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Sample records for cdse quantum dot

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

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Neetu, E-mail: singh.neetu1985@gmail.com; Kapoor, Avinashi [Department of Electronic Science, University of Delhi South Campus, New Delhi-110 021 (India); Kumar, Vinod [Department of Physics, University of the Free State, Bloemfontein, ZA9300 (South Africa); Mehra, R. M. [School of Engineering and Technology, Sharda University, Greater Noida-201 306, U.P. (India)

    2014-04-24

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

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

    International Nuclear Information System (INIS)

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

  3. Colloidal Synthesis And Characterization Of Cdse Quantum Dots Role Of CdSe Molar Ratio And Temperature

    OpenAIRE

    Hakan Aydamp305n; M. R. Karim; Mesut Balaban; Hilmi Unlu

    2015-01-01

    Semiconductor Cadmium selenide CdSe Quantum Dots QDs were synthesized via colloidal chemistry method at moderately lower growth temperatures. Optical absorption and photoluminescence PL spectroscopy techniques were used to characterize the optical properties of CdSe QDs. Optical properties of colloidal CdSe QDs were successfully controlled by changing the initial CdSe molar ratios and temperature. Optical absorption and PL spectrum both showed gradual red shift with increasing CdSe molar rati...

  4. CdSe Quantum Dots for Solar Cell Devices

    Directory of Open Access Journals (Sweden)

    A. B. Kashyout

    2012-01-01

    Full Text Available CdSe quantum dots have been prepared with different sizes and exploited as inorganic dye to sensitize a wide bandgap TiO2 thin films for QDs solar cells. The synthesis is based on the pyrolysis of organometallic reagents by injection into a hot coordinating solvent. This provides temporally discrete nucleation and permits controlled growth of macroscopic quantities of nanocrystallites. XRD, HRTEM, UV-visible, and PL were used to characterize the synthesized quantum dots. The results showed CdSe quantum dots with sizes ranging from 3 nm to 6 nm which enabled the control of the optical properties and consequently the solar cell performance. Solar cell of 0.08% performance under solar irradiation with a light intensity of 100 mW/cm2 has been obtained. CdSe/TiO2 solar cells without and with using mercaptopropionic acid (MPA as a linker between CdSe and TiO2 particles despite a Voc of 428 mV, Jsc of 0.184 mAcm-2, FF of 0.57, and η of 0.05% but with linker despite a Voc of 543 mV, Jsc of 0.318 mAcm-2 , FF of 0.48, and η of 0.08%, respectively.

  5. Exciton storage by Mn2+ in colloidal Mn2+-doped CdSe quantum dots

    NARCIS (Netherlands)

    Beaulac, R.; Archer, P.I.; van Rijssel, J.; Meijerink, A.; Gamelin, D.R.

    2008-01-01

    Colloidal Mn2+-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to τexc = 15 μs at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by ∼103 and are shown to arise from the creation of excitons by back energy transfer

  6. Highly conjugated water soluble CdSe quantum dots to multiwalled carbon nanotubes

    Institute of Scientific and Technical Information of China (English)

    Gui Zheng Zou

    2009-01-01

    Highly conjugated multiwalled carbon nanotube-quantum dot heterojunctions were synthesized by ethylene carbodiimide coupling procedure. The functional multiwalled carbon nanotube with carboxylic groups on sidewall could react with the amino group of L-cysteine capped CdSe quantum dots and then resulted in nanotube-quantum dot heterojunctions. Scanning electron microscopy was used to characterize the heterojunctions.

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

    Science.gov (United States)

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

    2005-01-01

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

  8. Colloidal Synthesis And Characterization Of Cdse Quantum Dots Role Of CdSe Molar Ratio And Temperature

    Directory of Open Access Journals (Sweden)

    Hakan Aydamp305n

    2015-08-01

    Full Text Available Semiconductor Cadmium selenide CdSe Quantum Dots QDs were synthesized via colloidal chemistry method at moderately lower growth temperatures. Optical absorption and photoluminescence PL spectroscopy techniques were used to characterize the optical properties of CdSe QDs. Optical properties of colloidal CdSe QDs were successfully controlled by changing the initial CdSe molar ratios and temperature. Optical absorption and PL spectrum both showed gradual red shift with increasing CdSe molar ratio and temperature. High-resolution transmission electron microscopy HRTEM technique were used to study the structural properties of CdSe QDs. Full width at half maximum FWHM values obtained from the emission spectrums were helped to prove the narrow size distribution which coincides with the matching results of HRTEM images and theoretical calculations.

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

    Energy Technology Data Exchange (ETDEWEB)

    Isnaeni,, E-mail: isnaeni@lipi.go.id; Sugiarto, Iyon Titok [Research Center for Physics, Indonesian Institute of Science, Building 442 Puspiptek Serpong, South Tangerang, Banten, Indonesia 15314 (Indonesia); Bilqis, Ratu; Suseno, Jatmiko Endro [Department of Physics, Diponegoro University, Jl. Prof. Soedarto, Tembalang, Semarang, Indonesia 50275 (Indonesia)

    2016-02-08

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

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

    Science.gov (United States)

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

    2016-02-01

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

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

    International Nuclear Information System (INIS)

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

  12. Enhancement of CdSe quantum dots luminescence by calcium ions

    International Nuclear Information System (INIS)

    Water soluble functionalized CdSe quantum dots (QDs) have been prepared via water based route technique by using safe and low cost materials at low temperature 75 °C. The XRD measurements of the functionalized CdSe quantum dots showed that these quantum dots have a cubic phase with zinc blend structure. The TEM measurements depicted that these quantum dots are mono-dispersed with spherical shape size about 4 nm. The HRTEM measurements confirmed that the prepared quantum dots have single crystalline cubic structure with lattice parameter 0.61 nm. The EDX measurements indicated that the prepared quantum dots are highly pure and there are no impurities in the structures. The influence of calcium metal ions on the FL intensity of the functionalized CdSe QDs was enhanced the FL intensity by 5-times at concentration 0.8 μM. The enhancement effect of Ca2+ ion on the fluorescence emission of CdSe QDs is found to be concentration dependence. - Highlights: ► Water soluble CdSe QDs have been prepared via a water based route technique. ► These QDs have a cubic phase with zinc blend structure. ► The FL intensity of CdSe QDs is enhanced due to Ca ions effect. ► The enhancement effect of Ca2+ ion FL of CdSe QDs is concentration dependence.

  13. Synthesis and characterization of CdSe colloidal quantum dots in organic solvent

    International Nuclear Information System (INIS)

    In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28-2.92 nm which is in good agreement with PL measurements. (authors)

  14. SYNTHESIS AND CHARACTERIZATION OF CdSe COLLOIDAL QUANTUM DOTS IN ORGANIC SOLVENT

    OpenAIRE

    Ion Geru; Olga Bordian; Constantin Loshmansky; Ion Culeac; Constantin Turta

    2014-01-01

    In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL) spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the rang...

  15. SYNTHESIS AND CHARACTERIZATION OF CdSe COLLOIDAL QUANTUM DOTS IN ORGANIC SOLVENT

    Directory of Open Access Journals (Sweden)

    Ion Geru

    2014-06-01

    Full Text Available In this paper we present experimental results on preparation and characterization of colloidal CdSe quantum dots in organic solvent. CdSe QDs were synthesized following a modified literature method. CdSe QDs were isolated by adding acetone to the cooled solution followed by centrifugation. CdSe QDs have been characterized by UV-Vis absorption and photoluminescent (PL spectroscopy. The average CdSe particles size estimated from the UV-Vis absorption spectra was found to be in the range 2.28-2.92 nm which is in good agreement with PL measurements.

  16. Composition-controlled optical properties of colloidal CdSe quantum dots

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties

  17. Composition-controlled optical properties of colloidal CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ayele, Delele Worku [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Department of Chemistry, Bahir Dar University, Bahir Dar (Ethiopia); Su, Wei-Nien, E-mail: wsu@mail.ntust.edu.tw [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Chou, Hung-Lung [Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Pan, Chun-Jern [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Hwang, Bing-Joe, E-mail: bjh@mail.ntust.edu.tw [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China)

    2014-12-15

    Graphical abstract: - Highlights: • The surface of CdSe QDs are modified with cadmium followed by selenium. • The optical properties of CdSe QDs can be controlled by manipulating the composition. • Surface compositional change affects the surface defects or traps and recombination. • The surface trapping state can be controlled by tuning the surface composition. • A change in composition shows a change in the carrier life time. - Abstract: A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

  18. Synthesis and size dependent optical studies in CdSe quantum dots via inverse micelle technique

    International Nuclear Information System (INIS)

    Cadmium selenide quantum dots (CdSe QDs) were successfully synthesized without using trioctylphosphine (TOP). The XRD pattern showed zinc-blend phase of the CdSe QDs. The absorption and PL spectra exhibit a strong blue shift as the QDs size decreases due to the quantum confinement effect. In addition, the quantum efficiency of CdSe QDs with TOP capping is higher than CdSe QDs with oleic acid capping. TEM image shows a spherical shape, compact and dense structure of CdSe QDs. A good agreement between the Tauc's model and experimentally measured absorption spectra of CdSe QDs is achieved. The FTIR peak at ∼1712 cm-1 spectra confirms the influence of oleic acid as a capping agent.

  19. Coherent phonons in CdSe quantum dots triggered by ultrafast electron transfer

    Directory of Open Access Journals (Sweden)

    Wachtveitl J.

    2013-03-01

    Full Text Available The origin of coherent oscillations in CdSe quantum dots and in the CdSe/methylviologen electron transfer system is studied. In CdSe/methylviologen coherent phonons are triggered by the electron transfer from the quantum dot to methylviologen.

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2013-11-12

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

  2. One pot synthesis of bi-linker stabilised CdSe quantum dots

    International Nuclear Information System (INIS)

    In this study we exploited the classic Murray's synthesis for generating a hydrophilic CdSe quantum dot system in a single step procedure, with the aim of directly obtaining a material responding to the characteristic of polarity required in many end applications. 6-phosphonohexanoic acid was used as both ligand for generating the active monomer during the synthesis of the quantum dots and final stabiliser. Diffraction measurements identified the cubic phase of cadmium selenide. Energy dispersive spectroscopy analysis revealed non-stoichiometric quantum dots, being the Cd/Se ratio 60/40. This feature suggests a configuration in which Cd2+ ions are present on the nanocrystal surface. Diffuse reflectance infrared Fourier transform analysis was applied in order to investigate the structure of the quantum dot system: the results indicate a configuration in which the carboxylic function of 6-phosphonohexanoic acid establishes only a partial interaction with the quantum dot surface, being set in a pseudo-ester configuration.

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

    Science.gov (United States)

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

    2012-10-01

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

  4. Synthesis of Highly Emissive CdSe Quantum Dots by Aqueous Precipitation Method

    OpenAIRE

    Bing Gao; Chao Shen; Shuanglong Yuan; Yunxia Yang; Guorong Chen

    2013-01-01

    CdSe quantum dots (QDs) with high quantum yield (QY) up to 76.57% are synthesized using the aqueous precipitation method. With the control of SeSO32- concentration in Se precursor, the nucleation speed and concentration of CdSe QDs are increased. The mass of obtained Cd2+ and Se2+ in nanocrystal is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). XRD and HRTEM are used to identify the crystal phase and morphology of the products which are pure CdSe crystals in th...

  5. Aqueous Synthesis and Characterization of TGA-capped CdSe Quantum Dots at Freezing Temperature

    OpenAIRE

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

    2012-01-01

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

  6. Synthesis of high quality CdSe quantum dots through a mild solution-phase synthetic route

    International Nuclear Information System (INIS)

    High quality CdSe quantum dots are synthesized through a solution-phase synthesis technique with Cd(CH3COO)2.2H2O and Na2SeSO3 as precursors. In this synthesis approach, the participation of a novel terpyridine derivative provides much better control over growth dynamics of CdSe quantum dots, resulting in the suppression of the Ostwald ripening process of the particle size distribution during growth. The CdSe quantum dots meet the all requirements of high quality quantum dots.

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

    OpenAIRE

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

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellul...

