Electrodeposition and characterization of CdSe semiconducting nanowires.

    PubMed

    Yu-Zhang, K; Guo, D Z; Mallet, J; Molinari, M; Loualiche, A; Troyon, M

    2008-04-01

    In this paper, we present our work on the electrodeposited CdSe semiconducting nanowires. Using a low cost and low temperature approach by electrochemistry, CdSe nanowires were successfully grown using polycarbonate template. Depending on the host pore dimension of the substrate, wire diameter can be varied from 400 nm down to 30 nm and wire length from a few microns to tens microns. The as-deposited nanowires exhibit predominantly metastable zinc blende (ZB) structure but after the heat treatment they become wurtzite (W) structure. A combination of different characterization techniques, such as X-ray diffraction, SEM, TEM-HRTEM and EDXS, was used to investigate the growth morphology, crystalline structure and defects in the nanowires. The luminescent properties of CdSe nanowires have also been studied by means of photoluminescence.

  19. CdSe nanocrystals formation in silica sonogels

    SciTech Connect

    Hummel, D.C.; Torriani, I.L.; Ramos, A.Y.; Craievich, A.F.; Rosa-Fox, N. De La; Esquivias, L.

    1994-12-31

    Host-matrix gels were prepared by hydrolysis of TEOS with the addition of cadmium nitrate, formamide as DCCA (drying control chemical additive) and submitted to a preselected dose of high power ultrasound. The impregnation of the dry ``sonogel`` with KSeCN solution under vacuum conditions promoted the formation of the CdSe nanocrystals and enhanced the mechanical properties of the matrix. A transparent red xerogel was obtained and characterized by optical spectroscopy, TEM and SAXS measurements. The results support a structural model of a porous matrix containing CdSe nanocrystals exhibiting a bimodal size distribution that depends on the Se content of the impregnating solutions. The blue shift of the optical absorption bands reveal the quantum-size confinement effects of CdSe nanocrystals.

  20. Laser cooling of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Nemova, Galina; Kashyap, Raman

    2014-05-01

    We present a theoretical scheme for laser cooling of the colloidal cadmium selenide (CbSe) QDs. The laser cooling process is based on the anti-Stokes fluorescence observed in QDs. We have considered laser cooling in the system of identical CdSe QDs laser pumped with energy of photons less than mean fluorescence energy. The dependences of all parameters of the system on the temperature have been taken into account. Following to our simulation the laser cooling with temperature drop ~100K can be realised with well technologically developed today passivated CdSe QDs.

  1. Piezo-phototronic effect of CdSe nanowires.

    PubMed

    Dong, Lin; Niu, Simiao; Pan, Caofeng; Yu, Ruomeng; Zhang, Yan; Wang, Zhong Lin

    2012-10-23

    The piezo-phototronic effect on transport properties of flexible CdSe NW devices is investigated. An optimum sensitivity of the flexible CdSe NW devices can be achieved by adjusting the applied strain and illumination intensity. The piezo-phototronic effect under compressive strain increases the internal electric field of the Schottky barrier, and assists the separation of the photo-excited electron-hole pairs, resulting in the increase of photocurrent. A trap-mediated mechanism is responsible for the decreased hole separation when the strain is larger than the critical strain.

  2. Scanning tunneling luminescence of individual CdSe nanowires.

    PubMed

    Lutz, Theresa; Kabakchiev, Alexander; Dufaux, Thomas; Wolpert, Christian; Wang, Zhe; Burghard, Marko; Kuhnke, Klaus; Kern, Klaus

    2011-08-22

    The local luminescence properties of individual CdSe nanowires composed of segments of zinc blende and wurtzite crystal structures are investigated by low-temperature scanning tunneling luminescence spectroscopy. Light emission from the wires is achieved by the direct injection of holes and electrons, without the need for coupling to tip-induced plasmons in the underlying metal substrate. The photon energy is found to increase with decreasing wire diameter due to exciton confinement. The bulk bandgap extrapolated from the energy versus diameter dependence is consistent with photon emission from the zinc blende-type CdSe sections.

  3. VLS synthesis of disordered CdSe nanowires and optical properties of an individual CdSe nanowire

    NASA Astrophysics Data System (ADS)

    Xiao, Bin-bin; Xu, Yue-bing

    2011-12-01

    Disordered CdSe nanowires have been successfully grown on silicon substrates by Au-catalyzed vapor-liquid-solid (VLS) mechanism. Scanning electron microscopy (SEM) reveals that the as-prepared products consist of a large quantity of 1D nanowire disordered predominantly perpendicular to the surface of the substrate. A plausible formation mechanism of disordered CdSe nanowires is proposed here. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) confirm on their hexagonal wurtzite crystallite structure. An intense red near-band edge emission (702 nm) is observed based on room temperature photoluminescence measurements of individual nanowire. This kind of CdSe nanostructures may be used in optoelectronics devices in the near future.

  4. Current Oscillations in Doped Thin Films of CdSe.

    DTIC Science & Technology

    The previously unreported phenomenon of current oscillations in doped thin films of cadmium selenide was explored. It was concluded that, with...appropriate processing, devices made with thin films of CdSe will exhibit current oscillations when high electric fields and illumination are applied, and that these oscillations have frequencies of 5 to 8000 Hz. (Author)

  5. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions.

    PubMed

    Robin, I C; Aichele, T; Bougerol, C; André, R; Tatarenko, S; Bellet-Amalric, E; Van Daele, B; Van Tendeloo, G

    2007-07-04

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 °C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  6. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates

    NASA Astrophysics Data System (ADS)

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.

  7. 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.

  8. Compressive and Tensile Stress in CdSe Semiconductor Quantum Dots

    SciTech Connect

    Meulenberg, R W; Jennings, T; Strouse, G F

    2004-06-02

    Compressive and tensile stress in colloidal CdSe quantum dots (QDs) is examined using resonance Raman spectroscopy. We find that the dispersion of the longitudinal optical phonon mode with size does not follow theoretical calculations based on phonon confinement models. To account for these deviations, the presence of compressive or tensile stress in the QDs was proposed. We find that CdSe QDs prepared via a single source precursor (SSP) method exhibit compressive stress, while CdSe QDs prepared via high temperature lyothermal methods exhibit tensile stress. Evidence is provided that the SSP CdSe QDs stress is directly related to a surface effect.

  9. Electron-Phonon Coupling in a CdSe Nanowire

    NASA Astrophysics Data System (ADS)

    Barrett, Christopher; Wang, Lin-Wang

    2012-02-01

    It is important to calculate the coupling between phonons and electrons in realistic nanostructures, e.g. to understand carrier cooling and dynamics in a nanowire. In this talk, we will present results of phonon spectrum calculations using a customized valence force field (VFF) method. This customized VFF method is developed to be fittable to the results of any ab-initio calculations, with density functional theory (DFT) results being used in this work. By fitting many different DFT calculations on different motifs and their perturbations, we have obtained in the custom VFF a very efficient method that closely reproduces DFT phonons for CdSe nanowires with (10-10) surfaces having Cd-Se dimerization. We have also combined the results of these phonon spectrum calculations with electronic structure calculations to obtain the electron-phonon coupling. We will present this result and and show how the electron-phonon coupling affects the carrier dynamics in the nanowire.

  10. Phonon spectrum in a CdSe nanowire

    NASA Astrophysics Data System (ADS)

    Barrett, Chris; Wang, Lin-Wang

    2011-03-01

    It is important to calculate the phonon spectrum of realistic nanowires, e.g. to understand its thermo conductivity or to calculate the electron-phonon interaction. In this talk, we will present results of phonon spectrum calculation using valence force field (VFF) method. An important issue is to construct the VFF to describe the surface atomic displacement. We have developed a general VFF formalism to fit our VFF result with the density functional theory (DFT) calculated surface atom displacement energies. In particular, the (10-10) CdSe surface is modelled with Cd-Se dimerization. We will discuss the quality of such VFF model. The phonon spectrum of the nanowire will be presented, and its implication on the phonon transport and electron-phonon coupling will also be discussed. This work is supported by U.S. Department of Energy BES, office of science, under Contract No. DE-AC02-05CH11231.

  11. Deformation potentials of CdSe quantum dots

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2004-06-02

    The size dependent deformation potentials of CdSe quantum dots are studied by first principle and semi-empirical pseudopotentials calculations. They find that the amplitude of the quantum dot deformation potential is only slightly larger than the bulk value, and this increase is mostly caused by the off {Lambda} point deformation potentials in the bulk, which are larger in amplitude than the {Lambda} point deformation potential.

  12. Fluorescence lifetime modification of single CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Brokmann, Xavier; Coolen, Laurent; Desbiolles, Pierre; Dahan, Maxime; Hermier, Jean-Pierre

    2004-03-01

    Narrow spectral emission, high brightness, and photon antibunching make colloidal semiconductor CdSe quantum dots promising systems both as biological probes or as single photon sources for quantum information processing. However, their fluorescence properties exhibit surprisingly rich behaviour as non-ergodic on/off fluorescence intermittency [1] or lifetime fluctuation [2] that deserve further studies. Here, we study the fluorescence lifetime and the total emission intensity from a single CdSe nanocrystal successively placed close and far from a dielectric interface. Correlated to an independent measurement of the nanocrystal orientation, we demonstrate the ability of this procedure to measure both radiative and non-radiative lifetime on these single emitters. Our results are found to be intimately related to the 2D nature of the emitting dipole [3], and demonstrate that the emitting state quantum efficiency of CdSe nanocrystals is routinely higher than 95 %. [1] X.Brokmann et al., PRL 90, 120601 (2003) [2] G. Schlegel et al., PRL 88, 137401 (2002) [3] S.A. Empedocles et al., Nature 399, 126 (1999)

  13. CdSe nanowires grown by using chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Gubur, H. Metin; Septekin, F.; Alpdogan, S.

    2015-10-01

    The Cadmium-selenide (CdSe) nanowire thin films were prepared on glass substrates by using chemical bath deposition (CBD) at 70 °C. Cadmium sulfate and sodium selenosulphate were used as Cd2+ and Se2- ion sources, respectively. The CdSe nanowire film was annealed in an air atmosphere at 573 K for 1 hour. X-ray diffraction (XRD) results showed that the nanowire films as-deposited and annealed had mixed cubic and hexagonal phase. Scanning electron microscopy (SEM) indicated that the CdSe nanowires had lengths ranging from 642 nm to 2.5 μm and diameters ranging from 46 nm to 211 nm. The optical properties of the as-deposited and the annealed nanowire films, an investigated by recording the transmission spectra by using an UV-visible spectrophotometer revealed that the energy band gap decreased (from 1.78 eV to 1.50 eV) upon annealing. The conductivity measurements made by using four-probe methods for both the annealed and the as-deposited films showed that the resistivity, conductivity and activation energy changed upon annealing.

  14. Deposition of CdSe by EC-ALE

    NASA Astrophysics Data System (ADS)

    Mathe, Mkhulu K.; Cox, Stephen M.; Flowers, Billy H.; Vaidyanathan, R.; Pham, Long; Srisook, Nattapong; Happek, Uwe; Stickney, John L.

    2004-10-01

    The optimization of a program for CdSe thin film deposition using electrochemical atomic layer epitaxy (EC-ALE) is reported. EC-ALE uses surface limited reactions, underpotential deposition, to form compound thin film deposits one atomic layer at a time on Au substrates. Cyclic voltammograms showing deposition of Cd and Se on the Au substrate were first performed to identify cycle potentials. CdSe thin films were formed using an automated flow deposition system, by alternately depositing Se and Cd atomic layers, forming a compound monolayer each cycle. In total, 200 cycle deposits were formed using a series of different potentials, to better optimize the deposition conditions. Electron probe microanalysis of the deposits showed Cd/Se ratio between 1.01 and 1.13. X-ray diffraction indicated the deposits were zinc blende, with a (1 1 1) preferred orientation. The thickness of the deposits were determined using ellipsometry, and found to be around 70 nm. AFM studies of the morphology of substrates and deposits indicated that conformal films were formed. The band gaps of the deposits was determined using UV-VIS absorption measurements, photoconductivity and reflection adsorption FTIR, and all suggested a value of 1.74 eV, consistent with literature values.

  15. 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.

  16. 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.

  17. 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.

  18. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots

    PubMed Central

    Tohgha, Urice; Deol, Kirandeep K.; Porter, Ashlin G.; Bartko, Samuel G.; Choi, Jung Kyu; Leonard, Brian M.; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2014-01-01

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

  19. 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.

  20. Low-temperature synthesis of CdSe nanocrystal quantum dots.

    PubMed

    Siy, Jacqueline T; Brauser, Eric M; Bartl, Michael H

    2011-01-07

    A method for fabricating colloidal CdSe nanocrystals at low reaction temperatures was developed. The transition from CdSe clusters to continuously-growing nanocrystals was found to be crucial in the formation of high-quality quantum dots with narrow size distribution and efficient, tunable optical properties.

  1. 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.

  2. Carrier transport dynamics in Mn-doped CdSe quantum dot sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Poudyal, Uma; Maloney, Francis S.; Sapkota, Keshab; Wang, Wenyong

    2017-10-01

    In this work quantum dot sensitized solar cells (QDSSCs) were fabricated with CdSe and Mn-doped CdSe quantum dots (QDs) using the SILAR method. QDSSCs based on Mn-doped CdSe QDs exhibited improved incident photon-to-electron conversion efficiency. Carrier transport dynamics in the QDSSCs were studied using the intensity modulated photocurrent/photovoltage spectroscopy technique, from which transport and recombination time constants could be derived. Compared to CdSe QDSSCs, Mn–CdSe QDSSCs exhibited shorter transport time constant, longer recombination time constant, longer diffusion length, and higher charge collection efficiency. These observations suggested that Mn doping in CdSe QDs could benefit the performance of solar cells based on such nanostructures.

  3. 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.

  4. CdSe nanocrystals: controlled growth and diameter-dependent photoluminescence

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Yang, Ping; Chen, Hsueh Shin; Huang, Baibiao; Shen, Jianxing

    2014-02-01

    Phosphonic and carboxylic acids were used as capping agents to fabricate CdSe nanocrystals (NCs) through organic synthesis, leading to a controlled growth of the NCs with adjustable morphologies from dots to rods. The binding energies and steric hindrance of ligands dramatically affected the growth kinetics of CdSe NCs, and therefore the resulting geometry of NCs. The detailed investigations of ligand effect on the growth of NCs and an efficient control over the NCs morphology were presented. CdSe nanorods (NRs) with various aspect ratios were created for studying relation between the diameter of NRs and photoluminescence (PL). Consequently, a synergic use of PL spectra and transmission electron microscopy images allowed us to systematically investigate the relationship between morphology and PL properties of as-prepared CdSe rods. The PL properties of CdSe NRs were finally found to be strongly diameter dependent and weakly related to their lengths.

  5. Single-crystal CdSe nanowires prepared via vapor-phase growth assisted with silicon.

    PubMed

    Wang, Z Y; Zhang, L D; Ye, C H; Fang, X S; Xiao, Z D; Kong, M G

    2005-12-01

    Hexagonal cadmium selenide (CdSe) nanowires, with diameter around 20 nm, were synthesized using a simple vapor-phase growth. Silicon (Si) powder acts as a source material assisting the synthesis, which is very important to the formation of the CdSe nanowires. We also suggest that self-catalysis at the Cd-terminated (0001) surface, together with the assistance action of Si, leads to the formation of wire-like structures to be formed. Meanwhile, the assistance of Si is responsible for the fineness and uniformity of the CdSe nanowires. The possible growth mechanism of the CdSe nanowires is proposed, and the optical property of the as-grown CdSe nanowires is characterized.

  6. Optical properties of an indium doped CdSe nanocrystal: A density functional approach

    SciTech Connect

    Salini, K.; Mathew, Vincent; Mathew, Thomas

    2016-05-06

    We have studied the electronic and optical properties of a CdSe nanocrystal doped with n-type impurity atom. First principle calculations of the CdSe nanocrystal based on the density functional theory (DFT), as implemented in the Vienna Ab Initio Simulation Package (VASP) was used in the calculations. We have introduced a single Indium impurity atom into CdSe nanocrystal with 1.3 nm diameter. Nanocrystal surface dangling bonds are passivated with hydrogen atom. The band-structure, density of states and absorption spectra of the doped and undopted nanocrystals were discussed. Inclusion of the n-type impurity atom introduces an additional electron in conduction band, and significantly alters the electronic and optical properties of undoped CdSe nanocrystal. Indium doped CdSe nannocrystal have potential applications in optoelectronic devices.

  7. Optical properties of CdSe nanowires -- Experiment and theory

    NASA Astrophysics Data System (ADS)

    Vietmeyer, Felix

    CdSe nanowires are one-dimensional semiconductor nanostructures with unique properties. The wires studied in this work possess diameters on the nanometer scale while diameters are on the order of tens of microns. For CdSe structures this has the consequence that size quantization effects are at play along the radial dimension while longitudinal dimensions are outside the confinement regime. Physical and electrical properties are therefore expected to be diameter dependent, but not very sensitive to variations in length. Another important aspect to consider is that the diameters studied span a range from small (i.e. d˜3-5 nm) where wires show discrete transitions akin to quantum dots all the way up to large (i.e. d˜25 nm). At the largest size studied, the material does not show size quantization effects and its properties are similar to bulk CdSe. One of the key questions I would like to answer is what characterizes the transition from a regime controlled by quantum effects (i.e. small diameter nanowires) to bulk-like semiconductors (i.e. large diameter wires). The tools used to carry out the characterization include a number of steady-state and time-resolved spectroscopic techniques that are used to probe semiconductor nanowires both on the ensemble and single nanowire level. For single wire level measurements, the tool of choice is optical microscopy. Using microscopy, individual nanowires can be identified and studied using various excitation and emission wavelengths to characterize their properties. Using emission and absorption spectroscopies, the electronic structure of the nanowire as well as how charges interact is revealed. It, in turn, allows identifying signatures that belong to photogenerated charges that exist as coulombically bound electron-hole pairs (excitons) and distinguish them from free charges.

  8. CdSe film surface property changes during growth

    SciTech Connect

    Smyntyna, V.A.; Gerasyutenko, V.A.; Korneeva, S.A.

    1988-04-01

    The morphology changes as a cadmium selenide film grows, as indicated by transmission and scanning electron microscopes, and the microcomposition also alters, so the conductivity as a function of thickness and of substrate temperature is examined to relate the surface electronic properties to the measured adsorption sensitivity. Cadmium self-doping occurring during CdSe film growth is followed by excess cadmium atoms accumulating on the surface, which form clusters and give rise to a nonmonotone dependence of the conductivity and adsorption sensitivity on thickness.

  9. 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

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

    PubMed

    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.

  11. 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.

  12. CdSe electronic structure and pulsed laser photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Abraham, Yonas; Ucer, K. B.; Williams, R. T.; Holzwarth, N. A. W.

    2002-03-01

    Photoelectron spectroscopy with pulsed laser excitation can provide a low-background, sensitive view of electonic states in the gap,(M. Yamada et al.), Surf. Sci. 349, L107-L110 (1996) photopopulated states above the Fermi level, and dynamics of the population.(R. T. Williams et al.) Radiation Measurements 33, 497-502 (2001) We report measurements of photoelecton emission from UHV-cleaved CdSe (11bar20) surfaces excited by 4.5 eV and 5.9 eV pulses of 150 fs duration from a Ti:sapphire laser. One-, two-, and three-photon excitation processes are observed and comparison with features of the electronic structure will be discussed. For the purposes of identifying defect and surface features, electronic structure calculations of the CdSe (11bar20) surface are being performed using the pwpaw code,( A. R. Tackett et al.), Comput. Phys. Comm. 35, 348-376 (2001) using both slab and semi-infinite geometries. We hope to simulate both ideal and stepped surfaces.

  13. Synthesis and applications of CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Rao, M. C.; Ravindranadh, K.; Shekhawat, M. S.

    2013-06-01

    Polymer nanoparticle composite materials have attracted the interest of a number of researchers, due to their synergistic and hybrid properties derived from several components. Whether in solution or in bulk, these materials offer unique mechanical, electrical, optical and thermal properties. CdSe nanoparticles have been prepared at room temperature. Cadmium chloride 99 mM of 4 mL is added to 2.2g Poly vinyl alcohol. The volume of solution is made up to 50 mL by bi-distilled water and the solution is left for 24 hours at room temperature to swell. After that the solution is warmed up to 60°C and stirred for 4 hours until viscous transparent solution is obtained. One milliliter of Sodium Hydrogen Selenide is dropped into the solution with gentle stirring. Solution is casted on flat glass plate dishes. After the solvent evaporation, a thin film containing CdSe nanoparticles are obtained. The film is washed with de-ionized water to remove other soluble salts before measurements.

  14. CdSe quantum dots synthesized by laser ablation in water and their photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Horoz, Sabit; Lu, Liyou; Dai, Qilin; Chen, Jiajun; Yakami, Baichhabi; Pikal, J. M.; Wang, Wenyong; Tang, Jinke

    2012-11-01

    CdSe quantum dots (QDs) have been prepared by a facile and clean synthesis method--laser ablation in water. The structural and luminescent properties of the CdSe QDs have been investigated. The CdSe QDs of wurtzite crystal structure have an average particle size of about 5 nm. The QDs can be attached to ZnO nanowires making them ideal for applications in QD-sensitized nanowire solar cells. A uniqueness of the QDs attached to the ZnO nanowires by this laser ablation method is that they do not contain ligands, and the preparation avoids the complicated process of ligand exchange.

  15. Quantum Dots Sensitized Solar Cell: Effect of CdSe Nanoparticles Purification Procedure of QD Sensitized Photoanodes

    NASA Astrophysics Data System (ADS)

    Yaacob, K. A.; Ishak, M. N.; Alias, N. N.

    2013-04-01

    In this research the effect of purification of CdSe nanoparticles for application in quantum dots sensitized solar cells (QDSSC) photoanodes are studied. The CdSe nanoparticles are attached to the titanium dioxide surface using a linker based approached (CdSe nanoparticles disperse in toluene) and direct mode attachment (CdSe re-disperse in dichloromethane (DCM)). Colloidal CdSe nanoparticles with estimated size of 3.0 nm were synthesized by hot injection method in trioctylphosphine oxide (TOPO) as stabilizing solvent. Prior to the sensitization, the CdSe nanoparticles were purified using a common purification step involving the alternate cycles of precipitation / redispersion in non-polar solvent and polar solvent. With increasing the number of purification, the concentrations of CdSe nanoparticles attached to the titanium dioxide were also increased; from 2.47 × 1015 dots/cc for 3 × wash CdSe nanoparticles to 3.70 × 1015 dots/cc for 4 × wash CdSe nanoparticles. Polysulfide electrolyte and Cu2S counterelectrodes were used to assemble a complete QDSSC. The highest efficiency of 0.05% was obtained from 4 × wash CdSe nanoparticles; Voc = 0.2V, Jsc = 0.34 mA/cm2 and FF = 0.07).

  16. Tuning luminescence and reducing reabsorption of CdSe quantum disks forluminescent solar concentrators.

    PubMed

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

    2015-08-21

    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.

  17. 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.

  18. Optical absorption, induced bleaching, and photoluminescence of CdSe nanoplatelets grown in cadmium octanoate matrix

    NASA Astrophysics Data System (ADS)

    Lyashchova, Alina; Dmytruk, Andriy; Dmitruk, Igor; Klimusheva, Gertruda; Mirnaya, Tetyana; Asaula, Vitaliy

    2014-02-01

    CdSe nanoparticles (NPs) are chemically synthesized in thermotropic ionic liquid crystalline (LC) phase of cadmium octanoate that was used as a nanoreactor. The nanocomposite samples are obtained by the rapid cooling of the LC phase to room temperature. Observed doublet structure in absorption spectra of the nanocomposites is characteristic for the two-dimensional CdSe nanoplatelets (NPLs). The thicknesses of the CdSe NPLs are 1.6, 1.9 and 2.3 nm as determined from the absorption spectra, and correspond to 4, 5 and 6 CdSe monolayers, respectively. Induced simultaneous bleaching of the doublet components observed under femtosecond laser excitation, as well as photoluminescence spectra and their kinetics are found compatible with the model of excitons with heavy- and light-hole valence bands confined in nanoplatelets.

  19. Optical absorption, induced bleaching, and photoluminescence of CdSe nanoplatelets grown in cadmium octanoate matrix.

    PubMed

    Lyashchova, Alina; Dmytruk, Andriy; Dmitruk, Igor; Klimusheva, Gertruda; Mirnaya, Tetyana; Asaula, Vitaliy

    2014-02-20

    CdSe nanoparticles (NPs) are chemically synthesized in thermotropic ionic liquid crystalline (LC) phase of cadmium octanoate that was used as a nanoreactor. The nanocomposite samples are obtained by the rapid cooling of the LC phase to room temperature. Observed doublet structure in absorption spectra of the nanocomposites is characteristic for the two-dimensional CdSe nanoplatelets (NPLs). The thicknesses of the CdSe NPLs are 1.6, 1.9 and 2.3 nm as determined from the absorption spectra, and correspond to 4, 5 and 6 CdSe monolayers, respectively. Induced simultaneous bleaching of the doublet components observed under femtosecond laser excitation, as well as photoluminescence spectra and their kinetics are found compatible with the model of excitons with heavy- and light-hole valence bands confined in nanoplatelets.

  20. Dielectric Properties of Cadmium Selenide (CdSe) Nanoparticles synthesized by solvothermal method

    NASA Astrophysics Data System (ADS)

    Suresh, S.; Arunseshan, C.

    2013-01-01

    Synthesis of nanoparticles of cadmium selenide (CdSe) was carried out using solvothermal method with cadmium nitrate and sodium selenite as precursors. Hydrazine hydrate and ethylenediamine tetra acetic acid were used as the capping agent to control the size of the nanoparticles. As their size decreases to their Bohr radius (usually around a few nanometers), all electronic properties change, and equally important, become dependent on size. In this size, a semiconductor nanoparticle transition occurs in which the electrons and holes are confined beyond their natural Bohr radius. The properties become dependent not only on size, but also on shape. The crystalline nature and particle size of the samples were characterized by Powder X-ray diffraction analysis (XRD). The morphology of prepared CdSe nanoparticles was studied by scanning electron microscope. Dielectric studies were carried out for the pelletized sample of CdSe nanoparticles. The ac conductivity of CdSe nanoparticle has been studied. The obtained results are discussed.

  1. 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.

  2. 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

  3. Optical properties of two-dimensional (2D) CdSe nanostructures

    NASA Astrophysics Data System (ADS)

    Cherevkov, S. A.; Baranov, A. V.; Fedorov, A. V.; Litvin, A. P.; Artemyev, M. V.; Prudnikau, A. V.

    2013-09-01

    The resonant and off-resonant Raman spectra of optical phonons in two-dimensional CdSe nanocrystals of 5, 6, and 7 monolayers are analysed. The spectra are dominated by SO and LO phonon bands of CdSe, whose frequencies are thickness-independent in the off-resonant Raman scattering but demonstrate an evident thickness dependence in the case of the resonant Raman scattering.

  4. 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)

  5. Ultrashort light pulse selfdifraction in Si and CdSe single crystals

    NASA Astrophysics Data System (ADS)

    Baltramejunas, R.; Vaitkus, J.; Veleckas, D.

    1981-10-01

    Interaction of mode-locked neodyme-glass laser pulses with Si and CdSe single crystals has been investigated. The dependence of light induced diffraction on time is demonstrated in differently doped Si and CdSe. the possibility to use semiconductors for light-coherence measurement is discussed and necessary conditions are determined. The influence of thermal heating is discussed. the mechanisms of recombination at high excitation level was determined in both materials.

  6. Size and temperature dependence of the tensile mechanical properties of zinc blende CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Fu, Bing; Chen, Na; Xie, Yiqun; Ye, Xiang; Gu, Xiao

    2013-11-01

    The effect of size and temperature on the tensile mechanical properties of zinc blende CdSe nanowires is investigated by all atoms molecular dynamic simulation. We found the ultimate tensile strength and Young's modulus will decrease as the temperature and size of the nanowire increase. The size and temperature dependence are mainly attributed to surface effect and thermally elongation effect. High reversibility of tensile behavior will make zinc blende CdSe nanowires suitable for building efficient nanodevices.

  7. Growth and Excitonic Emission of CdSe Ultra-Thin Quantum Wells Without Thickness Fluctuations

    NASA Astrophysics Data System (ADS)

    Alfaro-Martínez, Adrián; Hernández-Calderón, Isaac

    2007-04-01

    Due to the cation and anion surface reconstruction properties, one Cd-Se atomic layer epitaxy (ALE) cycle produces a coverage of 0.5 CdSe monolayers. In this work we demonstrate that even when an odd number of cycles are deposited to produce ultra-thin quantum wells, under the appropriate growth conditions, the photoluminescence spectrum indicates the absence of thickness fluctuations. A single excitonic peak is detected in the whole sample.

  8. White emission using mixtures of CdSe quantum dots and PMMA as a phosphor

    NASA Astrophysics Data System (ADS)

    Chung, Wonkeun; Park, Kwanhwi; Yu, Hong Jeong; Kim, Jihyun; Chun, Byung-Hee; Kim, Sung Hyun

    2010-02-01

    White light emitting diodes (LEDs) were fabricated using an InGaN 460 nm blue emission LED chip as the excitation source and CdSe quantum dots dispersed in PMMA as the phosphor. CdSe quantum dots were synthesized by the wet chemical method using CdO and Selenium powder as precursors. The three different size, 2.9, 3.4 and 4.3 nm in diameter, of CdSe quantum dots obtained using this method exhibited emission peaks at 555, 580 and 625 nm, respectively with a quantum yield of 10-30%. Mixed phosphors containing different weight ratio of CdSe and PMMA (1:0.1, 1:1, 1:5 and 1:10 wt%) were deposited on the LED chip to investigate the effects of different weight ratios of CdSe and PMMA on the performance of the white LEDs. The fabricated white LEDs that contained CdSe and PMMA weight ratio at 1:10 showed the best performance and the CIE color coordinates varied less with different applied currents. The luminous efficiency of single phosphor (580 nm CdSe) white LEDs was 5.62 lm/W with a CRI of 15.7, whereas the luminous efficiency of dual phosphors (555, 625 nm CdSe) white LEDs was 3.79 lm/W with a CRI of 61.4 at 20 mA. The CIE coordinates of single and dual phosphors white LEDs varied from (0.33, 0.28) to (0.29, 0.26) and from (0.39, 0.33) to (0.39, 0.32), respectively, when the working current ranged from 5 to 80 mA.

  9. Aqueous synthesis and characterization of TGA-capped CdSe quantum dots at freezing temperature.

    PubMed

    Sun, Qizhuang; Fu, Shasha; Dong, Tingmei; Liu, Shuxian; Huang, Chaobiao

    2012-07-11

    CdSe quantum dots (QDs) have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%).

  10. Power dependent phonon frequency within CdSe and CdMnSe nanosheets

    NASA Astrophysics Data System (ADS)

    Halder, Oindrila; Rath, S.

    2017-05-01

    The trend of tuning transitional materials in semiconductors is advancing everyday research. The composite behavior exhibited by doped nanoparticles is governed by many factors. These can either improve or adversely affect the desired electronic properties. In this work we have compared the Raman Scattering study of different power dependent excitations on CdSe nanosheets and manganese doped CdSe nanosheets and delved into the possibilities of their different electronic structures due to the phonon contribution.

  11. 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.

  12. Functional Si and CdSe quantum dots: synthesis, conjugate formation, and photoluminescence quenching by surface interactions.

    PubMed

    Sudeep, P K; Emrick, Todd

    2009-12-22

    Silicon quantum dots (QDs) were prepared with a corona of di-n-octyl phosphine oxides, by performing hydrosilylation chemistry on the surface of hydrogen-terminated Si QDs. These novel Si QDs proved well-suited to serve as "ligands" for other semiconductor QDs, such as CdSe, by interaction of the phosphine oxide corona with the CdSe surface. A pronounced photoluminescence quenching of CdSe quantum dots was observed upon introduction of the phosphine oxide functionalized Si QDs to a CdSe QD solution. Surface functionalization of the Si QDs proved critically important to observing these effects, as conventional (alkane-covered) Si QD samples gave no evidence of electronic interactions with TOPO-covered CdSe. In a comparative system, phosphine oxide terminated oligo(phenylene vinylene) molecules acting as CdSe QD ligands provide a similar fluorescence quenching, with exciton decay kinetics supporting the formation of an electronically interacting hybrid materials system.

  13. Vertically aligned CdSe nanowire arrays for energy harvesting and piezotronic devices.

    PubMed

    Zhou, Yu Sheng; Wang, Kai; Han, Weihua; Rai, Satish Chandra; Zhang, Yan; Ding, Yong; Pan, Caofeng; Zhang, Fang; Zhou, Weilie; Wang, Zhong Lin

    2012-07-24

    We demonstrated the energy harvesting potential and piezotronic effect in vertically aligned CdSe nanowire (NW) arrays for the first time. The CdSe NW arrays were grown on a mica substrate by the vapor-liquid-solid process using a CdSe thin film as seed layer and platinum as catalyst. High-resolution transmission electron microscopy image and selected area electron diffraction pattern indicate that the CdSe NWs have a wurtzite structure and growth direction along (0001). Using conductive atomic force microscopy (AFM), an average output voltage of 30.7 mV and maximum of 137 mV were obtained. To investigate the effect of strain on electron transport, the current-voltage characteristics of the NWs were studied by positioning an AFM tip on top of an individual NW. By applying normal force/stress on the NW, the Schottky barrier between the Pt and CdSe was found to be elevated due to the piezotronic effect. With the change of strain of 0.12%, a current decreased from 84 to 17 pA at 2 V bias. This paper shows that the vertical CdSe NW array is a potential candidate for future piezo-phototronic devices.

  14. Thermal conductivity of zinc blende and wurtzite CdSe nanostructures.

    PubMed

    Yang, Juekuan; Tang, Hao; Zhao, Yang; Zhang, Yin; Li, Jiapeng; Ni, Zhonghua; Chen, Yunfei; Xu, Dongyan

    2015-10-14

    Many binary octet compounds including CdSe can be grown in either the wurtzite (WZ) or zinc blende (ZB) phase, which has aroused great interest among the research community in understanding the phase dependence of the thermal transport properties of these compounds. So far, it has been debatable whether the ZB phase possesses higher thermal conductivity than the WZ phase. In this work, we report on thermal conductivity measurements of CdSe nanowires/nanoribbons with both WZ and ZB phases via a suspended device method. At room temperature, the thermal conductivity of all the ZB CdSe nanostructures measured in this work is higher than the bulk thermal conductivity of the WZ CdSe reported in the literature, suggesting that the bulk thermal conductivity of the ZB CdSe is higher than that of the WZ phase. Our result is different from previous experimental results in the literature for InAs nanowires which suggest similar thermal conductivity values for the bulk ZB and WZ InAs crystals. The higher thermal conductivity of the ZB CdSe can be explained by its lower anharmonicity and a smaller number of atoms per unit cell compared to the WZ phase.

  15. 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.

  16. Structural and transport properties of CdSe nanorods

    SciTech Connect

    Das, Sayantani Banerjee, Sourish; Dutta, Alo; Ghosh, Binita; Sinha, T. P.

    2015-06-24

    The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route. The selected area electron diffraction pattern, high resolution TEM and X-ray diffraction pattern indicate the cubic structure of the sample. The band gap of the sample is obtained using Tauc relation to UV-visible spectrum and found to be 1.92 eV. 1{sup st} order and 2{sup nd} order Raman bands are followed to investigate the behaviour of the phonon modes of the materials which is considered to be important to predict the potential of the material to microwave applications. Thermal behaviour of the sample is investigated using differential scanning calorimeter. Kissinger equation is used to calculate the activation energy of the sample, which is found to be 1.67 eV.

  17. Structural and transport properties of CdSe nanorods

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Dutta, Alo; Ghosh, Binita; Banerjee, Sourish; Sinha, T. P.

    2015-06-01

    The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route. The selected area electron diffraction pattern, high resolution TEM and X-ray diffraction pattern indicate the cubic structure of the sample. The band gap of the sample is obtained using Tauc relation to UV-visible spectrum and found to be 1.92 eV. 1st order and 2nd order Raman bands are followed to investigate the behaviour of the phonon modes of the materials which is considered to be important to predict the potential of the material to microwave applications. Thermal behaviour of the sample is investigated using differential scanning calorimeter. Kissinger equation is used to calculate the activation energy of the sample, which is found to be 1.67 eV.

  18. Electrically driven light emission from individual CdSe nanowires.

    PubMed

    Doh, Yong-Joo; Maher, Kristin N; Ouyang, Lian; Yu, Chun L; Park, Hongkun; Park, Jiwoong

    2008-12-01

    We report electroluminescence (EL) measurements carried out on three-terminal devices incorporating individual n-type CdSe nanowires. Simultaneous optical and electrical measurements reveal that EL occurs near the contact between the nanowire and a positively biased electrode or drain. The surface potential profile, obtained by using Kelvin probe microscopy, shows an abrupt potential drop near the position of the EL spot, while the band profile obtained from scanning photocurrent microscopy indicates the existence of an n-type Schottky barrier at the interface. These observations indicate that light emission occurs through a hole leakage or an inelastic scattering induced by the rapid potential drop at the nanowire-electrode interface.

  19. Laser-induced charge separation in CdSe nanowires.

    PubMed

    Schäfer, Sebastian; Wang, Zhe; Zierold, Robert; Kipp, Tobias; Mews, Alf

    2011-07-13

    A combination of electrostatic force microscopy and optical microscopy was used to investigate the charge state of individual CdSe nanowires upon local illumination with a focused laser beam. The nanowires were found to be positively charged at the excitation spot and negatively charged at the distant end(s). For high laser powers, the amount of accumulated charges increases logarithmically with the laser power. These effects are described by a diffusion-based model where the results are in good agreement with the experimentally observed effects. On the basis of this model the charge imbalance along the nanowire should establish in the course of nanoseconds. The net charge separation within homogeneous nanowires upon local illumination is of importance for several electronic devices.

  20. Carrier recombination dynamics in individual CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Vietmeyer, Felix; Frantsuzov, Pavel A.; Janko, Boldizsar; Kuno, Masaru

    2011-03-01

    Carrier dynamics in single CdSe nanowires (NWs) have been studied using various techniques. They include measurements of single wire emission intensities as a function of pump fluence, excitation intensity-dependent emission quantum yields, and excited-state lifetimes. Ensemble transient differential absorption studies of induced bleach dynamics have also been conducted. Results of these studies show superlinear growth of the emission intensity as a function of excitation intensity. This is corroborated by single nanowire emission quantum yields that vary as a function of excitation fluence and range from 0.1% to values over 10%. At the same time, measured emission lifetimes are short (<100 ps) while the nanowire band-edge bleach persists for over a nanosecond. To explain all of the abovementioned results, a kinetic model that accounts for both the nature of photogenerated carriers within the wires as well as their subsequent recombination dynamics has been developed.

  1. 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.

  2. Intraband relaxation in CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Guyot-Sionnest, Philippe; Shim, Moonsub; Matranga, Chris; Hines, Margaret

    1999-07-01

    The relaxation of the 1P to 1S electronic states of CdSe semiconductor nanocrystals is followed by infrared pump-probe spectroscopy. Fast (1 ps) and slow (>200 ps) components are observed. Using different capping molecules to control the hole states, we show how the intraband relaxation slows down as the hole is in a shallow trap, a deep trap, or a charge-separated complex, providing strong support for an electron-hole Auger coupling. The slow component corresponds to an energy relaxation rate orders of magnitude slower than in bulk systems. It may be the first indication of the phonon bottleneck effect long expected in strongly confined quantum dots.

  3. 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.

  4. Enhanced photogenerated carrier collection in hybrid films of bio-templated gold nanowires and nanocrystalline CdSe.

    PubMed

    Haberer, Elaine D; Joo, John H; Hodelin, Juan F; Hu, Evelyn L

    2009-10-14

    Hybrid films of bio-templated gold nanowires and chemical bath deposited nanocrystalline CdSe were fabricated. The conductivity of the gold nanowires within the hybrid material was controlled by gold electroless deposition. Photocurrent measurements were taken on gold nanowire films, CdSe chemical bath deposited films, and hybrid films. The incorporation of gold nanowires within the hybrid material clearly increased the extraction of photogenerated carriers within the CdSe. Photocurrent showed a direct correlation with gold nanowire conductivity.

  5. Enhanced photogenerated carrier collection in hybrid films of bio-templated gold nanowires and nanocrystalline CdSe

    NASA Astrophysics Data System (ADS)

    Haberer, Elaine D.; Joo, John H.; Hodelin, Juan F.; Hu, Evelyn L.

    2009-10-01

    Hybrid films of bio-templated gold nanowires and chemical bath deposited nanocrystalline CdSe were fabricated. The conductivity of the gold nanowires within the hybrid material was controlled by gold electroless deposition. Photocurrent measurements were taken on gold nanowire films, CdSe chemical bath deposited films, and hybrid films. The incorporation of gold nanowires within the hybrid material clearly increased the extraction of photogenerated carriers within the CdSe. Photocurrent showed a direct correlation with gold nanowire conductivity.

  6. Moléculas orgánicas obtenidas en simulaciones experimentales del medio interestelar.

    NASA Astrophysics Data System (ADS)

    Muñoz-Caro, Guillermo Manuel

    Las nubes moleculares son regiones de formación de estrellas, con temperaturas cinéticas entre 10-50 K y densidades de 103-106 átomos cm-3. Su materia está formada por gas y polvo interestelar. Estas partículas de polvo están cubiertas por una fina capa de hielo, de unos 0.01 μm, que contiene H2O y a menudo CO, CO2, CH3OH y NH3. El hielo es presumiblemente irradiado por fotones ultravioleta y rayos cósmicos en las zonas poco profundas de las nubes moleculares y las regiones circunestelares. En un sistema de vacío, P ˜ 10-7 mbar, simulamos la deposición de hielo a partir de 10 K y la irradiación ultravioleta por medio de una lámpara de descarga de hidrógeno activada con microondas. La evolución del hielo se observa por medio de un espectrómetro infrarrojo. De este modo es posible determinar la composición del hielo observado en el medio interestelar y predecir la presencia de moléculas aún no detectadas en el espacio, que han sido producto del procesamiento del hielo en nuestros experimentos. También es posible calentar el sistema hasta temperatura ambiente para sublimar el hielo depositado. Cuando el hielo ha sido previamente irradiado, se observa un residuo compuesto por moléculas orgánicas complejas, algunas prebióticas, como varios ácidos carboxílicos, aminas, amidas, ésteres y en menor proporción moléculas heterocíclicas y aminoácidos. Algunas de estas moléculas podrían detectarse en estado gaseoso por medio de observaciones milimétricas y de radio. También podrían estar presentes en el polvo cometario, cuyo análisis químico está planeado por las misiones Stardust y Rosetta. Mientras tanto, nuestro grupo está llevando a cabo el análisis de partículas de polvo interplanetario (IDPs), algunas de las cuales pueden ser de origen cometario. Al igual que ocurre con los productos obtenidos por irradiación del hielo en nuestros experimentos, algunas IDPs son ricas en material orgánico que contiene oxígeno.

  7. Multiple Exciton Generation Solar Cells Using CdSe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Gebreselassie, Haftom Mesfin; Sharma, R. B.; Chander, Nikhil

    2011-10-01

    Experimental and Simulation works of Nanostructured Solar Cells Using CdSe Quantum Dots have been analyzed and investigated. CdSe quantum dots have been synthesized from non coordinating and high boiling solvent Octadecene and a series of increasing CdSe particle sizes are produced. The synthesized CdSe quantum dots are highly examined under a Transmission Electron Microscope and four images of different sizes of CdSe quantum dots (5.8 nm, 6.4 nm, 7.0 nm and 7.7 nm) have been obtained. A 1.1×1.1 cm2 TiO2 electrode is prepared using indium tin oxide conducting glass and TiO2 nanoparticles. The Oleic acid terminated CdSe quantum dots are separated from the octadecene by using 100% ethanol and centrifuge machine of spin about 4000 rpm until the shaking gave no longer suspension. The CdSe quantum dot (5.8 nm) was adsorbed on TiO2 photoelectrode and used as sensitizer. The relationship of Bandgap energy, Emission wavelength with respect to quantum dot size have been simulated and investigated. In this paper work, a sandwich type cell configuration which is made up of TiO2 photoelectrode, graphite coated counter electrode, an electrolyte of iodine and potassium iodide have been used. This sandwich type cell has been exposed to sun light and we have achieved 0.32 V and 0.2 mA cm-2 of potential difference and current respectively.

  8. 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

  9. Nonradiative energy transfer in colloidal CdSe nanoplatelet films

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    Nonradiative energy transfer (NRET) has been extensively studied in colloidal nanocrystal (quantum dots) and nanorod (quantum wires) assemblies. In this work, we present the first account of spectroscopic evidence of NRET in solid thin films of CdSe based colloidal nanoplatelets (NPLs), also known as colloidal quantum wells. The NRET was investigated as a function of the concentration of two NPL populations with different vertical thicknesses via steady state and time resolved spectroscopy. NRET takes place from the NPLs with smaller vertical thickness (i.e., larger band gap) to the ones with a larger vertical thickness (i.e., smaller band gap) with efficiency up to ~60%. Here, we reveal that the NRET efficiency is limited in these NPL solid film assemblies due to the self-stacking of NPLs within their own population causing an increased distance between the donor-acceptor pairs, which is significantly different to previously studied colloidal quantum dot based architectures for nonradiative energy transfer.Nonradiative energy transfer (NRET) has been extensively studied in colloidal nanocrystal (quantum dots) and nanorod (quantum wires) assemblies. In this work, we present the first account of spectroscopic evidence of NRET in solid thin films of CdSe based colloidal nanoplatelets (NPLs), also known as colloidal quantum wells. The NRET was investigated as a function of the concentration of two NPL populations with different vertical thicknesses via steady state and time resolved spectroscopy. NRET takes place from the NPLs with smaller vertical thickness (i.e., larger band gap) to the ones with a larger vertical thickness (i.e., smaller band gap) with efficiency up to ~60%. Here, we reveal that the NRET efficiency is limited in these NPL solid film assemblies due to the self-stacking of NPLs within their own population causing an increased distance between the donor-acceptor pairs, which is significantly different to previously studied colloidal quantum dot based

  10. Fluorescent CdSe QDs containing Bacillus licheniformis bioprobes for Copper (II) detection in water.

    PubMed

    Yan, Zheng-Yu; Du, Qing-Qing; Wan, Dong-Yu; Lv, Hang; Cao, Zhi-Ran; Wu, Sheng-Mei

    2017-12-01

    Quantum dots (QDs) are semiconductor nanoparticles (NPs) that offer valuable functionality for cellular labeling, drug delivery, solar cells and quantum computation. In this study, we reported that CdSe QDs could be bio-synthesized in Bacillus licheniformis. After optimization, the obtained CdSe QDs exhibited a uniform particle size of 3.71±0.04nm with a maximum fluorescence emission wavelength at 550nm and the synthetical positive ratio can reach up to 87%. Spectral properties, constitution, particle sizes and crystalline phases of the CdSe QDs were systematically and integrally investigated. The CdSe QD-containing Bacillus licheniformis cells were further used as whole fluorescent bio-probes to detect copper (II) (Cu(2+)) in water, which demonstrated a low limit of detection (0.91μM). The assay also showed a good selectivity for Cu(2+) over other ions including Al(3+), Cd(2+), Mg(2+), K(+), Na(+), NH4(+), Zn(2+), CH3COO(+), Pb(2+) and I(-). Our study suggests the fluorescent CdSe QDs-containing Bacillus licheniformis bio-probes as a promising approach for detection of Cu(2+) in complex solution environment. Copyright © 2017. Published by Elsevier Inc.

  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. Encapsulation of highly confined CdSe quantum dots for defect free luminescence and improved stability

    NASA Astrophysics Data System (ADS)

    Kumari, Asha; Singh, Ragini Raj

    2017-05-01

    This is the first report on the generation of trap states and their effective elimination in highly confined CdSe quantum dots in order to obtain enhanced and stable optical properties prepared by aqueous route. Surface plays an important role in optical properties of quantum dots (QDs) and surface modification of quantum dots can improve optical properties. In present work luminescent CdSe QDs were prepared using 2-Mercaptoethanol (2-ME) as stabilizing agent and encapsulated by polymer. Different concentrations of 2-ME were used to tune the emission spectra with respect to their reduced size. Addition of 2-ME to CdSe QDs enhances the trap emission and quenching band edge emission due to (i) increased surface to volume ratio and; (ii) presence of high concentration of sulfide ions as confirmed from EDX analysis as sulfide ions possesses the hole scavenging characteristics. Polymer encapsulation of QDs was carried out to make them stable and to improve their optical properties. Even though there are previous reports addressing the improved optical properties by polymer encapsulation and silica encapsulation but experimentally it has not been reported yet experimentally. In this work we have synthesized and characterized water soluble polymer encapsulated QDs and proved the facts experimentally. Photoluminescence spectroscopy clearly reveals the role of polymer encapsulation in boosting the optical properties of CdSe QDs. FTIR spectra validate the presence of biocompatible functional groups on CdSe4/PEG (Polymer encapsulated QDs).

