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Sample records for ii quantum yields

  1. Cu(2+) inhibits photosystem II activities but enhances photosystem I quantum yield of Microcystis aeruginosa.

    PubMed

    Deng, Chunnuan; Pan, Xiangliang; Wang, Shuzhi; Zhang, Daoyong

    2014-08-01

    Responses of photosystem I and II activities of Microcystis aeruginosa to various concentrations of Cu(2+) were simultaneously examined using a Dual-PAM-100 fluorometer. Cell growth and contents of chlorophyll a were significantly inhibited by Cu(2+). Photosystem II activity [Y(II)] and electron transport [rETRmax(II)] were significantly altered by Cu(2+). The quantum yield of photosystem II [Y(II)] decreased by 29 % at 100 μg L(-1) Cu(2+) compared to control. On the contrary, photosystem I was stable under Cu(2+) stress and showed an obvious increase of quantum yield [Y(I)] and electron transport [rETRmax(I)] due to activation of cyclic electron flow (CEF). Yield of cyclic electron flow [Y(CEF)] was enhanced by 17 % at 100 μg L(-1) Cu(2+) compared to control. The contribution of linear electron flow to photosystem I [Y(II)/Y(I)] decreased with increasing Cu(2+) concentration. Yield of cyclic electron flow [Y(CEF)] was negatively correlated with the maximal photosystem II photochemical efficiency (F v/F m). In summary, photosystem II was the major target sites of toxicity of Cu(2+), while photosystem I activity was enhanced under Cu(2+) stress. PMID:24920130

  2. Action spectra of photosystems II and I and quantum yield of photosynthesis in leaves in State 1.

    PubMed

    Laisk, Agu; Oja, Vello; Eichelmann, Hillar; Dall'Osto, Luca

    2014-02-01

    The spectral global quantum yield (YII, electrons/photons absorbed) of photosystem II (PSII) was measured in sunflower leaves in State 1 using monochromatic light. The global quantum yield of PSI (YI) was measured using low-intensity monochromatic light flashes and the associated transmittance change at 810nm. The 810-nm signal change was calibrated based on the number of electrons generated by PSII during the flash (4·O2 evolution) which arrived at the PSI donor side after a delay of 2ms. The intrinsic quantum yield of PSI (yI, electrons per photon absorbed by PSI) was measured at 712nm, where photon absorption by PSII was small. The results were used to resolve the individual spectra of the excitation partitioning coefficients between PSI (aI) and PSII (aII) in leaves. For comparison, pigment-protein complexes for PSII and PSI were isolated, separated by sucrose density ultracentrifugation, and their optical density was measured. A good correlation was obtained for the spectral excitation partitioning coefficients measured by these different methods. The intrinsic yield of PSI was high (yI=0.88), but it absorbed only about 1/3 of quanta; consequently, about 2/3 of quanta were absorbed by PSII, but processed with the low intrinsic yield yII=0.63. In PSII, the quantum yield of charge separation was 0.89 as detected by variable fluorescence Fv/Fm, but 29% of separated charges recombined (Laisk A, Eichelmann H and Oja V, Photosynth. Res. 113, 145-155). At wavelengths less than 580nm about 30% of excitation is absorbed by pigments poorly connected to either photosystem, most likely carotenoids bound in pigment-protein complexes. PMID:24333386

  3. Structure-Triggered High Quantum Yield Luminescence and Switchable Dielectric Properties in Manganese(II) Based Hybrid Compounds.

    PubMed

    Wang, Zhong-Xia; Li, Peng-Fei; Liao, Wei-Qiang; Tang, Yuanyuan; Ye, Heng-Yun; Zhang, Yi

    2016-04-01

    Two new manganese(II) based organic-inorganic hybrid compounds, C11 H21 Cl3 MnN2 (1) and C11 H22 Cl4 MnN2 (2), with prominent photoluminescence and dielectric properties were synthesized by solvent modulation. Compound 1 with novel trigonal bipyramidal geometry exhibits bright red luminescence with a lifetime of 2.47 ms and high quantum yield of 35.8 %. Compound 2 with tetrahedral geometry displays intense long-lived (1.54 ms) green light emission with higher quantum yield of 92.3 %, accompanied by reversible solid-state phase transition at 170 K and a distinct switchable dielectric property. The better performance of 2 results from the structure, including a discrete organic cation moiety and inorganic metal anion framework, which gives the cations large freedom of motion. PMID:26864910

  4. Cobalt(II), Nickel(II) and Copper(II) complexes of a tetradentate Schiff base as photosensitizers: Quantum yield of 1O2 generation and its promising role in anti-tumor activity

    NASA Astrophysics Data System (ADS)

    Pradeepa, S. M.; Bhojya Naik, H. S.; Vinay Kumar, B.; Indira Priyadarsini, K.; Barik, Atanu; Ravikumar Naik, T. R.

    2013-01-01

    In the present investigation, a Schiff base N'1,N'3-bis[(E)-(5-bromo-2-hydroxyphenyl)methylidene]benzene-1,3-dicarbohydrazide and its metal complexes have been synthesized and characterized. The DNA-binding studies were performed using absorption spectroscopy, emission spectra, viscosity measurements and thermal denatuaration studies. The experimental evidence indicated that, the Co(II), Ni(II) and Cu(II) complexes interact with calf thymus DNA through intercalation with an intrinsic binding constant Kb of 2.6 × 104 M-1, 5.7 × 104 M-1 and 4.5 × 104 M-1, respectively and they exhibited potent photodamage abilities on pUC19 DNA, through singlet oxygen generation with quantum yields of 0.32, 0.27 and 0.30 respectively. The cytotoxic activity of the complexes resulted that they act as a potent photosensitizers for photochemical reactions.

  5. Quantum yield of charge separation in photosystem II: functional effect of changes in the antenna size upon light acclimation.

    PubMed

    Wientjes, Emilie; van Amerongen, Herbert; Croce, Roberta

    2013-09-26

    We have studied thylakoid membranes of Arabidopsis thaliana acclimated to different light conditions and have related protein composition to excitation energy transfer and trapping kinetics in Photosystem II (PSII). In high light: the plants have reduced amounts of the antenna complexes LHCII and CP24, the overall trapping time of PSII is only ∼180 ps, and the quantum efficiency reaches a value of 91%. In low light: LHCII is upregulated, the PSII lifetime becomes ∼310 ps, and the efficiency decreases to 84%. This difference is largely caused by slower excitation energy migration to the reaction centers in low-light plants due to the LHCII trimers that are not part of the C2S2M2 supercomplex. This pool of "extra" LHCII normally transfers energy to both photosystems, whereas it transfers only to PSII upon far-red light treatment (state 1). It is shown that in high light the reduction of LHCII mainly concerns the LHCII-M trimers, while the pool of "extra" LHCII remains intact and state transitions continue to occur. The obtained values for the efficiency of PSII are compared with the values of Fv/Fm, a parameter that is widely used to indicate the PSII quantum efficiency, and the observed differences are discussed. PMID:23534376

  6. Nonperturbative theory for the optical response to strong light of the light harvesting complex II of plants: Saturation of the fluorescence quantum yield

    NASA Astrophysics Data System (ADS)

    Richter, M.; Renger, Th.; Renger, G.; Knorr, A.

    2007-08-01

    Recent progress in resolution of the structure of the light harvesting complex II provides the basis for theoretical predictions on nonlinear optical properties from microscopic calculations. An approach to absorption and fluorescence is presented within the framework of Bloch equations using a correlation expansion of relevant many particle interactions. The equations derived within the framework of this theory are applied to describe fluorescence saturation phenomena. The experimentally observed decrease of the normalized fluorescence quantum yield from 1 to 0.0001 upon increasing the intensity of laser pulse excitation at 645nm by five orders of magnitude [R Schödel et al., Biophys. J. 71, 3370 (1996)] is explained by Pauli blocking effects of optical excitation and excitation energy transfer.

  7. Yield Improvement in Steel Casting (Yield II)

    SciTech Connect

    Richard A. Hardin; Christoph Beckermann; Tim Hays

    2002-02-18

    This report presents work conducted on the following main projects tasks undertaken in the Yield Improvement in Steel Casting research program: Improvement of Conventional Feeding and Risering Methods, Use of Unconventional Yield Improvement Techniques, and Case Studies in Yield Improvement. Casting trials were conducted and then simulated using the precise casting conditions as recorded by the participating SFSA foundries. These results present a statistically meaningful set of experimental data on soundness versus feeding length. Comparisons between these casting trials and casting trials performed more than forty years ago by Pellini and the SFSA are quite good and appear reasonable. Comparisons between the current SFSA feeding rules and feeding rules based on the minimum Niyama criterion reveal that the Niyama-based rules are generally less conservative. The niyama-based rules also agree better with both the trials presented here, and the casting trails performed by Pellini an d the SFSA years ago. Furthermore, the use of the Niyama criterion to predict centerline shrinkage for horizontally fed plate sections has a theoretical basis according to the casting literature reviewed here. These results strongly support the use of improved feeding rules for horizontal plate sections based on the Niyama criterion, which can be tailored to the casting conditions for a given alloy and to a desired level of soundness. The reliability and repeatability of ASTM shrinkage x-ray ratings was investigated in a statistical study performed on 128 x-rays, each of which were rated seven different times. A manual ''Feeding and Risering Guidelines for Steel Castings' is given in this final report. Results of casting trials performed to test unconventional techniques for improving casting yield are presented. These use a stacked arrangement of castings and riser pressurization to increase the casting yield. Riser pressurization was demonstrated to feed a casting up to four time s the

  8. Effects of Bleaching by Nitrogen Deficiency on the Quantum Yield of Photosystem II in Synechocystis sp. PCC 6803 Revealed by Chl Fluorescence Measurements.

    PubMed

    Ogawa, Takako; Sonoike, Kintake

    2016-03-01

    Estimation of photosynthesis by Chl fluorescence measurement of cyanobacteria is always problematic due to the interference from respiratory electron transfer and from phycocyanin fluorescence. The interference from respiratory electron transfer could be avoided by the use of DCMU or background illumination by blue light, which oxidizes the plastoquinone pool that tends to be reduced by respiration. On the other hand, the precise estimation of photosynthesis in cells with a different phycobilisome content by Chl fluorescence measurement is difficult. By subtracting the basal fluorescence due to the phycobilisome and PSI, it becomes possible to estimate the precise maximum quantum yield of PSII in cyanobacteria. Estimated basal fluorescence accounted for 60% of the minimum fluorescence, resulting in a large difference between the 'apparent' yield and 'true' yield under high phycocyanin conditions. The calculated value of the 'true' maximum quantum yield of PSII was around 0.8, which was similar to the value observed in land plants. The results suggest that the cause of the apparent low yield reported in cyanobacteria is mainly ascribed to the interference from phycocyanin fluorescence. We also found that the 'true' maximum quantum yield of PSII decreased under nitrogen-deficient conditions, suggesting the impairment of the PSII reaction center, while the 'apparent' maximum quantum yield showed a marginal change under the same conditions. Due to the high contribution of phycocyanin fluorescence in cyanobacteria, it is essential to eliminate the influence of the change in phycocyanin content on Chl fluorescence measurement and to evaluate the 'true' photosynthetic condition. PMID:26858287

  9. The Oxygen quantum yield in diverse algae and cyanobacteria is controlled by partitioning of flux between linear and cyclic electron flow within photosystem II.

    PubMed

    Ananyev, Gennady; Gates, Colin; Dismukes, G Charles

    2016-09-01

    We have measured flash-induced oxygen quantum yields (O2-QYs) and primary charge separation (Chl variable fluorescence yield, Fv/Fm) in vivo among phylogenetically diverse microalgae and cyanobacteria. Higher O2-QYs can be attained in cells by releasing constraints on charge transfer at the Photosystem II (PSII) acceptor side by adding membrane-permeable benzoquinone (BQ) derivatives that oxidize plastosemiquinone QB(-) and QBH2. This method allows uncoupling PSII turnover from its natural regulation in living cells, without artifacts of isolating PSII complexes. This approach reveals different extents of regulation across species, controlled at the QB(-) acceptor site. Arthrospira maxima is confirmed as the most efficient PSII-WOC (water oxidizing complex) and exhibits the least regulation of flux. Thermosynechococcus elongatus exhibits an O2-QY of 30%, suggesting strong downregulation. WOC cycle simulations with the most accurate model (VZAD) show that a light-driven backward transition (net addition of an electron to the WOC, distinct from recombination) occurs in up to 25% of native PSIIs in the S2 and S3 states, while adding BQ prevents backward transitions and increases the lifetime of S2 and S3 by 10-fold. Backward transitions occur in PSIIs that have plastosemiquinone radicals in the QB site and are postulated to be physiologically regulated pathways for storing light energy as proton gradient through direct PSII-cyclic electron flow (PSII-CEF). PSII-CEF is independent of classical PSI/cyt-b6f-CEF and provides an alternative proton translocation pathway for energy conversion. PSII-CEF enables variable fluxes between linear and cyclic electron pathways, thus accommodating species-dependent needs for redox and ion-gradient energy sources powered by a single photosystem. PMID:27117512

  10. Are Very Small Emission Quantum Yields Characteristic of Pure Metal-to-Ligand Charge-Transfer Excited States of Ruthenium(II)-(Acceptor Ligand) Chromophores?

    PubMed

    Tsai, Chia Nung; Mazumder, Shivnath; Zhang, Xiu Zhu; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

    2016-08-01

    Metal to ligand charge-transfer (MLCT) excited state emission quantum yields, ϕem, are reported in 77 K glasses for a series of pentaammine and tetraammine ruthenium(II) complexes with monodentate aromatic acceptor ligands (Ru-MDA) such as pyridine and pyrazine. These quantum yields are only about 0.2-1% of those found for their Ru-bpy (bpy = 2,2'-bipyridine) analogs in similar excited state energy ranges (hνem). The excited state energy dependencies of the emission intensity are characterized by mean radiative decay rate constants, kRAD, resolved from ϕem/τobs = kRAD (τobs = the observed emission decay lifetime; τobs(-1) = kRAD + kNRD; kNRD = nonradiative decay rate constant). Except for the Ru-pz chromophores in alcohol glasses, the values of kNRD for the Ru-MDA chromophores are slightly smaller, and their dependences on excited state energies are very similar to those of related Ru-bpy chromophores. In principle, one expects kRAD to be proportional to the product of (hνem)(3) and the square of the transition dipole moment (Me,g).(2) However, from experimental studies of Ru-bpy chromophores, an additional hνem dependence has been found that originates in an intensity stealing from a higher energy excited state with a much larger value of Me,g. This additional hνem dependence is not present in the kRAD energy dependence for Ru-MDA chromophores in the same energy regime. Intensity stealing in the phosphorescence of these complexes is necessary since the triplet-to-singlet transition is only allowed through spin-orbit coupling and since the density functional theory modeling implicates configurational mixing between states in the triplet spin manifold; this is treated by setting Me,g equal to the product of a mixing coefficient and the difference between the molecular dipole moments of the states involved, which implicates an experimental first order dependence of kRAD on hνem. The failure to observe intensity stealing for the Ru-MDA complexes suggests

  11. HYPERSENSITIVE TO HIGH LIGHT1 Interacts with LOW QUANTUM YIELD OF PHOTOSYSTEM II1 and Functions in Protection of Photosystem II from Photodamage in Arabidopsis[C][W][OPEN

    PubMed Central

    Jin, Honglei; Liu, Bing; Luo, Lujun; Feng, Dongru; Wang, Peng; Liu, Jun; Da, Qingen; He, Yanming; Qi, Kangbiao; Wang, Jinfa; Wang, Hong-Bin

    2014-01-01

    Under high-irradiance conditions, plants must efficiently protect photosystem II (PSII) from damage. In this study, we demonstrate that the chloroplast protein HYPERSENSITIVE TO HIGH LIGHT1 (HHL1) is expressed in response to high light and functions in protecting PSII against photodamage. Arabidopsis thaliana hhl1 mutants show hypersensitivity to high light, drastically decreased PSII photosynthetic activity, higher nonphotochemical quenching activity, a faster xanthophyll cycle, and increased accumulation of reactive oxygen species following high-light exposure. Moreover, HHL1 deficiency accelerated the degradation of PSII core subunits under high light, decreasing the accumulation of PSII core subunits and PSII–light-harvesting complex II supercomplex. HHL1 primarily localizes in the stroma-exposed thylakoid membranes and associates with the PSII core monomer complex through direct interaction with PSII core proteins CP43 and CP47. Interestingly, HHL1 also directly interacts, in vivo and in vitro, with LOW QUANTUM YIELD OF PHOTOSYSTEM II1 (LQY1), which functions in the repair and reassembly of PSII. Furthermore, the hhl1 lqy1 double mutants show increased photosensitivity compared with single mutants. Taken together, these results suggest that HHL1 forms a complex with LQY1 and participates in photodamage repair of PSII under high light. PMID:24632535

  12. Primary quantum yields of NO2 photodissociation

    NASA Technical Reports Server (NTRS)

    Gardner, Edward P.; Sperry, Paul D.; Calvert, Jack G.

    1987-01-01

    The quantum yields of formation of NO, O2, and NO2 loss are measured for NO2 vapor at low pressures (0.13-0.30 torr) irradiated at 334-405 nm wavelengths and temperature in the range 273-370 K in order to study the primary quantum efficiencies of NO2 photodecomposition. The temperature and wavelength dependences of the primary quantum efficiencies are examined. It is observed that the primary quantum efficiencies increase rapidly from near zero at 424 nm to near unity for excitation at wavelengths less than 394 nm. The theory of Pitts et al. (1964) that the energy deficiency for photodissociation of NO2 excited at wavelengths greater than 397.9 nm is due to the rotational and vibrational energy of the NO2 molecules is confirmed by the data. Values for the primary quantum yields of NO2 photodecomposition as a function of wavelength are presented.

  13. Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.

    PubMed

    Estupiñán-López, Carlos; Dominguez, Christian Tolentino; Cabral Filho, Paulo E; Fontes, Adriana; de Araujo, Renato E

    2014-01-01

    An essential parameter to evaluate the light emission properties of fluorophores is the fluorescence quantum yield, which quantify the conversion efficiency of absorbed photons to emitted photons. We detail here an alternative nonfluorescent method to determine the absolute fluorescence quantum yield of quantum dots (QDs). The method is based in the so-called Thermal Lens Spectroscopy (TLS) technique, which consists on the evaluation of refractive index gradient thermally induced in the fluorescent material by the absorption of light. Aqueous dispersion carboxyl-coated cadmium telluride (CdTe) QDs samples were used to demonstrate the Thermal Lens Spectroscopy technical procedure. PMID:25103802

  14. Spectroscopy characterization and quantum yield determination of quantum dots

    NASA Astrophysics Data System (ADS)

    Contreras Ortiz, S. N.; Mejía Ospino, E.; Cabanzo, R.

    2016-02-01

    In this paper we show the characterization of two kinds of quantum dots: hydrophilic and hydrophobic, with core and core/shell respectively, using spectroscopy techniques such as UV-Vis, fluorescence and Raman. We determined the quantum yield in the quantum dots using the quinine sulphate as standard. This salt is commonly used because of its quantum yield (56%) and stability. For the CdTe excitation, we used a wavelength of 549nm and for the CdSe/ZnS excitation a wavelength of 527nm. The results show that CdSe/ZnS (49%) has better fluorescence, better quantum dots, and confirm the fluorescence result. The quantum dots have shown a good fluorescence performance, so this property will be used to replace dyes, with the advantage that quantum dots are less toxic than some dyes like the rhodamine. In addition, in this work we show different techniques to find the quantum dots emission: fluorescence spectrum, synchronous spectrum and Raman spectrum.

  15. Quantum Yield of Gold-Cathode Photomultipliers

    NASA Technical Reports Server (NTRS)

    Childs, Charles B.

    1961-01-01

    Two gold-cathode EMI 6255G tubes have been investigated for their quantum yield between 3100 and 1900 A. The tubes had cathodes of different appearances. One of these, numbered 3012, had a slight bluish tinge and was very transparent to visible light; the other, numbered 3021, had a definite gold coloration. The relative quantum yield of each tube was determined with the aid of a Cary model 14 recording spectrophotometer used as a monochromator. The monochromator relative-energy output was determined from the current output of a sodium-salicylate-coated RCA 1P21 photomultiplier. Each gold-cathode tube was then operated at 3000 v, and the central 1.8 cm cube of the cathode was exposed to the monochromator output.

  16. Using the quantum yields of photosystem II and the rate of net photosynthesis to monitor high irradiance and temperature stress in chrysanthemum (Dendranthema grandiflora).

    PubMed

    Janka, Eshetu; Körner, Oliver; Rosenqvist, Eva; Ottosen, Carl-Otto

    2015-05-01

    Under a dynamic greenhouse climate control regime, temperature is adjusted to optimise plant physiological responses to prevailing irradiance levels; thus, both temperature and irradiance are used by the plant to maximise the rate of photosynthesis, assuming other factors are not limiting. The control regime may be optimised by monitoring plant responses, and may be promptly adjusted when plant performance is affected by extreme microclimatic conditions, such as high irradiance or temperature. To determine the stress indicators of plants based on their physiological responses, net photosynthesis (Pn) and four chlorophyll-a fluorescence parameters: maximum photochemical efficiency of PSII [Fv/Fm], electron transport rate [ETR], PSII operating efficiency [F'q/F'm], and non-photochemical quenching [NPQ] were assessed for potted chrysanthemum (Dendranthema grandiflora Tzvelev) 'Coral Charm' under different temperature (20, 24, 28, 32, 36 °C) and daily light integrals (DLI; 11, 20, 31, and 43 mol m(-2) created by a PAR of 171, 311, 485 and 667 μmol m(-2) s(-1) for 16 h). High irradiance (667 μmol m(-2) s(-1)) combined with high temperature (>32 °C) significantly (p < 0.05) decreased Fv/Fm. Under high irradiance, the maximum Pn and ETR were reached at 24 °C. Increased irradiance decreased the PSII operating efficiency and increased NPQ, while both high irradiance and temperature had a significant effect on the PSII operating efficiency at temperatures >28 °C. Under high irradiance and temperature, changes in the NPQ determined the PSII operating efficiency, with no major change in the fraction of open PSII centres (qL) (indicating a QA redox state). We conclude that 1) chrysanthemum plants cope with excess irradiance by non-radiative dissipation or a reversible stress response, with the effect on the Pn and quantum yield of PSII remaining low until the temperature reaches 28 °C and 2) the integration of online measurements to monitor photosynthesis and PSII

  17. Loss of quantum yield in extremely low light.

    PubMed

    Kirschbaum, Miko U F; Ohlemacher, Christian; Küppers, Manfred

    2004-04-01

    It has generally been assumed that the photosynthetic quantum yield of all C3 plants is essentially the same for all unstressed leaves at the same temperature and CO2 and O2 concentrations. However, some recent work by H.C. Timm et al. (2002, Trees 16:47-62) has shown that quantum yield can be reduced for some time after leaves have been exposed to darkness. To investigate under what light conditions quantum yield can be reduced, we carried out a number of experiments on leaves of a partial-shade (unlit greenhouse)-grown Coleus blumei Benth. hybrid. We found that after leaves had been exposed to complete darkness, quantum yield was reduced by about 60%. Only very low light levels were needed for quantum yield to be fully restored, with 5 micromol quanta m(-2) s(-1) being sufficient for 85% of the quantum yield of fully induced leaves to be achieved. Leaves regained higher quantum yields upon exposure to higher light levels with an estimated time constant of 130 s. It was concluded that the loss of quantum yield would be quantitatively important only for leaves growing in very dense understoreys where maximum light levels might not exceed 5 micromol quanta m(-2) s(-1) even in the middle of the day. Most leaves, even in understorey conditions, do, however, experience light levels in excess of 5 micromol quanta m(-2) s(-1) over periods where they obtain most of their carbon so that the loss of quantum yield would affect total carbon gain of those leaves only marginally. PMID:14722771

  18. One-pot green synthesis of high quantum yield oxygen-doped, nitrogen-rich, photoluminescent polymer carbon nanoribbons as an effective fluorescent sensing platform for sensitive and selective detection of silver(I) and mercury(II) ions.

    PubMed

    Wang, Zhong-Xia; Ding, Shou-Nian

    2014-08-01

    This work reports on a facile, economical, and green preparative strategy toward water-soluble, fluorescent oxygen-doped, nitrogen-rich, photoluminescent polymer carbon nanoribbons (ONPCRs) with a quantum yield of approximately 25.61% by the hydrothermal process using uric acid as a carbon-nitrogen source for the first time. The as-prepared fluorescent ONPCRs showed paddy leaf-like structure with 80-160 nm length and highly efficient fluorescent quenching ability in the presence of mercury(II) (Hg(2+)) or silver (Ag(+)) ions due to the formed nonfluorescent metal complexes via robust Hg(2+)-O or Ag(+)-N interaction with the O and N of fluorescent ONPCRs, which allowed the analysis of Hg(2+) and Ag(+) ions in a very simple method. By employing this sensor, excellent linear relationships existed between the quenching degree of the ONPCRs and the concentrations of Hg(2+) and Ag(+) ions in the range of 2.0 nM to 60 μM and 5.0 nM to 80 μM, respectively. By using ethylenediaminetetraacetate and ammonia as the masking agent of Hg(2+) and Ag(+) ions, respectively, Hg(2+) or Ag(+) ions were exclusively detected in coexistence with Ag(+) or Hg(2+) ions with high sensitivity, and the detection limits as low as 0.68 and 1.73 nM (3σ) were achieved, respectively, which also provided a reusable detection method for Hg(2+) and Ag(+) ions. Therefore, the easily synthesized fluorescent ONPCRs may have great potential applications in the detection of Hg(2+) and Ag(+) ions for biological assay and environmental protection. PMID:24979236

  19. On the photoelectric quantum yield of small dust particles

    NASA Astrophysics Data System (ADS)

    Kimura, Hiroshi

    2016-07-01

    Photoelectron emission is crucial to electric charging of dust particles around main-sequence stars and gas heating in various dusty environments. An estimate of the photoelectric processes contains an ill-defined parameter called the photoelectric quantum yield, which is the total number of electrons ejected from a dust particle per absorbed photon. Here we revisit the so-called small particle effect of photoelectron emission and provide an analytical model to estimate photoelectric quantum yields of small dust particles in sizes down to nanometers. We show that the small particle effect elevates the photoelectric quantum yields of nanoparticles up to by a factor of 103 for carbon, water ice, and organics, and a factor of 102 for silicate, silicon carbide, and iron. We conclude the surface curvature of the particles is a quantity of great importance to the small particle effect, unless the particles are submicrometers in radius or larger.

  20. High quantum yield ZnO quantum dots synthesizing via an ultrasonication microreactor method.

    PubMed

    Yang, Weimin; Yang, Huafang; Ding, Wenhao; Zhang, Bing; Zhang, Le; Wang, Lixi; Yu, Mingxun; Zhang, Qitu

    2016-11-01

    Green emission ZnO quantum dots were synthesized by an ultrasonic microreactor. Ultrasonic radiation brought bubbles through ultrasonic cavitation. These bubbles built microreactor inside the microreactor. The photoluminescence properties of ZnO quantum dots synthesized with different flow rate, ultrasonic power and temperature were discussed. Flow rate, ultrasonic power and temperature would influence the type and quantity of defects in ZnO quantum dots. The sizes of ZnO quantum dots would be controlled by those conditions as well. Flow rate affected the reaction time. With the increasing of flow rate, the sizes of ZnO quantum dots decreased and the quantum yields first increased then decreased. Ultrasonic power changed the ultrasonic cavitation intensity, which affected the reaction energy and the separation of the solution. With the increasing of ultrasonic power, sizes of ZnO quantum dots first decreased then increased, while the quantum yields kept increasing. The effect of ultrasonic temperature on the photoluminescence properties of ZnO quantum dots was influenced by the flow rate. Different flow rate related to opposite changing trend. Moreover, the quantum yields of ZnO QDs synthesized by ultrasonic microreactor could reach 64.7%, which is higher than those synthesized only under ultrasonic radiation or only by microreactor. PMID:27245962

  1. Investigating energy partitioning during photosynthesis using an expanded quantum yield convention

    NASA Astrophysics Data System (ADS)

    Ahn, Tae Kyu; Avenson, Thomas J.; Peers, Graham; Li, Zhirong; Dall'Osto, Luca; Bassi, Roberto; Niyogi, Krishna K.; Fleming, Graham R.

    2009-02-01

    In higher plants, regulation of excess absorbed light is essential for their survival and fitness, as it enables avoidance of a build up of singlet oxygen and other reactive oxygen species. Regulation processes (known as non-photochemical quenching; NPQ) can be monitored by steady-state fluorescence on intact plant leaves. Pulse amplitude modulated (PAM) measurements of chlorophyll a fluorescence have been used for over 20 years to evaluate the amount of NPQ and photochemistry (PC). Recently, a quantum yield representation of NPQ ( ΦNPQ), which incorporates a variable fraction of open reaction centers, was proposed by Hendrickson et al. [L. Hendrickson, R.T. Furbank, W.S. Chow, Photosynth. Res. 82 (2004) 73]. In this work we extend the quantum yield approach to describe the yields of reversible energy-dependent quenching ( ΦqE), state transitions to balance PC between photosystems II and I ( ΦqT), and photoinhibition quenching associated with damaged reaction centers ( ΦqI). We showed the additivity of the various quantum yield components of NPQ through experiments on wild-type and npq1 strains of Arabidopsis thaliana. The quantum yield approach enables comparison of ΦqE with data from a variety of techniques used to investigate the mechanism of qE. We showed that ΦqE for a series of A. thaliana genotypes scales linearly with the magnitude of zeaxanthin cation formation, suggesting that charge-transfer quenching is largely responsible for qE in plants.

  2. Quantum Yield of Single Surface Plasmons Generated by a Quantum Dot Coupled with a Silver Nanowire.

    PubMed

    Li, Qiang; Wei, Hong; Xu, Hongxing

    2015-12-01

    The interactions between surface plasmons (SPs) in metal nanostructures and excitons in quantum emitters (QEs) lead to many interesting phenomena and potential applications that are strongly dependent on the quantum yield of SPs. The difficulty in distinguishing all the possible exciton recombination channels hinders the experimental determination of SP quantum yield. Here, we experimentally measured for the first time the quantum yield of single SPs generated by the exciton-plasmon coupling in a system composed of a single quantum dot and a silver nanowire (NW). By utilizing the SP guiding property of the NW, the decay rates of all the exciton recombination channels, i.e., direct free space radiation channel, SP generation channel, and nonradiative damping channel, are quantitatively obtained. It is determined that the optimum emitter-NW coupling distance for the largest SP quantum yield is about 10 nm, resulting from the different distance-dependent decay rates of the three channels. These results are important for manipulating the coupling between plasmonic nanostructures and QEs and developing on-chip quantum plasmonic devices for potential nanophotonic and quantum information applications. PMID:26583200

  3. Quantum yield of conversion of the dental photoinitiator camphorquinone

    NASA Astrophysics Data System (ADS)

    Chen, Yin-Chu; Ferracane, Jack L.; Prahl, Scott A.

    2005-06-01

    The primary absorber in dental resins is the photoinitiators, which start the photo polymerization process. We studied the quantum yield of conversion of camphorquinone (CQ), a blue light photoinitiator, using 3M FreeLight LED lamp as the light curing unit. The molar extinction coefficient, ɛ469, of CQ was measured to be 46+/-2 cm-1/(mol/L) at 469 nm. The absorption coefficient change to the radiant exposure was measured at three different irradiances. The relationship between the CQ absorption coefficient and curing lamp radiant exposure was the same for different irradiances and fit an exponential function: μa469(H)= μao exp(-H/Hthreshold), where μao is 4.46+/-0.05 cm-1, and Hthreshold=43+/-4 J/cm2. Combining this exponential relationship with CQ molar extinction coefficient and the absorbed photon energy (i.e., the product of the radiant exposure with the absorption coefficient), we plotted CQ concentration [number of molecules/cm3] as a function of the accumulated absorbed photons per volume. The slope of the relationship is the quantum yield of the CQ conversion. Therefore, in our formulation (0.7 w% CQ with reducing agents 0.35 w% DMAEMA and 0.05 w% BHT) the quantum yield was solved to be 0.07+/-0.01 CQ conversion per absorbed photon.

  4. Spatial mapping of fluorophore quantum yield in diffusive media.

    PubMed

    Zhao, Yanyu; Roblyer, Darren

    2015-08-01

    Fluorescence quantum yield (QY) indicates the efficiency of the fluorescence process. The QY of many fluorophores is sensitive to local tissue environments, highlighting the possibility of using QY as an indicator of important parameters such as pH or temperature. QY is commonly measured by comparison to a well-known standard in nonscattering media. We propose a new imaging method, called quantum yield imaging (QYI), to spatially map the QY of a fluorophore within an optically diffusive media. QYI utilizes the wide-field diffuse optical technique spatial frequency domain imaging (SFDI) as well as planar fluorescence imaging. SFDI is used to measure the optical properties of the background media and the absorption contributed by the fluorophore. The unknown QY is then calculated by combining information from both modalities. A fluorescent sample with known QY is used to account for instrument response. To demonstrate QYI, rhodamine B and SNARF-5 were imaged in liquid phantoms with different background optical properties. The methanol:water ratio and pH were changed for rhodamine B and SNARF-5 solvents, respectively, altering the QY of each through a wide range. QY was determined with an agreement of 0.021 and 0.012 for rhodamine B and SNARF-5, respectively. PMID:26308165

  5. Synthesis of Luminescent Graphene Quantum Dots with High Quantum Yield and Their Toxicity Study

    PubMed Central

    Jiang, Dan; Chen, Yunping; Li, Na; Li, Wen; Wang, Zhenguo; Zhu, Jingli; Zhang, Hong; Liu, Bin; Xu, Shan

    2015-01-01

    High fluorescence quantum yield graphene quantum dots (GQDs) have showed up as a new generation for bioimaging. In this work, luminescent GQDs were prepared by an ameliorative photo-Fenton reaction and a subsequent hydrothermal process using graphene oxide sheets as the precursor. The as-prepared GQDs were nanomaterials with size ranging from 2.3 to 6.4 nm and emitted intense green luminescence in water. The fluorescence quantum yield was as high as 24.6% (excited at 340 nm) and the fluorescence was strongest at pH 7. Moreover, the influences of low-concentration (12.5, 25 μg/mL) GQDs on the morphology, viability, membrane integrity, internal cellular reactive oxygen species level and mortality of HeLa cells were relatively weak, and the in vitro imaging demonstrated GQDs were mainly in the cytoplasm region. More strikingly, zebrafish embryos were co-cultured with GQDs for in vivo imaging, and the results of heart rate test showed the intake of small amounts of GQDs brought little harm to the cardiovascular of zebrafish. GQDs with high quantum yield and strong photoluminescence show good biocompatibility, thus they show good promising for cell imaging, biolabeling and other biomedical applications. PMID:26709828

  6. Products and quantum yields for photolysis of chloroaromatics in water

    SciTech Connect

    Dulin, D.; Drossman, H.; Mill, T.