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

    Science.gov (United States)

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

    2015-05-01

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

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

    Science.gov (United States)

    Yi, Kui-Yu

    2016-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Qilin; Wang, Wenyong, E-mail: wwang5@uwyo.edu, E-mail: jtang2@uwyo.edu; Tang, Jinke, E-mail: wwang5@uwyo.edu, E-mail: jtang2@uwyo.edu [Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming 82071 (United States); Sabio, Erwin M. [Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071 (United States)

    2014-05-05

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

  11. Synthesis and characterization of monodisperse CdSe quantum dots in different organic solvents

    Institute of Scientific and Technical Information of China (English)

    He Rong; You Xiaogang; Tian Hongye; Gao Feng; Cui Daxiang; Gu Hongchen

    2006-01-01

    Nearly monodisperse CdSe quantum dots (QDs)have been prepared by a soft solution approach using air-stable reagents in different organic solvents.This scheme is a supplement to the conventional thermal decomposition of organometailic compounds at higher temperatures.CdSe nanocrystals of different sizes could be obtained by simply changing the solvent.This method is reproducible and simple and thus can be readily scaled up for industrial production.The reaction process was monitored by the temporal evolution of the UV-Vis absorption and room temperature photoluminensce spectra.The structures of the CdSe quantum dots were determined by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).The phase-transfer of oleic acid-stabilized CdSe nanocrystals into PBS buffer solutions was also studied for their potentials in biological applications.

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

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn; Chen, Guorong, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Zhang, Bo [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China)

    2014-05-21

    Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30 nm, and absorption peak from 475 nm to 510 nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO{sub 2} electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO{sub 2}'s to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2014-05-01

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

  15. The study of CdSe colloidal quantum dots synthesized in aqueous and organic media

    International Nuclear Information System (INIS)

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

  16. The synthesis of CdSe quantum dots with carboxyl group and study on their optical characteristics

    International Nuclear Information System (INIS)

    Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. Quantum dots are nanocrystal semiconductors which attract lots of research interests due to their peculiar optical properties. CdSe/ZnS quantum dots have been synthesized via pyrolysis of organometallic reagents. The color of the quantum dot changes from yellow-green to red as their size increases with reaction time. Photoluminescence quantum efficiency of CdSe quantum dots have been enhanced by passivating the surface of CdSe quantum dots with ZnS layers. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Insertion of CdSe quantum dots in ZnSe nanowires: Correlation of structural and chemical characterization with photoluminescence

    OpenAIRE

    Den Hertog, Martien; Elouneg-Jamroz, Miryam; Bellet-Amalric, Edith; Bounouar, Samir; Bougerol, Catherine; André, Régis; Genuist, Yann; Poizat, Jean-Philippe; Kheng, Kuntheak; Tatarenko, Serge

    2011-01-01

    ZnSe nanowires with CdSe quantum dot insertions were grown by molecular beam epitaxy using gold as a catalyst. Structural, chemical, and optical properties of the wires and quantum dots were characterized using electron microscopy and photoluminescence spectroscopy. We determined the crystalline structure, the chemical composition, and the size of the quantum dot and established a correlation between quantum dot size and luminescence. As expected, a blueshift of the luminescence was observed ...

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2015-02-01

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

  20. Surface-plasmon enhanced bright emission from CdSe quantum-dot nanocrystals

    OpenAIRE

    Okamoto, Koichi; Vyawahare, Saurabh; Scherer, Axel

    2006-01-01

    We obtained very bright light emission from CdSe quantum dots (QDs) by using the surface-plasmon (SP) coupling technique. 23-fold enhanced photoluminescence (PL) intensities and two-fold increased PL decay rates are observed when the QDs are located on evaporated gold films. This enhancement is not effective for CdSe cores with ZnS shells (ZnS/CdSe). The reason for this difference can be explained by using the SP dispersion diagram and by considering the SP coupling mechanism. We discuss the ...

  1. Aqueous Synthesis and Characterization of TGA-capped CdSe Quantum Dots at Freezing Temperature

    Directory of Open Access Journals (Sweden)

    Qizhuang Sun

    2012-07-01

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

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

    International Nuclear Information System (INIS)

    In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO2/OA-CdSe photoanode in a two-electrode device exhibited a photon-to-current conversion efficiency of 17.5% at 400 nm. At AM1.5G irradiation with 100 mW/cm2 light intensity, the QDSSCs based on OA-capped CdSe showed a power conversion efficiency of about 1%. The function of OA was to increase QD loading, extend the absorption range and possibly suppress the surface recombination.

  3. Study on the Interaction between CdSe Quantum Dots and Bovine Serum Albumin with Ultraviolet Visible Absorption Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    He You HAN; De Hong HU; Jian Gong LIANG; Zong Hai SHENG

    2006-01-01

    The interaction of CdSe quantum dots (QDs) with bovine serum albumin (BSA) has been investigated with ultraviolet visible absorption spectroscopy (UVAS). It was found that the absorption intensity of CdSe QDs significantly decreased after adding BSA solution, showing that CdSe QDs were bonded to BSA. The binding molar ratio was 1:1 and the binding constant was 9.7 × 106 L mol-1.

  4. Enhanced chemiluminescence CdSe quantum dots by histidine and tryptophan

    Science.gov (United States)

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

    2014-11-01

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

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

    Science.gov (United States)

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

    2016-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-14

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

  7. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    A Oudhia; P Bichpuria

    2014-02-01

    In the present work, we report green synthesis of tartaric acid (TA) and triethanolamine (TEA) capped cadmium selenide quantum dots (CdSe QDs) employing chemical bath deposition (CBD) method. The mechanism of capping using non-toxic binary capping agents is also discussed. Stable QDs of various sizes were obtained by varying pH of the bath. The structural, morphological and spectroscopic characterization of the as-prepared samples by XRD, SEM, optical absorption and photoluminescence (PL) is also reported.

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  10. Synthesis of Highly Emissive CdSe Quantum Dots by Aqueous Precipitation Method

    Directory of Open Access Journals (Sweden)

    Bing Gao

    2013-01-01

    Full Text Available CdSe quantum dots (QDs with high quantum yield (QY up to 76.57% are synthesized using the aqueous precipitation method. With the control of SeSO32- concentration in Se precursor, the nucleation speed and concentration of CdSe QDs are increased. The mass of obtained Cd2+ and Se2+ in nanocrystal is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES. XRD and HRTEM are used to identify the crystal phase and morphology of the products which are pure CdSe crystals in the cubic zinc blende phase and uniformly dispersed in the solution with the size between 2 nm and 2.3 nm. Results demonstrate that the emission wavelength of CdSe QDs is 500 nm~560 nm along with the increased temperature 50°C~90°C and prolonged time 5 min~25 min.

  11. Charge separation in contact systems with CdSe quantum dot layers

    International Nuclear Information System (INIS)

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO2 and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer (∼ 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface (recombination

  12. Charge separation in contact systems with CdSe quantum dot layers

    Energy Technology Data Exchange (ETDEWEB)

    Zillner, Elisabeth Franziska

    2013-03-06

    Quantum dot (QD) solar cells are a fast developing area in the field of solution processed photovoltaics. Central aspects for the application of QDs in solar cells are separation and transport of charge carriers in the QD layers and the formation of charge selective contacts. Even though efficiencies of up to 7% were reached in QD solar cells, these processes are not yet fully understood. In this thesis the mechanisms of charge separation, transport and recombination in CdSe QD layers and layer systems were studied. Charge separation was measured via surface photovoltage (SPV) at CdSe QD layers with thicknesses in the range of monolayers. To determine the influence of interparticle distance of QDs and trap states on the surface of QDs on charge separation, QDs with four different surfactant layers were studied. Layers of CdSe QDs were prepared on ITO, Si, SiO{sub 2} and CdS by dip coating under inert atmosphere. The layers were characterized by Rutherford backscattering spectrometry, UV-vis spectroscopy, step profilometry and scanning electron microscopy to determine the areal density, the absorption and thickness of CdSe QD monolayers. SPV measurements show that initial charge separation from the CdSe QDs on ITO only happened from the fi rst monolayer of QDs. Electrons, photo-excited in the fi rst monolayer of CdSe QDs, were trapped on the ITO surface. The remaining free holes were trapped in surface states and/or diffused into the neighboring QD layers. The thick surfactant layer ({approx} 1.6 nm) of pristine QDs had to be reduced by washing and/or ligand exchange for separation of photo-excited charge carriers. Both, interparticle distance and trap density, influenced the processes of charge separation and recombination. SPV transients of CdSe monolayers could be described by a single QD approximation model, based on Miller-Abrahams hopping of holes between the delocalized excitonic state, traps on the surface of the QD and the filled trap on the ITO surface

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

    International Nuclear Information System (INIS)

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

  14. Bacterial Interactions with CdSe Quantum Dots

    Science.gov (United States)

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

    2007-12-01

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

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

    Science.gov (United States)

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

    2013-12-26

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

  16. Fabrication of CdSe quantum dots/permutite luminescent materials

    Indian Academy of Sciences (India)

    Meihua Yu; Yilin Wang

    2015-09-01

    Permutite incorporating CdSe in mesopores has been prepared with a simple route. Firstly, mercaptosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH4 as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a partial dealumnization, which can introduce a large number of intracrystal mesopores, and the CdSe QDs were successfully incorporated in the mesopores with the wet impregnation method. Photoluminescence spectra, X-ray diffraction and scanning electron microscopy were used for the characterization of samples. The spectra analyses results showed that the illuminant colour of QDs/permutite powder was similar to the corresponding QDs colloid. X-ray diffraction measurements indicated that the (1 0 1) diffraction peak at 2 = 27° for QDs/permutite powder was the same as the raw permutite, and the energy-dispersive X-ray spectra demonstrated that Cd and Se elements existed in the CdSe QDs/permutite powder.

  17. EFFECT OF DIELECTRIC CONSTANT ON THE EXCITON GROUND STATE ENERGY OF CdSe QUANTUM DOTS

    Institute of Scientific and Technical Information of China (English)

    HUI PING

    2000-01-01

    The B-spline technique is used in the calculation of the exciton ground state energy based on the effective mass approximation (EMA) model.The exciton is confined in CdSe microspherical crystallites with a finite-height potential wall (dots).In this approach,(a) the wave function is allowed to penetrate to the outside of the dots; (b) the dielectric constants of the quantum dot and the surrounding material are considered to be different; and (c) the dielectric constant of the dots are size-dependent.The exciton energies as functions of radii of the dots in the range 0.5-3.5nm are calculated and compared with experimental and previous theoretical data.The results show that: (1) The exciton energy is convergent as the radius of the dot becomes very small.(2) A good agreement with the experimental data better than other theoretical results is achieved.(3) The penetration (or leaking) of the wave function and the difference of the dielectric constants in different regions are necessary for correcting the Coulomb interaction energy and reproducing experimental data.(4) The EMA model with B-spline technique can describe the status of excition confined in quantum dot very well.

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

    OpenAIRE

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

    2013-01-01

    We report the synthesis and optical characterisation of different triphenylamine-based hole capture materials able to anchor to CdSe quantum dots (QDs). Cyclic voltammetry studies indicate that these materials exhibit reversible electrochemical behaviour. Photoluminescence and transient absorption spectroscopy techniques are used to study interfacial charge transfer properties of the triphenylamine functionalized CdSe QDs. Specifically, we show that the functionalized QDs based on the most ea...

  19. Synthesis of CdSe quantum dots via paraffin liquid and oleic acid

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    This paper reported an efficient and rapid method to produce highly monodispersed CdSe quantum dots (QDs), in which the traditional tri10ylphosphine oxide (TOPO) was replaced by paraffin liquid as solvent and oleic acid as the reacting media. The experimental conditions and the properties of QDs had been studied in detail. The resulting samples were confirmed of uniform size distribution with transmission electronic microscopy (TEM), while UV-vis absorption and photoluminescence (PL) spectra clearly indicated that such synthesized QDs had good fluorescence properties.

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dradrach, K., E-mail: klaudia.dradrach@pwr.edu.pl; Bartkiewicz, S.; Miniewicz, A. [Department of Chemistry, Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2014-12-08

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

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

    Directory of Open Access Journals (Sweden)

    Denise Feder

    2011-12-01

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

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

    Science.gov (United States)

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

    2011-01-01

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

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

    Science.gov (United States)

    Avidan, Assaf; Pinkas, Iddo; Oron, Dan

    2012-04-24

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Kelley, Anne Myers

    2016-06-01

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

  7. Preparation of sodium titanate nanotubes modified by CdSe quantum dots and their photovoltaic characteristics

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Sodium titanate nanotubes have been prepared and modified chemically with CdSe quantum dots (QDs) using bifunctional modifiers (HS-COOH). Their photovoltaic characteristics have also been studied. The results indicate that the surface photovoltage response of nanotubes extends to the visible light region, and the intensity of surface photovoltage is enhanced after modification with CdSe QDs. The field-induced surface photovoltage spectroscopy (FISPS) shows that sodium titanate nanotubes have different photovoltaic response before and after modification. That is, the surface photovoltaic re-sponse of pure sodium titanate nanotubes increases with the enhancement of positive applied bias and decreases with the enhancement of negative applied bias. Meanwhile, the surface photovoltaic re-sponse of CdSe modified sodium titanate nanotubes is different from that of the pure sodium titanate nanotubes. The whole spectrum increases with the enhancement of applied bias at the first stage. However, when the applied bias reaches a certain value, the surface photovoltage response keeps in-creasing in some spectrum regions, while decreasing in other spectrum regions. This novel phe-nomenon is explained by using an electric field induced dipole model.