  13. CdSe nanocrystals ingrained dielectric nanocomposites: synthesis and photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Dey, Chirantan; Goswami, Madhumita; Karmakar, Basudeb

    2015-01-01

    Cadmium selenide (CdSe) nanocrystals ingrained dielectric nanocomposites in a B2O3-SiO2-Al2O3-Na2O-K2O borosilicate glass system were synthesized by a single step in situ melt quenching technique. The sizes of the nanocrystals as well as the band gap of the nanocomposites were controlled by both concentration of CdSe and post thermal treatment duration. The nanocomposites were characterized by different instrumental techniques including detailed photoluminescence studies. The sizes of the CdSe nanocrystals were found to alter in the range 4-16 nm as estimated from the effective mass approximation model and optical absorption spectroscopy. However, the TEM analysis revealed the generation of two different size ranges, 3-4 and 23-45 nm, of the particles within the dielectric matrix. Selected area diffraction (SAED) and x-ray diffraction (XRD) patterns authenticate the formation of hexagonal nanostructures of CdSe. These nanocomposites were found to be capable of exhibiting strong visible red luminescence around 715 nm on excitation at 446 nm. This has originated from the electron-hole recombination of CdSe nanocrystal and defects or traps related transitions. The properties of these nanocomposites advocate their significant applications as semiconductor based luminescent materials.

  14. Sonochemical synthesis of CdS and CdSe nanowires.

    PubMed

    Jiang, Li-Ping; Xu, Shu; Miao, Jian-Jun; Wang, Hui; Zhu, Jun-Jie

    2006-08-01

    A convenient sonochemical route was developed to fabricate one-dimensional (1D) CdS or CdSe assemblies via a simple template method with two-steps: Firstly, the colloid one dimensional cadmium hydroxide particles were prepared as templates under sonication; then, the colloid particles were converted into 1D CdS or CdSe assemblies via a replacement reaction after the surface nucleation and crystal growth processes. The as-prepared CdS and CdSe nanowires were characterized by XRD, TEM, XPS, and UV-visible Spectroscopy. The effects of the ultrasonic irradiation were discussed. It is believed that the ultrasound irradiation played a positive role in both the assembly of the colloid cadmium hydroxide particles into the 1D structure and the growth of CdSe and CdS nanowires. The effects of pH on the morphologies of the cadmium hydroxide template were also discussed. The band gaps of the as-prepared 1D CdSe and CdS assemblies were calculated to be 3.1 eV and 4.9 eV, respectively, indicating the quantum size effect. The as-prepared products might have potential applications in nanodevices in future.

  15. Electron shuttling across the interface of CdSe nanoparticles monitored by femtosecond laser spectroscopy

    SciTech Connect

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

    1999-03-18

    The formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with adsorbed electron acceptors (1,4-benzoquinone and 1,2-naphthoquinone) and the rise and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were investigated by femtosecond laser spectroscopy. The ultrashort (200--400 fs) rise times of the bleach at the band-gap energy of the CdSe NP as well as of the acceptor radical anion are found to increase with increasing the excitation energy. This suggests that the electron transfer from the CdSe NP to the quinone electron acceptor occurs after thermalization of the excited hot electrons. The decay times of the transient absorption for the electron acceptor radical anions are found to be comparable to that of the CdSe NP bleach recovery time (3 ps). This suggests that the surface quinones shuttle the electron from the conduction band to the valence band of the excited NP. The authors contrast this behavior with the excited-state dynamics of the recently investigated CdS-MV{sup 2+} system in which the electron acceptor does not shuttle the accepted electron back to the hole in CdS.

  16. Probing the size and environment induced phase transformation in CdSe quantum dots

    SciTech Connect

    Karakoti, Ajay S.; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Yang, Ping; Thevuthasan, Suntharampillai

    2011-11-17

    The structural and electronic properties of CdSe quantum dots in toluene and drop-casted on Si wafer were investigated by in-situ micro X-ray diffraction, X-ray photoelectron spectroscopy and UV-Vis absorption and emission spectroscopy. The in-situ micro diffraction data show that the CdSe quantum dots capped with TOPO or hexadecylamine (HDA) in toluene exhibit predominantly wurtzite crystal structure, which undergoes a phase transformation to zinc blende crystal structure following drop casting on Si and this phase transition increases with decreasing the size of the CdSe quantum dots. Decreasing the size of quantum dots also increases the Se vacancies that facilitate the phase transformation. The X-ray photoelectron spectra show a systematic increase in the core level binding energies of Cd 3d and Se 3d, the band gap and the Cd/Se ratio as the size of the quantum dots decreases from 6.6nm to 2.1nm. This is attributed to the quantum confinement of CdSe crystallites by the capping ligands in toluene which increases with decreasing the size of the quantum dots. However, drop-casting quantum dots on Si alter the density and arrangement of capping ligands and solvent molecules on the quantum dots which causes significant phase transformation.

  17. Flower-like CdSe ultrathin nanosheet assemblies for enhanced visible-light-driven photocatalytic H2 production.

    PubMed

    Peng, Yong; Shang, Lu; Bian, Tong; Zhao, Yufei; Zhou, Chao; Yu, Huijun; Wu, Li-Zhu; Tung, Chen-Ho; Zhang, Tierui

    2015-03-18

    Flower-like CdSe architectures composed of ultrathin nanosheets were prepared via a facile solvothermal method. A relationship was established between the solvothermal temperature and the product structure, and thus the photocatalytic activity. When compared with well-studied CdSe quantum dots, the ultrathin nanosheet assemblies exhibited a better photocatalytic H2 evolution activity under visible light irradiation.

  18. First principles study of O defects in CdSe

    NASA Astrophysics Data System (ADS)

    T-Thienprasert, J.; Limpijumnong, S.; Du, M.-H.; Singh, D. J.

    2012-08-01

    Recently, the vibrational signatures related to oxygen defects in oxygen-doped CdSe were measured using ultrahigh resolution Fourier transform infrared (FTIR) spectroscopy by Chen et al.(2008) [1]. They observed two absorption bands centered at ∼1991.77 and 2001.3 cm-1, which they attributed to the LVMs of OCd, in the samples grown with the addition of CdO and excess Se. For the samples claimed to be grown with even more excess Se, three high-frequency modes (1094.11, 1107.45, and 1126.33) were observed and assigned to the LVMs of OSe-VCd complex. In this work, we explicitly calculated the vibrational signatures of OCd and OSe-VCd complex defects based on first principles approach. The calculated vibrational frequencies of OCd and OSe-VCd complex are inconsistent with the frequencies observed by Chen et al., indicating that their observed frequencies are from other defects. Potential defects that could explain the experimentally observed modes are suggested.

  19. CdSe nanocrystal based chem-/bio- sensors.

    PubMed

    Somers, Rebecca C; Bawendi, Moungi G; Nocera, Daniel G

    2007-04-01

    Semiconductor nanocrystals (NCs) have found application in biology mostly as optical imaging agents where the photophysical properties of the NCs are insensitive to species in their environment. This tutorial review examines the application of CdSe NCs as optical sensing agents where the NC's photophysical properties are sensitive to species in their environment. For this case, the NC is modified at the surface with a conjugate, which interacts with an external agent by physical (i.e. recognition) or chemical means. Signal transduction in these chem-bio (CB) sensitive NCs is derived primarily from energy transfer between the NC and the external agent, which functions as the energy transfer acceptor or donor. Signaling may be obtained by directly detecting luminescence from the NC and/or the conjugate. New developments for the use of NCs as gain materials in micro-lasing cavities (distributed feedback gratings and spherical resonators) opens the way to designing CB-sensitive NCs for high-gain sensing applications.

  20. Uncovering Hot Hole Dynamics in CdSe Nanocrystals.

    PubMed

    Liu, Cunming; Peterson, Jeffrey J; Krauss, Todd D

    2014-09-04

    Single and multiple exciton relaxation dynamics of CdSe/CdZnS nanocrystal quantum dots (QDs) monitored at the two lowest optical transitions, 1Se-1S3/2 and 1Se-2S3/2, have been examined using ultrafast transient absorption (TA) spectroscopy. For the CdSe/CdZnS QDs studied, the 1Se-1S3/2 and 1Se-2S3/2 transitions are widely separated (∼180 meV) compared to bare CdSe QDs (∼50-100 meV), allowing for clearly distinguishable TA signals attributable to hot hole relaxation. Holes depopulate from the 2S3/2 state with a lifetime of 7 ± 2 ps, which is consistent with the predictions for hole relaxation via a phonon coupling pathway to lower-energy hole states, with possible contributions from hole trapping as well. These results suggest that tuning the surface chemistry of semiconductor QDs is a viable route to measure and possibly control their hot hole relaxation dynamics.

  1. Optical Properties of CdSe Nanocrystalline Photoanodes

    NASA Astrophysics Data System (ADS)

    Lesar, Amanda; Garuthara, Rohana

    2015-03-01

    Cadmium selenide (CdSe) nanocrystalline photoanodes were prepared by chemical solution deposition, with deposition time varied from 24 hours to 120 hours. Photoluminescence (PL) spectroscopy, reflectance and transmittance spectra, and photoelectric current were measured to optically characterize each sample. Photoelectric current was measured in a liquid junction configuration, with sodium sulfide as the electrolyte and platinum foil as the electrode. The PL, reflectance, and transmittance spectra were measured for each sample from 79 K to room temperature. Chemical solution deposition should lead to quantum size effects, as longer deposition times form larger size nanocrystals. Quantum size effects were observed, as longer depositions times led to a shift towards lower energy in the peak of the PL spectra. The temperature dependence of the PL peak energy position was also analyzed; as the temperature increased, the peak shifted towards higher energy. Using the reflectance and transmittance spectra, the absorption coefficient α was calculated, and the Tauc`s plot of (αhν) 2 versus (hν) was graphed. A correlation between the observed absorption edge and the PL spectra was seen, as the absorption edge energy was approximately equal to the PL energy peak.

  2. Digital Doping in Magic-Sized CdSe Clusters.

    PubMed

    Muckel, Franziska; Yang, Jiwoong; Lorenz, Severin; Baek, Woonhyuk; Chang, Hogeun; Hyeon, Taeghwan; Bacher, Gerd; Fainblat, Rachel

    2016-07-26

    Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)13 clusters on the discrete number of Mn(2+) ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn(2+) ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn(2+)-doped clusters therefore represent a system where magneto-optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications.

  3. Serotonin-Labeled CdSe Nanocrystals: Applications for Neuroscience

    NASA Astrophysics Data System (ADS)

    Kippeny, Tadd; Adkins, Erika; Adams, Scott; Thomlinson, Ian; Schroeter, Sally; Defelice, Louis; Blakely, Randy; Rosenthal, Sandra

    2000-03-01

    Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter which has been linked to the regulation of critical behaviors including sleep, appetite, and mood. The serotonin transporter (SERT) is a 12-transmembrane domain protein responsible for clearance of serotonin from extracellular spaces following release. In order to assess the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters we have measured the ability of serotonin-labeled CdSe nanocrystals (SNACs) to block the uptake of tritiated serotonin by the human and Drosophila serotonin transporters (hSERT and dSERT). Estimated Ki values, the SNAC concentration at which half of the serotonin transport activity is blocked, were determined by nonlinear regression to be Ki (hSERT ) = 74uM and Ki (dSERT ) = 29uM. These values and our inability to detect free serotonin indicate that SNACs selectively interact with the serotonin recognition site of the transporter. We have also exposed the SNACs to cells containing ionotropic serotonin receptors and have measured the electrical response of the cell using a two microelectrode voltage clamp. We find that serotonin receptors do respond to the SNACs and we measure currents similar to the free serotonin response. These results indicate that ligand-conjugated nanocrystals can be used to label both receptor and transporter proteins. Initial fluorescence labeling experiments will be discussed.

  4. Growth and properties of CdSe thin films by a new process of electrochemical selenization of Cd metal layers

    SciTech Connect

    Rastogi, A.C.; Balakrishnan, K.S.; Jain, K.

    1999-06-01

    Growth and properties of cadmium selenide semiconductor thin films prepared by a new electrochemical selenization process (ECS) are described. The as-formed CdSe thin films have large ({approximately}1 {micro}m) crystallites in hexagonal modification. The differential selenization kinetics in the intra- and intergrain regions causes the formation of stoichiometric CdSe film to be highly dependent on time. CdSe composition is independent of selenization parameters. Two direct optical band gaps at 2.09 and 1.44 eV, as opposed to a single gap at 1.7 eV, are observed in CdSe film selenized at 0.6 and 0.4 mA/cm{sup 2} current densities, respectively. A mechanism of selenization based on Cd ionization by oxygen reduction and reaction with cathodically released Se ions is proposed for the CdSe film formation.

  5. Preparation and characterization of CdSe colloidal quantum dots by pptical spectroscopy and 2D DOSY NMR

    NASA Astrophysics Data System (ADS)

    Geru, I.; Bordian, O.; Culeac, I.; Turta, C.; Verlan, V.; Barba, A.

    2015-02-01

    We present experimental results on preparation and characterization of colloidal CdSe quantum dots (QD) in organic solvent. CdSe QDs were synthesized following a modified literature method and have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy, as well as by 2D Diffusion Ordered Spectroscopy (DOSY) NMR. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28 - 2.92 nm, which correlates very well with the results obtained from NMR measurements. The PL spectrum for CdSe nanodots can be characterized by a narrow emission band with the peak maximum shifting from 508 to 566 nm in dependence of the CdSe nanoparticle size. The PL is dominated by a near-band-edge emission, accompanied by a weak broad band in the near IR, related to the surface shallow trap emission.

  6. Van der Waals materials for the passivation of monolayer closed-packed films of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Dennis Zi-Ren; Zhang, Datong; Creswell, Richard; Lu, Chenguang; Hu, Jiayang; Herman, Irving P.

    2015-03-01

    Van der Waals (vdW) materials are shown to protect CdSe quantum dots (QDs) from oxidization. Few-layer vdW materials, e.g. graphene and MoS2, were transferred onto a monolayer closed-packed CdSe quantum dots and were examined by photoluminescence (PL) after different time periods. By comparing the PL of CdSe QDs in uncovered areas and those covered by different numbers of layers of graphene and MoS2, we saw that vdW encapsulation slows down the aging of CdSe QDs dramatically. PL mapping results clearly showed better protection of the CdSe QDs under the central part of the vdW material compared to that at the edge; this can be explained by the diffusion of oxygen and water vapor from the edge of the vdW materials.

  7. Abundancias químicas de estrellas de Mercurio-Manganeso obtenidas con espectros EBASIM

    NASA Astrophysics Data System (ADS)

    Pintado, O. I.; Adelman, S. J.

    Se determinan las abundancias químicas de estrellas de HgMn usando espectros obtenidos con EBASIM en CASLEO en un rango de longitud de onda comprendido entre los 400 y 890 nm. Los valores iniciales de temperatura efectiva y gravedad superficial se calculan con la fotometría uvbyβ. Las abundancias se calculan usando WIDTH9 y SYNTHE. Los resultados se comparan análisis realizados por los autores usando espectros obtenidos con el espectrógrado REOSC del CASLEO, el espectrógrafo echelle del Telescopio Anglo-Australiano y el espectrógrafo Coudé del Dominion Astrophysical Observatory.

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

    SciTech Connect

    Huang, J.; Tang, Y.; Mulfort, Karen L.; Zhang, Xiaoyi

    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

  9. Synchronously pumped CdSe optical parametric oscillator in the 9-10 microm region.

    PubMed

    Watson, M A; O'Connor, M V; Shepherd, D P; Hanna, D C

    2003-10-15

    Continuous mode-locked operation of a singly resonant, synchronously pumped optical parametric oscillator (SPOPO) based on CdSe has produced idler output tuned over the range of 9.1-9.7 microm, the longest wavelength generated so far to our knowledge from a SPOPO. Average idler powers as high as approximately 70 mW are generated in the crystal. Tandem pumping with a diffraction-grating-tuned parametric oscillator in periodically poled lithium niobate provides a convenient and agile means of tuning the noncritically phase-matched CdSe device. The absence of any detrimental thermal effects in the CdSe crystal suggests that significant further power scaling should be possible, with idler tuning ranges extendable to cover 8-12 microm.

  10. Cytotoxicity testing of bare CdSe quantum dots and their encapsulated structure

    NASA Astrophysics Data System (ADS)

    Kumari, Asha; Singh, Ragini Raj

    2017-07-01

    In this work we have synthesized CdSe quantum dots (QDs) and their polymer encapsulated structures by wet chemical method for cytotoxicity testing. These QDs were synthesized by using aqueous solvent to make them hydrophilic because we want to use these for bioimaging purpose. The cytotoxicity is major concern to use these quantum dots in bio application because these are made up of heavy metal ions so to make these QDs nontoxic and to improve their optical properties we encapsulated these QDs by polymers. Thereafter we have studied the cytotoxicity of CdSe QDs and their polymer encapsulated structure.MTT method (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method) was used to study toxicity of QDs toward MDCK epithelial cell line. Effect of encapsulation on optical properties was analyzed by Photoluminescence spectroscopy. QDs encapsulated with polymer possess improved optical properties with greater fluorescence intensity and lesser cytotoxicity as compare to bare CdSe.

  11. 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.

  12. Strain Effect on the Electronic and Optical Properties of CdSe Nanowires

    NASA Astrophysics Data System (ADS)

    Huan, Hao; Chen, Li; Ye, Xiang

    2017-03-01

    First-principles density functional theory (DFT) simulations were carried out to study the strain dependence on the electronic and optical properties of cadmium selenide (CdSe) nanowires (NWs). The band structures, effective masses of electron and holes, dielectric properties, and other optical properties (such as extinction coefficient, optical reflectivity, and absorption coefficient) were calculated under both compressive and tensile uniaxial strains. Size-dependence was also discussed by comparing results among CdSe wires with various diameters. Simulation results show that an interesting band-switch behavior occurs at the valence bands regardless of size. The cause and the consequences of such band-switch behavior were also studied. Further strain dependence on corresponding electronic and optical properties were examined as well. Our results provide insights to possible mechanical tuning via strain on the electronic and optical properties of CdSe NWs.

  13. Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations

    NASA Astrophysics Data System (ADS)

    Botti, Silvana; Marques, Miguel A. L.

    2007-01-01

    Semiconducting nanoparticles are the building blocks of optical nanodevices as their electronic states, and therefore light absorption and emission, can be controlled by modifying their size and shape. CdSe is perhaps the most studied of these nanoparticles, due to the efficiency of its synthesis, the high quality of the resulting samples, and the fact that the optical gap is in the visible range. In this article, we study light absorption of CdSe nanostructures with sizes up to 1.5nm within density functional theory. We study both bulk fragments with wurtzite symmetry and fullerene-like core-cage structures. The comparison with recent experimental optical spectra allows us to confirm the synthesis of these fullerene-like CdSe clusters.

  14. Surface states and photovoltaic effects in CdSe quantum dot films

    SciTech Connect

    Kronik, L.; Ashkenasy, N.; Leibovitch, M.; Fefer, E.; Shapira, Y.; Gorer, S.; Hodes, G.

    1998-05-01

    Photovoltaic effects in CdSe quantum dot (QD) films have been studied using surface photovoltage spectroscopy and complementary methods. The results show that, contrary to previous studies, nonnegligible electric fields can exist in QD films. As a result, driftlike currents must be considered, in addition to the well-known diffusion like currents. However, it is found that the specific case of photovoltage sign reversal, observed after etching highly quantized CdSe QD films, is governed by diffusion like transport. The latter is highly influenced by preferential trapping of one type of charge carrier. The preferential trapping is shown to be surface localized and is strongly ambient dependent. It is shown that the photovoltaic properties of these CdSe QD films are dominated by their surface state distribution.

  15. Strain Effect on the Electronic and Optical Properties of CdSe Nanowires.

    PubMed

    Huan, Hao; Chen, Li; Ye, Xiang

    2017-12-01

    First-principles density functional theory (DFT) simulations were carried out to study the strain dependence on the electronic and optical properties of cadmium selenide (CdSe) nanowires (NWs). The band structures, effective masses of electron and holes, dielectric properties, and other optical properties (such as extinction coefficient, optical reflectivity, and absorption coefficient) were calculated under both compressive and tensile uniaxial strains. Size-dependence was also discussed by comparing results among CdSe wires with various diameters. Simulation results show that an interesting band-switch behavior occurs at the valence bands regardless of size. The cause and the consequences of such band-switch behavior were also studied. Further strain dependence on corresponding electronic and optical properties were examined as well. Our results provide insights to possible mechanical tuning via strain on the electronic and optical properties of CdSe NWs.

  16. 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

    2014-01-08

    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).

  17. Study on Growth Kinetics of CdSe Nanocrystals with a New Model

    PubMed Central

    2010-01-01

    A model which involves both bulk diffusion process and surface reaction process has been developed for describing the growth behaviour of nanoparticles. When the model is employed, hypothesising that either of the processes alone dominates the overall growth process is unnecessary. Conversely, the relative magnitude of contributions from both processes could be obtained from the model. Using this model in our system, the growth process of CdSe QDs demonstrated two different growth stages. During the first stage, the growth of CdSe QDs was dominated by bulk diffusion, whereas, neither the bulk diffusion process nor the surface reaction process could be neglected during the later stage. At last, we successfully modelled the Ostwald ripening of CdSe QDs with LSW theories. PMID:20672112

  18. Study on Growth Kinetics of CdSe Nanocrystals with a New Model.

    PubMed

    Su, Huaipeng; Dixon, Johndavid; Wang, Andrew Y; Low, Jeremy; Xu, Jian; Wang, Jingkang

    2010-03-25

    A model which involves both bulk diffusion process and surface reaction process has been developed for describing the growth behaviour of nanoparticles. When the model is employed, hypothesising that either of the processes alone dominates the overall growth process is unnecessary. Conversely, the relative magnitude of contributions from both processes could be obtained from the model. Using this model in our system, the growth process of CdSe QDs demonstrated two different growth stages. During the first stage, the growth of CdSe QDs was dominated by bulk diffusion, whereas, neither the bulk diffusion process nor the surface reaction process could be neglected during the later stage. At last, we successfully modelled the Ostwald ripening of CdSe QDs with LSW theories.

  19. Intrawire absorption and emission spectroscopies of individual CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Chatterjee, Rusha; McDonald, Matthew P.; Kuno, Masaru

    2015-08-01

    Concerted absorption and emission spectroscopies have been used to measure intrawire band edge absorption/emission energy variations along the length of individual CdSe nanowires (NWs). An effective mass model, previously used to explain the size-dependent linear absorption as well as Stokes shift of single CdSe NWs, has been used to rationalize the origin of observed absorption/emission heterogeneities. Associated intrawire Stokes shifts have likewise been used to estimate local exciton trap state densities as well as most probably trap depths. Mean densities of the order of 1020 and 1017 cm-3 have been obtained for small and large radii NWs, respectively, and represent the first exciton trap state density estimates for CdSe NWs. These concerted intrawire measurements broaden the scope of existing single wire microscopies and provide greater insight into the effects of size- and dielectric environment-induced inhomogeneities on the optical/electrical response of individual NWs.

  20. Simple synthesis of luminescent CdSe quantum dots from ascorbic acid and selenium dioxide.

    PubMed

    Wang, Yilin; Yu, Meihua; Yang, Kun; Lu, Jianping; Chen, Linqing

    2015-12-01

    A simple, low-cost and convenient method was developed for the synthesis of highly luminescent CdSe quantum dots (QDs) in an aqueous medium. Compared with previous methods, this synthesis was carried out in one pot using ascorbic acid (C6H8O6) to replace NaBH4 or N2H4·H2O as a reductant, and selenium dioxide to replace selenium or its other hazardous, expensive and unstable compounds as a precursor. The mechanism of CdSe QDs formation was elucidated. The influence of various experimental variables, including refluxing time, Cd/MSA and Cd/Se molar ratios, on the luminescent properties of the QDs were systematically investigated. X-Ray powder diffraction and transmission electron microscopy characterization indicated that the QDs had a pure cubic zinc-blended structure with a spherical shape.

  1. Tuning the emission of CdSe quantum dots by controlled trap enhancement.

    PubMed

    Baker, David R; Kamat, Prashant V

    2010-07-06

    Ligand exchange with 3-mercaptopropionic acid (MPA) has been successfully used to tune the emission intensity of trioctylphosphineoxide/dodecylamine-capped CdSe quantum dots. Addition of 3-mercaptopropionic acid (MPA) to CdSe quantum dot suspension enhances the deep trap emission with concurrent quenching of the band edge emission. The smaller sized quantum dots, because of larger surface/volume ratio, create a brighter trap emission and are more easily tuned. An important observation is that the deep trap emission which is minimal after synthesis is brightened to have a quantum yield of 1-5% and can be tuned based on the concentration of MPA in solution with the quantum dots. Photoluminescence decay and transient absorption measurements reveal the role of surface bound MPA in altering the photophysical properties of CdSe quantum dots.

  2. 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

  3. Structural Characterization Of CdSe and ZnSe Nanostructures

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, B.; Kalita, P. K.; Datta, P.

    2010-10-01

    Chemically bath deposited CdSe and ZnSe powder possesses mixed type structures whereas it is hexagonal wurtzite type in thin film form. SEM images of CdSe symmetrically exhibit the growth of spherical, rod and the rose(flower) type microstructures. ZnSe shows fine grain structures. The growth of microstructures in these selenides according to the growth direction along c-axis of hexagonal wurtzite crystal. Photoluminescence shows strong blue luminescence at 414 and 437 nm in CdSe nanoparticles. ZnSe shows strong PL at 650 nm that is attributed to the strong d-native traps. The blue shifted band gap luminescence at 392 nm shows the quantum confinement in ZnSe nanoparticles.

  4. In-situ EXAFS study of nucleation process of CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Sun, Z. H.; Oyanagi, H.; Uehara, M.; Yamashita, K.; Fukano, A.; Maeda, H.

    2009-11-01

    An in-situ EXAFS method is developed to study the nucleation and growth processes of nanocrystals by using a microfluidic reactor which converts the time-dependent kinetics to position-dependence. As an example, we measured the Se K-edge EXAFS spectra for CdSe nanocrystals along a microfluidic reactor channel and indicated strong time-dependence of the nucleation and growth at the beginning of the reaction. A rapid increase of the reaction yield within several seconds was observed. It is found that after injection of starting materials, the nucleation occurs abruptly and the CdSe nuclei concentration reaches the maximum and then declines rapidly.

  5. Blue luminescence and superstructures from magic size clusters of CdSe.

    PubMed

    Riehle, Frank S; Bienert, Roland; Thomann, Ralf; Urban, Gerald A

    2009-02-01

    In this letter, we present a low-temperature synthesis route revealing a new type of ultrasmall CdSe nanoparticle family with exceptional narrow blue emissions between 437 and 456 nm and full width at half-maxima below 20 nm. Transmission electron microscopy characterization shows the uniformity of the nanoparticles, which have a diameter of 1.6 nm. After surface modification, the spherical particles assemble into nanowires, demonstrating their potential as building blocks for the generation of highly ordered superstructures. They can also be used as single source precursors for the synthesis of CdSe nanocrystals.

  6. Highly luminescent two dimensional excitons in atomically thin CdSe nanosheets

    NASA Astrophysics Data System (ADS)

    Halder, O.; Pradhani, A.; Sahoo, P. K.; Satpati, B.; Rath, S.

    2014-05-01

    Atomically thin Cadmium Selenide (CdSe) nanosheets have been synthesized using a surfactant mediated growth technique. The transmission electron microscopy studies confirm the presence of single layered nanosheets with thickness 1.31 nm and their stacking structures which are complemented by the small angle x-ray scattering measurements. The strongly bound and polarized character of two dimensional excitonic states with enhanced oscillator strength yielding distinct narrow blue luminescence has been observed from the CdSe nanosheets using room temperature based optical studies.

  7. Highly luminescent two dimensional excitons in atomically thin CdSe nanosheets

    SciTech Connect

    Halder, O.; Pradhani, A.; Rath, S.; Sahoo, P. K.; Satpati, B.

    2014-05-05

    Atomically thin Cadmium Selenide (CdSe) nanosheets have been synthesized using a surfactant mediated growth technique. The transmission electron microscopy studies confirm the presence of single layered nanosheets with thickness 1.31 nm and their stacking structures which are complemented by the small angle x-ray scattering measurements. The strongly bound and polarized character of two dimensional excitonic states with enhanced oscillator strength yielding distinct narrow blue luminescence has been observed from the CdSe nanosheets using room temperature based optical studies.

  8. Luminescence blue-shift of CdSe nanowires beyond the quantum confinement regime

    NASA Astrophysics Data System (ADS)

    Yan, Yuan; Liao, Zhi-Min; Bie, Ya-Qing; Wu, Han-Chun; Zhou, Yang-Bo; Fu, Xue-Wen; Yu, Da-Peng

    2011-09-01

    Photoluminescence (PL) properties of individual CdSe nanowires with diameters beyond the quantum confinement regime have been studied. A blue-shift in the PL spectra was observed with decreasing nanowire diameter. We attribute the blue-shift to band-filling effect. Carrier density induced by surface vacancy doping and laser excitation is found to be high enough to meet the criterion of the band-filling effect and increases with decreasing nanowire diameter. Temperature dependent PL analysis and characterizations of a single CdSe nanowire based field-effect transistor were also performed.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO2/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/cm2 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 study of CdSe colloidal quantum dots synthesized in aqueous and organic media

    NASA Astrophysics Data System (ADS)

    Mikhailov, I. I.; Tarasov, S. A.; Solomonov, A. V.; Aleksandrova, O. A.; Matyushkin, L. B.; Mazing, D. S.

    2014-12-01

    The samples of CdSe colloidal quantum dots (CQDs) synthesized in aqueous and organic media are studied. The possibility of luminescence peak position control depending on nanoparticle growth process is demonstrated. The samples synthesized in organic medium revealed the luminescence color variation effect with nanoparticle growth. The relation of this effect with processes of nucleation and defect formation in nanoparticles is considered. The CQDs of CdSe coated with CdS shell are fabricated. The use of inorganic shell can provide a double increase of the luminescence quantum yield.

  11. 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.

  12. 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.

  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. Probing metabolic stability of CdSe nanoparticles: alkaline extraction of free cadmium from liver and kidney samples of rats exposed to CdSe nanoparticles

    PubMed Central

    Arslan, Zikri; Ates, Mehmet; McDuffy, Wanaki; Agachan, M. Sabri; Farah, Ibrahim O.; Yu, W. William; Bednar, Anthony J.

    2011-01-01

    Cadmium selenide nanoparticles (CdSe NPs) exhibit novel optoelectronic properties for potential biomedical applications. However, their metabolic stability is not fully understood because of the difficulties in measurement of free Cd from biological tissues of exposed individuals. In this study, alkaline dissolution with tetramethylammonium hydroxide (TMAH) is demonstrated for selective determination of free Cd and intact NPs from liver and kidney samples of animals that were exposed to thiol-capped CdSe NPs. Aqueous suspensions of CdSe NPs (3.2 nm) were used to optimize the conditions for extracting free Cd without affecting NPs. Nanoparticles were found to aggregate when heated in TMAH without releasing any significant Cd to solution. Performance of the method in discriminating free Cd and intact NPs were verified by Dogfish Liver (DOLT-4) certified reference material. The samples from the animals were digested in 4 mL TMAH at 70 °C to extract free Cd followed by analysis of aqueous phase by ICP-MS. Both liver and kidney contained significant levels of free Cd. Total Cd was higher in the liver, while kidney accumulated mostly free Cd such that up to 47.9% of total Cd in the kidney was free Cd when NPs were exposed to UV-light before injection. PMID:21700388

  15. 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.

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

    SciTech Connect

    Isnaeni, Yulianto, Nursidik; Suliyanti, Maria Margaretha

    2016-03-11

    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. Size dependent properties of one dimensional CdSe micro/nanostructures

    NASA Astrophysics Data System (ADS)

    Narula, Chetna; Chauhan, R. P.

    2017-09-01

    Cadmium Selenide (CdSe) micro/nanowires of different diameters were synthesized in polycarbonate membranes on copper substrate by template assisted electro-deposition method at room temperature. The structure, morphology, elemental, optical and electrical properties of CdSe micro/nanowires were investigated using X-ray Diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy and probe station assisted with Keithley source meter. Structural analysis by X-ray diffraction depicted polycrystalline nature with hexagonal phase of micro/nanowires at all diameters. An increase in the value of average crystallite size was seen with increase in diameter. Morphological investigation confirmed the micro/nanowire synthesis and revealed an ordered array of prepared CdSe micro/nanowires of uniform diameters and having high aspect ratios. Optical band gap is found to increase from 1.89eV to 2.24 eV as the diameter is decreased from 1 μm to 50 nm. Using the band gap values, refractive index and optical dielectric constants (static and high frequency) were also evaluated. The electrical conductivity of CdSe micro/nanowires varied from 21.58 × 102 Ω-1 m-1to 1.93 × 102 Ω-1 m-1 when diameter was decreased. These semiconducting micro/nanowires arrays of different diameters may have potential applications in future nanoscale based electronic and optoelectronic devices.

  18. A Biphasic Ligand Exchange Reaction on Cdse Nanoparticles: Introducing Undergraduates to Functionalizing Nanoparticles for Solar Cells

    ERIC Educational Resources Information Center

    Zemke, Jennifer M.; Franz, Justin

    2016-01-01

    Semiconductor nanoparticles, including cadmium selenide (CdSe) particles, are attractive as light harvesting materials for solar cells. In the undergraduate laboratory, the size-tunable optical and electronic properties can be easily investigated; however, these nanoparticles (NPs) offer another platform for application-based tunability--the NP…

  19. Guided CdSe Nanowires Parallelly Integrated into Fast Visible-Range Photodetectors.

    PubMed

    Shalev, Erga; Oksenberg, Eitan; Rechav, Katya; Popovitz-Biro, Ronit; Joselevich, Ernesto

    2017-01-24

    One-dimensional semiconductor nanostructures, such as nanowires (NWs), have attracted tremendous attention due to their unique properties and potential applications in nanoelectronics, nano-optoelectronics, and sensors. One of the challenges toward their integration into practical devices is their large-scale controlled assembly. Here, we report the guided growth of horizontal CdSe nanowires on five different planes of sapphire. The growth direction and crystallographic orientation are controlled by the epitaxial relationship with the substrate as well as by a graphoepitaxial effect of surface nanosteps and grooves. CdSe is a promising direct-bandgap II-VI semiconductor active in the visible range, with potential applications in optoelectronics. The guided CdSe nanowires were found to have a wurtzite single-crystal structure. Field-effect transistors and photodetectors were fabricated to examine the nanowire electronic and optoelectronic properties, respectively. The latter exhibited the fastest rise and fall times ever reported for CdSe nanostructures as well as a relatively high gain, both features being essential for optoelectronic applications.

  20. Nonvolatile multibit Schottky memory based on single n-type Ga doped CdSe nanowires.

    PubMed

    Wu, Di; Jiang, Yang; Yu, Yongqiang; Zhang, Yugang; Li, Guohua; Zhu, Zhifeng; Wu, Chunyan; Wang, Li; Luo, Linbao; Jie, Jiansheng

    2012-12-07

    Nonvolatile resistive switching has been observed for the first time in CdSe nanowire (NW)/Au Schottky barrier diodes, where a Schottky contact electrode and an Ohmic contact electrode were formed at the Au/CdSe NW and CdSe NW/In interfaces, respectively. The CdSe NWs Schottky devices were found to possess multibit storage ability in an individual nanowire, and exhibited excellent memory characteristics, with a resistance on/off ratio exceeding four orders of magnitude, a long retention time of over 10(4) s and a lower operating voltage of 2 V. By replacing the SiO(2)/Si substrate with a poly ethylene terephthalate substrate, flexible and transparent memory devices with superior stability under strain were realized. The resistive switching of CdSe NW/Au Schottky devices is understood by electron trapping and detrapping in the interfacial oxide layer. Our findings provide a viable way to create new functional high-density nonvolatile multibit memory devices compatible with simple processing techniques for normal one-dimensional nanomaterials.

  1. Nonvolatile multibit Schottky memory based on single n-type Ga doped CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Wu, Di; Jiang, Yang; Yu, Yongqiang; Zhang, Yugang; Li, Guohua; Zhu, Zhifeng; Wu, Chunyan; Wang, Li; Luo, Linbao; Jie, Jiansheng

    2012-12-01

    Nonvolatile resistive switching has been observed for the first time in CdSe nanowire (NW)/Au Schottky barrier diodes, where a Schottky contact electrode and an Ohmic contact electrode were formed at the Au/CdSe NW and CdSe NW/In interfaces, respectively. The CdSe NWs Schottky devices were found to possess multibit storage ability in an individual nanowire, and exhibited excellent memory characteristics, with a resistance on/off ratio exceeding four orders of magnitude, a long retention time of over 104 s and a lower operating voltage of 2 V. By replacing the SiO2/Si substrate with a poly ethylene terephthalate substrate, flexible and transparent memory devices with superior stability under strain were realized. The resistive switching of CdSe NW/Au Schottky devices is understood by electron trapping and detrapping in the interfacial oxide layer. Our findings provide a viable way to create new functional high-density nonvolatile multibit memory devices compatible with simple processing techniques for normal one-dimensional nanomaterials.

  2. 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. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  3. HPVB AND HPVZM SHAPED GROWTH OF CDZNTE, CDSE AND ZNSE CRYSTALS.

    SciTech Connect

    KOLESNIKOV,N.N.; JAMES,R.B.; BERZIGIAROVA,N.S.; KULAKOV,M.P.

    2002-07-07

    High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth processes have been applied for the manufacturing of Cd{sub 1-x}Zn{sub x}Te (x = 0.04-0.2), CdSe and ZnSe crystal tapes with sizes up to 120 x 120 x 12 mm. The influences of the technological parameters describing the growth processes on the crystal quality and some selected material properties are discussed. The dependence of the inclusion (bubbles) content on the deviation from melt stoichiometry is determined. A method for growing plates with low content of inclusions is described. High-resistivity crystal tapes of undoped CdZnTe (10{sup 10} Ohm x cm), CdSe (10{sup 11} Ohm x cm) and ZnSe (>10{sup 11} Ohm x cm) were prepared. The possibility of tape growth on oriented seeds is shown for the example of CdSe. The primary differences between HPVB and HPVZM results are described. The main HPVZM advantage for II-VI compound crystal growth is the possibility of obtaining crystals with more stoichiometric composition or with a controlled deviation from stoichiometry. Hence, HPVZM is preferable for growing high-resistivity II-VI crystals with low inclusion content and possibly with better transport properties. Keywords for this report are: Crystal growth, shaped crystal growth, ZnSe, CdSe, CdZnTe, CZT, HPVB, Bridgman, HPVZM, zone melting, radiation detectors.

  4. Guided CdSe Nanowires Parallelly Integrated into Fast Visible-Range Photodetectors

    PubMed Central

    2016-01-01

    One-dimensional semiconductor nanostructures, such as nanowires (NWs), have attracted tremendous attention due to their unique properties and potential applications in nanoelectronics, nano-optoelectronics, and sensors. One of the challenges toward their integration into practical devices is their large-scale controlled assembly. Here, we report the guided growth of horizontal CdSe nanowires on five different planes of sapphire. The growth direction and crystallographic orientation are controlled by the epitaxial relationship with the substrate as well as by a graphoepitaxial effect of surface nanosteps and grooves. CdSe is a promising direct-bandgap II–VI semiconductor active in the visible range, with potential applications in optoelectronics. The guided CdSe nanowires were found to have a wurtzite single-crystal structure. Field-effect transistors and photodetectors were fabricated to examine the nanowire electronic and optoelectronic properties, respectively. The latter exhibited the fastest rise and fall times ever reported for CdSe nanostructures as well as a relatively high gain, both features being essential for optoelectronic applications. PMID:28032987

  5. Size effect on the electronic and optical band gap of CdSe QD

    SciTech Connect

    Sisodia, Namita

    2014-04-24

    Present paper deals with a critical and comprehensive analysis of the dependence of photo emission (PE) electronic band gap and optical absorption (OA) excitonic band gap on the size of CdSe QD, via connecting it with excitonic absorbance wavelength. Excitonic absorbance wavelength is determined through an empirical fit of established experimental evidences. Effective excitonic charge and Bohr radius is determined as a function of size. Increase in size of the CdSe QD results in greater Bohr radius and smaller effective excitonic charge. Excitonic binding energy as a degree of size of QD is also calculated which further relates with the difference in PE electronic and OA optical band gaps. It is also shown that with increase in size of CdSe QD, the excitonic binding energy decreases which consequently increases differences in two band gaps. Our results are very well comparable with the established results. Explanation for the origin of the unusual optical properties of CdSe QD has been also discussed.

  6. A Biphasic Ligand Exchange Reaction on Cdse Nanoparticles: Introducing Undergraduates to Functionalizing Nanoparticles for Solar Cells

    ERIC Educational Resources Information Center

    Zemke, Jennifer M.; Franz, Justin

    2016-01-01

    Semiconductor nanoparticles, including cadmium selenide (CdSe) particles, are attractive as light harvesting materials for solar cells. In the undergraduate laboratory, the size-tunable optical and electronic properties can be easily investigated; however, these nanoparticles (NPs) offer another platform for application-based tunability--the NP…

  7. Resonant and Nonresonant Nonlinear Optical Spectroscopy of CDSE Quantum Dots for Nonlinear Photonic Applications

    DTIC Science & Technology

    2006-11-01

    excitations. 1. INTRODUCTION Colloidal semiconductor nanocrystals have drawn significant attention because of their distinct roles in nonlinear... colloidal semiconductor nanoscale materials significantly changes with resonant and nonresonant excitation processes. The processes leading to non...2. EXPERIMENT CdSe colloidal quantum-dot nanocrystals for Z- scan and DFWM spectroscopy were prepared by injecting Se solution (a mixture of

  8. Boltzmann equations and ab initio calculations: comparative study of cubic and wurtzite CdSe.

    PubMed

    Abbassi, A; Zarhri, Z; Azahaf, Ch; Ez-Zahraouy, H; Benyoussef, A

    2015-01-01

    The electronic and optical properties of CdSe in two phases, cubic and wurtzite, have been studied by first principal calculations using the density functional theory. The optical parameters such as transmittance, optical absorption, refractive index and extinction coefficient have been investigated. We have calculated also the band structure, and total/partial density of state using the full potential-linearized augmented plane wave method with the local density approximation, generalized gradient approximation and the modified Becke-Johnson functional (mBJ), implemented in the Wien2k package. With the mBJ approximation the gap found for cubic and wurtzite structure is direct and is equal to 1.85 and 1.7 eV respectively, what corresponds to the experiment results. The optical absorption is significant in the ultraviolet field while it becomes low beyond 600 nm in the visible light for CdSe in different structures. From λ = 400 nm the transmittance is stable and reaches 80 %. With Boltztrap package, we have investigated also that with increasing temperature, the electrical conductivity increases. During the calculation, the cubic structure has presented an isotropy. While for wurtzite CdSe, the propagation of waves into system is different in xx and zz directions. These results can be exploited in several applications of CdSe in optoelectronic devices.

  9. Femtosecond time-resolved energy transfer from CdSe nanoparticles to phthalocyanines

    NASA Astrophysics Data System (ADS)

    Dayal, S.; Królicki, R.; Lou, Y.; Qiu, X.; Berlin, J. C.; Kenney, M. E.; Burda, C.

    2006-07-01

    The first real-time observation of the early events during energy transfer from a photoexcited CdSe nanoparticle to an attached phthalocyanine molecule are presented in terms of a femtosecond spectroscopic pump-probe study of the energy transfer in conjugates of CdSe nanoparticles (NPs) and silicon phthalocyanines (Pcs) with 120 fs time resolution. Four different silicon phthalocyanines have been conjugated to CdSe NPs. All of these have proven potential for photodynamic therapy (PDT). In such NP-Pc conjugates efficient energy transfer (ET) from CdSe NPs to Pcs occurs upon selective photoexcitation of the NP moiety. Spectral analysis as well as time-resolved fluorescence up-conversion measurements revealed the structure and dynamics of the investigated conjugates. Femtosecond transient differential absorption (TDA) spectroscopy was used for the investigation of the non-radiative carrier and ET dynamics. The formation of excitons, trapped carriers states, as well as stimulated emission was monitored in the TDA spectra and the corresponding lifetimes of these states were recorded. The time component for energy transfer was found to be between 15 and 35 ps. The ET efficiencies are found to be 20-70% for the four Pc conjugates, according to fluorescence quenching experiments. Moreover, as a result of the conjugation between NP and the Pcs the photoluminescence efficiency of the Pc moieties in the conjugates do not strictly follow the quantum yields of the bare phthalocyanines.

  10. Ligand-assisted fabrication of hollow CdSe nanospheres via Ostwald ripening and their microwave absorption properties.

    PubMed

    Cao, Minhua; Lian, Huiqin; Hu, Changwen

    2010-12-01

    Hollow CdSe nanospheres were successfully synthesized by a ligand-assisted solvothermal method based on an Ostwald ripening mechanism. The hollow CdSe nanospheres were synthesized in benzyl alcohol under solvothermal conditions using Cd(Ac)2 and Se as the precursors, and tryptophan as a ligand. The resulting hollow structures consisted of small nanocrystallite building blocks. More importantly, the hollow CdSe nanospheres could be used as an excellent microwave absorber for cm- and mm-wave absorption, depending on the thickness of the absorber.

  11. Experimental study of the effect of addition of gold nanoparticles on CdSe quantum dots sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Indayani, Wahyu; Huda, Ichsanul; Herliansyah, Khuzaimah, Fasya; Musyaro'ah, Gunawan, Bodi; Endarko

    2017-01-01

    The effect of the gold nanoparticles on the quantum dots sensitized solar cells has been investigated. Gold nanoparticles were added in quantum dot CdSe before used as a sensitizer. The result showed that addition of colloidal gold nanoparticles could be enhanced the absorbance of quantum dot CdSe sensitizer. In this research, the QDSCs were arranged in the sandwich structure consecutively TiO2 as photoelectrode, gold nanoparticle, and quantum dot CdSe as a sensitizer, KI as electrolyte and black carbon as counter-electrode. The use of gold nanoparticles and quantum dot improved the average efficiency of the QDSC by about 104%.

  12. Ligand-assisted fabrication of hollow CdSe nanospheres viaOstwald ripening and their microwave absorption properties

    NASA Astrophysics Data System (ADS)

    Cao, Minhua; Lian, Huiqin; Hu, Changwen

    2010-12-01

    Hollow CdSe nanospheres were successfully synthesized by a ligand-assisted solvothermal method based on an Ostwald ripening mechanism. The hollow CdSe nanospheres were synthesized in benzyl alcohol under solvothermal conditions using Cd(Ac)2 and Se as the precursors, and tryptophan as a ligand. The resulting hollow structures consisted of small nanocrystallite building blocks. More importantly, the hollow CdSe nanospheres could be used as an excellent microwave absorber for cm- and mm-wave absorption, depending on the thickness of the absorber.

  13. Precisión de las velocidades radiales obtenidas con el REOSC

    NASA Astrophysics Data System (ADS)

    González, J. F.; Lapasset, E.

    Complementando una línea de trabajo iniciada con anterioridad discutimos la estabilidad del espectrógrafo REOSC de CASLEO en DC para la medición de velocidades radiales en base al análisis de observaciones realizadas en enero y abril de 1997. En esas oportunidades obtuvimos 26 espectros de estrellas patrones y 27 espectros de 3 estrellas usadas como estrellas de referencia en nuestro programa de cúmulos abiertos. Además tomamos 26 espectros de crepúsculo con el telescopio en posiciones cubriendo el rango H=-4,+4 y δ =-90,+30. Mediante correlaciones cruzadas derivamos la velocidad de 19 órdenes en cada uno de estos espectros. En base a un análisis estadístico de los datos obtenidos discutimos la contribución de los distintos factores que afectan a la dispersión de lectura observada. En particular, la flexión del instrumento no introduciría errores significativos cuando se observa con masas de aire menores que 2.0. La dispersión de los valores de velocidad medidos para espectros de alta relación S/N de una misma estrella resultó del orden de 0.5 km/s. La comparación con los valores de velocidad publicados por distintos autores para las estrellas patrones no permite distinguir ninguna diferencia sistemática apreciable de las velocidades de CASLEO, siendo la media cuadrática de los residuos del orden de 1.0 km/s.