    1986-01-01

    Photolysis of chlorobenzene, 2- and 4-chlorobiphenyl, and 2- and 4-chlorobiphenyl ethers in water with 250-300-nm light produce corresponding phenols or, in the case of 2-chlorobiphenyl ether, dibenzofuran exclusively. Quantum yields in most cases are very similar to those reported in hexane for the reduction process. 1,2,4-Trichlorobenzene and 2,3,7,8-tetrachlorodibenzodioxin (TC-DD) photolyze much less efficiently in water than in hexane. A common pathway for photolysis of monochloroaromatics involving aryl cations accounts well for the experimental observations. C-O rather than C-Cl cleavage in TCDD may be a major pathway for its loss. Half-lives for photolysis of these chloroaromatics in sunlight in water range from 460 years to 5 days; TCDD photolyzes in water with a half-life of about 4-5 days in summer at 40/sup 0/ latitude. 40 references, 1 figure, 8 tables.

  7. Luminescence quantum yields of gold nanoparticles varying with excitation wavelengths.

    PubMed

    Cheng, Yuqing; Lu, Guowei; He, Yingbo; Shen, Hongming; Zhao, Jingyi; Xia, Keyu; Gong, Qihuang

    2016-01-28

    Luminescence quantum yields (QYs) of gold nanoparticles including nanorods, nanobipyramids and nanospheres are measured elaborately at a single nanoparticle level with different excitation wavelengths. It is found that the QYs of the nanostructures are essentially dependent on the excitation wavelength. The QY is higher when the excitation wavelength is blue-detuned and close to the nanoparticles' surface plasmon resonance peak. A phenomenological model based on the plasmonic resonator concept is proposed to understand the experimental findings. The excitation wavelength dependent QY is attributed to the wavelength dependent coupling efficiency between the free electron oscillation and the intrinsic plasmon resonant radiative mode. These studies should contribute to the understanding of one-photon luminescence from metallic nanostructures and plasmonic surface enhanced spectroscopy. PMID:26731570

  8. Luminescence quantum yields of gold nanoparticles varying with excitation wavelengths

    NASA Astrophysics Data System (ADS)

    Cheng, Yuqing; Lu, Guowei; He, Yingbo; Shen, Hongming; Zhao, Jingyi; Xia, Keyu; Gong, Qihuang

    2016-01-01

    Luminescence quantum yields (QYs) of gold nanoparticles including nanorods, nanobipyramids and nanospheres are measured elaborately at a single nanoparticle level with different excitation wavelengths. It is found that the QYs of the nanostructures are essentially dependent on the excitation wavelength. The QY is higher when the excitation wavelength is blue-detuned and close to the nanoparticles' surface plasmon resonance peak. A phenomenological model based on the plasmonic resonator concept is proposed to understand the experimental findings. The excitation wavelength dependent QY is attributed to the wavelength dependent coupling efficiency between the free electron oscillation and the intrinsic plasmon resonant radiative mode. These studies should contribute to the understanding of one-photon luminescence from metallic nanostructures and plasmonic surface enhanced spectroscopy.

  9. Film quantum yields of EUV& ultra-high PAG photoresists

    SciTech Connect

    Hassanein, Elsayed; Higgins, Craig; Naulleau, Patrick; Matyi, Richard; Gallatin, Greg; Denbeaux, Gregory; Antohe, Alin; Thackery, Jim; Spear, Kathleen; Szmanda, Charles; Anderson, Christopher N.; Niakoula, Dimitra; Malloy, Matthew; Khurshid, Anwar; Montgomery, Cecilia; Piscani, Emil C.; Rudack, Andrew; Byers, Jeff; Ma, Andy; Dean, Kim; Brainard, Robert

    2008-01-10

    Base titration methods are used to determine C-parameters for three industrial EUV photoresist platforms (EUV-2D, MET-2D, XP5496) and twenty academic EUV photoresist platforms. X-ray reflectometry is used to measure the density of these resists, and leads to the determination of absorbance and film quantum yields (FQY). Ultrahigh levels ofPAG show divergent mechanisms for production of photo acids beyond PAG concentrations of 0.35 moles/liter. The FQY of sulfonium PAGs level off, whereas resists prepared with iodonium PAG show FQY s that increase beyond PAG concentrations of 0.35 moles/liter, reaching record highs of 8-13 acids generatedlEUV photons absorbed.

  10. Self-absorption correction for solid-state photoluminescence quantum yields obtained from integrating sphere measurements.

    PubMed

    Ahn, Tai-Sang; Al-Kaysi, Rabih O; Müller, Astrid M; Wentz, Katherine M; Bardeen, Christopher J

    2007-08-01

    A new method is presented for analyzing the effects of self-absorption on photoluminescence integrating sphere quantum yield measurements. Both the observed quantum yield and luminescence spectrum are used to determine the self-absorption probability, taking into account both the initial emission and subsequent absorption and reemission processes. The analysis is experimentally validated using the model system of the laser dye perylene red dispersed in a polymer film. This approach represents an improvement over previous methods that tend to overestimate the true quantum yield, especially in cases with high sample absorbance or quantum yield values. PMID:17764365

  11. Quantum spin Hall effect in inverted type-II semiconductors.

    PubMed

    Liu, Chaoxing; Hughes, Taylor L; Qi, Xiao-Liang; Wang, Kang; Zhang, Shou-Cheng

    2008-06-13

    The quantum spin Hall (QSH) state is a topologically nontrivial state of quantum matter which preserves time-reversal symmetry; it has an energy gap in the bulk, but topologically robust gapless states at the edge. Recently, this novel effect has been predicted and observed in HgTe quantum wells and in this Letter we predict a similar effect arising in Type-II semiconductor quantum wells made from InAs/GaSb/AlSb. The quantum well exhibits an "inverted" phase similar to HgTe/CdTe quantum wells, which is a QSH state when the Fermi level lies inside the gap. Due to the asymmetric structure of this quantum well, the effects of inversion symmetry breaking are essential. Remarkably, the topological quantum phase transition between the conventional insulating state and the quantum spin Hall state can be continuously tuned by the gate voltage, enabling quantitative investigation of this novel phase transition. PMID:18643529

  12. Near-unity photoluminescence quantum yield in MoS₂.

    PubMed

    Amani, Matin; Lien, Der-Hsien; Kiriya, Daisuke; Xiao, Jun; Azcatl, Angelica; Noh, Jiyoung; Madhvapathy, Surabhi R; Addou, Rafik; KC, Santosh; Dubey, Madan; Cho, Kyeongjae; Wallace, Robert M; Lee, Si-Chen; He, Jr-Hau; Ager, Joel W; Zhang, Xiang; Yablonovitch, Eli; Javey, Ali

    2015-11-27

    Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising material system for optoelectronic applications, but their primary figure of merit, the room-temperature photoluminescence quantum yield (QY), is extremely low. The prototypical 2D material molybdenum disulfide (MoS2) is reported to have a maximum QY of 0.6%, which indicates a considerable defect density. Here we report on an air-stable, solution-based chemical treatment by an organic superacid, which uniformly enhances the photoluminescence and minority carrier lifetime of MoS2 monolayers by more than two orders of magnitude. The treatment eliminates defect-mediated nonradiative recombination, thus resulting in a final QY of more than 95%, with a longest-observed lifetime of 10.8 ± 0.6 nanoseconds. Our ability to obtain optoelectronic monolayers with near-perfect properties opens the door for the development of highly efficient light-emitting diodes, lasers, and solar cells based on 2D materials. PMID:26612948

  13. Are Fluorescence Quantum Yields So Tricky to Measure? A Demonstration Using Familiar Stationery Products

    NASA Astrophysics Data System (ADS)

    Fery-Forgues*, Suzanne; Lavabre, Dominique

    1999-09-01

    Fluorescence quantum yields are used to quantify the efficiency of the emission process. In spite of the importance of these data, experimental directions for their acquisition are rarely given. A general procedure for determining the relative fluorescence quantum yield of solutions is described here, drawing attention to the many pitfalls that students may encounter. Starting materials are common yellow and pink highlighter pens.

  14. Local Density Fluctuations Predict Photoisomerization Quantum Yield of Azobenzene-Modified DNA.

    PubMed

    Kingsland, Addie; Samai, Soumyadyuti; Yan, Yunqi; Ginger, David S; Maibaum, Lutz

    2016-08-01

    Azobenzene incorporated into DNA has a photoisomerization quantum yield that depends on the DNA sequence near the azobenzene attachment site. We use Molecular Dynamics computer simulations to elucidate which physical properties of the modified DNA determine the quantum yield. We show for a wide range of DNA sequences that the photoisomerization quantum yield is strongly correlated with the variance of the number of atoms in close proximity to the outer phenyl ring of the azobenzene group. We infer that quantum yield is controlled by the availability of fluctuations that enable the conformational change. We demonstrate that these simulations can be used as a qualitative predictive tool by calculating the quantum yield for several novel DNA sequences, and confirming these predictions using UV-vis spectroscopy. Our results will be useful for the development of a wide range of applications of photoresponsive DNA nanotechnology. PMID:27428569

  15. Dielectric permittivity of quantum plasma. Part II

    NASA Astrophysics Data System (ADS)

    Bobylev, Yu. V.; Kuzelev, M. V.

    2014-05-01

    The transverse and longitudinal dielectric permittivities of isotropic quantum plasma are calculated in the quantum plasma models based on the Dirac and Pauli equations. The dispersion relations for transverse-longitudinal waves in quantum particle beams are derived. Relativistic longitudinal and transverse waves in cold isotropic quantum plasma in models based on the Klein-Gordon and Dirac equations, as well as spin waves in the model based on the Pauli equation, are considered. Conditions for wave-particle resonance interactions in relativistic quantum plasma are analyzed.

  16. Absolute 1* quantum yields for the ICN A state by diode laser gain versus absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Hess, Wayne P.; Leone, Stephen R.

    1987-01-01

    Absolute I* quantum yields were measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The temperature yields are obtained by the technique of time-resolved diode laser gain-versus-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 +/- 2% and it falls off to 53.4 +/- 2% and 44.0 +/- 4% at 284 and 248 respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I* quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I* yields. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I* yield results.

  17. High quantum yield graphene quantum dots decorated TiO2 nanotubes for enhancing photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Qu, Ailan; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

    2016-07-01

    Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO2 nanotubes (GQDs/TiO2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600-800 nm. The photocatalytic activity of prepared GQDs/TiO2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO2 nanotubes (TiO2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV-vis light irradiation (λ = 380-780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO2 composite.

  18. Gradient CdSe/CdS Quantum Dots with Room Temperature Biexciton Unity Quantum Yield.

    PubMed

    Nasilowski, Michel; Spinicelli, Piernicola; Patriarche, Gilles; Dubertret, Benoît

    2015-06-10

    Auger recombination is a major limitation for the fluorescent emission of quantum dots (QDs). It is the main source of QDs fluorescence blinking at the single-particle level. At high-power excitation, when several charge carriers are formed inside a QD, Auger becomes more efficient and severely decreases the quantum yield (QY) of multiexcitons. This limits the efficiency and the use of colloidal QDs in applications where intense light output is required. Here, we present a new generation of thick-shell CdSe/CdS QDs with dimensions >40 nm and a composition gradient between the core and the shell that exhibits 100% QY for the emission of both the monoexciton and the biexciton in air and at room temperature for all the QDs we have observed. The fluorescence emission of these QDs is perfectly Poissonian at the single-particle level at different excitation levels and temperatures, from 30 to 300 K. In these QDs, the emission of high-order (>2) multiexcitons is quite efficient, and we observe white light emission at the single-QD level when high excitation power is used. These gradient thick shell QDs confirm the suppression of Auger recombination in gradient core/shell structures and help further establish the colloidal QDs with a gradient shell as a very stable source of light even under high excitation. PMID:25990468

  19. Quantum yield and lifetime data analysis for the UV curable quantum dot nanocomposites.

    PubMed

    Cheng, Qi; Liu, Cui; Wei, Wenjun; Xu, Heng; You, Qingliang; Zou, Linling; Liu, Xueqing; Liu, Jiyan; Cao, Yuan-Cheng; Zheng, Guang

    2016-03-01

    The quantum yield (QY) and lifetime are the important parameters for the photoluminescent materials. The data here report the changes of the QY and lifetime for the quantum dot (QD) nanocomposite after the UV curing of the urethane acrylate prepolymer. The data were collected based on the water soluble CdTe QDs and urethane acrylate prepolymer. Colloidal QDs were in various concentration from 0.5×10(-3) molL(-1) to 10×10(-3) molL(-1), and 1% (wt%) 1173 was the photoinitiator. The QY before the curing was 56.3%, 57.8% and 58.6% for the QDs 510 nm, 540 nm and 620 nm, respectively. The QY after the curing was changed to 8.9%, 9.6% and 13.4% for the QDs 510 nm, 540 nm and 620 nm, respectively. Lifetime data showed that the lifetime was changed from 23.71 ns, 24.55 ns, 23.52 ns to 1.29 ns, 2.74 ns, 2.45 ns for the QDs 510 nm, 540 nm and 620 nm, respectively. PMID:26909375

  20. Quantum yield and lifetime data analysis for the UV curable quantum dot nanocomposites

    PubMed Central

    Cheng, Qi; Liu, Cui; Wei, Wenjun; Xu, Heng; You, Qingliang; Zou, Linling; Liu, Xueqing; Liu, Jiyan; Cao, Yuan-Cheng; Zheng, Guang

    2016-01-01

    The quantum yield (QY) and lifetime are the important parameters for the photoluminescent materials. The data here report the changes of the QY and lifetime for the quantum dot (QD) nanocomposite after the UV curing of the urethane acrylate prepolymer. The data were collected based on the water soluble CdTe QDs and urethane acrylate prepolymer. Colloidal QDs were in various concentration from 0.5×10−3 molL−1 to 10×10−3 molL−1, and 1% (wt%) 1173 was the photoinitiator. The QY before the curing was 56.3%, 57.8% and 58.6% for the QDs 510 nm, 540 nm and 620 nm, respectively. The QY after the curing was changed to 8.9%, 9.6% and 13.4% for the QDs 510 nm, 540 nm and 620 nm, respectively. Lifetime data showed that the lifetime was changed from 23.71 ns, 24.55 ns, 23.52 ns to 1.29 ns, 2.74 ns, 2.45 ns for the QDs 510 nm, 540 nm and 620 nm, respectively. PMID:26909375

  1. A Comprehensive Strategy to Boost the Quantum Yield of Luminescence of Europium Complexes

    NASA Astrophysics Data System (ADS)

    Lima, Nathalia B. D.; Gonçalves, Simone M. C.; Júnior, Severino A.; Simas, Alfredo M.

    2013-08-01

    Lanthanide luminescence has many important applications in anion sensing, protein recognition, nanosized phosphorescent devices, optoelectronic devices, immunoassays, etc. Luminescent europium complexes, in particular, act as light conversion molecular devices by absorbing ultraviolet (UV) light and by emitting light in the red visible spectral region. The quantum yield of luminescence is defined as the ratio of the number of photons emitted over the number of UV photons absorbed. The higher the quantum yield of luminescence, the higher the sensitivity of the application. Here we advance a conjecture that allows the design of europium complexes with higher values of quantum yields by simply increasing the diversity of good ligands coordinated to the lanthanide ion. Indeed, for the studied cases, the percent boost obtained on the quantum yield proved to be strong: of up to 81%, accompanied by faster radiative rate constants, since the emission becomes less forbidden.

  2. A Comprehensive Strategy to Boost the Quantum Yield of Luminescence of Europium Complexes

    PubMed Central

    Lima, Nathalia B. D.; Gonçalves, Simone M. C.; Júnior, Severino A.; Simas, Alfredo M.

    2013-01-01

    Lanthanide luminescence has many important applications in anion sensing, protein recognition, nanosized phosphorescent devices, optoelectronic devices, immunoassays, etc. Luminescent europium complexes, in particular, act as light conversion molecular devices by absorbing ultraviolet (UV) light and by emitting light in the red visible spectral region. The quantum yield of luminescence is defined as the ratio of the number of photons emitted over the number of UV photons absorbed. The higher the quantum yield of luminescence, the higher the sensitivity of the application. Here we advance a conjecture that allows the design of europium complexes with higher values of quantum yields by simply increasing the diversity of good ligands coordinated to the lanthanide ion. Indeed, for the studied cases, the percent boost obtained on the quantum yield proved to be strong: of up to 81%, accompanied by faster radiative rate constants, since the emission becomes less forbidden. PMID:23928866

  3. DETERMINATION OF APPARENT QUANTUM YIELD SPECTRA FOR THE FORMATION OF BIOLOGICALLY LABILE PHOTOPRODUCTS

    EPA Science Inventory

    Quantum yield spectra for the photochemical formation of biologically labile photoproducts from dissolved organic matter (DOM) have not been available previously, although they would greatly facilitate attempts to model photoproduct formation rates across latitudinal, seasonal, a...

  4. Primary quantum yields of ketyl radicals in photoreduction by amines. Abstraction of H from N

    SciTech Connect

    Inbar, S.; Linschitz, H.; Cohen, S.G.

    1980-02-13

    Results of laser flash photolysis studies of the primary reaction of benzophenone triplet with aliphatic amines in benzene solution are reported. Quantum yield of formation of benzophenone ketyl radical was 0.9 - 1.0. Quantum yields for reduction of ketone also were determined for various amines, and the effects of tert-butyl alcohol on radical formation was investigated. Data indicated that H is not abstracted from -CH/sub 3/ but is abstracted efficiently from -NH/sub 2/. The very high quantum yields observed with tertiary and secondary amines were thought to imply exciplex formation, but lower quantum yields with primary amines were conditionally attributed to higher ionization potentials. (BLM)

  5. Quantum cascade light emitting diodes based on type-II quantum wells

    SciTech Connect

    Lin, C.H.; Yang, R.Q.; Zhang, D.; Murry, S.J.; Pei, S.S.; Allerman, A.A.; Kurtz, S.R.

    1997-01-21

    The authors have demonstrated room-temperature CW operation of type-II quantum cascade (QC) light emitting diodes at 4.2 {micro}m using InAs/InGaSb/InAlSb type-II quantum wells. The type-II QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-II quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 {micro}W at 80 K, and 140 {micro}W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

  6. Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects

    SciTech Connect

    Inbar, S.; Linschitz, H.; Cohen, S.G.

    1981-03-11

    Nanosecond flash photolysis, steady irradiation, and deuterium substitution studies have been carried out on solutions of benzophenone with added reductants. Quantum yields (phi/sub ketyl/) for reduction in benzene of benzophenone triplet to ketyl radical, based on phi = 2 for benzhydrol (I), were approx. 1 for cyclohexane (II), tert-butylamine (III), 2-aminobutane (IV), cyclohexylamine (V), di-n-propylamine (VI), and triethylamine (VII), approx. 0.7 for 1,4-diazabicyclo(2.2.2)octane (VIII), and approx. 0 for tert-butyl alcohol (IX). Thus, quenching, without radical formation by H abstraction from N and/or ..cap alpha..-C, does not occur with common aliphatic amines but does with Dabco (VIII). The latter quenching is markedly increased by small additions of acetonitrile; the flash spectrum from this compound indicates formation of a triplet amine CT complex or radical ion pair. Triplet-reductant interaction rate constants, k/sur ir/, are high for the amines (approx. 10/sup 8/-10/sup 9/ M/sup -1/ s/sup -1/) but also show significant deuterium kinetic isotope effects: 1.9 with III-N-d/sub 2/; 1.4 with IV-N-d/sub 2/; 1.2-1.3 with IV-..cap alpha..-C-d. It is proposed that k/sub ir/ measures H atom abstraction, favored in the transition state by an initial charge-transfer interaction. Overall steady irradiation quantum yields of reduction by amines, phi/sub Red/, are much lower than phi/sub ketyl/. This is attributed to disproportionationreactions of ketyl and alkylaminyl radicals for primary and secondary amines, and, possibly, aminoalkyl radicals for tertiary amines. In the case of tert-butylamine, the rate constant for disproportionation is obtained from the decay kinetics of ketyl radical and leads to phi/sub Red/ in agreement with that directly measured.

  7. Measurement of Quantum Yield, Quantum Requirement, and Energetic Efficiency of the O2-Evolving System of Photosynthesis by a Simple Dye Reaction

    NASA Astrophysics Data System (ADS)

    Ros Barcelò, A.; Zapata, J. M.

    1996-11-01

    Photosynthesis is the conversion of absorbed radiant energy from sunlight into various forms of chemical energy by the chloroplasts of higher green plants. The overall process of photosynthesis consists of the oxidation of water (with the release of O2 as a product) and the reduction of CO2 to form carbohydrates. In the test tube electrons produced by the photolytic cleavage of H2) may be deviated from their true acceptor by inserting a suitable dye in the electron chain; i.e.; 2,6-dichlorophenol indophenol (DCPIP) (E'o = + 0.217 V), which is blue in the oxidized quinone form and which becomes colorless when reduced to the phenolic form. This dye-electrom acceptor also has the advantage that it accepts electroms directly from the quinone (Qa) electron-acceptor of the photosystem II< the reaction center associated with the O2-evolving (or water-slplitting) system. Based in the bleaching of DCPIP by illuminated spinach leaf chloroplasts, a classroom laboratory protocol has been developed to determine the quantum yield (QY = micromol O2 s-1 / micromol photons s-1, the quantum requirement (1/QY) and the energetic efficiency (f = chemical energy stored / light energy supplied) of the O2-evolving system of photosynthesis. Although values for the quantum yield, the quantum requirement and the energetic efficiency calculated in the classroom laboratory differ widely from those expected theoretically, these calculations are useful for illustrating the transformation of light energy into chemical energy by the chloroplasts of green plants.

  8. Ensemble brightening and enhanced quantum yield in size-purified silicon nanocrystals

    DOE PAGESBeta

    Miller, Joseph B.; Van Sickle, Austin R.; Anthony, Rebecca J.; Kroll, Daniel M.; Kortshagen, Uwe R.; Hobbie, Erik K.

    2012-07-18

    Here, we report on the quantum yield, photoluminescence (PL) lifetime and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in films assembled from themore » fractions, and we use a combination of measurement, simulation and modeling to link this ‘brightening’ to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.« less

  9. Ensemble brightening and enhanced quantum yield in size-purified silicon nanocrystals

    SciTech Connect

    Miller, Joseph B.; Van Sickle, Austin R.; Anthony, Rebecca J.; Kroll, Daniel M.; Kortshagen, Uwe R.; Hobbie, Erik K.

    2012-07-18

    Here, we report on the quantum yield, photoluminescence (PL) lifetime and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in films assembled from the fractions, and we use a combination of measurement, simulation and modeling to link this ‘brightening’ to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.

  10. Relational quadrilateralland II: The Quantum Theory

    NASA Astrophysics Data System (ADS)

    Anderson, Edward; Kneller, Sophie

    2014-04-01

    We provide the quantum treatment of the relational quadrilateral. The underlying reduced configuration spaces are ℂℙ2 and the cone over this. We consider exact free and isotropic HO potential cases and perturbations about these. Moreover, our purely relational kinematical quantization is distinct from the usual one for ℂℙ2, which turns out to carry absolutist connotations instead. Thus, this paper is the first to note absolute-versus-relational motion distinctions at the kinematical rather than dynamical level. It is also an example of value to the discussion of kinematical quantization along the lines of Isham, 1984. The relational quadrilateral is the simplest RPM whose mathematics is not standard in atomic physics (the triangle and four particles on a line are both based on 𝕊2 and ℝ3 mathematics). It is far more typical of the general quantum relational N-a-gon than the previously studied case of the relational triangle. We consider useful integrals as regards perturbation theory and the peaking interpretation of quantum cosmology. We subsequently consider problem of time (PoT) applications of this: quantum Kuchař beables, the Machian version of the semiclassical approach and the timeless naïve Schrödinger interpretation. These go toward extending the combined Machian semiclassical-Histories-Timeless Approach of [Int. J. Mod. Phys. D23 (2014) 1450014] to the case of the quadrilateral, which will be treated in subsequent papers.

  11. Enhanced performance of quantum dot solar cells based on type II quantum dots

    SciTech Connect

    Xu, Feng; Yang, Xiao-Guang; Luo, Shuai; Lv, Zun-Ren; Yang, Tao

    2014-10-07

    The characteristics of quantum dot solar cells (QDSCs) based on type II QDs are investigated theoretically. Based on a drift-diffusion model, we obtained a much higher open circuit voltage (V{sub oc}) as well as conversion efficiency in a type II QDSC, compared to type I QDSCs. The improved V{sub oc} and efficiency are mainly attributed to the much longer Auger recombination lifetime in type II QDs. Moreover, the influence of the carrier lifetime on devices' performance is discussed and clarified. In addition, an explicit criterion to determine the role of quantum dots in solar cells is put forward.

  12. Quantum Spin Hall Effect in Inverted Type II Semiconductors

    SciTech Connect

    Liu, Chaoxing; Hughes, Taylor L.; Qi, Xiao-Liang; Wang, Kang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    The quantum spin Hall (QSH) state is a topologically non-trivial state of quantum matter which preserves time-reversal symmetry; it has an energy gap in the bulk, but topologically robust gapless states at the edge. Recently, this novel effect has been predicted and observed in HgTe quantum wells. In this work we predict a similar effect arising in Type-II semiconductor quantum wells made from InAs/GaSb/AlSb. Because of a rare band alignment the quantum well band structure exhibits an 'inverted' phase similar to CdTe/HgTe quantum wells, which is a QSH state when the Fermi level lies inside the gap. Due to the asymmetric structure of this quantum well, the effects of inversion symmetry breaking and inter-layer charge transfer are essential. By standard self-consistent calculations, we show that the QSH state persists when these corrections are included, and a quantum phase transition between the normal insulator and the QSH phase can be electrically tuned by the gate voltage.

  13. [Fluorescence spectra and quantum yield of TiO2 nanocrystals synthesized by alcohothermal method].

    PubMed

    Song, Cui-Hong; Li, Yan-Ting; Li, Jing; Wei, Yong-Ju; Hu, Yu-Zhu; Wei, Yu

    2008-01-01

    Fluorescence spectra and fluorescence quantum yield of TiO2 nanocrystals were studied. Using tetra n-butyl titanate as a starting material, a facile alcohothermal technique was used to synthesize TiO2 nanocrystals. As can be seen from the transmittance electron microscopy (TEM) image, TiO2 nanocrystals with a relatively uniform particle size distribution of < 10 nm are present in the transparent sol. The transparent sol presents a strong stable fluorescence emission with a maximum at 450 nm, which is greatly dependent on the size quantization effects, defect energy level and the surface state of TiO2 nanocrystals. The quantum yield (gamma) of TiO2 was determined by the relative comparison procedure, using freshly prepared analytical purity quinine sulfate in 0.05 mol x L(-1) H2SO4 as a relative quantum yield standard. The emission quantum yield of TiO2 nanocrystals prepared in alcoholic media was calculated to be about 0.20 at wavelengths ranging from 330 to 370 nm, which was much higher than the values reported in previous works. So, it is supposed that nano-TiO2 will be applied as a potential quantum dots fluorescence probe in biological analysis. PMID:18422145

  14. A simple formulation of the CH2O photolysis quantum yields

    NASA Astrophysics Data System (ADS)

    Röth, E.-P.; Ehhalt, D. H.

    2015-07-01

    New expressions for the wavelength-dependent photolysis quantum yields of CH2O, Φj, are presented. They are based on combinations of functions of the type Ai/(1+exp[-(1/λ - 1/λ0i)/bi]). The parameters Ai, bi, and λ0i which have a physical meaning, are obtained by fits to the measured Φj data available from literature. The altitude dependence of the photolysis frequencies resulting from the new quantum yield expressions are compared to those derived from the Φj recommended by JPL and IUPAC.

  15. A simple formulation of the CH2O photolysis quantum yields

    NASA Astrophysics Data System (ADS)

    Röth, E.-P.; Ehhalt, D. H.

    2015-03-01

    New expressions for the various wavelength - dependent photolysis quantum yields of CH2O, Φj, are presented. They are based on combinations of functions of the type Ai/(1 + exp[-(1/λ -1/λ 0i)/bi]). The parameters Ai, bi, and λ0i which have a physical meaning are obtained by fits to the measured data of the Φji available from the literature. The altitude dependence of the photolysis frequencies resulting from the new quantum yield expressions are compared to those derived from the Φj recommended by JPL and IUPAC.

  16. Microanalysis of quantum dots with type II band alignments

    NASA Astrophysics Data System (ADS)

    Sarney, Wendy; Little, John; Svensson, Stefan

    2006-03-01

    We will discuss the structural characterization of a system consisting of undoped self-assembled InSb quantum dots having a type II band alignment with the surrounding In0.53Ga0.47As matrix. This differs from systems using conventional type-I quantum dots that must be doped and that rely on intersubband transitions for infrared photoresponse. Type II dots grown in a superlattice structure combine the advantages of quantum dots (3-dimensional confinement) with the tunability and photovoltaic operation of the type II superlattice. We grew a high surface density of InSb quantum dots with a narrow distribution of sizes and shapes and free of dislocations within the body of the dots. The dots are relaxed due to an array of misfit dislocations confined at the basal dot/matrix interface. This makes burying the dots with InGaAs not feasible without generating dislocations due to the large dot/matrix lattice mismatch. We are experimenting with strain-compensating or graded strain overlayers to lower the lattice mismatch.

  17. Measurement of the Fluorescence Quantum Yield Using a Spectrometer With an Integrating Sphere Detector.

    PubMed

    Gaigalas, Adolfas K; Wang, Lili

    2008-01-01

    A method is proposed for measuring the fluorescence quantum yield (QY) using a commercial spectrophotometer with a 150 mm integrating sphere (IS) detector. The IS detector is equipped with an internal cuvette holder so that absorbance measurements can be performed with the cuvette inside the IS. In addition, the spectrophotometer has a cuvette holder outside the IS for performing conventional absorbance measurements. It is shown that the fluorescence quantum yield can be obtained from a combination of absorbance measurements of the buffer and the analyte solution inside and outside the IS detector. Due to the simultaneous detection of incident and fluorescent photons, the absorbance measurements inside the IS need to be adjusted for the wavelength dependence of the photomultiplier detector and the wavelength dependence of the IS magnification factor. An estimate of the fluorescence emission spectrum is needed for proper application of the wavelength-dependent adjustments. Results are presented for fluorescein, quinine sulfate, myoglobin, rhodamine B and erythrosin B. The QY of fluorescein in 0.1 mol/L NaOH was determined as 0.90±0.02 where the uncertainty is equal to the standard deviation of three independent measurements. The method provides a convenient and rapid estimate of the fluorescence quantum yield. Refinements of the measurement model and the characteristics of the IS detector can in principle yield an accurate value of the absolute fluorescence quantum yield. PMID:27096110

  18. MnBr₂/18-crown-6 coordination complexes showing high room temperature luminescence and quantum yield.

    PubMed

    Hausmann, David; Kuzmanoski, Ana; Feldmann, Claus

    2016-04-21

    The reaction of manganese(ii) bromide and the crown ether 18-crown-6 in the ionic liquid [(n-Bu)3MeN][N(Tf)2] under mild conditions (80-130 °C) resulted in the formation of three different coordination compounds: MnBr2(18-crown-6) (), Mn3Br6(18-crown-6)2 () and Mn3Br6(18-crown-6) (). In general, the local coordination and the crystal structure of all compounds are driven by the mismatch between the small radius of the Mn(2+) cation (83 pm) and the ring opening of 18-crown-6 as a chelating ligand (about 300 pm). This improper situation leads to different types of coordination and bonding. MnBr2(18-crown-6) represents a molecular compound with Mn(2+) coordinated by two bromine atoms and only five oxygen atoms of 18-crown-6. Mn3Br6(18-crown-6)2 falls into a [MnBr(18-crown-6)](+) cation - with Mn(2+) coordinated by six oxygen atoms and Br - and a [MnBr(18-crown-6)MnBr4](-) anion. In this anion, Mn(2+) is coordinated by five oxygen atoms of the crown ether as well as by two bromine atoms, one of them bridging to an isolated (MnBr4) tetrahedron. Mn3Br6(18-crown-6), finally, forms an infinite, non-charged [Mn2(18-crown-6)(MnBr6)] chain. Herein, 18-crown-6 is exocyclically coordinated by two Mn(2+) cations. All compounds show intense luminescence in the yellow to red spectral range and exhibit remarkable quantum yields of 70% (Mn3Br6(18-crown-6)) and 98% (Mn3Br6(18-crown-6)2). The excellent quantum yield of Mn3Br6(18-crown-6)2 and its differentiation from MnBr2(18-crown-6) and Mn3Br6(18-crown-6) can be directly correlated to the local coordination. PMID:26956783

  19. Quantum statistical thermodynamics of hot finite nuclear systems: Temperatures and isotopic yield ratios

    SciTech Connect

    Majka, Z.; Staszel, P.; Cibor, J.; Natowitz, J.B.; Hagel, K.; Li, J.; Mdeiwayeh, N.; Wada, R.; Zhao, Y.