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Vibin, Muthunayagam [University of Kerala, Department of Biochemistry (India); Vinayakan, Ramachandran [National Institute for Interdisciplinary Science and Technology (CSIR), Photosciences and Photonics (India); John, Annie [Sree Chitra Tirunal Institute of Medical Sciences and Technology, Biomedical Technology Wing (India); Raji, Vijayamma; Rejiya, Chellappan S.; Vinesh, Naresh S.; Abraham, Annie, E-mail: annieab2@yahoo.co.in [University of Kerala, Department of Biochemistry (India)

    2011-06-15

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

  10. Directed Energy Transfer in Films of CdSe Quantum Dots: Beyond the Point Dipole Approximation

    DEFF Research Database (Denmark)

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

    2014-01-01

    Understanding of Förster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of...... QDs, so that the simple point-dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using...... distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate...

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

    OpenAIRE

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

    2015-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Magaryan K.A.

    2015-01-01

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

  13. Influence of nanocrystal size on the quantum dots sensitized solar cells’ performance with low temperature synthesized CdSe quantum dots

    International Nuclear Information System (INIS)

    Highlights: • Avoiding use of phosphine contained solvent makes the preparation of the CdSe QDs green. • The absorption range of the QDs plays an important role in the cell's performance. • Cu2S is more suitable than Pt as the counter electrode. - Abstract: The CdSe quantum dots (QDs) were synthesized with ethanol and glycerol under 50–160 °C in the present work. The reaction temperature is lower than the traditional solvent thermal method to fabricate the CdSe QDs around 250–350 °C. What’s more, the avoiding of the use of phosphine contained solvent make the whole reaction environmental friendly. Then 3-Mercaptopropionic (MPA) was used to exchange the CdSe QDs’ ligand of olic acid. After that, the MPA-capped CdSe QDs were tethered onto the TiO2’s substrate, which guarantee the high coverage of the CdSe QDs on the TiO2 photoanode and the absorption range of 450–560 nm of light harvest. Furthermore, through the results of the CdSe QD’s size for the cells’ performance, we compared the significance of the QDs’ absorption range, the electron injection from the conduction band of CdSe QDs’ to TiO2’s and polysulfide to the valance band of the CdSe QDs in the cells’ performance and discuss the mechanism to improve the efficiency of the QDSCs. Finally, the QDSCs with polysulfide solution and Cu2S as counter electrode show excellent cell performance with open-circuit voltage (Voc) of 0.6 V, short-circuit current density (Jsc) of 10.58 mA/cm2, fill factor (FF) of 0.564, and PCE of 3.7%

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

    Science.gov (United States)

    Ratnesh, R. K.; Mehata, Mohan Singh

    2015-09-01

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Veluthandath, Aneesh V.; Bisht, Prem B., E-mail: bisht@iitm.ac.in [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India)

    2015-12-21

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    International Nuclear Information System (INIS)

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

  20. White Light Electroluminescence by Organic-Inorganic Heterostructures with CdSe Quantum Dots as Red Light Emitters

    Directory of Open Access Journals (Sweden)

    Ilker Oner

    2011-01-01

    Full Text Available We have developed a white organic light-emitting diode featuring a double emission layer comprising a blue light-emitting conductive polymer as a host material for Cadmium Selenide (CdSe quantum dots as red light emitters and tris-(8-hydroxyquinoline aluminium thin layer for green light emission. The Commission Internationale de l'Eclairage coordinates of the emitting light of the device were found to be (0.32, 0.40 which were only slightly changed over a range of applied voltages between 5 and 10 volts. The use of CdSe nanocrystalline quantum dots (surface-stabilized with hexadecylamine/trioctylphosphine oxide ligands in the hybrid heterostructure with poly(9,9-di-n-octylfluorenyl-2,7-diyl conductive polymer was studied for a variety of CdSe concentrations developing the performance of the device in means of overcoming segregation problems in the blend. Besides, constituents' ratio was further examined for the exploration of possible energy transfer from polymer host material to the CdSe quantum dots as a key factor for well-balanced emission in the electroluminescent devices.

  1. Optical properties of electrically pumped CdSe quantum dot structures

    International Nuclear Information System (INIS)

    CdSe quantum dots (QDs) embedded into MgS barriers possess a high potential as active material for single photon emitters working at room temperature in the green spectral region because of the enhanced confinement of the carriers leading to an improved luminescence stability. We will present micro-electroluminescence (μ-EL) measurements on a resonant-cavity light emitting diode (RCLED) which was grown by molecular beam epitaxy containing an active region consisting of self-assembled CdSe QDs in a cavity and a distributed Bragg reflector. In this presentation we will focus on integrated μ-EL intensity measurements of the QD ensemble and single-QD emission lines in dependence on the applied voltage and sample temperature. The comparison of the results achieved for single QDs leads to an estimate of the sample temperature at the position of the active region during LED operation. In addition, we will compare these results to micro-photoluminescence measurements which were performed at the same sample position including the discussion of the change of PL characteristic by the variation of the external electric field

  2. Direct assembly of in situ templated CdSe quantum dots via crystalline lamellae structure of polyamide 66

    International Nuclear Information System (INIS)

    A simple concept is proposed for templating in situ synthesised CdSe quantum dots (QDs) into an organised nano-pattern using the crystalline lamellae structure of polyamide 66 (PA66). The morphology obtained for PA66 and the hybrid material on Si/SiOx solid substrate was characterised by means of atomic force microscope. Controlling the PA66 concentration in solution and the organic–inorganic interactions are found to be the keys factors to direct the assembly of CdSe QDs along the PA66 linear crystalline structure. This simple approach could be opened a new avenue for a large spectrum of innovative high-tech applications.

  3. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Li, Kuiying, E-mail: kuiyingli@ysu.edu.cn; Xue, Zhenjie

    2014-11-14

    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ E{sub g,nano-CdSe}. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs.

  4. Effect of ligand self-assembly on nanostructure and carrier transport behaviour in CdSe quantum dots

    International Nuclear Information System (INIS)

    Adjustment of the nanostructure and carrier behaviour of CdSe quantum dots (QDs) by varying the ligands used during QD synthesis enables the design of specific quantum devices via a self-assembly process of the QD core–shell structure without additional technologies. Surface photovoltaic (SPV) technology supplemented by X-ray diffractometry and infrared absorption spectroscopy were used to probe the characteristics of these QDs. Our study reveals that while CdSe QDs synthesized in the presence of and capped by thioglycolic acid, 3-mercaptopropionic acid, mercaptoethanol or α-thioglycerol ligands display zinc blende nanocrystalline structures, CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures, because different end groups in these ligands induce distinctive nucleation and growth mechanisms. Carboxyl end groups in the ligand served to increase the SPV response of the QDs, when illuminated by hν ≥ Eg,nano-CdSe. Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit photo-generated free charge carrier (FCC) transfer transitions of CdSe QDs illuminated by photon energy of 4.13 to 2.14 eV. The terminal hydroxyl group might better accommodate energy released in the non-radiative de-excitation process of photo-generated FCCs in the ligand's lowest unoccupied molecular orbital in the 300–580 nm wavelength region, when compared with other ligand end groups. - Highlights: • CdSe QDs modified by L-cysteine possess wurtzite nanocrystalline structures. • Carboxyl end groups in the ligand serve to increase the SPV response of CdSe QDs. • Terminal hydroxyl group in the ligand might accommodate non-radiative de-excitation process in CdSe QDs. • Increased length of the alkyl chains and side-chain radicals in the ligands partially inhibit carriers transport of CdSe QDs

  5. Hydrothermal Routes for the Synthesis of CdSe Core Quantum Dots

    OpenAIRE

    Schneider, Raphaël; Balan, Lavinia

    2012-01-01

    The synthesis of QDs in aqueous solution is still pursued in hopes of providing a material that is easily fabricated and functionalized. During many years, the synthesis of CdSe in aqueous media has been investigated with limited success due to the low quantum yields and poor crystallinity of the nanoparticles produced. Moreover, the fluorescence of the CdSe QDs obtained by this approach cannot be controlled over a wide range. Direct synthesis of CdSe QDs in water is however a promising alter...

  6. Chemical role of amines in the colloidal synthesis of CdSe quantum dots and their luminescence properties

    International Nuclear Information System (INIS)

    The role of organic amines in the colloidal synthesis of CdSe quantum dots (QDs) has been studied. CdSe QDs were synthesized from the source solutions containing 5 vol% of amines having various alkyl chain lengths, stereochemical sizes and electron donation abilities. The role of the additional amines was evaluated on the basis of the photoluminescence (PL) properties such as PL wavelength and intensity of the obtained CdSe QDs. The observed PL spectra were explained by the fact that the amines behaved as capping ligands on the surface of the QDs in the product colloidal solution and complex ligands for cadmium in the source solutions. It was shown that the particle size was controlled by the diffusion process depending on the mass and stereochemical shape of the amines, and the luminescence intensity increased with the increasing electron donation ability and capping density of the amines

  7. CdSe quantum dots stabilized by carboxylic-functionalized PVA: Synthesis and UV-vis spectroscopy characterization

    International Nuclear Information System (INIS)

    Quantum dots (QDs) have drawn the attention of the research community in the last decade due to their potential use in the fast developing area of nanotechnology. In this study, it is reported the synthesis and characterization CdSe nanoparticles using acid-functionalized poly(vinyl alcohol) (PVA-COOH) polymer as capping ligands via aqueous route at room temperature by methods of colloidal chemistry. Different molar concentrations of PVA-COOH were investigated aiming at producing stable nanoparticles using cadmium perchlorate and synthesized sodium selenosulfate. UV-vis spectroscopy was used to evaluate the kinetics and the relative stability of CdSe nanocrystals considering their size as-prepared and subsequent growth. The QDs sizes were estimated by the 'absorbance onset' from UV-vis spectroscopy spectra, considering theoretical and empirical methods. The results have indicated that precursor solution of PVA-COOH at concentration of 1.0 mol L-1 was effective on stabilizing colloidal CdSe QDs in aqueous suspension. Moreover, ultra-small CdSe nanocrystals were produced with calculated average particles size under 2.0 nm, indicating they were in the so-called 'quantum-size confinement range'. Hence, it was developed a relatively simple colloidal route using a single-step method to produce CdSe QDs water soluble and commercially available polymers that offers a window of opportunities to explore these novel nanohybrid materials.

  8. Bio-templated CdSe quantum dots green synthesis in the functional protein, lysozyme, and biological activity investigation

    International Nuclear Information System (INIS)

    Bifunctional fluorescence (CdSe Quantum Dots) – protein (Lysozyme) nanocomposites were synthesized at room temperature by a protein-directed, solution-phase, green-synthetic method. Fluorescence (FL) and absorption spectra showed that CdSe QDs were prepared successfully with Lyz. The average particle size and crystalline structure of QDs were investigated by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. With attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra and thermogravimetric (TG) analysis, it was confirmed that there is interaction between QDs and amide I, amide II groups in Lyz. FL polarization was measured and FL imaging was done to monitor whether QDs could be responsible for possible changes in the conformation and activity of Lyz. Interestingly, the results showed Lyz still retain the biological activity after formation of QDs, but the secondary structure of the Lyz was changed. And the advantage of this synthesis method is producing excellent fluorescent QDs with specifically biological function. -- Highlights: ► Lysozyme-directed green synthesis of CdSe quantum dots. ► Lysozyme still retain the biological activity after formation of CdSe. ► The method is the production of fluorescent QDs with highly specific and functions.