  14. Solution-based stoichiometric control over charge transport in nanocrystalline CdSe devices.

    PubMed

    Kim, David K; Fafarman, Aaron T; Diroll, Benjamin T; Chan, Silvia H; Gordon, Thomas R; Murray, Christopher B; Kagan, Cherie R

    2013-10-22

    Using colloidal CdSe nanowire (NW) field-effect transistors (FETs), we demonstrated the dependence of carrier transport on surface stoichiometry by chemically manipulating the atomic composition of the NW surface. A mild, room-temperature, wet-chemical process was devised to introduce cadmium, selenium, or sulfur adatoms at the surface of the NWs in completed devices. Changes in surface composition were tested for by energy dispersive spectroscopy and inductively coupled plasma-atomic emission spectroscopy and through the use of the vibrational reporter thiocyanate. We found that treatment with cadmium acetate enhances electron currents, while treatment with sodium selenide or sodium sulfide suppressed them. The efficacy of doping CdSe NWs through subsequent thermal diffusion of indium was highly dependent on the surface composition. While selenium-enriched CdSe NW FETs were characterized by little to no electron currents, when combined with indium, they yielded semimetallic devices. Sulfur-enriched, indium-doped devices also displayed dramatically enhanced electron currents, but to a lesser extent than selenium and formed FETs with desirable ION/IOFF >10(6). The atomic specificity of the electronic behavior with different surface chalcogens suggested indium was bound to chalcogens at the NW surface, indicating commonalities with and implications for indium-containing CdSe nanocrystal films. Low temperature measurements of indium-doped CdSe NW FETs showed no evidence of impurity scattering, further supporting the existence of an indium-chalcogen interaction at the surface rather than in the core of the NW.

  15. A facile method to synthesis high-quality CdSe quantum dots for large and tunable nonlinear absorption

    NASA Astrophysics Data System (ADS)

    Cao, Yawan; Wang, Chong; Zhu, Baohua; Gu, Yuzong

    2017-04-01

    The CdSe nanocrystals (NCs) were synthesized by a hot injection method in the atmospheric environment without any protective gas. The size of CdSe NC was tuned by controlling the growth time and the NCs' high-quality was confirmed by UV-visible spectroscopy, photoluminescence spectroscopy, X-ray diffraction and transmission electron microscopy. A large third-order nonlinear optical (NLO) absorption of CdSe NCs was obtained by using Z-scan technique with 30 ps excitation at 532 nm, which was tunable with variable size and the energy difference between the first exciton absorption peak and the laser wavelength. The NLO susceptibility of CdSe NCs can reach as high as 1.81 × 10-10 esu at the size of 3.3 nm and at resonance absorption peak.

  16. Open-to-air synthesis of monodisperse CdSe nanocrystals via microfluidic reaction and its kinetics

    NASA Astrophysics Data System (ADS)

    Luan, Weiling; Yang, Hongwei; Tu, Shan-tung; Wang, Zhiming

    2007-05-01

    Monodisperse zinc blende CdSe nanocrystals (NCs) ranged from 2.5 to 4.3 nm have been reproducibly synthesized directly open to air in a microfluidic reactor with PTFE capillaries acting as the reaction channels. The foregoing features led to superior operational stability, allowing the assessment of kinetic data such as temperature, dwelling time and ligand concentration. Red shifts of the absorption spectra were observed with increasing residence time and temperature. 'Crossover time' of size distribution was first reported in a microfluidic reactor preceded by encouraged Ostwald ripening at high reaction temperature. Oleic acid concentration influenced the formation of CdSe NCs, and high OA to Cd ratio resulted in large NCs size and decreased CdSe concentration. By systematic optimization of the parameters, CdSe NCs with FWHM for the photoluminescence peak in the range from 35 to 42 nm were thus made possible.

  17. Influence of nanocrystalline size on optical band gap in CdSe thin films prepared by DC sputtering

    NASA Astrophysics Data System (ADS)

    Khalaf, Mohammed Khammass; ALhilli, Baha A. M.; Khudiar, Ausama I.; Alzahra, Anwar Abd

    2016-01-01

    Cadmium selenide CdSe thin films have been deposited on glass substrate by using plasma sputtering at room temperature with different times of sputtering. The CdSe thin films are characterized using XRD. The crystallite size of the film is calculated from XRD data, which is found as 12.65 nm as-deposited. It is also found that crystallite size of CdSe thin films increased with thin films thickness. The optical properties concerning the absorption spectra were studied for the prepared thin films. The energy band gaps were found to be in the range of 2.21 eV to 1.8 eV. On varying the film thickness in the range of 350 nm to 600 nm, it was found that the optical band gap increased due to the nanocrystalline size of the CdSe thin films decreased.

  18. Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

    NASA Astrophysics Data System (ADS)

    Valligatla, Sreeramulu; Haldar, Krishna Kanta; Patra, Amitava; Desai, Narayana Rao

    2016-10-01

    The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

  19. 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.

  20. Facile synthesis and properties of CdSe quantum dots in a novel two-phase liquid/liquid system

    NASA Astrophysics Data System (ADS)

    Wang, Jidong; Wang, Xiaoyu; Tang, Hengshan; Gao, Zehua; He, Shengquan; Ke, Dandan; Zheng, Yue; Han, Shumin

    2017-10-01

    High-quantity CdSe QDs were synthesized in a novel two-phase liquid/liquid system. This system, ODE/water was stable and as-used solvents were almost nontoxic. The methodology leading to the successful synthesis of CdSe QDs was a typical, one-pot approach and the obtained CdSe QDs with zinc-blende phase structure exhibited excellent optical properties, narrow size distribution, higher particle uniformity and crystallinity. The mechanism of nucleation and growth of CdSe QDs were discussed by the possible thermodynamic equilibrium existing in ODE/water interface. This two-phase liquid/liquid system would broaden the synthesis of other semiconductor QDs.

  1. Controlled assembling of CdSe nanoparticles into the mesopores of SBA-15 via hot soap method

    NASA Astrophysics Data System (ADS)

    Bao, J.; Shen, Y.; Sun, Y.; Wu, J.; Chen, X.; Dai, N.; Zhang, J. C.

    2008-02-01

    We describe a hot soap method for assembling CdSe nanoparticles inside the channels of mesoporous SBA-15 materials. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), UV-vis absorption spectra, and fluorescence spectra have been successfully used to characterize the structure and the optical properties of the mesoporous materials. EDS analysis carried out on the pores of composite mesoporous silica shows strong Cd and Se signals, confirming the formation of CdSe nanoparticles inside the SBA-15 pores. TEM image shows that the CdSe nanoparticles are about 4-5 nm in sizes and uniformly dispersed inside the pores of mesoporous silica. In the UV-vis absorption spectra of the CdSe nanoparticles inside the SBA-15 hosts, a significant blue shift is detected and attributed to the confinement of channels of SBA-15.

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

    NASA Astrophysics Data System (ADS)

    Tyagi, Chetna; Sharma, Ambika

    2015-08-01

    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.

  3. CdSe magic-sized nuclei, magic-sized nanoclusters and regular nanocrystals: monomer effects on nucleation and growth.

    PubMed

    Yu, Kui

    2012-02-21

    Colloidal semiconductor quantum dots (QDs) have been well appreciated for their potential in nanophotonics with an unprecedented impact in various areas, including light emitting diodes (LEDs) and solar cells. There is an outstanding demand on the control of size and size distribution for the various applications, with rational design supported by fundamental understanding of nucleation and growth. This Research News introduces recent advances in the synthesis of colloidal CdSe magic-sized nuclei (MSN) exhibiting sharp bandgap emission, with a model proposed to illustrate the nature of monomers and their degree of supersaturation (DS) affecting the formation of various CdSe MSN, magic-sized nanoclusters (MSCs), and regular nanocrystals (RNCs). Also, this model addresses tuning the CdSe RNCs into the CdSe MSN with the presence of cadmium acetate (Cd(OAc)2) affecting the nature of the monomers.

  4. Deposition and characterization of CdSe nanoparticles layer on ITO/PET flexible substrate by electrophoretic deposition

    NASA Astrophysics Data System (ADS)

    Yaacob, Khatijah A.; Yi, Liang Shu; Ishak, Muhamad Nizam

    2017-07-01

    CdSe nanoparticles with various sizes were successfully synthesized using hot injection method. UV-vis Spectroscopy (UV-vis) was done to identify the absorption wavelength and then use to calculate the particle size of CdSe nanoparticles. The small nanoparticles were categorized as 2.77 nm, 3.06 nm and 3.52 nm whereas 4.06 nm and 5.43 nm were categorized as big nanoparticles. All these samples were undergone up to 4 times purification. Zeta Potential and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) were done on these purified CdSe nanoparticles for quantitative analysis. Then these nanoparticle were deposited on the flexible substrate using electrophoretic deposition technique. The deposition efficiency of CdSe nanoparticles was influenced by the applied voltage. The applied voltage for big nanoparticles was larger than the small nanoparticles. When number of purification increases, the applied voltage for small size CdSe nanoparticles showed a decreasing trend whereas big size CdSe nanoparticles showed the reverse pattern.

  5. Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    We present the enhanced photoluminescence (PL) of a corrugated Al2O3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al2O3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al2O3, the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al2O3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al2O3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al2O3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al2O3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.

  6. Electrochemical synthesis of photosensitive nano-nest like CdSe0.6Te0.4 thin films

    NASA Astrophysics Data System (ADS)

    Shinde, Surendra K.; Thombare, Jagannath V.; Dubal, Deepak P.; Fulari, Vijay J.

    2013-10-01

    Polycrystalline CdSe0.6Te0.4 thin films were deposited on stainless steel and ITO coated glass (ITO) substrates by using simple and inexpensive electrodeposition method. CdSe0.6 Te0.4 films are characterized by different characterization techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. FE-SEM studies reveal that the entire substrate surface is covered with CdSe0.6 Te0.4 nano-nest. Formation of CdSe0.6Te0.4 compound was confirmed from the FTIR studies. Optical absorption study shows the presence of direct transition and a considerable band gap, Eg = 1.7 eV. Surface wettability with solid-liquid interface showed hydrophilic nature with water contact angle 57° (<90°). Further photovoltaic activity of CdSe0.6Te0.4 films were studied by forming the photoelectrochemical cell having CdSe0.6Te0.4/1 M (Na2S + S + NaOH)/C cell configuration. The efficiency and fill factor of these PEC cells are found to be 0.64% and 0.49 respectively.

  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. Enhanced photoluminescence of corrugated Al2O3 film assisted by colloidal CdSe quantum dots.

    PubMed

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

    2017-05-19

    We present the enhanced photoluminescence (PL) of a corrugated Al2O3 film enabled by colloidal CdSe quantum dots. The colloidal CdSe quantum dots are fabricated directly on a corrugated Al2O3 substrate using an electrochemical deposition (ECD) method in a microfluidic system. The photoluminescence is excited by using a 150 nm diameter ultraviolet laser spot of a scanning near-field optical microscope. Owing to the electron transfer from the conduction band of the CdSe quantum dots to that of Al2O3, the enhanced photoluminescence effect is observed, which results from the increase in the recombination rate of electrons and holes on the Al2O3 surface and the reduction in the fluorescence of the CdSe quantum dots. A periodically-fluctuating fluorescent spectrum was exhibited because of the periodical wire-like corrugated Al2O3 surface serving as an optical grating. The spectral topographic map around the fluorescence peak from the Al2O3 areas covered with CdSe quantum dots was unique and attributed to the uniform deposition of CdSe QDs on the corrugated Al2O3 surface. We believe that the microfluidic ECD system and the surface enhanced fluorescence method described in this paper have potential applications in forming uniform optoelectronic films of colloidal quantum dots with controllable QD spacing and in boosting the fluorescent efficiency of weak PL devices.

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

    PubMed

    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.

  10. Synthesis of CdSe quantum dots using various long-chain fatty acids and their phase transfer.

    PubMed

    Zhang, Qiang; Zhang, Aiyu; Yang, Ping; Shen, Jianxing

    2013-06-01

    Monodispersed colloidal photoluminescent CdSe quantum dots (QDs) were synthesized via an organic approach by using cadmium oxide and elemental selenium as precursors, and long-chain fatty acids as surface ligands. The hydrocarbon chain length of the fatty acid was adjusted to investigate the effect on CdSe QDs. The fatty acid ligands with different hydrocarbon chain lengths showed an apparent effect on the nanocrystal nucleation and growth which is the key controlling the size, size distribution and crystal structure of resulting CdSe QDs. This effect was attributable to the steric hindrance of different hydrocarbon length of the fatty acids, which affected the reactivity of the monomers and nanocrystals during the nanocrystal nucleation and growth. The water-soluble CdSe QDs were obtained by encapsulating the CdSe ODs in oil phase with amphiphilic poly(styrene-co-maleic anhydride) (PSMA)-ethanolamine (EA) polymers, which made it possible for further applications of the CdSe QDs in aqueous environment such as surface functionalization for biological labeling and application in photocatalysis and photosensitization.

  11. CdSe quantum dot-fullerene hybrid nanocomposite for solar energy conversion: electron transfer and photoelectrochemistry.

    PubMed

    Bang, Jin Ho; Kamat, Prashant V

    2011-12-27

    The development of organic/inorganic hybrid nanocomposite systems that enable efficient solar energy conversion has been important for applications in solar cell research. Nanostructured carbon-based systems, in particular C(60), offer attractive strategies to collect and transport electrons generated in a light harvesting assembly. We have assembled CdSe-C(60) nanocomposites by chemically linking CdSe quantum dots (QDs) with thiol-functionalized C(60). The photoinduced charge separation and collection of electrons in CdSe QD-C(60) nanocomposites have been evaluated using transient absorption spectroscopy and photoelectrochemical measurements. The rate constant for electron transfer between excited CdSe QD and C(60) increased with the decreasing size of the CdSe QD (7.9 × 10(9) s(-1) (4.5 nm), 1.7 × 10(10) s(-1) (3.2 nm), and 9.0 × 10(10) s(-1) (2.6 nm)). Slower hole transfer and faster charge recombination and transport events were found to dominate over the forward electron injection process, thus limiting the deliverance of maximum power in CdSe QD-C(60)-based solar cells. The photoinduced charge separation between CdSe QDs and C(60) opens up new design strategies for developing light harvesting assemblies.

  12. Quantum confinement effect of CdSe induced by nanoscale solvothermal reaction.

    PubMed

    Lee, Jin-Wook; Im, Jeong-Hyuk; Park, Nam-Gyu

    2012-10-21

    We report a novel method, nanoscale solvothermal reaction (NSR), to induce the quantum confinement effect of CdSe on nanostructured TiO(2) by solvothermal route. The time-dependent growth of CdSe is observed in solution at room temperature, which is found to be accomplished instantly by heat-treatment in the presence of solvent at 1 atm. However, no crystal growth occurs upon heat-treatment in the absence of solvent. The nanoscale solvothermal growth of CdSe quantum dot is realized on the nanocrystalline oxide surface, where Cd(NO(3))(2)·4H(2)O and Na(2)SeSO(3) solutions are sequentially spun on nanostructured TiO(2), followed by heat-treatment at temperatures ranging from 100 °C to 250 °C. Size of CdSe increases from 4.4 nm to 5.3 nm, 8.7 nm and 14.8 nm, which results in decrease in optical band gap from 2.19 eV to, 1.95 eV, 1.74 eV and 1.75 eV with increasing the NSR temperature from 100 °C to 150 °C, 200 °C and 250 °C, respectively, which is indicative of the quantum confinement effect. Thermodynamic studies reveal that increase in the size of CdSe is related to increase in enthalpy, for instance, from 3.77 J mg(-1) for 100 °C to 8.66 J mg(-1) for 200 °C. Quantum confinement effect is further confirmed from the CdSe-sensitized solar cell, where onset wavelength in external quantum efficiency spectra is progressively shifted from 600 nm to 800 nm as the NSR temperature increases, which leads to a significant improvement of power conversion efficiency by a factor of more than four. A high photocurrent density of 13.7 mA cm(-2) is obtained based on CdSe quantum dot grown by NSR at 200 °C.

  13. Quantum confinement effect of CdSe induced by nanoscale solvothermal reaction

    NASA Astrophysics Data System (ADS)

    Lee, Jin-Wook; Im, Jeong-Hyuk; Park, Nam-Gyu

    2012-09-01

    We report a novel method, nanoscale solvothermal reaction (NSR), to induce the quantum confinement effect of CdSe on nanostructured TiO2 by solvothermal route. The time-dependent growth of CdSe is observed in solution at room temperature, which is found to be accomplished instantly by heat-treatment in the presence of solvent at 1 atm. However, no crystal growth occurs upon heat-treatment in the absence of solvent. The nanoscale solvothermal growth of CdSe quantum dot is realized on the nanocrystalline oxide surface, where Cd(NO3)2.4H2O and Na2SeSO3 solutions are sequentially spun on nanostructured TiO2, followed by heat-treatment at temperatures ranging from 100 °C to 250 °C. Size of CdSe increases from 4.4 nm to 5.3 nm, 8.7 nm and 14.8 nm, which results in decrease in optical band gap from 2.19 eV to, 1.95 eV, 1.74 eV and 1.75 eV with increasing the NSR temperature from 100 °C to 150 °C, 200 °C and 250 °C, respectively, which is indicative of the quantum confinement effect. Thermodynamic studies reveal that increase in the size of CdSe is related to increase in enthalpy, for instance, from 3.77 J mg-1 for 100 °C to 8.66 J mg-1 for 200 °C. Quantum confinement effect is further confirmed from the CdSe-sensitized solar cell, where onset wavelength in external quantum efficiency spectra is progressively shifted from 600 nm to 800 nm as the NSR temperature increases, which leads to a significant improvement of power conversion efficiency by a factor of more than four. A high photocurrent density of 13.7 mA cm-2 is obtained based on CdSe quantum dot grown by NSR at 200 °C.

  14. Synthesis of CdSe nanoparticles in the presence of aminodextran as stabilizing and capping agent.

    PubMed

    Sondi, Ivan; Siiman, Olavi; Matijević, Egon

    2004-07-15

    Water-dispersible Amdex-CdSe nanoparticle complexes with sufficient luminescence intensity were prepared at room temperature by rapidly mixing aqueous solutions of either sodium selenide or selenourea with those of cadmium chloride in the presence of amino-derivatized polysaccharides (Amdex) as stabilizing agent. It was shown that the size of CdSe crystallites decreased with increasing content of the polymer in the precipitation process. When present in a sufficient amount, Amdex was found to be an effective stabilizing and capping agent, producing CdSe nanocrystals of weak-to-medium luminescence intensity (maximum room temperature quantum yields of 15-16%). Furthermore, Amdex has proven to be an effective protective agent against photochemical degradation.

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

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

    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. These quantum dots were solubilized with mercaptoacetic acid and conjugated to adenine. Significant evidence for the internal staining of Bacillus subtilis (Gram positive) and Escherichia coli (Gram negative) using these structures is presented via steady-state emission, epifluorescence microscopy, transmission electron microscopy, and energy dispersive spectroscopy. In particular, the E. coli adenine auxotroph, and not the wild type, took up adenine coated quantum dots, and this only occurred in adenine deficient growth media. Labeling strength was enhanced by performing the incubation under room light. This process was examined with steady-state emission spectra and time-resolved luminescence profiles obtained from time-correlated-single-photon counting.

  16. Ultrafast Carrier Dynamics and Hot Electron Extraction in Tetrapod-Shaped CdSe Nanocrystals.

    PubMed

    Jing, Pengtao; Ji, Wenyu; Yuan, Xi; Qu, Songnan; Xie, Renguo; Ikezawa, Michio; Zhao, Jialong; Li, Haibo; Masumoto, Yasuaki

    2015-04-22

    The ultrafast carrier dynamics and hot electron extraction in tetrapod-shaped CdSe nanocrystals was studied by femtosecond transient absorption (TA) spectroscopy. The carriers relaxation process from the higher electronic states (CB2, CB3(2), and CB4) to the lowest electronic state (CB1) was demonstrated to have a time constant of 1.04 ps, resulting from the spatial electron transfer from arms to a core. The lowest electronic state in the central core exhibited a long decay time of 5.07 ns in agreement with the reported theoretical calculation. The state filling mechanism and Coulomb blockade effect in the CdSe tetrapod were clearly observed in the pump-fluence-dependent transient absorption spectra. Hot electrons were transferred from arm states into the electron acceptor molecules before relaxation into core states.

  17. Study of sub band gap absorption of Sn doped CdSe thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Jagdish; Rani, Mamta; Tripathi, S. K.

    2014-04-01

    The nanocrystalline thin films of Sn doped CdSe at different dopants concentration are prepared by thermal evaporation technique on glass substrate at room temperature. The effect of Sn doping on the optical properties of CdSe has been studied. A decrease in band gap value is observed with increase in Sn concentration. Constant photocurrent method (CPM) is used to study the absorption coefficient in the sub band gap region. Urbach energy has been obtained from CPM spectra which are found to increase with amount of Sn dopants. The refractive index data calculated from transmittance is used for the identification of oscillator strength and oscillator energy using single oscillator model which is found to be 7.7 and 2.12 eV, 6.7 and 2.5 eV for CdSe:Sn 1% and CdSe:Sn 5% respectively.

  18. Generation of fluorescent CdSe nanocrystals by short-pulse laser fragmentation

    NASA Astrophysics Data System (ADS)

    Zholudov, Yu. T.; Sajti, C. L.; Slipchenko, N. N.; Chichkov, B. N.

    2015-12-01

    A simple liquid-phase laser fragmentation approach, resulting in the rapid transformation of CdSe microcrystals into colloidal quantum dots (QDs), is presented. Laser fragmentation is achieved by irradiating a CdSe suspension in dimethylformamide with intense infrared, picosecond laser pulses followed by surface passivation with oleylamine or different types of phosphines. The generated QDs reveal perfect colloidal stability preventing agglomeration and precipitation, and show characteristic QD absorption and fluorescence characteristics, whereas their emission properties strongly depend on the surface states and applied capping ligands. These QDs show distinct photoemission under 405-nm single-photon and 800-nm multi-photon excitations in the 560- to 610-nm spectral region corresponding to the QDs size of about 1.5-2 nm in diameter which is confirmed by transmission electron microscopy.

  19. Photoelectrochemical properties of CdSe /SUB x/ Te /SUB 1-x/ semiconducting solid solutions

    SciTech Connect

    Kolbasov, G.Y.; Karpov, I.I.; Khanat, L.N.; Pavelets, A.M.

    1986-03-01

    This paper studies the photoelectrochemical properties of polycrystalline films of CdSe /SUB x/ Te /SUB 1-x/ solid solutions at x between 0.5 and 0.8. The spectral dependence of photolectro-chemical current is shown measured with a constant number of light quanta striking CdSe /SUB x/ Te /SUP 1-x/ electrodes with compositions. The results obtained indicate that there is no change in potential drop across the Helmholtz layer when the intensity of the light striking the sample is varied, and that ohmic losses at the photoelectrode are low for the light intensities used. Recombination-type losses of the photogenerated carriers which increae with decreasing superficial band bending are chiefly responsible for the decrease in photocurrent.

  20. Reassignment of the OSe-VCd complex in CdSe

    NASA Astrophysics Data System (ADS)

    Bastin, Dirk; Lavrov, E. V.; Weber, J.

    2014-02-01

    An IR absorption study of CdSe single crystals is presented. The as-received material revealed three absorption lines at 1094.2, 1107.5, and 1126.3 cm-1, which were previously assigned to the OSe-VCd complex [G. Chen et al., Phys. Rev. Lett. 101, 195502 (2008)] We show that each of the lines is accompanied by a number of weaker satellites with intensities which match the natural abundances of sulfur isotopes. In contrast to the original identification it is suggested that these peaks are local vibrational modes of a SOn complex. The three modes correspond to different orientations of the complex in the CdSe lattice. Arguments are presented in favor of 2 oxygen atoms (n = 2) in the complex. Measurements with uniaxial stress applied to the samples revealed defect symmetries and activation energies for the defect reorientation. The complex was found to be stable up to 750 °C.

  1. CdSe nanorods dominate photocurrent of hybrid CdSe-P3HT photovoltaic cell.

    PubMed

    Schierhorn, Martin; Boettcher, Shannon W; Peet, Jeffrey H; Matioli, Elison; Bazan, Guillermo C; Stucky, Galen D; Moskovits, Martin

    2010-10-26

    Photovoltaic devices based on organic semiconductors require charge-separating networks (bulk heterojunctions) for optimal performance. Here we report on the fabrication of organic-inorganic photovoltaic devices with tailored (n-type) CdSe nanorod arrays aligned perpendicularly to the substrate. The nanorod lengths varied from 58 ± 12 to 721 ± 15 nm, while the diameters and inter-rod spacings were kept constant at 89.5 ± 7.5 and 41.3 ± 9.9 nm, respectively. Short-circuit densities improved linearly with nanorod length, resulting in power conversion efficiencies of up to 1.38% for cells with nanorods 612 ± 46 nm long. Notably, the cell's efficiency was dominated by exciton generation in the CdSe nanorods.

  2. Electric field-induced emission enhancement and modulation in individual CdSe nanowires.

    PubMed

    Vietmeyer, Felix; Tchelidze, Tamar; Tsou, Veronica; Janko, Boldizsar; Kuno, Masaru

    2012-10-23

    CdSe nanowires show reversible emission intensity enhancements when subjected to electric field strengths ranging from 5 to 22 MV/m. Under alternating positive and negative biases, emission intensity modulation depths of 14 ± 7% are observed. Individual wires are studied by placing them in parallel plate capacitor-like structures and monitoring their emission intensities via single nanostructure microscopy. Observed emission sensitivities are rationalized by the field-induced modulation of carrier detrapping rates from NW defect sites responsible for nonradiative relaxation processes. The exclusion of these states from subsequent photophysics leads to observed photoluminescence quantum yield enhancements. We quantitatively explain the phenomenon by developing a kinetic model to account for field-induced variations of carrier detrapping rates. The observed phenomenon allows direct visualization of trap state behavior in individual CdSe nanowires and represents a first step toward developing new optical techniques that can probe defects in low-dimensional materials.

  3. Optical quenching of photoconductivity in CdSe single nanowires via waveguiding excitation.

    PubMed

    Gu, Fuxing; Wang, Pan; Yu, Huakang; Guo, Bing; Tong, Limin

    2011-05-23

    We demonstrate broadband optical quenching of photoconductivity in CdSe single nanowires with low excitation power. Using 1550-nm-wavelength light with 10-nW power for waveguiding excitation, we observe a typical responsivity of 0.5 A/W for quenching the photoconductivity established by 10-µW 660-nm-wavelength background light in a 403-nm-diameter CdSe nanowire, with detectable limit of the quenching power down to pW level at room temperature, which is several orders of magnitude lower than those reported previously. This large quenching effect originates from the enhanced light-defect interaction in the nanowires via waveguiding excitation. These results open new opportunities for noninvasive characterization of deep-level defect states in low-dimensional semiconductor nanomaterials, and novel optoelectronic applications of semiconductor nanowires such as high-sensitive broadband photodetection.

  4. Light-gated single CdSe nanowire transistor: photocurrent saturation and band gap extraction

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Chakraborty, Ritun; Kudera, Stefan; Krahne, Roman

    2015-11-01

    CdSe nanowires are popular building blocks for many optoelectronic devices mainly owing to their direct band gap in the visible range of the spectrum. Here we investigate the optoelectronic properties of single CdSe nanowires fabricated by colloidal synthesis, in terms of their photocurrent-voltage characteristics and photoconductivity spectra recorded at 300 and 18 K. The photocurrent is identified as the secondary photocurrent, which gives rise to a photoconductive gain of 35. We observe a saturation of the photocurrent beyond a certain voltage bias that can be related to the finite drift velocity of electrons. From the photoconductivity spectra, we determine the band gap energy of the nanowires as 1.728 eV, and we resolve low-energy peaks that can be associated with sub-bandgap states.

  5. Improved solar cell based on ZnO nanowires and CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Nadarajah, Athavan; Word, Robert C.; Konenkamp, Rolf

    2010-03-01

    We report a solar cell nanostructure that incorporates CdSe quantum dots embedded in a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and efficient collection of the carriers. Microscopic studies show the conversion of CdSe quantum dots into an inter-connected and continuous polycrystalline thin film upon annealing in cadmium chloride ambient. This structural change of the quantum dot layer destroys the quantum confinement and improves the charge transport in the layer significantly. It also provides for improved charge transfer to the adjacent contacting layers. The optimized solar cell exhibits an external quantum efficiency of 65 percent and an energy conversion efficiency above 2 percent.

  6. Ultrafast spectroscopy of quantum confined states in a single CdSe nanowire.

    PubMed

    Schumacher, Thorsten; Giessen, Harald; Lippitz, Markus

    2013-04-10

    We measure for the first time transient absorption spectra of individual CdSe nanowires with about 10 nm diameter. Confinement of the carrier wave functions leads to discrete states which can be described by a six-band effective mass model. Combining transient absorption and luminescence spectroscopy allows us to track the excitation dynamics in the visible and near-infrared spectral range. About 10% of all absorbed photons lead to an excitation of the lowest energy state. Of these excitations, less than 1% lead to a photon in the optical far-field. Almost all emission is reabsorbed by other parts of the nanowire. These findings might explain the low overall quantum efficiency of CdSe nanowires.

  7. Morphology of ultrathin CdSe quantum confinement layers in ZnSe matrices

    NASA Astrophysics Data System (ADS)

    Chinyama, K. G.; O'Donnell, K. P.; Rosenauer, A.; Gerthsen, D.

    1999-06-01

    Using a combination of transmission electron microscopy (TEM), high resolution TEM (HRTEM), digital analysis of lattice images (DALI), and correspondence analysis (CA) we present at near-atomic resolution the morphology of a nominal 2 monolayer (ML) cadmium selenide (CdSe) quantum well (QW) between ZnSe barriers. We reveal the presence of ˜10 ML zinc cadmium selenide (Zn xCd 1- xSe) alloy insertion layer of varying composition in a ZnSe matrix. A spotty pattern in the plane of the layer indicates the presence of self-assembled clusters or islands similar to the structures commonly referred to as quantum dots. Further analysis indicates that these clusters, of less than 10 nm in lateral extent, themselves contain sites highly saturated with CdSe. Analysis of photoluminescence (PL) spectra suggests that the emission originates predominantly from excitons trapped in these islands.

  8. Ultrathin CdSe in Plasmonic Nanogaps for Enhanced Photocatalytic Water Splitting

    PubMed Central

    2015-01-01

    Enhanced plasmonic fields are a promising way to increase the efficiency of photocatalytic water splitting. The availability of atomically thin materials opens up completely new opportunities. We report photocatalytic water splitting on ultrathin CdSe nanoplatelets placed in plasmonic nanogaps formed by a flat gold surface and a gold nanoparticle. The extreme field intensity created in these gaps increases the electron–hole pair production in the CdSe nanoplatelets and enhances the plasmon-mediated interfacial electron transfer. Compared to individual nanoparticles commonly used to enhance photocatalytic processes, gap-plasmons produce several orders of magnitude higher field enhancement, strongly localized inside the semiconductor sheet thus utilizing the entire photocatalyst efficiently. PMID:25937870

  9. Bovine serum albumin-directed synthesis of biocompatible CdSe quantum dots and bacteria labeling.

    PubMed

    Wang, Qisui; Ye, Fangyun; Fang, Tingting; Niu, Wenhan; Liu, Peng; Min, Xinmin; Li, Xi

    2011-03-01

    A simple method was developed for preparing CdSe quantum dots (QDs) using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd(2+)) in situ. Fluorescence (FL) and absorption spectra showed that the chelating time between BSA and Cd(2+), the molar ratio of BSA/Cd(2+), temperature, and pH are the crucial factors for the quality of QDs. The average QD particle size was estimated to be about 5 nm, determined by high-resolution transmission electron microscopy. With FL spectra, Fourier transform infrared spectra, and thermogravimetric analysis, an interesting mechanism was discussed for the formation of the BSA-CdSe QDs. The results indicate that there might be conjugated bonds between CdSe QDs and -OH, -NH, and -SH groups in BSA. In addition, fluorescence imaging suggests that the QDs we designed can successfully label Escherichia coli cells, which gives us a great opportunity to develop biocompatible tools to label bacteria cells.

  10. Film formation of CdSe quantum dot embedded phosphate glass on an FTO glass substrate

    NASA Astrophysics Data System (ADS)

    Han, Karam; Kim, Yoon Hwa; Im, Won Bin; Chung, Woon Jin

    2015-07-01

    A thick film with CdSe quantum dot (QD) embedded glass was formed on a fluorine-doped tin oxide (FTO) glass substrate. Phosphate glasses with different CdO and ZnSe concentrations were synthesized, and the heat treatment conditions were varied to determine the appropriate QD and film formation conditions. Phosphate glass with 1 mol. % CdO and 1.5 mol. % ZnSe showed controlled crystallization of CdSe QDs when they were heat treated at 550℃ for 1 hr. Absorption spectra and Raman spectroscopy identified the QD formation. Precursor glass was ground into powder and pasted onto FTO only and TiO2/FTO glass substrates via the screen printing method. Glass film embedded with QDs was successfully formed after sintering, thus demonstrating its potential for film applications. [Figure not available: see fulltext.

  11. Enhancement of Photoluminescence Intensity of CdSe Nanorods Doped in Cholesteric Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Huang, Chiu-Chang; Chou, Tsu-Ruey; Chen, Jun-Wei; Chao, Chih-Yu

    2015-02-01

    The enhancement of photoluminescence (PL) signals of CdSe nanorods caused by embedding in the cholesteric liquid crystals (CLCs) is demonstrated in this article. Three kinds of different CLCs have been used in this experiment, and the results have shown that the phenomenon of PL enhancement generally occurs in each sample. Moreover, the relations between the enhancement and the pitch of CLCs have been analyzed as well. It displays an inversely proportional property, that is, a greater enhancement of the PL signal is achieved in the samples with shorter pitches of CLCs. The highest PL amplification acquired in this study is 3.31 times. The enhancement phenomenon is attributed to the presence of oily streaks in CLCs, which possess advantages due to the excitation of CdSe nanorods. With the versatile properties that CLC have, this study suggests that the method could provide a potential way for PL signal manipulation in many optical fields.

  12. Direct growth of CdSe semiconductor quantum dots in glass matrix by femtosecond laser beam

    NASA Astrophysics Data System (ADS)

    Bell, G.; Filin, A. I.; Romanov, D. A.; Levis, R. J.

    2016-02-01

    Controllable, spatially inhomogeneous distributions of CdSe nanocrystals smaller than the exciton Bohr radius are grown in a glass matrix under combined action of sample heating (below the transformation temperature) and focused high-repetition femtosecond (fs) laser beam. Selective quantum dot precipitation is evidenced by position-dependent absorption and Raman spectra. The particle size is estimated as r = 2.1 ± 0.3 nm by comparing the measured absorption and Raman spectra with those obtained from the samples grown in glass by traditional heat-treatment procedure. Direct growth of CdSe quantum dots in glass is enabled by nonlinear excitation using a focused fs duration laser beam (as differentiated from other methods), and this opens an avenue for adjustable selective growth patterns.

  13. 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.

  14. Understanding the isothermal growth kinetics of cdse quantum dots through microfluidic reactor assisted combinatorial synthesis

    NASA Astrophysics Data System (ADS)

    Swain, Basudev; Hong, Myung Hwan; Kang, Lee-Seung; Lee, Chan Gi

    2016-11-01

    With the use of a microfluidic-assisted combinatorial reactor, the synthesis of CdSe quantum dots was optimized by varying one parameter at a time, and the isothermal growth kinetics of CdSe quantum dots using various models was analyzed. To understand precisely the nucleation and growth characteristics of CdSe quantum dots (QDs), we synthesized the CdSe QDs using various experimental conditions. Different model equations, like acceleratory growth-time curves, sigmoidal growth-time curves or Johnson-Mehl-Avrami-Kolmogorov (JMAK), acceleratory growthtime curves based on diffusion, geometric model growth-time curves, and nth order growth-time curves were fitted. Among all growth models, the JMAK model with α = 1 - {e^{ - {{(kt)}^n}}}, and n = 1 was the best fitting model with the MATLAB interactive curve-fitting procedure were used. Errors associated with the best-fitting model and statistics for the goodness of fit were analyzed. Most of the models were not as good as the other than the proposed model. The errors associated with the proposed model were minimal, and the growth kinetics and other associated statistical factors are very similar, for all the variables investigated. The minimal error associated with the reproducibility and the similar data for growth kinetics for all studied parameters indicated that microfluidic-assisted combinatorial synthesis can be used in the industrial production of QDs. By using the proposed model to obtain an understanding of growth of QDs, their size and properties can be managed and simulated.

  15. Excitation enhancement of CdSe quantum dots by single metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Yeechi; Munechika, Keiko; Jen-La Plante, Ilan; Munro, Andrea M.; Skrabalak, Sara E.; Xia, Younan; Ginger, David S.

    2008-08-01

    We study plasmon-enhanced fluorescence from CdSe /CdS/CdZnS/ZnS core/shell quantum dots near a variety of Ag and Au nanoparticles. The photoluminescence excitation (PLE) spectrum of quantum dots closely follows the localized surface plasmon resonance (LSPR) scattering spectrum of the nanoparticles. We measure excitation enhancement factors of ˜3 to 10 for different shapes of single metal nanoparticles.

  16. Optical properties of thin films of CdSe obtained by spray pyrolisis

    NASA Astrophysics Data System (ADS)

    Gonzalez, A. M. P.; Tepantlan, C. S.; Carrillo, F. R.

    2006-06-01

    In this paper the optical properties of CdSe thin films obtained by spray pyrolisis are presented. The films are prepared by Sodium Selenosulphate (Na2SSeO3) and Cadmium Chloride (CdC12) mixing in aqueous environment. Optical parameters of the films (refractive index, absorption coefficient and optical bangap) were calculated from transmittance spectra. The obtained values of the optical bangap are compared with the result obtained by other deposition methods.

  17. 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.

  18. Direct observation of electron-to-hole energy transfer in CdSe quantum dots.

    PubMed

    Hendry, E; Koeberg, M; Wang, F; Zhang, H; de Mello Donegá, C; Vanmaekelbergh, D; Bonn, M

    2006-02-10

    We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots. Time-resolved luminescence and terahertz spectroscopy reveal that the rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This constitutes the first direct, quantitative measurement of electron-to-hole energy transfer, the hypothesis behind the Auger cooling mechanism proposed in quantum dots, which is found to occur on a 1 +/- 0.15 ps time scale.

  19. Cytotoxicity and fluorescence studies of silica-coated CdSe quantum dots for bioimaging applications

    NASA Astrophysics Data System (ADS)

    Vibin, Muthunayagam; Vinayakan, Ramachandran; John, Annie; Raji, Vijayamma; Rejiya, Chellappan S.; Vinesh, Naresh S.; Abraham, Annie

    2011-06-01

    The toxicological effects of silica-coated CdSe quantum dots (QDs) were investigated systematically on human cervical cancer cell line. Trioctylphosphine oxide capped CdSe QDs were synthesized and rendered water soluble by overcoating with silica, using aminopropyl silane as silica precursor. The cytotoxicity studies were conducted by exposing cells to freshly synthesized QDs as a function of time (0-72 h) and concentration up to micromolar level by Lactate dehydrogenase assay, MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay, Neutral red cell viability assay, Trypan blue dye exclusion method and morphological examination of cells using phase contrast microscope. The in vitro analysis results showed that the silica-coated CdSe QDs were nontoxic even at higher loadings. Subsequently the in vivo fluorescence was also demonstrated by intravenous administration of the QDs in Swiss albino mice. The fluorescence images in the cryosections of tissues depicted strong luminescence property of silica-coated QDs under biological conditions. These results confirmed the role of these luminescent materials in biological labeling and imaging applications.

  20. Wire-supported CdSe nanowire array photoelectrochemical solar cells.

    PubMed

    Zhang, Luhui; Shi, Enzheng; Li, Zhen; Li, Peixu; Jia, Yi; Ji, Chunyan; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai; Cao, Anyuan

    2012-03-14

    Previous fiber-shaped solar cells are based on polymeric materials or dye-sensitized wide band-gap oxides. Here, we show that efficient fiber solar cells can be made from semiconducting nanostructures (e.g. CdSe) with smaller band-gap as the light absorption material. We directly grow a vertical array of CdSe nanowires uniformly around a core metal wire and make the device by covering the top of nanowires with a carbon nanotube (CNT) film as the porous transparent electrode. The CdSe-CNT fiber solar cells show power conversion efficiencies of 1-2% under AM 1.5 illumination after the nanowires are infiltrated with redox electrolyte. We do not use a secondary metal wire (e.g. Pt) as in conventional fiber-shaped devices, instead, the end part of the CNT film is condensed into a conductive yarn to serve as the secondary electrode. In addition, our CdSe nanowire-based photoelectrochemical fiber solar cells maintain good flexibility and stable performance upon rotation and bending to large angles.

  1. Atomistic Analysis of Room Temperature Quantum Coherence in Two-Dimensional CdSe Nanostructures.

    PubMed

    Pal, Sougata; Nijjar, Parmeet; Frauenheim, Thomas; Prezhdo, Oleg V

    2017-03-02

    Recent experiments on CdSe nanoplatelets synthesized with precisely controlled thickness that eliminates ensemble disorder have allowed accurate measurement of quantum coherence at room temperature. Matching exactly the CdSe cores of the experimentally studied particles and considering several defects, we establish the atomistic origins of the loss of coherence between heavy and light hole excitations in two-dimensional CdSe and CdSe/CdZnS core/shell structures. The coherence times obtained using molecular dynamics based on tight-binding density functional theory are in excellent agreement with the measured values. We show that a long coherence time is a consequence of both small fluctuations in the energy gap between the excited state pair, which is much less than thermal energy, and a slow decay of correlation between the energies of the two states. Anionic defects at the core/shell interface have little effect on the coherence lifetime, while cationic defects strongly perturb the electronic structure, destroying the experimentally observed coherence. By coupling to the same phonon modes, the heavy and light holes synchronize their energy fluctuations, facilitating long-lived coherence. We further demonstrate that the electronic excitations are localized close to the surface of these narrow nanoscale systems, and therefore, they couple most strongly to surface acoustic phonons. The established features of electron-phonon coupling and the influence of defects, surfaces, and core/shell interfaces provide important insights into quantum coherence in nanoscale materials in general.

  2. 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

    2015-04-08

    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.

  3. 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.

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

    SciTech Connect

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

    2016-02-08

    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.

  5. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    NASA Astrophysics Data System (ADS)

    Rangel-Kuoppa, Victor-Tapio

    2013-12-01

    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.

  6. Electrochemical Charging of CdSe Quantum Dots: Effects of Adsorption versus Intercalation.

    PubMed

    Puntambekar, Ajinkya; Wang, Qi; Miller, Lauren; Smieszek, Nicholas; Chakrapani, Vidhya

    2016-12-27

    Effects of electrochemical charging of quantum dots (QDs) have been reported previously, wherein optical and electrical properties could be modulated through cation adsorption and electron injection into the quantum-confined 1Se states. In this work, we report two different modes of electrochemical double-layer charging in CdSe QDs and their effects on the electronic and optical properties. We show that the charging mechanism at the interface involves cation intercalation for smaller ions, such as Li(+), Na(+), or K(+), and cation adsorption for larger bulky ions, such as tetrabutylammonium ions, where steric hindrance precludes intercalation. As a result, while cation adsorption leads to an increase in the absorbance in the mid-infrared spectral range, cation intercalation into the CdSe core results in an absorbance increase from the visible to infrared spectral range, an enhancement in radiative lifetime of e(-), an increase of 158% in the intensity of band-edge photoluminescence, and strong emission in the near-infrared spectral range as a result of the formation of Se vacancies. The nature of charging mechanisms is discussed using the results of combined photoluminescence, radiative lifetime, and X-ray photoemission studies. The cation-coupled electronic and optical modulation reported here in CdSe QDs have important implications for electrochromic smart windows, photovoltaics, and other devices.

  7. 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.

  8. Photosensitization of ZnO nanowires with CdSe quantum dots for photovoltaic devices.

    PubMed

    Leschkies, Kurtis S; Divakar, Ramachandran; Basu, Joysurya; Enache-Pommer, Emil; Boercker, Janice E; Carter, C Barry; Kortshagen, Uwe R; Norris, David J; Aydil, Eray S

    2007-06-01

    We combine CdSe semiconductor nanocrystals (or quantum dots) and single-crystal ZnO nanowires to demonstrate a new type of quantum-dot-sensitized solar cell. An array of ZnO nanowires was grown vertically from a fluorine-doped tin oxide conducting substrate. CdSe quantum dots, capped with mercaptopropionic acid, were attached to the surface of the nanowires. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dot-nanowire interface. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the photoanode. With a liquid electrolyte as the hole transport medium, quantum-dot-sensitized nanowire solar cells exhibited short-circuit currents ranging from 1 to 2 mA/cm2 and open-circuit voltages of 0.5-0.6 V when illuminated with 100 mW/cm2 simulated AM1.5 spectrum. Internal quantum efficiencies as high as 50-60% were also obtained.

  9. Photocatalytic Hydrogen Generation Efficiencies in One-Dimensional CdSe Heterostructures.

    PubMed

    Tongying, Pornthip; Plashnitsa, Vladimir V; Petchsang, Nattasamon; Vietmeyer, Felix; Ferraudi, Guillermo J; Krylova, Galyna; Kuno, Masaru

    2012-11-01

    To better understand the role nanoscale heterojunctions play in the photocatalytic generation of hydrogen, we have designed several model one-dimensional (1D) heterostructures based on CdSe nanowires (NWs). Specifically, CdSe/CdS core/shell NWs and Au nanoparticle (NP)-decorated core and core/shell NWs have been produced using facile solution chemistries. These systems enable us to explore sources for efficient charge separation and enhanced carrier lifetimes important to photocatalytic processes. We find that visible light H2 generation efficiencies in the produced hybrid 1D structures increase in the order CdSe < CdSe/Au NP < CdSe/CdS/Au NP < CdSe/CdS with a maximum H2 generation rate of 58.06 ± 3.59 μmol h(-1) g(-1) for CdSe/CdS core/shell NWs. This is 30 times larger than the activity of bare CdSe NWs. Using femtosecond transient differential absorption spectroscopy, we subsequently provide mechanistic insight into the role nanoscale heterojunctions play by directly monitoring charge flow and accumulation in these hybrid systems. In turn, we explain the observed trend in H2 generation rates with an important outcome being direct evidence for heterojunction-influenced charge transfer enhancements of relevant chemical reduction processes.

  10. Effect of environment on the preparation of CdSe quantum dots capped with mercaptoacetic acid.

    PubMed

    Wageh, S; Higazy, Anwer A; Al-Ghamdi, Ahmed A; Hassouna, Ahmed S

    2014-08-01

    We report a preparation of CdSe quantum dots in the presence of capping molecules under ambient air and argon atmospheres. The growth of the quantum dots with applying an equimolar ratio of precursor of Cd2+ and Se2- in the presence of a high percentage of the mercaptoacetic acid as capping molecules is studied. Quantum dots are characterized via EDX, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), UV-Vis optical absorption, Raman and infrared spectroscopy. Combination of EDX and Raman spectroscopy showed a graded diffusion of sulfur on the surface of CdSe quantum dots for the sample prepared under argon atmosphere, while the sample prepared under ambient air atmosphere the sulfur isn't diffused into the CdSe core. In addition, the sample prepared under air revealed a formation of oxides on the surface of the quantum dots. On the other hand, we have studied the nature of capping and how the surface of the quantum dots core is terminated for the prepared samples. In addition, we have studied the acoustic and optical phonons of the quantum dots cores.

  11. Ab initio Calculation of The Magnetic Properties of Oxygen Impurity Complexes in CdSe

    NASA Astrophysics Data System (ADS)

    Cheng, W.; Liu, L.; Yu, P. Y.

    2017-06-01

    We have investigated the magnetic dipole moments of interstitial oxygen molecules (O2) and their interactions in CdSe by using spin-dependent first-principle calculations based on the local density functional (DFT) theory. We constructed supercells of Cd64Se64 by repeating the primitive cell Cd2Se2 4×4×2 times. Then an O2 molecule aligned along c-axis was added to the center of the CdSe cage. The charge densities of the complexes were then computed for both spin-up and spin-down electrons. Their difference indicates that O2 molecule in CdSe is paramagnetic, although its magnetic dipole moment is lower than that in free space. Two such O2 molecules were then placed either (a) parallel to each other in side-by-side supercells or (b) in neighboring supercells on top of each other. The computed energies of the resultant magnetic structures suggest that the two O2 magnetic moments interact anti-ferromagnetically in case (a) but do not interact in (b).

  12. Optical properties of P3HT:tributylphosphine oxide-capped CdSe nanocomposites

    NASA Astrophysics Data System (ADS)

    Benchaabane, A.; Ben Hamed, Z.; Lahmar, A.; Sanhoury, M. A.; Kouki, F.; Zellama, K.; Zeinert, A.; Bouchriha, H.

    2016-08-01

    The optical properties of nanocomposite layers prepared by incorporation of tributylphosphine oxide (TBPO)-capped CdSe nanocrystals (NCs) in a P3HT polymer matrix are studied using different nanocrystal concentrations. Reflection spectra analyzed through Kim oscillator model lead to the determination of optical constants such as refractive index n, extinction coefficient k, dielectric permittivity ɛ and absorption coefficient α.Using the common Cauchy, Drude-Lorentz, Tauc and single-effective-oscillator theoretical models, we have determined the values of static refractive index n s and permittivity ɛ s, plasma frequency ω_{{p}}, carrier density N, optical band gap E g and oscillator and dispersion energies E0 and E d, respectively. It is found that TBPO-capped CdSe NCs concentration affects the optoelectronic parameters of the nanocomposite thin films. Moreover, the disorder of this hybrid system is also studied by the determination of Urbach energy, which increases with TBPO-capped CdSe concentration.