    1997-06-01

    We investigate the importance of the quantum statistics and deexcitation of primary fragments on the isotope yield ratio temperature determination. A phenomenological formula is presented which allows derivation of the temperature of the decaying nuclear system at the freeze-out time from the measured double yield ratios of two isotope pairs. This prescription is applied to the recent ALADIN and EOS Collaboration data. {copyright} {ital 1997} {ital The American Physical Society}

  20. Optimum doping achieves high quantum yields in GaAs photoemitters

    NASA Technical Reports Server (NTRS)

    Sonnenberg, H.

    1971-01-01

    Experimental data indicate that optimum doping exists. Measured quantum yield curves indicate optimum overall response is obtained in GaAs emitters with doping in high 10 to the 18th power per cu cm range. Doping for optimum response is not necessarily in this range.

  1. Separation of photoactive conformers based on hindered diarylethenes: efficient modulation in photocyclization quantum yields.

    PubMed

    Li, Wenlong; Jiao, Changhong; Li, Xin; Xie, Yongshu; Nakatani, Keitaro; Tian, He; Zhu, Weihong

    2014-04-25

    Endowing both solvent independency and excellent thermal bistability, the benzobis(thiadiazole)-bridged diarylethene system provides an efficient approach to realize extremely high photocyclization quantum yields (Φo-c , up to 90.6 %) by both separating completely pure anti-parallel conformer and suppressing intramolecular charge transfer (ICT). PMID:24668917

  2. Solvatochromic pyrene analogues of Prodan exhibiting extremely high fluorescence quantum yields in apolar and polar solvents.

    PubMed

    Niko, Yosuke; Kawauchi, Susumu; Konishi, Gen-ichi

    2013-07-22

    True colors: Novel pyrene analogues of Prodan exhibit outstanding photophysical properties with remarkably high fluorescence quantum yield (QY) in solvents ranging from apolar hexane to polar methanol (see figure). This is accompanied by strong solvatochromism and large Stokes shifts. These properties have not been previously achieved in enormous solvatochromic dyes, but are quite useful for emitting materials and imaging tools. PMID:23744761

  3. Control of the external photoluminescent quantum yield of emitters coupled to nanoantenna phased arrays

    SciTech Connect

    Guo, Ke; Verschuuren, Marc A.; Lozano, Gabriel

    2015-08-21

    Optical losses in metals represent the largest limitation to the external quantum yield of emitters coupled to plasmonic antennas. These losses can be at the emission wavelength, but they can be more important at shorter wavelengths, i.e., at the excitation wavelength of the emitters, where the conductivity of metals is usually lower. We present accurate measurements of the absolute external photoluminescent quantum yield of a thin layer of emitting material deposited over a periodic nanoantenna phased array. Emission and absorptance measurements of the sample are performed using a custom-made setup including an integrating sphere and variable angle excitation. The measurements reveal a strong dependence of the external quantum yield on the angle at which the optical field excites the sample. Such behavior is attributed to the coupling between far-field illumination and near-field excitation mediated by the collective resonances supported by the array. Numerical simulations confirm that the inherent losses associated with the metal can be greatly reduced by selecting an optimum angle of illumination, which boosts the light conversion efficiency in the emitting layer. This combined experimental and numerical characterization of the emission from plasmonic arrays reveals the need to carefully design the illumination to achieve the maximum external quantum yield.

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

    PubMed

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

    2016-04-26

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

  5. Excitation-energy dependence of the phosphorescence quantum yields of pyridinecarboxaldehyde vapors.

    PubMed

    Itoh, Takao

    2008-12-15

    Emission and excitation spectra of 3- and 4-pyridinecarboxaldehyde vapors have been measured at different pressures down to 10(-2)Torr. The phosphorescence quantum yield measured at low pressure as a function of excitation energy is nearly constant in the range of excitation energy corresponding to the S1(n, pi*) state, but it decreases abruptly at the S2(pi, pi*) threshold. The onset of the abrupt decrease of the yield corresponds to the location of the S2 absorption origin of each molecule, indicating that the nonradiative pathway depends on the type of the excited singlet state to which the molecule is initially excited. The relaxation processes are discussed based on the pressure and excitation-energy dependence of the phosphorescence quantum yield. PMID:18515180

  6. Quantum yield for carbon monoxide production in the 248 nm photodissociation of carbonyl sulfide (OCS)

    NASA Technical Reports Server (NTRS)

    Zhao, Z.; Stickel, R. E.; Wine, P. H.

    1995-01-01

    Tunable diode laser absorption spectroscopy has been coupled with excimer laser flash photolysis to measure the quantum yield for CO production from 248 nm photodissociation of carbonyl sulfide (OCS) relative to the well-known quantum yield for CO production from 248 nm photolysis of phosgene (Cl2CO2). The temporal resolution of the experiments was sufficient to distinguish CO formed directly by photodissociation from that formed by subsequent S((sup 3)P(sub J)) reaction with OCS. Under the experimental conditions employed, CO formation via the fast S((sup 1)D(sub 2)) + OCS reaction was minimal. Measurements at 297K and total pressures from 4 to 100 Torr N2 + N2O show the CO yield to be greater than 0.95 and most likely unity. This result suggests that the contribution of OCS as a precursor to the lower stratospheric sulfate aerosol layer is somewhat larger than previously thought.

  7. Implementing an ancilla-free 1{yields}M economical phase-covariant quantum cloning machine with superconducting quantum-interference devices in cavity QED

    SciTech Connect

    Yu Longbao; Ye Liu; Zhang Wenhai

    2007-09-15

    We propose a simple scheme to realize 1{yields}M economical phase-covariant quantum cloning machine (EPQCM) with superconducting quantum interference device (SQUID) qubits. In our scheme, multi-SQUIDs are fixed into a microwave cavity by adiabatic passage for their manipulation. Based on this model, we can realize the EPQCM with high fidelity via adiabatic quantum computation.

  8. Photosensitized electron transfer processes in SiO/sub 2/ colloids and sodium lauryl sulfate micellar sytems: correlation of quantum yields with interfacial surface potentials

    SciTech Connect

    Laane, C.; Willner, I.; Otvos, J.W.; Calvin, M.

    1981-10-01

    The effectiveness of negatively charged colloidal SiO/sub 2/ particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO/sub 4/) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS/sup 0/) with tris(2,2'-bi-pyridinium)ruthenium(II) (Ru(bipy)/sub 3//sup 2 +/) as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS) in the SiO/sub 2/ colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO/sub 4/ micellar solution. The higher quantum yields obtained with the SiO/sub 2/ colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts - i.e., Ru(bipy)/sub 3//sup 3 +/ and PVS/sup -/ - by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO/sub 2/ particles and NaLauSO/sub 4/ micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO/sub 2/ interface is characterized by much higher surface potential than the micellar interface. The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated shows that the quantum yield is not affected by surface potentials smaller than approx. = -40 mV. At larger potentials, the quantum yield increases rapidly. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS/sup 0/ reduction.

  9. Influence of the Inner-Shell Architecture on Quantum Yield and Blinking Dynamics in Core/Multishell Quantum Dots.

    PubMed

    Bajwa, Pooja; Gao, Feng; Nguyen, Anh; Omogo, Benard; Heyes, Colin D

    2016-03-01

    Choosing the composition of a shell for QDs is not trivial, as both the band-edge energy offset and interfacial lattice mismatch influence the final optical properties. One way to balance these competing effects is by forming multishells and/or gradient-alloy shells. However, this introduces multiple interfaces, and their relative effects on quantum yield and blinking are not yet fully understood. Here, we undertake a systematic, comparative study of the addition of inner shells of a single component versus gradient-alloy shells of cadmium/zinc chalogenides onto CdSe cores, and then capping with a thin ZnS outer shell to form various core/multishell configurations. We show that architecture of the inner shell between the CdSe core and the outer ZnS shell significantly influences both the quantum yield and blinking dynamics, but that these effects are not correlated-a high ensemble quantum yield doesn't necessarily equate to reduced blinking. Two mathematical models have been proposed to describe the blinking dynamics-the more common power-law model and a more recent multiexponential model. By binning the same data with 1 and 20 ms resolution, we show that the on times can be better described by the multiexponential model, whereas the off times can be better described by the power-law model. We discuss physical mechanisms that might explain this behavior and how it can be affected by the inner-shell architecture. PMID:26693950

  10. Absolute I(asterisk) quantum yields for the ICN A state by diode laser gain-vs-absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Hess, Wayne P.; Leone, Stephen R.

    1987-01-01

    Absolute I(asterisk) quantum yields have been measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The yields are obtained by the technique of time-resolved diode laser gain-vs-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 + or - 2 percent and it falls off to 53.4 + or - 2 percent and 44.0 + or - 4 percent at 284 and 248 nm, respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I(asterisk) quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I(asterisk) yields reported here. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I(asterisk) quantum yield results.

  11. Fluorescence Quantum Yield Measurements of Fluorescent Proteins: A Laboratory Experiment for a Biochemistry or Molecular Biophysics Laboratory Course

    ERIC Educational Resources Information Center

    Wall, Kathryn P.; Dillon, Rebecca; Knowles, Michelle K.

    2015-01-01

    Fluorescent proteins are commonly used in cell biology to assess where proteins are within a cell as a function of time and provide insight into intracellular protein function. However, the usefulness of a fluorescent protein depends directly on the quantum yield. The quantum yield relates the efficiency at which a fluorescent molecule converts…

  12. Influence of the QD luminescence quantum yield on photocurrent in QD/graphene hybrid structures

    NASA Astrophysics Data System (ADS)

    Reznik, Ivan A.; Gromova, Yulia A.; Zlatov, Andrei S.; Baranov, Mikhail A.; Orlova, Anna O.; Moshkalev, Stanislav A.; Maslov, Vladimir G.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2016-04-01

    Photoinduced changes in luminescent and photoelectrical properties of the hybrid structure based on CdSe/ZnS QDs and multilayer graphene nanobelts were studied. It was shown that an irradiation of the structures by 365 nm mercury line in doses up to 23 J led to growth of QD luminescent quantum yield and photocurrent in the QD/graphene structures. This confirms the proximity of the rates of the QD luminescence decay and energy/charge transfer from QDs to graphene, and opens an opportunity to photoinduced control of the photoelectric response of the graphene based hybrid structures with semiconductor quantum dots.

  13. An experimental and theoretical mechanistic study of biexciton quantum yield enhancement in single quantum dots near gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A.; Chen, Ou; Zou, Shengli; Zhao, Jing

    2015-04-01

    In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures.In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance

  14. An experimental and theoretical mechanistic study of biexciton quantum yield enhancement in single quantum dots near gold nanoparticles.

    PubMed

    Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A; Chen, Ou; Zou, Shengli; Zhao, Jing

    2015-04-21

    In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures. PMID:25806486

  15. Photodissociation of quantum state-selected diatomic molecules yields new insight into ultracold chemistry

    NASA Astrophysics Data System (ADS)

    McDonald, Mickey; McGuyer, Bart H.; Lee, Chih-Hsi; Apfelbeck, Florian; Zelevinsky, Tanya

    2016-05-01

    When a molecule is subjected to a sufficiently energetic photon it can break apart into fragments through a process called ``photodissociation''. For over 70 years this simple chemical reaction has served as a vital experimental tool for acquiring information about molecular structure, since the character of the photodissociative transition can be inferred by measuring the 3D photofragment angular distribution (PAD). While theoretical understanding of this process has gradually evolved from classical considerations to a fully quantum approach, experiments to date have not yet revealed the full quantum nature of this process. In my talk I will describe recent experiments involving the photodissociation of ultracold, optical lattice-trapped, and fully quantum state-resolved 88Sr2 molecules. Optical absorption images of the PADs produced in these experiments reveal features which are inherently quantum mechanical in nature, such as matter-wave interference between output channels, and are sensitive to the quantum statistics of the molecular wavefunctions. The results of these experiments cannot be predicted using quasiclassical methods. Instead, we describe our results with a fully quantum mechanical model yielding new intuition about ultracold chemistry.

  16. Type II Hydride Transferases from Different Microorganisms Yield Nitrite and Diarylamines from Polynitroaromatic Compounds▿ †

    PubMed Central

    van Dillewijn, Pieter; Wittich, Rolf-Michael; Caballero, Antonio; Ramos, Juan-Luis

    2008-01-01

    Homogenous preparations of XenB of Pseudomonas putida, pentaerythritol tetranitrate reductase of Enterobacter cloacae, and N-ethylmaleimide reductase of Escherichia coli, all type II hydride transferases of the Old Yellow Enzyme family of flavoproteins, are shown to reduce the polynitroaromatic compound 2,4,6-trinitrotoluene (TNT). The reduction of this compound yields hydroxylaminodinitrotoluenes and Meisenheimer dihydride complexes, which, upon condensation, yield stoichiometric amounts of nitrite and diarylamines, implying that type II hydride transferases are responsible for TNT denitration, a process with important environmental implications for TNT remediation. PMID:18791007

  17. Preparation of carbon quantum dots with a high quantum yield and the application in labeling bovine serum albumin

    NASA Astrophysics Data System (ADS)

    Liu, Pengpeng; Zhang, Changchang; Liu, Xiang; Cui, Ping

    2016-04-01

    An economic and green approach of manufacturing carbon quantum dots (CQDs) with a high quantum yield (denoted with HQY-CQDs) and the application in labeling bovine serum albumin (BSA) were described in detail in this work. Firstly, the cheap resources of citric acid and glycine were pyrolysed in drying oven for preparing the CQDs. Then the product was immersed in tetrahydrofuran for 8 h. HQY-CQDs were obtained by removing tetrahydrofuran from the supernate and were evaluated that they possessed a much higher quantum yield compared with that without dealing with tetrahydrofuran and a wonderful photo-bleaching resistance. Such HQY-CQDs could be functionalized by N-hydroxysuccinimide and successively combined with BSA covalently. Thus fluorescent labeling on BSA was realized. The HQY-CQDs were demonstrated with transmission electron microscopy and the chemical modification with N-hydroxysuccinimide was proved by infrared and X-ray photoelectron spectra. Labeling BSA with the HQY-CQDs was confirmed by gel electrophoresis and fluorescence imaging.

  18. Photoluminescence and quantum yields of organic/inorganic hybrids prepared through formic acid solvolysis

    NASA Astrophysics Data System (ADS)

    Fu, Lianshe; Sá Ferreira, R. A.; Fernandes, M.; Nunes, S. C.; de Zea Bermudez, V.; Hungerford, Graham; Rocha, J.; Carlos, L. D.

    2008-03-01

    Three undoped di-urea cross-linked poly(oxyethylene) (POE)/siloxane hybrid matrices, classed as di-ureasils, incorporating POE segments with different lengths were prepared through the carboxylic acid solvolysis sol-gel method using formic acid. The resulting hybrids were characterized by X-ray diffraction, Fourier transform mid-infrared spectroscopy, 29Si and cross-polarization 13C magic-angle spinning nuclear magnetic resonance and photoluminescence spectroscopy. The hybrids' structure is essentially independent of the polymer chain length and the materials are room temperature white-light emitters with emission quantum yields of ˜10 ± 1% and lifetime average values between 2 and 4 ns. For the di-ureasil host with short polymer chains the solvolysis method favours the increase of the PL quantum yields relatively to conventional sol-gel route.

  19. Quantum yield and excitation rate of single molecules close to metallic nanostructures.

    PubMed

    Holzmeister, Phil; Pibiri, Enrico; Schmied, Jürgen J; Sen, Tapasi; Acuna, Guillermo P; Tinnefeld, Philip

    2014-01-01

    The interaction of dyes and metallic nanostructures strongly affects the fluorescence and can lead to significant fluorescence enhancement at plasmonic hot spots, but also to quenching. Here we present a method to distinguish the individual contributions to the changes of the excitation, radiative and non-radiative rate and use this information to determine the quantum yields for single molecules. The method is validated by precisely placing single fluorescent dyes with respect to gold nanoparticles as well as with respect to the excitation polarization using DNA origami nanostructures. Following validation, measurements in zeromode waveguides reveal that suppression of the radiative rate and enhancement of the non-radiative rate lead to a reduced quantum yield. Because the method exploits the intrinsic blinking of dyes, it can generally be applied to fluorescence measurements in arbitrary nanophotonic environments. PMID:25370834

  20. Quantum yield and excitation rate of single molecules close to metallic nanostructures

    PubMed Central

    Holzmeister, Phil; Pibiri, Enrico; Schmied, Jürgen J.; Sen, Tapasi; Acuna, Guillermo P.; Tinnefeld, Philip

    2014-01-01

    The interaction of dyes and metallic nanostructures strongly affects the fluorescence and can lead to significant fluorescence enhancement at plasmonic hot spots, but also to quenching. Here we present a method to distinguish the individual contributions to the changes of the excitation, radiative and non-radiative rate and use this information to determine the quantum yields for single molecules. The method is validated by precisely placing single fluorescent dyes with respect to gold nanoparticles as well as with respect to the excitation polarization using DNA origami nanostructures. Following validation, measurements in zeromode waveguides reveal that suppression of the radiative rate and enhancement of the non-radiative rate lead to a reduced quantum yield. Because the method exploits the intrinsic blinking of dyes, it can generally be applied to fluorescence measurements in arbitrary nanophotonic environments. PMID:25370834

  1. A quantum yield determination of O/1D/ production from ozone via laser flash photolysis

    NASA Technical Reports Server (NTRS)

    Philen, D. L.; Davis, D. D.; Watson, R. T.

    1977-01-01

    The quantum yield of electronically excited atomic oxygen produced from ozone photolysis was measured at 298 K from wavelengths of 293.0 to 316.5 nm. The reaction of the atomic oxygen with N2O to form excited NO2 was used to monitor the O production; a frequency-doubled flashlamp-pumped dye laser which provided tunable ultraviolet in the desired spectral region with 0.1-nm linewidth served as the photolysis source. The atomic oxygen quantum yield was found to be constant below 300 nm, with a sharp decrease centered at 308 nm and a diminution to less than one tenth of the constant value by 313.5 nm.

  2. Photo-dissociation quantum yields of mammalian oxyhemoglobin investigated by a nanosecond laser technique

    SciTech Connect

    Yang Ningli; Zhang Shuyi . E-mail: zhangsy@nju.edu.cn; Kuo Paokuang; Qu Min; Fang Jianwen; Li Jiahuang; Hua Zichun

    2007-02-23

    The photo-dissociations of oxyhemoglobin of several mammals, such as human, bovine, pig, horse, and rabbit, have been studied. By means of optical pump-probe technique, the quantum yields for photo-dissociation of these oxyhemoglobin have been determined at pH 7 and 20 {sup o}C. A nanosecond laser at 532 nm is used as the pumping source, and a xenon lamp through a monochrometer provides a probe light at 432 nm. The experimental results show that the quantum yields of these mammalian oxyhemoglobin are different from each other, especially for that of rabbit. By analyzing the amino acid sequences and tetramer structures as well as the flexibility and hydrophobicity of the different hemoglobin, possible explanations for the differences are proposed.

  3. Photocurrent Quantum Yield in Suspended Carbon Nanotube p-n Junctions.

    PubMed

    Aspitarte, Lee; McCulley, Daniel R; Minot, Ethan D

    2016-09-14

    We study photocurrent generation in individual suspended carbon nanotube p-n junctions using spectrally resolved scanning photocurrent microscopy. Spatial maps of the photocurrent allow us to determine the length of the p-n junction intrinsic region, as well as the role of the n-type Schottky barrier. We show that reverse-bias operation eliminates complications caused by the n-type Schottky barrier and increases the length of the intrinsic region. The absorption cross-section of the CNT is calculated using an empirically verified model, and the effect of substrate reflection is determined using FDTD simulations. We find that the room temperature photocurrent quantum yield is approximately 30% when exciting the carbon nanotube at the S44 and S55 excitonic transitions. The quantum yield value is an order of magnitude larger than previous estimates. PMID:27575386

  4. Quantum Yield Determination Based on Photon Number Measurement, Protocols for Firefly Bioluminescence Reactions.

    PubMed

    Niwa, Kazuki

    2016-01-01

    Quantum yield (QY), which is defined as the probability of photon production by a single bio/chemiluminescence reaction, is an important factor to characterize luminescence light intensity emitted diffusively from the reaction solution mixture. Here, methods to measure number of photons to determine QY according to the techniques of national radiometry standards are described. As an example, experiments using firefly bioluminescence reactions are introduced. PMID:27424895

  5. Excitation-emission spectra and fluorescence quantum yields for fresh and aged biogenic secondary organic aerosols

    SciTech Connect

    Lee, Hyun Ji; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.

    2013-05-10

    Certain biogenic secondary organic aerosols (SOA) become absorbent and fluorescent when exposed to reduced nitrogen compounds such as ammonia, amines and their salts. Fluorescent SOA may potentially be mistaken for biological particles by detection methods relying on fluorescence. This work quantifies the spectral distribution and effective quantum yields of fluorescence of SOA generated from two monoterpenes, limonene and a-pinene, and two different oxidants, ozone (O3) and hydroxyl radical (OH). The SOA was generated in a smog chamber, collected on substrates, and aged by exposure to ~100 ppb ammonia vapor in air saturated with water vapor. Absorption and excitation-emission matrix (EEM) spectra of aqueous extracts of aged and control SOA samples were measured, and the effective absorption coefficients and fluorescence quantum yields (~0.005 for 349 nm excitation) were determined from the data. The strongest fluorescence for the limonene-derived SOA was observed for excitation = 420+- 50 nm and emission = 475 +- 38 nm. The window of the strongest fluorescence shifted to excitation = 320 +- 25 nm and emission = 425 +- 38 nm for the a-pinene-derived SOA. Both regions overlap with the excitation-emission matrix (EEM) spectra of some of the fluorophores found in primary biological aerosols. Our study suggests that, despite the low quantum yield, the aged SOA particles should have sufficient fluorescence intensities to interfere with the fluorescence detection of common bioaerosols.

  6. Photochemistry of matrix-isolated and thin film acid chlorides: Quantum yields and product structures

    SciTech Connect

    Rowland, B.; Hess, W.P.; Winter, P.R.; Ellison, G.B.; Radziszewski, J.G.

    1999-02-18

    Ultraviolet photoexcitation of matrix-isolated CH{sub 3}COCl, CH{sub 3}CH{sub 2}COCl, and CH{sub 3}CH{sub 2}CH{sub 2}CH{sub 2}COCl produces HCl{center_dot}CH{sub 2}{double_bond}C{double_bond}O, HCl{center_dot}CH{sub 3}CHC{double_bond}C{double_bond}O, and HCl{center_dot}CH{sub 3}CH{sub 2}CH{sub 2}CHC{double_bond}C{double_bond}O complexes. The authors report precursor and matrix dependent reaction quantum yields. Quantum yield values decrease with increasing alkyl chain length due to a reduced number of {alpha} H-atoms available for the elimination reaction and steric considerations. The authors found quantum yields in neat matrixes to be roughly half that in argon or xenon matrixes and assign structures for HCL and ketene complexes in argon and xenon matrixes by comparing IR spectra ab initio electronic structure calculations. In argon matrixes, the product complex HCl frequently is strongly shifted whereas the ketene remains unshifted with respect to matrix-isolated ketene. In xenon matrixes, HCl{center_dot}ketene complexes display absorption bands indicative of two distinct structures. Differences between HCl{center_dot}ketene structures in argon and xenon matrixes are attributed to size differences of the matrix lattice.

  7. High Photoluminescence Quantum Yield in Band Gap Tunable Bromide Containing Mixed Halide Perovskites.

    PubMed

    Sutter-Fella, Carolin M; Li, Yanbo; Amani, Matin; Ager, Joel W; Toma, Francesca M; Yablonovitch, Eli; Sharp, Ian D; Javey, Ali

    2016-01-13

    Hybrid organic-inorganic halide perovskite based semiconductor materials are attractive for use in a wide range of optoelectronic devices because they combine the advantages of suitable optoelectronic attributes and simultaneously low-cost solution processability. Here, we present a two-step low-pressure vapor-assisted solution process to grow high quality homogeneous CH3NH3PbI3-xBrx perovskite films over the full band gap range of 1.6-2.3 eV. Photoluminescence light-in versus light-out characterization techniques are used to provide new insights into the optoelectronic properties of Br-containing hybrid organic-inorganic perovskites as a function of optical carrier injection by employing pump-powers over a 6 orders of magnitude dynamic range. The internal luminescence quantum yield of wide band gap perovskites reaches impressive values up to 30%. This high quantum yield translates into substantial quasi-Fermi level splitting and high "luminescence or optically implied" open-circuit voltage. Most importantly, both attributes, high internal quantum yield and high optically implied open-circuit voltage, are demonstrated over the entire band gap range (1.6 eV ≤ Eg ≤ 2.3 eV). These results establish the versatility of Br-containing perovskite semiconductors for a variety of applications and especially for the use as high-quality top cell in tandem photovoltaic devices in combination with industry dominant Si bottom cells. PMID:26691065

  8. Luminescent carbon quantum dots with high quantum yield as a single white converter for white light emitting diodes

    NASA Astrophysics Data System (ADS)

    Feng, X. T.; Zhang, F.; Wang, Y. L.; Zhang, Y.; Yang, Y. Z.; Liu, X. G.

    2015-11-01

    Carbon quantum dots (CQDs) with high quantum yield (51.4%) were synthesized by a one-step hydrothermal method using thiosalicylic acid and ethylenediamine as precursor. The CQDs have the average diameter of 2.3 nm and possess excitation-independent emission wavelength in the range from 320 to 440 nm excitation. Under an ultraviolet (UV) excitation, the CQDs aqueous solutions emit bright blue fluorescence directly and exhibit broad emission with a high spectral component ratio of 67.4% (blue to red intensity to total intensity). We applied the CQDs as a single white-light converter for white light emitting diodes (WLEDs) using a UV-LED chip as the excitation light source. The resulted WLED shows superior performance with corresponding color temperature of 5227 K and the color coordinates of (0.34, 0.38) belonging to the white gamut.

  9. Luminescent carbon quantum dots with high quantum yield as a single white converter for white light emitting diodes

    SciTech Connect

    Feng, X. T.; Zhang, Y.; Liu, X. G.; Zhang, F.; Wang, Y. L.; Yang, Y. Z.

    2015-11-23

    Carbon quantum dots (CQDs) with high quantum yield (51.4%) were synthesized by a one-step hydrothermal method using thiosalicylic acid and ethylenediamine as precursor. The CQDs have the average diameter of 2.3 nm and possess excitation-independent emission wavelength in the range from 320 to 440 nm excitation. Under an ultraviolet (UV) excitation, the CQDs aqueous solutions emit bright blue fluorescence directly and exhibit broad emission with a high spectral component ratio of 67.4% (blue to red intensity to total intensity). We applied the CQDs as a single white-light converter for white light emitting diodes (WLEDs) using a UV-LED chip as the excitation light source. The resulted WLED shows superior performance with corresponding color temperature of 5227 K and the color coordinates of (0.34, 0.38) belonging to the white gamut.

  10. Magnetoexcitons in type-II semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Fuster, Gonzalo; Barticevic, Zdenka; Pacheco, Monica; Oliveira, Luiz E.

    2004-03-01

    We present a theoretical investigation of excitons in type-II semiconductor quantum dots (QD). In these systems the confinement of electrons inside the QD and the hole outside the QD produces a ring-like structure [1-2]. Recently, Ribeiro et al [3], in a magnetophotoluminescence study of type-II InP/GaAs self-assembled quantum dots, observed Aharonov-Bohm-type oscillations characteristic of the ring topology for neutral excitons. Using a simple model they have derived the groundstate hole energy as a function of the magnetic field, and obtained values for the ring parameters which are in good agreement with the measured values. However, some of the features observed experimentally, in the photoluminescence intensity, can not be well explained under that approach. In this work we present a more realistic model which considers the finite width of the ring and the electron-hole interaction included via a perturbative approach. The calculations are performed within the oneparticle formalism using the effective mass approximation. The confinement potential for electrons is modelled as the superposition of a quantum well potential along the axial direction, and a parabolic lateral confinement potential. The energies for the hole in the ring plane are calculated using the method of reference [4]. Theoretical calculations are in good agreement with the experimental results of reference [3] provided that excitonic effects are properly taken into account. References 1. A.O. Govorov et al., Physica E 13 , 297 (2002). 2. K. L. Janssens et al. Phys. Rev B64, 155324 (2001), and Phys. Rev. B66, 075314 (2002). 3. E. Ribeiro, G. Medeiros-Ribeiro, and W.Carvalho Jr., and A.O. Govorov, condmat/0304092 (2003). 4. Z. Barticevic, G. Fuster, and M. Pacheco,Phys. Rev. B 65, 193307 (2002).

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

    PubMed

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

    2013-07-10

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

  12. Maxwell's demon. (II) A quantum-theoretic exorcism

    NASA Astrophysics Data System (ADS)

    Gyftopoulos, Elias P.

    2002-05-01

    In Part II of this two-part paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics. The key idea of the unified theory is that von Neumann's concept of a homogeneous ensemble of identical systems, identically prepared, is valid not only for a density operator ρ equal to a projector (every member of the ensemble is assigned the same projector, ρi=| ψi> < ψi|= ρi2, or the same wave function ψ i as any other member) but also for a density operator that is not a projector (every member of the ensemble is assigned the same density operator, ρ>ρ 2, as any other member). So, the latter ensemble is not a statistical mixture of projectors. The broadening of the validity of the homogeneous ensemble is consistent with the quantum-theoretic postulates about observables, measurement results, and value of any observable. In the context of the unified theory, among the many novel results is the theorem that each molecule of a system in a thermodynamic equilibrium state has zero value of momentum, that is, each molecule is at a standstill and, therefore, there are no molecules to be sorted as swift and slow. Said differently, if Maxwell were cognizant of quantum theory, he would not have conceived of the idea of the demon. It is noteworthy that the zero value of momentum is not the result of averaging over different momenta of many molecules. Under the specified conditions, it is the quantum-theoretic value of the momentum of any one molecule, and the same result is valid even if the system consists of only one molecule.

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

    PubMed

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

    2005-11-15

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

  14. Photoluminescence quantum yield of PbS nanocrystals in colloidal suspensions

    SciTech Connect

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

    2015-04-14

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

  15. Investigating photoluminescence quantum yield of silicon nanocrystals formed in SiOx with different initial Si excess

    NASA Astrophysics Data System (ADS)

    Chung, Nguyen Xuan; Limpens, Rens; Gregorkiewicz, Tom

    2015-09-01

    Optical properties of silicon nanocrystals dispersed in SiO2 matrix were investigated in terms of photoluminescence quantum yield at room temperature. Two multilayer samples, prepared from substoichiometric silicon oxide layers by annealing at 1150°C were used to investigate the influence of Si concentration. Significant reduction of photoluminescence quantum yield and a very specific change of its excitation energy dependence upon variation of silicon excess are concluded from the experimental data. Possible mechanisms leading to these changes are discussed.

  16. Quantum yield of photosensitized singlet oxygen (a[sup 1][Delta][sub g]) production in solid polystyrene

    SciTech Connect

    Scurlock, R.D.; Martire, D.O.; Ogilby, P.R. . Dept. of Chemistry); Taylor, V.L.; Clough, R.L. )

    1994-08-15

    The quantum yield of singlet oxygen (a[sup 1][Delta][sub g]), produced by energy transfer from the photosensitizer acridine, has been determined by two independent spectroscopic methods in solid polystyrene. Upon 355-nm pulsed-laser irradiation of acridine at 1.3 mJ/pulse, the O[sub 2](a[sup 1][Delta][sub g]) quantum yield in polystyrene [[phi][sub [Delta

  17. Quantum yields for photochemical production of NO2 from organic nitrates at tropospherically relevant wavelengths.

    PubMed

    Higgins, Christina M; Evans, Louise A; Lloyd-Jones, Guy C; Shallcross, Dudley E; Tew, David P; Orr-Ewing, Andrew J

    2014-04-17

    Absorption cross-sections and quantum yields for NO2 production (ΦNO2) are reported for gaseous methyl, ethyl, n-propyl, and isopropyl nitrate at 294 K. Absorption cross-sections in the wavelength range of 240-320 nm agree well with prior determinations. NO2 quantum yields at photoexcitation wavelengths of 290, 295, and 315 nm are unity within experimental uncertainties for all of the alkyl nitrates studied and are independent of bath gas (N2) pressure for total sample pressures in the range of 250-700 Torr. When averaged over all wavelengths and sample pressures, values of ΦNO2 are 1.03 ± 0.05 (methyl nitrate), 0.98 ± 0.09 (ethyl nitrate), 1.01 ± 0.04 (n-propyl nitrate), and 1.00 ± 0.05 (isopropyl nitrate), with uncertainties corresponding to 1 standard deviation. Absorption cross-sections for ethyl nitrate, isopropyl nitrate, and two unsaturated dinitrate compounds, but-3-ene-1,2-diyl dinitrate and (Z)-but-2-ene-1,4-diyl dinitrate in acetonitrile solution, are compared to gas-phase values, and over the wavelength range of 260-315 nm, the gas-phase values are well-reproduced by dividing the liquid-phase cross-sections by 2.0, 1.6, 1.7, and 2.2, respectively. Reasonable estimates of the gas-phase absorption cross-sections for low-volatility organic nitrates can therefore be obtained by halving the values for acetonitrile solutions. The quantum yield for NO2 formation from photoexcitation of but-3-ene-1,2-diyl dinitrate at 290 nm is significantly lower than those for the alkyl (mono) nitrates: a best estimate of ΦNO2 ≤ 0.25 is obtained from the experimental measurements. PMID:24684215

  18. Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles.