  9. Optical and photoelectric properties of nanocrystalline SnO{sub 2} - CdSe quantum dot structures

    Energy Technology Data Exchange (ETDEWEB)

    Dobrovolsky, Alexandr; Drozdov, Konstantin; Khokhlov, Dmitry [Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Vasiliev, Roman; Maslova, Olga [Faculty of Material Science, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation); Rumyantseva, Marina; Gaskov, Alexander; Ryabova, Ludmila [Faculty of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow (Russian Federation)

    2010-04-15

    Microstructure, optical and photoelectric properties of nanocrystalline porous SnO{sub 2} films on an insulating substrate with colloidal CdSe quantum dots as a sensitizer have been studied. SnO{sub 2} films consist of nanocrystallites with the average size of {proportional_to}20 nm combined into agglomerates as large as {proportional_to}1 {mu}m. CdSe quantum dots with the mean size of {proportional_to}3.5 nm were incorporated into porous SnO{sub 2} films by dipping the substrates into a colloidal solution of CdSe quantum dots. Transport and photoelectric properties of the structures were studied in the temperature interval 77 - 300 K. Optical properties were investigated in the visible spectral range. Persistent photoconductivity at the room temperature has been observed. Possible mechanisms of the persistent photoconductivity for this composite system are discussed. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Annealing Effect on Photovoltaic Performance of CdSe Quantum-Dots-Sensitized TiO2 Nanorod Solar Cells

    Directory of Open Access Journals (Sweden)

    Yitan Li

    2012-01-01

    Full Text Available Large area rutile TiO2 nanorod arrays were grown on F:SnO2 (FTO conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs were deposited onto single-crystalline TiO2 nanorod arrays by a chemical bath deposition (CBD method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO2 nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dots-sensitized TiO2 nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing treatment. At the same time, an improved photovoltaic performance was obtained for quantum-dots-sensitized solar cell using the annealed CdSe-TiO2 nanostructure electrode. The power conversion efficiency improved from 0.59% to 1.45% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by annealing treatment.

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

    Science.gov (United States)

    Powell, Lauren C. J.

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

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

    Science.gov (United States)

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

    2016-08-01

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

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

    Science.gov (United States)

    Deepika; Dhar, Rakesh; Mohan, Devendra

    2015-12-01

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

  14. A sensitive electrochemical aptasensor based on water soluble CdSe quantum dots (QDs) for thrombin determination

    Energy Technology Data Exchange (ETDEWEB)

    Li Yanfen; Han Min [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Bai Hongyan [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); College of Biological and Chemical Engineering, Jiaxing College, Jiaxing 314001 (China); Wu Yong [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Dai Zhihui, E-mail: daizhihuii@njnu.edu.cn [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China); Bao Jianchun, E-mail: baojianchun@njnu.edu.cn [Jiangsu Laboratory of New Power Batteries, Jiangsu Key Laboratory of Biofuctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097 (China)

    2011-08-01

    A novel aptamer biosensor with easy operation and good sensitivity, specificity, stability and reproducibility was developed by immobilizing the aptamer on water soluble CdSe quantum dots (QDs) modified on the top of the glassy carbon electrode (GCE). Methylene blue (MB) was intercalated into the aptamer sequence and used as an electrochemical marker. CdSe QDs improved the electrochemical signal because of their larger surface area and ion centers of CdSe QDs may also had a major role on amplifying the signal. The higher ion concentration caused more combination of aptamer which caused larger signal. The thrombin was detected by differential pulse voltammetry (DPV) quantitatively. Under optimal conditions, the two linear ranges were obtained from 3 to 13 {mu}g mL{sup -1} and from 14 to 31 {mu}g mL{sup -1}, respectively. The detection limit was 0.08 {mu}g mL{sup -1} at 3{sigma}. The constructed biosensor had better responses compared with that in the absence of the CdSe QDs immobilizing. The control experiment was also carried out by using BSA, casein and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by fluorescence method which could provide a promising platform for fabrication of aptamer based biosensors.

  15. Direct assembly of in situ templated CdSe quantum dots via crystalline lamellae structure of polyamide 66

    Energy Technology Data Exchange (ETDEWEB)

    Cheval, Nicolas; Brooks, Richard [University of Nottingham, Division of Materials, Mechanics and Structures, Faculty of Engineering (United Kingdom); Fahmi, Amir, E-mail: Amir.Fahmi@hochschule-Rhein-waal.de [Rhein-Waal University of Applied Sciences, Faculty of Technology and Bionics (Germany)

    2012-03-15

    A simple concept is proposed for templating in situ synthesised CdSe quantum dots (QDs) into an organised nano-pattern using the crystalline lamellae structure of polyamide 66 (PA66). The morphology obtained for PA66 and the hybrid material on Si/SiO{sub x} solid substrate was characterised by means of atomic force microscope. Controlling the PA66 concentration in solution and the organic-inorganic interactions are found to be the keys factors to direct the assembly of CdSe QDs along the PA66 linear crystalline structure. This simple approach could be opened a new avenue for a large spectrum of innovative high-tech applications.

  16. Cytotoxic effect of CdSe quantum dots on mouse embryonic development

    Institute of Scientific and Technical Information of China (English)

    Wen-hsiung CHAN; Nion-heng SHIAO

    2008-01-01

    Aim: The aim of this study was to examine the cytotoxic effect of quantum dots (QD), a novel luminescent material, on early post-implantation embryonic development. Methods: Mouse blastocysts were incubated in medium with or without CdSe-core QD (250 or 500 nmol/L) for 24 h. Cell apoptosis was analyzed by terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling assay and Annexin V/propidium iodide staining, and proliferation was investigated by dual differential staining. Pre-implantation and post-implantation development was assessed by in vitro and in vivo analyses, respectively. Results: The apoptotic staining analysis showed that CdSe-core QD induced apoptosis in mouse blastocysts in a dose-dependent manner. Pretreatment of blastocysts with CdSe-core QD inhibited cell proliferation, primarily in the inner cell mass. CdSe-core QD also inhibited post-implantation embryonic development; fewer CdSe-core QD-pretreated blastocysts reached the later stages of development com-pared to the controls. The pre-implantation development of morulas into blasto-cysts was also inhibited by CdSe-core QD. Furthermore, CdSe-core QD at 500 nmol/L were associated with resorption of post-implantation blastocysts and a decrease in fetal weight. The cytotoxicity of CdSe QD in embryonic development was significantly reduced by the addition of a ZnS coating. Conclusion: Our results show that CdSe-core QD induce apoptosis in mouse blastocysts, inhibit cell proliferation, retard early post-implantation blastocyst development, and in-crease early-stage blastocyst death in vitro and in vivo.

  17. Hyperbranched polyether hybrid nanospheres with CdSe quantum dots incorporated for selective detection of nitric oxide

    DEFF Research Database (Denmark)

    Liu, Shuiping; Jin, Lanming; Chronakis, Ioannis S.;

    2014-01-01

    In this work, hybrid nanosphere vehicles consisting of cadmium selenide quantum dots (CdSe QDs) were synthesized for nitric oxide (NO) donating and real-time detecting. The nanospheres with QDs being encapsulation have spherical outline with dimension of ~127 nm. The fluorescence properties of the...... mHP conjugated QDs are sensitivity and high selectivity for NO against oxidation products from NO. The QDs-mHP-NO nanospheres provide perspectives for designing a new class of biocompatible NO donating and imaging systems....

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

    Science.gov (United States)

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

    2013-03-01

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

  19. Au2+ ion-beam irradiation effects on optical properties of CdSe and CdS quantum dots

    International Nuclear Information System (INIS)

    The effects of Au+ ion irradiation on the optical properties of CdS and CdSe quantum dots synthesized by chemical methods are studied. The ion-induced changes are studied using UV/Vis absorption, fluorescence spectroscopy and transmission electron microscopy experimental methods. It is observed that the size of the particle is found to increase with the ion fluence resulting in a shift of optical absorption peak to longer wavelength and confirmed by transmission electron microscopy measurements. The nonlinear optical properties are studied through Z-scan technique. These quantum dots show multiphoton absorption properties with 800 nm wavelength, 110 femtosecond laser pulse excitations. The photoluminescence studies show the emission peak shift to higher wavelength with the ion fluence

  20. Surface plasmon resonance enhanced photoluminescence from Au coated periodic arrays of CdSe quantum dots and polymer composite thin film

    International Nuclear Information System (INIS)

    We have fabricated an arrayed CdSe quantum dots composite thin film that can enhance the photoluminescence of CdSe under the 488 nm laser irradiation by tuning the gold surface plasmon resonance frequency. This thin film consists of a gold coated periodic array of hybrid material of CdSe and poly(methyl methacrylate) on indium tin oxide coated glass substrate. The main surface plasmon resonance was red shifted as we increased the column diameter of the array. By adjusting the column diameters and lattice constants of the array to coincide with the 488 nm excitation wavelength, an evident increase in luminescence intensity was obtained due to the surface plasmon resonance of gold. As a result of likely efficient energy transfer from gold surface plasmon resonance to CdSe, the photoluminescence intensity of CdSe has been increased to 248% at 570 nm. This composite film has many potential applications in high efficient optoelectronic devices

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

    Science.gov (United States)

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

    2012-12-01

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2016-06-15

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

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

    Science.gov (United States)

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

    2004-09-01

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

  5. Biomimetic Synthesis of CdSe Quantum Dots through Emulsion Liquid Membrane System of Gas-Liquid Transport

    Institute of Scientific and Technical Information of China (English)

    LIU,LU(刘璐); WU,Qing-Sheng,(吴庆生); DING,Ya-Ping(丁亚平); LIU,Hua-Jie(柳华杰); ZHANG,Bao-Quan(张保权)

    2004-01-01

    The cadmium selenide quantum dots (QD) have been synthesized by template-control in an emulsion liquid membrane system.The system consisted of kerosene as solvent,L152 (dialkylene succinimide) as surfactant,N7301 (trialiphatic amine,R3N,R=Cs-C10) as carrier,0.1 mol/L CdC12 solution as internal-aqueous phase and H2Se gas as external phase.Additive organic template agent in internal-aqueous phase was necessary to form CdSe QD.The influence of the nature of template and its concentration on sizes of the formed CdSe QD has also been studied.Transmission electron microscopy showed that the sizes of the products could be controlled down to 3-4nm.X-ray diffraction analysis revealed that the crystals had cubic structure.The formation process and the optical properties of CdSe QD have also been presented.

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

    Science.gov (United States)

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

    2015-01-01

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

  7. Influence of the solvent environments on the spectral features of CdSe quantum dots with and without ZnS shell

    Energy Technology Data Exchange (ETDEWEB)

    Ibnaouf, K.H., E-mail: kheo90@gmail.com [Al Imam Mohammad Ibn Saud Islamic University (IMSIU), Physics Department, College of Science, P.O. Box 90905, Riyadh 11623 (Saudi Arabia); Prasad, Saradh; Al Salhi, M.S.; Hamdan, A. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Research Chair for Laser Diagnosis of Cancer, King Saud University (Saudi Arabia); Zaman, M.B. [CEREM, College of Engineering, King Saud University (Saudi Arabia); Advanced Medical Research Institute of Canada, Sudbury (Canada); El Mir, L. [Al Imam Mohammad Ibn Saud Islamic University (IMSIU), Physics Department, College of Science, P.O. Box 90905, Riyadh 11623 (Saudi Arabia)

    2014-05-01

    The spectral properties of 5 nm size of bare CdSe and (CdSe)ZnS core–shell quantum dots (QDs) have been recorded and investigated under different solvent environments with different polarities and different concentrations. The results showed that the spectral profile of absorption did not change for both quantum dots in different solvents under a wide range of concentrations. On the other hand, the photoluminescence (PL) spectra of (CdSe)ZnS core–shell quantum dots in non-polar solvents showed two bands; the primary around 420 nm and the secondary around 620 nm. In contrast, the PL spectra of bare CdSe in non-polar solvents, showed a very strong band around 590 nm, with a total absence of the primary wavelength band at 420 nm. Under high polar solvent environments, bare CdSe showed a new peak around 420 nm, which was totally absent in non-polar solvent. Therefore, the solvent plays an important role in the PL spectra of bare CdSe and (CdSe)ZnS core–shell quantum dots.

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

    International Nuclear Information System (INIS)

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

  9. Poly(3-hexylthiophene) - CdSe quantum dot bulk heterojunction solar cells: Influence of the functional end-group of the polymer

    KAUST Repository

    Palaniappan, Kumaranand

    2009-06-23

    The synthesis of H/thiol terminated P3HT from Br/allyl-terminated P3HT precursor was analyzed. The photovoltaic response of blends were prepared of H/thiol terminated P3HT with spherical CdSe quantum dots(QD) and compares the results with regioregular H/Br and Br/aryl-terminated P3HT. Phase segregation was carried by mixing relatively polar pyridine treated CdSe QD with nonpolar P3HT. The experiment revealed that a high loading of CdSe is necessary for an efficient charge transport and different loading ratios of CdSe has been investigated to correlate the photovoltaic response as a function of ration between donor H/thiol-P3ht polymer and acceptor Cdse QD. The results show that H/Br-P3HT, H/thiol- and Br/allyl-terminated P3HT exhibits better performance and Cdse quantum dots were used to obtain results.