  13. Electrochemiluminescent detection of Pb2+ by graphene/gold nanoparticles and CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Lu, Liping; Guo, Linqing; Li, Jiao; Kang, Tianfang; Cheng, Shuiyuan

    2016-12-01

    A highly sensitive electrochemiluminescent detection method for lead ions (Pb(II)) was fabricated based on the distance-dependent quenching of the electrochemiluminescence from CdSe quantum dots by nanocomposites of graphene and gold nanoparticles. Graphene/gold nanoparticles were electrochemically deposited onto a glassy carbon electrode through the constant potential method. Thiol-labeled DNA was then assembled on the surface of the electrode via gold-sulfur bonding, following which the amino-labeled terminal of the DNA was linked to carboxylated CdSe quantum dots by the formation of amide bonds. The 27-base aptamer was designed with two different domains: the immobilization and detection sequences. The immobilization sequence was paired with 12 complementary bases and immobilized on the gold electrode; the single-stranded detection sequence, rich in G bases, formed a G-quadruplex (G4) structure in the presence of Pb2+. The formation of G4 shortens the distance between the CdSe quantum dots and the Au electrode, which decreases the electrochemiluminescent intensity in a linear fashion, proportional to the concentration of Pb(II). The linear range of the sensor was 10-10 to 10-8 mol/L (R = 0.9819) with a detection limit of 10-10 mol/L. This sensor detected Pb(II) in real water samples with satisfactory results.

  14. Photoinduced Surface Oxidation and Its Effect on the Exciton Dynamics of CdSe Quantum Dots

    SciTech Connect

    Hines, Douglas A.; Becker, Matthew A.; Kamat, Prashant V.

    2012-11-14

    With increased interest in semiconductor nanoparticles for use in quantum dot solar cells there comes a need to understand the long-term photostability of such materials. Colloidal CdSe quantum dots (QDs) were suspended in toluene and stored in combinations of light/dark and N{sub 2}/O{sub 2} to simulate four possible benchtop storage environments. CdSe QDs stored in a dark, oxygen-free environment were observed to better retain their optical properties over the course of 90 days. The excited state lifetimes, determined through femtosecond transient absorption spectroscopy, of air-equilibrated samples exposed to light exhibit a decrease in average lifetime (0.81 ns) when compared to samples stored in a nitrogen/dark environment (8.3 ns). A photoetching technique commonly used for controlled reduction of QD size was found to induce energetic trap states to CdSe QDs and accelerate the rate of electron-hole recombination. X-ray absorption near edge structure (XANES) analysis confirms surface oxidation, the extent of which is shown to be dependent on the thickness of the ligand shell.

  15. Hybrid nanocomposites of CdSe nanocrystals distributed in complexing thiophene-based copolymers.

    PubMed

    Aldakov, Dmitry; Jiu, Tonggang; Zagorska, Malgorzata; de Bettignies, Rémi; Jouneau, Pierre-Henri; Pron, Adam; Chandezon, Frédéric

    2010-07-21

    Two types of conjugated polymers were prepared with the goal to blend them with rod-like CdSe nanocrystals. The polymers of the first type were synthesized through copolymerization of 3-octylthiophene and 3-methylene-ethylcarboxylate-thiophene to give polythiophene with solubilizing alkyl groups and methylene ester functional groups (PE series). Post-polymerization hydrolysis of the ester type polymers yielded acid-type ones (PA series). Photoluminescence (PL) quenching in these polymers induced by their titration with nanocrystals solution was chosen as a measure of the polymer-nanocrystal interactions. PL of polyacids turned out to be more efficiently quenched as compared to the case of polymers with ester groups which was interpreted as an indication of better electronic communication between the hybrid components. Infrared (IR) spectroscopy confirmed efficient coordination of the carboxylic groups to CdSe. Voltammetric studies combined with UV-vis spectroelectrochemistry enabled the determination of energy levels alignment of the molecular composite components which turned out to be of staggered type-appropriate for photovoltaic applications. The obtained blends of polyacids with CdSe nanocrystals, when studied by transmission electron microscopy (TEM), revealed the presence of an interpenetrating network in which nanorods were homogeneously distributed within the polymer matrix without any indication of agglomerates formation both on the film surface and in the cross-section. Blends with polymers containing ester groups were less homogeneous which could be explained by weaker polymer-nanocrystals interactions. Photovoltaic cells based on these hybrid materials are also discussed.

  16. 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.

  17. Interaction of the CdSe quantum dots with plant cell walls.

    PubMed

    Djikanović, Daniela; Kalauzi, Aleksandar; Jeremić, Milorad; Xu, Jianmin; Mićić, Miodrag; Whyte, Jeffrey D; Leblanc, Roger M; Radotić, Ksenija

    2012-03-01

    There is an increasing application of quantum dots (QDs) in plant science, as markers for the cells or their cell walls (CWs). In a plant cell the CW is a first target place for external agents. We studied interaction of CdSe QDs with CWs isolated from a conifer -Picea omorika (Panč) Purkynĕ branch. Binding of CdSe QDs was followed by using fluorescence microscopy, fluorescence and FT-IR spectroscopy. The aim of the study was to see whether the QDs induce structural changes in the CW, as well as to find out which kind of interactions between QDs and CWs occur and to which particular constituent polymers QDs preferably bind. The isolated CW is an appropriate object for study of the interactions with nanoparticles. The results show that in the CW, CdSe predominantly binds to cellulose, via OH groups and to lignin, via the conjugated CC/C-C chains. The differences in interaction of wet and dry CWs with QDs/chloroform were also studied. In the reaction of the dry CW sample with QDs/chloroform, hydrophobic interactions are dominant. When water was added after QDs/chloroform, hydrophilic interactions enable a partial reconstruction of the CC chains. The results have an implication on the use of the QDs in plant bio-imaging.

  18. Directed Two-Photon Absorption in CdSe Nanoplatelets Revealed by k-Space Spectroscopy.

    PubMed

    Heckmann, Jan; Scott, Riccardo; Prudnikau, Anatol V; Antanovich, Artsiom; Owschimikow, Nina; Artemyev, Mikhail; Climente, Juan I; Woggon, Ulrike; Grosse, Nicolai B; Achtstein, Alexander W

    2017-10-11

    We show that two-photon absorption (TPA) is highly anisotropic in CdSe nanoplatelets, thus promoting them as a new class of directional two-photon absorbers with large cross sections. Comparing two-dimensional k-space spectroscopic measurements of the one-photon and two-photon excitation of an oriented monolayer of platelets, it is revealed that TPA into the continuum is a directional phenomenon. This is in contrast to one-photon absorption. The observed directional TPA is shown to be related to fundamental band anisotropies of zincblende CdSe and the ultrastrong anisotropic confinement. We recover the internal transition dipole distribution and find that this directionality arises from the intrinsic directionality of the underlying Bloch and envelope functions of the states involved. We note that the photoemission from the CdSe platelets is highly anisotropic following either one- or two-photon excitation. Given the directionality and high TPA cross-section of these platelets, they may, for example, find employment as efficient logic AND elements in integrated photonic devices, or directional photon converters.

  19. 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.

  20. Large stokes shift of Ag doped CdSe quantum dots via aqueous route.

    PubMed

    Huang, Jian; Jiang, Yang; Duan, Hongyan; Liu, Chao; Mi, Longfei; Lan, Xinzheng; Zhou, Hongyang; Zhong, Honghai

    2013-10-01

    Monodispersed and luminescent Ag-doped CdSe semiconductor quantum dots (d-dots) were synthesized by an aqueous route assisted with electrochemical preparation of Se source with 3-mercaptopropionic acid as stabilizer. The silver dopants were incorporated into the host crystals via cation-exchange mechanism. X-ray diffraction patterns revealed that the as-synthesized CdSe:Ag d-dots were well retained in the zinc blende structure. The CdSe:Ag d-dots that exhibited uniform size distribution and good crystallnity could be observed by High-resolution transmission electron microscopy (HRTEM), with average diameter of 2.7 nm. Successful doping was confirmed by X-ray photoelectron spectroscopy survey spectra. The peculiar Ag-related photoluminescence showed strong intensity, and at the same time, intrinsic band-edge exciton emission of CdSe QDs was suppressed. The dopant emission exhibited larger Stockes shift of - 0.51 eV than that of the band-gap emission, and varied from 546 to 583 nm by changing electrolytic time. Possible radiative recombination mechanism of the aqueous Ag-doped CdSe d-dots was discussed. The results demonstrated that doping can be an effective way to manipulate the optical properties of semiconductor nanocrystals.

  1. 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.

  2. Synthesis and properties of CdSe Quantum Dot sensitized ZnO nanocomposites

    NASA Astrophysics Data System (ADS)

    Jain, Shefali; Sharma, Shailesh N.; Kumar, Mahesh

    2011-12-01

    In this work, zinc oxide nanocrystals with an average particle size of 13-22 nm are readily synthesized in aqueous medium by the wet synthesis method. Different sized nanocrystals obtained with change in calcination temperature are characterized by PL photoluminescence (PL) and UV-vis absorption spectroscopies, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The average crystal size of the as prepared ZnO nanopowder is determined by XRD and was found to be in good agreement with the UV-vis absorption analysis. The quality of different ZnO nanopowders is confirmed by XRD spectra. On the basis of different characterizations, ZnO calcined for 1 h (due to its large size and less agglomeration) is chosen for synthesis of ZnO-CdSe nanocomposites with variable sized CdSe QD's (Quantum Dots). Nano-composites are synthesized using bifunctional linker molecule Mercaptopropionic Acid (MPA), and by directly adsorbing CdSe QD's over the surface of ZnO nanocrystals. The difference in charge transfer mechanism in ZnO-CdSe nanocomposites due to different crystallite size of CdSe QD's is studied. Higher crystallinity of ZnO-CdSe nanocomposites can be determined from XRD characterization. Size and mode of attachment in various ZnO-CdSe nanocomposites are determined by SEM studies.

  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. Electrochemical synthesis of morphology-controlled segmented CdSe nanowires.

    PubMed

    Shpaisman, Nava; Givan, Uri; Patolsky, Fernando

    2010-04-27

    Morphology, that is, the study of form comprising shape, size, and structure, is important for materials research in general. For nanostructured materials, popularly known as nanomaterials, morphology has a special significance since form, in this case, dictates physical and chemical properties. Unlike bulk materials, properties of nanomaterials are strongly correlated to form. Here, we present a novel strategy for the synthesis of morphology-controlled segmented CdSe semiconductor nanowires based on a straightforward sweep voltammetry approach of preprogrammed characteristics. It was found here that, by simply and simultaneously modulating the basic parameters of each cyclic voltammetry cycle during the nanowire growth process, scan rate, and cycle potential range, we can achieve a precise control over the morphology of the semiconductor material segment, density, and dimensions, obtained after each voltammetric cycle. The morphology of CdSe segments was found to be controlled by the extent of co-deposition of metal cadmium together with the deposition of CdSe. Thus "dense" CdSe segments and "nondense" segments can be achieved in the absence and presence of cadmium metal co-deposition, respectively. Accompanied by the density modulation achieved by the potential range applied, it was also observed that a fine control over each segment's length, varying between few tenths to few hundred nanometers, can be achieved by simple altering the scan rate of each cycle along the wire. Also, we propose a simple mechanism that accounts for the formation of segments of controlled morphology. This is the first report on the synthesis of "segmented" CdSe nanowires of controlled morphology, density, and length of each segment, by simple single-step cycle voltammetry preprogrammed sequences from a single electrodeposition solution. In addition, this novel strategy may be applied for the synthesis of additional analogue semiconductor materials of importance (e.g., CdS, CdTe, etc

  5. Ability of the marine bacterium Pseudomonas fluorescens BA3SM1 to counteract the toxicity of CdSe nanoparticles.

    PubMed

    Poirier, Isabelle; Kuhn, Lauriane; Demortière, Arnaud; Mirvaux, Boris; Hammann, Philippe; Chicher, Johana; Caplat, Christelle; Pallud, Marie; Bertrand, Martine

    2016-10-04

    In the marine environment, bacteria from estuarine and coastal sediments are among the first targets of nanoparticle pollution; it is therefore relevant to improve the knowledge of interactions between bacteria and nanoparticles. In this work, the response of the marine bacterium Pseudomonas fluorescens BA3SM1 to CdSe nanocrystals (CdSe NPs) of 3nm (NP3) and 8nm (NP8) in diameter was evaluated through microscopic, physiological, biochemical and proteomic approaches. Transmission electron microscopy images showed that NP3 were able to penetrate the bacteria, while NP8 were highly concentrated around the cells, embedded in large exopolysaccharides. In our experimental conditions, both CdSe NP sizes induced a decrease in respiration during the stationary growth phase, while only NP8 caused growth retardation and a decrease in pyoverdine production. Proteomic analyses highlighted that the strain responded to CdSe NP toxicity by inducing various defence mechanisms such as cell aggregation, extracellular CdSe NP sequestration, effective protection against oxidative stress, modifications of envelope organization and properties, and cadmium export. In addition, BA3SM1 presented a biosorption capacity of 1.6×10(16)NP3/g dry weight and 1.7×10(15)NP8/g dry weight. This strain therefore appears as a promising agent for NP bioremediation processes. Proteomic data are available via ProteomeXchange with identifier PXD004012. To the best of our knowledge, this is the first report focussing on the effects of CdSe colloidal nanocrystals (CdSe NPs) on a marine strain of Pseudomonas fluorescens. CdSe NPs are extensively used in the industry of renewable energies and it is regrettably expected that these pollutants will sometime soon appear in the marine environment through surface runoff, urban effluents and rivers. Bacteria living in estuarine and coastal sediments will be among the first targets of these new pollutants. The pseudomonads are frequently found in these ecosystems

  6. The preparation of anisotropic hybrid nanostructures based on CdSe and CdS by the ligand combination method.

    PubMed

    Song, Xiaohui; Vladislav, Kamysbayev; Liu, Cuicui; Xu, Weichang

    2017-03-17

    CdSe and CdS nanoparticles (NPs) are type I II-VI semiconductor materials with excellent optical properties. Usually various shapes of these NPs show a strong emission only from a CdSe or CdS single domain, while the emission from a CdSe core combined with a CdS shell is effectively suppressed due to the ultrafast hole relaxation from the CdS shell into the CdSe core. Therefore, the design and synthesis of heteronanostructures based on CdSe or CdS is of paramount importance in designing the ways of integrating these useful semiconductor materials into complex hybrid structures. Here we demonstrate the ligand-combination inducing growth method to prepare anisotropic core-shell (semiconductor-semiconductor) heteronanostructures, as well as anisotropic Au-semiconductor heteronanostructures. The NPs' anisotropic shape was confirmed by tilting a grid in TEM and their elemental composition was ascertained using EDX mapping in STEM mode. Furthermore, the photoluminescence excitation spectra were studied showing potential applications based on their unique optical properties. We believe that the mechanism investigation, the synthetic control, the obtained novel hybrid nanostructures and their optical properties will open doors to future studies on heterostructures based on semiconductors.

  7. Effect of surface passivating ligand on structural and optoelectronic properties of polymer : CdSe quantum dot composites

    NASA Astrophysics Data System (ADS)

    Kumari, Kusum; Kumar, Umesh; Sharma, Shailesh N.; Chand, Suresh; Kakkar, Rita; Vankar, V. D.; Kumar, Vikram

    2008-12-01

    We demonstrate the effect of surface passivation of cadmium selenide quantum dots (CdSe QDs) (~5-7 nm) by tri-n-octylphosphene-oxide (TOPO) and oleic acid (OA) on the structural and optoelectronic properties of their respective polymer : CdSe composites by dispersing them in poly(2-methoxy-5(2-ethylhexyloxy)-1,4-phenylinevinylene) and poly(3-hexylthiophene) polymers. It has been found that OA passivated-QDs (~7 nm), as compared with TOPO passivated CdSe QDs (~5 nm), are of (i) high quality that provide better steric stability against coagulation, homogeneity and photostability to their respective polymer : CdSe composites, (ii) show low value of Stern-Volmer quenching constant (KSV) calculated from photoluminescence quenching measurements. These effects have been attributed to (i) CdSe(OA) (~7 nm) particles having relatively smaller surface energies compared with CdSe(TOPO) (~5 nm) particles thus showing lesser quenching capabilities (ii) dominance of respective processes of photoinduced Förster energy transfer between host polymer (donors) and guest CdSe nanocrystals (acceptors) in polymer : CdSe(OA) composites and charge transfer in polymer : CdSe(TOPO) composites.

  8. 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

  9. 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.

  10. 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.

  11. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

    PubMed

    Zhao, Tianshuo; Goodwin, Earl D; Guo, Jiacen; Wang, Han; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-09-22

    Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.

  12. A novel toxicity mechanism of CdSe nanoparticles to Saccharomyces cerevisiae: enhancement of vacuolar membrane permeabilization (VMP).

    PubMed

    Sun, Meiqing; Yu, Qilin; Liu, Ming; Chen, Xiaoyan; Liu, Zhe; Zhou, Hao; Yuan, Yingjin; Liu, Lu; Li, Mingchun; Zhang, Chengdong

    2014-09-05

    Cadmium selenide (CdSe) nanoparticles are implemented in a wide range of applications, but their potential risk to the ecosystem, especially to the organisms essential for the maintenance of ecosystem homeostasis, such as fungal populations, plants and bacteria, remains to be elucidated. In this study, we investigated their toxicity to one of the most important fungal model organisms, Saccharomyces cerevisiae. Growth inhibition assays revealed that the synthesized CdSe nanoparticles with the sizes of 20-30 nm had strong inhibitory effect on yeast growth (IC50=80 ppm). This toxicity was not attributed to mitochondrial dysfunction and autophagy, but was dependent on End3-mediated endocytosis, and was associated with reactive oxygen species (ROS) accumulation and an enhancement of vacuolar membrane permeabilization (VMP). These results reveal a key role of the vacuole during the interaction between CdSe nanoparticles and yeast cells.

  13. Diameter- and current-density-dependent growth orientation of hexagonal CdSe nanowire arrays via electrodeposition.

    PubMed

    Sun, Hongyu; Li, Xiaohong; Chen, Yan; Guo, Defeng; Xie, Yanwu; Li, Wei; Liu, Baoting; Zhang, Xiangyi

    2009-10-21

    Controlling the growth orientation of semiconductor nanowire arrays is of vital importance for their applications in the fields of nanodevices. In the present work, hexagonal CdSe nanowire arrays with various preferential growth orientations have been successfully yielded by employing the electrodeposition technique using porous alumina as templates (PATs). We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying either the nanopore diameter of the PATs or the deposited current density, which has significant effects on the optical properties of the CdSe nanowires. The present study provides an alternative approach to tuning the growth direction of electrodeposited nanowires and thus is of importance for the fabrication of nanodevices with controlled functional properties.

  14. Diameter- and current-density-dependent growth orientation of hexagonal CdSe nanowire arrays via electrodeposition

    NASA Astrophysics Data System (ADS)

    Sun, Hongyu; Li, Xiaohong; Chen, Yan; Guo, Defeng; Xie, Yanwu; Li, Wei; Liu, Baoting; Zhang, Xiangyi

    2009-10-01

    Controlling the growth orientation of semiconductor nanowire arrays is of vital importance for their applications in the fields of nanodevices. In the present work, hexagonal CdSe nanowire arrays with various preferential growth orientations have been successfully yielded by employing the electrodeposition technique using porous alumina as templates (PATs). We demonstrate by experimental and theoretical efforts that the growth orientation of the CdSe nanowires can be effectively manipulated by varying either the nanopore diameter of the PATs or the deposited current density, which has significant effects on the optical properties of the CdSe nanowires. The present study provides an alternative approach to tuning the growth direction of electrodeposited nanowires and thus is of importance for the fabrication of nanodevices with controlled functional properties.

  15. CdSe optical parametric oscillator operating at 12.07 μm with 170 mW output

    NASA Astrophysics Data System (ADS)

    Yuan, Jinhe; Chen, Yi; Duan, Xiaoming; Yao, Baoquan; Dai, Tongyu; Ju, Youlun

    2017-07-01

    A CdSe optical parametric oscillator (OPO) was demonstrated to operate at 12.07 μm with a maximum output power of 170 mW at a pulse repetition frequency of 1.2 kHz pumped at 2.09 μm with 14.64 W from an acousto-optic Q-switched Ho:YAG laser. To the best of our knowledge, 12.07 μm is the longest wavelength obtained with a 2-μm laser-pumped CdSe OPO. Besides, the angular tuning curve for type II CdSe was also investigated, and the idler wavelength from the OPO could be tuned from 10.24 to 12.07 μm.

  16. Electronic structure and optical absorption spectra of CdSe covered with ZnSe and ZnS epilayers

    NASA Astrophysics Data System (ADS)

    Yun, So Jeong; Lee, Geunsik; Kim, Jai Sam; Shin, Seung Koo; Yoon, Young-Gui

    2006-02-01

    Using the first-principles methods we compute the electronic structure and the absorption spectra for a wurtzite CdSe (0001) slab covered with zincblende ZnSe and ZnS epilayers. For each structure we compute the DOS and the imaginary part of the dielectric function. We find that the semiconductor passivation shifts the 'near Fermi-level' states of the bare CdSe slab down to lower energy levels. The migration suggests the decrease of surface effects and energy loss. We observe the substantial reduction of the abnormal peaks in the absorption spectra of the bare CdSe slab, which seems to be a consequence of the DOS migration. This is consistent with the experimental results that a proper passivation enhance the luminescence efficiency. We also study the case that the epilayer surface is terminated with PH 3 and find the PH 3 passivation also reduces the surface state to some extent.

  17. 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.

  18. Controlling the cytotoxicity of CdSe magic-sized quantum dots as a function of surface defect density.

    PubMed

    Silva, Anielle Christine Almeida; Silva, Marcelo José Barbosa; da Luz, Felipe Andrés Cordero; Silva, Danielle Pereira; de Deus, Samantha Luara Vieira; Dantas, Noelio Oliveira

    2014-09-10

    Quantum dots are potentially very useful as fluorescent probes in biological systems. However, they are inherently cytotoxic because of their constituents. We controlled the cytotoxicity of CdSe magic-sized quantum dots (MSQDs) as a function of surface defect density by altering selenium (Se) concentration during synthesis. Higher Se concentrations reduced the cytotoxicity of the CdSe MSQDs and diminished mRNA expression of methallothionein because of the low cadmium ions (Cd(2+)) concentration adsorbed on the surface of the MSQDs. These results agree with luminescence spectra, which show that higher Se concentrations decrease the density of surface defects. Therefore, our results describe for the first time a simple way of controlling the cytotoxicity of CdSe MSQDs and making them safer to use as fluorescence probes in biological systems.

  19. CdSe white quantum dots-based white light-emitting diodes with high color rendering index

    NASA Astrophysics Data System (ADS)

    Su, Yu-Sheng; Hsiao, Chih-Chun; Chung, Shu-Ru

    2016-09-01

    A white light emission CdSe quantum dots (QDs) can be prepared by chemical route under 180°C. An organic oleic acid (OA) is used to react with CdO to form Cd-OA complex. Hexadecylamine (HDA) and 1-Octadecene (ODE) were used as co-surfactants. By controlling the reaction time, a white light emission CdSe QDs can be obtained after reacts for 3 to 10 min. The luminescence spectra compose two obvious emission peaks and entire visible light ranges from 400 to 650 nm. Based on TEM measurement result, spherical morphologies with particle size 2.39+/-0.27 nm can be obtained. The quantum yields (QYs) of white CdSe QD are between 20 and 60 %, which depends on reaction time. A white CdSe QDs were mixed with UV cured gel (OPAS-226) with weight ratios 50.0 wt. %, and putted the mixture into reflective cup (3020, 13 mil) as convert type. The white LEDs have controllable CIE coordinates and correlated color temperature (CCT). The luminous efficacy of the device is less than 3 lm/W, but the color rendering index (CRI) for all devices are higher than 80. Since the luminous efficacy of hybrid devices has a direct dependence on the external QY of the UV-LED as well, the luminous efficacy can be improved by well dispersion of CdSe QDs in UV gel matrix and using optimized LED chips. Therefore, in this study, we provide a new and simple method to prepare high QY of white CdSe QDs and its have a potential to applicate in solid-state lighting.

  20. 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

  1. Dislocation-driven growth of porous CdSe nanorods from CdSe.(ethylenediamine)0.5 nanorods

    NASA Astrophysics Data System (ADS)

    Kim, Hyung-Bae; Jang, Du-Jeon

    2015-12-01

    Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe.(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe.(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal-treatment time as the fractional amplitude of the surface-state-related component increases.Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe.(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe.(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal

  2. Theoretical calculations of structural, electronic, and elastic properties of CdSe1-x Te x : A first principles study

    NASA Astrophysics Data System (ADS)

    M, Shakil; Muhammad, Zafar; Shabbir, Ahmed; Muhammad Raza-ur-rehman, Hashmi; M, A. Choudhary; T, Iqbal

    2016-07-01

    The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of CdSe1-x Te x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA+U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure CdSe and CdTe binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.

  3. Synthesis and optical characterisation of triphenylamine-based hole extractor materials for CdSe quantum dots.

    PubMed

    Planells, Miquel; Reynolds, Luke X; Bansode, Umesh; Chhatre, Shraddha; Ogale, Satishchandra; Robertson, Neil; Haque, Saif A

    2013-05-28

    We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most easily oxidised triphenylamine display efficient hole-extraction and long-lived charge separation. The present findings should help identify new strategies to control charge transfer QD-based optoelectronic devices.

  4. 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

  5. Anisotropy of optical transitions in ordered ensemble of CdSe quantum rods.

    PubMed

    Mukhina, Maria V; Maslov, Vladimir G; Baranov, Alexander V; Artemyev, Mikhail V; Orlova, Anna O; Fedorov, Anatoly V

    2013-09-01

    We report on the observation of spectral dependence of absorption anisotropy in a CdSe quantum rod (QR) ensemble, which is aligned in a polymer film with a nanocrystal concentration of 2×10(-5) M. The experimental data on the polarization direction and anisotropy factor were obtained for the lowest excitonic transition and the second group of transitions in the QR. The nonzero constant value of anisotropy was investigated for the high-energy transitions, and is evidence of the one-dimensional confinement in the QR.

  6. Electrical conduction mechanism in annealed and light soaked silver doped CdSe thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Jagdish; Tripathi, S. K.

    2015-08-01

    Thin films of silver (Ag) doped CdSe are prepared on glass substrates by thermal evaporation technique in inert gas atmosphere. SEM micrograph reveals uniform and homogenous distribution of nanoparticles on the glass substrates. The composition of the film is investigated by EDX analysis. Thin films are thermally annealed and light soaked to study the thermally and optically induced effect. Electrical conduction in annealed thin films exhibits different conduction mechanisms in low and high temperature region while conduction in light soaked thin films is single thermally activated process. The activation energies for dark and photoconductivities are also investigated.

  7. (Time-resolved fluorescence studies of surface recombination in CdSe electrodes)

    SciTech Connect

    Not Available

    1991-01-01

    The long range goal of our investigations is to understand the dynamics of heterogeneous electron transfer reactions. The primary method we use to monitor the carrier dynamics is the fluorescence of the bandgap emission. This all optical approach circumvents the limitations of photopotential and photocurrent methods. Before such studies on a reactive system can be informative, it is necessary to understand the dynamics of the photogenerated carriers under nonreactive conditions. Presently we are concentrating on carrier dynamics in the materials, cadmium selenide (CdSe) and cadmium sulfide (CdS). Under these conditions the carriers recombine either directly or through intragap electronic states. 2 refs., 1 fig.

  8. Diameter scaling of the optical band gap in individual CdSe nanowires.

    PubMed

    Myalitsin, Anton; Strelow, Christian; Wang, Zhe; Li, Zhen; Kipp, Tobias; Mews, Alf

    2011-10-25

    The diameter dependence of the optical band gap of single CdSe nanowires (NWs) is investigated by a combination of atomic force microscopy, scanning fluorescence microscopy, and transmission electron microscopy. We find a good congruence of the experimental data to calculations within the effective mass approximation taking into account quantization, exciton Coulomb interaction, and dielectric mismatch. The experimental data are furthermore compared to different theoretical approaches. We discuss the influence of alternating wurtzite and zinc blende segments along the NWs on their optical properties.

  9. 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.

  10. 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.

  11. 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.

  12. Size effects and breakdown of the power-law blinking statistics of CdSe nanorods.

    PubMed

    Tang, Jau

    2007-09-27

    In this study, the dependence of sample size and light intensity on the fluorescence intermittency of semiconductor nanorods is investigated. We present a model with diffusion-controlled electron-transfer reactions involving anomalous diffusion in energy configuration space. This model leads to a general formula t(-m) exp[-(Gammat)n] for the temporal behavior of blinking statistics, where m and n are related to the time dependence of the spectral diffusion. We reanalyze the experimental data of the long-time bending tail of CdSe nanorods and elucidate the size effects of the bending rates and activation energy.

  13. Optimal packing size of non-ligated CdSe nanoclusters for microstructure synthesis

    SciTech Connect

    Tefera, Anteneh G.; Mochena, Mogus D.; Johnson, Elijah; Dickerson, James

    2014-09-14

    Structural and electrostatic properties of nanoclusters of CdSe of diameter 1–2 nm are studied with first principle calculations to determine the optimal size for synthesizing microstructures. Based on robustness of the core structure, i.e., the retention of tetrahedral geometry, hexagonal ring structure, and overall wu{sup ¨}rtzite structure to surface relaxations, we conclude that nanoclusters of ~2 nm diameter are the best candidates to form a dense microstructure with minimal interstitial space. Se-terminated surfaces retain a zigzag structure as Se atoms are pulled out and Cd atoms are pulled in due to relaxation, therefore, are best suited for inter-nanocluster formations.

  14. Anisotropy of electron-phonon interaction in nanoscale CdSe platelets as seen via off-resonant and resonant Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Cherevkov, S. A.; Fedorov, A. V.; Artemyev, M. V.; Prudnikau, A. V.; Baranov, A. V.

    2013-07-01

    The off-resonant and resonant Raman spectra of optical phonons in colloidal CdSe nanoplatelets (NPLs) with the thickness of 4, 5, and 6 CdSe monolayers are analyzed. These spectra are dominated by SO and LO phonon bands of CdSe whose frequencies are thickness independent in the off-resonant Raman but demonstrate evident thickness dependence similar to that observed for confined optical phonons in CdSe quantum dots in the resonant Raman. The results show that conventional optical phonons propagating along the NPL lateral planes contribute mainly to the off-resonant Raman while confined optical phonons propagating in the perpendicular direction dominate the Raman spectra excited in the resonance with confined exciton transitions of CdSe NPLs. An anisotropic electron-phonon interaction is proposed to be responsible for this effect in the CdSe NPLs. A formation of Cd-S monolayer on the surface of CdSe NPLs treated by thiol-containing ligands is also detected in Raman spectra.

  15. Magneto-optical spectrum and the effective excitonic Zeeman splitting energies of Mn and Co-doped CdSe nanowires

    SciTech Connect

    Xiong, Wen; Chen, Wensuo

    2013-12-21

    The electronic structure of Mn and Co-doped CdSe nanowires are calculated based on the six-band k·p effective-mass theory. Through the calculation, it is found that the splitting energies of the degenerate hole states in Mn-doped CdSe nanowires are larger than that in Co-doped CdSe nanowires when the concentration of these two kinds of magnetic ions is the same. In order to analysis the magneto-optical spectrum of Mn and Co-doped CdSe nanowires, the four lowest electron states and the four highest hole states are sorted when the magnetic field is applied, and the 10 lowest optical transitions between the conduction subbands and the valence subbands at the Γ point in Mn and Co-doped CdSe nanowires are shown in the paper, it is found that the order of the optical transitions at the Γ point almost do not change although two different kinds of magnetic ions are doped in CdSe nanowires. Finally, the effective excitonic Zeeman splitting energies at the Γ point are found to increase almost linearly with the increase of the concentration of the magnetic ions and the magnetic field; meanwhile, the giant positive effective excitonic g factors in Mn and Co-doped CdSe nanowires are predicted based on our theoretical calculation.

  16. Surface control of CdSe nanocrystals by UV-exposure in air and successive thermal treatment under ultra high vacuum

    NASA Astrophysics Data System (ADS)

    Choi, Hyun-Ju; Wang, Seok-Joo; Kim, Hyuncheol; Park, Hyung-Ho; Chang, Ho Jung; Jeon, Hyeongtag

    2008-08-01

    Colloidal CdSe nanocrystals were synthesized through a solution process. The CdSe nanocrystals coated on Si(1 0 0) wafers were UV-exposed in either an air or argon atmosphere to distinguish the effect of generated ozone from UV-radiation at 365 nm on the removal of surface capping pyridine molecules. The pyridine on the CdSe nanocrystal's surface could be effectively removed by the ozone generated during UV-exposure with an accompanying highly oxidized surface state of the CdSe nanocrystals. For the removal of surface oxides of CdSe nanocrystals, a successive thermal treatment under ultra high vacuum (UHV) was adopted. The optical energy bandgap measured by using UV-vis absorption spectroscopy showed a red shift with treatment with an increase of annealing temperature. The electronic energy structure of UHV-annealed CdSe nanocrystals film was analyzed in situ using X-ray absorption and photoelectron spectroscopy. A great resemblance was found between the values of the optical and electron energy bandgaps of effectively surface-treated CdSe nanocrystals film after UHV-annealing at 400 °C.

  17. Effect of deposition temperature on the structural and optical properties of CdSe QDs thin films deposited by CBD method

    SciTech Connect

    Laatar, F.; Harizi, A.; Smida, A.; Hassen, M.; Ezzaouia, H.

    2016-06-15

    Highlights: • Synthesis of CdSe QDs with L-Cysteine capping agent for applications in nanodevices. • The films of CdSe QDs present uniform and good dispersive particles at the surface. • Effect of bath temperature on the structural and optical properties of CdSe QDs thin films. • Investigation of the optical constants and dispersion parameters of CdSe QDs thin films. - Abstract: Cadmium selenide quantum dots (CdSe QDs) thin films were deposited onto glass substrates by a chemical bath deposition (CBD) method at different temperatures from an aqueous solution containing L-Cysteine (L-Cys) as capping agent. The evolution of the surface morphology and elemental composition of the CdSe films were studied by AFM, SEM, and EDX analyses. Structural and optical properties of CdSe thin films were investigated by XRD, UV–vis and PL spectroscopy. The dispersion behavior of the refractive index is described using the single oscillator Wemple-DiDomenico (W-D) model, and the physical dispersion parameters are calculated as a function of deposition temperature. The dispersive optical parameters such as average oscillator energy (E{sub o}), dispersion energy (E{sub d}), and static refractive index (n{sub o}) were found to vary with the deposition temperature. Besides, the electrical free carrier susceptibility (χ{sub e}) and the carrier concentration of the effective mass ratio (N/m*) were evaluated according to the Spitzer-Fan model.

  18. Effect of air-annealing on the morphological, microstructural and optical properties of CdSe NCs grown into porous anodic alumina template

    NASA Astrophysics Data System (ADS)

    Laatar, F.; Hassen, M.; Smida, A.; Riahi, R.; Bel Haj Mohamed, N.; Ezzaouia, H.

    2015-07-01

    In this work, cadmium selenide nanocrystals (CdSe NCs) were embedded into porous anodic alumina (PAA) template by simple immersion in aqueous solution containing L-cysteine (Cys) functionalized CdSe NCs and water. The prepared samples were heat treated at different temperatures between 150 and 300 °C during 30 min under air. The effect of thermal treatment under air on the CdSe NCs/PAA has been shown from morphological, microstructural and optical studies. Several characterization techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) spectroscopy were used to investigate the surface morphology and microstructural properties of CdSe nanoparticles on the PAA template as function of air-annealing temperature. XRD study shows the transformation phase of deposited CdSe nanoparticles on the PAA template from cubic structure to hexagonal structure at 300 °C. The morphology of CdSe nanorods array which are into the PAA surface were exhibited by AFM scan. Optical properties of CdSe NCs into PAA have been studied at different air-annealing temperatures using optical absorption and photoluminescence (PL) spectroscopy. The results showed that the crystal quality was significantly improved with the annealing temperature increase, bringing about an enhancement in PL and a decrease in optical band gap from 2.44 to 2.2 eV exhibiting a red shift.

  19. The Magic-Size Nanocluster (CdSe)34 as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets.

    PubMed

    Wang, Yuanyuan; Zhang, Ying; Wang, Fudong; Giblin, Daryl E; Hoy, Jessica; Rohrs, Henry W; Loomis, Richard A; Buhro, William E

    2014-04-08

    Reaction of Cd(OAc)2·2H2O and selenourea in primary-amine/secondary-amine cosolvent mixtures affords crystalline CdSe quantum platelets at room temperature. Their crystallinity is established by X-ray diffraction analysis (XRD), high-resolution transmission electron microscopy (TEM), and their sharp extinction and photoluminescence spectra. Reaction monitoring establishes the magic-size nanocluster (CdSe)34 to be a key intermediate in the growth process, which converts to CdSe quantum platelets by first-order kinetics with no induction period. The results are interpreted to indicate that the critical crystal-nucleus size for CdSe under these conditions is in the range of (CdSe)34 to (CdSe)68. The nanocluster is obtained in isolated form as [(CdSe)34(n-octylamine)16(di-n-pentylamine)2], which is proposed to function as crystal nuclei that may be stored in a bottle.

  20. 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.

  1. 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.

  2. Improved performance of colloidal CdSe quantum dot-sensitized solar cells by hybrid passivation.

    PubMed

    Huang, Jing; Xu, Bo; Yuan, Chunze; Chen, Hong; Sun, Junliang; Sun, Licheng; Agren, Hans

    2014-11-12

    A hybrid passivation strategy is employed to modify the surface of colloidal CdSe quantum dots (QDs) for quantum dot-sensitized solar cells (QDSCs), by using mercaptopropionic acid (MPA) and iodide anions through a ligand exchange reaction in solution. This is found to be an effective way to improve the performance of QDSCs based on colloidal QDs. The results show that MPA can increase the coverage of the QDs on TiO2 electrodes and facilitate the hole extraction from the photoxidized QDs, and simultaneously, that the iodide anions can remedy the surface defects of the CdSe QDs and thus reduce the recombination loss in the device. This hybrid passivation treatment leads to a significant enhancement of the power conversion efficiency of the QDSCs by 41%. Furthermore, an optimal ratio of iodide ions to MPA was determined for favorable hybrid passivation; results show that excessive iodine anions are detrimental to the loading of the QDs. This study demonstrates that the improvement in QDSC performance can be realized by using a combination of different functional ligands to passivate the QDs, and that ligand exchange in solution can be an effective approach to introduce different ligands.

  3. Fingerprint detection and using intercalated CdSe nanoparticles on non-porous surfaces.

    PubMed

    Algarra, Manuel; Radotić, Ksenija; Kalauzi, Aleksandar; Mutavdžić, Dragosav; Savić, Aleksandar; Jiménez-Jiménez, José; Rodríguez-Castellón, Enrique; da Silva, Joaquim C G Esteves; Guerrero-González, Juan José

    2014-02-17

    A fluorescent nanocomposite based on the inclusion of CdSe quantum dots in porous phosphate heterostructures, functionalized with amino groups (PPH-NH2@CdSe), was synthesized, characterized and used for fingerprint detection. The main scopes of this work were first to develop a friendly chemical powder for detecting latent fingerprints, especially in non-porous surfaces; their further intercalation in PPH structure enables not to spread the fluorescent nanoparticles, for that reason very good fluorescent images can be obtained. The fingerprints, obtained on different non-porous surfaces such as iron tweezers, mobile telephone screen and magnetic band of a credit card, treated with this powder emit a pale orange luminescence under ultraviolet excitation. A further image processing consists of contrast enhancement that allows obtaining positive matches according to the information supplied from a police database, and showed to be more effective than that obtained with the non-processed images. Experimental results illustrate the effectiveness of proposed methods. Copyright © 2014 Elsevier B.V. All rights reserved.

  4. 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.

  5. 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.

  6. 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

    2015-06-07

    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.

  7. Shape dependence of band-edge exciton fine structure in CdSe nanocrystals.

    PubMed

    Zhao, Qingzhong; Graf, Peter A; Jones, Wesley B; Franceschetti, Alberto; Li, Jingbo; Wang, Lin-Wang; Kim, Kwiseon

    2007-11-01

    The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a "dark" ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a "quasi-bright" ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length.

  8. Directed emission of CdSe nanoplatelets originating from strongly anisotropic 2D electronic structure.

    PubMed

    Scott, Riccardo; Heckmann, Jan; Prudnikau, Anatol V; Antanovich, Artsiom; Mikhailov, Aleksandr; Owschimikow, Nina; Artemyev, Mikhail; Climente, Juan I; Woggon, Ulrike; Grosse, Nicolai B; Achtstein, Alexander W

    2017-09-18

    Intrinsically directional light emitters are potentially important for applications in photonics including lasing and energy-efficient display technology. Here, we propose a new route to overcome intrinsic efficiency limitations in light-emitting devices by studying a CdSe nanoplatelets monolayer that exhibits strongly anisotropic, directed photoluminescence. Analysis of the two-dimensional k-space distribution reveals the underlying internal transition dipole distribution. The observed directed emission is related to the anisotropy of the electronic Bloch states governing the exciton transition dipole moment and forming a bright plane. The strongly directed emission perpendicular to the platelet is further enhanced by the optical local density of states and local fields. In contrast to the emission directionality, the off-resonant absorption into the energetically higher 2D-continuum of states is isotropic. These contrasting optical properties make the oriented CdSe nanoplatelets, or superstructures of parallel-oriented platelets, an interesting and potentially useful class of semiconductor-based emitters.

  9. Magnetic and dielectric study of Fe-doped CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Banerjee, Sourish; Bandyopadhyay, Sudipta; Sinha, Tripurari Prasad

    2017-08-01

    Nanoparticles of cadmium selenide (CdSe) and Fe (5% and 10%) doped CdSe have been synthesized by soft chemical route and found to have cubic structure. The magnetic field dependent magnetization measurement of the doped samples indicates the presence of anti-ferromagnetic order. The temperature dependent magnetization (M-T) measurement under zero field cooled and field cooled conditions has also ruled out the presence of ferromagnetic component in the samples at room temperature as well as low temperature. In order to estimate the anti-ferromagnetic coupling among the doped Fe atoms, an M-T measurement at 500 Oe has been carried out, and the Curie-Weiss temperature θ of the samples has been estimated from the inverse of susceptibility versus temperature plots. The dielectric relaxation peaks are observed in the spectra of imaginary part of dielectric constant. The temperature dependent relaxation time is found to obey the Arrhenius law having activation energy 0.4 eV for Fe doped samples. The frequency dependent conductivity spectra are found to obey the power law. [Figure not available: see fulltext.

  10. Tuning luminescent properties of CdSe nanoclusters by phosphine surface passivation

    NASA Astrophysics Data System (ADS)

    Lysova, Iryna; Anton, Halina; Dmitruk, Igor; Mely, Yves

    2016-12-01

    Appropriate surface ligands are required for tuning the physicochemical and photophysical properties of nanoclusters (NCs). These surface ligands are especially critical for passivating the small (CdSe)33,34 NCs where the majority of atoms are at the NC surface. In this study, triphenylphosphine (TPP), trioctylphosphine (TOP) and tris(pentafluorophenyl)phosphine (TPFP) have been tested as capping agents for alkylamine-coated CdSe NCs. TPP and TOP compounds are found to increase the quantum yield of photoluminescence (PL) from 0.15% to 0.6% and 0.53%, respectively, and to preserve this increased PL with time, probably by preventing charge leakage as a result of their binding to Se atoms. Since no dramatic change in the shape of NCs’ PL spectrum occurs after surface treatment, both the exciton band and the low-energy broad band in magic NCs are thought to describe the intrinsic luminescence properties of the NCs. As a result, the PL increase due to Se passivation is thought to be mainly caused by a decrease in the efficiency of the NC nonradiative pathways.

  11. Hydrophilic CdSe thin films by low cost spray pyrolysis technique and annealing effects

    NASA Astrophysics Data System (ADS)

    Logu, T.; Sankarasubramanian, K.; Soundarrajan, P.; Sethuraman, K.

    2015-03-01

    Cadmium selenide (CdSe) thin films were deposited on glass substrates at 200°C by homemade chemical spray pyrolysis technique. The as-deposited films were annealed in air atmosphere for 3 hrs, at two different temperatures (350 and 450°C). The as-deposited film has been observed to possess uniform surface with crystalline sphalerite cubic structure and optical band gap of E g = 2.4 eV. It is worth noting that after annealing, metastable cubic sphalerite phase transforms into stable well crystalline hexagonal wurtzite phase. The optical band gap was found to decrease from 2.4 eV to 1.75 eV. The average surface roughness is 1.5 nm for the as-deposited film which rises to 4.2 nm after annealing the film in air atmosphere. The contact angle was found to vary from 94° ± 1° to 81° ± 1° with annealing temperature. In addition, from Wenzel's relation it is concluded that CdSe thin film is hydrophilic in nature. [Figure not available: see fulltext.

  12. Effect of Ligands on Characteristics of (CdSe)13 Quantum Dot

    SciTech Connect

    Gao, Yang; Zhou, Bo; Kang, Seung-gu; Xin, Minsi; Yang, Ping; Dai, Xing; Wang, Zhigang; Zhou, Ruhong

    2014-01-01

    The widespread applications of quantum dots (QDs) have spurred an increasing interest in the study of their coating ligands, which can not only protect the electronic structures of the central QDs, but also control their permeability through biological membranes with both size and shape. In this work, we have used density functional theory (DFT) to investigate the electronic structures of (CdSe)13 passivated by OPMe2(CH2)nMe ligands with different lengths and various numbers of branches (Me=methyl group, n = 0, 1-3). Our results show that the absorption peak in the ultraviolet-visible (UV-vis) spectra displays a clear blue-shift, on the scale of ~100 nm, upon the binding of ligands. Once the total number of ligands bound with (CdSe)13 reached a saturated number (9 or 10), no more blue-shift occurred in the absorption peak in the UV-vis spectra. On the other hand, the aliphatic chain length of ligands has a negligible effect on the optical properties of the QD core. Analyses of the bonding characteristics confirm that optical transitions are dominantly governed by the central QD core rather than the organic passivation. Interestingly, the density of states (DOS) share similar characteristics as vibrational spectra, even though there is no coordination vibration mode between the ligands and the central QD. These findings might provide insights on the material design for the passivation of quantum dots for biomedical applications.

  13. Role of the polymer matrix on the photoluminescence of embedded CdSe quantum dots.

    PubMed

    Tselikov, Gleb I; Timoshenko, Victor Yu; Golovan, Leonid A; Plenge, Jürgen; Shatalova, Alina M; Shandryuk, Georgiy A; Kutergina, Irina Yu; Merekalov, Alexey S; Rühl, Eckart; Talroze, Raisa V

    2015-04-07

    The photoluminescence (PL) of CdSe quantum dots (QDs) that form stable nanocomposites with polymer liquid crystals (LCs) as smectic C hydrogen-bonded homopolymers from a family of poly[4-(n-acryloyloxyalkyloxy)benzoic acids] is reported. The matrix that results from the combination of these units with methoxyphenyl benzoate and cholesterol-containing units has a cholesteric structure. The exciton PL band of QDs in the smectic matrix is redshifted with respect to QDs in solution, whereas a blueshift is observed with the cholesteric matrix. The PL lifetimes and quantum yield in cholesteric nanocomposites are higher than those in smectic ones. This is interpreted in terms of a higher order of the smectic matrix in comparison to the cholesteric one. CdSe QDs in the ordered smectic matrix demonstrate a splitting of the exciton PL band and an enhancement of the photoinduced differential transmission. These results reveal the effects of the structure of polymer LC matrices on the optical properties of embedded QDs, which offer new possibilities for photonic applications of QD-LC polymer nanocomposites. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Photoluminescence enhancement of CdSe quantum dots: a case of organogel-nanoparticle symbiosis.

    PubMed

    Wadhavane, Prashant D; Galian, Raquel E; Izquierdo, M Angeles; Aguilera-Sigalat, Jordi; Galindo, Francisco; Schmidt, Luciana; Burguete, M Isabel; Pérez-Prieto, Julia; Luis, Santiago V

    2012-12-19

    Highly fluorescent organogels (QD-organogel), prepared by combining a pseudopeptidic macrocycle and different types of CdSe quantum dots (QDs), have been characterized using a battery of optical and microscopic techniques. The results indicate that the presence of the QDs not only does not disrupt the supramolecular organization of the internal fibrillar network of the organogel to a significant extent, but it also decreases the critical concentration of gelator needed to form stable and thermoreversible organogels. Regarding the photophysical properties of the QDs, different trends were observed depending on the presence of a ZnS inorganic shell around the CdSe core. Thus, while the core-shell QDs preserve their photophysical properties in the organogel medium, a high to moderate increase of the fluorescence intensity (up to 528%) and the average lifetime (up to 1.7), respectively, was observed for the core QDs embedded in the organogel. The results are relevant for the development of luminescent organogels based on quantum dots, which have potential applications as advanced hybrid materials in different fields.