    PubMed

    Boyer, John-Christopher; van Veggel, Frank C J M

    2010-08-01

    In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF(4): 2% Er(3+), 20% Yb(3+) nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample. PMID:20820726

  19. A general quantitative pH sensor developed with dicyandiamide N-doped high quantum yield graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Zhu Lian; Gao, Ming Xuan; Wang, Ting Ting; Wan, Xiao Yan; Zheng, Lin Ling; Huang, Cheng Zhi

    2014-03-01

    A general quantitative pH sensor for environmental and intracellular applications was developed by the facile hydrothermal preparation of dicyandiamide (DCD) N-doped high quantum yield (QY) graphene quantum dots (GQDs) using citric acid (CA) as the carbon source. The obtained N-doped GQDs have excellent photoluminesence (PL) properties with a relatively high QY of 36.5%, suggesting that N-doped chemistry could promote the QY of carbon nanomaterials. The possible mechanism for the formation of the GQDs involves the CA self-assembling into a nanosheet structure through intermolecular H-bonding at the initial stage of the reaction, and then the pure graphene core with many function groups formed through the dehydration between the carboxyl and hydroxyl of the intermolecules under hydrothermal conditions. These N-doped GQDs have low toxicity, and are photostable and pH-sensitive between 1.81 to 8.96, giving a general pH sensor with a wide range of applications from real water to intracellular contents.A general quantitative pH sensor for environmental and intracellular applications was developed by the facile hydrothermal preparation of dicyandiamide (DCD) N-doped high quantum yield (QY) graphene quantum dots (GQDs) using citric acid (CA) as the carbon source. The obtained N-doped GQDs have excellent photoluminesence (PL) properties with a relatively high QY of 36.5%, suggesting that N-doped chemistry could promote the QY of carbon nanomaterials. The possible mechanism for the formation of the GQDs involves the CA self-assembling into a nanosheet structure through intermolecular H-bonding at the initial stage of the reaction, and then the pure graphene core with many function groups formed through the dehydration between the carboxyl and hydroxyl of the intermolecules under hydrothermal conditions. These N-doped GQDs have low toxicity, and are photostable and pH-sensitive between 1.81 to 8.96, giving a general pH sensor with a wide range of applications from real water

  20. Self-consistent calculations of optical properties of type I and type II quantum heterostructures

    NASA Astrophysics Data System (ADS)

    Shuvayev, Vladimir A.

    In this Thesis the self-consistent computational methods are applied to the study of the optical properties of semiconductor nanostructures with one- and two-dimensional quantum confinements. At first, the self-consistent Schrodinger-Poisson system of equations is applied to the cylindrical core-shell structure with type II band alignment without direct Coulomb interaction between carriers. The electron and hole states and confining potential are obtained from a numerical solution of this system. The photoluminescence kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The results are applied to the radiative recombination in the system of ZnTe/ZnSe stacked quantum dots. A good agreement with both continuous wave and time-resolved experimental observations is found. It is shown that size distribution results in the photoluminescence decay that has essentially non-exponential behavior even at the tail of the decay where the carrier lifetime is almost the same due to slowly changing overlap of the electron and hole wavefunctions. Also, a model situation applicable to colloidal core-shell nanowires is investigated and discussed. With respect to the excitons in type I quantum wells, a new computationally efficient and flexible approach of calculating the characteristics of excitons, based on a self-consistent variational treatment of the electron-hole Coulomb interaction, is developed. In this approach, a system of self-consistent equations describing the motion of an electron-hole pair is derived. The motion in the growth direction of the quantum well is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently. This approach is applied to a shallow quantum well with the delta-potential profile, for which analytical expressions for the exciton binding energy and the ground state eigenfunctions are obtained, and to the quantum well with the square potential profile with several

  1. Diurnal changes of photosynthetic quantum yield in the intertidal macroalga Sargassum thunbergii under simulated tidal emersion conditions

    NASA Astrophysics Data System (ADS)

    Yu, Yong Qiang; Zhang, Quan Sheng; Tang, Yong Zheng; Li, Xue Meng; Liu, Hong Liang; Li, Li Xia

    2013-07-01

    In this study, a three-way factorial experimental design was used to investigate the diurnal changes of photosynthetic activity of the intertidal macroalga Sargassum thunbergii in response to temperature, tidal pattern and desiccation during a simulated diurnal light cycle. The maximum (Fv/Fm) and effective (ΦPSII) quantum yields of photosystem II (PSII) were estimated by chlorophyll fluorescence using a pulse amplitude modulated fluorometer. Results showed that this species exhibited sun-adapted characteristics, as evidenced by the daily variation of Fv/Fm and ΦPSII. Both yield values decreased with increasing irradiance towards noon and recovered rapidly in the afternoon suggesting a dynamic photoinhibition. The photosynthetic quantum yield of S. thunbergii thalli varied significantly with temperature, tidal pattern and desiccation. Thalli were more susceptible to light-induced damage at high temperature of 25 °C and showed complete recovery of photosynthetic activity only when exposed to 8 °C. In contrast with the mid-morning low tide period, although there was an initial increase in photosynthetic yield during emersion, thalli showed a greater degree of decline at the end of emersion and remained less able to recover when low tide occurred at mid-afternoon. Short-term air exposure of 2 h did not significantly influence the photosynthesis. However, when exposed to moderate conditions (4 h desiccation at 15 °C or 6 h desiccation at 8 °C), a significant inhibition of photosynthesis was followed by partial or complete recovery upon re-immersion in late afternoon. Only extreme conditions (4 h desiccation at 25 °C or 6 h desiccation at 15 °C or 25 °C) resulted in the complete inhibition, with little indication of recovery until the following morning, implying the occurrence of chronic PSII damage. Based on the magnitude of effect, desiccation was the predominant negative factor affecting the photosynthesis under the simulated daytime irradiance period. These

  2. Montelukast photodegradation: elucidation of Ф-order kinetics, determination of quantum yields and application to actinometry.

    PubMed

    Maafi, Mounir; Maafi, Wassila

    2014-08-25

    A recently developed Ф-order semi-emperical integrated rate-law for photoreversible AB(2Ф) reactions has been successfully applied to investigate Montelukast sodium (Monte) photodegradation kinetics in ethanol. The model equations also served to propose a new stepwise kinetic elucidation method valid for any AB(2Ф) system and its application to the determination of Monte's forward (Ф(λ(irr))(A-->B)) and reverse (Ф(λ(irr))(B-->A)) quantum yields at various irradiation wavelengths. It has been found that Ф(λ(irr))(A-->B) undergoes a 15-fold increase with wavelength between 220 and 360 nm, with the spectral section 250-360 nm representing Monte effective photodegradation causative range. The reverse quantum yield values were generally between 12 and 54% lower than those recorded for Ф(λ(irr))(A-->B), with the trans-isomer (Monte) converting almost completely to its cis-counterpart at high irradiation wavelengths. Furthermore, the potential use of Monte as an actinometer has been investigated, and an actinometric method was proposed. This study demonstrated the usefulness of Monte for monochromatic light actinometry for the dynamic range 258-380 nm. PMID:24835854

  3. Photoisomerization dynamics of a rhodopsin-based molecule (potential molecular switch) with high quantum yields

    NASA Astrophysics Data System (ADS)

    Allen, Roland; Jiang, Chen-Wei; Zhang, Xiu-Xing; Fang, Ai-Ping; Li, Hong-Rong; Xie, Rui-Hua; Li, Fu-Li

    2015-03-01

    It is worthwhile to explore the detailed reaction dynamics of various candidates for molecular switches, in order to understand, e.g., the differences in quantum yields and switching times. Here we report density-functional-based simulations for the rhodopsin-based molecule 4-[4-Methylbenzylidene]-5-p-tolyl-3,4-dihydro-2H-pyrrole (MDP), synthesized by Sampedro et al. We find that the photoisomerization quantum yields are remarkably high: 82% for cis-to-trans, and 68% for trans-to-cis. The lifetimes of the S1 excited state in cis-MDP in our calculations are in the range of 900-1800 fs, with a mean value of 1270 fs, while the range of times required for full cis-to-trans isomerization are 1100-2000 fs, with a mean value of 1530 fs. In trans-MDP, the calculated S1 excited state lifetimes are 860-2140 fs, with a mean value of 1330 fs, and with the full trans-to-cis isomerization completed about 200 fs later. In both cases, the dominant reaction mechanism is rotation around the central C =C bond (connected to the pyrroline ring), and de-excitation occurs at an avoided crossing between the ground state and the lowest singlet state, near the midpoint of the rotational pathway. Research Fund for the Doctoral Program of Higher Education of China; Fundamental Research Funds for the Central Universities; Robert A. Welch Foundation; National Natural Science Foundation of China.

  4. Photoisomerization dynamics of a rhodopsin-based molecule (potential molecular switch) with high quantum yields

    NASA Astrophysics Data System (ADS)

    Jiang, Chen-Wei; Zhang, Xiu-Xing; Fang, Ai-Ping; Li, Hong-Rong; Xie, Rui-Hua; Li, Fu-Li; Allen, Roland E.

    2015-02-01

    It is worthwhile to explore the detailed reaction dynamics of various candidates for molecular switches, in order to understand, e.g., the differences in quantum yields and switching times. Here we report density-functional-based simulations for the rhodopsin-based molecule 4-[4-methylbenzylidene]-5-p-tolyl-3,4-dihydro-2H-pyrrole (MDP), synthesized by Sampedro et al We find that the photoisomerization quantum yields are remarkably high: 82% for cis-to-trans, and 68% for trans-to-cis. The lifetimes of the S1 excited state in cis-MDP in our calculations are in the range of 900-1800 fs, with a mean value of 1270 fs, while the range of times required for full cis-to-trans isomerization are 1100-2000 fs, with a mean value of 1530 fs. In trans-MDP, the calculated S1 excited state lifetimes are 860-2140 fs, with a mean value of 1330 fs, and with the full trans-to-cis isomerization completed about 200 fs later. In both cases, the dominant reaction mechanism is rotation around the central C=C bond (connected to the pyrroline ring), and de-excitation occurs at an avoided crossing between the ground state and the lowest singlet state, near the midpoint of the rotational pathway. Perhaps remarkably, but apparently because of electrostatic repulsion, the direction of rotation is the same for both reactions.

  5. Determination of photoluminescence quantum yields of scattering media with an integrating sphere: direct and indirect illumination.

    PubMed

    Würth, Christian; Resch-Genger, Ute

    2015-06-01

    The ever-increasing use of fluorescent nanomaterials and micrometer-sized beads in the life and material sciences requires reliable procedures for the measurement of the key performance parameter fluorescence quantum yield (Φf) of scattering particle dispersions and reference systems to evaluate the performance of such measurements. This encouraged us to systematically study, both theoretically and experimentally, the optical determination of photoluminescent quantum yield as a function of the scattering and absorption properties of the sample and the illumination geometry with an integrating sphere method. The latter included measurements with a direct and an indirect illumination. As a representative and easy-to-prepare reference system, we used ethanolic dispersions of 250 nm sized silica particles and the dye rhodamine 101 and systematically varied the concentration of the dye and particles within the typical ranges of spectroscopic and (bio)analytical applications of fluorescent nanomaterials. Based on our measurements, we recommend indirect sample illumination geometry for the accurate measurement of Φf of samples with low or unknown absorption and high scattering coefficients such as dispersions of luminescent particles or fluorescent reporters in biological matrices. This finding is of utmost relevance for all (bio)analytical applications of fluorescent nanomaterials ranging from particle labels and probes over assay platforms to safety barcodes. PMID:25955619

  6. Photophysics of protoporphyrin ions in vacuo: Triplet-state lifetimes and quantum yields

    NASA Astrophysics Data System (ADS)

    Calvo, M. Reyes; Andersen, Jens Ulrik; Hvelplund, Preben; Nielsen, Steen Brøndsted; Pedersen, Ulrik V.; Rangama, Jimmy; Tomita, Shigeo; Forster, James S.

    2004-03-01

    Lifetimes of triplet-state molecules and triplet quantum yields are important parameters in photobiology as they determine the generation of singlet-oxygen upon irradiation with visible light. Here we report lifetimes of protoporphyrin IX (pp) in vacuo measured in an ion storage ring. We find that after 532 nm photon absorption, pp- (free base and negatively charged carboxylate) and pp+ (single protonation of ring nitrogen) have triplet-state lifetimes of 12 and 6 ms, respectively. After 415 or 390 nm absorption the lifetime of the anion is shorter (1.5 and 0.6 ms) as expected from the increase in temperature. Triplet quantum yields of pp- and pp+ are similar, 0.6-0.7, close to values reported for the free base and monocation in solution. The other channel, direct decay to the electronic ground state and subsequent dissociation of vibrationally excited ions, is much faster than triplet-singlet intersystem crossing. We measured lifetimes of 63 μs, 96 μs, and 0.3 ms after 390, 415, and 532 nm excitation, respectively. A fit of a statistical model to the pp- decay results in an Arrhenius activation energy of 0.5±0.2 eV for CO2 loss and a low preexponential factor (106-1010 s-1), indicative of an entropic barrier.

  7. Comparison of methods and achievable uncertainties for the relative and absolute measurement of photoluminescence quantum yields.

    PubMed

    Würth, Christian; Grabolle, Markus; Pauli, Jutta; Spieles, Monika; Resch-Genger, Ute

    2011-05-01

    The photoluminescence quantum yield (Φ(f)) that presents a direct measure for the efficiency of the conversion of absorbed photons into emitted photons is one of the spectroscopic key parameters of functional fluorophores. It determines the suitability of such materials for applications in, for example, (bio)analysis, biosensing, and fluorescence imaging as well as as active components in optical devices. The reborn interest in accurate Φ(f) measurements in conjunction with the controversial reliability of reported Φ(f) values of many common organic dyes encouraged us to compare two relative and one absolute fluorometric method for the determination of the fluorescence quantum yields of quinine sulfate dihydrate, coumarin 153, fluorescein, rhodamine 6G, and rhodamine 101. The relative methods include the use of a chain of Φ(f) transfer standards consisting of several "standard dye" versus "reference dye" pairs linked to a golden Φ(f) standard that covers the ultraviolet and visible spectral region, and the use of different excitation wavelengths for standard and sample, respectively. Based upon these measurements and the calibration of the instruments employed, complete uncertainty budgets for the resulting Φ(f) values are derived for each method, thereby providing evaluated standard operation procedures for Φ(f) measurements and, simultaneously, a set of assessed Φ(f) standards. PMID:21473570

  8. Solvent effect on the relative quantum yield and fluorescence quenching of 2DAM.

    PubMed

    Nagaraja, D; Melavanki, R M; Patil, N R; Kusanur, R A

    2014-09-15

    The relative quantum yield of diethyl 2-acetamido-2-((3-oxo-3H-benzo[f]chromen-1-yl)methyl)malonate [2DAM] is estimated using single point method with quinine sulfate as standard reference. The quantum yield varies between 0.1161 and 0.3181 depending on the nature of the solvent. The rates of radiative and non radiative decay constants are also calculated. The fluorescence quenching of [2DAM] by aniline is studied at room temperature, by steady state, in five different solvents namely acetonitrile (AN), 1,4 dioxane (DX), 1,2 dichloroethane (DCE), tetrahydrofuran (THF) and toluene (TOL), in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern Volmer plots for all solvents. Various parameters for the quenching process are determined by ground state complex, sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern Volmer (SV) plot is due to both static and dynamic processes. Further, finite sink approximation model is used to check whether these bimolecular reactions were diffusion limited or not. The values of distance parameter R' and diffusion co efficient D are determined and then compared with the values of encounter distance R and diffusion coefficient D calculated using Stokes-Einstein equation. PMID:24769383

  9. Solvent effect on the relative quantum yield and fluorescence quenching of 2DAM

    NASA Astrophysics Data System (ADS)

    Nagaraja, D.; Melavanki, R. M.; Patil, N. R.; Kusanur, R. A.

    2014-09-01

    The relative quantum yield of diethyl 2-acetamido-2-((3-oxo-3H-benzo[f]chromen-1-yl)methyl) malonate [2DAM] is estimated using single point method with quinine sulfate as standard reference. The quantum yield varies between 0.1161 and 0.3181 depending on the nature of the solvent. The rates of radiative and non radiative decay constants are also calculated. The fluorescence quenching of [2DAM] by aniline is studied at room temperature, by steady state, in five different solvents namely acetonitrile (AN), 1,4 dioxane (DX), 1,2 dichloroethane (DCE), tetrahydrofuran (THF) and toluene (TOL), in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern Volmer plots for all solvents. Various parameters for the quenching process are determined by ground state complex, sphere of action static quenching model and finite sink approximation model. The magnitudes of these rate parameters indicate that positive deviation in the Stern Volmer (SV) plot is due to both static and dynamic processes. Further, finite sink approximation model is used to check whether these bimolecular reactions were diffusion limited or not. The values of distance parameter R‧ and diffusion co efficient D are determined and then compared with the values of encounter distance R and diffusion coefficient D calculated using Stokes-Einstein equation.

  10. Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles

    NASA Astrophysics Data System (ADS)

    Boyer, John-Christopher; van Veggel, Frank C. J. M.

    2010-08-01

    In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF4: 2% Er3+, 20% Yb3+ nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample.In this communication we describe a technique for measuring the absolute quantum yields (QYs) of upconverting nanomaterials based on the use of a commercially available fluorimeter and an integrating sphere. Using this setup, we have successfully acquired luminescence efficiency data (pump laser, absorbed pump, and visible emitted intensities) for lanthanide-doped upconverting nanoparticles. QYs in the range of 0.005% to 0.3% were measured for several NaYF4: 2% Er3+, 20% Yb3+ nanoparticles with particle sizes ranging from 10 to 100 nm while a QY of 3% was measured for a bulk sample. Electronic supplementary information (ESI) available: Experimental details, powder XRDs and TEM micrographs of the samples. See DOI: 10.1039/c0nr00253d

  11. Solvent effect on the relative quantum yield and fluorescence quenching of a newly synthesized coumarin derivative.

    PubMed

    Nagaraja, D; Melavanki, R M; Patil, N R; Geethanjali, H S; Kusanur, R A

    2015-08-01

    We estimated the relative florescence quantum yield (Φ) of 8-methoxy-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin [8MDTC] using a single-point method with quinine sulfate in 0.1 M of sulfuric acid used as a standard reference. The fluorescence lifetimes, radiative and non-radiative decay rate constants are calculated. Relative quantum yields were found to be less in the non-polar solvents, indicating that the solute exhibits less fluorescence in a non-polar environment. The fluorescence quenching of [8MDTC] by aniline was studied at room temperature by examining the steady state in five different solvents in order to explore various possible quenching mechanisms. The experimental results show a positive deviation in Stern-Volmer plots in all solvents. Ground state complex and sphere of action static quenching models were used to interpret the results. Many quenching rate parameters were calculated using these models. The values of these parameters suggest that the sphere of action static quenching model agrees well with the experimental results. Further, a finite sink approximation model was used to check whether these bimolecular reactions were diffusion limited or not. The values of the distance parameter R' and the diffusion coefficient D were determined and are compared with the values of the encounter distance R and diffusion coefficient D calculated using the Stokes-Einstein equation. PMID:25214175

  12. Carbon dots with high fluorescence quantum yield: the fluorescence originates from organic fluorophores

    NASA Astrophysics Data System (ADS)

    Shi, Lei; Yang, Jian Hai; Zeng, Hai Bo; Chen, Yong Mei; Yang, Sheng Chun; Wu, Chao; Zeng, Hao; Yoshihito, Osada; Zhang, Qiqing

    2016-07-01

    In this contribution, we have shown that the organic fluorophores, 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA) and 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-7-carboxylic acid (TPCA), are the main ingredients and fluorescence origins of N,S-CDs via systematic analyses. It inspires us to deeply analyze and understand the fluorescence origins of carbon dots with high fluorescence quantum yields, which will expand their applications.In this contribution, we have shown that the organic fluorophores, 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA) and 5-oxo-3,5-dihydro-2H-thiazolo [3,2-a] pyridine-7-carboxylic acid (TPCA), are the main ingredients and fluorescence origins of N,S-CDs via systematic analyses. It inspires us to deeply analyze and understand the fluorescence origins of carbon dots with high fluorescence quantum yields, which will expand their applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00451b

  13. Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux

    NASA Technical Reports Server (NTRS)

    Barnes, C.; Tibbitts, T.; Sager, J.; Deitzer, G.; Bubenheim, D.; Koerner, G.; Bugbee, B.; Knott, W. M. (Principal Investigator)

    1993-01-01

    Photosynthesis is fundamentally driven by photon flux rather than energy flux, but not all absorbed photons yield equal amounts of photosynthesis. Thus, two measures of photosynthetically active radiation have emerged: photosynthetic photon flux (PPF), which values all photons from 400 to 700 nm equally, and yield photon flux (YPF), which weights photons in the range from 360 to 760 nm according to plant photosynthetic response. We selected seven common radiation sources and measured YPF and PPF from each source with a spectroradiometer. We then compared these measurements with measurements from three quantum sensors designed to measure YPF, and from six quantum sensors designed to measure PPF. There were few differences among sensors within a group (usually <5%), but YPF values from sensors were consistently lower (3% to 20%) than YPF values calculated from spectroradiometric measurements. Quantum sensor measurements of PPF also were consistently lower than PPF values calculated from spectroradiometric measurements, but the differences were <7% for all sources, except red-light-emitting diodes. The sensors were most accurate for broad-band sources and least accurate for narrow-band sources. According to spectroradiometric measurements, YPF sensors were significantly less accurate (>9% difference) than PPF sensors under metal halide, high-pressure sodium, and low-pressure sodium lamps. Both sensor types were inaccurate (>18% error) under red-light-emitting diodes. Because both YPF and PPF sensors are imperfect integrators, and because spectroradiometers can measure photosynthetically active radiation much more accurately, researchers should consider developing calibration factors from spectroradiometric data for some specific radiation sources to improve the accuracy of integrating sensors.

  14. Effective dynamics in Bianchi type II loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Corichi, Alejandro; Montoya, Edison

    2012-05-01

    We numerically investigate the solutions to the effective equations of the Bianchi II model within the “improved” loop quantum cosmology dynamics. The matter source is a massless scalar field. We perform a systematic study of the space of solutions, and focus on the behavior of several geometrical observables. We show that the big bang singularity is replaced by a bounce and the pointlike singularities do not saturate the energy density bound. There are up to three directional bounces in the scale factors, one global bounce in the expansion, the shear presents up to four local maxima and can be zero at the bounce. This allows for solutions with density larger than the maximal density for the isotropic and Bianchi I cases. The asymptotic behavior is shown to behave like that of a Bianchi I model, and the effective solutions connect anisotropic solutions even when the shear is zero at the bounce. All known facts of Bianchi I are reproduced. In the “vacuum limit,” solutions are such that almost all the dynamics is due to the anisotropies. Since Bianchi II plays an important role in the Bianchi IX model and the Belinskii, Khalatnikov, Lifshitz conjecture, our results can provide an intuitive understanding of the behavior in the vicinity of general spacelike singularities, when loop-geometric corrections are present.

  15. Effect of PMMA impregnation on the fluorescence quantum yield of sol-gel glasses doped with quinine sulfate

    NASA Astrophysics Data System (ADS)

    Meneses-Nava, M. A.; Barbosa-García, O.; Díaz-Torres, L. A.; Chávez-Cerda, S.; Torres-Cisneros, M.; King, T. A.

    2001-08-01

    The fluorescence quantum yield of quinine sulfate in sol-gel and PMMA impregnated glasses is measured. The observed quantum yield improvement in the sol-gel matrix, compared to ethanol, is interpreted as a reduction of non-radiative relaxation channels by isolation of the molecules by the cage of the glass. PMMA impregnated sol-gel glasses show an extra improvement of the fluorescence yield, which is interpreted as a reduction of the free space and the rigid fixation of the molecules to the matrix.

  16. SU-E-T-191: First Principle Calculation of Quantum Yield in Photodynamic Therapy

    SciTech Connect

    Abolfath, R; Guo, F; Chen, Z; Nath, R

    2014-06-01

    Purpose: We present a first-principle method to calculate the spin transfer efficiency in oxygen induced by any photon fields especially in MeV energy range. The optical pumping is mediated through photosensitizers, e.g., porphyrin and/or ensemble of quantum dots. Methods: Under normal conditions, oxygen molecules are in the relatively non-reactive triplet state. In the presence of certain photosensitizer compounds such as porphyrins, electromagnetic radiation of specific wavelengths can excite oxygen to highly reactive singlet state. With selective uptake of photosensitizers by certain malignant cells, photon irradiation of phosensitized tumors can lead to selective killing of cancer cells. This is the basis of photodynamic therapy (PDT). Despite several attempts, PDT has not been clinically successful except in limited superficial cancers. Many parameters such as photon energy, conjugation with quantum dots etc. can be potentially combined with PDT in order to extend the role of PDT in cancer management. The key quantity for this optimization is the spin transfer efficiency in oxygen by any photon field. The first principle calculation model presented here, is an attempt to fill this need. We employ stochastic density matrix description of the quantum jumps and the rate equation methods in quantum optics based on Markov/Poisson processes and calculate time evolution of the population of the optically pumped singlet oxygen. Results: The results demonstrate the feasibility of our model in showing the dependence of the optical yield in generating spin-singlet oxygen on the experimental conditions. The adjustable variables can be tuned to maximize the population of the singlet oxygen hence the efficacy of the photodynamic therapy. Conclusion: The present model can be employed to fit and analyze the experimental data and possibly to assist researchers in optimizing the experimental conditions in photodynamic therapy.

  17. Effect of capsid proteins to ICG mass ratio on fluorescent quantum yield of virus-resembling optical nano-materials

    NASA Astrophysics Data System (ADS)

    Gupta, Sharad; Ico, Gerardo; Matsumura, Paul; Rao, A. L. N.; Vullev, Valentine; Anvari, Bahman

    2012-03-01

    We recently reported construction of a new type of optical nano-construct composed of genome-depleted plant infecting brome mosaic virus (BMV) doped with Indocyanine green (ICG), an FDA-approved chromophore. We refer to these constructs as optical viral ghosts (OVGs) since only the capsid protein (CP) subunits of BMV remain to encapsulate ICG. To utilize OVGs as effective nano-probes in fluorescence imaging applications, their fluorescence quantum yield needs to be maximized. In this study, we investigate the effect of altering the CP to ICG mass ratio on the fluorescent quantum yield of OVGs. Results of this study provide the basis for construction of OVGs with optimal amounts of CP and ICG to yield maximal fluorescence quantum yield.

  18. Foliar application of isopyrazam and epoxiconazole improves photosystem II efficiency, biomass and yield in winter wheat.

    PubMed

    Ajigboye, Olubukola O; Murchie, Erik; Ray, Rumiana V

    2014-09-01

    A range of fungicides including epoxiconazole, azoxystrobin and isopyrazam, were applied to winter wheat at GS 31/32 to determine their effect on photosystem II (PSII) efficiency, biomass and yield. Frequent, repeated measurements of chlorophyll fluorescence were carried on plants grown under different water regimes in controlled environment and in the field to establish the transiency of fluorescence changes in relation to fungicide application. Application of the succinate dehydrogenase inhibitor isopyrazam in a mixture with the triazole epoxiconazole increased PSII efficiency associated with a 28% increase in biomass in the controlled environment and 4% increase in grain yield in the field in the absence of disease pressure. Application of isopyrazam and epoxiconazole increased efficiency of PSII photochemistry (Fv'/Fm') as early as 4h following application associated with improved photosynthetic gas exchange and increased rates of electron transport. We reveal a strong, positive relationship between Fv'/Fm' and CO2 assimilation rate, stomatal conductance and transpiration rate in controlled environment and Fv'/Fm' detected just after anthesis on the flag leaf at GS 73 and grain yield in field. We conclude that application of a specific combination of fungicides with positive effects of plant physiology in the absence of disease pressure results in enhanced biomass and yield in winter wheat. Additionally, an accurate and frequent assessment of photosynthetic efficiency of winter wheat plants can be used to predict yield and biomass in the field. PMID:25175650

  19. Second Preliminary Report on X-ray Yields from OMEGA II Targets

    SciTech Connect

    Fournier, K B; May, M J; MacLaren, S A; Coverdale, C A; Davis, J F

    2006-08-28

    We present details about X-ray yields measured with LLNL and SNL diagnostics in soft and moderately hard X-ray bands from laser-driven, doped-aerogel targets shot on 07/14/06 during the OMEGA II test series. Yields accurate to {+-}25% in the 5-15 keV band are measured with Livermore's HENWAY spectrometer. Yields in the sub-keV to 3.2 keV band are measured with LLNL's DANTE diagnostic, the DANTE yields may be 35-40% too large. SNL ran a PCD-based diagnostic that also measured X-ray yields in the spectral region above 4 keV, and also down to the nearly sub-keV range. The PCD and HENWAY and DANTE numbers are compared. The time histories of the X-ray signals are measured with LLNL's H11 PCD, and from two SNL PCDs with comparable filtering. There is a persistent disagreement between the H11 PCD and SNL PCD measured FWHM, which is shown not to be due to analysis techniques. The recommended X-ray waveform is that from the SNL PCD p66k10, which was recorded on a fast, high-bandwidth TDS 6804 oscilloscope, and which are not plotted here.

  20. Secondary Electron Yield and Groove Chamber Tests in PEP-II

    SciTech Connect

    Le Pimpec, F.; Kirby, R.E.; Markiewicz, Thomas W.; Pivi, MTF; Raubenheimer, Tor O.; Seeman, J.; Wang, L.; /SLAC

    2007-11-06

    Possible remedies for the electron cloud in positron damping ring (DR) of the International Linear Collider (ILC) includes thin-film coatings, surface conditioning, photon antechamber, clearing electrodes and chamber with grooves or slots [1]. We installed chambers in the PEP-II Low Energy Ring (LER) to monitor the secondary electron yield (SEY) of TiN, TiZrV (NEG) and technical accelerator materials under the effect of electron and photon conditioning in situ. We have also installed chambers with rectangular grooves in straight sections to test this possible mitigation technique. In this paper, we describe the ILC R&D ongoing effort at SLAC to reduce the electron cloud effect in the damping ring, the chambers installation in the PEP-II and latest results.

  1. Gold Doping of Silver Nanoclusters: A 26-Fold Enhancement in the Luminescence Quantum Yield.

    PubMed

    Soldan, Giada; Aljuhani, Maha A; Bootharaju, Megalamane S; AbdulHalim, Lina G; Parida, Manas R; Emwas, Abdul-Hamid; Mohammed, Omar F; Bakr, Osman M

    2016-05-01

    A high quantum yield (QY) of photoluminescence (PL) in nanomaterials is necessary for a wide range of applications. Unfortunately, the weak PL and moderate stability of atomically precise silver nanoclusters (NCs) suppress their utility. Herein, we accomplished a ≥26-fold PL QY enhancement of the Ag29 (BDT)12 (TPP)4 cluster (BDT: 1,3-benzenedithiol; TPP: triphenylphosphine) by doping with a discrete number of Au atoms, producing Ag29-x Aux (BDT)12 (TPP)4 , x=1-5. The Au-doped clusters exhibit an enhanced stability and an intense red emission around 660 nm. Single-crystal XRD, mass spectrometry, optical, and NMR spectroscopy shed light on the PL enhancement mechanism and the probable locations of the Au dopants within the cluster. PMID:27060602

  2. Surface structures for enhancement of quantum yield in broad spectrum emission nanocrystals

    DOEpatents

    Schreuder, Michael A.; McBride, James R.; Rosenthal, Sandra J.

    2014-07-22

    Disclosed are inorganic nanoparticles comprising a body comprising cadmium and/or zinc crystallized with selenium, sulfur, and/or tellurium; a multiplicity of phosphonic acid ligands comprising at least about 20% of the total surface ligand coverage; wherein the nanocrystal is capable of absorbing energy from a first electromagnetic region and capable of emitting light in a second electromagnetic region, wherein the maximum absorbance wavelength of the first electromagnetic region is different from the maximum emission wavelength of the second electromagnetic region, thereby providing a Stokes shift of at least about 20 nm, wherein the second electromagnetic region comprises an at least about 100 nm wide band of wavelengths, and wherein the nanoparticle exhibits has a quantum yield of at least about 10%. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

  3. Raman microscope and quantum yield studies on the primary photochemistry of A2-visual pigments.

    PubMed Central

    Barry, B; Mathies, R A; Pardoen, J A; Lugtenburg, J

    1987-01-01

    The 77-K resonance Raman vibrational spectrum of intact goldfish rod photoreceptors containing 3,4-dehydro (A2) retinal is dominated by scattering from the 9-cis component of the steady state at all excitation wavelengths. Intact goldfish photoreceptors were regenerated with an A1-retinal chromophore to determine whether this behavior is caused by the protein or the chromophore. The resulting Raman spectrum was typical of an A1-pigment exhibiting significant scattering from all three components of the steady state: rhodopsin, bathorhodopsin, and isorhodopsin. Furthermore, regeneration of bovine opsin with A2-retinal produces a characteristic "A2-Raman spectrum" that is dominated by scattering from the 9-cis pigment. We conclude that the differences between the Raman spectra of the A1-and A2-pigments are caused by some intrinsic difference in the photochemical properties of the retinal chromophores. To quantitate these observations, the 77-K adsorption spectra and the photochemical quantum yields (phi) of the native A2-goldfish and the regenerated A2-bovine pigments were measured. In the goldfish A2-pigment, the value of phi 4 (9-cis----trans) is 0.05; phi 3 (trans----9-cis) is 0.10; and phi 2 (trans----11-cis) is 0.35. By contrast, in the bovine A1-pigment, these quantum yields are 0.10, 0.053, and 0.50, respectively. The reduced value of phi 4 and the increased value of phi 3 in the goldfish pigment confirms that the 9-cis isomer is photochemically more stable in A2-pigments. PMID:3676440

  4. Photonic effects on the radiative decay rate and luminescence quantum yield of doped nanocrystals.

    PubMed

    Senden, Tim; Rabouw, Freddy T; Meijerink, Andries

    2015-02-24

    Nanocrystals (NCs) doped with luminescent ions form an emerging class of materials. In contrast to excitonic transitions in semiconductor NCs, the optical transitions are localized and not affected by quantum confinement. The radiative decay rates of the dopant emission in NCs are nevertheless different from their bulk analogues due to photonic effects, and also the luminescence quantum yield (QY, important for applications) is affected. In the past, different theoretical models have been proposed to describe the photonic effects for dopant emission in NCs, with little experimental validation. In this work we investigate the photonic effects on the radiative decay rate of luminescent doped NCs using 4 nm LaPO4 NCs doped with Ce(3+) or Tb(3+) ions in different refractive index solvents and bulk crystals. We demonstrate that the measured influence of the refractive index on the radiative decay rate of the Ce(3+) emission, having near unity QY, is in excellent agreement with the theoretical nanocrystal-cavity model. Furthermore, we show how the nanocrystal-cavity model can be used to quantify the nonunity QY of Tb(3+)-doped LaPO4 NCs and demonstrate that, as a general rule, the QY is higher in media with higher refractive index. PMID:25584627

  5. Aeronomical determinations of the quantum yields of O (1S) and O (1D) from dissociative recombination of O2(+)

    NASA Technical Reports Server (NTRS)

    Yee, Jeng-Hwa; Abreu, Vincent J.; Colwell, William B.