  10. Facile solution growth of vertically aligned ZnO nanorods sensitized with aqueous CdS and CdSe quantum dots for photovoltaic applications

    Directory of Open Access Journals (Sweden)

    Luan Chunyan

    2011-01-01

    Full Text Available Abstract Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate. CdS and CdSe colloidal quantum dots are assembled onto ZnO nanorods array using water-soluble nanocrystals capped as-synthesized with a short-chain bifuncional linker thioglycolic acid. The solar cells co-sensitized with both CdS and CdSe quantum dots demonstrate superior efficiency compared with the cells using only one type of quantum dots. A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55. The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

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

    Science.gov (United States)

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

    2016-05-01

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

  12. Boosting the cell efficiency of CdSe quantum dot sensitized solar cell via a modified ZnS post-treatment

    International Nuclear Information System (INIS)

    Highlights: • Large improvement of the cell efficiency of CdSe QDSSC was achieved through a modified ZnS post-treatment by introducing a ZnSe in between CdSe QDs and ZnS • The introduction of ZnSe in post-treatment increased the cell stability. • The thickness of ZnSe was found to be crucial. • The role of ZnSe is ascribed to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality. -- Abstract: We report here a large improvement of cell performance of CdSe quantum dot sensitized solar cell (QDSSC) by a modified ZnS post-treatment, being carried out by introducing a ZnSe thin layer before ZnS deposition through a successive ion layer adsorption reaction (SILAR) method. CdSe quantum dots were deposited onto TiO2 surface using a chemical bath deposition method. Photovoltaic measurements showed that the introduction of ZnSe layer can significantly increase the photocurrent of CdSe QDSSC, resulting in a large enhancement of the solar energy conversion efficiency of the cell. On variation of the numbers of ZnSe deposition cycle, the effect of the thickness of ZnSe was investigated. The maximum energy conversion efficiency of 3.46% was achieved for CdSe QDSSC with ZnSe/ZnS treatment, showing a 22% increment compared to that of with ZnS treatment. Moreover, it was found that the introduction of ZnSe improved the stability of CdSe QDSSC. The benefit role of ZnSe was ascribed to its intermediate lattice parameter to CdSe and ZnS, which leads to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality

  13. Correlation between crystal growth and photosensitization of nanostructured TiO2 electrodes using supporting Ti substrates by self-assembled CdSe quantum dots

    International Nuclear Information System (INIS)

    Crystal growth of semiconductor quantum dots (QDs) adsorbed on nanostructured TiO2 electrodes is important not only for crystallographic studies but also for improving the photovoltaic efficiency of semiconductor-sensitized solar cells. In this study, nanostructured TiO2 electrodes using supporting Ti substrates were prepared. These electrodes are then adsorbed with self-assembled CdSe QDs as photosensitizers to investigate the crystal growth and photoelectrochemical current properties. Average diameters of the CdSe QDs can be estimated from optical absorption spectra by using photoacoustic (PA) technique. PA technique is a powerful tool for evaluating the optical absorption of opaque and scattered samples because of the detection by photothermal phenomenon. When the adsorption time increases, the CdSe QDs diameter increases and then shows saturation for all the cases. Normal solution growth plus suppression (negative growth) contributions can be derived by PA spectroscopic analysis. Both of them depend on adsorption temperatures for CdSe QDs formation. Photosensitization of the nanostructured TiO2 electrodes in the visible region resulting from CdSe QDs deposition can be clearly observed. Incident photon to current conversion efficiency (IPCE) of CdSe QDs adsorbed at high temperature formation is smaller than that adsorbed at low temperature one, indicating the increase of recombination centers with increasing adsorption temperature. This implies that negative growth, or dissolving effect, produces much more recombination centers inside of CdSe QDs and/or interface between the QDs and TiO2

  14. Morphologically controlled electrodeposition of CdSe on mesoporous TiO2 film for quantum dot-sensitized solar cells

    International Nuclear Information System (INIS)

    Highlights: • CdSe QDs were deposited onto mesoporous TiO2 film via a one-step electrodeposition method. • The morphology and microstructure of TiO2/CdSe photoanodes can be controlled by electrodeposition current density. • A ZnS coating layer and thermal annealing could further enhance the performance of the TiO2/CdSe photoanodes. • A maximum power conversion efficiency of 2.72% was achieved with the optimum TiO2/CdSe/ZnS photoanodes. -- Abstract: CdSe quantum dots (QDs)-sensitized mesoporous TiO2 (TiO2/CdSe) films were fabricated using a facile one-step electrodeposition method in an aqueous electrolyte. This technique has the advantage of being simple, low cost, and easily scalable to the sensitization of large-area panels. By adjusting the electrodeposition current density, the morphology and microstructure of the prepared TiO2/CdSe films can be precisely controlled, which influences the photovoltaic performances of quantum dot-sensitized solar cells based on the TiO2/CdSe films. At a moderate current density of 0.2 mA cm−2, CdSe QDs can penetrate deep into the inner pores of the mesoporous TiO2 film, thus leading to a dense and uniform distribution of QDs throughout the whole TiO2 matrix, while higher current densities result in growth of larger, isolated CdSe nanoclusters. Furthermore, a ZnS passivation layer coated on TiO2/CdSe photoanodes and thermal annealing could significantly improve the photovoltaic performance. As a result, a quantum dot-sensitized solar cell based on a TiO2/CdSe/ZnS photoanode (350 °C, 30 min calcination), polysulfide electrolyte and Pt counter electrode achieves a power conversion efficiency of 2.72% under AM 1.5 G one sun illumination

  15. Many-body pseudopotential theory of excitons in InP and CdSe quantum dots

    International Nuclear Information System (INIS)

    We present a pseudopotential approach to the calculation of the excitonic spectrum of semiconductor quantum dots. Starting from a many-body expansion of the exciton wave functions in terms of single-substitution Slater determinants constructed from pseudopotential single-particle wave functions, our method permits an accurate and detailed treatment of the intraconfiguration electron-hole Coulomb and exchange interactions, while correlation effects can be included in a controlled fashion by allowing interconfiguration coupling. We calculate the exciton fine structure of InP and CdSe nanocrystals in the strong-confinement regime. We find a different size dependence for the electron-hole exchange interaction than previously assumed (i.e., R-2 instead of R-3). Our calculated exciton fine structure is compared with recent experimental results obtained by size-selective optical spectroscopies. copyright 1999 The American Physical Society

  16. A nanocomposite prepared from helical carbon nanotubes, polyallylamine hydrochloride and CdSe quantum dots for electrochemiluminescent determination of dopamine

    International Nuclear Information System (INIS)

    A nanocomposite consisting of helical carbon nanotubes, polyallylamine hydrochloride and CdSe quantum dots was synthesized and used for the electrochemiluminescent determination of dopamine in presence of peroxodisulfate. The nanocomposite was characterized by transmission electron microscopy, UV-absorption and photoluminescence spectroscopy. The electrochemical process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimized conditions, the ECL intensity decreases linearly with the concentration of dopamine in the 1.0 × 10-9 mol · L-1 to 2.0 × 10-5 mol · L-1 range, with a 0.2 × 10-9 mol · L-1 detection limit. The method represents a rapid, simple and sensitive protocol for the determination of dopamine. (author)

  17. Formulating CdSe quantum dots for white light-emitting diodes with high color rendering index

    Energy Technology Data Exchange (ETDEWEB)

    Li, Fei [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100190 (China); Li, Wan-Nan [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Fu, Shao-Yun, E-mail: syfu@mail.ipc.ac.cn [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Xiao, Hong-Mei [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-10-25

    Generation of white light using CdSe quantum dots (QDs) alone presents exciting possibilities for solid state lighting technology. In this work, Cd(Ac){sub 2}·2H{sub 2}O and Na{sub 2}SeSO{sub 3} are used as precursors to synthesize CdSe-QDs with an average diameter ranging from 2.77 to 4.65 nm at the low temperature from 60 to 180 °C. Smaller CdSe-QDs with an average diameter of 2.29 nm are got by an oxidation etching process using H{sub 2}O{sub 2} as oxidant. The structural and optical properties of these QDs are investigated and proper formulation of CdSe QDs with various sizes is carefully designed to achieve white light with a high color rendering index (CRI). It is observed for the first time that the as-prepared white light-emitting diodes from single CdSe-QDs show the Commission Inernationale del’Eclairage coordinate (CIE) of (0.30,0.34) very close to that (0.33,0.33) of pure white light and a high CRI of 84. Owing to these advantages, the as-prepared white light-emitting diodes from a single compound are promising for lighting applications. - Highlights: • CdSe-quantum dots (QDs) with a continuously changing size from 2.31 to 4.74 nm are prepared. • The obtained CdSe-QDs emit lights with tunable colors in the whole visible range. • The obtained mixture sample generates white light with a high color rendering index of 84. • The sample yields white light with the CIE coordinate (0.30, 0.34) very close to that of pure white light.

  18. Citrate-capped quantum dots of CdSe for the selective photometric detection of silver ions in aqueous solutions

    International Nuclear Information System (INIS)

    A simple strategy for the synthesis of water soluble, luminescent, citrate-capped CdSe quantum dots (Q-CdSe) and their applications to selective detection of silver ions are described. The steady state photoluminescence (PL) spectra show single, narrow emission band at ca. 554 nm without any contribution from the trap states. The effect of various ions including physiologically important metal ions (viz. K+, Ca2+, Fe3+, Zn2+, Mg2+, Mn2+, Cu2+, Ag+, Pb2+ and Cd2+), on the PL intensity of citrate-capped Q-CdSe has been studied. Among these, selective luminescence quenching with Ag+ ion was found to be predominant. Under the optimum conditions, the response was linear between 1.7 and 18 μM. The quenching constant KSV was found to be ca. 3.4 x 105 M-1. The mechanism of photoluminescence quenching of Q-CdSe by metal ions (Ag+) is also discussed. Based on these studies, the potential use of Q-CdSe as a luminescent probe for the selective detection of silver ion has been proposed. -- Graphical abstract: A simple strategy for the synthesis of water soluble, luminescent, citrate-capped quantum dots of CdSe (Q-CdSe) has been developed. The effect of various ions including physiologically important metal ions (viz. K+, Ca2+, Fe3+, Zn2+, Mg2+, Mn2+, Cu2+, Ag+, Pb2+ and Cd2+), on the luminescence intensity of citrate-capped Q-CdSe has been studied. Among these, a significant luminescence quenching only by Ag+ ions was observed which suggests the potential use of Q-CdSe as a luminescent sensor for the selective optical detection of silver ions in a physiological condition.

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

    International Nuclear Information System (INIS)

    Generation of white light using CdSe quantum dots (QDs) alone presents exciting possibilities for solid state lighting technology. In this work, Cd(Ac)2·2H2O and Na2SeSO3 are used as precursors to synthesize CdSe-QDs with an average diameter ranging from 2.77 to 4.65 nm at the low temperature from 60 to 180 °C. Smaller CdSe-QDs with an average diameter of 2.29 nm are got by an oxidation etching process using H2O2 as oxidant. The structural and optical properties of these QDs are investigated and proper formulation of CdSe QDs with various sizes is carefully designed to achieve white light with a high color rendering index (CRI). It is observed for the first time that the as-prepared white light-emitting diodes from single CdSe-QDs show the Commission Inernationale del’Eclairage coordinate (CIE) of (0.30,0.34) very close to that (0.33,0.33) of pure white light and a high CRI of 84. Owing to these advantages, the as-prepared white light-emitting diodes from a single compound are promising for lighting applications. - Highlights: • CdSe-quantum dots (QDs) with a continuously changing size from 2.31 to 4.74 nm are prepared. • The obtained CdSe-QDs emit lights with tunable colors in the whole visible range. • The obtained mixture sample generates white light with a high color rendering index of 84. • The sample yields white light with the CIE coordinate (0.30, 0.34) very close to that of pure white light

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

    Science.gov (United States)

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

    2012-09-01

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

  1. Au-assisted growth of anisotropic and epitaxial cdse colloidal nanocrystals via in situ dismantling of quantum dots

    KAUST Repository

    Fernàndez-Altable, Víctor

    2015-03-10

    Metallic nanocrystals have been revealed in the past years as valuable materials for the catalytic growth of semiconductor nanowires. Yet, only low melting point metals like Bi have been reported to successfully assist the growth of elongated CdX (X = S, Se, Te) systems in solution, and the possibility to use plasmonic noble metals has become a challenging task. In this work we show that the growth of anisotropic CdSe nanostructures in solution can also be efficiently catalyzed by colloidal Au nanoparticles, following a preferential crystallographic alignment between the metallic and semiconductor domains. Noteworthy, we report the heterodox use of semiconductor quantum dots as a homogeneous and tunable source of reactive monomer species to the solution. The mechanistic studies reveal that the in situ delivery of these cadmium and chalcogen monomer species and the formation of AuxCdy alloy seeds are both key factors for the epitaxial growth of elongated CdSe domains. The implementation of this method suggests an alternative synthetic approach for the assembly of different semiconductor domains into more complex heterostructures.