  15. Dislocation-driven CdS and CdSe nanowire growth.

    PubMed

    Wu, Haoyu; Meng, Fei; Li, Linsen; Jin, Song; Zheng, Gengfeng

    2012-05-22

    We report the synthesis of CdS and CdSe nanowires (NWs) and nanoribbons (NRs) with gold catalysts by H(2)-assisted chemical vapor deposition. Nanopods and nanocones were obtained without catalysts at higher system pressure. Transmission electron microscopy (TEM) studies, including two-beam TEM and displaced-aperture dark-field TEM characterization, were used to investigate the NW growth mechanism. Dislocation contrast and twist contours have been routinely observed within the synthesized one-dimensional (1D) CdS and CdSe NWs, suggesting the operation of the dislocation-driven NW growth mechanism under our experimental conditions. The Burgers vectors of dislocations and the associated Eshelby twists were measured and quantified. We hypothesize that gold nanoparticles provide nucleation sites to initiate the growth of CdS/CdSe NWs and lead to the formation of dislocations that continue to drive and sustain 1D growth at a low supersaturation level. Our study suggests that the dislocation-driven mechanism may also contribute to the growth of other 1D nanomaterials that are commonly considered to grow via the vapor-liquid-solid mechanism.

  16. Direct Measurement of Single CdSe Nanowire Extinction Polarization Anisotropies.

    PubMed

    McDonald, Matthew P; Vietmeyer, Felix; Kuno, Masaru

    2012-08-16

    The origin of sizable absorption polarization anisotropies (ρabs) in one-dimensional (1D) semiconductor nanowires (NWs) has been debated. Invoked explanations employ either classical or quantum mechanical origins, where the classical approach suggests dielectric constant mismatches between the NW and its surrounding environment as the predominant source of observed polarization sensitivities. At the same time, the confinement-influenced mixing of states suggests a sizable contribution from polarization-sensitive transition selection rules. Sufficient evidence exists in the literature to support either claim. However, in all cases, these observations stem from excitation polarization anisotropy (ρexc) studies, which only indirectly measure ρabs. In this manuscript, we directly measure the band edge extinction polarization anisotropies (ρext) of individual CdSe NWs using single NW extinction spectroscopy. Observed polarization anisotropies possess distinct spectral features and wavelength dependencies that correlate well with theoretical transition selection rules derived from a six-band k·p theory used to model the electronic structure of CdSe NWs.

  17. Experimental determination of single CdSe nanowire absorption cross sections through photothermal imaging.

    PubMed

    Giblin, Jay; Syed, Muhammad; Banning, Michael T; Kuno, Masaru; Hartland, Greg

    2010-01-26

    Absorption cross sections ((sigma)abs) of single branched CdSe nanowires (NWs) have been measured by photothermal heterodyne imaging (PHI). Specifically, PHI signals from isolated gold nanoparticles (NPs) with known cross sections were compared to those of individual CdSe NWs excited at 532 nm. This allowed us to determine average NW absorption cross sections at 532 nm of (sigma)abs = (3.17 +/- 0.44) x 10(-11) cm2/microm (standard error reported). This agrees well with a theoretical value obtained using a classical electromagnetic analysis ((sigma)abs = 5.00 x 10(-11) cm2/microm) and also with prior ensemble estimates. Furthermore, NWs exhibit significant absorption polarization sensitivities consistent with prior NW excitation polarization anisotropy measurements. This has enabled additional estimates of the absorption cross section parallel ((sigma)abs) and perpendicular ((sigma)abs(perpendicular) to the NW growth axis, as well as the corresponding NW absorption anisotropy ((rho)abs). Resulting values of (sigma)abs = (5.6 +/- 1.1) x 10(-11) cm2/microm, (sigma)abs(perpendicular) = (1.26 +/- 0.21) x 10(-11) cm2/microm, and (rho)abs = 0.63+/- 0.04 (standard errors reported) are again in good agreement with theoretical predictions. These measurements all indicate sizable NW absorption cross sections and ultimately suggest the possibility of future direct single NW absorption studies.

  18. Cellular uptake induced biotoxicity of surface-modified CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Sanwlani, Shilpa; Rawat, Kamla; Pal, Meena; Bohidar, Himadri B.; Verma, Anita Kamra

    2014-05-01

    Cellular uptake of quantum dots (QDs) by cells is of utmost importance for establishing QDs as biostable fluorescent markers that facilitate early diagnosis and detection of cancer. The surface states of QDs are critical to enhance the cellular uptake. Biocompatible CDSe QDs were synthesized using mercaptopropionic acid, amino-ethanethiol HCl, cyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetrabutylammonium iodide (TBAI), and sodium dodecyl sulfate were functionalized using ligand-exchange method. Cytocompatibility and cellular uptake of QDs were evaluated in human embryonic kidney cells (HEK-29), and breast cancer cells (MCF-7) as reduced cytotoxicity is desirable for biological applications. Approximately, 60 % cytotoxicity was observed in all surface-coated QDs and QD100 in 72 h in both the cell lines, except TBAI that indicated 30 % cytotoxicity in 72 h, and only 10 % in 24 h. Glutathione, the detoxifying molecule, is detrimental for understanding the oxidative stress of the cell. The QDs showed enhanced Glutathione- S-transferase (GST) activity in the MCF-7 cell line. In HEK, CdSe per se was also able to induce a high level of GST. QDs toxicity may either be related to the induction of reactive oxygen species or the direct release of metal ions. Optimization of QDs in terms of quantification and DNA damage is imperative for realistic biological applications.

  19. Yeast Populations Evolve to Resist CdSe Quantum Dot Toxicity.

    PubMed

    Strtak, Alexandra; Sathiamoorthy, Sarmitha; Tang, Peter S; Tsoi, Kim M; Song, Fayi; Anderson, James B; Chan, Warren C W; Shin, Jumi A

    2017-04-19

    Engineered nanomaterials are used globally in biomedical, electronic, and optical devices, and are often discarded into the environment. Cell culture experiments have shown that many inorganic nanoparticles are toxic to eukaryotic cells. Here, we show that populations of eukaryotic cells can evolve to survive chronic exposure to toxic CdSe semiconductor quantum dots (QDs). We grew yeast Saccharomyces cerevisiae for 24 days in liquid medium containing QDs prepared daily at half the minimum inhibitory concentration (MIC50) of the progenitor yeast cells. After 24 days, the cells grew normally under constant exposure to QDs. We concluded that these cells evolved to resist QD toxicity. Surprisingly, when we removed QDs from the growth medium, some of the evolved cells grew poorly, i.e., they grew better in the presence of QDs. Finally, genetic analysis confirmed that the ubiquitin ligase gene bul1 was mutated in the evolved cells, which suggests that this gene may be implicated in increased CdSe QD tolerance. This study shows that chronic exposure to QDs can exert selective pressure causing irreversible genetic changes leading to adaptation.

  20. High-Temperature Microfluidic Synthesis of CdSe Nanocrystals inNanoliter Droplets

    SciTech Connect

    Chan, Emory M.; Alivisatos, A. Paul; Mathies, Richard A.

    2005-06-09

    The high-temperature synthesis of CdSe nanocrystals innanoliter-volume droplets flowing in a perfluorinated carrier fluidthrough a microfabricated reactor is presented. A flow-focusing nanojetstructure with a step increase in channel height reproducibly generatedoctadecene droplets in Fomblin Y 06/6 perfluorinated polyether atcapillary numbers up to 0.81 and with a droplet:carrier fluid viscosityratio of 0.035. Cadmium and selenium precursors flowing in octadecenedroplets through a high-temperature (240-300 degrees C) glassmicroreactor produced high quality CdSe nanocrystals, as verified byoptical spectroscopy and transmission electron microscopy. Isolating thereaction solution in droplets prevented particle deposition andhydrodynamic dispersion, allowing the reproducible synthesis ofnanocrystals at three different temperatures and four different residencetimes in the span of four hours. Our synthesis of a wide range ofnanocrystals at high temperatures, high capillary numbers, and lowviscosity ratio illustrates the general utility of droplet-basedmicrofluidic reactors to encapsulate nanoliter volumes of organic oraqueous solutions and to precisely control chemical or biochemicalreactions.

  1. Hard-disk behavior and beyond in Langmuir films of CdSe nanoparticles.

    PubMed

    Ozturk, Birol; Behin-Aein, Ghazal; Flanders, Bret N

    2005-05-10

    Harnessing the spontaneous behavior of a population of particles is an attractive approach to the fabrication of targeted nanostructures. Underlying this goal is the interparticle potential, as it dictates the spontaneous behavior of the system. To this end, we present methodology for using quantitative film balance studies of trioctylphosphine oxide (TOPO) stabilized CdSe nanoparticles to determine their effective interparticle potential on the air-water interface. A simple protocol for reducing the quantity of excess TOPO to negligible levels of surface activity is established. In studying clean populations of 2.08, 2.22, 2.36, 2.49, 2.63, and 2.91 nm nanoparticles, quantitative agreement between their pressure-area isotherms and the Carnahan-Starling hard-disk equation of state is achieved. This analysis indicates that CdSe nanoparticles of a given diameter behave how hard disks with significantly smaller diameters would behave. This finding suggests that an attractive contribution to the interparticle potential, such as the dipolar potential, plays a significant role in the spontaneous organization of these particles.

  2. Opto-electrical energy conversion by thin electrolytic CdSe films on Ni substrates

    NASA Astrophysics Data System (ADS)

    Glenis, G. X.; Athanassopoulou, M. D.; Argyropoulos, Th G.; Dervos, C. T.

    2015-02-01

    Thin-films (300 nm) of zinc-blende (cubic structure) CdSe (111) electrolytically deposited on nickel substrates had their surface characteristics investigated by XRD, SEM, and profilometry scans. A metal-CdSe-metal structure was formed by positioning a Au electrode on top of CdSe and the I-V characteristics of the resulting device were investigated in the dark and under low intensities (≤0.2 mW cm-2) of diffused solar radiation. The experimental results show that the illuminated structure is an active device that produces electric power in the 2nd quadrant of the I-V curve. This response may be related to the Ni-to-CdSe interface, where carriers are effectively generated as a result of deep energy level formations, spatially confined in the interfacial region of the depletion layer width of the Ni-CdSe junction. A potential energy diagram is proposed to present the spatially and energetically confined deep-level parameters, the operation principles (carrier generation and transport processes) across the structure and link them to the obtained I-V response. A mathematical modeling based on the Schokley-Read-Hall recombination theory confirms the experimentally obtained current profiles of illuminated junctions. Such opto-electrical tranducers might be implemented in multilayer photovoltaic hetero-structures to enhance their conversion efficiencies and reduce their operating temperatures.

  3. Structural and optical properties of solvothermal synthesized nearly monodispersed CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Shahi, A. K.; Pandey, B. K.; Singh, B. P.; Gopal, R.

    2016-09-01

    Water soluble nearly monodisperse CdSe nanocrystals have been successfully synthesized via aqueous phase solvothermal route in non ionic surfactant glycolic acid ethoxylate 4-non phenyl ether (GAEPE). X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) are used to determine the phase, structural parameters such as lattice constants, strain, x-ray density and specific surface area, morphology, shape and size distribution, respectively, whereas optical properties are studied by UV-visible absorption and photoluminescence (PL) spectroscopy. All the diffraction peaks of XRD pattern indexed to wurtzite phase of hexagonal system of CdSe and crystallite sizes estimated to be 13-29 nm along some stronger and narrower peaks which is also consistent with TEM measurement while crystallinity and defects have been analyzed with selective area electron diffraction (SAED) pattern. Optical absorption spectrum shows that the as prepared sample exhibits primary and secondary absorption band centered at 2.15 eV and 1.82 eV, respectively, which is blue shifted as compared to bulk value (1.74 eV) of band gap due to quantum confinement effect. Photoluminescence spectrum shows sharp excitonic emission band centered at 583 nm which is nearer to primary band gap energy.

  4. CdSe nanocrystal sensitized anatase TiO2 (001) tetragonal nanosheet-array films for photovoltaic application.

    PubMed

    Feng, Shuanglong; Yang, Junyou; Liu, Ming; Liu, Yong

    2013-02-01

    CdSe nanocrystal sensitized TiO2 nanosheet array heterostructure films were fabricated by a two-step method. Firstly, a single crystalline anatase TiO2 tetragonal nanosheet-array film on a transparent conductive fluorine-doped tin oxide (FTO) substrate was successfully prepared by hydrothermal method. Then, CdSe nanocrystalline sensitizers were deposited on the TiO2 nanosheet array by CBD method. The products were characterized with XRD, SEM, TEM and UV-vis absorption spectroscopy. The effect of the CdSe nanocrystal deposition time and the length of the TiO2 sheet on the photovoltaic performance of the resulting CdSe/TiO2 nanosheet array electrodes were also investigated. In comparison with the non-sensitized TiO2 nanosheet array, the photocurrent of CdSe sensitized TiO2 nanosheet has a great enhancement, which gives some insight to the fundamental mechanism of the performance improvement.

  5. 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.

  6. Effects of culture conditions of Pseudomonas aeruginosa strain RB on the synthesis of CdSe nanoparticles.

    PubMed

    Ayano, Hiroyuki; Kuroda, Masashi; Soda, Satoshi; Ike, Michihiko

    2015-04-01

    Cadmium selenide (CdSe) was synthesized by Pseudomonas aeruginosa strain RB in a culture containing lactic acid as a carbon source, 1 mM selenite, and 1 mM cadmium under various conditions. High purity (1.02-1.16 of the atomic ratio of Se to Cd) and efficient synthesis of biogenic CdSe nanoparticles were observed at 25-30°C, 0.05-10 g L(-1) NaCl, and neutral pH conditions compared with other tested conditions. However, the size and shape of synthesized CdSe nanoparticles were not changed by changing culture conditions. The contents of S and Se in the particles respectively increased under alkaline and weak acidic conditions. Furthermore, high temperature (>37°C), high salinity (>10 g L(-1) NaCl), and alkaline pH affected the CdSe-synthesizing rate by strain RB. This report is the first optimizing the culture conditions for synthesizing biogenic CdSe nanoparticles in a batch processing.

  7. 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.

  8. Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

    NASA Astrophysics Data System (ADS)

    Magaryan, K. A.; Eremchev, I. Y.; Karimullin, K. R.; Knyazev, M. V.; Mikhailov, M. A.; Vasilieva, I. A.; Klimusheva, G. V.

    2015-09-01

    Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene) were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8). A comparative analysis of the obtained data with previous results was performed.

  9. Controlled synthesis of CdSe quantum dots by a microwave-enhanced process: a green approach for mass production.

    PubMed

    Ayele, Delele Worku; Chen, Hung-Ming; Su, Wei-Nien; Pan, Chun-Jern; Chen, Liang-Yih; Chou, Hung-Lung; Cheng, Ju-Hsiang; Hwang, Bing-Joe; Lee, Jyh-Fu

    2011-05-09

    A method that does not employ hot-injection techniques has been developed for the size-tunable synthesis of high-quality CdSe quantum dots (QDs) with zinc blende structure. In this environmentally benign synthetic route, which uses less toxic precursors, solvents, and capping ligands, CdSe QDs that absorb visible light are obtained. The size of the as-prepared CdSe QDs and thus their optical properties can be manipulated by changing the microwave reaction conditions. The QDs were characterized by XRD, TEM, UV/Vis, FTIR, time-resolved fluorescence spectroscopy, and fluorescence spectrophotometry. In this approach, the reaction is conducted in open air and at a much lower temperature than in hot-injection techniques. The use of microwaves in this process allows for a highly reproducible and effective synthesis protocol that is fully adaptable for mass production and can be easily employed to synthesize a variety of semiconductor QDs with the desired properties. Possible applications of the CdSe QDs were assessed by deposition on TiO(2) films.

  10. Incidence of the core composition on the stability, the ROS production and the toxicity of CdSe quantum dots.

    PubMed

    Kauffer, Florence-Anaïs; Merlin, Christophe; Balan, Lavinia; Schneider, Raphaël

    2014-03-15

    Mercaptosuccinic acid-capped CdSe and alloyed CdSe(S) QDs were prepared in aqueous solution at 100 and 170°C, respectively. These dots were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-vis and photoluminescence spectroscopies. The dots were found to be of similar size (ca. 2nm) but differ in their composition and surface chemistry. The photostability of the QDs was found to correlate with their ability to produce reactive oxygen species (ROS) upon light activation. CdSe QDs produce hydroxyl radicals immediately after irradiation due to their modest photostability, while CdSe(S) QDs start to generate the hydroxyl radicals only once they start to be bleached (ca. 30min). Cytotoxicity experiments conducted on Escherichia coli cells revealed that CdSe QDs were the more toxic despite being the least loaded in cadmium. In addition, consistent with ROS assays, the cytotoxicity of the CdSe QDs appeared light-dependent and is in accordance with a light-dependent oxidative stress observed with an oxyR-based whole cell biosensor. Our results demonstrate the crucial role played by nanoparticles synthesis process on their PL properties, their stability and their toxicity.

  11. 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.

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

    SciTech Connect

    Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia E-mail: grchen@ecust.edu.cn; Chen, Guorong E-mail: grchen@ecust.edu.cn; Zhang, Bo

    2014-05-21

    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 TiO{sub 2} 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 TiO{sub 2}'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 TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

  13. Synthesis of Tapered CdS Nanobelts and CdSe Nanowires with Good Optical Property by Hydrogen-Assisted Thermal Evaporation.

    PubMed

    Wang, Min; Fei, Guangtao

    2009-07-10

    The tapered CdS nanobelts and CdSe nanowires were prepared by hydrogen-assisted thermal evaporation method. Different supersaturation leads to two different kinds of 1D nanostructures. The PL measurements recorded from the as-prepared tapered CdS nanobelts and CdSe nanowires show only a bandgap emission with relatively narrow full-width half maximum, which means that they possess good optical property. The as-synthesized high-quality tapered CdS nanobelts and CdSe nanowires may be excellent building blocks for photonic devices.

  14. 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.

  15. 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.

  16. Synthesis and Characterizations of Pb-modified CdSe Aqueous Quantum Dots and Their Applications in Quantum Dot-Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Lu, Cheng-Hsin

    Quantum Dots (QDs) are semiconductor nanocrystals with typical size ranges around 1-20 nm. They exhibit distinctive size-dependent photoluminescence (PL) properties due to the quantum confinement effect. QDs have great potentials in display, lighting, lasing, bioimaging, fluorescent label, sensor, photodetector, and photovoltaic applications, and have been widely studied in the past decades. Cadmium selenide (CdSe) QDs have been synthesized using an environmentally friendly, aqueous method under low temperature. While traditional QDs synthesized by hot injection method using organic solvent generally exhibit edge-state emission with narrow peaks, aqueous quantum dots (AQDs) tend to have trap-state emissions with broad peaks. The objective of this thesis is to investigate how Pb modifications in CdSe AQDs synthesis can affect the optoelectronic properties of the QDs and how these modifications affect their corresponding photovoltaic performance in quantum dot-sensitized solar cell (QDSSC) applications. Lead (Pb) precursor has been introduced either during the synthesis or after the synthesis of CdSe AQDs forming either Pb-doped or Pb-coated CdSe QDs, respectively. Pb-doped CdSe QDs exhibit red-shift in both absorption and emission spectra while Pb-coated CdSe QDs exhibit blue-shift in both absorption and emission spectra along with the generation of more surface defects. Although blue-shifted absorption indicating a narrower absorption range and the surface defects providing undesired recombination pathways are detrimental to solar cell performance, however surprisingly, we found that QDSSCs made from Pb-coated CdSe QDs actually had better solar cell performance than that made from Pb-doped CdSe QDs. We attributed this finding to a protection/passivation layer formed in-situ when the coated Pb react with the iodide/triiodide electrolyte during solar cell operation resulting in QDSSCs with better charge injection and stability.

  17. 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.

  18. 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

    2013-03-04

    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.

  19. 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.

  20. Surface Passivation of CdSe Quantum Dots in All Inorganic Amorphous Solid by Forming Cd1−xZnxSe Shell

    PubMed Central

    Xia, Mengling; Liu, Chao; Zhao, Zhiyong; Wang, Jing; Lin, Changgui; Xu, Yinsheng; Heo, Jong; Dai, Shixun; Han, Jianjun; Zhao, Xiujian

    2017-01-01

    CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd1−xZnxSe shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd1−xZnxSe core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials. PMID:28169376

  1. Assembly of CdSe onto mesoporous TiO 2 films induced by a self-assembled monolayer for quantum dot-sensitized solar cell applications

    NASA Astrophysics Data System (ADS)

    Chong, Lai-Wan; Chien, Huei-Ting; Lee, Yuh-Lang

    A self-assembled monolayer (SAM) of 3-mercaptopropyl-trimethyoxysilane (MPTMS) is pre-assembled onto a mesoporous TiO 2 film and is used as a surface-modified layer to induce the growth of CdSe QDs in the successive ionic layer adsorption and reaction (SILAR) process. Due to the specific interaction of the terminal thiol groups to CdSe, the MPTMS SAM is found to increase the nucleation and growth rates of CdSe in the SILAR process, leading to a well covering and higher uniform CdSe layer which has a superior ability, compared with the electrode without MPTMS, in inhibiting the charge recombination at the electrode/electrolyte interface. Furthermore, the performance of the CdSe-sensitized TiO 2 electrode can further be improved by an additional heat annealing after film deposition, attributable to a better interfacial connection between CdSe and TiO 2, as well as a better connection among CdSe QDs. The CdSe-sensitized solar cell prepared by the present strategy can achieve an energy conversion efficiency of 2.65% under the illumination of one sun (AM 1.5, 100 mW cm -2).

  2. 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.

  3. Influence of acid and alkaline sources on optical, structural and photovoltaic properties of CdSe nanoparticles precipitated from aqueous solution

    NASA Astrophysics Data System (ADS)

    Coria-Monroy, C. Selene; Sotelo-Lerma, Mérida; Hu, Hailin

    2016-06-01

    CdSe is a widely researched material for photovoltaic applications. One of the most important parameters of the synthesis is the pH value, since it determines the kinetics and the mechanism of the reaction and in consequence, the optical and morphological properties of the products. We present the synthesis of CdSe in solution with strict control of pH and the comparison of ammonia and KOH as alkaline sources and diluted HCl as acid medium. CdSe formation was monitored with photoluminescence emission spectra (main peak in 490 nm, bandgap of CdSe nanoparticles). XRD patterns indicated that CdSe nanoparticles are mainly of cubic structure for ammonia and HCl, but the hexagonal planes appear with KOH. Product yield decreases with pH and also decreases with KOH at constant pH value since ammonia has a double function, as complexing agent and alkaline source. Changes in morphology were observed in SEM images as well with the different alkaline source. The effect of alkaline sources on photovoltaic performance of hybrid organic solar cells with CdSe and poly(3-hexylthiophene) as active layers was clearly observed, indicating the importance of synthesis conditions on optoelectronic properties of promising semiconductor nanomaterials for solar cell applications.

  4. Comparative experiments of graphene covalently and physically binding CdSe quantum dots to enhance the electron transport in flexible photovoltaic devices.

    PubMed

    Jung, Mi-Hee; Chu, Moo-Jung

    2014-08-07

    In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.

  5. Surface Passivation of CdSe Quantum Dots in All Inorganic Amorphous Solid by Forming Cd1-xZnxSe Shell

    NASA Astrophysics Data System (ADS)

    Xia, Mengling; Liu, Chao; Zhao, Zhiyong; Wang, Jing; Lin, Changgui; Xu, Yinsheng; Heo, Jong; Dai, Shixun; Han, Jianjun; Zhao, Xiujian

    2017-02-01

    CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd1-xZnxSe shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd1-xZnxSe core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials.

  6. Characterization of defects in colloidal CdSe nanocrystals by the modified thermostimulated luminescence technique

    SciTech Connect

    Katsaba, A. V. Fedyanin, V. V.; Ambrozevich, S. A.; Vitukhnovsky, A. G.; Lobanov, A. N.; Selyukov, A. S.; Vasiliev, R. B.; Samatov, I. G.; Brunkov, P. N.

    2013-10-15

    The temperature dependencies of the luminescence spectra of 5-nm-diameter CdSe semiconductor nanocrystals synthesized by colloidal-chemistry methods are investigated. The two bands observed in these spectra around 2.01 and 1.37 eV correspond to band-to-band transitions and luminescence of defect states, respectively. A model explaining the temperature behavior of the luminescence band intensities both upon cooling and heating is put forward. A new modification of spectrally resolved thermostimulated luminescence technique making it possible to determine the activation energies and the character of traps responsible for the temperature dependence of the luminescence intensities is suggested. This technique is used to obtain the activation energies of the emission and capture of electrons at traps (190 and 205 meV, respectively) and to determine the depth of the electron level (57 meV) responsible for luminescence in the 1.37-eV region.

  7. Thickness dependent optical and electrical properties of CdSe thin films

    NASA Astrophysics Data System (ADS)

    Purohit, A.; Chander, S.; Nehra, S. P.; Lal, C.; Dhaka, M. S.

    2016-05-01

    The effect of thickness on the optical and electrical properties of CdSe thin films is investigated in this paper. The films of thickness 445 nm, 631 nm and 810 nm were deposited on glass and ITO coated glass substrates using thermal evaporation technique. The deposited thin films were thermally annealed in air atmosphere at temperature 100°C and were subjected to UV-Vis spectrophotometer and source meter for optical and electrical analysis respectively. The absorption coefficient is observed to increase with photon energy and found maximum in higher photon energy region. The extinction coefficient and refractive index are also calculated. The electrical analysis shows that the electrical resistivity is observed to be decreased with thickness.

  8. 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

  9. Recombination dynamics of band edge excitons in quasi-two-dimensional CdSe nanoplatelets.

    PubMed

    Biadala, Louis; Liu, Feng; Tessier, Mickael D; Yakovlev, Dmitri R; Dubertret, Benoit; Bayer, Manfred

    2014-03-12

    We report a time-resolved study of the photoluminescence of CdSe colloidal nanoplatelets with two different thicknesses. By studying the exciton recombination dynamics we assess the exciton fine structure in these systems. The splitting between bright and dark excitons is enhanced compared to epitaxial quantum well structures as result of dielectric confinement. Despite of strong variations in the absolute magnitude, by comparison with literature data we find a relatively slightly varying bright-dark exciton lifetime ratio in very different CdSe-based colloidal nanostructures, regardless of growth technique and of core and shell properties such as materials, dimensions, etc. This finding points to a universal mechanism in the dark exciton recombination.

  10. 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.

  11. Photoinduced fluorescence enhancement in CdSe /ZnS quantum dot monolayers: Influence of substrate

    NASA Astrophysics Data System (ADS)

    Uematsu, Takafumi; Maenosono, Shinya; Yamaguchi, Yukio

    2006-07-01

    Photoinduced fluorescence enhancement (PFE) of CdSe /ZnS core/shell quantum dot (QD) films on SiOx substrates was investigated. The fluorescence intensity of the QD film on SiO1.9 was greatly enhanced by continuous irradiation in vacuum, while the same QD film on SiO0.6 showed a small enhancement of the fluorescence intensity. After irradiation, the rate of fluorescence decay of the QD film on SiO0.6 was smaller than that of the QD film on SiO1.9. Our results suggest that the origin of PFE derives from the photoejection of electrons into the substrate, and that the oxygen-excess-related defects work as trap sites for the electrons.

  12. All-optical modulation by plasmonic excitation of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Pacifici, Domenico; Lezec, Henri J.; Atwater, Harry A.

    2007-07-01

    Photonics is a promising candidate technology for information processing, communication and data storage. Essential building blocks, such as logic elements and modulators, have been demonstrated. However, because of weak nonlinear light-matter interactions, these components typically require high power densities and large interaction volumes, limiting their application in dense chip-based integration. A solution may be found in surface plasmon polaritons (SPPs), guided electromagnetic waves that propagate with high field confinement along a metal-dielectric interface. We demonstrate an all-optical modulator in which efficient interaction between two light beams at different wavelengths is achieved by converting them into co-propagating SPPs interacting by means of a thin layer of CdSe quantum dots (QDs). The high SPP field confinement and high QD-absorption cross-section enable optical modulation at low power densities (~102 W cm-2) in micrometre-scale planar devices.

  13. 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.

  14. Optical characterization of CdSe quantum dots with metal chalcogenide ligands in solutions and solids

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Q.; Cao, X. A.

    2011-07-01

    The exchange of the original organic ligands of colloidal CdSe core and CdSe/CdS/ZnS core/multishell quantum dots (QDs) with inorganic metal chalcogenide ligands (SnS44-) resulted in carrier delocalization in solutions and enhanced inter-QD electronic coupling in solids, as inferred from peak redshift and broadening of the absorption and photoluminescence (PL) spectra. The SnS4-capped QDs retained strong excitonic absorption but suffered significant PL quenching. Mild thermal treatment below 350 °C transformed the SnS4 ligands into a more conductive phase, leading to stronger coupling yet complete PL quenching. These findings suggest that QD solids with metal chalcogenide ligands may have high quantum yields of photocurrent generation and can be used as functional blocks in thin-film solar cells for efficient solar energy conversion.

  15. Auger-Limited Carrier Recombination and Relaxation in CdSe Colloidal Quantum Wells.

    PubMed

    Baghani, Erfan; O'Leary, Stephen K; Fedin, Igor; Talapin, Dmitri V; Pelton, Matthew

    2015-03-19

    Using time-resolved photoluminescence spectroscopy, we show that two-exciton Auger recombination dominates carrier recombination and cooling dynamics in CdSe nanoplatelets, or colloidal quantum wells. The electron-hole recombination rate depends only on the number of electron-hole pairs present in each nanoplatelet, and is consistent with a two-exciton recombination process over a wide range of exciton densities. The carrier relaxation rate within the conduction and valence bands also depends only on the number of electron-hole pairs present, apart from an initial rapid decay, and is consistent with the cooling rate being limited by reheating due to Auger recombination processes. These Auger-limited recombination and relaxation dynamics are qualitatively different from the carrier dynamics in either colloidal quantum dots or epitaxial quantum wells.

  16. Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Do, Thanh Nhut; Ong, Xuanwei; Chan, Yinthai; Tan, Howe-Siang

    2016-12-01

    We describe a model to explain the features of the ultrafast transient absorption (TA) spectra of CdSe core type quantum dots (QDs). The measured TA spectrum consists of contributions by the ground state bleach (GSB), stimulated emission (SE) and excited state absorption (ESA) processes associated with the three lowest energy transition of the QDs. We model the shapes of the GSB, SE and ESA spectral components after fits to the linear absorption. The spectral positions of the ESA components take into account the biexcitonic binding energy. In order to obtain the correct weightage of the GSB, SE and ESA components to the TA spectrum, we enumerate the set of coherence transfer pathways associated with these processes. From our fits of the experimental TA spectra of 65 Å diameter QDs, biexcitonic binding energies for the three lowest energy transitions are obtained.

  17. Hot-electron luminescence in aged electrodeposited CdSe liquid-junction solar cell

    SciTech Connect

    Silberstein, R.P.; Tomkiewicz, M.

    1983-01-01

    We have utilized Raman spectroscopy and scanning Auger electron spectroscopy (AES) to probe the surface of polycrystalline, electrodeposited CdSe photoelectrodes which have been aged in a polysulfide electrolyte under illumination and in darkness. We have observed characteristic ''hot-electron'' luminescence at multiples of ..omega../sub LO/ (CdS) = 305 cm/sup -1/ in the light-aged electrode, indicating that a surface layer of CdS has been formed. AES profiling shows that extensive substitution of S for Se has occurred, in the light-aged electrode alone, to a depth of approx.600 A. Measurements at 300 K suggest that Raman scattering can be a useful, in situ, contactless, nondestructive probe of CdS formation.

  18. Ordered structures based on self-organized Au and CdSe nanoparticles

    SciTech Connect

    Zaporozhets, M. A.; Savilov, S. V.; Zhigalina, O. M.; Sul'yanov, S. N.; Volkov, V. V.; Nikolaichik, V. I.; Gubin, S. P.; Avilov, A. S.

    2012-05-15

    Methods for obtaining cadmium selenide and gold nanoparticles have been developed. The sizes of the nanoparticles are determined and the morphology, structure, and chemical composition of these nanoparticles and their ensembles are studied by a complex of structural methods: electron diffraction, X-ray diffraction, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, and small-angle X-ray scattering. Gold nanoparticles are mainly spherical and have an average size of 10 nm. They are single-phase and have an fcc crystal structure. Samples of synthesized CdSe nanoparticles contain monodisperse spherical particles 12 nm in size with a wurtzite structure. The deposition of nanoparticles on a carbon substrate is accompanied by their self-organization into a closely packed two-dimensional structure with a pronounced texture in which all nanoparticles are oriented in the [001] direction perpendicularly to the carbon substrate plane.

  19. Selective recognition of dysprosium(III) ions by enhanced chemiluminescence CdSe quantum dots.

    PubMed

    Hosseini, Morteza; Ganjali, Mohammad R; Vaezi, Zahra; Faridbod, Farnoush; Arabsorkhi, Batool; Sheikhha, Mohammad H

    2014-01-01

    The intensity of emitted light from CdSe quantum dots (QDs)-H2O2 is described as a novel chemiluminescence (CL) reaction for determination of dysprosium. This reaction is based on the catalytic effect of Dy(3+) ions, 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 8.3×10(-7)-5.0×10(-6)M, the detection limit of 6.0×10(-8)M, and the relative standard deviation for five determinations of 2.5×10(-6)M Dy(3+) 3.2%. The main experimental advantage of the proposed method is its selective to Dy(3+) ions compared with common coexisting cations, therefore, it was successfully applied for the determination of dysprosium ions in water samples.

  20. Parameters influencing the performance and stability of CdSe MIS solar cells

    SciTech Connect

    Rickus, E.

    1982-09-01

    CdSe MIS solar cells with ZnSe as ''I-layer'' are very insensitive to oxidative ambients and to humidity even in the unsealed state. They show lower sensitivity to ''I-film'' thickness-variations than native-oxide devices. The use of wide-bandgap semiconductor as ''I-film'' opens new ways to influence the energetic position of the potential barrier caused by the ''I-layer''. Expecially doping of the ZnSe-film results in a distinct enhancement of the fill factor. AM 1-efficiencies of 6.6 percent on 1 cm/sup 2/ active area have been achieved with relatively low effort. Further optimizations will enhance the efficiency of this simple, economic solar cell.

  1. Transient charge technique investigation of HgI/sub 2/ and CdSe nuclear detectors

    SciTech Connect

    Roth, M.; Burger, A.; Nissenbaum, J.; Schieber, M.

    1987-02-01

    The use of the Transient Charge Technique (TCT) for the evaluation of high resistivity Mercuric Iodide and Cadmium Selenide nuclear radiation detectors is suggested. It has been shown that the real values of mobilities and trapping times of electrons and holes in HgI/sub 2/ can be easily obtained from the analysis of the voltage transient response to drift of charge carriers created by alpha particles. This allows one to evaluate the bulk transport properties of the material and, additionally, to estimate accurately the surface recombination velocity of the carriers. Preliminary results on the shape of voltage transients in CdSe are also reported, and the limitations of the use of the TCT for characterization of both materials are discussed.

  2. Magnetic polaron on dangling-bond spins in CdSe colloidal nanocrystals.

    PubMed

    Biadala, Louis; Shornikova, Elena V; Rodina, Anna V; Yakovlev, Dmitri R; Siebers, Benjamin; Aubert, Tangi; Nasilowski, Michel; Hens, Zeger; Dubertret, Benoit; Efros, Alexander L; Bayer, Manfred

    2017-03-13

    Non-magnetic colloidal nanostructures can demonstrate magnetic properties typical for diluted magnetic semiconductors because the spins of dangling bonds at their surface can act as the localized spins of magnetic ions. Here we report the observation of dangling-bond magnetic polarons (DBMPs) in 2.8-nm diameter CdSe colloidal nanocrystals (NCs). The DBMP binding energy of 7 meV is measured from the spectral shift of the emission lines under selective laser excitation. The polaron formation at low temperatures occurs by optical orientation of the dangling-bond spins (DBSs) that result from dangling-bond-assisted radiative recombination of spin-forbidden dark excitons. Modelling of the temperature dependence of the DBMP-binding energy and emission intensity shows that the DBMP is composed of a dark exciton and about 60 DBSs. The exchange integral of one DBS with the electron confined in the NC is ∼0.12 meV.

  3. Microwave synthesis of CdSe and CdTe nanocrystals in nonabsorbing alkanes.

    PubMed

    Washington, Aaron L; Strouse, Geoffrey F

    2008-07-16

    Controlling nanomaterial growth via the "specific microwave effect" can be achieved by selective heating of the chalcogenide precursor. The high polarizability of the precursor allows instantaneous activation and subsequent nucleation leading to the synthesis of CdSe and CdTe in nonmicrowave absorbing alkane solvents. Regardless of the desired size, narrow dispersity nanocrystals can be isolated in less than 3 min with high quantum efficiencies and elliptical morphologies. The reaction does not require a high temperature injection step, and the alkane solvent can be easily removed. In addition, batch-to-batch variance in size is 4.2 +/- 0.14 nm for 10 repeat experimental runs. The use of a stopped-flow reactor allows near continuous automation of the process leading to potential industrial benefits.

  4. Photon echo studies of biexcitons and coherences in colloidal CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Colonna, Anne E.; Yang, Xiujuan; Scholes, Gregory D.

    2005-04-01

    The cover picture shows the size-dependent photoluminescence from CdSe colloidal quantum dots that were investigated in the work [1]. Ultrafast photon echo experiments were undertaken in conjunction with simulations based on a realistic many-body theory, shown in the picture, to ascertain the significance of many-body contributions to the third-order nonlinear response.The first author Anne E. Colonna undertook this research during a summer internship in the Department of Chemistry, University of Toronto. She is currently pursuing graduate studies at École Polytechnique, Saclay, in the Laboratoire d'Optique et Biosciences.The author Gregory D. Scholes is an Assistant Professor in the Department of Chemistry, University of Toronto. His research interests include synthesis and shape control of quantum dots, as well as the application of ultrafast laser spectroscopy to investigate the electronic structure of inorganic and organic semiconductors.

  5. Generation of Rashba spin-orbit coupling in CdSe nanowire by ionic liquid gate.

    PubMed

    Zhang, Shan; Tang, Ning; Jin, Weifeng; Duan, Junxi; He, Xin; Rong, Xin; He, Chenguang; Zhang, Lisheng; Qin, Xudong; Dai, Lun; Chen, Yonghai; Ge, Weikun; Shen, Bo

    2015-02-11

    Spintronic devices rely on the spin degree of freedom (DOF), and spin orbit coupling (SOC) is the key to manipulate spin DOF. Quasi-one-dimensional structures, possessing marked anisotropy gives more choice for the manipulation of the spin DOF since the concrete SOC form varies along with crystallographic directions. The anisotropy of the Dresselhaus SOC in cadmium selenide (CdSe) nanobelt and nanowire was studied by circular photogalvanic effect. It was demonstrated that the Dresselhaus SOC parameter is zero along the [0001] crystallographic direction, which suppresses the spin relaxation and increases the spin diffusion length, and thus is beneficial to the spin manipulation. To achieve a device structure with Rashba SOC presence and Dresselhaus SOC absence for manipulating the spin DOF, an ionic liquid gate was produced on a nanowire grown along the [0001] crystallographic direction, and the Rashba SOC was induced by gating, as expected.

  6. Broad spectral photocurrent enhancement in Au-decorated CdSe nanowires.

    PubMed

    Chakraborty, Ritun; Greullet, Fanny; George, Chandramohan; Baranov, Dmitry; Di Fabrizio, Enzo; Krahne, Roman

    2013-06-21

    Metal-semiconductor hybrid nanostructures promise improved photoconductive performance due to plasmonic properties of the metal portions and intrinsic electric fields at the metal-semiconductor interface that possibly enhance charge separation. Here we report gold decorated CdSe nanowires as a novel functional material and investigate the influence of gold decoration on the lateral facets on the photoconductive properties. Gold decorated nanowires show typically an at least ten-fold higher photocurrent as compared to their bare counterparts. Interestingly, the photocurrent enhancement is wavelength independent, although the plasmon resonance related to the gold particles appears in the absorption spectra. Our experiments show that light scattering and Schottky fields associated with the metal-semiconductor interface are at the origin of the photocurrent enhancement.

  7. Exciton recombination dynamics in CdSe nanowires: bimolecular to three-carrier Auger kinetics.

    PubMed

    Robel, István; Bunker, Bruce A; Kamat, Prashant V; Kuno, Masaru

    2006-07-01

    Ultrafast relaxation dynamics of charge carriers in CdSe quantum wires with diameters between 6 and 8 nm are studied as a function of carrier density. At high electron-hole pair densities above 10(19) cm(-3) the dominant process for carrier cooling is the "bimolecular" Auger recombination of one-dimensional (1D) excitons. However, below this excitation level an unexpected transition from a bimolecular (exciton-exciton) to a three-carrier Auger relaxation mechanism occurs. Thus, depending on excitation intensity, electron-hole pair relaxation dynamics in the nanowires exhibit either 1D or 0D (quantum dot) character. This dual nature of the recovery kinetics defines an optimal intensity for achieving optical gain in solution-grown nanowires given the different carrier-density-dependent scaling of relaxation rates in either regime.

  8. 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.

  9. 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.

  10. 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.

  11. Auger-Limited Carrier Recombination and Relaxation in CdSe Colloidal Quantum Wells

    SciTech Connect

    Baghani, Erfan; O'Leary, Stephen K.; Fedin, Igor; Talapin, Dimitri V.; Pelton, Matthew

    2015-03-19

    Using time-resolved photoluminescence spectroscopy, we show that two-exciton Auger recombination dominates carrier recombination and cooling dynamics in CdSe nanoplatelets, or colloidal quantum wells. The electron-hole recombination rate depends only on the number of electron-hole pairs present in each nanoplatelet, and is consistent with a twoexciton recombination process over a wide range of exciton densities. The carrier relaxation rate within the conduction and valence bands also depends only on the number of electron-hole pairs present, apart from an initial rapid decay, and is consistent with the cooling rate being limited by reheating due to Auger recombination processes. These Auger-limited recombination and relaxation dynamics are qualitatively different from the carrier dynamics in either colloidal quantum dots or epitaxial quantum wells. TOC FIGURE:

  12. 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.

  13. Persistent Inter-Excitonic Quantum Coherence in CdSe Quantum Dots

    PubMed Central

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

    2014-01-01

    The creation and manipulation of quantum superpositions is a fundamental goal for the development of materials with novel optoelectronic properties. In this letter, we report persistent (~80 fs lifetime) quantum coherence between the 1S and 1P excitonic states in zinc-blende colloidal CdSe quantum dots at room temperature, measured using Two-Dimensional Electronic Spectroscopy. We demonstrate that this quantum coherence manifests as an intradot phenomenon, the frequency of which depends on the size of the dot excited within the ensemble of QDs. We model the lifetime of the coherence and demonstrate that correlated interexcitonic fluctuations preserve relative phase between excitonic states. These observations suggest an avenue for engineering long-lived interexcitonic quantum coherence in colloidal quantum dots. PMID:24719679

  14. Purcell effect for CdSe /ZnSe quantum dots placed into hybrid micropillars

    NASA Astrophysics Data System (ADS)

    Robin, I. C.; André, R.; Balocchi, A.; Carayon, S.; Moehl, S.; Gérard, J. M.; Ferlazzo, L.

    2005-12-01

    This letter reports the observation of the Purcell effect for CdSe /ZnSe quantum dots located in a hybrid micropillar. The sample consist of a λ /2-ZnSe cavity sandwiched between two SiO2/TiO2 Bragg reflectors. Time-resolved photoluminescence (PL) measurements on a series of single-quantum dots were used to probe the Purcell effect in a 1.1μm diameter pillar. A three-fold enhancement of quantum-dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar. The variation of the PL decay shortening from dot to dot is interpreted calculating the theoretical maximal Purcell factor for the different modes resonant with the dots.

  15. AgCl-doped CdSe quantum dots with near-IR photoluminescence.

    PubMed

    Kotin, Pavel Aleksandrovich; Bubenov, Sergey Sergeevich; Mordvinova, Natalia Evgenievna; Dorofeev, Sergey Gennadievich

    2017-01-01

    We report the synthesis of colloidal CdSe quantum dots doped with a novel Ag precursor: AgCl. The addition of AgCl causes dramatic changes in the morphology of synthesized nanocrystals from spherical nanoparticles to tetrapods and finally to large ellipsoidal nanoparticles. Ellipsoidal nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found.

  16. 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.

  17. AgCl-doped CdSe quantum dots with near-IR photoluminescence

    PubMed Central

    Bubenov, Sergey Sergeevich; Mordvinova, Natalia Evgenievna; Dorofeev, Sergey Gennadievich

    2017-01-01

    We report the synthesis of colloidal CdSe quantum dots doped with a novel Ag precursor: AgCl. The addition of AgCl causes dramatic changes in the morphology of synthesized nanocrystals from spherical nanoparticles to tetrapods and finally to large ellipsoidal nanoparticles. Ellipsoidal nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found. PMID:28685116

  18. Aqueous synthesis and characterization of Ni, Zn co-doped CdSe QDs

    NASA Astrophysics Data System (ADS)

    Thirugnanam, N.; Govindarajan, D.

    2016-01-01

    Ni, Zn co-doped CdSe quantum dots (QDs) were synthesized by chemical precipitation method through aqueous route. The prepared QDs were characterized by X-ray diffraction (XRD) technique, UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy and high resolution transmission electron microscopy (HRTEM). XRD technique results indicate that the prepared samples have a zinc blende cubic phase. From UV-Vis absorption spectroscopy technique, the prepared samples were blue shifted with respect to their bulk counter part due to quantum confinement effect. Among different doping ratios examined, a maximum PL emission intensity was observed for CdSe:Ni(1 %):Zn(1 %) QDs. HRTEM pictures show that the prepared QDs were in spherical shape.

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

    PubMed

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

    2015-06-08

    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

  20. Magnetic polaron on dangling-bond spins in CdSe colloidal nanocrystals

    NASA Astrophysics Data System (ADS)

    Biadala, Louis; Shornikova, Elena V.; Rodina, Anna V.; Yakovlev, Dmitri R.; Siebers, Benjamin; Aubert, Tangi; Nasilowski, Michel; Hens, Zeger; Dubertret, Benoit; Efros, Alexander L.; Bayer, Manfred

    2017-07-01

    Non-magnetic colloidal nanostructures can demonstrate magnetic properties typical for diluted magnetic semiconductors because the spins of dangling bonds at their surface can act as the localized spins of magnetic ions. Here we report the observation of dangling-bond magnetic polarons (DBMPs) in 2.8-nm diameter CdSe colloidal nanocrystals (NCs). The DBMP binding energy of 7 meV is measured from the spectral shift of the emission lines under selective laser excitation. The polaron formation at low temperatures occurs by optical orientation of the dangling-bond spins (DBSs) that result from dangling-bond-assisted radiative recombination of spin-forbidden dark excitons. Modelling of the temperature dependence of the DBMP-binding energy and emission intensity shows that the DBMP is composed of a dark exciton and about 60 DBSs. The exchange integral of one DBS with the electron confined in the NC is ∼0.12 meV.

  1. Tuning the Surface Structure and Optical Properties of CdSe Clusters Using Coordination Chemistry

    SciTech Connect

    Cossairt, Brandi M.; Juhas, Pavol; Billinge, Simon J.L.; Owen, Jonathan S.

    2012-03-26

    A series of nonstoichiometric CdSe clusters with lowest energy electronic absorptions between 409 and 420 nm has been prepared from cadmium 1-naphthoate, 2-naphthoate, 4-thiomethyl-1-naphthaote, and 1-naphthalene thiolate complexes and diphenylphosphine selenide (DPPSe). Pair distribution function analysis of X-ray diffraction data, ligand exchange experiments, and NMR molecular weight analyses suggest the nanocrystal core changes minimally among these clusters despite significant changes to their absorption and luminescence spectra. Photoluminescence excitation spectra obtained at 77 K reveal an energy transfer process between the surface-trapped excited state and the naphthalene-containing ligands that leads to ligand phosphorescence. A Dexter energy transfer mechanism is proposed to explain the observation of ligand phosphorescence on excitation of the cluster. These compounds demonstrate that cluster absorption and trap luminescence can be controlled with surface coordination chemistry.

  2. 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.