    1989-01-01

    Data from the visible-airglow experiment on the Atmosphere Explorer-E satellite have been used to determine the quantum yields of O (1S) and O (1D) from the dissociative recombination of O2(+) based on a constant total recombination rate from each vibrational level. A range of values between 0.05 and 0.18 has been obtained for the quantum yield of O (1S) and shows a positive correlation with the extent of the vibrational excitation of O2(+). The quantum yield of O (1D) has been measured to be 0.9 + or - 0.2, with no apparent dependence on the vibrational distribution of O2(+).

  6. Quantum yield measurements of light-induced H₂ generation in a photosystem I-[FeFe]-H₂ase nanoconstruct.

    PubMed

    Applegate, Amanda M; Lubner, Carolyn E; Knörzer, Philipp; Happe, Thomas; Golbeck, John H

    2016-01-01

    The quantum yield for light-induced H2 generation was measured for a previously optimized bio-hybrid cytochrome c 6-crosslinked PSI(C13G)-1,8-octanedithiol-[FeFe]-H2ase(C97G) (PSI-H2ase) nanoconstruct. The theoretical quantum yield for the PSI-H2ase nanoconstruct is 0.50 molecules of H2 per photon absorbed, which equates to a requirement of two photons per H2 generated. Illumination of the PSI-H2ase nanoconstruct with visible light between 400 and 700 nm resulted in an average quantum yield of 0.10-0.15 molecules of H2 per photon absorbed, which equates to a requirement of 6.7-10 photons per H2 generated. A possible reason for the difference between the theoretical and experimental quantum yield is the occurrence of non-productive PSI(C13G)-1,8-octanedithiol-PSIC13G (PSI-PSI) conjugates, which would absorb light without generating H2. Assuming the thiol-Fe coupling is equally efficient at producing PSI-PSI conjugates as well as in producing PSI-H2ase nanoconstructs, the theoretical quantum yield would decrease to 0.167 molecules of H2 per photon absorbed, which equates to 6 photons per H2 generated. This value is close to the range of measured values in the current study. A strategy that purifies the PSI-H2ase nanoconstructs from the unproductive PSI-PSI conjugates or that incorporates different chemistries on the PSI and [FeFe]-H2ase enzyme sites could potentially allow the PSI-H2ase nanoconstruct to approach the expected theoretical quantum yield for light-induced H2 generation. PMID:25527460

  7. Solution-based synthesis of high yield CZTS (Cu2ZnSnS4) spherical quantum dots

    NASA Astrophysics Data System (ADS)

    Rajesh, G.; Muthukumarasamy, N.; Subramanian, E. P.; Venkatraman, M. R.; Agilan, S.; Ragavendran, V.; Thambidurai, M.; Velumani, S.; Yi, Junsin; Velauthapillai, Dhayalan

    2015-01-01

    High yield CZTS quantum dots have been synthesized using simple precursors by chemical precipitation technique. Formation mechanism of CZTS spherical quantum dots also has been investigated. According to the mechanism, copper sulfide nuclei firstly forms, and serves as the starting point for the nucleation and growth of CZTS. X-ray diffraction pattern, X-ray photoelectron spectra (XPS) and Raman spectra reveals the formation of pure kesterite structure Cu2ZnSnS4 nanoparticles. HRTEM analysis reveals the formation of CZTS quantum dots with an average particle size of ∼8.3 nm. The elemental distribution of CZTS quantum dots studied using STEM elemental mapping reveals that Cu, Zn, Sn and S are present in the sample. The photoluminescence spectra of CZTS exhibit a broad red emission band at 657 nm. The optical band gap is shifted to the higher energy side and it shows the presence of quantum confinement effect.

  8. Absolute Photoluminescence Quantum Yields of IR-26 Dye, PbS, and PbSe Quantum Dots

    SciTech Connect

    Semonin, Octavi Escala; Johnson, Justin C; Luther, Joseph M; Midgett, Aaron G; Nozik, Arthur J; Beard, Matthew C

    2010-08-19

    In this study, we have directly measured the photoluminescence quantum yield (Φ{sub PL}) of IR-26 at a range of concentrations and the Φ{sub PL} of PbS and PbSe QDs for a range of sizes. We find that the Φ{sub PL} of IR-26 has a weak concentration dependence due to reabsorption, with a Φ{sub PL} of 0.048 ± 0.002% for low concentrations, lower than previous reports by a full order of magnitude. We also find that there is a dramatic size dependence for both PbS and PbSe QDs, with the smallest dots exhibiting a Φ{sub PL} in excess of 60%, while larger dots fall below 3%. A model, including nonradiative transition between electronic states and energy transfer to ligand vibrations, appears to explain this size dependence. These findings provide both a better characterization of photoluminescence for near-infrared emitters and some insight into how improved QDs can be developed.

  9. Quantum yields and reaction times of photochromic diarylethenes: nonadiabatic ab initio molecular dynamics for normal- and inverse-type.

    PubMed

    Wiebeler, Christian; Schumacher, Stefan

    2014-09-11

    Photochromism is a light-induced molecular process that is likely to find its way into future optoelectronic devices. In further optimization of photochromic materials, light-induced conversion efficiencies as well as reaction times can usually only be determined once a new molecule was synthesized. Here we use nonadiabatic ab initio molecular dynamics to study the electrocyclic reaction of diarylethenes, comparing normal- and inverse-type systems. Our study highlights that reaction quantum yields can be successfully predicted in accord with experimental findings. In particular, we find that inverse-type diarylethenes show a significantly higher reaction quantum yield and cycloreversion on times typically as short as 100 fs. PMID:25140609

  10. Final Report on X-ray Yields from OMEGA II Targets

    SciTech Connect

    Fournier, K B; May, M J; MacLaren, S A; Coverdale, C A; Davis, J F

    2007-06-20

    We present details about X-ray yields measured with Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) diagnostics in soft and moderately hard X-ray bands from laser-driven, doped-aerogel targets shot on 07/14/06 during the OMEGA II test series. Yields accurate to {+-}25% in the 5-15 keV band are measured with Livermore's HENWAY spectrometer. Yields in the sub-keV to 3.2 keV band are measured with LLNL's DANTE diagnostic, the DANTE yields are accurate to 10-15%. SNL ran a PCD-based diagnostic that also measured X-ray yields in the spectral region above 4 keV, and also down to the sub-keV range. The PCD and HENWAY and DANTE numbers are compared. The time histories of the moderately hard (h{nu} > 4 keV) X-ray signals are measured with LLNL's H11 PCD, and from two SNL PCDs with comparable filtration. There is general agreement between the H11 PCD and SNL PCD measured FWHM except for two of the shorter-laser-pulse shots, which is shown not to be due to analysis techniques. The recommended X-ray waveform is that from the SNL PCD p66k10, which was recorded on a fast, high-bandwidth TDS 6804 oscilloscope. X-ray waveforms from target emission in two softer spectral bands are also shown; the X-ray emissions have increasing duration as the spectral content gets softer.

  11. Low-Pressure Photolysis of 2,3-Pentanedione in Air: Quantum Yields and Reaction Mechanism.

    PubMed

    Bouzidi, Hichem; Djehiche, Mokhtar; Gierczak, Tomasz; Morajkar, Pranay; Fittschen, Christa; Coddeville, Patrice; Tomas, Alexandre

    2015-12-24

    Dicarbonyls in the atmosphere mainly arise from secondary sources as reaction products in the degradation of a large number of volatile organic compounds (VOC). Because of their sensitivity to solar radiation, photodissociation of dicarbonyls can dominate the fate of these VOC and impact the atmospheric radical budget. The photolysis of 2,3-pentanedione (PTD) has been investigated for the first time as a function of pressure in a static reactor equipped with continuous wave cavity ring-down spectroscopy to measure the HO2 radical photostationary concentrations along with stable species. We showed that (i) Stern-Volmer plots are consistent with low OH-radical formation yields in RCO + O2 reactions, (ii) the decrease of the photodissociation rate due to pressure increase from 26 to 1000 mbar is of about 30%, (iii) similarly to other dicarbonyls, the Stern-Volmer analysis shows a curvature at the lower pressure investigated, which may be assigned to the existence of excited singlet and triplet PTD states, (iv) PTD photolysis at 66 mbar leads to CO2, CH2O and CO with yields of (1.16 ± 0.04), (0.33 ± 0.02) and (0.070 ± 0.005), respectively, with CH2O yield independent of pressure up to 132 mbar and CO yield in agreement with that obtained at atmospheric pressure by Bouzidi et al. (2014), and (v) the PTD photolysis mechanism remains unchanged between atmospheric pressure and 66 mbar. As a part of this work, the O2 broadening coefficient for the absorption line of HO2 radicals at 6638.21 cm(-1) has been determined (γO2 = 0.0289 cm(-1) atm(-1)). PMID:26608471

  12. Modeling of the redox state dynamics in photosystem II of Chlorella pyrenoidosa Chick cells and leaves of spinach and Arabidopsis thaliana from single flash-induced fluorescence quantum yield changes on the 100 ns-10 s time scale.

    PubMed

    Belyaeva, N E; Schmitt, F-J; Paschenko, V Z; Riznichenko, G Yu; Rubin, A B

    2015-08-01

    The time courses of the photosystem II (PSII) redox states were analyzed with a model scheme supposing a fraction of 11-25 % semiquinone (with reduced [Formula: see text]) RCs in the dark. Patterns of single flash-induced transient fluorescence yield (SFITFY) measured for leaves (spinach and Arabidopsis (A.) thaliana) and the thermophilic alga Chlorella (C.) pyrenoidosa Chick (Steffen et al. Biochemistry 44:3123-3132, 2005; Belyaeva et al. Photosynth Res 98:105-119, 2008, Plant Physiol Biochem 77:49-59, 2014) were fitted with the PSII model. The simulations show that at high-light conditions the flash generated triplet carotenoid (3)Car(t) population is the main NPQ regulator decaying in the time interval of 6-8 μs. So the SFITFY increase up to the maximum level [Formula: see text]/F 0 (at ~50 μs) depends mainly on the flash energy. Transient electron redistributions on the RC redox cofactors were displayed to explain the SFITFY measured by weak light pulses during the PSII relaxation by electron transfer (ET) steps and coupled proton transfer on both the donor and the acceptor side of the PSII. The contribution of non-radiative charge recombination was taken into account. Analytical expressions for the laser flash, the (3)Car(t) decay and the work of the water-oxidizing complex (WOC) were used to improve the modeled P680(+) reduction by YZ in the state S 1 of the WOC. All parameter values were compared between spinach, A. thaliana leaves and C. pyrenoidosa alga cells and at different laser flash energies. ET from [Formula: see text] slower in alga as compared to leaf samples was elucidated by the dynamics of [Formula: see text] fractions to fit SFITFY data. Low membrane energization after the 10 ns single turnover flash was modeled: the ∆Ψ(t) amplitude (20 mV) is found to be about 5-fold smaller than under the continuous light induction; the time-independent lumen pHL, stroma pHS are fitted close to dark estimates. Depending on the flash energy used at 1

  13. Aerogels from CdSe/CdS Nanorods with Ultra-long Exciton Lifetimes and High Fluorescence Quantum Yields.

    PubMed

    Sánchez-Paradinas, Sara; Dorfs, Dirk; Friebe, Sebastian; Freytag, Axel; Wolf, Andreas; Bigall, Nadja C

    2015-10-28

    Hydrogels are fabricated from CdSe/CdS seeded nanorod building blocks by the addition of hydrogen peroxide and converted to aerogels by supercritical drying. The aerogels show higher photoluminescence quantum yields and longer lifetimes than the hydrogels and the nanoparticle solutions. A model for this observation is derived. PMID:26332446

  14. ABSORBANCE, ABSORPTION COEFFICIENT, AND APPARENT QUANTUM YIELD: A COMMENT ON AMBIGUITY IN THE USE OF THESE OPTICAL CONCEPTS

    EPA Science Inventory

    Several important optical terms such as "absorbance" and "absorption coefficient" are frequently used ambiguously in the current peer-reviewed literature. Since they are important terms that are required to derive other quantities such as the "apparent quantum yield" of photoprod...

  15. PHYSIOLOGICAL LIMITATION OF PHYTOPLANKTON PHOTOSYNTHESIS IN THE EASTERN EQUATORIAL PACIFIC DETERMINED FROM VARIABILITY IN THE QUANTUM YIELD OF FLUORESCENCE

    EPA Science Inventory

    On a transect study in the eastern equatorial Pacific, from the high-nutrient, low-chlorophyll tropical waters to the oligotrophic subtropical waters, we determined the variability in the maximum change in the quantum yield of chlorophyll fluorescence by means of a fast repetitio...

  16. Laboratory Study of Nitrate Photolysis in Antarctic Snow: Quantum Yield and Isotope Effects

    NASA Astrophysics Data System (ADS)

    Meusinger, C.; Berhanu, T. A.; Erbland, J.; Jost, R.; Bhattacharya, S. K.; Savarino, J. P.; Johnson, M. S.

    2013-12-01

    Post-depositional processes alter the nitrate concentration and its isotopic composition in the top layers of snow at low snow accumulation sites, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. Photolysis of nitrate in the snowpack was shown to be the major nitrate loss mechanism from the snowpack. Here a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption by flushing the snow with pure N2 at 100 % humidity during irradiation with UV light from a Xenon lamp. A selection of UV filters allowed examination of the 200 and 300 nm absorption bands of nitrate and to emulate actinic fluxes similar to those in Dome C. Irradiated snow was sampled in 1 cm sections and analyzed for nitrate concentration and isotopic composition (δ15N, δ18O and Δ17O); the actinic flux was measured at similar sections in the snow. The quantum yield was observed to decrease from 0.44 to 0.05 within what corresponds to weeks of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate and one of trapped or buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NOx emissions may be increased significantly due to the observed quantum yield in this study influencing predicted boundary layer chemistry including ozone concentrations. An average photolytic isotopic fractionation of 15ɛ = -15×1.2 ‰ was found for the experiments without a wavelength filter. These results are ascribed to excitation of the 200 nm nitrate absorption band. Blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, showed a photolytic fractionation constant of 15ɛ = -47.9 × 6.8 ‰ which lies within the fractionation determined in the field

  17. Microstructural characterization of quantum dots with type-II band alignments

    NASA Astrophysics Data System (ADS)

    Sarney, W. L.; Little, J. W.; Svensson, S. P.

    2006-06-01

    We are investigating the structural, electrical, and infrared (IR) optical properties of a new material system comprising undoped self-assembled quantum dots having a type-II band alignment with the surrounding matrix. This materials system is fundamentally different from those using conventional type-I quantum dots that must be doped and that rely on intersubband transitions for IR photoresponse. Type-II quantum dots operate in the photovoltaic mode with IR photoresponse arising from electron-hole pair production involving three-dimensionally confined states in the dots and quantum well states in the matrix material. In this paper, we discuss the structural characterization of molecular beam epitaxy (MBE)-grown InSb quantum dots embedded in an In 0.53Ga 0.47As matrix lattice-matched to an InP substrate.

  18. High precision tracking and the measurement of B(Z yields b b )/B(Z yields hadrons) with the Mark II at the SLC

    SciTech Connect

    Schumm, B.A.

    1991-03-01

    During the 1990 run of the Mark II at the SLC, the precision tracking system achieved a preliminary impact parameter resolution of 35.8 {plus minus} 1.3 {mu}m for high momentum tracks, which is the quadrature sum of 25 {plus minus} 5 {mu}m of intrinsic resolution smearing dominated by misalignments and other geometrical effects. A method is proposed by which this system can be used to measure B(Z {yields} b{rvec b}/B(Z {yields} hadrons)) with minimal systematic error. 6 refs., 3 figs.

  19. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis

    PubMed Central

    Meiling, Till T.; Cywiński, Piotr J.; Bald, Ilko

    2016-01-01

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. PMID:27334409

  20. Integrated semiconductor quantum dot scintillation detector: Ultimate limit for speed and light yield

    DOE PAGESBeta

    Oktyabrsky, Serge; Yakimov, Michael; Tokranov, Vadim; Murat, Pavel

    2016-03-30

    Here, a picosecond-range timing of charged particles and photons is a long-standing challenge for many high-energy physics, biophysics, medical and security applications. We present a design, technological pathway and challenges, and some properties important for realization of an ultrafast high-efficient room-temperature semiconductor scintillator based on self-assembled InAs quantum dots (QD) embedded in a GaAs matrix. Low QD density (<; 1015 cm-3), fast (~5 ps) electron capture, luminescence peak redshifted by 0.2-0.3 eV from GaAs absorption edge with fast decay time (0.5-1 ns) along with the efficient energy transfer in the GaAs matrix (4.2 eV/pair) allows for fabrication of a semiconductormore » scintillator with the unsurpassed performance parameters. The major technological challenge is fabrication of a large volume (> 1 cm3 ) of epitaxial QD medium. This requires multiple film separation and bonding, likely using separate epitaxial films as waveguides for improved light coupling. Compared to traditional inorganic scintillators, the semiconductor-QD based scintillators could have about 5x higher light yield and 20x faster decay time, opening a way to gamma detectors with the energy resolution better than 1% and sustaining counting rates MHz. Picosecond-scale timing requires segmented low-capacitance photodiodes integrated with the scintillator. For photons, the proposed detector inherently provides the depth-of-interaction information.« less

  1. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis.

    PubMed

    Meiling, Till T; Cywiński, Piotr J; Bald, Ilko

    2016-01-01

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. PMID:27334409

  2. Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

    NASA Astrophysics Data System (ADS)

    Joo, Jinmyoung; Defforge, Thomas; Loni, Armando; Kim, Dokyoung; Li, Z. Y.; Sailor, Michael J.; Gautier, Gael; Canham, Leigh T.

    2016-04-01

    The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO2 solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yield (>32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.

  3. White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis

    NASA Astrophysics Data System (ADS)

    Meiling, Till T.; Cywiński, Piotr J.; Bald, Ilko

    2016-06-01

    In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.

  4. Effects of inter-nanocrystal distance on luminescence quantum yield in ensembles of Si nanocrystals

    SciTech Connect

    Valenta, J. Greben, M.; Gutsch, S.; Hiller, D.; Zacharias, M.

    2014-12-15

    The absolute photoluminescence (PL) quantum yield (QY) of multilayers of Silicon nanocrystals (SiNCs) separated by SiO{sub 2} barriers were thoroughly studied as function of the barrier thickness, excitation wavelength, and temperature. By mastering the plasma-enhanced chemical vapor deposition growth, we produce a series of samples with the same size-distribution of SiNCs but variable interlayer barrier distance. These samples enable us to clearly demonstrate that the increase of barrier thickness from ∼1 to larger than 2 nm induces doubling of the PL QY value, which corresponds to the change of number of close neighbors in the hcp structure. The temperature dependence of PL QY suggests that the PL QY changes are due to a thermally activated transport of excitation into non-radiative centers in dark NCs or in the matrix. We estimate that dark NCs represent about 68% of the ensemble of NCs. The PL QY excitation spectra show no significant changes upon changing the barrier thickness and no clear carrier multiplication effects. The dominant effect is the gradual decrease of the PL QY with increasing excitation photon energy.

  5. Ultrasmall Organic Nanoparticles with Aggregation-Induced Emission and Enhanced Quantum Yield for Fluorescence Cell Imaging.

    PubMed

    Xu, Suying; Bai, Xilin; Ma, Jingwen; Xu, Minmin; Hu, Gaofei; James, Tony D; Wang, Leyu

    2016-08-01

    The use of fluorescence probes for biomedical imaging has attracted significant attention over recent years owing to their high resolution at cellular level. The probes are available in many formats including small particle size based imaging agents which are considered to be promising candidates, due to their excellent stabilities. Yet, concerns over the potential cytotoxicity effects of inorganic luminescent particles have led to questions about their suitability for imaging applications. Exploration of alternatives inspired us to use organic fluorophores with aggregation-induced emission (AIE), prepared by functionalizing the amine group on tetraphenylethene with 3,5-bis(trifluoromethyl)phenyl isocyanate. The as-synthesized novel AIE fluorophore (TPE-F) display enhanced quantum yield and longer lifetime as compared with its counterparts (4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetraaniline, TPE-AM). Furthermore, the TPE-F was encapsulated into small-size organic nanoparticles (NPs; dynamic light scattering size, ∼10 nm) with polysuccinimide (PSI). The biocompatibility, excellent stability, bright fluorescence, and selective cell targeting of these NPs enable the as-prepared TPE-F NPs to be suitable for specific fluorescence cell imaging. PMID:27349933

  6. Quantum energy inequalities and local covariance II: categorical formulation

    NASA Astrophysics Data System (ADS)

    Fewster, Christopher J.

    2007-11-01

    We formulate quantum energy inequalities (QEIs) in the framework of locally covariant quantum field theory developed by Brunetti, Fredenhagen and Verch, which is based on notions taken from category theory. This leads to a new viewpoint on the QEIs, and also to the identification of a new structural property of locally covariant quantum field theory, which we call local physical equivalence. Covariant formulations of the numerical range and spectrum of locally covariant fields are given and investigated, and a new algebra of fields is identified, in which fields are treated independently of their realisation on particular spacetimes and manifestly covariant versions of the functional calculus may be formulated.

  7. Modern Quantum Field Theory II - Proceeeings of the International Colloquium

    NASA Astrophysics Data System (ADS)

    Das, S. R.; Mandal, G.; Mukhi, S.; Wadia, S. R.

    1995-08-01

    The Table of Contents for the book is as follows: * Foreword * 1. Black Holes and Quantum Gravity * Quantum Black Holes and the Problem of Time * Black Hole Entropy and the Semiclassical Approximation * Entropy and Information Loss in Two Dimensions * Strings on a Cone and Black Hole Entropy (Abstract) * Boundary Dynamics, Black Holes and Spacetime Fluctuations in Dilation Gravity (Abstract) * Pair Creation of Black Holes (Abstract) * A Brief View of 2-Dim. String Theory and Black Holes (Abstract) * 2. String Theory * Non-Abelian Duality in WZW Models * Operators and Correlation Functions in c ≤ 1 String Theory * New Symmetries in String Theory * A Look at the Discretized Superstring Using Random Matrices * The Nested BRST Structure of Wn-Symmetries * Landau-Ginzburg Model for a Critical Topological String (Abstract) * On the Geometry of Wn Gravity (Abstract) * O(d, d) Tranformations, Marginal Deformations and the Coset Construction in WZNW Models (Abstract) * Nonperturbative Effects and Multicritical Behaviour of c = 1 Matrix Model (Abstract) * Singular Limits and String Solutions (Abstract) * BV Algebra on the Moduli Spaces of Riemann Surfaces and String Field Theory (Abstract) * 3. Condensed Matter and Statistical Mechanics * Stochastic Dynamics in a Deposition-Evaporation Model on a Line * Models with Inverse-Square Interactions: Conjectured Dynamical Correlation Functions of the Calogero-Sutherland Model at Rational Couplings * Turbulence and Generic Scale Invariance * Singular Perturbation Approach to Phase Ordering Dynamics * Kinetics of Diffusion-Controlled and Ballistically-Controlled Reactions * Field Theory of a Frustrated Heisenberg Spin Chain * FQHE Physics in Relativistic Field Theories * Importance of Initial Conditions in Determining the Dynamical Class of Cellular Automata (Abstract) * Do Hard-Core Bosons Exhibit Quantum Hall Effect? (Abstract) * Hysteresis in Ferromagnets * 4. Fundamental Aspects of Quantum Mechanics and Quantum Field Theory

  8. Biosolar cells: global artificial photosynthesis needs responsive matrices with quantum coherent kinetic control for high yield.

    PubMed

    Purchase, R L; de Groot, H J M

    2015-06-01

    This contribution discusses why we should consider developing artificial photosynthesis with the tandem approach followed by the Dutch BioSolar Cells consortium, a current operational paradigm for a global artificial photosynthesis project. We weigh the advantages and disadvantages of a tandem converter against other approaches, including biomass. Owing to the low density of solar energy per unit area, artificial photosynthetic systems must operate at high efficiency to minimize the land (or sea) area required. In particular, tandem converters are a much better option than biomass for densely populated countries and use two photons per electron extracted from water as the raw material into chemical conversion to hydrogen, or carbon-based fuel when CO2 is also used. For the average total light sum of 40 mol m(-2) d(-1) for The Netherlands, the upper limits are many tons of hydrogen or carbon-based fuel per hectare per year. A principal challenge is to forge materials for quantitative conversion of photons to chemical products within the physical limitation of an internal potential of ca 2.9 V. When going from electric charge in the tandem to hydrogen and back to electricity, only the energy equivalent to 1.23 V can be stored in the fuel and regained. A critical step is then to learn from nature how to use the remaining difference of ca 1.7 V effectively by triple use of one overpotential for preventing recombination, kinetic stabilization of catalytic intermediates and finally generating targeted heat for the release of oxygen. Probably the only way to achieve this is by using bioinspired responsive matrices that have quantum-classical pathways for a coherent conversion of photons to fuels, similar to what has been achieved by natural selection in evolution. In appendix A for the expert, we derive a propagator that describes how catalytic reactions can proceed coherently by a convergence of time scales of quantum electron dynamics and classical nuclear dynamics. We

  9. Adaptation to high CO2 concentration in an optimal environment: radiation capture, canopy quantum yield and carbon use efficiency

    NASA Technical Reports Server (NTRS)

    Monje, O.; Bugbee, B.

    1998-01-01

    The effect of elevated [CO2] on wheat (Triticum aestivum L. Veery 10) productivity was examined by analysing radiation capture, canopy quantum yield, canopy carbon use efficiency, harvest index and daily C gain. Canopies were grown at either 330 or 1200 micromoles mol-1 [CO2] in controlled environments, where root and shoot C fluxes were monitored continuously from emergence to harvest. A rapidly circulating hydroponic solution supplied nutrients, water and root zone oxygen. At harvest, dry mass predicted from gas exchange data was 102.8 +/- 4.7% of the observed dry mass in six trials. Neither radiation capture efficiency nor carbon use efficiency were affected by elevated [CO2], but yield increased by 13% due to a sustained increase in canopy quantum yield. CO2 enrichment increased root mass, tiller number and seed mass. Harvest index and chlorophyll concentration were unchanged, but CO2 enrichment increased average life cycle net photosynthesis (13%, P < 0.05) and root respiration (24%, P < 0.05). These data indicate that plant communities adapt to CO2 enrichment through changes in C allocation. Elevated [CO2] increases sink strength in optimal environments, resulting in sustained increases in photosynthetic capacity, canopy quantum yield and daily C gain throughout the life cycle.

  10. On the use of the thermal lens effect for measuring absolute luminescence quantum yields of transition metal complexes

    NASA Astrophysics Data System (ADS)

    Degen, Joachim; Reinecke, Klaus; Schmidtke, Hans-Herbert

    1992-05-01

    The thermal lens effect or thermal blooming of a laser beam passing through an absorbing medium is used to determine the fraction of absorbed laser power which is converted into heat. By this photocaloric method absolute luminescence quantum yields Φ can be evaluated covering the full range of possible Φ values. A check with organic standards for which quantum yields of 1, 0.52 and 0 are reported, supplies values of 0.99, 0.52 and 0.04, respectively. The sample of compounds [Ru(bipy) 3]X 2, X  Cl, ClO 4, and bipy  bipyridine, were studied using different concentrations in water and methanol solution at room temperature. The results strongly depend on the counter ion: for the Cl -- and (ClO 4) --salts quantum yields of Φ = 0.31 and 0.79, respectively, are obtained, which may be explained by different polarization conditions. The yields are, on the other hand, independent from the solvent and from the concentration, which was considered ranging from 10 -4 to 2.5 × 10 -5 M. Thermal blooming was also observed from [Ru(bipy) 3]Cl 2 contained in KBr pellets, measuring at various temperatures.

  11. Red Drop in the Quantum Yield of Fluorescence of Sonicated Algae

    PubMed Central

    Das, M.; Rabinowitch, E.; Szalay, L.

    1968-01-01

    The change of the quantum yield of fluorescence, Φ, with the frequency of exciting light, was investigated in Chlorella, Anacystis, and Porphyridium suspensions, and in sonicates from these cells prepared under aerobic and anaerobic conditions. In case of Chlorella, sonicates were made in acid and in alkaline media (pH 4.65 and 7.80). In the alkaline medium, a drop of Φ towards the longer waves was found to begin at 1.466 × 104 cm-1 (682 nm) in sonicates, and in suspension. In the acid medium, the drop began at 1.471 × 104 cm-1 (680 nm), 1.418 × 104 cm-1 (705 nm), and 1.389 × 104 cm-1 (720 nm) in suspension, anaerobic sonicate, and aerobic sonicate, respectively. The results indicate that the cause of the change in the red drop is preferential destruction of a long-wave component of chlorophyll a (such as Chl a 693). The amount of this component remaining after sonication is larger in alkaline than in acid sonicates. With Anacystis and Porphyridium, only alkaline suspensions (pH 7.80) could be used for sonication, because in acid medium, the phycobilin-chlorophyll complex is rapidly broken and phycobilin extracted from the cell. In Anacystis, the red drop begins at 1.562 × 104 cm-1 (640 nm) and 1.538 × 104 cm-1 (650 nm) in suspension and sonicate, respectively; in Porphyridium, it starts at 1.550 × 104 cm-1 (645 nm) in both cases. These results suggest that sonication in alkaline medium (pH 7.80) destroys some Chl a 693 in Anacystis, but not in Porphyridium. PMID:5679392

  12. Measurement of quantum yield of up-conversion Luminescence in Er(3+)-doped nano-glass-ceramics.

    PubMed

    Rodríguez, V D; Tikhomirov, V K; Méndez-Ramos, J; del-Castillo, J; Görller-Walrand, C

    2009-03-01

    A measurement of quantum yield of up-conversion luminescence has been done for the Er(3+)-doped transparent oxyfluoride glass-ceramics 32(SiO,)9(AlO1.5)31.5(CdF2)18.5(PbF2)5.5(ZnF2): 3.5(ErF3) mol%, where most of Er3+ dopants partition in 8 nm diameter nano-crystals Er10Pb25F65. The yield was found by newly proposed method using the pump power dependence of the resonant luminescence. The result of the measurement points out that a theoretical maximum of 50% may be reached for the up-conversion luminescence yield in this material. This high yield is shown to be due to low phonon energy and short inter-dopant distances in the nano-crystals. PMID:19435083

  13. Short-Term Flooding Effects on Gas Exchange and Quantum Yield of Rabbiteye Blueberry (Vaccinium ashei Reade) 1

    PubMed Central

    Davies, Frederick S.; Flore, James A.

    1986-01-01

    Roots of 1.5-year-old `Woodard' rabbiteye blueberry plants (Vaccinium ashei Reade) were flooded in containers or maintained at container capacity over a 5-day period. Carbon assimilation, and stomatal and residual conductances were monitored on one fully expanded shoot/plant using an open flow gas analysis system. Quantum yield was calculated from light response curves. Carbon assimilation and quantum yield of flooded plants decreased to 64 and 41% of control values, respectively, after 1 day of flooding and continued decreasing to 38 and 27% after 4 days. Stomatal and residual conductances to CO2 also decreased after 1 day of flooding compared with those of unflooded plants with residual conductance severely limiting carbon assimilation after 4 days of flooding. Stomatal opening occurred in 75 to 90 minutes and rate of opening was unaffected by flooding. PMID:16664791

  14. Laser flash photolysis of ozone - O/1D/ quantum yields in the fall-off region 297-325 nm

    NASA Technical Reports Server (NTRS)

    Brock, J. C.; Watson, R. T.

    1980-01-01

    The wavelength dependence of the quantum yield for O(1D) production from ozone photolysis has been determined between 297.5 nm and 325 nm in order to resolve serious discrepancies among previous studies. The results of this investigation are compared to earlier work by calculating atmospheric production rate constants for O(1D). It is found that for the purpose of calculating this rate constant, there is now good agreement among three studies at 298 K. Furthermore, it appears that previous data on the temperature dependence of the O(1D) quantum yield fall-off is adequate for determining the vertical profile of the O(1D) production rate constant. Several experimental difficulties associated with using NO2(asterisk) chemiluminescence to monitor O(1D) have been identified.

  15. Rigidifying Fluorescent Linkers by Metal-Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

    SciTech Connect

    Wei, ZW; Gu, ZY; Arvapally, RK; Chen, YP; McDougald, RN; Ivy, JF; Yakovenko, AA; Feng, DW; Omary, MA; Zhou, HC

    2014-06-11

    We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 +/- 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

  16. Rigidifying Fluorescent Linkers by Metal–Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

    SciTech Connect

    Wei, Zhangwen; Gu, Zhi-Yuan; Arvapally, Ravi K.; Chen, Ying-Pin; Ivy, Joshua F.; Yakovenko, Andrey A.; Feng, Dawei; Omary, Mohammad A.; Zhou, Hong-Cai

    2014-06-11

    We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal–organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm⁻¹ blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

  17. Calculated quantum yield of photosynthesis of phytoplankton in the Marine Light-Mixed Layers (59 deg N, 21 deg W)

    NASA Technical Reports Server (NTRS)

    Carder, K. L.; Lee, Z. P.; Marra, John; Steward, R. G.; Perry, M. J.

    1995-01-01

    The quantum yield of photosynthesis (mol C/mol photons) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of phi calculated using the nonlinear regreesion method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.