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

    International Nuclear Information System (INIS)

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

  3. A Novel Approach to the Fabrication of CdSe Quantum Dots in Aqueous Solution: Procedures for Controlling Size, Fluorescence Intensity, and Stability over Time

    Directory of Open Access Journals (Sweden)

    M. J. Almendral-Parra

    2014-01-01

    Full Text Available This paper report a straightforward approach for the synthesis of CdSe quantum dots (CdSe QDs in aqueous solution. This method, performed in homogeneous phase, affords optimal sizes and high quantum yields for each application desired. It is an a la carte procedure for the synthesis of nanoparticles aimed at their later application. By controlling the experimental conditions, CdSe QDs of sizes ranging between 2 and 6 nm can be obtained. The best results were achieved in an ice-bath thermostated at 4°C, using mercaptoacetic acid as dispersant. Under these conditions, a slow growth of quantum nanocrystals was generated and this was controlled kinetically by the hydrolysis of SeSO32- to generate Se2-   in situ, one of the forming species of the nanocrystal. The organic dispersant mercaptoacetate covalently binds to the Cd2+ ion, modifying the diffusion rate of the cation, and plays a key role in the stabilization of CdSe QDs. In optimum conditions, when kept in their own solution CdSe QDs remain dispersed over 4 months. The NPs obtained under optimal conditions show high fluorescence, which is a great advantage as regards their applications. The quantum efficiency is also high, owing to the formation under certain conditions of a nanoshell of Cd(OH2, values of 60% being reached.

  4. Magnetic field and position effects on the absorption coefficient of a shallow donor in CdSe quantum dot

    International Nuclear Information System (INIS)

    The influence of impurity position, magnetic field and size on the donor binding energy and absorption coefficient associated with transitions between the electron bound to a donor and the first conduction subband have been studied for CdSe quantum dots with infinite potential confinement. We have used a variational procedure within the effective mass approximation. We present results for the absorption coefficient as a function of the photon energy for several field strengths and arbitrary impurity positions. It is found that for all sizes of the dot the absorption peak associated with an on-centre donor impurity is negligible and the most significant contribution comes from a donor located near the edge. The threshold absorption peak is strongly shifted toward high energies when the donor moves from the edge to the center accompanied with an important diminution of the intensity. While for large dot the threshold absorption peak is approximately insensitive to the donor position, we have also found that the application of magnetic field shifts the threshold absorption peak toward high energy and reduces the intensity of absorption coefficient. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Caram, Justin R.; Zheng, Haibin; Rolczynski, Brian S.; Griffin, Graham B.; Engel, Gregory S., E-mail: gsengel@uchicago.edu [Department of Chemistry, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States); Dahlberg, Peter D. [Graduate Program in the Biophysical Sciences, The Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States); Dolzhnikov, Dmitriy S.; Talapin, Dmitri V. [Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

    2014-02-28

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

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

    Science.gov (United States)

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

    2011-08-01

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

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

    OpenAIRE

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

    2015-01-01

    In optoelectronic devices based on quantum dot arrays, thin nanolayers of gold are preferred as stable metal contacts and for connecting recombination centers. The optimal morphology requirements are uniform arrays with precisely controlled positions and sizes over a large area with long range ordering since this strongly affects device performance. To understand the development of gold layer nanomorphology, the detailed mechanism of structure formation are probed with time-resolved grazing i...

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

    Science.gov (United States)

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

    2016-05-01

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

  9. HREM image simulation of CdSe quantum dots electrodeposited on [111] gold

    International Nuclear Information System (INIS)

    HREM images of CdSe nanocrystals on Au substrate were calculated for different relative shift of the Au and CdSe unit cells. The calculations proved that the added shift had significant influence on the images of the CdSe nanocrystals with thickness from 0.7 nm to 3.5 nm in the case of no tilt imaging condition. Experimental images exhibiting 1/3[422]Au and [10.0]CdSe patterns were simulated. A good fit between the experimental and calculated images were obtained in the tilted condition where the calculated images were very similar for different shifts. The thickness of the CdSe nanocrystals was estimated to be ca. 3 nm. (author)

  10. Electrodeposition of CdSe quantum dots and its application to an electrochemiluminescence immunoassay for α-fetoprotein

    International Nuclear Information System (INIS)

    We report on the first label-free electrochemiluminescence (ECL) immunosensor for α-fetoprotein (AFP). It is based on the use of CdSe quantum dots that were electrodeposited directly on a gold electrode from an electrolyte (containing cadmium sulfate, EDTA and selenium dioxide) by cycling the potential between 0 and -1.2 V (vs. SCE) for 60 s. The electrodeposited dots were characterized by scanning electron microscopy and energy dispersive spectroscopy. Under optimal conditions, the specific immunoreaction between AFP and anti-AFP resulted in a decrease of the ECL signal because of the steric hindrance and the transfer inhibition by peroxodisulfate. The quenching effect of the immunoreaction on the intensity of the ECL was used to establish a calibration plot which is linear in the range from 0.05 to 200 ng mL-1. The detection limit is 2 pg mL-1. The assay is highly sensitive and satisfactorily reproducible. In our opinion it opens new avenues to apply ECL in label-free biological assays. (author)

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2016-07-15

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

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

    Science.gov (United States)

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

    2016-07-01

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

  14. Size tuning of MAA capped CdSe and CdSe/CdS quantum dots and their stability in different pH environments

    International Nuclear Information System (INIS)

    The present work reports synthesis of mercaptoacetic acid capped CdSe nanoparticles soluble in water at different temperatures and with different precursor ratios. This enabled to tune the particle size of QDs from 2.7 to 5.8 nm. The particles consist of nanocrystals; with mixed phase, hexagonal wurtzite as well as sphalerite cubic and are luminescent with quantum yield 10%. The quantum yield up to 20% has been obtained by growing a shell of CdS over the CdSe. HR-TEM images, XRD patterns and the photoluminescence excitation spectra shows epitaxial growth of CdS shell over CdSe and with average size 3.2 ± 1.2 and 4.7 ± 1.2 nm for CdSe and CdSe/CdS quantum dots respectively. FT-IR spectrum and the negative zeta potential value together confirms the attachment of mercaptoacetic acid to the QD surface, where the carboxylic acid group is facing towards solvent and provides stability due to electrostatic hindrance. Further, the QDs are checked for their stability and the luminescence in environments of different pH (4–11 pH). Both CdSe and CdSe/CdS agglomerate with total elimination of fluorescence for 4 pH medium, and no shift in the fluorescence emission peak observed for the 6–9 pH, therefore QDs can be applicable as the fluorescence tags in this specific range of pH. - Highlights: • Synthesis of MAA capped CdSe and CdSe/CdS core/shell QDs. • Synthesis temperature and precursor ratio controls the growth of QDs. • PLE spectra shows four kind of absorption features for CdSe QDs. • Growth of CdS shell over CdSe core has not affected the energy levels of the core. • CdSe and CdSe/CdS QDs are not stable in low pH (less than 6) environments

  15. Seed-mediated synthesis, properties and application of γ-Fe2O3-CdSe magnetic quantum dots

    International Nuclear Information System (INIS)

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around γ-Fe2O3 magnetic cores was performed at high temperature (300 deg. C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells. - Graphical abstract: (a) HRTEM image of oleic acid capped MPs. The size of MPs ranges from 8 to 10 nm. (b) XRD pattern of γ-Fe2O3 MPs. Highlights: → The fabrication of MQDs through a seed-mediated approach has been demonstrated. → The formation and assembly of these bi-functional nanocomposites have been elucidated. → The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components. → MQDs with thin silica coating were successfully employed in the labeling of cancer cell membranes.

  16. Two-layer ZnO nanowire arrays: Fabrication and its photovoltaic property sensitized by CdSe and CdS quantum dots

    International Nuclear Information System (INIS)

    Two-layer ZnO nanowire arrays have been synthesized by a low temperature hydrothermal method. The two-layer structure enables the absorption of CdSe and CdS quantum dots (QDs) on different nanostructured layers, respectively. Solar cell based on the QD sensitized ZnO nanowire arrays is fabricated. Because sequential light adsorption of different sensitizers happens in two different layers, the photoanode can reduce the interaction possibility among different QDs and extend the absorption range, and result in improved photovoltaic properties. - Highlights: • Two-layer ZnO nanowire array has been synthesized by a low temperature hydrothermal. • A two-layer quantum dot sensitized ZnO nanowire array solar cell has been fabricated. • The structure can reduce interaction possibility among different quantum dots. • The structure can extend the range of light absorption

  17. Two-layer ZnO nanowire arrays: Fabrication and its photovoltaic property sensitized by CdSe and CdS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Jingzhi [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore); State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012 (China); Wang, Jianxiong; Sun, Xiaowei [School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore)

    2015-09-01

    Two-layer ZnO nanowire arrays have been synthesized by a low temperature hydrothermal method. The two-layer structure enables the absorption of CdSe and CdS quantum dots (QDs) on different nanostructured layers, respectively. Solar cell based on the QD sensitized ZnO nanowire arrays is fabricated. Because sequential light adsorption of different sensitizers happens in two different layers, the photoanode can reduce the interaction possibility among different QDs and extend the absorption range, and result in improved photovoltaic properties. - Highlights: • Two-layer ZnO nanowire array has been synthesized by a low temperature hydrothermal. • A two-layer quantum dot sensitized ZnO nanowire array solar cell has been fabricated. • The structure can reduce interaction possibility among different quantum dots. • The structure can extend the range of light absorption.

  18. Energy transfer in hybrid CdSe quantum dots vs. labelled molecular chaperone systems by imaging microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Tani, Toshiro; Oda, Masaru [Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan); Department of Applied Physics, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan); Horiuchi, Hiromi; Usukura, Eiji; Sakai, Hiroshi [Department of Applied Physics, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan); Ohtaki, Akashi [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan); Yohda, Masafumi [Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan); Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Kogane-i, Tokyo 184-8588 (Japan)

    2009-04-15

    Resonant energy transfer in hybrid CdSe quantum dot (QD) conjugated with Cy5-labelled molecular chaperone systems is observed with single molecule imaging technique. Photonic QDs are the core-shell type nanocrystals covered with organic surfactants on the outermost surfaces, i.e. CdSe/ZnS/TOPO's, and prefoldin (PFD) is used as prototype molecular chaperons. PFD is a jellyfish-shaped hexameric co-chaperone of group II chaperonins, which recognize hydrophobic portion of denatured proteins and encapsulate them within its central cavity. So the CdSe/ZnS/TOPO QDs can also be captured be cause of its surface similarity to the denatured proteins. We have found one possible reaction pathway to get such artificial complex in aqueous solutions with keeping bioactivities of the proteins. Performance of the complex is evaluated by TIRF imaging microscopy. As the proteins are transparent in visible wavelength region, labeling dyes, Cy5, which also work as acceptors, are connected to detect their behaviors microscopically. Foerster type energy transfer is observed from the QD donors to Cy5-labeled PFD acceptors in single molecule level, which can be a distinct evidence for the complex formation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    International Nuclear Information System (INIS)

    Binding energies of the exciton and the interband optical transition energies are studied in a CdSe/Pb1-xCdxSe/CdSe spherical quantum dot-quantum well nanostructure taking into account the geometrical confinement effect. The core and shell are taken as the same material. The initial and final states of energy and the overlap integrals of electron and hole wave functions are determined by the oscillator strength. The oscillator strength and the radiative transition life time with the dot radius are investigated for various Cd alloy content in the core and shell materials

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

    Science.gov (United States)

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

    2016-05-21

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

  1. Synthesis of water-soluble CdSe quantum dots by ligand exchange with p-sulfonatocalix(n)arene (n = 4, 6) as fluorescent probes for amino acids

    International Nuclear Information System (INIS)