  3. Room-temperature processing of CdSe quantum dots with tunable sizes

    NASA Astrophysics Data System (ADS)

    Joo, So-Yeong; Jeong, Da-Woon; Lee, Chan-Gi; Kim, Bum-Sung; Park, Hyun-Su; Kim, Woo-Byoung

    2017-06-01

    In this work, CdSe quantum dots (QDs) with tunable sizes have been fabricated via photo-induced chemical etching at room temperature, and the related reaction mechanism was investigated. The surface of QDs was oxidized by the holes generated through photon irradiation of oxygen species, and the obtained oxide layer was dissolved in an aqueous solution of 3-amino-1-propanol (APOL) with an APOL:H2O volume ratio of 5:1. The generated electrons promoted QD surface interactions with amino groups, which ultimately passivated surface defects. The absorption and photoluminescence emission peaks of the produced QDs were clearly blue-shifted about 26 nm with increasing time, and the resulting quantum yield for an 8 h etched sample was increased from 20% to 26%, as compared to the initial sample.

  4. Persistent Inter-Excitonic Quantum Coherence in CdSe Quantum Dots.

    PubMed

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

    2014-01-02

    The creation and manipulation of quantum superpositions is a fundamental goal for the development of materials with novel optoelectronic properties. In this letter, we report persistent (~80 fs lifetime) quantum coherence between the 1S and 1P excitonic states in zinc-blende colloidal CdSe quantum dots at room temperature, measured using Two-Dimensional Electronic Spectroscopy. We demonstrate that this quantum coherence manifests as an intradot phenomenon, the frequency of which depends on the size of the dot excited within the ensemble of QDs. We model the lifetime of the coherence and demonstrate that correlated interexcitonic fluctuations preserve relative phase between excitonic states. These observations suggest an avenue for engineering long-lived interexcitonic quantum coherence in colloidal quantum dots.

  5. Thickness dependent optical and electrical properties of CdSe thin films

    SciTech Connect

    Purohit, A. Chander, S.; Nehra, S. P.; Lal, C.; Dhaka, M. S.

    2016-05-06

    The effect of thickness on the optical and electrical properties of CdSe thin films is investigated in this paper. The films of thickness 445 nm, 631 nm and 810 nm were deposited on glass and ITO coated glass substrates using thermal evaporation technique. The deposited thin films were thermally annealed in air atmosphere at temperature 100°C and were subjected to UV-Vis spectrophotometer and source meter for optical and electrical analysis respectively. The absorption coefficient is observed to increase with photon energy and found maximum in higher photon energy region. The extinction coefficient and refractive index are also calculated. The electrical analysis shows that the electrical resistivity is observed to be decreased with thickness.

  6. Electrochemical photovoltaic cells CdSe thin film electrodes. Final report, June 1979-June 1980

    SciTech Connect

    Russak, M.A.; Reichman, J.; DeCarlo, J.; Creter, C.

    1980-07-01

    Progress on developing stable, thin-film CdSe electrodes with sunlight conversion efficiency of 10% for use with aqueous polysulfide electrolytes in frontwall and backwall illuminated EPCs is reported. The main effort has been directed towards establishing the relationships among thin-film processing, resultant electronic properties and I-V performance in order to produce electrodes with maximum power conversion efficiency. The most encouraging results have been obtained with CdSe thin-film electrodes produced in two ways for frontwall cells. Films were deposited on titanium at approximately 100/sup 0/C with a high Se/Cd ratio and then heat treated in air at 350 to 400/sup 0/C. These films usually have a very fine grained microstructure after heat treatment and the resultant electrodes exhibit fairly square I-V characteristics with fill factors of 0.6 or greater and high current output. The overall power efficiency of these electrodes is limited by relatively low output voltages. At present, power conversion efficiencies of 3 to 5% can be obtained reproducibly at simulated AM2 conditions with electrodes processed in this manner. The second type of film that has yielded very promising results is deposited on titanium at substrate temperatures greater than 400/sup 0/C. The interesting feature of these electrodes is their increased open circuit voltage. However, the current output and fill factor are lower. As a result, the power conversion efficiency of these electrodes is 3 to 4%. Backwall electrodes with an efficiency of greater than 4% and short circuit densities near theoretical for AM2 conditions have been produced.

  7. Orbital alignment at the internal interface of arylthiol functionalized CdSe molecular hybrids

    SciTech Connect

    Li, Zhi; Schlaf, Rudy; Mazzio, Katherine A.; Okamoto, Ken; Luscombe, Christine K.

    2015-04-21

    Organic-inorganic nanoparticle molecular hybrid materials are interesting candidates for improving exciton separation in organic solar cells. The orbital alignment at the internal interface of cadmium selenide (ArS-CdSe) hybrid materials functionalized with covalently attached arylthiolate moieties was investigated through X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). A physisorbed interface between arylthiol (ArSH) ligands and CdSe nanoparticles was also investigated for comparison. This interface was created via a multi-step thin film deposition procedure in-vacuo, where the surface was characterized after each experimental step. This enabled the direct comparison of ArSH/CdSe interfaces produced via physisorption and ArS-CdSe covalently attached hybrid materials, which rely on a chemical reaction for their synthesis. All material depositions were performed using an electrospray deposition, which enabled the direct injection of solution-originating molecular species into the vacuum system. This method allows XPS and UPS measurements to be performed immediately after deposition without exposure to the atmosphere. Transmission electron microscopy was used to determine the morphology and particle size of the deposited materials. Ultraviolet-visible spectroscopy was used to estimate the optical band gap of the CdSe nanoparticles and the HOMO-LUMO gap of the ArSH ligands. These experiments showed that hybridization via covalent bonds results in an orbital realignment at the ArSH/CdSe interface in comparison to the physisorbed interface. The orbital alignment within the hybrid caused a favorable electron injection barrier, which likely facilitates exciton-dissociation while preventing charge-recombination.

  8. Orbital alignment at the internal interface of arylthiol functionalized CdSe molecular hybrids

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Mazzio, Katherine A.; Okamoto, Ken; Luscombe, Christine K.; Schlaf, Rudy

    2015-04-01

    Organic-inorganic nanoparticle molecular hybrid materials are interesting candidates for improving exciton separation in organic solar cells. The orbital alignment at the internal interface of cadmium selenide (ArS-CdSe) hybrid materials functionalized with covalently attached arylthiolate moieties was investigated through X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). A physisorbed interface between arylthiol (ArSH) ligands and CdSe nanoparticles was also investigated for comparison. This interface was created via a multi-step thin film deposition procedure in-vacuo, where the surface was characterized after each experimental step. This enabled the direct comparison of ArSH/CdSe interfaces produced via physisorption and ArS-CdSe covalently attached hybrid materials, which rely on a chemical reaction for their synthesis. All material depositions were performed using an electrospray deposition, which enabled the direct injection of solution-originating molecular species into the vacuum system. This method allows XPS and UPS measurements to be performed immediately after deposition without exposure to the atmosphere. Transmission electron microscopy was used to determine the morphology and particle size of the deposited materials. Ultraviolet-visible spectroscopy was used to estimate the optical band gap of the CdSe nanoparticles and the HOMO-LUMO gap of the ArSH ligands. These experiments showed that hybridization via covalent bonds results in an orbital realignment at the ArSH/CdSe interface in comparison to the physisorbed interface. The orbital alignment within the hybrid caused a favorable electron injection barrier, which likely facilitates exciton-dissociation while preventing charge-recombination.

  9. Study of binary and ternary organic hybrid CdSe quantum dot photodetector

    NASA Astrophysics Data System (ADS)

    Ramar, M.; Kajal, S.; Pal, Prabir; Srivastava, R.; Suman, C. K.

    2015-09-01

    The hybrid binary and ternary photodetectors (PDs) were fabricated from P3HT-PC71BM with CdSe quantum dot (QD) materials. The absorption spectra of P3HT:PC71BM (named as B1), P3HT:CdSe (B2) and P3HT:CdSe:PC71BM (T) active blended material were analyzed in the wavelength range from 350 to 800 nm. The current density-voltage characteristics of the device were measured in dark and under illumination for study of detector detectivities and the contact with electrode. The ratio at -0.5 V for PDs B1, B2 and T is 1.1 × 102, 1.9 × 102 and 1.8 × 103, respectively. The values of detectivity for B1, B2 and T are 1 × 1010, 2 × 1010 and 7 × 1011 Jones, respectively. The for PD T is ten times in comparison with B1 and B2 PDs. The linear dynamic range (LDR) value for ternary device is more than double to both binary PDs. The absorption by CdSe QD increases the photon efficiency in the ternary detector, and at the same time the ternary detectors have high detectivity in broad spectral range. The responsivity of current to the light intensity exponent θ for detector B1, B2 and T is ~0.55, 0.55 and 0.62, respectively, which represents a complex process of electron hole generation, recombination and trapping within active material.

  10. Sonocatalytic degradation of methylene blue by a novel graphene quantum dots anchored CdSe nanocatalyst.

    PubMed

    Sajjadi, Saeed; Khataee, Alireza; Kamali, Mehdi

    2017-11-01

    Cadmium selenide/graphene quantum dots (CdSe/GQDs) nanocatalyst with small band gap energy and a large specific surface area was produced via a facile three-step sonochemical-hydrothermal process. The features of the as-prepared CdSe, GQDs and CdSe/GQDs samples were characterized by photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), diffuse-reflectance spectrophotometer (DRS), and Brunauer-Emmett-Teller (BET) analysis. The sonocatalytic activity of the synthesized CdSe/GQDs was effectively accelerated compared with that of pure CdSe nanoparticles in degradation of methylene blue (MB). The influence of the CdSe/GQDs dosage (0.25-1.25g/L), initial MB concentration (20-30mg/L), initial solution pH (3-12), and ultrasonic output power (200-600W/L) were examined on the sonocatalytic treatment of MB aqueous solutions. The degradation efficiency (DE%) of 99% attained at 1g/L of CdSe/GQDs, 20mg/L of MB, pH of 9, and an output power of 200W/L at 90min of ultrasonic irradiation. Furthermore, DE% increased with addition of K2S2O8 and H2O2 as the enhancers via producing more free radicals. However, addition of sulfate, carbonate, and chloride as radical sweeper decreased DE%. Furthermore, well-reusability of the CdSe/GQDs sonocatalyst was demonstrated for 5 successive runs and some of the sonocatalytic generated intermediates were indicated by GC-MS analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. 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.

  12. Electrochemical preparation of vertically aligned, hollow CdSe nanotubes and their p-n junction hybrids with electrodeposited Cu2O

    NASA Astrophysics Data System (ADS)

    Debgupta, Joyashish; Devarapalli, Ramireddy; Rahman, Shakeelur; Shelke, Manjusha V.; Pillai, Vijayamohanan K.

    2014-07-01

    Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, ``as grown'' CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ~470 μA cm-2) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar device prepared with electrodeposited CdSe films (not nanotubes) and Cu2O on FTO. This has been attributed to the hollow 1-D nature of CdSe NTs, which provides enhanced inner and outer surface areas for better absorption of light and also assists faster transport of photogenerated charge carriers.Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, ``as grown'' CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ~470 μA cm-2) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar

  13. Fortification of CdSe quantum dots with graphene oxide. Excited state interactions and light energy conversion.

    PubMed

    Lightcap, Ian V; Kamat, Prashant V

    2012-04-25

    Graphene based 2-D carbon nanostructures provide new opportunities to fortify semiconductor based light harvesting assemblies. Electron and energy transfer rates from photoexcited CdSe colloidal quantum dots (QDs) to graphene oxide (GO) and reduced graphene oxide (RGO) were isolated by analysis of excited state deactivation lifetimes as a function of degree of oxidation and charging in (R)GO. Apparent rate constants for energy and electron transfer determined for CdSe-GO composites were 5.5 × 10(8) and 6.7 × 10(8) s(-1), respectively. Additionally, incorporation of GO in colloidal CdSe QD films deposited on conducting glass electrodes was found to enhance the charge separation and electron conduction through the QD film, thus allowing three-dimensional sensitization. Photoanodes assembled from CdSe-graphene composites in quantum dot sensitized solar cells display improved photocurrent response (~150%) over those prepared without GO.

  14. Increased carrier mobility and lifetime in CdSe quantum dot thin films through surface trap passivation and doping.

    PubMed

    Straus, Daniel B; Goodwin, E D; Gaulding, E Ashley; Muramoto, Shin; Murray, Christopher B; Kagan, Cherie R

    2015-11-19

    Passivating surface defects and controlling the carrier concentration and mobility in quantum dot (QD) thin films is prerequisite to designing electronic and optoelectronic devices. We investigate the effect of introducing indium in CdSe QD thin films on the dark mobility and the photogenerated carrier mobility and lifetime using field-effect transistor (FET) and time-resolved microwave conductivity (TRMC) measurements. We evaporate indium films ranging from 1 to 11 nm in thickness on top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films and anneal the QD films at 300 °C to densify and drive diffusion of indium through the films. As the amount of indium increases, the FET and TRMC mobilities and the TRMC lifetime increase. The increase in mobility and lifetime is consistent with increased indium passivating midgap and band-tail trap states and doping the films, shifting the Fermi energy closer to and into the conduction band.

  15. Temperature dependence of excitonic radiative decay in CdSe quantum dots: the role of surface hole traps.

    PubMed

    Califano, Marco; Franceschetti, Alberto; Zunger, Alex

    2005-12-01

    Using atomistic, semiempirical pseudopotential calculations, we show that if one assumes the simplest form of a surface state in a CdSe nanocrystal--an unpassivated surface anion site--one can explain theoretically several puzzling aspects regarding the observed temperature dependence of the radiative decay of excitons. In particular, our calculations show that the presence of surface states leads to a mixing of the dark and bright exciton states, resulting in a decrease of 3 orders of magnitude of the dark-exciton radiative lifetime. This result explains the persistence of the zero-phonon emission line at low temperature, for which thermal population of higher-energy bright-exciton states is negligible. Thus, we suggest that surface states are the controlling factor of dark-exciton radiative recombination in currently synthesized colloidal CdSe nanocrystals.

  16. Vacuum evaporated CdSe /SUB 1-x/ Te /SUB x/ thin films for electrochemical photovoltaic cells

    SciTech Connect

    Russak, M.A.; Creter, C.

    1984-03-01

    CdSe /SUB 1-x/ Te /SUB x/ thin films have been produced over a wide range of x values by concurrent vacuum evaporation of the constituent elements. The most consistent results in terms of producing single-phase material were obtained when substrate temperatures were in the range of 350/sup 0/-450/sup 0/C. Photoelectrochemical evaluation of the resultant thin films indicated postdeposition heat-treatment and surface etching were necessary to maximize photovoltaic outputs. A dependence of photoelectrochemical behavior, bandgap, and efficiency on x value was also found. The maximum efficiency recorded was 7.4% for a CdSe /SUB 0.8/ Te /SUB 0.2/ composition under simulated AM2 conditions.

  17. Polarization-sensitive nanowire photodetectors based on solution-synthesized CdSe quantum-wire solids.

    PubMed

    Singh, Amol; Li, Xiangyang; Protasenko, Vladimir; Galantai, Gabor; Kuno, Masaru; Xing, Huili Grace; Jena, Debdeep

    2007-10-01

    Polarization-sensitive photodetectors are demonstrated using solution-synthesized CdSe nanowire (NW) solids. Photocurrent action spectra taken with a tunable white light source match the solution linear absorption spectra of the NWs, showing that the NW network is responsible for the device photoconductivity. Temperature-dependent transport measurements reveal that carriers responsible for the dark current through the nanowire solids are thermally excited across CdSe band gap. The NWs are aligned using dielectrophoresis between prepatterned electrodes using conventional optical photolithography. The photocurrent through the NW solid is found to be polarization-sensitive, consistent with complementary absorption (emission) measurements of both single wires and their ensembles. The range of solution-processed semiconducting NW materials, their facile synthesis, ease of device fabrication, and compatibility with a variety of substrates make them attractive for potential nanoscale polarization-sensitive photodetectors.

  18. Cd/Hg cationic substitution in magic-sized CdSe clusters: Optical characterization and theoretical studies

    NASA Astrophysics Data System (ADS)

    Antanovich, Artsiom; Prudnikau, Anatol; Gurin, Valerij; Artemyev, Mikhail

    2015-07-01

    We examine conversion of magic-sized CdSe clusters (MSCs) into HgSe ones by means of Cd/Hg cation exchange. With this procedure Cd8Cd17- and Cd32-selenide clusters can be converted into corresponding Hg8-, Hg17- and Hg32-selenide ones. Upon cationic exchange MSCs behavior differs from that of bulkier counterparts - larger (2-3 nm) quantum dots. Unlike CdSe colloidal quantum dots, magic-sized clusters are converted in fast and complete manner without a formation of intermediate mixed CdxHg1-x compounds that was established on the basis of optical absorption spectroscopy and chemical composition analysis. These assumptions were supported by DFT quantum chemical calculations performed for Cd8-, Cd17- and Hg8-, Hg17-selenide model clusters. Energies of experimental and calculated optical transitions were compared in order to prove the isostructural character of cationic substitution in magic-sized clusters.

  19. Ligand capping effect for dye solar cells with a CdSe quantum dot sensitized ZnO nanorod photoanode.

    PubMed

    Sun, Xiao Wei; Chen, Jing; Song, Jun Ling; Zhao, De Wei; Deng, Wei Qiao; Lei, Wei

    2010-01-18

    We report a quantum dot sensitized solar cell (QDSSC) with a thioglycolic acid (TGA) capped CdSe quantum dot (QD) sensitized ZnO nanorod photoanode. As revealed by UV-Vis absorption spectrum and transmission electron microscopy, the quantum dots can be effectively adsorbed onto ZnO nanorods. By studying the emission decay, the quenching of the CdSe QDs by ZnO nanorod was verified, and an electron transfer (from QD to ZnO) rate constant of 1 x 10(8) s(-1) was obtained. The efficiency of the as-prepared QDSSC was 0.66% and an incident power conversion efficiency of 22% at 400 nm was achieved.

  20. Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions.

    PubMed

    Raevskaya, Alexandra E; Stroyuk, Alexander L; Kuchmiy, Stephan Ya

    2006-10-01

    Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.

  1. Rapid synthesis of magnetic/luminescent (Fe3O4/CdSe) nanocomposites by microwave irradiation

    NASA Astrophysics Data System (ADS)

    Zedan, Abdallah F.; Abdelsayed, Victor; Mohamed, Mona B.; El-Shall, M. Samy

    2013-01-01

    A rapid microwave-assisted synthesis and detailed characterization of a bifunctional nanocomposite composed of a magnetic core, Fe3O4, and a semiconductor shell, CdSe, are reported. Magnetite Fe3O4 nanoparticles are synthesized and used as seeds for the heterogeneous nucleation and growth of the CdSe nanoshells. The optical properties of the nanocomposites are assessed by UV-Vis and photoluminescence measurements. In addition, the crystalline phase and size distribution of the nanocrystals are determined by XRD and TEM, respectively. The results indicate that the as-prepared nanocomposites are nearly monodisperse with an average size of 10 nm and a quantum yield of 13 %. The synthesized nanocomposites clearly provide both magnetic and luminescent properties which could be useful for simultaneous detection and separation possibly in biomedical applications.

  2. Thiolated DAB dendrimers and CdSe quantum dots nanocomposites for Cd(II) or Pb(II) sensing.

    PubMed

    Algarra, M; Campos, B B; Alonso, B; Miranda, M S; Martínez, A M; Casado, C M; Esteves da Silva, J C G

    2012-01-15

    Four different generation of thiol-DAB dendrimers were synthesized, S-DAB-G(x) (x=1, 2, 3 and 5), and coupled with CdSe quantum dots, to obtain fluorescent nanocomposites as metal ions sensing. Cd(II) and Pb(II) showed the higher enhancement and quenching effects respectively towards the fluorescence of S-DAB-G(5)-CdSe nanocomposite. The fluorescence enhancement provoked by Cd(II) can be linearized using a Henderson-Hasselbalch type equation and the quenching provoked by Pb(II) can be linearized by a Stern-Volmer equation. The sensor responds to Cd(II) ion in the 0.05-0.7μM concentration range and to Pb(II) ion in the 0.01-0.15mM concentration range with a LOD of 0.06mM. The sensor has selectivity limitations but its dendrimer configuration has analytical advantages.

  3. Photoelectrochemical Characterization of Polycrystalline CdSe, CdTe and CuInSe2 Semiconductor Films

    NASA Astrophysics Data System (ADS)

    Koutsikou, R.; Bouroushian, M.

    2010-01-01

    Useful optical parameters of thin semiconducting films can be determined by electrochemical and electrical techniques. This work is an attempt to characterize cathodically electrodeposited binary cadmium chalcogenide (CdSe, CdTe) and ternary Cu-chalcopyrite (CuInSe2) films by photoelectrochemical techniques. Namely, photovoltammetry, photocurrent spectroscopy and onset potential method. Some fundamentals, regarding the estimation of band gap energy and flat band potential values of these semiconductors, are briefly discussed.

  4. Temperature- and field-dependent energy transfer in CdSe nanocrystal aggregates studied by magneto-photoluminescence spectroscopy.

    PubMed

    Blumling, Daniel E; Tokumoto, Takahisa; McGill, Stephen; Knappenberger, Kenneth L

    2012-08-21

    The influence of temperature and applied magnetic fields on photoluminescence (PL) emission and electronic energy transfer (ET) of both isolated and aggregated CdSe nanocrystals was investigated. Following 400-nm excitation, temperature-dependent, intensity-integrated and energy-resolved PL measurements were used to quantify the emission wavelength and amplitude of isolated CdSe nanocrystals. The results indicated an approximately three-fold increase in PL intensity upon decreasing the temperature from 300 K to 6 K; this was attributed to a reduction of charge carrier access to nanocrystal surface trap states and suppression of thermal loss channels. Temperature-dependent PL measurements of aggregated CdSe nanocrystals, which included both energy-donating and -accepting particles, were analyzed using a modified version of Förster theory. Temperature-dependent ET efficiency increased from 0.55 to 0.75 upon decreasing the sample temperature from 225 K to 6 K, and the ET data contained the same trend observed for the PL of isolated nanoclusters. The application of magnetic fields to increase nanocrystal ET efficiency was studied using magneto-photoluminescence measurements recorded at a sample temperature of 1.6 K. We demonstrated that the exciton fine structure population of the donor was varied using applied magnetic fields, which in turn dictated the PL yield and the resultant ET efficiency of the CdSe nanocrystal aggregate system. The experimental data indicated an ET efficiency enhancement of approximately 7%, which was limited by the random orientation of the spherical nanocrystals in the thin film.

  5. Synthesis, Surface Studies, Composition and Structural Characterization of CdSe, Core/Shell, and Biologically Active Nanocrystals

    PubMed Central

    Rosenthal, Sandra J.; McBride, James; Pennycook, Stephen J.; Feldman, Leonard C.

    2011-01-01

    Nanostructures, with their very large surface to volume ratio and their non-planar geometry, present an important challenge to surface scientists. New issues arise as to surface characterization, quantification and interface formation. This review summarizes the current state of the art in the synthesis, composition, surface and interface control of CdSe nanocrystal systems, one of the most studied and useful nanostructures. PMID:21479151

  6. Effects of soluble cadmium salts versus CdSe quantum dots on the growth of planktonic Pseudomonas aeruginosa.

    PubMed

    Priester, John H; Stoimenov, Peter K; Mielke, Randall E; Webb, Samuel M; Ehrhardt, Christopher; Zhang, Jin Ping; Stucky, Galen D; Holden, Patricia A

    2009-04-01

    With their increased use, engineered nanomaterials (ENMs) will enterthe environment where they may be altered by bacteria and affect bacterial processes. Metallic ENMs, such as CdSe quantum dots (QDs), are toxic due to the release of dissolved heavy metals, but the effects of cadmium ions versus intact QDs are mostly unknown. Here, planktonic Pseudomonas aeruginosa PG201 bacteria were cultured with similar total cadmium concentrations as either fully dissolved cadmium acetate (Cd(CH3COO)2) or ligand capped CdSe QDs, and cellular morphology, growth parameters, intracellular reactive oxygen species (ROS), along with the metal and metalloid fates were measured. QDs dissolved partially in growth media, but dissolution was less in biotic cultures compared to sterile controls. Dose-dependent growth effects were similar for low concentrations of either cadmium salts or QDs, but effects differed above a concentration threshold of 50 mg/L(total cadmium basis) where (1) the growth of QD-treated cells was more impaired, (2) the membranes of QD-grown cells were damaged, and (3) QD-grown cells contained QD-sized CdSe cytoplasmic inclusions in addition to Se0 and dissolved cadmium. For most concentrations, intracellular ROS were higher for QD-versus cadmium salts-grown bacteria. Taken together, QDs were more toxic to this opportunistic pathogen than cadmium ions, and were affected by cells through QD extracellular stabilization, intracellular enrichment and cell-associated decay.

  7. Reconstructing a solid-solid phase transformation pathway in CdSe nanosheets with associated soft ligands

    PubMed Central

    Wang, Zhongwu; Wen, Xiao-Dong; Hoffmann, Roald; Son, Jae Sung; Li, Ruipeng; Fang, Chia-Chen; Smilgies, Detlef-M.; Hyeon, Taeghwan

    2010-01-01

    Integrated single-crystal-like small and wide-angle X-ray diffraction images of a CdSe nanosheet under pressure provide direct experimental evidence for the detailed pathway of transformation of the CdSe from a wurtzite to a rock-salt structure. Two consecutive planar atomic slips [(001) 〈110〉 in parallel and (102) with a distortion angle of ∼40°] convert the wurtzite-based nanosheet into a saw-like rock-salt nanolayer. The transformation pressure is three times that in the bulk CdSe crystal. Theoretical calculations are in accord with the mechanism and the change in transformation pressure, and point to the critical role of the coordinated amines. Soft ligands not only increase the stability of the wurtzite structure, but also improve its elastic strength and fracture toughness. A ligand extension of 2.3 nm appears to be the critical dimension for a turning point in stress distribution, leading to the formation of wurtzite (001)/zinc-blende (111) stacking faults before rock-salt nucleation. PMID:20855580

  8. 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

  9. Ab Initio Study of the Effects of Surface Chemistry and Size on Xray Absorption Spectra of CdSe Nanoparticles

    NASA Astrophysics Data System (ADS)

    Whitley, Heather; Prendergast, David; Ogitsu, Tadashi; Schwegler, Eric

    2009-03-01

    The specificity of their opto-electronic properties with respect to size, shape, and surface chemistry, as well as cost-effective solution based methods of synthesis, make CdSe nanoparticles a material of choice for use in novel opto-electronic devices, such as photovoltaics and field effect transistors. Developing methods by which these nanomaterials can be systematically engineered to meet specific device goals is largely dependent on understanding how surface passivation and reconstruction affect the properties of a given nanomaterial. Xray absorption spectroscopy (XAS) is an ideal method for structural analysis, but its application to studying nanomaterial surfaces is nontrivial due to the convolution of the absorption of surface atoms with those within the nanomaterial. We utilize ab initio methods to investigate the dependence of the Cd L-edge xray absorption cross-section on the size and passivation for Cd atoms both at the surface and within the core of CdSe nanomaterials. We aim to enable routine surface characterization of CdSe nanomaterials via XAS. Prepared by LLNL under Contract DE-AC52 07NA27344.

  10. Porous networks of CdSe nanocrystal chains from ultrafine Cd(OH)2 nanowires and their composite materials.

    PubMed

    Ko, Sungwook; Kim, Jeong Won; Moon, Geon Dae; Shim, Hee-Sang; Kim, Won Bae; Jeong, Unyong

    2010-03-16

    Long ultrathin Cd(OH)(2) nanowires have been selectively grown on silica colloids in a basic aqueous condition. The Cd(OH)(2) nanowires could be detached from the surface of the silica colloids by simply applying ultrasonication and then transformed into isolated CdSe nanocrystal chains. When the transformation into CdSe was conducted without detaching the Cd(OH)(2) nanowires, nanoporous CdSe shells composed of wire-like nanocrystal chains were produced. The good solubility of the Cd(OH)(2) nanowires in both hydrophilic and hydrophobic solvents facilitated the formation of composites with quantum dots, magnetic particles, organic molecules, and polymers. Embedding premade quantum dots possessed broad light absorption range and enhanced photoluminescence. Large amount of superparamagnetic particles endowed a fast magnetic response in addition to the fluorescence. Composites of organic/nanocrystal chains were readily fabricated by employing the electrostatic attraction between the positively charged Cd(OH)(2) nanowires and negatively charged polymers or small molecules.

  11. 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.

  12. Improving the sensitivity of indirect-type organic X-ray detector by blending with CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Kim, B.; Lee, J.; Kang, J.

    2017-01-01

    In this study, The blending effect of CdSe quantum dots (QDs) dispersed in a poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) active layer was investigated to improve the sensitivity of indirect-type X-ray detectors. 3 different sizes of CdSe QDs (5, 7, and 9 nm) were blended in P3HT:PCBM (weight ratio of 1:1) layers. The 5 nm-QD blended condition showed relatively high short circuit current density (Jsc), power conversion efficiency (PCE), and sensitivity. The optimal amount of 5nm-QDs in the P3HT:PCBM layer was also investigated in the range of 0 to 4 mg. As the final outcome, the detector fabricated with 3 mg of 5 nm-QDs in the active layer showed the highest sensitivity of 220.08 nC/mR·cm2, which was 28% higher than the sensitivity of the pristine P3HT:PCBM detector. Through the addition of the optimal amount of CdSe QDs to the P3HT:PCBM layer, the sensitivity of the X-ray detector was enhanced due to the increment of photon-absorption and charge transport.

  13. Understanding the electronic structure of CdSe quantum dot-fullerene (C60) hybrid nanostructure for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Sarkar, Sunandan; Rajbanshi, Biplab; Sarkar, Pranab

    2014-09-01

    By using the density-functional tight binding method, we studied the electronic structure of CdSe quantum dot(QD)-buckminsterfullerene (C60) 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-C60 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 C60-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-C60 hybrid systems. This type II band alignment indicates the possibility of application of this nanohybrid for photovoltaic purpose.

  14. HPVB and HPVZM shaped growth of CdZnTe, CdSe, and ZnSe crystals

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Nikolai N.; James, Ralph B.; Berzigiarova, Nadejda S.; Kulakov, Mihail P.

    2003-01-01

    High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth has been applied for manufacturing Cd1-xZnxTe (x = 0.04 - 0.2), CdSe and ZnSe crystal tapes with sizes up to 120×120×12 mm. The influence of the technological parameters of the growth process on the crystal quality and some properties is discussed. The dependence of the inclusion (bubbles) content on deviation from the melt stoichiometry is determined. The method for growing plates with low content of the inclusions is described. High-resistivity crystal tapes of undoped CdZnTe (1010 Ohm×cm), CdSe (1011 Ohm×cm) and ZnSe (>1011 Ohm×cm) were prepared. Possibility of the tape growth on the oriented seed is shown on example of CdSe. The difference between HPVB and HPVZM results is described. Main HPVZM advantage for II-VI compound crystal growth is possibility of obtaining crystals with stoichiometric composition or with controlled deviation from stoichiometry. Hence HPVZM is preferable for growing high-resistivity II-VI crystals with low inclusion content.

  15. Bioinspired, direct synthesis of aqueous CdSe quantum dots for high-sensitive copper(II) ion detection.

    PubMed

    Bu, Xiaohai; Zhou, Yuming; He, Man; Chen, Zhenjie; Zhang, Tao

    2013-11-21

    Luminescent CdSe semiconductor quantum dots (QDs), which are coated with a denatured bovine serum albumin (dBSA) shell, have been directly synthesized via a bioinspired approach. The dBSA coated CdSe QDs are ultrasmall (d < 2.0 nm) with a narrow size distribution and exhibit a strong green fluorescent emission at about 525 nm. They can be stored for months at room temperature and possess excellent stability against ultraviolet irradiation, high salt concentration, and a wide physiological range of pH. Systematic experimental investigations have shown the contribution of dBSA with free cysteine residues for both their effective ion chelating and surface passivating interactions during the formation and stabilization of CdSe QDs. The luminescent QDs are used for copper(II) ion detection due to their highly sensitive and selective fluorescence quenching response to Cu(2+). The concentration dependence of the quenching effect can be best described by the typical Stern-Volmer equation in a linearly proportional concentration of Cu(2+) ranging from 10 nM to 7.5 μM with a detection limit of 5 nM. As confirmed by various characterization results, a possible quenching mechanism is given: Cu(2+) ions are first reduced to Cu(+) by the dBSA shell and then chemical displacement between Cu(+) and Cd(2+) is performed at the surface of the ultrasmall metallic core to impact the fluorescence performance.

  16. A simple and scalable graphenepatterning method and its application in CdSe nanobelt/graphene Schottky junction solar cells

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Gan, Lin; Dai, Lun; Dai, Yu; Guo, Xuefeng; Meng, Hu; Yu, Bin; Shi, Zujin; Shang, Kuanping; Qin, Guogang

    2011-04-01

    We have developed a simple and scalable graphenepatterning method using electron-beam or ultraviolet lithography followed by a lift-off process. This method, with the merits of: high pattern resolution and high alignment accuracy, being free from additional etching or harsh processes, being universal to arbitrary substrates, and being compatible to Si microelectronic technology, can easily be applied to diverse graphene-based devices, especially in array-based applications, where large-scale graphene patterns are desired. We have applied this method to fabricate CdSe nanobelt (NB)/graphene Schottky junction solar cells, which have potential applications in integrated nano-optoelectronic systems. A typical as-fabricated solar cell shows excellent photovoltaic behavior, with an open-circuit voltage of ~0.51 V, a short-circuit current density of ~5.75 mA cm-2, and an energy conversion efficiency of ~1.25%. We attribute the high performance of the cell to the as-patterned high-performance graphene, which can form an ideal Schottky contact with CdSe NB. Our results suggest that both the developed graphenepatterning method and the as-fabricated CdSe NB/graphene Schottky junction solar cells have reachable application prospects.

  17. Phosphine-free synthesis of CdSe quantum dots in a new co-capping ligand system.

    PubMed

    Wang, Chun; Jiang, Yang; Zhang, Zhongping; Li, Guohua; Chen, Lanlan; Jie, Jiansheng

    2009-08-01

    High-quality CdSe quantum dots with zinc blende structure were successfully synthesized via a new cheaper, greener phosphine-free route, using environmentally friendly N,N-dimethyl-oleoyl amide as the solvent of Se. The process eliminates trioctylphoshine from the synthesis, using oleic acid (OA) as a primary capping ligand and benzophenone (BP) as a secondary ligand in the noncoordinating solvent. It has been found that the addition of BP can improve the size distribution (below 10%) of as-synthesized CdSe quantum dots greatly, and the nucleation and growth process can also be well-separated. Moreover, a comprehensive examination on the control of particle size and size distribution was performed by systematically varying the BP/OA molar ratio. The phosphine-free route enables us to obtain high-quality CdSe quantum dots with sharp UV-vis absorption peak, size ranging from 2.8 to 6.8 nm, and narrow full width of half-maximum between 27 and 35 nm with purely band-edge luminescence, and without any post-synthesis processing.

  18. 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

    2015-01-09

    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.

  19. Continuous-flow synthesis of CdSe quantum dots: a size-tunable and scalable approach.

    PubMed

    Mirhosseini Moghaddam, Mojtaba; Baghbanzadeh, Mostafa; Sadeghpour, Amin; Glatter, Otto; Kappe, C Oliver

    2013-08-26

    In recent years, continuous-flow/microreactor processing for the preparation of colloidal nanocrystals has received considerable attention. The intrinsic advantages of microfluidic reactors have opened new opportunities for the size-controlled synthesis of nanocrystals either in the laboratory or on a large scale. Herein, an experimentally simple protocol for the size-tunable continuous-flow synthesis of rather monodisperse CdSe quantum dots (QDs) is presented. CdSe QDs are manufactured by using cadmium oleate as cadmium source, selenium dioxide as selenium precursor, and 1-octadecene as solvent. Exploiting selenium dioxide as selenium source and 1-octadecene as solvent allows execution of the complete process in open air without any requirement for air-free manipulations using a glove box or Schlenk line. Continuous-flow processing is performed with a stainless steel coil of 1.0 mm inner diameter pumping the combined precursor solution through the reactor by applying a standard HPLC pump. The effect of different reaction parameters, such as temperature, residence time, and flow rate, on the properties of the resulting CdSe QDs was investigated. A temperature increase from 240 to 260 °C or an extension of the residence time from 2 to 20 min affords larger nanocrystals (range 3-6 nm) whereas the size distribution does not change significantly. Longer reaction times and higher temperatures result in QDs with lower quantum yields (range 11-28 %). The quality of the synthesized CdSe QDs was confirmed by UV/Vis and photoluminescence spectroscopy, small-angle X-ray scattering, and high-resolution transmission electron microscopy. Finally, the potential of this protocol for large-scale manufacturing was evaluated and by operating the continuous-flow process for 87 min it was possible to produce 167 mg of CdSe QDs (with a mean diameter of 4 nm) with a quantum yield of 28 %.

  20. 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

  1. Fe2+-doped CdSe single crystal: growth, spectroscopic and laser properties, potential use as a 6 µm broadband amplifier

    NASA Astrophysics Data System (ADS)

    Frolov, M. P.; Gordienko, V. M.; Korostelin, Yu V.; Kozlovsky, V. I.; Podmar'kov, Yu P.; Potemkin, F. V.; Skasyrsky, Ya K.

    2017-02-01

    We report on the successful growth of single crystals of Fe2+:CdSe by seeded physical vapor transport (SPVT) technique with doping within the growing process and subsequent annealing in Se vapor. Luminescence lifetime measurements, spectroscopic studies of 5E-5T2 transition of Fe2+ in CdSe, and laser experiments were performed. The lifetime of the 5T2 energy level was measured to be 20  ±  5 ns at a room temperature (RT) of 290 K. At liquid nitrogen (LN) temperature, luminescence kinetics displayed a non-exponential decay, which can be fitted to a bi-exponential function with time constants τ 1  =  6 µs and τ 2  =  29 µs. As much as 3.2 mJ of output energy at 5.2 µm with 27% absorbed pump energy slope efficiency of an Fe2+:CdSe laser was achieved at RT under 2.94 µm nanosecond Er:YAG laser pumping. The Fe2+:CdSe laser was tuned from 4.63 to 6.10 µm. Obtained characteristics of Fe2+:CdSe indicate that the crystal can be considered a promising medium for amplification of femtosecond pulses in the middle infrared range up to 6 µm.

  2. Electrochemical preparation of vertically aligned, hollow CdSe nanotubes and their p-n junction hybrids with electrodeposited Cu2O.

    PubMed

    Debgupta, Joyashish; Devarapalli, Ramireddy; Rahman, Shakeelur; Shelke, Manjusha V; Pillai, Vijayamohanan K

    2014-08-07

    Vertically aligned, hollow nanotubes of CdSe are grown on fluorine doped tin oxide (FTO) coated glass substrates by ZnO nanowire template-assisted electrodeposition technique, followed by selective removal of the ZnO core using NH4OH. A detailed mechanism of nucleation and anisotropic growth kinetics of nanotubes have been studied by a combination of characterization tools such as chronoamperometry, SEM and TEM. Interestingly, "as grown" CdSe nanotubes (CdSe NTs) on FTO coated glass plates behave as n-type semiconductors exhibiting an excellent photo-response (with a generated photocurrent density value of ∼ 470 μA cm(-2)) while in contact with p-type Cu2O (p-type semiconductor, grown separately on FTO plates) because of the formation of a n-p heterojunction (type II). The observed photoresponse is 3 times higher than that of a similar device prepared with electrodeposited CdSe films (not nanotubes) and Cu2O on FTO. This has been attributed to the hollow 1-D nature of CdSe NTs, which provides enhanced inner and outer surface areas for better absorption of light and also assists faster transport of photogenerated charge carriers.

  3. 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.

  4. 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.

  5. Catalytic and catalyst-free synthesis of CdSe nanostructures with single-source molecular precursor and related device application.

    PubMed

    Zhang, Youxiang; Tang, Yun; Lee, Kwan; Ouyang, Min

    2009-01-01

    Air-stable single-source molecular precursor is applied for controlled size and morphology synthesis of one-dimensional and quasi-one-dimensional CdSe nanostructures. Two different growth approaches are compared to control the growth of nanostructures. When combined with well-defined Au colloidal catalysts, the use of single-source molecular precursor allows diameter control synthesis of monodispersed CdSe nanowires from 10-30 nm via a vapor-liquid-solid mechanism. In addition, a variety of CdSe nanostructures with different morphologies can be achieved and tuned without assistance of metallic catalysts by carefully manipulating dynamic thermal decomposition process of single-source molecular precursor. The new level of synthetic control afforded by our present work opens up new opportunities for using as-synthesized CdSe nanostructures as model systems for fundamental studies as well as building blocks for larger scale functional device assembly. Importantly, we demonstrate that a single CdSe tripod can be natively configured as a nanoscale phototransistor in which photocurrent created between two tripod arms can be efficiently modulated by applying a gate voltage through the third arm.

  6. Electron hopping between Wurtzite CdSe Quantum Dots Linked by Molecules

    NASA Astrophysics Data System (ADS)

    Chu, Iek-Heng; Radulaski, Marina; Vukmirovic, Nenad; Cheng, Hai-Ping; Wang, Lin-Wang

    2011-03-01

    Recent experimental results show that the transport properties of quantum dot (QD) arrays will be tremendously improved after attached by cross-linking molecules. Here, we present an ab initio study on the electron hopping rates between wurtzite CdSe QDs connected by Sn 2 S6 molecules. The conduction band minima (CBM) transports among connected QDs are calculated. The charge patching method (CPM) is used to construct the charge density of the QDs and the connected systems. The folded spectrum method (FSM) was applied to find the band edge states and the electronic coupling between the neighboring QDs. Electron-phonon couplings are calculated to yield the reorganization energy. The electron hopping rate is then calculated by Marcus theory and its corresponding quantum treatments. Hopping rates for three different sizes of QDs, and two different types of molecular attachments are also presented here for comparison. Supported by DOE/BES-DE-FG02-02ER45995, DOE/BES-DE-AC02-05CH11231 and NSF/DMR-0804407, and computers from NERSC.

  7. Bent Polytypic ZnSe and CdSe Nanowires Probed by Photoluminescence.

    PubMed

    Kim, Yejin; Im, Hyung Soon; Park, Kidong; Kim, Jundong; Ahn, Jae-Pyoung; Yoo, Seung Jo; Kim, Jin-Gyu; Park, Jeunghee

    2017-03-15

    Nanowires (NWs) have witnessed tremendous development over the past two decades owing to their varying potential applications. Semiconductor NWs often contain stacking faults due to the presence of coexisting phases, which frequently hampers their use. Herein, it is investigated how stacking faults affect the optical properties of bent ZnSe and CdSe NWs, which are synthesized using the vapor transport method. Polytypic zinc blende-wurtzite structures are produced for both these NWs by altering the growth conditions. The NWs are bent by the mechanical buckling of poly(dimethylsilioxane), and micro-photoluminescence (PL) spectra were then collected for individual NWs with various bending strains (0-2%). The PL measurements show peak broadening and red shifts of the near-band-edge emission as the bending strain increases, indicating that the bandgap decreases with increasing the bending strain. Remarkably, the bandgap decrease is more significant for the polytypic NWs than for the single phase NWs. This work provides insights into flexible electronic devices of 1D nanostructures by engineering the polytypic structures.

  8. 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.

  9. 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.

  10. Quenching dynamics in CdSe nanoparticles: surface-induced defects upon dilution.

    PubMed

    Hartmann, Lucia; Kumar, Abhishek; Welker, Matthias; Fiore, Angela; Julien-Rabant, Carine; Gromova, Marina; Bardet, Michel; Reiss, Peter; Baxter, Paul N W; Chandezon, Frédéric; Pansu, Robert B

    2012-10-23

    We have analyzed the decays of the fluorescence of colloidal CdSe quantum dots (QDs) suspensions during dilution and titration by the ligands. A ligand shell made of a combination of trioctylphosphine (TOP), oleylamine (OA), and stearic acid (SA) stabilizes the as-synthesized QDs. The composition of the shell was analyzed and quantified using high resolution liquid state 1H nuclear magnetic resonance (NMR) spectroscopy. A quenching of the fluorescence of the QDs is observed upon removal of the ligands by diluting the stock solution of the QDs. The fluorescence is restored by the addition of TOP. We analyze the results by assuming a binomial distribution of quenchers among the QDs and predict a linear trend in the time-resolved fluorescence decays. We have used a nonparametric analysis to show that for our QDs, 3.0 ± 0.1 quenching sites per QD on average are revealed by the removal of TOP. We moreover show that the quenching rates of the quenching sites add up. The decay per quenching site can be compared with the decay at saturation of the dilution effect. This provides a value of 2.88 ± 0.02 for the number of quenchers per QD. We extract the quenching dynamics of one site. It appears to be a process with a distribution of rates that does not involve the ligands.

  11. Structure and Ultrafast Dynamics of White-Light-Emitting CdSe Nanocrystals

    SciTech Connect

    Bowers, Michael J; McBride, James; Garrett, Maria Danielle; Sammons, Jessica A.; Dukes, Albert; Schreuder, Michael A.; Watt, Tony L.; Lupini, Andrew R; Pennycook, Stephen J; Rosenthal, Sandra

    2009-01-01

    White-light emission from ultrasmall CdSe nanocrystals offers an alternative approach to the realization of solid-state lighting as an appealing technology for consumers. Unfortunately, their extremely small size limits the feasibility of traditional methods for nanocrystal characterization. This paper reports the first images of their structure, which were obtained using aberration-corrected atomic number contrast scanning transmission electron microscopy (Z-STEM). With subangstrom resolution, Z-STEM is one of the few available methods that can be used to directly image the nanocrystal's structure. The initial images suggest that they are crystalline and approximately four lattice planes in diameter. In addition to the structure, for the first time, the exciton dynamics were measured at different wavelengths of the white-light spectrum using ultrafast fluorescence upconversion spectroscopy. The data suggest that a myriad of trap states are responsible for the broad-spectrum emission. It is hoped that the information presented here will provide a foundation for the future development and improvement of white-light-emitting nanocrystals.

  12. Size dependent tunnel diode effects in gold tipped CdSe nanodumbbells

    NASA Astrophysics Data System (ADS)

    Saraf, Deepashri; Kumar, Ashok; Kanhere, Dilip; Kshirsagar, Anjali

    2017-02-01

    We report simulation results for scanning tunneling spectroscopy of gold-tipped CdSe nanodumbbells of lengths ˜27 Å and ˜78 Å. Present results are based on Bardeen, Tersoff, and Hamann formalism that takes inputs from ab initio calculations. For the shorter nanodumbbell, the current-voltage curves reveal negative differential conductance, the characteristic of a tunnel diode. This behaviour is attributed to highly localized metal induced gap states that rapidly decay towards the center of the nanodumbbell leading to suppression in tunneling. In the longer nanodumbbell, these gap states are absent in the central region, as a consequence of which zero tunneling current is observed in that region. The overall current-voltage characteristics for this nanodumbbell are observed to be largely linear near the metal-semiconductor interface and become rectifying at the central region, the nature being similar to its parent nanorod. The cross-sectional heights of these nanodumbbells also show bias-dependence where we begin to observe giant Stark effect features in the semiconducting central region of the longer nanodumbbell.

  13. Effect of oxygen on the properties of encapsulated polycrystalline CdSe films

    SciTech Connect

    Lee, M.J.; Langford, R.M.; Wright, S.W.; Judge, C.P.; Chater, R.J.

    2000-04-01

    This paper presents a comprehensive study of the effects of annealing silicon dioxide encapsulated CdSe films in oxygen on the microstructure, resistivity, photosensitivity and energy levels. The energy levels were investigated by using the independent methods of thermally stimulated current, photocurrent spectral response, and Hall measurements. The film structure is wurtzite with grains of average size 0.25 {micro}m, which extend through the thickness of the films. Annealing the films in oxygen at 450 C increases the resistivity from 10 ohm cm to 10{sup 6} ohm cm. The electron mobility, which has an activation energy of 0.08 eV, remains constant at about 100 cm{sup 2}V{sup {minus}1}s{sup {minus}1} during the anneal steps. The change in the resistivity is due to a combination of thermal rearrangement and oxygen diffusing uniformly into the films. Various energy levels ranging from 0.11 eV to 1.3 eV were detected and the density of all these decreased on annealing.

  14. Directed energy transfer in films of CdSe quantum dots: beyond the point dipole approximation.

    PubMed

    Zheng, Kaibo; Žídek, Karel; Abdellah, Mohamed; Zhu, Nan; Chábera, Pavel; Lenngren, Nils; Chi, Qijin; Pullerits, Tõnu

    2014-04-30

    Understanding of Förster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of QDs, so that the simple point-dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using ultrafast transient absorption spectroscopy and theoretical modeling. Pairwise interdot transfer time was determined in the range of 1.5 to 2 ns by spectral analyses which enable separation of the FRET contribution from intrinsic exciton decay. A rational model is suggested by taking into account the distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate dynamics of directed energy transfer in ordered multilayer QD films, which we also observe experimentally. The Monte Carlo simulations reveal that three ideal QD monolayers can provide exciton funneling efficiency above 80% from the most distant layer. Thereby, utilization of directed energy transfer can significantly improve light harvesting efficiency of QD devices.