  18. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry

    SciTech Connect

    Meusinger, Carl; Johnson, Matthew S.; Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joel

    2014-06-28

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow. Reported quantum yields for the main reaction spans orders of magnitude – apparently a result of whether nitrate is located at the air-ice interface or in the ice matrix – constituting the largest uncertainty in models of snowpack NO{sub x} emissions. Here, a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption and recombination by flushing the snow during irradiation with UV light. A selection of UV filters allowed examination of the effects of the 200 and 305 nm absorption bands of nitrate. Nitrate concentration and photon flux were measured in the snow. The quantum yield for loss of nitrate was observed to decrease from 0.44 to 0.003 within what corresponds to days of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate, and one of buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NO{sub x} emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ∼1%, much lower than reported for aqueous chemistry. A companion paper presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study.

  19. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry

    NASA Astrophysics Data System (ADS)

    Meusinger, Carl; Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joel; Johnson, Matthew S.

    2014-06-01

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow. Reported quantum yields for the main reaction spans orders of magnitude - apparently a result of whether nitrate is located at the air-ice interface or in the ice matrix - constituting the largest uncertainty in models of snowpack NOx emissions. Here, a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption and recombination by flushing the snow during irradiation with UV light. A selection of UV filters allowed examination of the effects of the 200 and 305 nm absorption bands of nitrate. Nitrate concentration and photon flux were measured in the snow. The quantum yield for loss of nitrate was observed to decrease from 0.44 to 0.003 within what corresponds to days of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate, and one of buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NOx emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ˜1%, much lower than reported for aqueous chemistry. A companion paper presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study.

  20. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry.

    PubMed

    Meusinger, Carl; Berhanu, Tesfaye A; Erbland, Joseph; Savarino, Joel; Johnson, Matthew S

    2014-06-28

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow. Reported quantum yields for the main reaction spans orders of magnitude - apparently a result of whether nitrate is located at the air-ice interface or in the ice matrix - constituting the largest uncertainty in models of snowpack NOx emissions. Here, a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption and recombination by flushing the snow during irradiation with UV light. A selection of UV filters allowed examination of the effects of the 200 and 305 nm absorption bands of nitrate. Nitrate concentration and photon flux were measured in the snow. The quantum yield for loss of nitrate was observed to decrease from 0.44 to 0.003 within what corresponds to days of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate, and one of buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NOx emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ∼1%, much lower than reported for aqueous chemistry. A companion paper presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study. PMID:24985636

  1. Proton-transfer and hydrogen-bond interactions determine fluorescence quantum yield and photochemical efficiency of bacteriophytochrome

    PubMed Central

    Toh, K. C.; Stojković, Emina A.; van Stokkum, Ivo H. M.; Moffat, Keith; Kennis, John T. M.

    2010-01-01

    Phytochromes are red-light photoreceptor proteins that regulate a variety of responses and cellular processes in plants, bacteria, and fungi. The phytochrome light activation mechanism involves isomerization around the C15═C16 double bond of an open-chain tetrapyrrole chromophore, resulting in a flip of its D-ring. In an important new development, bacteriophytochrome (Bph) has been engineered for use as a fluorescent marker in mammalian tissues. Here we report that an unusual Bph, RpBphP3 from Rhodopseudomonas palustris, denoted P3, is fluorescent. This Bph modulates synthesis of light-harvesting complex in combination with a second Bph exhibiting classical photochemistry, RpBphP2, denoted P2. We identify the factors that determine the fluorescence and isomerization quantum yields through the application of ultrafast spectroscopy to wild-type and mutants of P2 and P3. The excited-state lifetime of the biliverdin chromophore in P3 was significantly longer at 330–500 ps than in P2 and other classical phytochromes and accompanied by a significantly reduced isomerization quantum yield. H/D exchange reduces the rate of decay from the excited state of biliverdin by a factor of 1.4 and increases the isomerization quantum yield. Comparison of the properties of the P2 and P3 variants shows that the quantum yields of fluorescence and isomerization are determined by excited-state deprotonation of biliverdin at the pyrrole rings, in competition with hydrogen-bond rupture between the D-ring and the apoprotein. This work provides a basis for structure-based conversion of Bph into an efficient near-IR fluorescent marker. PMID:20435909

  2. Isotropic loop quantum cosmology with matter. II. The Lorentzian constraint

    NASA Astrophysics Data System (ADS)

    Hinterleitner, Franz; Major, Seth

    2003-12-01

    The Lorentzian Hamiltonian constraint is solved for isotropic loop quantum cosmology coupled to a massless scalar field. As in the Euclidean case, the discreteness of quantum geometry removes the classical singularity from the quantum Friedmann models. In spite of the absence of the classical singularity, a modified DeWitt initial condition is incompatible with a late-time smooth behavior. Further, the smooth behavior is recovered only for positive or negatives times but not both. An important feature, which is shared with the Euclidean case, is a minimal initial energy of the order of the Planck energy required for the system to evolve dynamically. By forming wave packets of the matter field, an explicit evolution in terms of an internal time is obtained.

  3. Supercurrent in the quantum Hall regime, part II

    NASA Astrophysics Data System (ADS)

    Amet, Francois; Ke, Chung Ting; Borzenets, Ivan; Wang, Jiyingmei; Watanabe, Kenji; Taniguchi, Takashi; Deacon, Russel; Yamamoto, Michihisa; Bomze, Yuriy; Tarucha, Seigo; Finkelstein, Gleb

    A novel promising route for creating topological states and excitations is to combine superconductivity and the quantum Hall effect. Despite this potential, signatures of superconductivity in the quantum Hall regime remain scarce, and a superconducting current through a Landau-quantized two-dimensional electron gas has so far eluded experimental observation. High-mobility graphene/BN heterostructures exhibit the quantum Hall effect at relatively low field and are therefore particularly suitable to study the fate of the Josephson effect in that regime. Here, we report the observation of a superconducting current through graphene at fields as high as 2 Tesla. In that regime, the normal-state resistance is quantized but pockets of superconductivity still persist at small current bias. We will describe their bias and temperature dependence. Magnetic field interference patterns in the supercurrent inform on possible mechanisms mediating this supercurrent.

  4. Type II InAs/GaAsSb quantum dots: Highly tunable exciton geometry and topology

    SciTech Connect

    Llorens, J. M.; Wewior, L.; Cardozo de Oliveira, E. R.; Alén, B.; Ulloa, J. M.; Utrilla, A. D.; Guzmán, A.; Hierro, A.

    2015-11-02

    External control over the electron and hole wavefunctions geometry and topology is investigated in a p-i-n diode embedding a dot-in-a-well InAs/GaAsSb quantum structure with type II band alignment. We find highly tunable exciton dipole moments and largely decoupled exciton recombination and ionization dynamics. We also predicted a bias regime where the hole wavefunction topology changes continuously from quantum dot-like to quantum ring-like as a function of the external bias. All these properties have great potential in advanced electro-optical applications and in the investigation of fundamental spin-orbit phenomena.

  5. Evaluation of a commercial integrating sphere setup for the determination of absolute photoluminescence quantum yields of dilute dye solutions.

    PubMed

    Würth, Christian; Lochmann, Cornelia; Spieles, Monika; Pauli, Jutta; Hoffmann, Katrin; Schüttrigkeit, Tanja; Franzl, Thomas; Resch-Genger, Ute

    2010-07-01

    The commercial availability of stand-alone setups for the determination of absolute photoluminescence quantum yields (Phi(f)) in conjunction with the increasing use of integrating sphere accessories for spectrofluorometers is expected to have a considerable influence not only on the characterization of chromophore systems for use in optical and opto-electronic devices, but also on the determination of this key parameter for (bio)analytically relevant dyes and functional luminophores. Despite the huge potential of systems measuring absolute Phi(f) values and the renewed interest in dependable data, evaluated protocols for even the most elementary case, the determination of the fluorescence quantum yield of transparent dilute solutions of small organic dyes with integrating sphere methods, are still missing. This encouraged us to evaluate the performance and sources of uncertainty of a simple commercial integrating sphere setup with dilute solutions of two of the best characterized fluorescence quantum yield standards, quinine sulfate dihydrate and rhodamine 101, strongly differing in spectral overlap between absorption and emission. Special attention is dedicated to illustrate common pitfalls of this approach, thereby deriving simple procedures to minimize measurement uncertainties and improve the comparability of data for the broad community of users of fluorescence techniques. PMID:20615286

  6. Quantum yields and energy partitioning in the ultraviolet photodissociation of 1,2 dibromo-tetrafluoroethane (Halon-2402)

    NASA Astrophysics Data System (ADS)

    Zou, Peng; McGivern, W. Sean; Sorkhabi, Osman; Suits, Arthur G.; North, Simon W.

    2000-11-01

    The photodissociation of 1,2 dibromo-tetrafluoroethane (Halon-2402) has been investigated at 193 nm using photofragment translational spectroscopy with vacuum ultraviolet ionization and at 193, 233, and 266 nm using state-selected translational spectroscopy with resonance-enhanced multiphoton ionization. The product branching ratios, angular distributions, and translational energy distributions were measured at these wavelengths, providing insight into the ultraviolet photodissociation dynamics of CF2BrCF2Br. The total bromine atom quantum yields were found to be 1.9±0.1 at both 193 and 233 nm and 1.4±0.1 at 266 nm. The first C-Br bond dissociation energy was determined to be 69.3 kcal/mol from ab initio calculations. The second C-Br bond dissociation energy was determined to be 16±2 kcal/mol by modeling of the bromine quantum yield. In addition, variational Rice-Ramsperger-Kassel-Marcus theory was used to calculate the secondary dissociation rates for a range of dissociation energies above threshold. These results suggest that CF2CF2Br photofragments with sufficient internal energies will undergo secondary dissociation prior to collisional stabilization under atmospheric conditions. Based on the measured translational energy distributions and product branching ratios, a model is proposed to describe the wavelength-dependent bromine quantum yield and the implications of these results to atmospheric chemistry are discussed.

  7. Quantum dynamics of hydrogen atoms on graphene. II. Sticking

    SciTech Connect

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H.; Burghardt, Irene

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated.

  8. Wavelength and temperature-dependent apparent quantum yields for photochemical formation of hydrogen peroxide in seawater.

    PubMed

    Kieber, David J; Miller, Gary W; Neale, Patrick J; Mopper, Kenneth

    2014-04-01

    Wavelength and temperature-dependent apparent quantum yields (AQYs) were determined for the photochemical production of hydrogen peroxide using seawater obtained from coastal and oligotrophic stations in Antarctica, the Pacific Ocean at Station ALOHA, the Gulf of Mexico, and at several sites along the East Coast of the United States. For all samples, AQYs decreased exponentially with increasing wavelength at 25 °C, ranging from 4.6 × 10(-4) to 10.4 × 10(-4) at 290 nm to 0.17 × 10(-4) to 0.97 × 10(-4) at 400 nm. AQYs for different seawater samples were remarkably similar irrespective of expected differences in the composition and concentrations of metals and dissolved organic matter (DOM) and in prior light exposure histories; wavelength-dependent AQYs for individual seawater samples differed by less than a factor of two relative to respective mean AQYs. Temperature-dependent AQYs increased between 0 and 35 °C on average by a factor of 1.8 per 10 °C, consistent with a thermal reaction (e.g., superoxide dismutation) controlling H2O2 photochemical production rates in seawater. Taken together, these results suggest that the observed poleward decrease in H₂O₂ photochemical production rates is mainly due to corresponding poleward decreases in irradiance and temperature and not spatial variations in the composition and concentrations of DOM or metals. Hydrogen peroxide photoproduction AQYs and production rates were not constant and not independent of the photon exposure as has been implicitly assumed in many published studies. Therefore, care should be taken when comparing and interpreting published H₂O₂ AQY or photochemical production rate results. Modeled depth-integrated H₂O₂ photochemical production rates were in excellent agreement with measured rates obtained from in situ free-floating drifter experiments conducted during a Gulf of Maine cruise, with differences (ca. 10%) well within measurement and modeling uncertainties. Results from this study

  9. Extreme ultraviolet photoresists: Film quantum yields and LER of thin film resists

    NASA Astrophysics Data System (ADS)

    Higgins, Craig

    Extreme ultraviolet (EUV) is the leading candidate for a commercially viable solution for next generation lithography. The development of EUV chemically amplified photoresists and processes are critical to the future lithographic requirements of the microelectronics industry. To meet the necessary requirements for both integrated circuit (IC) specifications and cost, the resolution, line-edge roughness (LER) and sensitivity all need to be reduced. Unfortunately, a fundamental trade-off has been observed between these three crucial elements. We have predicted that the best way to obtain the required resolution, line-edge roughness and sensitivity (RLS) is to create more acid molecules per photon absorbed. This quantity is referred to as the film quantum yield (FQY). Utilizing increased photoacid generator (PAG) concentrations, the impact of FQY on the overall resist lithographic performance is characterized. However, despite significant improvements in RLS performance, LER continues to fall significantly short of industry requirements. Lithographic exposures have shown that LER increases significantly as film thickness decreases (< 50 nm) for 193 nm and EUV wavelengths. LER degradation is a significant problem for future technology nodes where film thicknesses of 50 nm or less will be necessary to help mitigate pattern collapse. Understanding the mechanistic cause of the thickness dependent LER degradation is therefore very critical for future needs of the lithographic community. Investigations highlight key concerns related to the image degradation of ultra-thin film photoresists (< 50 nm) with the aim of better understanding the correlation between resist LER, acid diffusion and glass transition temperature. Meeting the required LER will become increasingly difficult for future technology nodes due to thin film effects. Therefore, alternative processes and LER mitigation techniques are likely required for the implementation of EUV. Studies have demonstrated that

  10. Enhanced upconversion quantum yield near spherical gold nanoparticles - a comprehensive simulation based analysis.

    PubMed

    Fischer, Stefan; Kumar, Deepu; Hallermann, Florian; von Plessen, Gero; Goldschmidt, Jan Christoph

    2016-03-21

    Photon upconversion is promising for many applications. However, the potential of lanthanide doped upconverter materials is typically limited by low absorption coefficients and low upconversion quantum yields (UCQY) under practical irradiance of the excitation. Modifying the photonic environment can strongly enhance the spontaneous emission and therefore also the upconversion luminescence. Additionally, the non-linear nature of the upconversion processes can be exploited by an increased local optical field introduced by photonic or plasmonic structures. In combination, both processes may lead to a strong enhancement of the UCQY at simultaneously lower incident irradiances. Here, we use a comprehensive 3D computation-based approach to investigate how absorption, upconversion luminescence, and UCQY of an upconverter are altered in the vicinity of spherical gold nanoparticles (GNPs). We use Mie theory and electrodynamic theory to compute the properties of GNPs. The parameters obtained in these calculations were used as input parameters in a rate equation model of the upconverter β-NaYF4: 20% Er3+. We consider different diameters of the GNP and determine the behavior of the system as a function of the incident irradiance. Whether the UCQY is increased or actually decreased depends heavily on the position of the upconverter in respect to the GNP. Whereas the upconversion luminescence enhancement reaches a maximum around a distance of 35 nm to the surface of the GNP, we observe strong quenching of the UCQY for distances <40 nm and a UCQY maximum around 125 to 150 nm, in the case of a 300 nm diameter GNP. Hence, the upconverter material needs to be placed at different positions, depending on whether absorption, upconversion luminescence, or UCQY should be maximized. At the optimum position, we determine a maximum UCQY enhancement of 117% for a 300 nm diameter GNP at a low incident irradiance of 0.01 W/cm2. As the irradiance increases, the

  11. Biosolar cells: global artificial photosynthesis needs responsive matrices with quantum coherent kinetic control for high yield

    PubMed Central

    Purchase, R. L.; de Groot, H. J. M.

    2015-01-01

    This contribution discusses why we should consider developing artificial photosynthesis with the tandem approach followed by the Dutch BioSolar Cells consortium, a current operational paradigm for a global artificial photosynthesis project. We weigh the advantages and disadvantages of a tandem converter against other approaches, including biomass. Owing to the low density of solar energy per unit area, artificial photosynthetic systems must operate at high efficiency to minimize the land (or sea) area required. In particular, tandem converters are a much better option than biomass for densely populated countries and use two photons per electron extracted from water as the raw material into chemical conversion to hydrogen, or carbon-based fuel when CO2 is also used. For the average total light sum of 40 mol m−2 d−1 for The Netherlands, the upper limits are many tons of hydrogen or carbon-based fuel per hectare per year. A principal challenge is to forge materials for quantitative conversion of photons to chemical products within the physical limitation of an internal potential of ca 2.9 V. When going from electric charge in the tandem to hydrogen and back to electricity, only the energy equivalent to 1.23 V can be stored in the fuel and regained. A critical step is then to learn from nature how to use the remaining difference of ca 1.7 V effectively by triple use of one overpotential for preventing recombination, kinetic stabilization of catalytic intermediates and finally generating targeted heat for the release of oxygen. Probably the only way to achieve this is by using bioinspired responsive matrices that have quantum–classical pathways for a coherent conversion of photons to fuels, similar to what has been achieved by natural selection in evolution. In appendix A for the expert, we derive a propagator that describes how catalytic reactions can proceed coherently by a convergence of time scales of quantum electron dynamics and classical nuclear dynamics

  12. Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor.

    PubMed

    Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

    2013-11-29

    In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using 'greener' chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50–75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 10(3) mA cm−2 and 17.7 mW cm−2 at 8 V; it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system. PMID:24192490

  13. Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor

    NASA Astrophysics Data System (ADS)

    Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

    2013-11-01

    In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using ‘greener’ chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50-75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 103 mA cm-2 and 17.7 mW cm-2 at 8 V it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system.

  14. Quantum diffusion with drift and the Einstein relation. II

    SciTech Connect

    De Roeck, Wojciech; Fröhlich, Jürg; Schnelli, Kevin

    2014-07-15

    This paper is a companion to Paper I [W. De Roeck, J. Fröhlich, and K. Schnelli, “Quantum diffusion with drift and the Einstein relation. I,” J. Math. Phys. 55, 075206 (2014)]. The purpose of this paper is to describe and prove a certain number of technical results used in Paper I, but not proven there. Both papers concern long-time properties (diffusion, drift) of the motion of a driven quantum particle coupled to an array of thermal reservoirs. The main technical results derived in the present paper are: (1) an asymptotic perturbation theory applicable for small driving force, and (2) the construction of time-dependent correlation functions of particle observables.

  15. Experimental Measurements of the Secondary Electron Yield in the Experimental Measurement of the Secondary Electron Yield in the PEP-II Particle Accelerator Beam Line

    SciTech Connect

    Pivi, M.T.F.; Collet, G.; King, F.; Kirby, R.E.; Markiewicz, T.; Raubenheimer, T.O.; Seeman, J.; Le Pimpec, F.; /PSI, Villigen

    2010-08-25

    Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders (LC) such as ILC and CLIC. To test a series of promising possible electron cloud mitigation techniques as surface coatings and grooves, in the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed several test vacuum chambers including (i) a special chamber to monitor the variation of the secondary electron yield of technical surface materials and coatings under the effect of ion, electron and photon conditioning in situ in the beam line; (ii) chambers with grooves in a straight magnetic-free section; and (iii) coated chambers in a dedicated newly installed 4-magnet chicane to study mitigations in a magnetic field region. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the LC damping ring, focusing on the first experimental area and on results of the reduction of the secondary electron yield due to in situ conditioning.

  16. AUTOMATED BIOCHEMICAL IDENTIFICATION OF BACTERIAL FISH PATHOGENS USING THE ABBOTT QUANTUM II

    EPA Science Inventory

    The Quantum II, originally designed by Abbott Diagnostics for automated rapid identification of members of Enterobacteriaceae, was adapted for the identification of bacterial fish pathogens. he instrument operates as a spectrophotometer at a wavelength of 492.600 nm. ample cartri...

  17. Quantum Bio-Informatics II From Quantum Information to Bio-Informatics

    NASA Astrophysics Data System (ADS)

    Accardi, L.; Freudenberg, Wolfgang; Ohya, Masanori

    2009-02-01

    The problem of quantum-like representation in economy cognitive science, and genetics / L. Accardi, A. Khrennikov and M. Ohya -- Chaotic behavior observed in linea dynamics / M. Asano, T. Yamamoto and Y. Togawa -- Complete m-level quantum teleportation based on Kossakowski-Ohya scheme / M. Asano, M. Ohya and Y. Tanaka -- Towards quantum cybernetics: optimal feedback control in quantum bio informatics / V. P. Belavkin -- Quantum entanglement and circulant states / D. Chruściński -- The compound Fock space and its application in brain models / K. -H. Fichtner and W. Freudenberg -- Characterisation of beam splitters / L. Fichtner and M. Gäbler -- Application of entropic chaos degree to a combined quantum baker's map / K. Inoue, M. Ohya and I. V. Volovich -- On quantum algorithm for multiple alignment of amino acid sequences / S. Iriyama and M. Ohya --Quantum-like models for decision making in psychology and cognitive science / A. Khrennikov -- On completely positive non-Markovian evolution of a d-level system / A. Kossakowski and R. Rebolledo -- Measures of entanglement - a Hilbert space approach / W. A. Majewski -- Some characterizations of PPT states and their relation / T. Matsuoka -- On the dynamics of entanglement and characterization ofentangling properties of quantum evolutions / M. Michalski -- Perspective from micro-macro duality - towards non-perturbative renormalization scheme / I. Ojima -- A simple symmetric algorithm using a likeness with Introns behavior in RNA sequences / M. Regoli -- Some aspects of quadratic generalized white noise functionals / Si Si and T. Hida -- Analysis of several social mobility data using measure of departure from symmetry / K. Tahata ... [et al.] -- Time in physics and life science / I. V. Volovich -- Note on entropies in quantum processes / N. Watanabe -- Basics of molecular simulation and its application to biomolecules / T. Ando and I. Yamato -- Theory of proton-induced superionic conduction in hydrogen-bonded systems

  18. Quantum phase transition from superparamagnetic to quantum superparamagnetic state in ultrasmall Cd(1-x)Cr(II)(x)Se quantum dots?

    PubMed

    Zheng, Weiwei; Kumar, Pushpendra; Washington, Aaron; Wang, Zhenxing; Dalal, Naresh S; Strouse, Geoffrey F; Singh, Kedar

    2012-02-01

    Despite a long history of success in formation of transition-metal-doped quantum dots (QDs), the origin of magnetism in diluted magnetic semiconductors (DMSs) is yet a controversial issue. Cr(II)-doped II-VI DMSs are half-metallic, resulting in high-temperature ferromagnetism. The magnetic properties reflect a strong p-d exchange interaction between the spin-up Cr(II) t(2g) level and the Se 4p. In this study, ultrasmall (~3.1 nm) Cr(II)-doped CdSe DMSQDs are shown to exhibit room-temperature ferromagnetism, as expected from theoretical arguments. Surprisingly, a low-temperature phase transition is observed at 20 K that is believed to reflect the onset of long-range ordering of the single-domain DMSQD. PMID:22074220

  19. Quantum Efficiency Characterization and Optimization of a Tungsten Transition-Edge Sensor for ALPS II

    NASA Astrophysics Data System (ADS)

    Bastidon, Noëmie; Horns, Dieter; Lindner, Axel

    2016-07-01

    The ALPS II experiment, Any Light Particle Search II at DESY in Hamburg, will look for sub-eV mass new fundamental bosons (e.g., axion-like particles, hidden photons, and other weakly interacting sub-eV particles) in the next years by means of a light-shining-through-wall setup. The ALPS II photosensor is a tungsten transition-edge sensor (W-TES) optimized for 1064 nm photons. This TES, operated at 80 mK, has already allowed single infrared photon detections as well as non-dispersive spectroscopy with very low background rates. The demonstrated quantum efficiency for such TES is up to 95 % (1064 nm) as has been already demonstrated by the US National Institute of Standards and Technology. A back-to-back measurement of the ALPS TES quantum efficiency using a calibrated charge-coupled device camera has lead to a first estimation of 30 %. Improvement methods are discussed.

  20. In cellulo Evaluation of Phototransformation Quantum Yields in Fluorescent Proteins Used As Markers for Single-Molecule Localization Microscopy

    PubMed Central

    Avilov, Sergiy; Berardozzi, Romain; Gunewardene, Mudalige S.; Adam, Virgile; Hess, Samuel T.; Bourgeois, Dominique

    2014-01-01

    Single-molecule localization microscopy of biological samples requires a precise knowledge of the employed fluorescent labels. Photoactivation, photoblinking and photobleaching of phototransformable fluorescent proteins influence the data acquisition and data processing strategies to be used in (Fluorescence) Photoactivation Localization Microscopy ((F)-PALM), notably for reliable molecular counting. As these parameters might depend on the local environment, they should be measured in cellulo in biologically relevant experimental conditions. Here, we measured phototransformation quantum yields for Dendra2 fused to actin in fixed mammalian cells in typical (F)-PALM experiments. To this aim, we developed a data processing strategy based on the clustering optimization procedure proposed by Lee et al (PNAS 109, 17436–17441, 2012). Using simulations, we estimated the range of experimental parameters (molecular density, molecular orientation, background level, laser power, frametime) adequate for an accurate determination of the phototransformation yields. Under illumination at 561 nm in PBS buffer at pH 7.4, the photobleaching yield of Dendra2 fused to actin was measured to be (2.5±0.4)×10−5, whereas the blinking-off yield and thermally-activated blinking-on rate were measured to be (2.3±0.2)×10−5 and 11.7±0.5 s−1, respectively. These phototransformation yields differed from those measured in poly-vinyl alcohol (PVA) and were strongly affected by addition of the antifading agent 1,4-diazabicyclo[2.2.2]octane (DABCO). In the presence of DABCO, the photobleaching yield was reduced 2-fold, the blinking-off yield was decreased more than 3-fold, and the blinking-on rate was increased 2-fold. Therefore, DABCO largely improved Dendra2 photostability in fixed mammalian cells. These findings are consistent with redox-based bleaching and blinking mechanisms under (F)-PALM experimental conditions. Finally, the green-to-red photoconversion quantum yield of Dendra2 was

  1. Quantum Computation and Quantum Information

    NASA Astrophysics Data System (ADS)

    Nielsen, Michael A.; Chuang, Isaac L.

    2010-12-01

    Part I. Fundamental Concepts: 1. Introduction and overview; 2. Introduction to quantum mechanics; 3. Introduction to computer science; Part II. Quantum Computation: 4. Quantum circuits; 5. The quantum Fourier transform and its application; 6. Quantum search algorithms; 7. Quantum computers: physical realization; Part III. Quantum Information: 8. Quantum noise and quantum operations; 9. Distance measures for quantum information; 10. Quantum error-correction; 11. Entropy and information; 12. Quantum information theory; Appendices; References; Index.

  2. Photolysis quantum yield measurements in the near-UV; a critical analysis of 1-(2-nitrophenyl)ethyl photochemistry.

    PubMed

    Corrie, John E T; Kaplan, Jack H; Forbush, Biff; Ogden, David C; Trentham, David R

    2016-05-11

    The photolysis quantum yield, Qp, of 1-(2-nitrophenyl)ethyl phosphate (caged Pi) measured in the near-UV (342 nm peak with 60 nm half-bandwidth) is 0.53 and is based on results reported in 1978 (Biochemistry, 17, 1929-1935). This article amplifies methodology for determining that Qp in view of different recent estimates. Some general principles together with other examples relating to measurement of Qp values are discussed together with their relevance to biological research. PMID:27050155

  3. Dynamics of uniform quantum gases, II: Magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Bosse, J.; Pathak, K. N.; Singh, G. S.

    2010-03-01

    A general expression for temperature-dependent magnetic susceptibility of quantum gases composed of particles possessing both charge and spin degrees of freedom has been obtained within the framework of the generalized random phase approximation. The conditions for the existence of dia-, para-, and ferro-magnetism have been analyzed in terms of a parameter involving single-particle charge and spin. The limit T→0 retrieves the expressions for the Landau and the Pauli susceptibilities for an electron gas. It is found for a Bose gas that on decreasing the temperature, it passes either through a diamagnetic incomplete Meissner-effect regime or through a paramagnetic-ferromagnetic large magnetization fluctuation regime before going to the Meissner phase at T=T.

  4. Exact path integral for 3D quantum gravity. II.

    NASA Astrophysics Data System (ADS)

    Honda, Masazumi; Iizuka, Norihiro; Tanaka, Akinori; Terashima, Seiji

    2016-03-01

    Continuing the work [Phys. Rev. Lett. 115, 161304 (2015)], we discuss various aspects of three-dimensional quantum gravity partition function in anti-de Sitter spacetime in the semiclassical limit. The partition function is holomorphic and is the one which we obtained by using the localization technique of Chern-Simons theory in Phys. Rev. Lett. 115, 161304 (2015). We obtain a good expression for it in the summation form over Virasoro characters for the vacuum and primaries. A key ingredient for that is an interpretation of boundary-localized fermion. We also check that the coefficients in the summation form over Virasoro characters of the partition function are positive integers and satisfy the Cardy formula. These give a physical interpretation that these coefficients represent the number of primary fields in the dual conformal field theory in the large k limit.

  5. Ground state of the holes localized in II-VI quantum dots with Gaussian potential profiles

    NASA Astrophysics Data System (ADS)

    Semina, M. A.; Golovatenko, A. A.; Rodina, A. V.

    2016-01-01

    We report on a theoretical study of the hole states in II-IV quantum dots of spherical and ellipsoidal shapes, described by smooth potential confinement profiles that can be modeled by Gaussian functions in all three dimensions. The universal dependencies of the hole energy, g factor, and localization length on the quantum dot barrier height, as well as the ratio of effective masses of the light and heavy holes are presented for the spherical quantum dots. The splitting of the fourfold degenerate ground state into two doublets is derived for anisotropic (oblate or prolate) quantum dots. Variational calculations are combined with numerical ones in the framework of the Luttinger Hamiltonian. Constructed trial functions are optimized by comparison with the numerical results. The effective hole g factor is found to be independent of the quantum dot size and barrier height and is approximated by a simple universal expression depending only on the effective mass parameters. The results can be used for interpreting and analyzing experimental spectra measured in various structures with quantum dots of different semiconductor materials.

  6. ``Simplest Molecule'' Clarifies Modern Physics II. Relativistic Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Harter, William; Reimer, Tyle

    2015-05-01

    A ``simplest molecule'' consisting of CW- laser beam pairs helps to clarify relativity from poster board - I. In spite of a seemingly massless evanescence, an optical pair also clarifies classical and quantum mechanics of relativistic matter and antimatter. Logical extension of (x,ct) and (ω,ck) geometry gives relativistic action functions of Hamiltonian, Lagrangian, and Poincare that may be constructed in a few ruler-and-compass steps to relate relativistic parameters for group or phase velocity, momentum, energy, rapidity, stellar aberration, Doppler shifts, and DeBroglie wavelength. This exposes hyperbolic and circular trigonometry as two sides of one coin connected by Legendre contact transforms. One is Hamiltonian-like with a longitudinal rapidity parameter ρ (log of Doppler shift). The other is Lagrange-like with a transverse angle parameter σ (stellar aberration). Optical geometry gives recoil in absorption, emission, and resonant Raman-Compton acceleration and distinguishes Einstein rest mass, Galilean momentum mass, and Newtonian effective mass. (Molecular photons appear less bullet-like and more rocket-like.) In conclusion, modern space-time physics appears as a simple result of the more self-evident Evenson's axiom: ``All colors go c.''

  7. "simplest Molecule" Clarifies Modern Physics II. Relativistic Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Reimer, T. C.; Harter, W. G.

    2014-06-01

    A "simplest molecule" consisting of CW-laser beam pairs helps to clarify relativity in Talk I. In spite of a seemingly massless evanescence, an optical pair also clarifies classical and quantum mechanics of relativistic matter and anti-matter. *Logical extension of (x,ct) and (ω,ck) geometry gives relativistic action functions of Hamiltonian, Lagrangian, and Poincare that may be constructed in a few ruler-and-compass steps to relate relativistic parameters for group or phase velocity, momentum, energy, rapidity, stellar aberration, Doppler shifts, and DeBroglie wavelength. This exposes hyperbolic and circular trigonometry as two sides of one coin connected by Legendre contact transforms. One is Hamiltonian-like with a longitudinal rapidity parameter ρ (log of Doppler shift). The other is Lagrange-like with a transverse angle parameter σ (stellar aberration). Optical geometry gives recoil in absorption, emission, and resonant Raman-Compton acceleration and distinguishes Einstein rest mass, Galilean momentum mass, and Newtonian effective mass. (Molecular photons appear less bullet-like and more rocket-like.) In conclusion, modern space-time physics appears as a simple result of the more self-evident Evenson's axiom: "All colors go c."

  8. Study of concentration-dependent quantum yield of Rhodamine 6G by gold nanoparticles using thermal-lens technique

    NASA Astrophysics Data System (ADS)

    Kumar, B. Rajesh; Basheer, N. Shemeena; Kurian, Achamma; George, Sajan D.

    2014-06-01

    Tailoring optical properties of the dye molecules using metal nanoparticles is a burgeoning area of research. In this work, we report our results on the studies of how the absorption and emission behavior of Rhodamine 6G dye is tailored using gold nanoparticles. Furthermore, the influence of dye concentration on these properties for a given concentration of nanoparticles in the dye-nanoparticle mixture is investigated. In addition, the difference between the concentration-dependent fluorescence quantum yield of the dye molecules is measured in the absence and presence of nanoparticles using the dual-beam thermal-lens technique. Our absorption spectral studies show additional spectral features due to nanoparticle aggregation on interaction with cationic Rhodamine 6G dye. Dye concentration-dependent steady-state fluorescence studies in the presence of nanoparticles indicate a blue shift in peak fluorescence emission wavelength. The quantum yield value measured using thermal-lens technique exhibit a non-monotonic behavior with dye concentration with substantial quenching for lower dye concentrations. The results are interpreted in terms of dye-nanoparticle interaction and the formation of dye shell around the nanoparticle.