    A simple, rapid ligand exchange route to prepare highly fluorescent, stable and water-soluble CdSe quantum dots (QDs) is reported by using p-sulfonatocalix(n)arene (SFCA(n), n = 4 or 6) instead of original trioctylphosphine oxide (TOPO) ligands. The ligands were found to have a profound effect on the luminescence response of QDs to amino acids. The SFCA(4) coated CdSe QDs were sensitive to methionine. On the other hand, SFCA(6) coated CdSe QDs turned out to be sensitive to phenylalanine. To demonstrate the detection capability of these new probes, SFCA(n) (n = 4, 6) coated CdSe QDs were used to detect methionine and phenylalanine in physiological buffer solution. Under optimal conditions, the relative fluorescence intensities of the SFCA(n) coated QDs (n = 4, 6) increased linearly with increasing concentration of amino acids. Methionine and phenylalanine enhanced the luminescence of SFCA(n) coated QDs with a concentration dependence that was best described by a Langmuir-type equation. The possible mechanism is also discussed

  2. Aqueous phase-synthesized small CdSe quantum dots: adsorption layer structure and strong band-edge and surface trap emission

    International Nuclear Information System (INIS)

    We synthesized, in aqueous solution at room temperature, small water-soluble CdSe quantum dots (QDs) with strong photoluminescence (PL) and then correlated the PL with their adsorption layer structure. For synthesizing the QDs, their initial synthesis condition was controlled to form small Cd-containing species capable of passivating dangling bonds on the CdSe core surface. Each CdSe QD (d ∼ 2.5 nm) consisted of a CdSe core (d ∼ 2.1 nm), a cysteine (cys)-ligand shell, and an adsorption layer composed of Cd–cys complexes (mainly CdL(-H)−, cys ≡ H2L), cys (as L2−), Cd(OH)2, and CdOx (x ≥ 1). Our CdSe QDs showed strong blue band-edge PL as well as strong green surface trap PL. Their PL quantum yield (QY) of ∼18% was unexpectedly high, considering their extremely small core size and their absence of any wide-bandgap inorganic shell. We attributed the QY to their adsorption layer species. The small weakly charged Cd–cys complex and the small neutral cadmium oxides in the adsorption layer could relatively readily diffuse into the unprotected surface sites on the core. These wide-bandgap species coalesced selectively on the unprotected surface sites with minimal spatial disturbance to the preexisting surface Cd-ligand coordination, and passivated them effectively. These decreased nonradiative recombination of the excitons significantly and thus led to the unexpectedly high QYs.

  3. Electrochemiluminescence biosensor based on CdSe quantum dots for the detection of thrombin

    International Nuclear Information System (INIS)

    A novel QDs electrochemiluminescence (ECL) biosensor for the determination of thrombin was described. The CdSe QDs solution was dripped onto the clear surface of the ITO and then immersed in PBS which contained EDC and NHS as a coupling agent to activate the carboxyl-terminated surface of the CdSe QDs. The ITO electrode was immersed in the PBS containing 0.4 μM aptamer, followed by rinsing with PBS and dried with N2 again, then dipped in the BSA solution for 30 min to decrease the non-specific binding. After that, the aptamer modified ITO was soaked in PBS to remove unbound aptamer. Under optimal conditions, the linear range was obtained from 0 to 64 μg mL−1 with a correlation coefficient of 0.9986 (n = 16). The control experiment was also carried out by using BSA, lysozyme and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by electrochemical method which could provide a promising platform for fabrication of aptamer based biosensors.

  4. One-Step Synthesis of High-Quality Water-Soluble CdSe Quantum Dots Capped by N-Acetyl-L-cysteine via Hydrothermal Method and Their Characterization

    OpenAIRE

    Chunjin Wei; Jinyu Li; Fang Gao; Shuxia Guo; Yongcui Zhou; Dan Zhao

    2015-01-01

    Novel water-soluble CdSe quantum dots (QDs) have been prepared with N-acetyl-L-cysteine as new stabilizer through a one-step hydrothermal route. The influence of experimental conditions, including reaction time, molar ratio of reactants, and pH value, on the luminescent properties of the obtained CdSe QDs has been systematically investigated. The characterization of as-prepared QDs was carried out through different methods. In particular, we realized qualitative and semiquantitative studies o...

  5. A comparative study about toxicity of CdSe quantum dots on reproductive system development of mice and controlling this toxicity by ZnS coverage

    Directory of Open Access Journals (Sweden)

    Akram Valipoor

    2015-10-01

    Full Text Available Objective(s:Medicinal benefits of quantum dots have been proved in recent years but there is little known about their toxicity especially in vivo toxicity. In order to use quantum dots in medical applications, studies ontheir in vivo toxicity is important. Materials and Methods: CdSe:ZnS quantum dots were injected in 10, 20, and 40 mg/kg doses to male mice10 days later, mice were sacrificed and five micron slides were prepared structural and optical properties of quantum dots were evaluated using XRD. Results:  Histological studies of testis tissue showed high toxic effect of CdSe:ZnS  in 40 mg/kg group. Histological studies of epididymis did not show any effect of quantum dots in terms of morphology and tube structure. Mean concentration of LH and testosterone and testis weight showed considerable changes in mice injected with 40 mg/kg dose of CdSe:ZnS compared to control group. However, FSH and body weight did not show any difference with control group. Conclusion: Although it has been reported that CdSe is highly protected from the environment by its shell, but  this study showed high toxicity for CdSe:ZnS when it is used in vivo which could be suggested that shell could contribute to increased toxicity of quantum dots. Considering lack of any previous study on this subject, our study could potentially be used as an basis for further extensive studies investigating the effects of quantum dots toxicity on development of male sexual system.

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

    Science.gov (United States)

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

    2012-12-01

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

  7. Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

    Institute of Scientific and Technical Information of China (English)

    Xiao Long Rong; Qin Zhao; Guan Hong Tao

    2012-01-01

    A new and convenient route is developed to synthesize CdSe and core-shell CdSe/CdS quantum dots (QDs) in aqueous solution.The gaseous precursors,H2Se and H2S,generated on-line by reducing SeO32-with NaBH4 and the reaction between Na2S and diluted H2SO4,are used to form high-quality CdSe and CdSe/CdS QDs,respectively.The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield (3% and 20%) and narrow full-width-at-half-maximum (43 nm and 38 nm).The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals,and can be readily extended to the large-scale aqueous synthesis of QDs.(C) 2012 Guan Hong Tao.Published by Elsevier B.V.on behalf of Chinese Chemical Society.All rights reserved.

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

    Science.gov (United States)

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

    2015-02-01

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

  9. Quantum dots

    CERN Document Server

    Borovitskaya, Elena

    2002-01-01

    In this book, leading experts on quantum dot theory and technology provide comprehensive reviews of all aspects of quantum dot systems. The following topics are covered: (1) energy states in quantum dots, including the effects of strain and many-body effects; (2) self-assembly and self-ordering of quantum dots in semiconductor systems; (3) growth, structures, and optical properties of III-nitride quantum dots; (4) quantum dot lasers. Contents: Low-Dimensional Systems (E Borovitskaya & M S Shur); Energy States in Quantum Dots (A J Williamson); Self-Organized Quantum Dots (A R Woll et al.); Grow

  10. Solid-state chemiluminescence assay for ultrasensitive detection of antimony using on-vial immobilization of CdSe quantum dots combined with liquid–liquid–liquid microextraction

    International Nuclear Information System (INIS)

    Graphical abstract: -- Highlights: •Solid-state chemiluminescence based on CdSe QDs was developed. •QDs immobilization in a vial was achieved in a simple and fast way. •Antimony detection was achieved by inhibition of the CdSe QDs/H2O2 CL reaction. •LLLME allowed improving the selectivity and sensitivity of the CL assay. •The capping ligand played a critical role in the selectivity of the CL system. -- Abstract: On-vial immobilized CdSe quantum dots (QDs) are applied for the first time as chemiluminescent probes for the detection of trace metal ions. Among 17 metal ions tested, inhibition of the chemiluminescence when CdSe QDs are oxidized by H2O2 was observed for Sb, Se and Cu. Liquid–liquid–liquid microextraction was implemented in order to improve the selectivity and sensitivity of the chemiluminescent assay. Factors influencing both the CdSe QDs/H2O2 chemiluminescent system and microextraction process were optimized for ultrasensitive detection of Sb(III) and total Sb. In order to investigate the mechanism by which Sb ions inhibit the chemiluminescence of the CdSe QDs/H2O2 system, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV–vis absorption and fluorescence measurements were performed. The selection of the appropriate CdSe QDs capping ligand was found to be a critical issue. Immobilization of QDs caused the chemiluminescence signal to be enhanced by a factor of 100 as compared to experiments carried out with QDs dispersed in the bulk aqueous phase. Under optimized conditions, the detection limit was 6 ng L−1 Sb and the repeatability expressed as relative standard deviation (N = 7) was about 1.3%. An enrichment factor of 95 was achieved within only 3 min of microextraction. Several water samples including drinking, spring, and river waters were analyzed. The proposed method was validated against CRM NWTM-27.2 fortified lake water, and a recovery study was performed with different types of water samples. Sb recoveries

  11. Fabrication, Characterization, and Optimization of CdS and CdSe Quantum Dot-Sensitized Solar Cells with Quantum Dots Prepared by Successive Ionic Layer Adsorption and Reaction

    Directory of Open Access Journals (Sweden)

    H. K. Jun

    2014-01-01

    Full Text Available CdS and CdSe quantum dot-sensitized solar cells (QDSSCs were used for the study of determining the optimum preparation parameters that could yield the best solar cell performance. The quantum dots (QDs were coated on the surface of mesoporous TiO2 layer deposited on FTO substrate using the successive ionic layer adsorption and reaction (SILAR method. In this method the QDs are allowed to grow on TiO2 by dipping the TiO2 electrode successively in two different solutions for predetermined times. This method allows the fabrication of QDs in a facile way. Three preparation parameters that control the QD fabrication were investigated: concentration of precursor solutions, number of dipping cycles (SILAR cycles, and dipping time in each solution. CdS based QDSSC showed optimum performance when the QDs were prepared from precursor solutions having the concentration of 0.10 M using 4 dipping cycles with the dipping time of 5 minutes in each solution. For CdSe QDSSC, the optimum performance was achieved with QDs prepared from 0.03 M precursor solutions using 7 dipping cycles with 30 s dipping time in each solution. The QDs deposited on TiO2 surface were characterized using UV-vis absorption spectroscopy, FESEM, and TEM imaging.

  12. One-Step Synthesis of High-Quality Water-Soluble CdSe Quantum Dots Capped by N-Acetyl-L-cysteine via Hydrothermal Method and Their Characterization

    Directory of Open Access Journals (Sweden)

    Chunjin Wei

    2015-01-01

    Full Text Available Novel water-soluble CdSe quantum dots (QDs have been prepared with N-acetyl-L-cysteine as new stabilizer through a one-step hydrothermal route. The influence of experimental conditions, including reaction time, molar ratio of reactants, and pH value, on the luminescent properties of the obtained CdSe QDs has been systematically investigated. The characterization of as-prepared QDs was carried out through different methods. In particular, we realized qualitative and semiquantitative studies on CdSe QDs through X-ray photoelectron spectroscopy and electron diffraction spectroscopy. The results show that the as-prepared CdSe QDs exhibit a high quantum yield (up to 26.7%, high stability, and monodispersity and might be widely used in biochemical detection and biochemical research.

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

    Science.gov (United States)

    Liu, Huilin; Fang, Guozhen; Wang, Shuo

    2014-05-15

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

  14. Synthesis and Optical Properties of CdSe Quantum Dots with Carboxy%羧基CdSe荧光量子点的制备及其荧光特性研究

    Institute of Scientific and Technical Information of China (English)

    薛秀恒; 王菊花; 盛俊; 梅林

    2011-01-01

    以氯化镉、硒粉为前驱体,巯基乙酸(TGA)为稳定剂,制备了羧基CdSe量子点,并研究了其荧光特性与影响因素.结果表明,反应温度、反应时间与反应体系的pH值是影响量子点生长和荧光性能的主要因素.制备羧基CdSe量子点的最优条件为反应温度90℃、pH=11、n(Cd):n(Se)=2:1.制备的羧基CdSe量子点的粒径随反应时间的延长而逐渐增大,量子点荧光稳定性好,荧光强度高,光漂白时间延长.%The CdSe quantum dots with carboxy have been synthesized with Se and CdCl2 as the precursor and thioglycolic acid(HSCH2COOH) as the stabilizer. The experiment results show that reaction temperature, time, and pH have great impact on the growth and luminescence of CdSe quantum dots. The molar ratio of n(Cd)∶ n(Se) is 2 ∶1, the reaction pH is 11, the resulting mixture solution is heated to 90℃ and refluxed to 2~8h for obtaining the CdSe QDs with earboxy. Size of CdSe quantum dots with carboxy is increased with reaction time. CdSe quantum dots are photo-stable and have a strong emission spectrum and a long photobleaching time.