  15. Direct Observation of Photoexcited Hole Localization in CdSe Nanorods

    SciTech Connect

    Yang, Ye; Wu, Kaifeng; Shabaev, Andrew; Efros, Alexander L.; Lian, Tianquan; Beard, Matthew C.

    2016-07-08

    Quantum-confined 1D semiconductor nanostructures are being investigated for hydrogen generation photocatalysts. In the photoreaction, after fast electron transfer, holes that remain in the nanostructure play an important role in the total quantum yield of hydrogen production. Unfortunately, knowledge of hole dynamics is limited due to lack of convenient spectroscopic signatures. Here, we directly probe hole localization dynamics within CdSe nanorods (NRs) by combining transient absorption (TA) and time-resolved terahertz (TRTS) spectroscopy. We show that when methylene blue is used as an electron acceptor, the resulting electron transfer occurs with a time constant of 3.5 +/- 0.1 ps and leaves behind a delocalized hole. However, the hole quickly localizes in the Coulomb potential well generated by the reduced electron acceptor near the NR surface with time constant of 11.7 +/- 0.2 ps. Our theoretical investigation suggests that the hole becomes confined to a ~ +/-0.8 nm region near the reduced electron acceptor and the activation energy to detrap the hole from the potential well can be as large as 235 meV.

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

    SciTech Connect

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

    2016-05-23

    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.

  17. Size Dependence of Fluorescence Blinking Statistics from CdSe Nanorods

    NASA Astrophysics Data System (ADS)

    Wang, Siying; Querner, Claudia; Emmons, Thomas; Drndic, Marija; Crouch, Catherine

    2007-03-01

    We report fluorescence blinking statistics measured from single CdSe nanorods (NRs) of seven different sizes with aspect ratios ranging from 3 to 11. The off-times follow a power-law probability distribution; on-times follow a truncated power law distribution, P(τon)˜τon^-αe^-τon/τc. At fixed excitation intensity, the truncation rate 1/τc increases with increasing aspect ratio. For a particular sample, 1/τc increases gradually with increasing excitation intensity. Examining 1/τc vs. single-particle photon absorption rate for all samples indicates that the shape dependence of the absorption cross-section does not fully account for the observed variation in crossover time τc. Surprisingly, we observe no significant difference between core and core/shell nanorods or core rods with different surface ligands. Our results suggest that NR internal structural defects or degree of quantum confinement may contribute to the shape dependence of the crossover time.

  18. CdSe quantum-dot-sensitized solar cell with ∼100% internal quantum efficiency.

    PubMed

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

    2010-11-23

    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 TiO(2) film (NQD/TiO(2)), aqueous Na(2)S or Li(2)S electrolyte, and a Pt counter electrode. We show that light harvesting efficiency (LHE) of the NQD/TiO(2) 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/TiO(2) 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 Li(2)S 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.

  19. Nanodomain fragmentation and local rearrangements in CdSe under pressure

    PubMed Central

    Leoni, Stefano; Ramlau, Reiner; Meier, Katrin; Schmidt, Marcus; Schwarz, Ulrich

    2008-01-01

    Structural transformations in extended solids result from local atomic rearrangements and phase growth mechanisms. A broad class of technologically relevant properties critically depends on local structural issues connected with domain sizes, domain boundary geometries, and defects. However, a precise understanding of structural transformation mechanisms and domain formation is still an open question. Here, we demonstrate the feasibility of very detailed mechanistic investigations in real materials as a prerequisite for intelligent property control. We address the problem of domain fragmentation in bulk CdSe under pressure, jointly by molecular dynamics simulations, high-pressure experiments, and HR-TEM imaging. We show that domain fragmentation is taking place in the high-pressure regime, where nucleation events generate both zinc blende (B3) and wurtzite (B4) structural motifs and, in turn, cause the final lamellar appearance observable by high-resolution TEM. A changed nucleation pattern and a modified B3/B4 ratio represents the system's response to modified external stress conditions. PMID:19052229

  20. Time-resolved emission spectroscopy of CdSe quantum dots in polar and nonpolar solvents

    NASA Astrophysics Data System (ADS)

    Kloepfer, Jeremiah; Bradforth, Stephen; Nadeau, Jay

    2004-03-01

    Nanocrystal quantum dots (QD) offer the opportunity to study semiconductors in liquid environments. QD biological labels in water are often protected from emission quenching and surface oxidation. We wish to exploit these processes to construct novel "on/off" sensors based on energy and electron transfer. These systems offer the chance to probe the semiconductor surface-solvent interface. Time-correlated-single-photon-counting was used to measure the emission lifetimes of several QD-solvent systems. Typical lifetimes could be divided into fast single exponential ( 100 ps) and slow stretched exponential ( 10 ns) decays. CdSe and ZnS(CdSe) were prepared in non-polar solvents with high quantum yields. QD were solubilized in water with thiol-compounds, polymer/protein coats, and micelles/vesicles. Large changes in the emission profiles of the different systems were observed. Systems in water experienced a reduction in quantum yield and loss of the longtime emission decay. Surface oxidation lead to a recovery of the longtime decay which matched that of the ZnS-capped counterpart in non-polar solvents. Lifetimes of QD in the presence of energy/electron transfer donors/acceptors was measured to test the viability of constructing nanocrystal sensors that exploit these processes.

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

    DOE PAGES

    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

  2. The role of ligands in the optical and electronic spectra of CdSe nanoclusters

    SciTech Connect

    Kilina, Svletana; Sergei, Ivanov A; Victor, Klimov I; Sergei, Tretiak

    2008-01-01

    We investigate the impact of ligands on morphology, electronic structure, and optical response of the Cd33Se33 cluster, which already overlapps in size with the smallest synthesized CdSe quantum dots (QDs). Our Density Functional Theory (DFT) calculations demonstrate significant surface reorganization both for the bare cluster and for the cluster capped by amine and phosphine oxide ligand models. We observe strong surface-ligand interactions leading to substantial charge redistribution and polarization effects on the surface. This effect results in the appearance of hybridized states, where the electronic density is spread over the cluster and the ligands. Neither the ligand's nor hybridized molecular orbitals appear as trap states inside or near the band gap of the QD. Instead, being optically dark, dense hybridized states from the edges of the valence and the conduction bands could open new relaxation channels for high energy photoexcitations. Comparing quantum dots passivated by different ligands, we found that hybridized states are denser in at the edge of the conduction band of the cluster ligated with phosphine oxide molecules than that with primary amines. Such a different manifestation of ligand binding may potentially lead to the faster electron relaxation in dots passivated by phosphine oxide than by amine ligands, which is in agreement with experimental data.

  3. Contactless microwave study of dispersive transport in thin film CdSe

    NASA Astrophysics Data System (ADS)

    Grabtchak, Serguei Yu; Cocivera, Michael

    1996-01-01

    The contactless microwave technique was used to measure light-induced transients in the power absorbed by thin films of polycrystalline CdSe. Because the rise time of the microwave cavity was 60 ns, the analysis was limited to 100 ns or longer. Measurement of these transients at a number of fixed frequencies across the ``dark'' resonance frequency made reconstruction of the difference signal possible. This signal, which represents the difference between the ``dark'' and ``light'' Lorentz resonance curves, was determined at various times during the decay. Analysis of these signals provided the time dependence for the changes in the real and imaginary parts of the dielectric constant, which correspond to the densities of the trapped and free electrons. The decays of these parameters were characterized by three time domains. At the shortest times, the two parameters did not have the same time dependence. At intermediate times, the densities of both the trapped and free electrons had the same time dependence characterized by a power law decay, and a mechanism consistent with these results involves rapid equilibration between the free electrons and those in the shallow traps. Decay in this region was consistent with a dispersive transport mechanism. Intensity effects indicate saturation of the shallow traps. The third region occurred at the break in the power law dependence indicating a bimolecular recombination process. Measurements at higher temperatures indicate a change from a bimolecular to a monomolecular recombination mechanism.

  4. Picosecond energy transfer and multiexciton transfer outpaces Auger recombination in binary CdSe nanoplatelet solids

    NASA Astrophysics Data System (ADS)

    Rowland, Clare E.; Fedin, Igor; Zhang, Hui; Gray, Stephen K.; Govorov, Alexander O.; Talapin, Dmitri V.; Schaller, Richard D.

    2015-05-01

    Fluorescence resonance energy transfer (FRET) enables photosynthetic light harvesting, wavelength downconversion in light-emitting diodes (LEDs), and optical biosensing schemes. The rate and efficiency of this donor to acceptor transfer of excitation between chromophores dictates the utility of FRET and can unlock new device operation motifs including quantum-funnel solar cells, non-contact chromophore pumping from a proximal LED, and markedly reduced gain thresholds. However, the fastest reported FRET time constants involving spherical quantum dots (0.12-1 ns; refs , , ) do not outpace biexciton Auger recombination (0.01-0.1 ns; ref. ), which impedes multiexciton-driven applications including electrically pumped lasers and carrier-multiplication-enhanced photovoltaics. Few-monolayer-thick semiconductor nanoplatelets (NPLs) with tens-of-nanometre lateral dimensions exhibit intense optical transitions and hundreds-of-picosecond Auger recombination, but heretofore lack FRET characterizations. We examine binary CdSe NPL solids and show that interplate FRET (˜6-23 ps, presumably for co-facial arrangements) can occur 15-50 times faster than Auger recombination and demonstrate multiexcitonic FRET, making such materials ideal candidates for advanced technologies.

  5. 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.

  6. Resonance Raman and photoluminescence excitation profiles and excited-state dynamics in CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Baker, Joshua A.; Kelley, David F.; Kelley, Anne Myers

    2013-07-01

    Resonance Raman excitation profiles for the longitudinal optical (LO) phonon fundamental and its first overtone have been measured for organic ligand capped, wurtzite form CdSe nanocrystals of ˜3.2 nm diameter dissolved in chloroform. The absolute differential Raman cross-section for the fundamental is much larger when excited at 532 or 543 nm, on the high-frequency side of the lowest-wavelength absorption maximum, than for excitation in the 458-476 nm range although the absorbance is higher at the shorter wavelengths. That is, the quantum yield for resonance Raman scattering is reduced for higher-energy excitation. In contrast, the photoluminescence quantum yield is relatively constant with wavelength. The optical absorption spectrum and the resonance Raman excitation profiles and depolarization dispersion curves are reproduced with a model for the energies, oscillator strengths, electron-phonon couplings, and dephasing rates of the multiple low-lying electronic excitations. The Huang-Rhys factor for LO phonon in the lowest excitonic transition is found to lie in the range S = 0.04-0.14. The strong, broad absorption feature about 0.5 eV above the lowest excitonic peak, typically labeled as the 1P3/21Pe transition, is shown to consist of at least two significant components that vary greatly in the magnitude of their electron-phonon coupling.

  7. Interaction of β-cyclodextrin-capped CdSe quantum dots with inorganic anions and cations.

    PubMed

    Shang, Zhuo Bin; Hu, Shuang; Wang, Yu; Jin, Wei Jun

    2011-01-01

    A facile method was developed for the preparation of water soluble β-Cyclodextrin (β-CD)-modified CdSe quantum dots (QDs) (β-CD-QDs) by directly replacing the oleic acid ligands on the QDs surface with β-CD in an alkaline aqueous solution. The as-prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of β-CD-QDs. Among them, H(2)PO(4)(-) exhibited the largest quenching effect. For the polyprotic acids (HO)(3)AO, the effect of acidic anions on the fluorescence of β-CD-QDs was in the order: monoanion (HO)(2)AO(2)(-) > dianion (HO)AO(3)(2-) > trianion AO(4)(3-). After photoactivation for several days in the presence of anions at alkaline pH, the β-CD-QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the β-CD-QDs was investigated further. It was found that Ag(+), Hg(2+) and Co(2+) have significant quenching effect on the fluorescence of the β-CD-QDs. The Stern-Volmer quenching constants increased in the order: Hg(2+) < Co(2+)

  8. Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

    SciTech Connect

    Albert, VV; Ivanov, SA; Tretiak, S; Kilina, SV

    2011-07-07

    Simulations of ligated semiconductor quantum dots (QDs) and their physical properties, such as morphologies, QD-ligand interactions, electronic structures, and optical transitions, are expected to be very sensitive to computational methodology. We utilize Density Functional Theory (DFT) and systematically study how the choice of density functional, atom-localized basis set, and a solvent affects the physical properties of the Cd{sub 33}Se{sub 33} cluster ligated with a trimethyl phosphine oxide ligand. We have found that qualitative performance of all exchange-correlation (XC) functionals is relatively similar in predicting strong QD-ligand binding energy ({approx}1 eV). Additionally, all functionals predict shorter Cd-Se bond lengths on the QD surface than in its core, revealing the nature and degree of QD surface reconstruction. For proper modeling of geometries and QD-ligand interactions, however, augmentation of even a moderately sized basis set with polarization functions (e.g., LANL2DZ* and 6-31G*) is very important. A polar solvent has very significant implications for the ligand binding energy, decreasing it to 0.2-0.5 eV. However, the solvent model has a minor effect on the optoelectronic properties, resulting in persistent blue shifts up to {approx}0.3 eV of the low-energy optical transitions. For obtaining reasonable energy gaps and optical transition energies, hybrid XC functionals augmented by a long-range Hartree-Fock orbital exchange have to be applied.

  9. Size dependent tunnel diode effects in gold tipped CdSe nanodumbbells.

    PubMed

    Saraf, Deepashri; Kumar, Ashok; Kanhere, Dilip; Kshirsagar, Anjali

    2017-02-07

    We report simulation results for scanning tunneling spectroscopy of gold-tipped CdSe nanodumbbells of lengths ∼27 Å and ∼78 Å. Present results are based on Bardeen, Tersoff, and Hamann formalism that takes inputs from ab initio calculations. For the shorter nanodumbbell, the current-voltage curves reveal negative differential conductance, the characteristic of a tunnel diode. This behaviour is attributed to highly localized metal induced gap states that rapidly decay towards the center of the nanodumbbell leading to suppression in tunneling. In the longer nanodumbbell, these gap states are absent in the central region, as a consequence of which zero tunneling current is observed in that region. The overall current-voltage characteristics for this nanodumbbell are observed to be largely linear near the metal-semiconductor interface and become rectifying at the central region, the nature being similar to its parent nanorod. The cross-sectional heights of these nanodumbbells also show bias-dependence where we begin to observe giant Stark effect features in the semiconducting central region of the longer nanodumbbell.

  10. Study of substrate diffusion in epitaxial n-type CdSe films grown on GaAs (001) by pulsed laser ablation

    SciTech Connect

    Park, J.; Rouleau, C.M.; Lowndes, D.H.

    1998-04-01

    N-type CdSe films with thicknesses of 470--630 nm were grown on (001) and 2{degree}-miscut GaAs wafers by ArF (193 nm) pulsed laser ablation of stoichiometric CdSe targets at platen temperatures (T{sub p}) of 250--425 C in vacuum and ambient Ar gas. Film-substrate interdiffusion was studied with Auger depth profiling, as well as energy dispersive x-ray fluorescent spectroscopy (EDS). Both techniques showed that extensive interdiffusion took place at the film-substrate interface for CdSe films grown at T{sub p} {ge} 355 C but was greatly reduced at T{sub p} = 250 C. Tilting the substrate to be approximately parallel to the ablation plume as well as decreasing the ambient gas pressure also reduced film-substrate interdiffusion.

  11. 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)

  12. The properties of vacuum-evaporated CdS and CdSe double layered films doping with copper and chlorine

    SciTech Connect

    Gu, P.F.; Li, H.F.; Zhu, Z.C.; Tang, J.F.

    1993-12-31

    The effect of doping with copper and chlorine on various properties of vacuum-evaporated CdS and CdSe double layers has been studied. The properties specifically studied were: (1) the dark conductivity and photoconductivity as functions of the doping concentration and the ratio of copper to chlorine, (2) the response time of various photoconductive films and (3) the optical absorption and spectral response. It was found that the dark conductivity decreases and the photoconductivity increases significantly if the ratio of Cu to Cl is suitable. The response time was about 5--10 ms for doping films and more than 100 ms for undoping ones. The optical absorption increases and the spectral response moves to a longer wavelength as the concentration of CdSe increases. The response wavelength can be changed by adjusting the thickness ratio of CdS to CdSe.

  13. 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.

  14. 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

    2010-11-08

    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.

  15. 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.

  16. The influence of sequential ligand exchange and elimination on the performance of P3HT: CdSe quantum dot hybrid solar cells.

    PubMed

    Lee, Donggu; Lim, Jaehoon; Park, Myeongjin; Kim, Jun Young; Song, Jiyun; Kwak, Jeonghun; Lee, Seonghoon; Char, Kookheon; Lee, Changhee

    2015-11-20

    We report on a sequential ligand exchange and elimination process for the fast and easy surface modification of CdSe quantum dots (QDs) in order to improve the electronic interaction between poly(3-hexylthiophene) (P3HT) and CdSe QDs in P3HT:CdSe hybrid solar cells. We systematically investigated the influence of surface treatment on the insulating ligand shell of CdSe QDs using (1)H-NMR analysis, and correlated their influence on the photovoltaic properties of P3HT:CdSe hybrid solar cells. A decrease in the average thickness of the ligand shells directly improved carrier transport properties. Moreover, the presence of remnant 1-hexylamine ligands provided efficient surface trap passivation. As a result, overall solar cell performance (especially fill factor and power conversion efficiency) was enhanced and the recombination mechanism was dominated by monomolecular recombination due to enhanced carrier collection length (l(C0)).

  17. ZnO nanosheets decorated with CdSe and TiO2 for the architecture of dye-sensitized solar cells.

    PubMed

    Kim, Young Tae; Park, Mi Yeong; Choi, Kang Ho; Tai, Wei Sheng; Shim, Won Hyun; Park, Sun-Young; Kang, Jae-Wook; Lee, Kyu Hwan; Jeong, Yongsoo; Kim, Young Dok; Lim, Dong Chan

    2011-03-01

    Pure and TiO2- and CdSe-deposited ZnO nanosheets aligned vertically to the surface of ITO (Indium tin oxide) are prepared using electrodeposition, which is used for building blocks of dye sensitized solar cell. A significant improvement in the photovoltaic efficiency can be obtained by depositing TiO2 or CdSe on ZnO. Photoluminescence spectra show that the TiO2 and CdSe nanostructures suppress the recombination of the electron-hole pair of ZnO. We suggest that the interface charge transfer at TiO2-ZnO and CdSe-ZnO should be responsible for the suppression of the electron-hole pair recombination and enhanced solar cell efficiency by TiO2 and CdSe nanostructures.

  18. A simple and facile synthesis of MPA capped CdSe and CdSe/CdS core/shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Sukanya, D.; Sagayaraj, P.

    2015-06-01

    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).

  19. LETTER TO THE EDITOR: Photoluminescence properties of single CdSe quantum dots in ZnSe obtained by self-organized growth

    NASA Astrophysics Data System (ADS)

    Shen, M. Y.; Goto, T.; Kurtz, E.; Zhu, Z.; Yao, T.

    1998-03-01

    The photoluminescence of single CdSe quantum dots in ZnSe grown by molecular beam epitaxy and that of the same system grown by atomic layer epitaxy were investigated. The spectral diffusion and on/off behaviour of single CdSe quantum dots were observed, and the spectral diffusion range was only about 1 meV. The spectral peak shifting became quicker as the temperature rose. The spectral change from blue-shift to red-shift (or vice versa) was much quicker than that found in CdSe quantum dots synthesized as colloids. The phenomena are qualitatively explained by a Stark effect which originated from an Auger ionization process. The spectral diffusion may be a common property among single quantum dots.

  20. Optically enhanced SnO2/CdSe core/shell nanostructures grown by sol-gel spin coating method

    NASA Astrophysics Data System (ADS)

    Kumar, Vijay; Rajaram, P.; Goswami, Y. C.

    2015-08-01

    Synthesis of SnO2/CdSe metal oxide/ chalcogenide nanostructures on glass micro slides using ultrasonic sol-gel process followed by spin coating has been reported. Stannous chloride, cadmium chloride and selenium dioxide compounds were used for Sn, Cd and Se precursors respectively. Ethylene glycol was used as complexing agent. The samples were characterized by XRD, SEM, AFM and UV-spectrophotometer. All the peaks shown in diffractograms are identified for SnO2. Peak broadening observed in core shell due to stress behavior of CdSe lattice. Scanning electron microscope and AFM exhibits the conversion of cluster in to nanorods structures forms. Atomic force microscope shows the structures in nanorods form and a roughness reduced 1.5194 nm by the deposition of CdSe. Uv Visible spectra shows a new absorption edge in the visible region make them useful for optoelectronic applications.

  1. Optically enhanced SnO{sub 2}/CdSe core/shell nanostructures grown by sol-gel spin coating method

    SciTech Connect

    Kumar, Vijay Goswami, Y. C.; Rajaram, P.

    2015-08-28

    Synthesis of SnO{sub 2}/CdSe metal oxide/ chalcogenide nanostructures on glass micro slides using ultrasonic sol-gel process followed by spin coating has been reported. Stannous chloride, cadmium chloride and selenium dioxide compounds were used for Sn, Cd and Se precursors respectively. Ethylene glycol was used as complexing agent. The samples were characterized by XRD, SEM, AFM and UV-spectrophotometer. All the peaks shown in diffractograms are identified for SnO{sub 2}. Peak broadening observed in core shell due to stress behavior of CdSe lattice. Scanning electron microscope and AFM exhibits the conversion of cluster in to nanorods structures forms. Atomic force microscope shows the structures in nanorods form and a roughness reduced 1.5194 nm by the deposition of CdSe. Uv Visible spectra shows a new absorption edge in the visible region make them useful for optoelectronic applications.

  2. Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Sauvage, Frédéric; Davoisne, Carine; Philippe, Laetitia; Elias, Jamil

    2012-10-01

    We investigated CdSe-sensitized TiO2 solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO2 gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO2 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 TiO2-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 TiO2 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 (Voc = 485 mV, Jsc = 4.26 mA cm -2, ff=0.37).

  3. 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

    2012-10-05

    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).

  4. Effect of CdSe nanoparticles on the fluorescence spectra of conjugate polymer P3HT: An experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Mastour, Nouha; Bouchriha, Habib

    2016-11-01

    In this work we have investigated the effect of CdSe nanoparticles (Nps) on the fluorescence spectra of conjugate polymer Poly(3-hexylthiophene-2,5-diyl) (P3HT). The fluorescence intensity is significantly decreased in both solution and solid films by the incorporation of CdSe Nps. This observed effect in the nanocomposite P3HT-CdSe is analyzed by using the Franck-Condon theory which reproduces correctly the decrease of the fluorescence with the Nps concentration and permits to reach the Huang-Rhys factor and the relaxation energy which are shown efficient to explain the fluorescence quenching.

  5. CdSe-CdS nanoheteroplatelets with efficient photoexcitation of central CdSe region through epitaxially grown CdS wings.

    PubMed

    Prudnikau, Anatol; Chuvilin, Andrey; Artemyev, Mikhail

    2013-10-02

    We synthesized a new type of optically active semiconductor nanoheterostructure based on CdSe nanoplatelets with epitaxially grown CdS flat branches or wings. CdS branches work as efficient photonic antenna in the blue spectral region, enhancing the excitation of CdSe band edge emission. The formation of CdSe-CdS nanoheteroplatelets instead of CdSe/CdS core-shell nanoplatelets was achieved using short-chain Cd ethylhexanoate and sulfur in octadecene as precursors for CdS overgrowth in the presence of acetate salt.

  6. General shape control of colloidal CdS, CdSe, CdTe quantum rods and quantum rod heterostructures.

    PubMed

    Shieh, Felice; Saunders, Aaron E; Korgel, Brian A

    2005-05-12

    We report a general synthetic method for the formation of shape-controlled CdS, CdSe and CdTe nanocrystals and mixed-semiconductor heterostructures. The crystal growth kinetics can be manipulated by changing the injection rate of the chalcogen precursor, allowing the particle shape-spherical or rodlike-to be tuned without changing the underlying chemistry. A single injection of precursor leads to isotropic spherical growth, whereas multiple injections promote epitaxial growth along the length of the c-axis. This method was extended to produce linear type I and type II semiconductor nanocrystal heterostructures.

  7. Properties of electrospun CdS and CdSe filled poly(methyl methacrylate) (PMMA) nanofibres

    SciTech Connect

    Mthethwa, T.P.; Moloto, M.J.; De Vries, A.; Matabola, K.P.

    2011-04-15

    Graphical abstract: SEM images of CdS/PMMA showing coiling as loading of CdS nanoparticles is increased. Thermal stability is increased with increase in %loading of both CdS and CdSe nanoparticles. Research highlights: {yields} TOPO-capped CdS and HDA-capped CdSe nanoparticles were synthesized and fully characterized. {yields} The nanoparticles were mixed with the polymer, PMMA using electrospinning technique using 2, 5 and 10% weight loadings. {yields} The mixture was spun to produce fibres with optical and thermal properties showing significant change and also the increase in loading causing bending or spiraling. {yields} Both TEM images for nanoparticles and SEM for fibres shows the morphology and sizes of the particles. -- Abstract: Electrospinning technique was used to fabricate poly(methyl methacrylate) (PMMA) fibres incorporating CdS and CdSe quantum dots (nanoparticles). Different nanoparticle loadings (2, 5 and 10 wt% with respect to PMMA) were used and the effect of the quantum dots on the properties of the fibres was studied. The optical properties of the hybrid composite fibres were investigated by photoluminescence and UV-vis spectrophotometry. Scanning electron microscopy (SEM), X-ray diffraction and FTIR spectrophotometry were also used to investigate the morphology and structure of the fibres. The optical studies showed that the size-tunable optical properties can be achieved in the polymer fibres by addition of quantum dots. SEM images showed that the morphologies of the fibres were dependent on the added amounts of quantum dots. A spiral type of morphology was observed with an increase in the concentration of CdS and CdSe nanoparticles. Less beaded structures and bigger diameter fibres were obtained at higher quantum dot concentrations. X-ray diffractometry detected the amorphous peaks of the polymer and even after the quantum dots were added and the FTIR analysis shows that there was no considerable interaction between the quantum dots and the

  8. Scanning near-field optical microscope working with a CdSe /ZnS quantum dot based optical detector

    NASA Astrophysics Data System (ADS)

    Aigouy, L.; Samson, B.; Julié, G.; Mathet, V.; Lequeux, N.; Nı. Allen, C.; Diaf, H.; Dubertret, B.

    2006-06-01

    We have developed a scanning near-field optical microscope that uses a subwavelength-sized silica sphere covered with CdSe /ZnS quantum dots as a fluorescent optical detector. Due to the good photostability of these semiconducting particles, we are routinely able to perform several successive scans without a noticeable decrease of fluorescence signals. As an example, we will show some images of the light immediately transmitted through 300nm wide slits made in a thin gold film. We will also discuss the advantages of such fluorescent probes compared to other near-field optical techniques.

  9. 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.

  10. Synthesis of CdSe quantum dots with luminescence in the violet region of the solar spectrum.

    PubMed

    Shukla, Nisha; Nigra, Michael M

    2010-01-01

    We have designed a simple, one-step synthesis of CdSe quantum dots with photoluminescence frequencies ranging from the red through to the violet region of the solar spectrum. The photoluminescence peaks have FWHM of 30 nm indicating absorption over a narrow range of wavelengths. The effect of solvent type and solvent boiling point on the physical and photoluminescence properties of the quantum dots has been studied. High boiling point, non-polar solvents shift the photoluminescence peak to longer wavelengths and low boiling point, polar solvents shift the photoluminescence peak to shorter wavelengths.

  11. Temperature and Wavelength Dependence of Energy Transfer Process Between Quantized States and Surface States in CdSe Quantum Dots.

    PubMed

    Zhang, Lei; Xu, Qinfeng; Liu, Mingliang; Kong, Lingbin; Jiao, Mengmeng; Mu, Haifeng; Wang, Dehua; Wang, Honggang; Chen, Jiannong; Yang, Chuanlu

    2017-12-01

    Temperature and wavelength dependence of energy transfer (ET) process between quantized states and surface trap states of CdSe quantum dots was investigated, respectively. The experimental results demonstrate that the photoluminescence (PL) intensity of the quantized states decreases with respect to the trap state emission, especially at lower temperatures. The observed ET process between quantized states and trap states which is influenced by the thermal population behavior. At the same temperature, the silver films can greatly enhance the energy transfer (ET) rate from the quantized states to trap states due to surface plasmonic coupling effect.

  12. Luminescence of CdSe quantum dots near a layer of silver nanoparticles ion-synthesized in sapphire

    NASA Astrophysics Data System (ADS)

    Galyametdinov, Yu. G.; Shamilov, R. R.; Nuzhdin, V. I.; Valeev, V. F.; Stepanov, A. L.

    2016-11-01

    We study the characteristics of the luminescence of composite films based on polymethyl methacrylate with CdSe quantum dots deposited from solution onto the surface of a sapphire substrate containing a preliminarily formed layer with ion-synthesized silver nanoparticles. The sapphire layer with silver nanoparticles exhibits selective plasmon absorption in the visible spectral range with a peak at 463 nm. Enhancement in the exciton luminescence intensity of quantum dots with a peak at 590 nm is observed upon excitation at wavelengths lying in the region of plasmon resonance of metal nanoparticles, as well as luminescence quenching for quantum dots located in the vicinity of silver nanoparticles.

  13. Competition effects among size, dimensionality and pressure on modulating bandgap of CdSe and ZnO nanocrystals

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao Bao; Sheng, Hong Chao; Gu, Xiao Yan; Shi, Ming Xiao

    2015-12-01

    Size, dimensionality and pressure play important roles on modulating band gap (Eg) of semiconductor nanocrystals, and have attracted extensive attention in recent years. In this letter, a simple thermodynamic model is developed and the competition relation among size, dimensionality and pressure effects on Eg is discussed. The accuracy of our prediction is confirmed by the experimental data and simulation results of CdSe and ZnO nanocrystals. This model provides a new insight into the size, dimensionality and pressure effects on Eg and guides the optimal selection as design quantum devices.

  14. Size and ligand effects on the electrochemical and spectroelectrochemical responses of CdSe nanocrystals.

    PubMed

    Querner, Claudia; Reiss, Peter; Sadki, Said; Zagorska, Malgorzata; Pron, Adam

    2005-09-07

    The electrochemical properties of CdSe quantum dots with electrochemically inactive surface ligands (TOPO) have been investigated in comparison with the analogous nanocrystals containing electrochemically active oligoaniline ligands. The TOPO-capped nanocrystals have been studied in a wide size range (from 3 to 6.5 nm) with the goal to amplify the influence of the quantum confinement effect on the electrochemical response. The determined HOMO and LUMO levels have been found in good agreement with the ones obtained from photoluminescence studies and those predicted theoretically. Ligand exchange with aniline tetramer significantly influences the voltammetric peaks associated with the HOMO oxidation and the LUMO reduction of the quantum dots, which are shifted to higher and lower potentials, respectively. These shifts are interpreted in terms of the positive ligand charging which precedes the oxidation of the nanocrystals and the insulating nature of the ligand in the case of the nanocrystal reduction. The ligand-nanocrystal interactions have also been studied by UV-Vis-NIR and Raman spectroelectrochemistry in comparison with a specially prepared model compound which, apart from the anchoring function is identical to the grafted oligoaniline ligand. Both spectroelectrochemical techniques clearly indicate the same nature of the oxidation/reduction pathway for both the model compound and the grafted ligand. The influence of the grafting is manifested by a shift in the onset of the ligand oxidation as compared to the case of the "free" model compound. Since both components (ligands and nanocrystals) mutually influence their electrochemical and spectroelectrochemical properties, the newly developed system can be considered as a true molecular hybrid. Such hybrids are of interest because the potential zone of the ligand electroactivity is well separated from that of the nanocrystals and, as a result, the organic part can be electrochemically switched between the

  15. 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)]. Copyright © 2010 Elsevier B.V. All rights reserved.

  16. Determination of dispersive optical constants of nanocrystalline CdSe (nc-CdSe) thin films

    SciTech Connect

    Sharma, Kriti; Al-Kabbi, Alaa S.; Saini, G.S.S.; Tripathi, S.K.

    2012-06-15

    Highlights: ► nc-CdSe thin films are prepared by thermal vacuum evaporation technique. ► TEM analysis shows NCs are spherical in shape. ► XRD reveals the hexagonal (wurtzite) crystal structure of nc-CdSe thin films. ► The direct optical bandgap of nc-CdSe is 2.25 eV in contrast to bulk (1.7 eV). ► Dispersion of refractive index is discussed in terms of Wemple–DiDomenico single oscillator model. -- Abstract: The nanocrystalline thin films of CdSe are prepared by thermal evaporation technique at room temperature. These thin films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). The transmission spectra are recorded in the transmission range 400–3300 nm for nc-CdSe thin films. Transmittance measurements are used to calculate the refractive index (n) and absorption coefficient (α) using Swanepoel's method. The optical band gap (E{sub g}{sup opt}) has been determined from the absorption coefficient values using Tauc's procedure. The optical constants such as extinction coefficient (k), real (ε{sub 1}) and imaginary (ε{sub 2}) dielectric constants, dielectric loss (tan δ), optical conductivity (σ{sub opt}), Urbach energy (E{sub u}) and steepness parameter (σ) are also calculated for nc-CdSe thin films. The normal dispersion of refractive index is described using Wemple–DiDomenico single-oscillator model. Refractive index dispersion is further analysed to calculate lattice dielectric constant (ε{sub L}).

  17. Reassignment of the O{sub Se}−V{sub Cd} complex in CdSe

    SciTech Connect

    Bastin, Dirk; Lavrov, E. V.; Weber, J.

    2014-02-21

    An IR absorption study of CdSe single crystals is presented. The as-received material revealed three absorption lines at 1094.2, 1107.5, and 1126.3 cm{sup −1}, which were previously assigned to the O{sub Se}−V{sub Cd} complex [G. Chen et al., Phys. Rev. Lett. 101, 195502 (2008)] We show that each of the lines is accompanied by a number of weaker satellites with intensities which match the natural abundances of sulfur isotopes. In contrast to the original identification it is suggested that these peaks are local vibrational modes of a SO{sub n} complex. The three modes correspond to different orientations of the complex in the CdSe lattice. Arguments are presented in favor of 2 oxygen atoms (n = 2) in the complex. Measurements with uniaxial stress applied to the samples revealed defect symmetries and activation energies for the defect reorientation. The complex was found to be stable up to 750 °C.

  18. Dimensionality of nanoscale TiO2 determines the mechanism of photoinduced electron injection from a CdSe nanoparticle

    DOE PAGES

    Tafen, De Nyago; Long, Run; Prezhdo, Oleg V.

    2014-03-10

    Assumptions about electron transfer (ET) mechanisms guide design of catalytic, photovoltaic, and electronic systems. We demonstrate that the mechanism of ET from a CdSe quantum dot (QD) into nanoscale TiO2 depends on TiO2 dimensionality. The injection into a TiO2 QD is adiabatic due to strong donor–acceptor coupling, arising from unsaturated chemical bonds on the QD surface, and low density of acceptor states. In contrast, the injection into a TiO2 nanobelt (NB) is nonadiabatic, because the state density is high, the donor–acceptor coupling is weak, and multiple phonons accommodate changes in the electronic energy. The CdSe adsorbant breaks symmetry of delocalizedmore » TiO2 NB states, relaxing coupling selection rules, and generating more ET channels. Both mechanisms can give efficient ultrafast injection. Furthermore, the dependence on system properties is very different for the two mechanisms, demonstrating that the fundamental principles leading to efficient charge separation depend strongly on the type of nanoscale material.« less

  19. Ultrafast carrier dynamics of CdSe quantum dots prepared by pulse laser deposition for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Mahat, Meg; Yakami, Baichhabi; Qilin Dai, Qilin; Tang, Jinke; Pikal, Jon

    2013-03-01

    Quantum-dot sensitized solar cells are a promising alternative to existing photovoltaic technology. Over the last decade solution based colloidal quantum dots (QDs) have been extensively studied. Here we have carried out ultrafast transient absorption measurements on CdSe QDs fabricated using pulse laser deposition (PLD) in order to understand the carrier relaxation dynamics in these nanostructures. The differential transmission measurements show that the PLD QDs have a very fast decay process resulting in a recovery time of less than 10 picoseconds. This is in stark contrast to the colloidal QDs that show a decay process of more than 4 nanoseconds. We also find that the fast decay process observed in the PLD QDs is a function of the carriers density generated in CdSe QDs. To understand these carrier relaxation processes and improve the optical properties of the QDs we perform transient absorption measurements on PLD QDs prepared in different media (e.g. water, methanol, ethanol), under different growth conditions, and with and without ligand. We present a comparison study of the carrier relaxation dynamics in these PLD grown QDs to provide insight into the competing relaxation effects and guide their use in Quantum-dot sensitized solar cells. DOE

  20. Graphene oxide based CdSe photocatalysts: Synthesis, characterization and comparative photocatalytic efficiency of rhodamine B and industrial dye

    SciTech Connect

    Ghosh, Trisha; Lee, Jeong-Ho; Meng, Ze-Da; Ullah, Kefayat; Park, Chong-Yeon; Nikam, Vikram; Oh, Won-Chun

    2013-03-15

    Highlights: ► CdSe–graphene is synthesized by hydrothermal method. ► Three molar solutions of CdSe were used making three different composites. ► RhB and Texbrite MST-L were used as sample dye solutions. ► Texbrite MST-L is photo degraded in visible light. ► UV-spectroscopic analysis was done to measure degradation. - Abstract: CdSe–graphene composites were prepared using simple “hydrothermal method” where the graphene surface was modified using different molar solutions of cadmium selenide (CdSe) in aqueous media. The characterization of CdSe–graphene composites were studied by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), and with transmission electron microscope (TEM). The catalytic activities of CdSe-composites were evaluated by degradation of rhodamine B (RhB) and commercial industrial dye “Texbrite MST-L (TXT-MST)” with fixed concentration. The degradation was observed by the decrease in the absorbance peak studied by UV spectrophotometer. The decrease in the dye concentration indicated catalytic degradation effect by CdSe–graphene composites.

  1. Improved efficiency of bulk heterojunction hybrid solar cells by utilizing CdSe quantum dot-graphene nanocomposites.

    PubMed

    Eck, Michael; Pham, Chuyen Van; Züfle, Simon; Neukom, Martin; Sessler, Martin; Scheunemann, Dorothea; Erdem, Emre; Weber, Stefan; Borchert, Holger; Ruhstaller, Beat; Krüger, Michael

    2014-06-28

    We present a significant efficiency enhancement of hybrid bulk heterojunction solar cells by utilizing CdSe quantum dots attached to reduced graphene oxide (rGO) as the electron accepting phase, blended with the PCPDTBT polymer. The quantum dot attachment to rGO was achieved following a self-assembly approach, recently developed, using thiolated reduced graphene oxide (TrGO) to form a TrGO-CdSe nanocomposite. Therefore, we are able to obtain TrGO-CdSe quantum dot/PCPDTBT bulk-heterojunction hybrid solar cells with power conversion efficiencies of up to 4.2%, compared with up to 3% for CdSe quantum dot/PCPDTBT devices. The improvement is mainly due to an increase of the open-circuit voltage from 0.55 V to 0.72 V. We found evidence for a significant change in the heterojunction donor-acceptor blend nanomorphology, observable by a more vertical alignment of the TrGO-quantum dot nanocomposites in the z-direction and a different nanophase separation in the x-y direction compared to the quantum dot only containing device. Moreover, an improved charge extraction and trap state reduction were observed for TrGO containing hybrid solar cells.

  2. TiO₂ nanotubes sensitized with CdSe via RF magnetron sputtering for photoelectrochemical applications under visible light irradiation.

    PubMed

    Fernandes, Jesum A; Migowski, Pedro; Fabrim, Zacarias; Feil, Adriano F; Rosa, Guilherme; Khan, Sherdil; Machado, Guilherme J; Fichtner, Paulo F P; Teixeira, Sérgio R; Santos, Marcos J L; Dupont, Jairton

    2014-05-21

    Highly ordered TiO2 NT arrays were easily decorated with CdSe via RF magnetron sputtering. After deposition thermal annealing at different temperatures was performed to obtain an improved TiO2/CdSe interface. The heterostructures were characterized by RBS, SEM, XRD, HRTEM, UV-Vis, EIS, IPCE and current versus voltage curves. The sensitized semiconducting electrodes display an enhanced photocurrent density of ca. 2 mA cm(-2) at 0.6 V (vs. Ag/AgCl) under visible light (λ > 400 nm). The sensitized photoelectrodes displayed 3 and 535-fold enhanced photocurrent when compared to bare TiO2 NTs under 1 sun and under visible light illumination, respectively. IES results confirmed the improved charge transfer across the TiO2/CdSe/electrolyte interface after annealing at 400 °C. Incident photon-to-electron conversion efficiency measurements confirmed the efficient sensitization by allowing photoresponse in the visible range.

  3. Photoluminescence characteristics of CdSe quantum dots: role of exciton-phonon coupling and defect/trap states

    NASA Astrophysics Data System (ADS)

    Kushavah, Dushyant; Mohapatra, P. K.; Ghosh, Pintu; Singh, Mamraj; Vasa, P.; Bahadur, D.; Singh, B. P.

    2017-07-01

    In this paper, we report temperature dependent photoluminescence (PL) characteristics of CdSe colloidal QDs with average diameter ~2.8 nm. Temperature dependence of strongly confined exciton PL peak position, linewidth and intensity were investigated in 30 K to 300 K temperature range. Our studies reveal nearly four times weaker exciton-LO phonon coupling than bulk CdSe crystal. Theoretically, it should be vanishingly small due to near identical electron and hole charge distributions in strongly confined QDs. On the other hand, exciton-acoustic phonon coupling is an order of magnitude larger than its bulk counterpart. Observed finite value of exciton-LO phonon coupling and enhanced exciton-acoustic phonon coupling are due to piezoelectric strain fields. PL intensity exhibits anomalous behavior in the temperature range 100-230 K. This has been explained by thermally activated detrapping of the charge carriers trapped in the potential wells formed at the interface adjoining dislocations/stacking faults developed during the synthesis process. Above 230 K, PL is partially quenched by thermal escape of charge carriers from luminescing exciton state to higher lying nonluminescing states.

  4. Se EXAFS study of the elevated wurtzite to rock salt structural phase transition in CdSe nanocrystals

    SciTech Connect

    Tolbert, S.H.; Alivisatos, A.P. |

    1993-09-01

    High pressure Se EXAFS data has been obtained on 2.7 nm radius CdSe semiconductor nanocrystals. This system is observed to undergo a solid-solid phase transition at 6.5 GPa which is approximately twice the reported value for bulk CdSe. In combination with high pressure optical absorption experiments, EXAFS data can be used to identify the high-pressure phase structure as rock salt. EXAFS data can be fit with equations of state to yield pressure volume curves. Resultant values of bulk modulus and its derivative with respect to pressure are B{sub o} = 37 {plus_minus} 5 GPa and B{sub o}{prime} = 11 {plus_minus} 3. A thermodynamic model for the data is presented in which the internal energy in each phase is modified by a surface energy term. Differences in surface energy are used to explain the elevation in phase transition pressure. The model can be used to estimate a value for the surface energy in the rock salt phase; 1.9 {plus_minus} 0.3 N/m is obtained in comparison to 0.9 {plus_minus} 0. 1 N/m for the wurtzite phase.

  5. Shell-dependent electroluminescence from colloidal CdSe quantum dots in multilayer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Jing, Pengtao; Zheng, Jinju; Zeng, Qinghui; Zhang, Youlin; Liu, Xiaomin; Liu, Xueyan; Kong, Xianggui; Zhao, Jialong

    2009-02-01

    We report electroluminescence (EL) of colloidal CdSe/CdS, CdSe/ZnS, and CdSe/CdS/CdZnS/ZnS core/shell quantum dots (QDs) in multilayer light-emitting diodes (LEDs) fabricated by spin coating a near monolayer of the core/shell QDs on cross-linkable hole transporting layers. It is found that CdSe/CdS QD-LEDs exhibit a faster decrease in EL quantum efficiency (˜2% at a brightness of 100 cd/m2) with increasing current density and lower maximum brightness than those of CdSe/ZnS QD-LEDs. A more significant redshift and spectral broadening of the EL observed in CdSe core/shell QDs with a CdS or CdS/CdZnS/ZnS shell than with a ZnS shell indicate that the electron wave function can penetrate into the shell under electric field. The difference in device performance and EL spectra results from conduction band offsets between the CdSe cores and CdS or ZnS shells, suggesting the existence of the exciton ionization in the QD-LEDs.

  6. Characterization and polymerization of thienylphenyl and selenylphenyl amines and their interaction with CdSe quantum dots.

    PubMed

    Lana-Villarreal, Teresa; Font-Sanchis, Enrique; Sastre-Santos, Angela; Fernández-Lázaro, Fernando; Gómez, Roberto

    2011-04-18

    Hybrid quantum-dot-sensitized solar cells show promising novel optoelectronic properties. An adequate design of such cells requires a deep understanding of the characteristics of each component, including their interactions. In this context, the electrochemical properties of two different hole-transporting materials (HTMs) and their chemical interactions with trioctylphosphine-capped CdSe quantum dots are investigated to evaluate their potential use in hybrid quantum-dot-sensitized solar cells. Tris[4-(thien-2-yl)phenyl]amine (TTPA) and tris[4-(selen-2-yl)phenyl]amine (TSePA) are studied in the solid state as thin films deposited on a conducting substrate. Spectroelectrochemical studies evidence both solid-state electropolymerization and doping. Upon addition of TSePA or partially polymerized TTPA to a colloidal solution of trioctylphosphine-capped CdSe quantum dots, the steady-state photoluminescence is quenched. This suggests that the quantum dots and the HTM strongly interact, probably through an excited-state charge-transfer mechanism. The combination of all these pieces of information indicates that polymerized TTPA and TSePA are potential candidates as HTMs for hybrid quantum-dot-sensitized solar cells.

  7. 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.

  8. Size-controlled CdSe quantum dots to boost light harvesting capability and stability of perovskite photovoltaic cells.

    PubMed

    Lintangpradipto, Muhammad Naufal; Tsevtkov, Nikolai; Moon, Byeong Cheul; Kang, Jeung Ku

    2017-07-20

    Here, we report that incorporation of size-controlled CdSe quantum dots (QDs) into perovskite photovoltaic cells (PSCs) boosts their light harvesting capability. X-ray photoemission and optical absorption spectroscopy analyses also show that the electronic structure of CdSe QDs makes them efficient charge transfer mediators between perovskite and Spiro-MeOTAD layers. In addition, electrochemical impedance spectroscopy experiments demonstrate that QDs help to decrease charge transfer resistance at the interfaces. Additionally, time-correlated single photon counting measurements show that small (2 nm) QDs enhance visible light collection of PSCs in the short wavelength region via Förster resonance energy transfer while large (4 nm) QDs improve light collection of PSCs in the long wavelength region via enhanced light backscattering at the perovskite/QD interface. Moreover, the photocurrent density in the PSCs with QDs retained over 95% of the initial value in a 100 h stability test, thus supporting that the perovskite layer that has been encapsulated with QDs acts to prevent penetration of water molecules through the perovskite layer. Consequently, these results support that utilization of size-controlled hybrid QDs could open up a new route to realize high-performance PSCs even under humid conditions.

  9. Surfactant-free (CdSe and CdSe-CdTe) semiconducting nanoparticle mixed MEH-PPV thin films

    NASA Astrophysics Data System (ADS)

    Verma, Deepak; Dutta, V.

    2017-08-01

    Hybrid absorbing layers of poly (2-methoxy, 5-(2-ethyl-hexyloxy)-p-phenyl vinylene) (MEH-PPV)) having surfactant-free CdSe and CdTe-CdSe nanoparticles that have been spin coated on glass substrates. The absorbance and photoluminescence spectra on these hybrid thin films have shown the role of the dispersion science of nanoparticles in the polymer matrix. 1HNMR spectra of the polymer mixed nanoparticle solutions have established the chemical interaction between MEH-PPV and nanoparticles. It confirms the relative shift and broadening in the peak located at δ  =  3.96 ppm, known as the alkoxy site for MEH-PPV. Cyclic voltammetry measurements on these hybrid thin films have shown the proper charge transfer compatibility between the MEH-PPV and trioctylphosphine oxide (TOPO)-free nanoparticles. The nanoparticles of the CdTe and CdSe mixed MEH-PPV hybrid layer confirm the better charge transfer in comparison to CdTe—MEH-PPV thin films. The study will help in establishing the parameters required to prepare hybrid absorber thin films for solar cell application.

  10. Magnetic-field-dependent spin decoherence and dephasing in room-temperature CdSe nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Fumani, A. Khastehdel; Berezovsky, J.