  9. Fluorescence quantum yields of a series of red and near-infrared dyes emitting at 600-1000 nm.

    PubMed

    Rurack, Knut; Spieles, Monika

    2011-02-15

    The determination of the fluorescence quantum yields (QY, Φ(f)) of a series of fluorescent dyes that span the absorption/excitation and emission ranges of 520-900 and 600-1000 nm is reported. The dyes encompass commercially available rhodamine 101 (Rh-101, Φ(f) = 0.913), cresyl violet (0.578), oxazine 170 (0.579), oxazine 1 (0.141), cryptocyanine (0.012), HITCI (0.283), IR-125 (0.132), IR-140 (0.167), and four noncommercial cyanine dyes with specific spectroscopic features, all of them in dilute ethanol solution. The QYs have been measured relative to the National Institute of Standards and Technology's standard reference material (SRM) 936a (quinine sulfate, QS) on a traceably characterized fluorometer, employing a chain of transfer standard dyes that include coumarin 102 (Φ(f) = 0.764), coumarin 153 (0.544), and DCM (0.435) as links between QS and Rh-101. The QY of Rh-101 has also been verified in direct measurements against QS using two approaches that rely only on instrument correction. In addition, the effects of temperature and the presence of oxygen on the fluorescence quantum yield of Rh-101 have been assessed. PMID:21250654

  10. Zn(II)-Coordinated Quantum Dot-FRET Nanosensors for the Detection of Protein Kinase Activity

    PubMed Central

    Lim, Butaek; Park, Ji-In; Lee, Kyung Jin; Lee, Jin-Won; Kim, Tae-Wuk; Kim, Young-Pil

    2015-01-01

    We report a simple detection of protein kinase activity using Zn(II)-mediated fluorescent resonance energy transfer (FRET) between quantum dots (QDs) and dye-tethered peptides. With neither complex chemical ligands nor surface modification of QDs, Zn(II) was the only metal ion that enabled the phosphorylated peptides to be strongly attached on the carboxyl groups of the QD surface via metal coordination, thus leading to a significant FRET efficiency. As a result, protein kinase activity in intermixed solution was efficiently detected by QD-FRET via Zn(II) coordination, especially when the peptide substrate was combined with affinity-based purification. We also found that mono- and di-phosphorylation in the peptide substrate could be discriminated by the Zn(II)-mediated QD-FRET. Our approach is expected to find applications for studying physiological function and signal transduction with respect to protein kinase activity. PMID:26213934

  11. Enhanced fluorescence yields through cavity quantum-electrodynamic effects in microdroplets

    SciTech Connect

    Barnes, M.D.; Whitten, W.B.; Ramsey, J.M. )

    1994-07-01

    Measurements of the integrated fluorescence yield per molecule of Rhodamine 6G (R6G) in 4--16-[mu]m-diameter levitated microdroplets show a size dependence that is attributed to a net increase in the fluorescence decay rate for the smaller (4--5-[mu]m) droplets. The average fluorescence yield in 4-[mu]m droplets (for which we have previously observed emission-rate enhancement) is approximately a factor of 2 larger than the yield measured for larger droplets for which emission-rate enhancement does not occur. These results suggest that there is little emission-rate inhibition in this system, even though the fluorescence emission spectrum overlaps several cavity resonances. A mechanism based on spectral diffusion is postulated for the apparent absence of cavity-inhibited emission and is illustrated by Monte Carlo calculations using time-dependent line-shape functions.

  12. Ultrafast dynamics of type-II GaSb/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Komolibus, K.; Piwonski, T.; Gradkowski, K.; Reyner, C. J.; Liang, B.; Huyet, G.; Huffaker, D. L.; Houlihan, J.

    2015-01-01

    In this paper, room temperature two-colour pump-probe spectroscopy is employed to study ultrafast carrier dynamics in type-II GaSb/GaAs quantum dots. Our results demonstrate a strong dependency of carrier capture/escape processes on applied reverse bias voltage, probing wavelength and number of injected carriers. The extracted timescales as a function of both forward and reverse bias may provide important information for the design of efficient solar cells and quantum dot memories based on this material. The first few picoseconds of the dynamics reveal a complex behaviour with an interesting feature, which does not appear in devices based on type-I materials, and hence is linked to the unique carrier capture/escape processes possible in type-II structures.

  13. Time-dependent toroidal compactification proposals and the Bianchi type II model: Classical and quantum solutions

    NASA Astrophysics Data System (ADS)

    Socorro, J.; Toledo Sesma, L.

    2016-03-01

    In this work we construct an effective four-dimensional model by compactifying a ten-dimensional theory of gravity coupled with a real scalar dilaton field on a time-dependent torus without the contributions of fluxes as first approximation. This approach is applied to anisotropic cosmological Bianchi type II model for which we study the classical coupling of the anisotropic scale factors with the two real scalar moduli produced by the compactification process. Also, we present some solutions to the corresponding Wheeler-DeWitt (WDW) equation in the context of Standard Quantum Cosmology and we claim that these quantum solution are generic in the moduli scalar field for all Bianchi Class A models. Also we give the relation to these solutions for asymptotic behavior to large argument in the corresponding quantum solution in the gravitational variables and compare with Bohm's solutions, finding that this corresponds to the lowest-order WKB approximation.

  14. Photocapacitance study of type-II GaSb/GaAs quantum ring solar cells

    SciTech Connect

    Wagener, M. C.; Botha, J. R.; Carrington, P. J.; Krier, A.

    2014-01-07

    In this study, the density of states associated with the localization of holes in GaSb/GaAs quantum rings are determined by the energy selective charging of the quantum ring distribution. The authors show, using conventional photocapacitance measurements, that the excess charge accumulated within the type-II nanostructures increases with increasing excitation energies for photon energies above 0.9 eV. Optical excitation between the localized hole states and the conduction band is therefore not limited to the Γ(k = 0) point, with pseudo-monochromatic light charging all states lying within the photon energy selected. The energy distribution of the quantum ring states could consequently be accurately related from the excitation dependence of the integrated photocapacitance. The resulting band of localized hole states is shown to be well described by a narrow distribution centered 407 meV above the GaAs valence band maximum.

  15. Relaxation and coherent oscillations in the spin dynamics of II-VI diluted magnetic quantum wells

    NASA Astrophysics Data System (ADS)

    Ungar, F.; Cygorek, M.; Tamborenea, P. I.; Axt, V. M.

    2015-10-01

    We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic quantum wells in the presence of spin-orbit interaction. We extend a recent study where it was shown that the spin-orbit interaction and the exchange sd coupling in bulk and quantum wells can compete resulting in qualitatively new dynamics when they act simultaneously. We concentrate on Hg1-x-yMnxCdyTe quantum wells, which have a highly tunable Rashba spin-orbit coupling. Our calculations use a recently developed formalism which incorporates electronic correlations originating from the exchange sd-coupling. We find that the dependence of electronic spin oscillations on the excess energy changes qualitatively depending on whether or not the spin-orbit interaction dominates or is of comparable strength with the sd interaction.

  16. Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Kolokolov, Kanstantin I.; Ning, Cun-Zheng

    2003-01-01

    Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

  17. Excitonic transitions in highly efficient (GaIn)As/Ga(AsSb) type-II quantum-well structures

    SciTech Connect

    Gies, S.; Kruska, C.; Berger, C.; Hens, P.; Fuchs, C.; Rosemann, N. W.; Veletas, J.; Stolz, W.; Koch, S. W.; Heimbrodt, W.; Ruiz Perez, A.; Hader, J.; Moloney, J. V.

    2015-11-02

    The excitonic transitions of the type-II (GaIn)As/Ga(AsSb) gain medium of a “W”-laser structure are characterized experimentally by modulation spectroscopy and analyzed using microscopic quantum theory. On the basis of the very good agreement between the measured and calculated photoreflectivity, the type-I or type-II character of the observable excitonic transitions is identified. Whereas the energetically lowest three transitions exhibit type-II character, the subsequent energetically higher transitions possess type-I character with much stronger dipole moments. Despite the type-II character, the quantum-well structure exhibits a bright luminescence.

  18. Energy distribution and quantum yield for photoemission from air-contaminated gold surfaces under ultraviolet illumination close to the threshold

    NASA Astrophysics Data System (ADS)

    Hechenblaikner, Gerald; Ziegler, Tobias; Biswas, Indro; Seibel, Christoph; Schulze, Mathias; Brandt, Nico; Schöll, Achim; Bergner, Patrick; Reinert, Friedrich T.

    2012-06-01

    The kinetic energy distributions of photo-electrons emitted from gold surfaces under illumination by UV-light close to the threshold (photon energy in the order of the material work function) are measured and analyzed. Samples are prepared as chemically clean through Ar-ion sputtering and then exposed to atmosphere for variable durations before quantum yield measurements are performed after evacuation. During measurements, the bias voltage applied to the sample is varied and the resulting emission current measured. Taking the derivative of the current-voltage curve yields the energy distribution which is found to closely resemble the distribution of total energies derived by DuBridge for emission from a free electron gas. We investigate the dependence of distribution shape and width on electrode geometry and contaminant substances adsorbed from the atmosphere, in particular, to water and hydro-carbons. Emission efficiency increases initially during air exposure before diminishing to zero on a timescale of several hours, whilst subsequent annealing of the sample restores emissivity. A model fit function, in good quantitative agreement with the measured data, is introduced which accounts for the experiment-specific electrode geometry and an energy dependent transmission coefficient. The impact of large patch potential fields from contact potential drops between sample and sample holder is investigated. The total quantum yield is split into bulk and surface contributions which are tested for their sensitivity to light incidence angle and polarization. Our results are directly applicable to model parameters for the contact-free discharge system onboard the Laser Interferometer Space Antenna (LISA) Pathfinder spacecraft.

  19. Elevated carbon dioxide and ozone effects on peanut. II. Seed yield and quality

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tropospheric O3 is an air pollutant that is toxic to plants, causing changes in leaf biochemistry and physiology that lead to reductions in growth and yield. In many O3-sensitive crops, the adverse effects of O3 are ameliorated by elevated CO2, although the extent of protection by elevated CO2 vari...

  20. Spectroscopy and dynamics of charge transfer excitons in type-II band aligned quantum confined heterostructures

    NASA Astrophysics Data System (ADS)

    Kushavah, Dushyant; Mohapatra, P. K.; Rustagi, K. C.; Bahadur, D.; Vasa, P.; Singh, B. P.

    2015-05-01

    We illustrate effect of charge transfer (CT) in type-II quantum confined heterostructure by comparing CdSe quantum dots (QDs), CdSe/CdTe heterostructure quantum dots (HQDs) and CdSe/CdTe/CdSe quantum well-quantum dots (QWQDs) heterostructures. CdSe core QDs were synthesized using a kinetic growth method where QD size depends on reaction time. For shell coating we used modified version of successive ionic layer adsorption and reaction (SILAR). Size of different QDs ˜5 to 7 nm were measured by transmission electron microscopy (TEM). Strong red shift from ˜597 to ˜746 nm in photoluminescence (PL) spectra from QDs to QWQDs shows high tunability which is not possible with single constituent semiconductor QDs. PL spectra have been recorded at different temperatures (10K-300K). Room temperature time correlated single photon counting (TCSPC) measurements for QDs to QWQDs show three exponential radiative decay. The slowest component decay constant in QWQDs comes around eight fold to ˜51 ns as compared to ˜6.5 ns in HQD suggesting new opportunities to tailor the radiative carrier recombination rate of CT excitons.

  1. Quantum Dot Channel (QDC) FETs with Wraparound II-VI Gate Insulators: Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Jain, F.; Lingalugari, M.; Kondo, J.; Mirdha, P.; Suarez, E.; Chandy, J.; Heller, E.

    2016-08-01

    This paper presents simulations predicting the feasibility of 9-nm wraparound quantum dot channel (QDC) field-effect transistors (FETs). In particular, II-VI lattice-matched layers which reduce the density of interface states, serving as top (tunnel gate), side, and bottom gate insulators, have been simulated. Quantum simulations show FET operation with voltage swing of ~0.2 V. Incorporation of cladded quantum dots, such as SiO x -Si and GeO x -Ge, under the gate tunnel oxide results in electrical transport in one or more quantum dot layers which form a quantum dot superlattice (QDSL). Long-channel QDC FETs have experimental multistate drain current (I D)-gate voltage (V G) and drain current (I D)-drain voltage (V D) characteristics, which can be attributed to the manifestation of extremely narrow energy minibands formed in the QDSL. An approach for modeling the multistate I D-V G characteristics is reported. The multistate characteristics of QDC FETs permit design of compact two-bit multivalued logic circuits.

  2. Spectroscopy and dynamics of charge transfer excitons in type-II band aligned quantum confined heterostructures

    SciTech Connect

    Kushavah, Dushyant; Mohapatra, P. K.; Vasa, P.; Singh, B. P.; Rustagi, K. C.; Bahadur, D.

    2015-05-15

    We illustrate effect of charge transfer (CT) in type-II quantum confined heterostructure by comparing CdSe quantum dots (QDs), CdSe/CdTe heterostructure quantum dots (HQDs) and CdSe/CdTe/CdSe quantum well-quantum dots (QWQDs) heterostructures. CdSe core QDs were synthesized using a kinetic growth method where QD size depends on reaction time. For shell coating we used modified version of successive ionic layer adsorption and reaction (SILAR). Size of different QDs ∼5 to 7 nm were measured by transmission electron microscopy (TEM). Strong red shift from ∼597 to ∼746 nm in photoluminescence (PL) spectra from QDs to QWQDs shows high tunability which is not possible with single constituent semiconductor QDs. PL spectra have been recorded at different temperatures (10K-300K). Room temperature time correlated single photon counting (TCSPC) measurements for QDs to QWQDs show three exponential radiative decay. The slowest component decay constant in QWQDs comes around eight fold to ∼51 ns as compared to ∼6.5 ns in HQD suggesting new opportunities to tailor the radiative carrier recombination rate of CT excitons.

  3. Polarization anisotropy of the emission from type-II quantum dots

    NASA Astrophysics Data System (ADS)

    Klenovský, P.; Hemzal, D.; Steindl, P.; Zíková, M.; Křápek, V.; Humlíček, J.

    2015-12-01

    We study the polarization response of the emission from type-II GaAsSb capped InAs quantum dots. The theoretical prediction based on the calculations of the overlap integrals of the single-particle states obtained in the k ⃗.p ⃗ framework is given. This is verified experimentally by polarization resolved photoluminescence measurements on samples with the type-II confinement. We show that the polarization anisotropy might be utilized to find the vertical position of the hole wave function and its orientation with respect to crystallographic axes of the sample. A proposition for usage in the information technology as a room temperature photonic gate operating at the communication wavelengths as well as a simple model to estimate the energy of fine-structure splitting for type-II GaAsSb capped InAs QDs are given.

  4. Iridium Cyclometalated Complexes in Host-Guest Chemistry: A Strategy for Maximizing Quantum Yield in Aqueous Media.

    PubMed

    Alrawashdeh, Lubna R; Cronin, Michael P; Woodward, Clifford E; Day, Anthony I; Wallace, Lynne

    2016-07-01

    The weaker emission typically seen for iridium(III) cyclometalated complexes in aqueous medium can be reversed via encapsulation in cucurbit[10]uril (Q[10]). The Q[10] cavity is shown to effectively maximize quantum yields for the complexes, compared to any other medium. This may provide significant advantages for a number of sensor applications. NMR studies show that the complexes are accommodated similarly within the host molecule, even with cationic substituents attached to the ppy ligands, indicating that the hydrophobic effect is the dominant driving force for binding. Cavity-encapsulated 1:1 host-guest species dominate the emission, but 1:2 species are also indicated, which also give some enhancement of intensity. Results demonstrate that the enhancement is due primarily to much lower rates of nonradiative decay but also suggest that the encapsulation can cause a change in character of the emitting state. PMID:27315543

  5. Developing a diagnostic model for estimating terrestrial vegetation gross primary productivity using the photosynthetic quantum yield and Earth Observation data.

    PubMed

    Ogutu, Booker O; Dash, Jadunandan; Dawson, Terence P

    2013-09-01

    This article develops a new carbon exchange diagnostic model [i.e. Southampton CARbon Flux (SCARF) model] for estimating daily gross primary productivity (GPP). The model exploits the maximum quantum yields of two key photosynthetic pathways (i.e. C3 and C4 ) to estimate the conversion of absorbed photosynthetically active radiation into GPP. Furthermore, this is the first model to use only the fraction of photosynthetically active radiation absorbed by photosynthetic elements of the canopy (i.e. FAPARps ) rather than total canopy, to predict GPP. The GPP predicted by the SCARF model was comparable to in situ GPP measurements (R(2)  > 0.7) in most of the evaluated biomes. Overall, the SCARF model predicted high GPP in regions dominated by forests and croplands, and low GPP in shrublands and dry-grasslands across USA and Europe. The spatial distribution of GPP from the SCARF model over Europe and conterminous USA was comparable to those from the MOD17 GPP product except in regions dominated by croplands. The SCARF model GPP predictions were positively correlated (R(2)  > 0.5) to climatic and biophysical input variables indicating its sensitivity to factors controlling vegetation productivity. The new model has three advantages, first, it prescribes only two quantum yield terms rather than species specific light use efficiency terms; second, it uses only the fraction of PAR absorbed by photosynthetic elements of the canopy (FAPARps ) hence capturing the actual PAR used in photosynthesis; and third, it does not need a detailed land cover map that is a major source of uncertainty in most remote sensing based GPP models. The Sentinel satellites planned for launch in 2014 by the European Space Agency have adequate spectral channels to derive FAPARps at relatively high spatial resolution (20 m). This provides a unique opportunity to produce global GPP operationally using the Southampton CARbon Flux (SCARF) model at high spatial resolution. PMID:23687009

  6. Modeling the quantum yields of herbicide 2,4-D decay in UV/H2O2 process.

    PubMed

    Chu, W

    2001-08-01

    The photodecay of herbicide 2,4-D in a hydrogen peroxide-aided photolysis process was studied and modeled. The decay rate of 2,4-D was known to be low in the natural environment, but rate improvement was achieved in an H2O2/UV system. The 2,4-D decay quantum yields under ultraviolet (UV) light at 253.7 nm increased from 4.86 x 10(-6) to 1.30 x 10(-4) as the ratio of [H2O2]/[2,4-D] increased from 0.05 to 12.5. Apparently, in the presence of UV light, the decay rate of 2,4-D could be greatly improved as the concentration of hydrogen peroxide increased. However, the efficiency of 2,4-D photodecay was retarded if the concentration of H2O2 was overdosed, because the excess hydrogen peroxide consumes the hydroxyl radicals (HO*) in the solution, resulting in a much weaker oxidant HO2*. The decay of 2,4-D was also pH dependent. A ranking of acid (highest), base (middle) and neutral (lowest) was observed owing to the property change of reactants and the shifting of dominant mechanisms among photolysis, photohydrolysis and chemical oxidation. Two mathematical models were proposed to predict the quantum yield for various [H2O2]/[2,4-D] ratios and initial pH levels, in which very good correlation was found for the ranges of regular application. PMID:11513426

  7. Analysis of ice-binding sites in fish type II antifreeze protein by quantum mechanics.

    PubMed Central

    Cheng, Yuhua; Yang, Zuoyin; Tan, Hongwei; Liu, Ruozhuang; Chen, Guangju; Jia, Zongchao

    2002-01-01

    Many organisms living in cold environments can survive subzero temperatures by producing antifreeze proteins (AFPs) or antifreeze glycoproteins. In this paper we investigate the ice-binding surface of type II AFP by quantum mechanical methods, which, to the best of our knowledge, represents the first time that molecular orbital computational approaches have been applied to AFPs. Molecular mechanical approaches, including molecular docking, energy minimization, and molecular dynamics simulation, were used to obtain optimal systems for subsequent quantum mechanical analysis. We selected 17 surface patches covering the entire surface of the type II AFP and evaluated the interaction energy between each of these patches and two different ice planes using semi-empirical quantum mechanical methods. We have demonstrated the weak orbital overlay phenomenon and the change of bond orders in ice. These results consistently indicate that a surface patch containing 19 residues (K37, L38, Y20, E22, Y21, I19, L57, T56, F53, M127, T128, F129, R17, C7, N6, P5, G10, Q1, and W11) is the most favorable ice-binding site for both a regular ice plane and an ice plane where water O atoms are randomly positioned. Furthermore, for the first time the computation results provide new insights into the weakening of the ice lattice upon AFP binding, which may well be a primary factor leading to AFP-induced ice growth inhibition. PMID:12324437

  8. Entangled quantum electronic wavefunctions of the Mn4CaO5 cluster in photosystem II

    NASA Astrophysics Data System (ADS)

    Kurashige, Yuki; Chan, Garnet Kin-Lic; Yanai, Takeshi

    2013-08-01

    It is a long-standing goal to understand the reaction mechanisms of catalytic metalloenzymes at an entangled many-electron level, but this is hampered by the exponential complexity of quantum mechanics. Here, by exploiting the special structure of physical quantum states and using the density matrix renormalization group, we compute near-exact many-electron wavefunctions of the Mn4CaO5 cluster of photosystem II, with more than 1 × 1018 quantum degrees of freedom. This is the first treatment of photosystem II beyond the single-electron picture of density functional theory. Our calculations support recent modifications to the structure determined by X-ray crystallography. We further identify multiple low-lying energy surfaces associated with the structural distortion seen using X-ray crystallography, highlighting multistate reactivity in the chemistry of the cluster. Direct determination of Mn spin-projections from our wavefunctions suggests that current candidates that have been recently distinguished using parameterized spin models should be reassessed. Through entanglement maps, we reveal rich information contained in the wavefunctions on bonding changes in the cycle.

  9. Entangled quantum electronic wavefunctions of the Mn₄CaO₅ cluster in photosystem II.

    PubMed

    Kurashige, Yuki; Chan, Garnet Kin-Lic; Yanai, Takeshi

    2013-08-01

    It is a long-standing goal to understand the reaction mechanisms of catalytic metalloenzymes at an entangled many-electron level, but this is hampered by the exponential complexity of quantum mechanics. Here, by exploiting the special structure of physical quantum states and using the density matrix renormalization group, we compute near-exact many-electron wavefunctions of the Mn4CaO5 cluster of photosystem II, with more than 1 × 10(18) quantum degrees of freedom. This is the first treatment of photosystem II beyond the single-electron picture of density functional theory. Our calculations support recent modifications to the structure determined by X-ray crystallography. We further identify multiple low-lying energy surfaces associated with the structural distortion seen using X-ray crystallography, highlighting multistate reactivity in the chemistry of the cluster. Direct determination of Mn spin-projections from our wavefunctions suggests that current candidates that have been recently distinguished using parameterized spin models should be reassessed. Through entanglement maps, we reveal rich information contained in the wavefunctions on bonding changes in the cycle. PMID:23881496

  10. From rainfed agriculture to stress-avoidance irrigation: II. Sustainability, crop yield, and profitability

    NASA Astrophysics Data System (ADS)

    Vico, Giulia; Porporato, Amilcare

    2011-02-01

    The optimality of irrigation strategies may be sought with respect to a number of criteria, including water requirements, crop yield, and profitability. To explore the suitability of different demand-based irrigation strategies, we link the probabilistic description of irrigation requirements under stochastic hydro-climatic conditions, provided in a companion paper [Vico G, Porporato A. From rainfed agriculture to stress-avoidance irrigation: I. A generalized irrigation scheme with stochastic soil moisture. Adv Water Resour 2011;34(2):263-71], to crop-yield and economic analyses. Water requirements, application efficiency, and investment costs of different irrigation methods, such as surface, sprinkler and drip irrigation systems, are described via a unified conceptual and theoretical approach, which includes rainfed agriculture and stress-avoidance irrigation as extreme cases. This allows us to analyze irrigation strategies with respect to sustainability, productivity, and economic return, using the same framework, and quantify them as a function of climate, crop, and soil parameters. We apply our results to corn ( Zea mays), a food staple and biofuel source, which is currently mainly irrigated through surface systems. As our analysis shows, micro-irrigation maximizes water productivity, but more traditional solutions may be more profitable at least in some contexts.

  11. Secondary Electron Yield Measurements and Groove Chambers Tests in the PEP-II Beam Line Straights Sections

    SciTech Connect

    Pivi, M.T.F.; King, F.; Kirby, R.E.; Markiewicz, T; Raubenheimer, T.O.; Seeman, J.; Wang, L.; /SLAC

    2008-07-03

    Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders such as ILC and CLIC [1, 2]. In the Positron Low Energy Ring (LER) of the PEP-II accelerator, we have installed vacuum chambers with rectangular grooves in a straight magnetic-free section to test this promising possible electron cloud mitigation technique. We have also installed a special chamber to monitor the secondary electron yield of TiN and TiZrV (NEG) coating, Copper, Stainless Steel and Aluminum under the effect of electron and photon conditioning in situ in the beam line. In this paper, we describe the ongoing R&D effort to mitigate the electron cloud effect for the ILC damping ring, the latest results on in situ secondary electron yield conditioning and recent update on the groove tests in PEP-II.

  12. Aharonov-Bohm Beats in Excitonic Luminescence from Quantum Rings and Type-II Quantum Dots

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Luis; Shahbazyan, Tigran

    2005-03-01

    We study the absorption spectrum of neutral magnetoexcitons confined in ring-like structures. Despite their neutral character, excitons exhibit strong modulation effects on the energy and oscillator strength in the presence of magnetic fields [1] that have been recently observed [2]. We calculate the absorption coefficient α for neutral excitons confined in circular ring geometries with radii Re for electrons and Rh for holes. A particularly interesting situation comes about when Re!=Rh and a net radial charge polarization arises. In this case, we consider an attractive Coulomb interaction proportional to (Re- Rh)-1 and the excitonic absorption peak shows oscillatory behavior as function of the applied magnetic field both in position and amplitude. Such oscillations strongly depend on the dipole moment P=e(Rh-Re) of the exciton and on the dielectric constant of the system. Such intensity changes could in principle be experimentally observed with single dot spectroscopy in quantum rings [3]. Supported by the NSF-IMC and NSF-RUI [1] A.O. Govorov et al. Phys. Rev. B 66 081309 (2002); A.O. Govorov et al. Physica E 13, 297 (2002). [2] E. Ribeiro et al. Phys Rev. Lett. 92 126402 (2004). [3] R.J. Warburton et al. Nature 405 (6789) 926 (2000).

  13. Searching for quantum gravity with high-energy atmospheric neutrinos and AMANDA-II

    NASA Astrophysics Data System (ADS)

    Kelley, John Lawrence

    2008-06-01

    The AMANDA-II detector, operating since 2000 in the deep ice at the geographic South Pole, has accumulated a large sample of atmospheric muon neutrinos in the 100 GeV to 10 TeV energy range. The zenith angle and energy distribution of these events can be used to search for various phenomenological signatures of quantum gravity in the neutrino sector, such as violation of Lorentz invariance (VLI) or quantum decoherence (QD). Analyzing a set of 5511 candidate neutrino events collected during 1387 days of livetime from 2000 to 2006, we find no evidence for such effects and set upper limits on VLI and QD parameters using a maximum likelihood method. Given the absence of new flavor-changing physics, we use the same methodology to determine the conventional atmospheric muon neutrino flux above 100 GeV.

  14. Trion X+ in vertically coupled type II quantum dots in threading magnetic field.

    PubMed

    Horta-Piñeres, Sindi; Escorcia-Salas, Gene Elizabeth; Mikhailov, Ilia D; Sierra-Ortega, José

    2012-01-01

    We analyze the energy spectrum of a positively charged exciton confined in a semiconductor heterostructure formed by two vertically coupled, axially symmetrical type II quantum dots located close to each other. The electron in the structure is mainly located inside the dots, while the holes generally move in the exterior region close to the symmetry axis. The solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and anti-bonding lowest-lying of the trion states corresponding to the different quantum dots morphologies, dimensions, separation between them, thicknesses of the wetting layers, and the magnetic field strength. PMID:23013605

  15. Mn(II/III) complexes as promising redox mediators in quantum-dot-sensitized solar cells.

    PubMed

    Haring, Andrew J; Pomatto, Michelle E; Thornton, Miranda R; Morris, Amanda J

    2014-09-10

    The advancement of quantum dot sensitized solar cell (QDSSC) technology depends on optimizing directional charge transfer between light absorbing quantum dots, TiO2, and a redox mediator. The nature of the redox mediator plays a pivotal role in determining the photocurrent and photovoltage from the solar cell. Kinetically, reduction of oxidized quantum dots by the redox mediator should be rapid and faster than the back electron transfer between TiO2 and oxidized quantum dots to maintain photocurrent. Thermodynamically, the reduction potential of the redox mediator should be sufficiently positive to provide high photovoltages. To satisfy both criteria and enhance power conversion efficiencies, we introduced charge transfer spin-crossover Mn(II/III) complexes as promising redox mediator alternatives in QDSSCs. High photovoltages ∼ 1 V were achieved by a series of Mn poly(pyrazolyl)borates, with reduction potentials ∼ 0.51 V vs Ag/AgCl. Back electron transfer (recombination) rates were slower than Co(bpy)3, where bpy = 2,2'-bipyridine, evidenced by electron lifetimes up to 4 orders of magnitude longer. This is indicative of a large barrier to electron transport imposed by spin-crossover in these complexes. Low solubility prevented the redox mediators from sustaining high photocurrent due to mass transport limits. However, with high fill factors (∼ 0.6) and photovoltages, they demonstrate competitive efficiencies with Co(bpy)3 redox mediator at the same concentration. More positive reduction potentials and slower recombination rates compared to current redox mediators establish the viability of Mn poly(pyrazolyl)borates as promising redox mediators. By capitalizing on these characteristics, efficient Mn(II/III)-based QDSSCs can be achieved with more soluble Mn-complexes. PMID:25137595

  16. Crystal-Phase Control by Solution-Solid-Solid Growth of II-VI Quantum Wires.

    PubMed

    Wang, Fudong; Buhro, William E

    2016-02-10

    A simple and potentially general means of eliminating the planar defects and phase alternations that typically accompany the growth of semiconductor nanowires by catalyzed methods is reported. Nearly phase-pure, defect-free wurtzite II-VI semiconductor quantum wires are grown from solid rather than liquid catalyst nanoparticles. The solid-catalyst nanoparticles are morphologically stable during growth, which minimizes the spontaneous fluctuations in nucleation barriers between zinc blende and wurtzite phases that are responsible for the defect formation and phase alternations. Growth of single-phase (in our cases the wurtzite phase) nanowires is thus favored. PMID:26731426

  17. Development of superconducting contacts for the CRESST II 66-channel superconducting quantum interference device readout system.

    PubMed

    Majorovits, B; Henry, S; Kraus, H

    2007-07-01

    The CRESST experiment is designed to search for weakly interacting massive particle dark matter with cryogenic detectors. CRESST II will use up to 33 CaWO(4) crystals with a total mass of approximately 10 kg. These many detectors require a readout system based on 66-channel superconducting quantum interference devices (SQUIDs). In this article we report on the development of a modular superconducting connector for the 66-channel SQUID readout circuit. We show that the technique developed reliably produces superconducting contacts. PMID:17672757

  18. Development of superconducting contacts for the CRESST II 66-channel superconducting quantum interference device readout system

    SciTech Connect

    Majorovits, B.; Henry, S.; Kraus, H.

    2007-07-15

    The CRESST experiment is designed to search for weakly interacting massive particle dark matter with cryogenic detectors. CRESST II will use up to 33 CaWO{sub 4} crystals with a total mass of {approx}10 kg. These many detectors require a readout system based on 66-channel superconducting quantum interference devices (SQUIDs). In this article we report on the development of a modular superconducting connector for the 66-channel SQUID readout circuit. We show that the technique developed reliably produces superconducting contacts.

  19. Exciton storage in type-II quantum dots using the optical Aharonov-Bohm effect

    SciTech Connect

    Climente, Juan I.; Planelles, Josep

    2014-05-12

    We investigate the bright-to-dark exciton conversion efficiency in type-II quantum dots subject to a perpendicular magnetic field. To this end, we take the exciton storage protocol recently proposed by Simonin and co-workers [Phys. Rev. B 89, 075304 (2014)] and simulate its coherent dynamics. We confirm the storage is efficient in perfectly circular structures subject to weak external electric fields, where adiabatic evolution is dominant. In practice, however, the efficiency rapidly degrades with symmetry lowering. Besides, the use of excited states is likely unfeasible owing to the fast decay rates. We then propose an adaptation of the protocol which does not suffer from these limitations.

  20. Optical Anisotropy in Type-II ZnTe/ZnSe Submonolayer Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ji, Haojie; Dhomkar, Siddharth; Tamargo, Maria; Kuskovsky, Igor

    2014-03-01

    Type-II semiconductor quantum dots (QDs) characterized by spatial separation of charge carriers are good candidates for photovoltaics and photon manipulation applications. Implementation of practical devices requires detail understandings of the QD morphology, the mechanism of strain relief and defect formation. Here we report our study of polarization dependent photoluminescence (PL) in type-II ZnTe/ZnSe submonolayer QD superlattices, grown by migration-enhanced epitaxy. We show that the PL does not depend on the polarization state of excitation and exhibits strong linear polarization, indicating strong anisotropy in this material. We spectrally analyze the degree of linear polarization in samples grown with different Te fluxes, spacer thicknesses and number of periods. Based on our observations, we propose several reasons for the optical anisotropy, focusing on the anisotropic shape of the QDs and the anisotropy at the interfaces in the superlattices.

  1. A Novel Method For Predicting Carbon Monoxide Apparent Quantum Yield Spectra in Coastal Water Using Remote Sensing Reflectance Data

    NASA Astrophysics Data System (ADS)

    Reader, H. E.; Miller, W. L.