    2013-10-01

    We perform and analyze a series of time-resolved Faraday rotation measurements of coherent spin dynamics in a room-temperature ensemble of CdSe nanocrystal quantum dots (NCQDs) to study the decoherence and dephasing mechanisms that limit the transverse spin lifetime. Coherent spin lifetimes on the order of nanoseconds have been previously observed in CdSe NCQDs, but the presence of multiple components with distinct dynamics and strong inhomogeneous dephasing have made it difficult to study the relevant spin decay mechanisms quantitatively. Here, we obtain reliable fitting results by ensuring that cross-correlations between model parameters are minimized for the parameters of interest. Furthermore, we characterize the morphological inhomogeneity of the NCQD ensemble using transmission electron microscopy to constrain the model parameters that specify inhomogeneous dephasing. We find that g-factor inhomogeneity-induced dephasing (gID) is not sufficient to explain the magnetic-field-dependent decay of the spin signal. We propose an additional decoherence mechanism arising from rapid transitions between the fine structure states of the exciton referred to as fine-structure decoherence (FSD). By including both gID and FSD in the model, excellent fits are obtained to the data, including a prominent short-time-scale feature, which has typically been excluded from the fits in previous work.

  11. Self-powered flexible and transparent photovoltaic detectors based on CdSe nanobelt/graphene Schottky junctions.

    PubMed

    Gao, Zhiwei; Jin, Weifeng; Zhou, Yu; Dai, Yu; Yu, Bin; Liu, Chu; Xu, Wanjin; Li, Yanping; Peng, Hailin; Liu, Zhongfan; Dai, Lun

    2013-06-21

    Flexible and transparent electronic and optoelectronic devices have attracted more and more research interest due to their potential applications in developing portable, wearable, low-cost, and implantable devices. We have fabricated and studied high-performance flexible and transparent CdSe nanobelt (NB)/graphene Schottky junction self-powered photovoltaic detectors for the first time. Under 633 nm light illumination, typical photosensitivity and responsivity of the devices are about 1.2 × 10(5) and 8.7 A W(-1), respectively. Under 3500 Hz switching frequency, the response and recovery times of them are about 70 and 137 μs, respectively, which, to the best of our knowledge, are the best reported values for nanomaterial based Schottky junction photodetectors up to date. The detailed properties of the photodetectors, such as the influences of incident light wavelength and light intensity on the external quantum efficiency and speed, are also investigated. Detailed discussions are made in order to understand the observed phenomena. Our work demonstrates that the self-powered flexible and transparent CdSe NB/graphene Schottky junction photovoltaic detectors have a bright application prospect.

  12. Ligand-controlled rates of photoinduced electron transfer in hybrid CdSe nanocrystal/poly(viologen) films.

    PubMed

    Tagliazucchi, Mario; Tice, Daniel B; Sweeney, Christina M; Morris-Cohen, Adam J; Weiss, Emily A

    2011-12-27

    This paper describes a study of the rates of photoinduced electron transfer (PET) from CdSe quantum dots (QDs) to poly(viologen) within thin films, as a function of the length of the ligands passivating the QDs. Ultrafast (<10 ps), quantitative PET occurs from CdSe QDs coated with HS-(CH(2))(n)-COOH for n = 1, 2, 5, and 7 to viologen units. The observed decrease in the magnitude of the PET rate constant with n is weaker than that expected from the decay of the electron tunneling probability across extended all-trans mercaptocarboxylic acids but well-described by electron tunneling across a collapsed ligand shell. The PET rate constants for films with n = 10 and 15 are much slower than those expected based on the trend for n = 1-7; this deviation is ascribed to the formation of bundles of ligands on the surface of the QD that make the tunneling process prohibitively slow by limiting access of the viologen units to the surfaces of the QDs. This study highlights the importance of molecular-level morphology of donor and acceptor materials in determining the rate and yield of interfacial photoinduced electron transfer in thin films.

  13. Asymmetric tunneling rates for electrons and holes at CdSe quantum dot/carbon nanotube interfaces

    NASA Astrophysics Data System (ADS)

    Ismail-Beigi, Sohrab; Jiang, Jie

    2014-03-01

    Decorating carbon nanotubes with CdSe quantum dots (QDs) is one potential approach for creating high efficiency photovoltaics. Our collaborators at Yale recently produced a ligand-free covalent attachment of CdSe QDs to carbon nanotubes through an organic ligand exchange mechanism. Our prior first principles work described the energetics of the various binding processes and rationalized the experimental growth methodology. After a brief review of the system, we will describe our intriguing finding that excited electrons and holes tunnel with different rates out of the QD and into the carbon nanotubes. The asymmetric tunneling rate itself can, in principle, boost the separation of photo-excited charge at the interface even if there are insufficient band energy differences across the interface. We describe our results for the tunneling rates computed using (i) a brute force approach with increasing simulation cell size to remove periodic effects, and (ii) a Green's function method that directly connects the QD to a thermodynamically large electron reservoir (e.g., a very long pristine nanotube). Supported by NSF SOLAR DMR 0934520.

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

    PubMed

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

    2013-08-07

    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.

  15. Structural, optical and electrical characterization of vacuum-evaporated nanocrystalline CdSe thin films for photosensor applications

    NASA Astrophysics Data System (ADS)

    Kumar, Vipin; Sharma, D. K.; Sharma, Kapil; Dwivedi, D. K.

    2016-11-01

    II-VI nanocrystalline semiconductors offer a wide range of applications in electronics, optoelectronics and photonics. Thin films of CdSe were deposited onto ultra-clean glass substrates by vacuum evaporation method. The as-deposited films were annealed in vacuum at 350 K. The structural, elemental, morphological, optical and electrical investigations of annealed films were carried out. The X-ray diffraction pattern of the films shows that films were polycrystalline in nature having hexagonal structure with preferential orientation of grains along (002) plane. SEM image indicates that the films were uniform and well covered to the glass substrate. EDAX analysis confirms the stoichiometric composition of the film. Raman spectra were used to observe the characteristic vibrational modes of CdSe. The energy band gap of these films was obtained by absorption spectra. The films were found to have a direct type of transition of band gap occurring at 1.75 eV. The dark electrical conductivity and photoconductivity reveals that the films were semiconducting in nature indicating the suitability of these films for photosensor applications. The Hall effect measurement reveals that the films have n-type electrical conductivity.

  16. 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.

  17. The effect of differential temperatures on the latent heat in the nucleation of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    This work studied the effect of differential temperatures on the latent heat in the nucleation of CdSe quantum dots (QDs). The result showed that, by the formula of phase change, with increasing the reaction temperature, the latent heat in the nucleation of QDs reduced. CdSe QDs with the size-dispersion from 2.7 to 3.6 nm were synthesized via oleic acid-paraffin liquid system by controlling the reaction temperature from 180 to 220 °C. Synthesized QDs were characterized by UV-vis absorption spectra and X-ray diffraction (XRD). The result of UV-vis absorption spectra showed that with increasing of reaction temperature, the first absorption peak was red-shifted and the size of QD increased. The result of XRD showed that the synthesized QDs were zinc-blende structure. Project supported by the National Natural Science Fund of China (No. 11204046), the International Science and Technology Cooperation Project of China (No. 2014DFA00670) and the Guizhou Province International Science and Technology Cooperation Project of China (No. QKHG[2011]7001)

  18. Annealing-induced optical and sub-band-gap absorption parameters of Sn-doped CdSe thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Jagdish; Tripathi, S. K.

    2016-01-01

    Thin films of Sn-doped CdSe were prepared by thermal evaporation onto glass substrates in an argon gas atmosphere and annealed at different temperatures. Structural evaluation of the films was carried out using X-ray diffraction and their stoichiometry studied by energy-dispersive X-ray analysis. The films exhibit a preferred orientation along the hexagonal direction of CdSe. The optical transmittance of the films shows a red shift of the absorption edge with annealing. The fundamental absorption edge corresponds to a direct energy gap with a temperature coefficient of 3.34 × 10-3 eV K-1. The refractive index, optical conductivity and real and imaginary parts of the dielectric constants were found to increase after annealing. The sub-band gap absorption coefficient was evaluated using the constant photocurrent method. It varies exponentially with photon energy. The Urbach energy, the density of defect states, and the steepness of the density of localized states were evaluated from the sub-band-gap absorption.

  19. 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. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Charge separation in type II tunneling structures of close-packed CdTe and CdSe nanocrystals.

    PubMed

    Gross, Dieter; Susha, Andrei S; Klar, Thomas A; Da Como, Enrico; Rogach, Andrey L; Feldmann, Jochen

    2008-05-01

    We report on charge separation between type II aligned CdTe and CdSe nanocrystals. Two types of electrostatically bound nanocrystal structures have been studied: first, clusters of nanocrystals hold together by Ca(II) ions in aqueous solution and, second, thin film structures of nanocrystals created with layer-by-layer deposition in combination with polyelectrolytes. In both types of structures, short interparticle distances of less than 1 nm have been achieved, whereby the isolating organic ligands on the nanocrystal surfaces and/or the polymer monolayers act as tunneling barriers between nanocrystals. We have observed an efficient quenching of photoluminescence and a reduced emission lifetime for CdTe nanocrystals in both types of type II heterostructures. This result is explained by a spatial charge separation of the photoexcited electron-hole pairs due to tunneling of charge carriers through the thin organic layer between CdTe and CdSe nanocrystals. Type II heterostructures demonstrated here may find future applications in photovoltaics.

  1. 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.

  2. Isolation of a selenite-reducing and cadmium-resistant bacterium Pseudomonas sp. strain RB for microbial synthesis of CdSe nanoparticles.

    PubMed

    Ayano, Hiroyuki; Miyake, Masaki; Terasawa, Kanako; Kuroda, Masashi; Soda, Satoshi; Sakaguchi, Toshifumi; Ike, Michihiko

    2014-05-01

    Bacteria capable of synthesizing CdSe from selenite and cadmium ion were enriched from a soil sample. After repeated transfer of the soil-derived bacterial cultures to a new medium containing selenite and cadmium ion 42 times (during 360 days), an enrichment culture that can simultaneously remove selenite and cadmium ion (1 mM each) from the liquid phase was obtained. The culture's color became reddish-brown, indicating CdSe nanoparticle production, as confirmed by energy-dispersive x-ray spectra (EDS). As a result of isolation operations, the bacterium that was the most responsible for synthesizing CdSe, named Pseudomonas sp. RB, was obtained. Transmission electron microscopy and EDS revealed that this strain accumulated nanoparticles (10-20 nm) consisting of selenium and cadmium inside and on the cells when cultivated in the same medium for the enrichment culture. This report is the first describing isolation of a selenite-reducing and cadmium-resistant bacterium. It is useful for CdSe nanoparticle synthesis in the simple one-vessel operation. Copyright © 2013 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

  3. Cadmium telluride (CdTe) and cadmium selenide (CdSe) leaching behavior and surface chemistry in response to pH and O2.

    PubMed

    Zeng, Chao; Ramos-Ruiz, Adriana; Field, Jim A; Sierra-Alvarez, Reyes

    2015-05-01

    Cadmium telluride (CdTe) and cadmium selenide (CdSe) are increasingly being applied in photovoltaic solar cells and electronic components. A major concern is the public health and ecological risks associated with the potential release of toxic cadmium, tellurium, and/or selenium species. In this study, different tests were applied to investigate the leaching behavior of CdTe and CdSe in solutions simulating landfill leachate. CdTe showed a comparatively high leaching potential. In the Toxicity Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET), the concentrations of cadmium released from CdTe were about 1500 and 260 times higher than the regulatory limit (1 mg/L). In contrast, CdSe was relatively stable and dissolved selenium in both leaching tests was below the regulatory limit (1 mg/L). Nonetheless, the regulatory limit for cadmium was exceeded by 5- to 6- fold in both tests. Experiments performed under different pH and redox conditions confirmed a marked enhancement in CdTe and CdSe dissolution both at acidic pH and under aerobic conditions. These findings are in agreement with thermodynamic predictions. Taken as a whole, the results indicate that recycling of decommissioned CdTe-containing devices is desirable to prevent the potential environmental release of toxic cadmium and tellurium in municipal landfills.

  4. CdS or CdSe decorated TiO2 nanotube arrays from spray pyrolysis deposition: use in photoelectrochemical cells.

    PubMed

    Shin, Kahee; Seok, Sang Il; Im, Sang Hyuk; Park, Jong Hyeok

    2010-04-14

    In the present work we report on an investigation of TiO(2) nanotube arrays sensitized by low band-gap materials, such as CdS and CdSe, prepared by the one-step spray pyrolysis deposition method, which is very suitable for mass production, and their performance in photoelectrochemical cells.

  5. The use of heat transfer fluids in the synthesis of high-quality CdSe quantum dots, core/shell quantum dots, and quantum rods.

    PubMed

    Asokan, Subashini; Krueger, Karl M; Alkhawaldeh, Ammar; Carreon, Alessandra R; Mu, Zuze; Colvin, Vicki L; Mantzaris, Nikos V; Wong, Michael S

    2005-10-01

    Fluorescent semiconductor nanoparticles, or quantum dots, have potential uses as an optical material, in which the optoelectronic properties can be tuned precisely by particle size. Advances in chemical synthesis have led to improvements in size and shape control, cost, and safety. A limiting step in large-scale production is identified to be the raw materials cost, in which a common synthesis solvent, octadecene, accounts for most of the materials cost for a batch of CdSe quantum dots. Thus, less expensive solvents are needed. In this paper, we identify heat transfer fluids, a class of organic liquids commonly used in chemical process industries to transport heat between unit operations, as alternative solvents for quantum dot synthesis. We specifically show that two heat transfer fluids can be used successfully in the synthesis of CdSe quantum dots with uniform particle sizes. We show that the synthesis chemistry for CdSe/CdS core/shell quantum dots and CdSe quantum rods can also be performed in heat transfer fluids. With the aid of a population balance model, we interpret the effect of different HT fluids on QD growth kinetics in terms of solvent effects, i.e., solvent viscosity, CdSe bulk solubility in the solvent, and surface free energy.

  6. Electronic structure and ferromagnetism of boron doped bulk and surface CdSe: By generalized gradient approximation and generalized gradient approximation plus modified Becke and Johnson calculations

    NASA Astrophysics Data System (ADS)

    Fan, S. W.; Ding, L. J.; Yao, K. L.

    2013-09-01

    Using the full potential linearized augment plane wave method with the generalized gradient approximation (GGA) and GGA plus modified Becke and Johnson (GGA+mBJ) potential, the electronic structures and ferromagnetism for the boron doped bulk and surface CdSe are investigated. Calculations show that the substitutional boron for selenium in CdSe could induce spin polarized localized states in the gap and generate local magnetic moments 3.00 μB with one dopant atom. Energy difference between the antiferromagnetic and ferromagnetic phase suggests that BSe favors the ferromagnetic ground state. Electronic structures indicate the magnetic moments mainly provided by the doped boron atoms, and carriers mediated double exchange mechanism plays crucial role in forming the ferromagnetism. Ferromagnetic boron doped CdSe (100) films could be realized by using the high energy boron ions injection to form the non-surface doped configurations. The cadmium vacancy would reduce the ferromagnetism and lead the boron doped CdSe to magnetic metallicity. Formation energy for the four high symmetry doped configurations indicates BSe could be realized by using Cd-rich condition.

  7. Tuning Hole and Electron Transfer from Photo-excited CdSe Quantum Dot to Phenol Derivatives: Effect of Electron Donating and Withdrawing Moiety.

    PubMed

    Ghosh, Hirendra Nath; Debnath, Tushar; Sebastian, Deepa; Maiti, Sourav

    2017-03-27

    Charge transfer processes from photo-excited CdSe QDs to phenol derivatives with electron donating (4-methoxy) and electron withdrawing (4-nitro) moiety have been demonstrated by using steady state and time-resolved emission and femto-second transient absorption spectroscopy. Steady state and time-resolved emission studies suggest that in presence of both 4-nitro phenol (4NP) and 4-methoxy phenol (4MP) CdSe QDs luminescence gets quenched. Stern-Volmer analysis suggests both static and dynamic mechanisms are active for both the QD/phenol composites. Cyclic volatmetric analysis recommends that photo-excited CdSe QDs can donate electron to 4NP and hole to 4MP. To reconfirm both electron and hole transfer mechanism CdSe/CdS quasi type-II and CdSe/CdTe type-II core-shell NC were synthesized and the photoluminescence quenching were monitored in absence and in presence of both 4NP and 4MP where systematically hole and electron transfer were restricted. Our studies suggest that indeed electron and hole transfer take place from photo-excited CdSe to 4NP and 4MP respectively. To monitor the charge transfer dynamics in both the systems in early time scale, we have employed femtosecond transient absorption (TA) spectroscopic techniques. Both electron and hole transfer and charge recombination dynamics have been discussed and effect of electron donating and withdrawing group has been demonstrated.

  8. Efficient CdSe quantum dot-sensitized solar cells prepared by an improved successive ionic layer adsorption and reaction process.

    PubMed

    Lee, Hyojoong; Wang, Mingkui; Chen, Peter; Gamelin, Daniel R; Zakeeruddin, Shaik M; Grätzel, Michael; Nazeeruddin, Md K

    2009-12-01

    In pursuit of efficient quantum dot (QD)-sensitized solar cells based on mesoporous TiO(2) photoanodes, a new procedure for preparing selenide (Se(2-)) was developed and used for depositing CdSe QDs in situ over TiO(2) mesopores by the successive ionic layer adsorption and reaction (SILAR) process in ethanol. The sizes and density of CdSe QDs over TiO(2) were controlled by the number of SILAR cycles applied. After some optimization of these QD-sensitized TiO(2) films in regenerative photoelectrochemical cells using a cobalt redox couple [Co(o-phen)(3)(2+/3+)], including addition of a final layer of CdTe, over 4% overall efficiencies were achieved at 100 W/m(2) with about 50% IPCE at its maximum. Light-harvesting properties and transient voltage decay/impedance measurements confirmed that CdTe-terminated CdSe QD cells gave better charge-collection efficiencies and kinetic parameters than corresponding CdSe QD cells. In a preliminary study, a CdSe(Te) QD-sensitized TiO(2) film was combined with an organic hole conductor, spiro-OMeTAD, and shown to exhibit a promising efficiency of 1.6% at 100 W/m(2) in inorganic/organic hybrid all-solid-state cells.

  9. 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

    2012-12-07

    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

  10. Exciton delocalization and hot hole extraction in CdSe QDs and CdSe/ZnS type 1 core shell QDs sensitized with newly synthesized thiols

    NASA Astrophysics Data System (ADS)

    Singhal, Pallavi; Ghorpade, Prashant V.; Shankarling, Ganapati S.; Singhal, Nancy; Jha, Sanjay K.; Tripathi, Raj M.; Ghosh, Hirendra N.

    2016-01-01

    The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady state absorption study suggests the exciton delocalization from CdSe QDs in the presence of the thiols. However similar features were not observed in the presence of a ZnS shell over a CdSe core, instead a broadening in the excitonic peak was observed with both APT and ADPT but not with AAT. This exciton delocalization and broadening in the excitonic peak was also confirmed by ultrafast transient absorption studies. Steady state and time resolved emission studies show hole transfer from photo-excited QDs and CSQDs to the thiols. A signature of hot hole extraction was observed in transient absorption studies which was confirmed by fluorescence upconversion studies. Both hot and thermalized hole transfer rates from CdSe QDs and CdSe/ZnS CSQDs to the thiols were determined using the fluorescence up-conversion technique. Experiments with different ZnS shell thicknesses have been carried out which suggest that hole transfer is possible till 2.5 monolayer of the ZnS shell. To the best of our knowledge we are reporting for the first time the extraction of hot holes from CdSe/ZnS type I CSQDs by a molecular adsorbate.The present work describes ultrafast thermalized and hot hole transfer processes from photo-excited CdSe quantum dots (QDs) and CdSe/ZnS core-shell QDs (CSQDs) to newly synthesized thiols. Three thiols namely 2-mercapto-N-phenylacetamide (AAT), 3-mercapto-N-phenylpropanamide (APT) and 3-mercapto-N-(4-methoxyphenyl) propanamide (ADPT) were synthesized and their interaction with both CdSe QDs and CdSe/ZnS CSQDs was monitored. Steady

  11. Synthesis and Physical Properties Characterization of CdSe1-ySy Nanolayers Deposited by Chemical Bath Deposition at Low-Temperature Treatment

    NASA Astrophysics Data System (ADS)

    Flores-Mena, J. E.; Contreras-Rascón, J. I.; Diaz-Reyes, J.; Castillo-Ojeda, R. S.

    In this work, we present the synthesis and structural and optical characterizations of CdSe1-y S y deposited by chemical bath deposition (CBD) technique on corning glass at a temperature of 20 ± 2 °C. The sulfur molar fraction was varied from 0 to 42.13 %, which was realized by varying the thiourea volume added to the growth solution in the range from 0 to 30 mL. The chemical stoichiometry was estimated by energy dispersive spectrometry (EDS). The CdSe1-y S y showed hexagonal wurtzite crystalline phase that was found by X-ray diffraction (XRD) analysis and Raman spectroscopy. The average grain size range of the films was 1.48-1.68 nm that was determined using the Debye-Scherrer equation W(002) direction and was confirmed by high-resolution transmission electron microscopy (HRTEM). Raman scattering shows that the lattice dynamics is characteristic of bimodal behavior and the multipeaks adjust to the first optical longitudinal mode for the CdSeS, in all cases, Raman spectra show two dominant vibrational bands about 208 and 415 cm-1 associated at CdSe-1LO-like and CdSe-2LO-like. CdSe1-y S y band gap energy can be varied from 1.86 to 2.16 eV by varying the thiourea volume added in growth solution in the investigated range obtained by transmittance measurements at room temperature. The room temperature photoluminescence shows a dominant radiation band at about 3.0 eV that can be associated with exciton bonded to donor impurity and the quantum confinement because of the grain size is less than the Bohr radius.

  12. 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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets

    NASA Astrophysics Data System (ADS)

    Bose, Sumanta; Song, Zhigang; Fan, W. J.; Zhang, D. H.

    2016-04-01

    The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ṡ p model with valence force field considerations. Volumetrically larger NPLs have lower photon emission energy due to limited quantum confinement, but a greater transition matrix element (TME) due to larger electron-hole wavefunction overlap. The optical gain characteristics depend on several factors such as TME, Fermi factor, carrier density, NPL dimensions, material composition, and dephasing rate. There is a red shift in the peak position, more so with an increase in thickness than lateral size. For an increasing carrier density, the gain spectrum undergoes a slight blue shift due to band filling effect. For a fixed carrier density, the Fermi factor is higher for volumetrically larger NPLs and so is the difference between the quasi-Fermi level separation and the effective bandgap. The transparency injection carrier density (and thus input current density threshold) is dimension dependent and falls for volumetrically larger NPLs, as they can attain the requisite exciton count for transparency with a relatively lower density. Between CdSe and CdS, CdSe has lower emission energy due to smaller bandgap, but a higher TME due to lower effective mass. CdS, however, has a higher so hole contribution due to a lower spin-orbit splitting energy. Both CdSe and CdS NPLs are suitable candidates for short-wavelength LEDs and lasers in the visible spectrum, but CdSe is expected to exhibit better optical performance.

  14. Effect of lateral size and thickness on the electronic structure and optical properties of quasi two-dimensional CdSe and CdS nanoplatelets

    SciTech Connect

    Bose, Sumanta; Fan, W. J. Zhang, D. H.; Song, Zhigang

    2016-04-14

    The effect of lateral size and vertical thickness of CdSe and CdS nanoplatelets (NPLs) on their electronic structure and optical properties are investigated using an effective-mass envelope function theory based on the 8-band k ⋅ p model with valence force field considerations. Volumetrically larger NPLs have lower photon emission energy due to limited quantum confinement, but a greater transition matrix element (TME) due to larger electron-hole wavefunction overlap. The optical gain characteristics depend on several factors such as TME, Fermi factor, carrier density, NPL dimensions, material composition, and dephasing rate. There is a red shift in the peak position, more so with an increase in thickness than lateral size. For an increasing carrier density, the gain spectrum undergoes a slight blue shift due to band filling effect. For a fixed carrier density, the Fermi factor is higher for volumetrically larger NPLs and so is the difference between the quasi-Fermi level separation and the effective bandgap. The transparency injection carrier density (and thus input current density threshold) is dimension dependent and falls for volumetrically larger NPLs, as they can attain the requisite exciton count for transparency with a relatively lower density. Between CdSe and CdS, CdSe has lower emission energy due to smaller bandgap, but a higher TME due to lower effective mass. CdS, however, has a higher so hole contribution due to a lower spin-orbit splitting energy. Both CdSe and CdS NPLs are suitable candidates for short-wavelength LEDs and lasers in the visible spectrum, but CdSe is expected to exhibit better optical performance.

  15. 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.

  16. Contactless microwave study of shallow traps in thin-film CdSe

    NASA Astrophysics Data System (ADS)

    Grabtchak, Serguei Yu.; Cocivera, Michael

    1994-12-01

    The contactless microwave technique was used to measure light-induced transients in the power absorption by thin films of polycrystalline CdSe. Because the rise time of the detector was 500 ns, the analysis was limited 1 μsec or longer. Measurement of these transients at a number of fixed frequencies across the ``dark'' resonance frequency made reconstruction of the difference signal possible. This signal, which represents the difference between the ``dark'' and ``light'' Lorentz resonance curves, was determined at various times during the decay. Analysis of these signals provided the changes in the real and imaginary parts of the dielectric constant as a function of time. The decays of these parameters were characterized by the sum of two exponential terms: τ1=16.9 μsec and τ2=261.5 μsec for the change in the imaginary part, and τ1=18.5 μsec and τ2=283 μsec for the change in the real part. The close agreement of these values indicates the simultaneous presence of both trapped and free electrons having identical decay times. A mechanism consistent with these results involves rapid equilibration between the free electrons and those in the two shallow traps. Decay from each trap is the rate limiting step, and the time to reach thermodynamic equilibrium must be less than 500 ns. The initial electron densities in the two traps were 2.1×1018 and 1.0×1018 cm-3, and the corresponding concentrations of the free electrons were 3.6×1017 and 1.4×1017 cm-3. For the free electrons, the values for the drift mobility were 2.1 and 1.8 cm2/V s, respectively. Using the harmonic-oscillator model for trapped electrons, the trap energies were 0.096 eV for the fast decay and 0.152 eV for the slower decay. The initial changes in a real part of the dielectric constant were 44.9 and 11.9, respectively. Thus, the photoinduced concentrations of electrons in naturally existing shallow traps are sufficient to effect large changes in the dielectric constant on a short time scale.

  17. 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.

  18. Computational Prediction of Structures and Optical Excitations for Nanoscale Ultrasmall ZnS and CdSe Clusters.

    PubMed

    Nguyen, Kiet A; Pachter, Ruth; Day, Paul N

    2013-08-13

    Small semiconductor nanoclusters are important for understanding the initial formation and growth of quantum dots and also for application, for example in the tunability provided by size. However, electronic structures and effects of capping ligands have not been systematically characterized. Thus, ground and excited state calculations using coupled-cluster methods were carried out to provide benchmarks for evaluating the applicability of density functional theory (DFT) and time-dependent DFT (TDDFT) with different functionals for the ground and excited states, respectively. Our computed data suggests that the popular B3LYP functional does not deliver optimal results for the ground and excited state. While the PBE0 functional was found to provide a good description for both the ground and excited states for small bare (ZnS)n and bare and ligated (CdSe)n clusters, the results for the hydrated (ZnS)n clusters were found to deteriorate significantly. However, the errors appear to decrease with increasing cluster size. Excitation energies obtained with the long-range hybrid CAM-B3LYP and CA-B3LYP were found to provide more consistent results for both anhydrous and hydrated (ZnS)n clusters. However, their performance in spectral predictions for larger clusters requires further study. Using PBE0, electronic structures of the ground and excited states for (ZnS)n and (CdSe)n up to n = 37 using DFT and TDDFT, respectively, were re-examined. With the exception of the cage-core (ZnS)13, (CdSe)13, and (CdSe)14, small (ZnS)n and (CdSe)n are predicted to be spheroids and tubular structures (6, 8-12, 15-19) with squares and hexagons, similar to the structures of carbon single-wall nanotubes. Wurtzite (n = 23-27, 36, 37) and cage-core (n = 29-35) structures are energetically more favorable for larger clusters. We find that water and amines increase the intensities and blue shift the excitations of bare clusters. One photon absorption spectra predicted by TDDFT with the PCM

  19. Probing structure-induced optical behavior in a new class of self-activated luminescent 0D/1D CaWO₄ metal oxide – CdSe nanocrystal composite heterostructures

    SciTech Connect

    Han, Jinkyu; McBean, Coray; Wang, Lei; Hoy, Jessica; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Sfeir, Matthew Y.; Fischer, Daniel A.; Taylor, Gordon T.; Misewich, James A.; Wong, Stanislaus S.

    2015-01-30

    In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dot (QDs) coupled with (ii) both one and zero-dimensional (1D and 0D) motifs of self-activated luminescence CaWO₄ metal oxides. Specifically, ~4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ~230 nm in diameter and ~3 μm in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ~ 80 nm) of CaWO₄ through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementary electron microscopy and spectroscopy (i.e. IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO₄ as compared with unbound CaWO₄. We propose that a photo-induced electron transfer process occurs from CaWO₄ to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO₄ nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO₄ within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO₄ itself.

  20. Photoconductivity of composite structures based on porous SnO{sub 2} sensitized with CdSe nanocrystals

    SciTech Connect

    Drozdov, K. A.; Kochnev, V. I.; Dobrovolsky, A. A.; Vasiliev, R. B.; Babynina, A. V.; Rumyantseva, M. N.; Gaskov, A. M.; Ryabova, L. I.; Khokhlov, D. R.

    2013-03-15

    The introduction of CdSe nanocrystals (colloidal quantum dots) into a porous SnO{sub 2} matrix brings about the appearance of photoconductivity in the structures. Sensitization is a consequence of charge exchange between the quantum dots and the matrix. Photoconductivity spectral measurements show that the nanocrystals embedded into the matrix are responsible for the optical activity of the structure. The photoconductivity of the structures sensitized with different-sized quantum dots is studied in the temperature range from 77 to 300 K. It is shown that the maximum photoconductivity is attained by introducing nanocrystals of the minimum size (2.7 nm). The mechanisms of charge-carrier transport in the matrix and the charge-exchange kinetics are discussed.

  1. Investigation of light induced effect on density of states of Pb doped CdSe thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Jagdish; Singh, Baljinder; Tripathi, S. K.

    2016-05-01

    Thin films of Pb doped CdSe are deposited on the glass substrates by thermal evaporation technique using inert gas condensation method. The prepared thin films are light soaked under vacuum of 2×10-3 mbar for two hour. The absorption coefficient in the sub-band gap region has been studied using Constant Photocurrent Method (CPM). The absorption coefficient in the sub-band gap region follows an exponential Urbach tail. The value of Urbach energy and number density of defect states have been calculated from the absorption coefficient in the sub-band gap region and found to increase after light soaking treatment. The energy distribution of the occupied density of states below Fermi level has been evaluated using derivative procedure of the absorption coefficient.

  2. Thermally induced effect on sub-band gap absorption in Ag doped CdSe thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Jagdish; Sharma, Kriti; Bharti, Shivani; Tripathi, S. K.

    2015-05-01

    Thin films of Ag doped CdSe have been prepared by thermal evaporation using inert gas condensation (IGC) method taking Argon as inert gas. The prepared thin films are annealed at 363 K for one hour. The sub-band gap absorption spectra in the as deposited and annealed thin films have been studied using constant photocurrent method (CPM). The absorption coefficient in the sub-band gap region is described by an Urbach tail in both as deposited and annealed thin films. The value of Urbach energy and number density of trap states have been calculated from the absorption coefficient in the sub-band gap region which have been found to increase after annealing treatment indicating increase in disorderness in the lattice. The energy distribution of the occupied density of states below Fermi level has also been studied using derivative procedure of absorption coefficient.

  3. Spin Dynamics and Optical Nonlinearities in Layered GaSe and Colloidal CdSe Nanocrystal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tang, Yanhao

    In this thesis, we studied spin dynamics, optical nonlinearity and the optical Stark effect in bulk GaSe, mono- and few-layer GaSe, and colloidal CdSe nanocrystal quantum dots (NQDs), respectively. Control of the spin has been a long-term goal due to its potential applications in quantum information processing. Candidates for spintronics should have a long spin lifetime and allow for generation of a high initial spin polarization. GaSe caught our attention due to its orbitally nondegenerate valence bands, which are in contrast to the degenerate heavy and light hole valence bands in conventional III-V and II-VI semiconductors, like GaAs and CdSe. With time- and polarization-resolved photoluminescence, we demonstrated the generation of initial spin polarization as high as 0.9 followed by bi-exponential spin relaxation at 10 K (˜30 ps and ≥300 ps), owing to such orbitally nondegenerate valence bands in GaSe. We also directly revealed the initial spin and population relaxation as transitions from triplet excitons to singlet excitions via spin-flip of the electron or hole. Contrary to semiconductor transition metal dichalcogenides, MX2 (M=Mo,W; X=S,Se,Te), GaSe is a direct band gap semiconductor in bulk, but transforms to an indirect band gap semiconductor in a monolayer as the maximum of the valence band is shifted away from the Gamma point. Associated with such a valence band in monolayer GaSe, ferromagnetism has been predicted upon hole doping due to a strong electronic exchange field. To study the electronic structure of GaSe in mono- and few-layer GaSe, we measured layer- and frequency-dependent second-harmonic generation (SHG) in GaSe from monolayer to ≥100 layers and determined a second-order optical nonlinearity chi(2) in the multi-slab system. We found reduced a chi(2) in GaSe with thickness < 7 layers, tentatively attributed to the predicted increase in the band gap. How quantum confinement affects the light-matter interaction in colloidal CdSe

  4. Alternate monolayers of CdSe nanocrystals and perylene tetracarboxylate: quantum dot hypersensitization for dye-sensitized solar cells.

    PubMed

    Vercelli, B; Zotti, G; Berlin, A

    2012-06-27

    Mono- and multilayers from CdSe nanocrystal dispersion and perylene tetracarboxylate solution are reported for the first time. The layers were investigated by UV-visible spectroscopy, cyclic voltammetry, photoconductivity, and photoelectrochemical techniques. The n-type organic semiconductor gives enhanced photoconductivity to the CdSe-NC multilayer structure. The photoactive perylene monolayer acts also as hypersensitizer of CdSe-NC structures. The perylene-modified CdSe-NC monolayer on indium tin oxide (ITO) electrode in a three-electrode photoelectrochemical cell upon illumination in the presence of oxygen generates an intense steady photocurrent as high as 10-20 times that expected from the individual contributions of perylene and CdSe-NCs. The hypersensitization mechanism is discussed on the basis of the energy level diagram of the components.

  5. 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.

  6. Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

    NASA Astrophysics Data System (ADS)

    Jiang, Tong-Tong; Shao, Wei-Jia; Yin, Nai-Qiang; Liu, Ling; Song, Jiang-Lu-Qi; Zhu, Li-Xin; Xu, Xiao-Liang

    2014-08-01

    The coupling of local surface plasmon (LSP) of nanoparticle and surface plasmon (SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots (QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.

  7. Characterization and 2D self-assembly of CdSe quantum dots at the air-water interface.

    PubMed

    Gattás-Asfura, Kerim M; Constantine, Celeste A; Lynn, Matthew J; Thimann, Daniel A; Ji, Xiaojun; Leblanc, Roger M

    2005-10-26

    Langmuir film properties, UV-vis spectroscopy, epifluorescence microscopy, and transmission electron microscopy were used to study CdSe quantum dots (QDs) in 2D. By combining these results, it was possible to determine the molar absorptivity, limiting nanoparticle area, luminescence property, and arrangement of the QDs in the monolayer films at the air-water interface. Either trioctylphosphine oxide (TOPO) or 1-octadecanethiol (ODT) stabilized the QDs. The data collected reveal that TOPO forms close-packed monolayers on the surface of the QDs and that ODT-stabilized QDs undergo alkyl chains interdigitation. It was also found that varying the nanoparticle size, nature of surfactant, surface pressure, and mixed monolayers could help engineer the 2D self-assembly of the QDs at the air-water interface. Of practical importance is the transfer of these monolayer films onto hydrophilic or hydrophobic solid substrates, which could be successfully accomplished via the Langmuir-Blodgett film deposition technique.

  8. Fiber and fabric solar cells by directly weaving carbon nanotube yarns with CdSe nanowire-based electrodes.

    PubMed

    Zhang, Luhui; Shi, Enzheng; Ji, Chunyan; Li, Zhen; Li, Peixu; Shang, Yuanyuan; Li, Yibin; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai; Cao, Anyuan

    2012-08-21

    Electrode materials are key components for fiber solar cells, and when combined with active layers (for light absorption and charge generation) in appropriate ways, they enable design and fabrication of efficient and innovative device structures. Here, we apply carbon nanotube yarns as counter electrodes in combination with CdSe nanowire-grafted primary electrodes (Ti wire) for making fiber and fabric-shaped photoelectrochemical cells with power conversion efficiencies in the range 1% to 2.9%. The spun-twist long nanotube yarns possess both good electrical conductivity and mechanical flexibility compared to conventional metal wires or carbon fibers, which facilitate fabrication of solar cells with versatile configurations. A unique feature of our process is that instead of making individual fiber cells, we directly weave single or multiple nanotube yarns with primary electrodes into a functional fabric. Our results demonstrate promising applications of semiconducting nanowires and carbon nanotubes in woven photovoltaics.

  9. Insertion of CdSe quantum dots in ZnSe nanowires: MBE growth and microstructure analysis

    NASA Astrophysics Data System (ADS)

    den Hertog, M.; Elouneg-Jamroz, M.; Bellet-Amalric, E.; Bounouar, S.; Bougerol, C.; André, R.; Genuist, Y.; Poizat, J. P.; Kheng, K.; Tatarenko, S.

    2011-05-01

    ZnSe nanowire growth has been successfully achieved on ZnSe (1 0 0) and (1 1 1)B buffer layers deposited on GaAs substrates. Cubic [1 0 0] oriented ZnSe nanowires or [0 0 0 1] oriented hexagonal NWs are obtained on (1 0 0) substrates while [1 1 1] oriented cubic mixed with [0 0 0 1] oriented hexagonal regions are obtained on (1 1 1)B substrates. Most of the NWs are perpendicular to the surface in the last case. CdSe quantum dots were successfully incorporated in the ZnSe NWs as demonstrated by transmission electron microscopy, energy filtered TEM and high angle annular dark field scanning TEM measurements.

  10. On-surface formation of metal nanowire transparent top electrodes on CdSe nanowire array-based photoconductive devices.

    PubMed

    Azulai, Daniel; Givan, Uri; Shpaisman, Nava; Belenkova, Tatyana Levi; Gilon, Hagit; Patolsky, Fernando; Markovich, Gil

    2012-06-27

    A simple wet chemical approach was developed for a unique on-surface synthesis of transparent conductive films consisting of ultrathin gold/silver nanowires directly grown on top of CdSe nanowire array photoconductive devices enclosed in polycarbonate membranes. The metal nanowire film formed an ohmic contact to the semiconductor nanowires without additional treatment. The sheet resistance and transparency of the metal nanowire arrays could be controlled by the number of metal nanowire layers deposited, ranging from ∼98-99% transmission through the visible range and several kOhm/sq sheet resistance for a single layer, to 80-85% transmission and ∼100 Ohm/sq sheet resistance for 4 layers.

  11. Exciton-phonon coupling efficiency in CdSe quantum dots embedded in ZnSe nanowires

    NASA Astrophysics Data System (ADS)

    Bounouar, S.; Morchutt, C.; Elouneg-Jamroz, M.; Besombes, L.; André, R.; Bellet-Amalric, E.; Bougerol, C.; den Hertog, M.; Kheng, K.; Tatarenko, S.; Poizat, J. Ph.

    2012-01-01

    Exciton luminescence of a CdSe quantum dot (QD) inserted in a ZnSe nanowire is strongly influenced by the dark exciton states. Because of the small size of these QDs (2-5 nm), exchange interaction between hole and electron is highly enhanced and we measured large energy splitting between bright and dark exciton states (ΔE∈[4,9.2] meV) and large spin-flip rates between these states. Statistics on many QDs showed that this splitting depends on the QD size. Moreover, we measured an increase of the spin-flip rate to the dark states with increasing energy splitting. We explain this observation with a model, taking into account the fact that the exciton-phonon interaction depends on the bright to dark exciton energy splitting, as well as on the size and shape of the exciton wave function. It also has consequences on the exciton line intensity at high temperature.

  12. Fluorescence modulation of single CdSe nanowires by charge injection through the tip of an atomic-force microscope.

    PubMed

    Schäfer, Sebastian; Wang, Zhe; Kipp, Tobias; Mews, Alf

    2011-09-23

    We demonstrate a direct correlation between the charge state and photoluminescence (PL) intensity of individual CdSe nanowires by actively charging them and performing electrostatic force microscopy and PL measurements simultaneously. While the injection of positive charges leads to an immediate PL quenching, a small amount of injected electrons can lead to an increase of the PL intensity. We directly observed the migration of excess charges into the substrate, which leads to a recovery of the PL. Further, we show that the PL of individual NWs can be actively switched between on and off states by charging with the atomic-force microscope tip. We propose a model based on charge trapping and migration into the substrate to explain our results.

  13. Fast monolayer adsorption and slow energy transfer in CdSe quantum dot sensitized ZnO nanowires.

    PubMed

    Zheng, Kaibo; Žídek, Karel; Abdellah, Mohamed; Torbjörnsson, Magne; Chábera, Pavel; Shao, Shuyan; Zhang, Fengling; Pullerits, Tõnu

    2013-07-25

    A method for CdSe quantum dot (QD) sensitization of ZnO nanowires (NW) with fast adsorption rate is applied. Photoinduced excited state dynamics of the quantum dots in the case of more than monolayer coverage of the nanowires is studied. Transient absorption kinetics reveals an excitation depopulation process of indirectly attached quantum dots with a lifetime of ~4 ns. Photoluminescence and incident photon-to-electron conversion efficiency show that this process consists of both radiative e-h recombination and nonradiative excitation-to-charge conversion. We argue that the latter occurs via interdot energy transfer from the indirectly attached QDs to the dots with direct contact to the nanowires. From the latter, fast electron injection into ZnO occurs. The energy transfer time constant is found to be around 5 ns.

  14. Structure and Composition of Cu Doped CdSe Nanocrystals Using Soft X-ray Absorption Spectroscopy

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Hanif, K M; Willey, T M; Strouse, G F; Terminello, L J

    2004-06-04

    The local structure and composition of Cu ions dispersed in CdSe nanocrystals is examined using soft x-ray absorption near edge spectroscopy (XANES). Using Cu L-edge XANES and X-ray photoelectron measurements (XPS), we find that the Cu ions exist in the Cu(I) oxidation state. We also find that the observed Cu L-edge XANES signal is directly proportional to the molar percent of Cu present in our final material. Se L-edge XANES indicates changes in the Se density of states with Cu doping, due to a chemical bonding effect, and supports a statistical doping mechanism. Photoluminescence (PL) measurements indicate the Cu ions may act as deep electron traps. We show that XANES, XPS, and PL are a powerful combination of methods to study the electronic and chemical structure of dopants in nanostructured materials.

  15. 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

  16. Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots.

    PubMed

    Zhu, Huiguang; Prakash, Arjun; Benoit, Denise N; Jones, Christopher J; Colvin, Vicki L

    2010-06-25

    Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 degrees C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on the solubility of the metal salts used to form shells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can lead to homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dot cores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 degrees C) yields the thinnest shells (d < 1 nm) while the same process at higher temperatures (180 degrees C) forms thicker shells (d approximately 1-2 nm). The growth of the shell structures, average particle size, size distribution, and shape were examined using optical spectroscopy, transmission electron microscopy, x-ray diffraction, and transmittance small angle x-ray scattering. The photoluminescence quantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from 26% to 46% as compared to 10% for the CdSe cores. This method was further generalized to CdZnS shells by mixing cadmium and zinc acetate precursors. The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus 36%) as compared to the CdSe/ZnS prepared under similar conditions. These low temperature methods for shell growth are readily amenable to scale-up and can provide a route for economical and less energy intensive production of quantum dots.

  17. Low temperature synthesis of ZnS and CdZnS shells on CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Zhu, Huiguang; Prakash, Arjun; Benoit, Denise N.; Jones, Christopher J.; Colvin, Vicki L.

    2010-06-01

    Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleate and grow core and core-shell semiconductor nanocrystals. In this work, we generate highly monodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as 65 °C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine and trioctylphosphine oxide have marked effects on the solubility of the metal salts used to form shells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can lead to homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dot cores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 °C) yields the thinnest shells (d < 1 nm) while the same process at higher temperatures (180 °C) forms thicker shells (d ~ 1-2 nm). The growth of the shell structures, average particle size, size distribution, and shape were examined using optical spectroscopy, transmission electron microscopy, x-ray diffraction, and transmittance small angle x-ray scattering. The photoluminescence quantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from 26% to 46% as compared to 10% for the CdSe cores. This method was further generalized to CdZnS shells by mixing cadmium and zinc acetate precursors. The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus 36%) as compared to the CdSe/ZnS prepared under similar conditions. These low temperature methods for shell growth are readily amenable to scale-up and can provide a route for economical and less energy intensive production of quantum dots.

  18. Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers.

    PubMed

    Ehamparam, Ramanan; Pavlopoulos, Nicholas G; Liao, Michael W; Hill, Lawrence J; Armstrong, Neal R; Pyun, Jeffrey; Saavedra, S Scott

    2015-09-22

    Conduction and valence band energies (ECB, EVB) for CdSe nanorods (NRs) functionalized with Au nanoparticle (NP) tips are reported here, referenced to the vacuum scale. We use (a) UV photoemission spectroscopy (UPS) to measure EVB for NR films, utilizing advanced approaches to secondary electron background correction, satellite removal to enhance spectral contrast, and correction for shifts in local vacuum levels; and (b) waveguide-based spectroelectrochemistry to measure ECB from onset potentials for electron injection into NR films tethered to ITO. For untipped CdSe NRs, both approaches show EVB = 5.9-6.1 eV and ECB = 4.1-4.3 eV. Addition of Au tips alters the NR band edge energies and introduces midgap states, in ways that are predicted to influence the efficiency of these nanomaterials as photoelectrocatalysts. UPS results show that Au tipping shifts EVB closer to vacuum by up to 0.4 eV, shifts the apparent Fermi energy toward the middle of the band gap, and introduces additional states above EVB. Spectroelectrochemical results confirm these trends: Au tipping shifts ECB closer to vacuum, by 0.4-0.6 eV, and introduces midgap states below ECB, which are assigned as metal-semiconductor interface (MSI) states. Characterization of these band edge energies and understanding the origins of MSI states is needed to design energy conversion systems with proper band alignment between the light absorbing NR, the NP catalyst, and solution electron donors and acceptors. The complementary characterization protocols presented here should be applicable to a wide variety of thin films of heterogeneous photoactive nanomaterials, aiding in the identification of the most promising material combinations for photoelectrochemical energy conversion.

  19. 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.

  20. Fiber and fabric solar cells by directly weaving carbon nanotube yarns with CdSe nanowire-based electrodes

    NASA Astrophysics Data System (ADS)

    Zhang, Luhui; Shi, Enzheng; Ji, Chunyan; Li, Zhen; Li, Peixu; Shang, Yuanyuan; Li, Yibin; Wei, Jinquan; Wang, Kunlin; Zhu, Hongwei; Wu, Dehai; Cao, Anyuan

    2012-07-01

    Electrode materials are key components for fiber solar cells, and when combined with active layers (for light absorption and charge generation) in appropriate ways, they enable design and fabrication of efficient and innovative device structures. Here, we apply carbon nanotube yarns as counter electrodes in combination with CdSe nanowire-grafted primary electrodes (Ti wire) for making fiber and fabric-shaped photoelectrochemical cells with power conversion efficiencies in the range 1% to 2.9%. The spun-twist long nanotube yarns possess both good electrical conductivity and mechanical flexibility compared to conventional metal wires or carbon fibers, which facilitate fabrication of solar cells with versatile configurations. A unique feature of our process is that instead of making individual fiber cells, we directly weave single or multiple nanotube yarns with primary electrodes into a functional fabric. Our results demonstrate promising applications of semiconducting nanowires and carbon nanotubes in woven photovoltaics.Electrode materials are key components for fiber solar cells, and when combined with active layers (for light absorption and charge generation) in appropriate ways, they enable design and fabrication of efficient and innovative device structures. Here, we apply carbon nanotube yarns as counter electrodes in combination with CdSe nanowire-grafted primary electrodes (Ti wire) for making fiber and fabric-shaped photoelectrochemical cells with power conversion efficiencies in the range 1% to 2.9%. The spun-twist long nanotube yarns possess both good electrical conductivity and mechanical flexibility compared to conventional metal wires or carbon fibers, which facilitate fabrication of solar cells with versatile configurations. A unique feature of our process is that instead of making individual fiber cells, we directly weave single or multiple nanotube yarns with primary electrodes into a functional fabric. Our results demonstrate promising applications