    2010-12-01

    Photochemical oxidation of chromophoric dissolved organic matter (CDOM) is the major source of carbon monoxide to the surface ocean. Bacterial consumption and air-sea exchange comprise the two known sinks for CO in marine systems. Though the two loss terms are relatively efficient, CO remains supersaturated with respect to the atmosphere in the surface ocean. Global oceanic estimates of CO photoproduction range from 30-84Tg CO/year (Zafiriou 2003, Fichot and Miller 2010). The variation in estimates is largely due to the difficulty in predicting the efficiency of photoproduction (i.e. Apparent Quantum Yield; AQY). Though the AQY for CO photoproduction appears to be relatively constant, there is indication that terrestrially derived sources, such as those found in estuarine environments, produce CO more efficiently than marine derived sources (Ziolkowski 2000). Since variation among sources is likely in the global ocean, accurate assignment of AQY to variable water types is required to accurately predict CO photoproduction. Deriving the correct apparent quantum yield from remotely sensed data would lead to better predictions of large scale CO photoproduction from optical data. Thirty-eight (38) AQY spectra for CO photoproduction were determined by monthly sampling during spring tides in three dark water locations on the coast of Georgia, USA, from November 2008 to September 2009. Sapelo Sound, a marine dominated system, receives little to no freshwater input over the year, while Altamaha Sound drains the largest watershed in the state of Georgia, and has largely variably freshwater input. Doboy Sound, situated between Sapelo Sound and Altamaha Sound, is largely marine dominated, though in periods of high flow on the Altamaha River, receives some fresh water overflow. The coast of Georgia is dominated by Spartina alterniflora salt marshes, and thus also has a strong non-point source of terrestrially derived carbon. CO apparent quantum yields were determined by

  2. Quantum wave packet study of nonadiabatic effects in O({sup 1}D) + H{sub 2} {yields} OH + H

    SciTech Connect

    Gray, S.K.; Petrongolo, C.; Drukker, K.; Schatz, G.C.

    1999-11-25

    The authors develop a wave packet approach to treating the electronically nonadiabatic reaction dynamics of O({sup 1}D) + H{sub 2} {yields} OH + H, allowing for the 1{sup 1}A{prime} and 2{sup 1}A{prime} potential energy surfaces and couplings, as well as the three internal nuclear coordinates. Two different systems of coupled potential energy surfaces are considered, a semiempirical diatomics-in-molecules (DIM) system due to Kuntz, Niefer, and Sloan, and a recently developed ab initio system due to Dobbyn and Knowles (DK). Nonadiabatic quantum results, with total angular momentum J = 0, are obtained and discussed. Several single surface calculations are carried out for comparison with the nonadiabatic results. Comparisons with trajectory surface hopping (TSH) calculations, and with approximate quantum calculations, are also included. The electrostatic coupling produces strong interactions between the 1{sup 1}A{prime} and 2{sup 1}A{prime} states at short range (where these states have a conical intersection) and weak but, interestingly, nonnegligible interactions between these states at longer range. The wave packet results show that if the initial state is chosen to be effectively the 1A{prime} state (for which insertion to form products occurs on the adiabatic surface), then there is very little difference between the adiabatic and coupled surface results. In either case the reaction probability is a relatively flat function of energy, except for resonant oscillations. However, the 2A{prime} reaction, dynamics (which involves a collinear transition state) is strongly perturbed by nonadiabatic effects in two distinct ways. At energies above the transition state barrier, the diabatic limit is dominant, and the 2A{prime} reaction probability is similar to that for 1A{double{underscore}prime}, which has no coupling with the other surfaces. At energies below the barrier, the authors find a significant component of the reaction probability from long range electronic

  3. Preparation and photophysical studies of [Ln(hfac)3DPEPO], Ln = Eu, Tb, Yb, Nd, Gd; interpretation of total photoluminescence quantum yields.

    PubMed

    Congiu, Martina; Alamiry, Mohamed; Moudam, Omar; Ciorba, Serena; Richardson, Patricia R; Maron, Laurent; Jones, Anita C; Richards, Bryce S; Robertson, Neil

    2013-10-01

    Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime. PMID:23900430

  4. Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence

    NASA Astrophysics Data System (ADS)

    Hou, Juan; Wang, Wei; Zhou, Tianyu; Wang, Bo; Li, Huiyu; Ding, Lan

    2016-05-01

    Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A possible formation mechanism has thus been proposed including dehydration, polymerization and carbonization. Furthermore, the N-CDs could serve as a facile and label-free probe for the detection of iron and fluorine ions with detection limits of 50 nmol L-1 and 75 nmol L-1, respectively.Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A

  5. The quantum interference effects in the SC II 4247 Å line of the second solar spectrum

    SciTech Connect

    Smitha, H. N.; Nagendra, K. N.; Stenflo, J. O.; Bianda, M.; Ramelli, R. E-mail: knn@iiap.res.in E-mail: mbianda@irsol.ch

    2014-10-10

    The Sc II 4247 Å line formed in the chromosphere is one of the lines well known, like the Na I D{sub 2} and Ba II D{sub 2}, for its prominent triple-peak structure in Q/I and the underlying quantum interference effects governing it. In this paper, we try to study the nature of this triple-peak structure using the theory of F-state interference including the effects of partial frequency redistribution (PRD) and radiative transfer (RT). We compare our results with the observations taken in a quiet region near the solar limb. In spite of accounting for PRD and RT effects, it has not been possible to reproduce the observed triple-peak structure in Q/I. While the two wing PRD peaks (on either side of central peak) and the near wing continuum can be reproduced, the central peak is completely suppressed by the enhanced depolarization resulting from the hyperfine structure splitting. This suppression remains for all the tested widely different one-dimensional model atmospheres or for any multi-component combinations of them. While multidimensional RT effects may improve the fit to the intensity profiles, they do not appear capable of explaining the enigmatic central Q/I peak. This leads us to suspect that some aspect of quantum physics is missing.

  6. How quantum entanglement in DNA synchronizes double-strand breakage by type II restriction endonucleases.

    PubMed

    Kurian, P; Dunston, G; Lindesay, J

    2016-02-21

    Macroscopic quantum effects in living systems have been studied widely in pursuit of fundamental explanations for biological energy transport and sensing. While it is known that type II endonucleases, the largest class of restriction enzymes, induce DNA double-strand breaks by attacking phosphodiester bonds, the mechanism by which simultaneous cutting is coordinated between the catalytic centers remains unclear. We propose a quantum mechanical model for collective electronic behavior in the DNA helix, where dipole-dipole oscillations are quantized through boundary conditions imposed by the enzyme. Zero-point modes of coherent oscillations would provide the energy required for double-strand breakage. Such quanta may be preserved in the presence of thermal noise by the enzyme's displacement of water surrounding the DNA recognition sequence. The enzyme thus serves as a decoherence shield. Palindromic mirror symmetry of the enzyme-DNA complex should conserve parity, because symmetric bond-breaking ceases when the symmetry of the complex is violated or when physiological parameters are perturbed from optima. Persistent correlations in DNA across longer spatial separations-a possible signature of quantum entanglement-may be explained by such a mechanism. PMID:26682627

  7. Analysis of the Mode-Specific Excited-State Energy Distribution and Wavelength-Dependent Photoreaction Quantum Yield in Rhodopsin

    PubMed Central

    Kim, Judy E.; Tauber, Michael J.; Mathies, Richard A.

    2003-01-01

    The photoreaction quantum yield of rhodopsin is wavelength dependent: φ(λ) is reduced by up to 5% at wavelengths to the red of 500 nm but is invariant (φ = 0.65 ± 0.01) between 450 and 500 nm (Kim et al., 2001). To understand this nonstatistical internal conversion process, these results are compared with predictions of a Landau-Zener model for dynamic curve crossing. The initial distribution of excess photon energy in the 28 Franck-Condon active vibrational modes of rhodopsin is defined by a fully thermalized sum-over-states vibronic calculation. This calculation reveals that absorption by high-frequency unreactive modes (e.g., C=C stretches) increases as the excitation wavelength is shifted from 570 to 450 nm whereas relatively less energy is deposited into reactive low-frequency modes. This result qualitatively explains the experimentally observed wavelength dependence of φ(λ) for rhodopsin and reveals the importance of delocalized, torsional modes in the reactive pathway. PMID:12668457

  8. Low cost 3D-printing used in an undergraduate project: an integrating sphere for measurement of photoluminescence quantum yield

    NASA Astrophysics Data System (ADS)

    Tomes, John J.; Finlayson, Chris E.

    2016-09-01

    We report upon the exploitation of the latest 3D printing technologies to provide low-cost instrumentation solutions, for use in an undergraduate level final-year project. The project addresses prescient research issues in optoelectronics, which would otherwise be inaccessible to such undergraduate student projects. The experimental use of an integrating sphere in conjunction with a desktop spectrometer presents opportunities to use easily handled, low cost materials as a means to illustrate many areas of physics such as spectroscopy, lasers, optics, simple circuits, black body radiation and data gathering. Presented here is a 3rd year undergraduate physics project which developed a low cost (£25) method to manufacture an experimentally accurate integrating sphere by 3D printing. Details are given of both a homemade internal reflectance coating formulated from readily available materials, and a robust instrument calibration method using a tungsten bulb. The instrument is demonstrated to give accurate and reproducible experimental measurements of luminescence quantum yield of various semiconducting fluorophores, in excellent agreement with literature values.

  9. Photodissociation of methylnitrite in the vacuum ultraviolet. I. Identification and quantum yields of electronically excited NO products

    NASA Astrophysics Data System (ADS)

    Lahmani, F.; Lardeux, C.; Lavollée, M.; Solgadi, D.

    1980-08-01

    The fluorescence of the photofragments resulting from vacuum ultraviolet photodissociation of methyl nitrite (CH3ONO) in the gas phase has been studied using synchrotron radiation from Orsay Electron Storage Ring (ACO) as the source of excitation. In the spectral region between 1100 and 1600 Å where CH3ONO shows a diffuse absorption spectrum, the formation of NO in A 2Σ+ (v'=0,1,2), C 2Π and D 2Σ+ has been identified by time and energy-resolved spectra. The quantum yields of the photodissociation channels leading to the NO (A,C,D) states have been determined by comparison of the emission intensity with that of pure NO directly excited in A 2Σ+, C 2Π, v'=0, D 2Σ+, v'=0: φ (CH3ONO→NO A)=0.18±0.03 at λexc=1440 Å; φ (CH3ONO→NO C, v'=0)=0.07±0.02 at λexc=1380 Å; and φ (CH3ONO→NO D, v'=0)=0.05±0.02 at λexc=1200 Å.

  10. Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence.

    PubMed

    Hou, Juan; Wang, Wei; Zhou, Tianyu; Wang, Bo; Li, Huiyu; Ding, Lan

    2016-06-01

    Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A possible formation mechanism has thus been proposed including dehydration, polymerization and carbonization. Furthermore, the N-CDs could serve as a facile and label-free probe for the detection of iron and fluorine ions with detection limits of 50 nmol L(-1) and 75 nmol L(-1), respectively. PMID:27180833

  11. Accounting for the decrease of photosystem photochemical efficiency with increasing irradiance to estimate quantum yield of leaf photosynthesis.

    PubMed

    Yin, Xinyou; Belay, Daniel W; van der Putten, Peter E L; Struik, Paul C

    2014-12-01

    Maximum quantum yield for leaf CO2 assimilation under limiting light conditions (Φ CO2LL) is commonly estimated as the slope of the linear regression of net photosynthetic rate against absorbed irradiance over a range of low-irradiance conditions. Methodological errors associated with this estimation have often been attributed either to light absorptance by non-photosynthetic pigments or to some data points being beyond the linear range of the irradiance response, both causing an underestimation of Φ CO2LL. We demonstrate here that a decrease in photosystem (PS) photochemical efficiency with increasing irradiance, even at very low levels, is another source of error that causes a systematic underestimation of Φ CO2LL. A model method accounting for this error was developed, and was used to estimate Φ CO2LL from simultaneous measurements of gas exchange and chlorophyll fluorescence on leaves using various combinations of species, CO2, O2, or leaf temperature levels. The conventional linear regression method under-estimated Φ CO2LL by ca. 10-15%. Differences in the estimated Φ CO2LL among measurement conditions were generally accounted for by different levels of photorespiration as described by the Farquhar-von Caemmerer-Berry model. However, our data revealed that the temperature dependence of PSII photochemical efficiency under low light was an additional factor that should be accounted for in the model. PMID:25149653

  12. Optimization of optical excitation of upconversion nanoparticles for rapid microscopy and deeper tissue imaging with higher quantum yield.

    PubMed

    Zhan, Qiuqiang; He, Sailing; Qian, Jun; Cheng, Hao; Cai, Fuhong

    2013-01-01

    Relatively low quantum yield (QY), time-consuming scanning and strong absorption of light in tissue are some of the issues present in the development of upconversion nanoparticles (UCNPs) for biomedical applications. In this paper we systematically optimize several aspects of optical excitation of UCNPs to improve their applicability in bioimaging and biotherapy. A novel multi-photon evanescent wave (EW) excitation modality is proposed for UCNP-based microscopy. The scanning-free, ultrahigh contrast and high spatiotemporal resolution method could simultaneously track a few particles in a large area with a speed of ³⁺up to 350 frames per second. The HeLa cancer cell membrane imaging was successfully performed using NaYF₄: 20% Yb³⁺/2Er³⁺ targeting nanoparticles. Studies with different tissues were made to illustrate the impact of optical property parameters on the deep imaging ability of 920-nm band excitation. In the experiments a semiconductor laser with a 920 nm wavelength was used to excite UCNPs in tissue phantom at five depths. Our experimental and computational results have shown that in UCNP-based diffusion optical imaging with 920-nm laser excitation could lead to larger imaging depth range compared to traditional 974-nm excitation in a wide dynamic range of tissue species. As the QY is power density dependent, a pulsed laser is proposed to improve the QY of UCNPs. This proposal is promising in drastically increasing the imaging depth and efficiency of photodynamic therapy. PMID:23650478

  13. Controls of the quantum yield and saturation light of isoprene emission in different-aged aspen leaves.

    PubMed

    Niinemets, Ülo; Sun, Zhihong; Talts, Eero

    2015-12-01

    Leaf age alters the balance between the use of end-product of plastidic isoprenoid synthesis pathway, dimethylallyl diphosphate (DMADP), in prenyltransferase reactions leading to synthesis of pigments of photosynthetic machinery and in isoprene synthesis, but the implications of such changes on environmental responses of isoprene emission have not been studied. Because under light-limited conditions, isoprene emission rate is controlled by DMADP pool size (SDMADP ), shifts in the share of different processes are expected to particularly strongly alter the light dependency of isoprene emission. We examined light responses of isoprene emission in young fully expanded, mature and old non-senescent leaves of hybrid aspen (Populus tremula x P. tremuloides) and estimated in vivo SDMADP and isoprene synthase activity from post-illumination isoprene release. Isoprene emission capacity was 1.5-fold larger in mature than in young and old leaves. The initial quantum yield of isoprene emission (αI ) increased by 2.5-fold with increasing leaf age primarily as the result of increasing SDMADP . The saturating light intensity (QI90 ) decreased by 2.3-fold with increasing leaf age, and this mainly reflected limited light-dependent increase of SDMADP possibly due to feedback inhibition by DMADP. These major age-dependent changes in the shape of the light response need consideration in modelling canopy isoprene emission. PMID:26037962

  14. Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: Correcting for absorption/re-emission

    SciTech Connect

    MacDougall, Sean K. W.; Ivaturi, Aruna; Marques-Hueso, Jose; Richards, Bryce S.

    2014-06-15

    The internal photoluminescent quantum yield (iPLQY) – defined as the ratio of emitted photons to those absorbed – is an important parameter in the evaluation and application of luminescent materials. The iPLQY is rarely reported due to the complexities in the calibration of such a measurement. Herein, an experimental method is proposed to correct for re-emission, which leads to an underestimation of the absorption under broadband excitation. Although traditionally the iPLQY is measured using monochromatic sources for linear materials, this advancement is necessary for nonlinear materials with wavelength dependent iPLQY, such as the application of up-conversion to solar energy harvesting. The method requires an additional measurement of the emission line shape that overlaps with the excitation and absorption spectra. Through scaling of the emission spectrum, at the long wavelength edge where an overlap of excitation does not occur, it is possible to better estimate the value of iPLQY. The method has been evaluated for a range of nonlinear material concentrations and under various irradiances to analyze the necessity and boundary conditions that favor the proposed method. Use of this refined method is important for a reliable measurement of iPLQY under a broad illumination source such as the Sun.

  15. Effect of morphology on spectral properties of magneto-trion X+ in vertically coupled type II quantum dots

    NASA Astrophysics Data System (ADS)

    Horta-Piñeres, Sindi; Elizabeth Escorcia-Salas, G.; Mikhailov, I. D.; Sierra-Ortega, J.

    2014-11-01

    The energy spectrum of a positively charged exciton confined in vertically coupled type II quantum dots with different morphologies in the presence of the external magnetic field is studied. The effect of the quantum dot morphology on the curves of the lowest energy levels as functions of the magnetic field is analyzed. It is shown that a strong correlation presented in this system generates the Aharonov-Bohm oscillations of the lower energy levels similar to those in wide quantum ring. The novel curves of the trion energies dependences on the external magnetic field for the disk-like, lens-like, and cone-like structures are presented.

  16. Kinetics and quantum yield of photoluminescence of EuFOD{sub 3} doped into a nanoporous glass with the help of supercritical CO{sub 2}

    SciTech Connect

    Bagratashvili, V N; Tsypina, S I; Chutko, E A; Gerasimova, V I; Gordienko, V M

    2008-08-31

    The kinetics of photoluminescence of a EuFOD{sub 3} metalloorganic compound doped into a nanoporous Vycor glass by the method of supercritical fluid impregnation is studied. The lifetime of luminescence of EuFOD{sub 3} molecules in pores excited by an excimer XeCl laser was 40 {mu}s, which is considerably smaller than this lifetime (150-890 {mu}s) in solutions. The quantum yield of luminescence of EuFOD{sub 3} was estimate as {approx}4x10{sup -4}. (laser applications and other topics in quantum electronics)

  17. Upconverting core-shell nanocrystals with high quantum yield under low irradiance: On the role of isotropic and thick shells

    SciTech Connect

    Fischer, Stefan; Goldschmidt, Jan Christoph; Johnson, Noah J. J.; Pichaandi, Jothirmayanantham; Veggel, Frank C. J. M. van

    2015-11-21

    Colloidal upconverter nanocrystals (UCNCs) that convert near-infrared photons to higher energies are promising for applications ranging from life sciences to solar energy harvesting. However, practical applications of UCNCs are hindered by their low upconversion quantum yield (UCQY) and the high irradiances necessary to produce relevant upconversion luminescence. Achieving high UCQY under practically relevant irradiance remains a major challenge. The UCQY is severely limited due to non-radiative surface quenching processes. We present a rate equation model for migration of the excitation energy to show that surface quenching does not only affect the lanthanide ions directly at the surface but also many other lanthanide ions quite far away from the surface. The average migration path length is on the order of several nanometers and depends on the doping as well as the irradiance of the excitation. Using Er{sup 3+}-doped β-NaYF{sub 4} UCNCs, we show that very isotropic and thick (∼10 nm) β-NaLuF{sub 4} inert shells dramatically reduce the surface-related quenching processes, resulting in much brighter upconversion luminescence at simultaneously considerably lower irradiances. For these UCNCs embedded in poly(methyl methacrylate), we determined an internal UCQY of 2.0% ± 0.2% using an irradiance of only 0.43 ± 0.03 W/cm{sup 2} at 1523 nm. Normalized to the irradiance, this UCQY is 120× higher than the highest values of comparable nanomaterials in the literature. Our findings demonstrate the important role of isotropic and thick shells in achieving high UCQY at low irradiances from UCNCs. Additionally, we measured the additional short-circuit current due to upconversion in silicon solar cell devices as a proof of concept and to support our findings determined using optical measurements.

  18. Upconverting core-shell nanocrystals with high quantum yield under low irradiance: On the role of isotropic and thick shells

    NASA Astrophysics Data System (ADS)

    Fischer, Stefan; Johnson, Noah J. J.; Pichaandi, Jothirmayanantham; Goldschmidt, Jan Christoph; van Veggel, Frank C. J. M.

    2015-11-01

    Colloidal upconverter nanocrystals (UCNCs) that convert near-infrared photons to higher energies are promising for applications ranging from life sciences to solar energy harvesting. However, practical applications of UCNCs are hindered by their low upconversion quantum yield (UCQY) and the high irradiances necessary to produce relevant upconversion luminescence. Achieving high UCQY under practically relevant irradiance remains a major challenge. The UCQY is severely limited due to non-radiative surface quenching processes. We present a rate equation model for migration of the excitation energy to show that surface quenching does not only affect the lanthanide ions directly at the surface but also many other lanthanide ions quite far away from the surface. The average migration path length is on the order of several nanometers and depends on the doping as well as the irradiance of the excitation. Using Er3+-doped β-NaYF4 UCNCs, we show that very isotropic and thick (˜10 nm) β-NaLuF4 inert shells dramatically reduce the surface-related quenching processes, resulting in much brighter upconversion luminescence at simultaneously considerably lower irradiances. For these UCNCs embedded in poly(methyl methacrylate), we determined an internal UCQY of 2.0% ± 0.2% using an irradiance of only 0.43 ± 0.03 W/cm2 at 1523 nm. Normalized to the irradiance, this UCQY is 120× higher than the highest values of comparable nanomaterials in the literature. Our findings demonstrate the important role of isotropic and thick shells in achieving high UCQY at low irradiances from UCNCs. Additionally, we measured the additional short-circuit current due to upconversion in silicon solar cell devices as a proof of concept and to support our findings determined using optical measurements.

  19. The enhancement of fluorescence quantum yields of anilino naphthalene sulfonic acids by inclusion of various cyclodextrins and cucurbit[7]uril

    NASA Astrophysics Data System (ADS)

    Sueishi, Yoshimi; Fujita, Tomonori; Nakatani, Shinichiro; Inazumi, Naoya; Osawa, Yoshihiro

    2013-10-01

    The association constants (K) for the inclusion complexation of four kinds of cyclodextrins (CDs (β- and γ-), 2,6-di-O-methylated β-CD, and 2,3,6-tri-O-methylated β-CD) and cucurbit[7]uril (CB[7]) with 1,8- and 2,6-anilinonaphthalene sulfonic acids (ANSs) were determined from fluorescence spectra enhanced by inclusion. Various CDs and CB[7] form stable 1:1 inclusion complexes with 1,8- and 2,6-ANSs: K = 80-11 700 M-1 for 2,6-ANS and 50-195 M-1 for 1,8-ANS. The high stability of the inclusion complexes of 2,6-ANS with CB[7] and 2,6-di-O-methylated β-CD is shown. Further, we determined the fluorescence quantum yields (Φ values) for the inclusion complexes of ANSs by using a fluorescence spectrophotometer equipped with a half-moon unit. The Φ values of 1,8- and 2,6-ANSs were largely enhanced by the inclusion of methylated β-CDs and did not correlate with the degree of stability (K) of the inclusion complexes. We characterized the structures of the inclusion complexes by 2D ROESY-NMR measurements. In addition, the microenvironmental polarity inside the hydrophobic CD and CB[7] cavities was evaluated using the fluorescence probe 2,6-ANS. Based on the emission mechanism and the aspect of inclusion in a hydrophobic cavity, we have suggested that the microenvironmental polarity and viscosity for the excited state of ANS plays an important role for the Φ values of inclusion complexes.

  20. Quantum coherence enabled determination of the energy landscape in light-harvesting complex II.

    PubMed

    Calhoun, Tessa R; Ginsberg, Naomi S; Schlau-Cohen, Gabriela S; Cheng, Yuan-Chung; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R

    2009-12-24

    The near-unity efficiency of energy transfer in photosynthesis makes photosynthetic light-harvesting complexes a promising avenue for developing new renewable energy technologies. Knowledge of the energy landscape of these complexes is essential in understanding their function, but its experimental determination has proven elusive. Here, the observation of quantum coherence using two-dimensional electronic spectroscopy is employed to directly measure the 14 lowest electronic energy levels in light-harvesting complex II (LHCII), the most abundant antenna complex in plants containing approximately 50% of the world's chlorophyll. We observe that the electronically excited states are relatively evenly distributed, highlighting an important design principle of photosynthetic complexes that explains the observed ultrafast intracomplex energy transfer in LHCII. PMID:20014871

  1. Theoretical studies of excitons in type II CdSe/CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Miloszewski, Jacek M.; Tomić, Stanko; Binks, David

    2014-06-01

    We present a method for calculating exciton and bi-exciton energies in type-II colloidal quantum dots. Our methodology is based on an 8-band k · p Hamiltonian of the zinc- blend structure, which incorporates the effects of spin-orbit interaction, strain between the core and the shell and piezoelectric potentials. Exciton states are found using the configuration interaction (CI) method that explicitly includes the effects of Coulomb interaction, as well as exchange and correlation between many-electron configurations. We pay particular attention to accurate modelling of the electrostatic interaction between quasiparticles. The model includes surface polarization and self-polarization effects due to the large difference in dielectric constants at the boundary of the QD.

  2. Optical anisotropy in type-II ZnTe/ZnSe submonolayer quantum dots

    NASA Astrophysics Data System (ADS)

    Ji, H.; Dhomkar, S.; Wu, R.; Shuvayev, V.; Deligiannakis, V.; Tamargo, M. C.; Ludwig, J.; Lu, Z.; Smirnov, D.; Wang, A.; Kuskovsky, I. L.

    2016-06-01

    Linearly polarized photoluminescence is observed for type-II ZnTe/ZnSe submonolayer quantum dots (QDs). The comparison of spectral dependence of the degree of linear polarization (DLP) among four samples indicates that the optical anisotropy is mostly related to the elongation of ZnTe QDs. Numerical calculations based on the occupation probabilities of holes in px and py orbitals are performed to estimate the lateral aspect ratio of the QDs, and it is shown that it varies between 1.1 and 1.4. The value of anisotropic exchange splitting for bright excitonic states is found to be ˜200 μeV from the measurement of the degree of circular polarization as a function of the magnetic field. The results also show that heavy-light hole mixing ratio is about 0.16.

  3. Analysis of the photosystem II by modelling the fluorescence yield transients during 10 seconds after a 10 ns pulse

    NASA Astrophysics Data System (ADS)

    Belyaeva, Natalya E.; Schmitt, Franz-Josef; Paschenko, Vladimir Z.; Riznichenko, Galina Yu.; Rubin, Andrew B.

    2014-10-01

    The dynamics of the photosystem II (PS II) redox states is imitated over nine orders of magnitude in time. Our simulations focus on the information of the chlorophyll a fluorescence induced by a 10 ns laser flash. The PS II model analyzes differences in the PS II reaction between leaves (A. Thaliana, spinach) and thermophilic Chlorella cells.

  4. Photovoltaic detector based on type II heterostructure with deep AlSb/InAsSb/AlSb quantum well in the active region for the midinfrared spectral range

    SciTech Connect

    Mikhailova, M. P. Andreev, I. A.; Moiseev, K. D.; Ivanov, E. V.; Konovalov, G. G.; Mikhailov, M. Yu.; Yakovlev, Yu. P.

    2011-02-15

    Photodetectors for the spectral range 2-4 {mu}m, based on an asymmetric type-II heterostructure p-InAs/AlSb/InAsSb/AlSb/(p, n)GaSb with a single deep quantum well (QW) or three deep QWs at the heterointerface, have been grown by metal-organic vapor phase epitaxy and analyzed. The transport, luminescent, photoelectric, current-voltage, and capacitance-voltage characteristics of these structures have been examined. A high-intensity positive and negative luminescence was observed in the spectral range 3-4 {mu}m at high temperatures (300-400 K). The photosensitivity spectra were in the range 1.2-3.6 {mu}m (T = 77 K). Large values of the quantum yield ({eta} = 0.6-0.7), responsivity (S{sub {lambda}} = 0.9-1.4 A W{sup -1}), and detectivity (D*{sub {lambda}} = 3.5 Multiplication-Sign 10{sup 11} to 10{sup 10} cm Hz{sup 1/2} W{sup -1}) were obtained at T = 77-200 K. The small capacitance of the structures (C = 7.5 pF at V = -1 V and T = 300 K) enabled an estimate of the response time of the photodetector at {tau} = 75 ps, which corresponds to a bandwidth of about 6 GHz. Photodetectors of this kind are promising for heterodyne detection of the emission of quantum-cascade lasers and IR spectroscopy.

  5. Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, B.; Oszwałdowski, R.; Schweidenback, L.; Russ, A. H.; Pientka, J. M.; Tsai, Y.; Chou, W.-C.; Fan, W. C.; Murphy, J. R.; Cartwright, A. N.; Sellers, I. R.; Petukhov, A. G.; Žutić, I.; McCombe, B. D.; Petrou, A.

    2015-07-01

    We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe /(Zn ,Mn )Se system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the (Zn ,Mn )Te /ZnSe system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies EMP in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe /(Zn ,Mn )Se system the magnetic polaron shows conventional behavior with EMP decreasing with increasing temperature T and increasing magnetic field B . In contrast, EMP in the (Zn ,Mn )Te /ZnSe system has unconventional dependence on temperature T and magnetic field B ; EMP is weakly dependent on T as well as on B . We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.

  6. Electronic and optical properties of single excitons and biexcitons in type-II quantum dot nanocrystals

    SciTech Connect

    Koc, Fatih; Sahin, Mehmet E-mail: mehsahin@gmail.com

    2014-05-21

    In this study, a detailed investigation of the electronic and optical properties (i.e., binding energies, absorption wavelength, overlap of the electron-hole wave functions, recombination oscillator strength, etc.) of an exciton and a biexciton in CdTe/CdSe core/shell type-II quantum dot heterostructures has been carried out in the frame of the single band effective mass approximation. In order to determine the electronic properties, we have self-consistently solved the Poisson-Schrödinger equations in the Hartree approximation. We have considered all probable Coulomb interaction effects on both energy levels and also on the corresponding wave functions for both single exciton and biexciton. In addition, we have taken into account the quantum mechanical exchange-correlation effects in the local density approximation between same kinds of particles for biexciton. Also, we have examined the effect of the ligands and dielectric mismatch on the electronic and optical properties. We have used a different approximation proposed by Sahin and Koc [Appl. Phys. Lett. 102, 183103 (2013)] for the recombination oscillator strength of the biexciton for bound and unbound cases. The results obtained have been presented comparatively as a function of the shell thicknesses and probable physical reasons in behind of the results have been discussed in a detail.

  7. Determination of Phosphorescence Quantum Yield of Singlet Oxygen O 2( 1Δ g) Photosensitized by Phenalenone in Air-Saturated Carbon Tetrachloride

    NASA Astrophysics Data System (ADS)

    Shimizu, Okiyasu; Watanabe, Jun; Imakubo, Keiichi; Naito, Shizuo

    1998-11-01

    The phosphorescence quantum yield Φ P (=einsteins emitted/einsteins absorbed by sensitizer) of singlet oxygen (1O2) was measured for an air-saturated CCl4 solution of phenalenone (PH) used as a photosensitizer, by means of a photon-counting technique based on the use of a near-IR-sensitive photomultiplier. Employment of steady-state excitation allowed for the determination of the absolute quantum yield of Φ P=(1.38±0.05)×10-3 in CCl4. The result was obtained by direct comparison of the areas under the corrected emission spectra of 1O2 and of quinine bisulfate (QBS) in 1N H2SO4 as a luminescence standard.

  8. Accurate quantum yields by laser gain vs absorption spectroscopy - Investigation of Br/Br(asterisk) channels in photofragmentation of Br2 and IBr

    NASA Technical Reports Server (NTRS)

    Haugen, H. K.; Weitz, E.; Leone, S. R.

    1985-01-01

    Various techniques have been used to study photodissociation dynamics of the halogens and interhalogens. The quantum yields obtained by these techniques differ widely. The present investigation is concerned with a qualitatively new approach for obtaining highly accurate quantum yields for electronically excited states. This approach makes it possible to obtain an accuracy of 1 percent to 3 percent. It is shown that measurement of the initial transient gain/absorption vs the final absorption in a single time-resolved signal is a very accurate technique in the study of absolute branching fractions in photodissociation. The new technique is found to be insensitive to pulse and probe laser characteristics, molecular absorption cross sections, and absolute precursor density.

  9. Enhanced carrier multiplication in engineered quasi-type-II quantum dots

    PubMed Central

    Cirloganu, Claudiu M.; Padilha, Lazaro A.; Lin, Qianglu; Makarov, Nikolay S.; Velizhanin, Kirill A.; Luo, Hongmei; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.

    2014-01-01

    One process limiting the performance of solar cells is rapid cooling (thermalization) of hot carriers generated by higher-energy solar photons. In principle, the thermalization losses can be reduced by converting the kinetic energy of energetic carriers into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this process is enhanced in quantum dots, although not sufficiently high to considerably boost the power output of practical devices. Here we demonstrate that thick-shell PbSe/CdSe nanostructures can show almost a fourfold increase in the CM yield over conventional PbSe quantum dots, accompanied by a considerable reduction of the CM threshold. These structures enhance a valence-band CM channel due to effective capture of energetic holes into long-lived shell-localized states. The attainment of the regime of slowed cooling responsible for CM enhancement is indicated by the development of shell-related emission in the visible observed simultaneously with infrared emission from the core. PMID:24938462

  10. Enhanced carrier multiplication in engineered quasi-type-II quantum dots.

    PubMed

    Cirloganu, Claudiu M; Padilha, Lazaro A; Lin, Qianglu; Makarov, Nikolay S; Velizhanin, Kirill A; Luo, Hongmei; Robel, Istvan; Pietryga, Jeffrey M; Klimov, Victor I

    2014-01-01

    One process limiting the performance of solar cells is rapid cooling (thermalization) of hot carriers generated by higher-energy solar photons. In principle, the thermalization losses can be reduced by converting the kinetic energy of energetic carriers into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this process is enhanced in quantum dots, although not sufficiently high to considerably boost the power output of practical devices. Here we demonstrate that thick-shell PbSe/CdSe nanostructures can show almost a fourfold increase in the CM yield over conventional PbSe quantum dots, accompanied by a considerable reduction of the CM threshold. These structures enhance a valence-band CM channel due to effective capture of energetic holes into long-lived shell-localized states. The attainment of the regime of slowed cooling responsible for CM enhancement is indicated by the development of shell-related emission in the visible observed simultaneously with infrared emission from the core. PMID:24938462