  15. The influence of capping thioalkyl acid on the growth and photoluminescence efficiency of CdTe and CdSe quantum dots

    International Nuclear Information System (INIS)

    The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100 deg. C and under hydrothermal conditions (150 deg. C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles.

  16. Poly(glycidyl methacrylate) grafted CdSe quantum dots by surface-initiated atom transfer radical polymerization: Novel synthesis, characterization, properties, and cytotoxicity studies

    Energy Technology Data Exchange (ETDEWEB)

    Bach, Long Giang; Islam, Md. Rafiqul [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of); Lee, Doh Chang [Department of Chemical and Biomolecular Engineering, KAIST Institute for the Nanocentury (KINC), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Lim, Kwon Taek, E-mail: ktlim@pknu.ac.kr [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of)

    2013-10-15

    A novel approach for the synthesis of poly(glycidyl methacrylate) grafted CdSe quantum dot (QDs) (PGMA-g-CdSe) was developed. The PGMA-g-CdSe nanohybrids were synthesized by the surface-initiated atom transfer radical polymerization of glycidyl methacrylate from the surface of the strategic initiator, CdSe-BrIB QDs prepared by the interaction of 2-bromoisobutyryl bromide (BrIB) and CdSe-OH QDs. The structure, morphology, and optical property of the PGMA-g-CdSe nanohybrids were analyzed by FT-IR, XPS, TGA, XRD, TEM, and PL. The as-synthesized PGMA-g-CdSe nanohybrids having multi-epoxide groups were employed for the direct coupling of biotin via ring-opening reaction of the epoxide groups to afford the Biotin-f-PGMA-g-CdSe nanobioconjugate. The covalent immobilization of biotin onto PGMA-g-CdSe was confirmed by FT-IR, XPS, and EDX. Biocompatibility and imaging properties of the Biotin-f-PGMA-g-CdSe were investigated by MTT bioassay and PL analysis, respectively. The cell viability study suggested that the biocompatibility was significantly enhanced by the functionalization of CdSe QDs by biotin and PGMA.

  17. Thermodynamic Equilibrium-Driven Formation of Single-Sized Nanocrystals: Reaction Media Tuning CdSe Magic-Sized versus Regular Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kui [SIMS, NRC of Canada; Hu, Michael Z. [ORNL; Wang, Ruibing [SIMS, NRC of Canada; Le Piolet, Mickael [SIMS, NRC of Canada; Frotey, Marion [SIMS, NRC of Canada; Zaman, Md. Badruz [SIMS, NRC of Canada; Wu, Xiaohua [IMS, NRC of Canada; Leek, Donald M. [SIMS, NRC of Canada; Tao, Ye [IMS, NRC of Canada; Wilkinson, Diana [SIMS, NRC of Canada; Li, Chunsheng [National Research Council of Canada

    2010-01-01

    A concept for the fundamental science of nanoparticle synthesis, thermodynamic equilibrium-driven formation of colloidal single-sized nanoparticle ensembles, is proposed and demonstrated in this manuscript, which addresses the controlled formation of CdSe magic-sized and regular quantum dots (MSQDs and RQDs). During formation, the former are magic-sized nuclei without further growth in size, while the latter experience nucleation and growth. Both MSQDs and RQDs exhibit bandgap emission, while the former have homogeneous spectra broadening only and the latter both homogeneous and inhomogeneous spectra broadening. The former are single-sized and the latter have size distribution. With continuous and homogeneous nucleation, the thermodynamically driven formation of MSQDs was realized via our one-pot noninjection approach, which features highly synthetic reproducibility and large-scale capability. With the proper tuning of the synthetic parameters, such as the nature of the reaction medium, that affect the thermodynamic equilibria, various CdSe MSQDs and RQDs were synthesized discriminately under otherwise identical synthetic formulation and reaction conditions; the reaction media were noncoordinating 1-octadecene, coordinating trioctylphosphine, and mixtures of the two. The nature of Cd precursors, affected also by the reaction media, plays a major role in the formation of MSQDs versus RQDs. The present investigation on the thermodynamically driven formation of CdSe single-sized nanoparticles via tuning of the reaction medium, mainly, brings novel insights into the formation mechanism and into the surface ligands of the resulting colloidal nanocrystals. More importantly, the present study provides novel experimental design and approaches to single-sized nanoparticles desired for various applications.

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

    Directory of Open Access Journals (Sweden)

    Gholamreza Amiri

    2016-12-01

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

  19. Equilibrium structures of PbSe and CdSe colloidal quantum dots detected by dielectric spectroscopy

    NARCIS (Netherlands)

    Kortschot, R. J.; Van Rijssel, J.; Moes, Relinde; Erné, B. H.

    2014-01-01

    The permanent electrical dipole moment of colloidal quantum dots is important for their optoelectronic properties and can be determined by dielectric spectroscopy. Until now, however, colloidal interactions have not been taken into account in the interpretation of the spectra. Here, dielectric spect

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

    Science.gov (United States)

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

    2008-08-01

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

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

    International Nuclear Information System (INIS)

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

  2. Self-assembly of CdSe quantum dots and colloidal titanium dioxide on copolymer microspheres (PS) for CdSe/PS and TiO{sub 2}/CdSe/PS sub-microspheres with yolk–shell structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Qingchun, E-mail: qczhao@ustc.edu

    2015-07-30

    Highlights: • CdSe/PS sub-microspheres composite were prepared via self-assembly of CdSe quantum dots on modified PS surface. • TiO{sub 2}/CdSe/PS sub-microspheres were prepared via self-assembly of colloidal titanium dioxide on CdSe/PS sub-microspheres surface. • TiO{sub 2}/CdSe/PS sub-microspheres with yolk–shell structure. • TiO{sub 2}/CdSe/PS sub-microspheres with yolk–shell structure can improve the efficiency of charge separation. - Abstract: Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, chemical/biological sensors, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in nanostructures. In this paper, relying on the interaction including van der Waals forces and hydrogen bond, CdSe/PS sub-microspheres composite and TiO{sub 2}/CdSe/PS sub-microspheres with yolk–shell structure were prepared via self-assembly of CdSe quantum dots and colloidal titanium dioxide on modified PS surface. The morphology, structure and composition obtained products were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy disperse X-ray spectroscopy (EDX). Transmission electron microscopy (TEM) investigations show the CdSe quantum dots and colloidal titanate were assembled on the surface of PS sub-microspheres. CdSe QD-polymer sub-microspheres composites in which the QDs retain their original emission efficiency can be obtained. TiO{sub 2}/CdSe/PS sub-microspheres with yolk–shell structure can improve the efficiency of charge separation.

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

    International Nuclear Information System (INIS)

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

  4. Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

    International Nuclear Information System (INIS)

    We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature

  5. Surface-modified CdSe quantum dots for the sensitive and selective determination of Cu(II) in aqueous solutions by luminescent measurements

    International Nuclear Information System (INIS)

    The use of water-soluble luminescent CdSe quantum dots (QDs), whose surface was modified either with 2-mercaptoethane sulphonic acid or with 2-mercaptoacetic acid, was investigated for the sensitive and selective determination of copper(II) ions in aqueous solutions. A pH 5.5 was selected for measurement. Also, the effect of the presence of different surfactant agents in the sample solution, in order to stabilize the fluorescent signals of the QDs in water, has been investigated. A 10-3 M of dodecyltrimethylammonium chloride final concentration was selected. Fluorescence signals were found to be stable for at least several days in such conditions. Higher sensitivity was obtained for the sulphonic-modified CdSe QDs. Detection limits for Cu(II) of 0.2 μg l-1, a dynamic range up to 30 μg l-1, and a R.S.D. of ±2.8% for 10 replicates of a 2.5 μg l-1 Cu(II) solution were obtained as analytical performance characteristics. Besides, the influence on the fluorescence signal of foreign cations, including Na+, K+, Ca2+, Mg2+, Zn2+, Mn2+, Co3+, Ag+, Hg2+ and Fe3+ was studied (to avoid inner filter effect, the colourless complex FeF63- was investigated instead of Fe3+). Results showed a high selectivity of the sulphonic-modified QDs towards Cu(II) ions. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations as compared to other already described luminescence QDs-based analytical methods for metal ions determinations. Analytical applicability of the QDs has been demonstrated by tap and fountain water analysis. Results of Cu(II) determinations were in good agreement to those obtained by using an alternative analytical method

  6. Piezo and photoelectric coupled nanogenerator using CdSe quantum dots incorporated ZnO nanowires in ITO/ZnO NW/Si structure

    International Nuclear Information System (INIS)

    We report the fabrication of ITO/n-ZnO NW/p-Si sandwiched structure and its photoelectric and piezoelectric conversion properties. This hybrid cell was designed to harvest simultaneously both solar and mechanical energies. ZnO nanowires used in the work were grown on p-type Si substrates employing seed mediated low-temperature aqueous solution method. The synthesized ZnO nanowires were characterized by XRD, SEM and EDX characterization for their structural and morphological evaluation. The as-grown ZnO nanowires showed good crystallinity with c-axis preferable orientation. Free ZnO nanowires and CdSe quantum dots were also incorporated with the vertically grown nanowires and their response in harvesting optical and mechanical energies were investigated. The piezoelectric and photoelectric coupled effects of a ZnO nanowire device in the simultaneous conversion of both optical and mechanical energies have been studied for the first time with the goal of designing piezoelectric and photoelectric hybrid nanogenerator. This presented ITO/n-ZnO NW/p-Si heterojunction architecture is envisaged as a potentially valuable candidate for the next generation energy harvesting devices. Graphene-coated ITO was also used and its response was studied. - Highlights: ► Fabricated an unique sandwich type ITO/n-ZnO NW/p-Si nanogenerator. ► Simultaneous harvesting of both light and mechanical energy achieved. ► CdSe incorporation with ZnO nanowires increased the performance of the device. ► First report integrated both nanogenerator and solar cell in a same surface. ► Incorporating nanoantenna this structure can harvest light, heat and sound

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Delage, M-E [UniversityLaval, Quebec, QC (Canada); Centre Hospitalier Universityde Quebec, Quebec, QC (Canada); Lecavalier, M-E; Lariviere, D [UniversityLaval, Quebec, QC (Canada); Allen, C [UniversityLaval, Quebec, QC (Canada); Centre d' optique, photonique et laser (COPL), UniversityLaval, Quebec, QC (Canada); Beaulieu, L [Centre Hospitalier Universityde Quebec, Quebec, QC (Canada)

    2014-06-01

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

  9. Use of Cdse/ZnS quantum dots for sensitive detection and quantification of paraquat in water samples

    Energy Technology Data Exchange (ETDEWEB)

    Durán, Gema M. [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain); IRICA (Regional Institute of Applied Scientific Research), Avenida Camilo José Cela, s/n., 13071 Ciudad Real (Spain); Contento, Ana M. [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain); Ríos, Ángel, E-mail: Angel.Rios@uclm.es [Department of Analytical Chemistry and Food Technology, University of Castilla – La Mancha, Avenida Camilo José Cela, 10, 13004 Ciudad Real (Spain)

    2013-11-01

    Graphical abstract: -- Highlights: •Analytical use of CdSe/ZnS quantum dots. •Methodology for water solubilization of CdSe/ZnS QDs. •Sensitive and selective reaction with paraquat herbicide. •Application to water samples. -- Abstract: Based on the highly sensitive fluorescence change of water-soluble CdSe/ZnS core-shell quantum dots (QD) by paraquat herbicide, a simple, rapid and reproducible methodology was developed to selectively determine paraquat (PQ) in water samples. The methodology enabled the use of simple pretreatment procedure based on the simple water solubilization of CdSe/ZnS QDs with hydrophilic heterobifunctional thiol ligands, such as 3-mercaptopropionic acid (3-MPA), using microwave irradiation. The resulting water-soluble QDs exhibit a strong fluorescence emission at 596 nm with a high and reproducible photostability. The proposed analytical method thus satisfies the need for a simple, sensible and rapid methodology to determine residues of paraquat in water samples, as required by the increasingly strict regulations for health protection introduced in recent years. The sensitivity of the method, expressed as detection limits, was as low as 3.0 ng L{sup −1}. The lineal range was between 10–5 × 10{sup 3} ng L{sup −1}. RSD values in the range of 71–102% were obtained. The analytical applicability of proposed method was demonstrated by analyzing water samples from different procedence.

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

    Energy Technology Data Exchange (ETDEWEB)

    Alaraby, Mohamed [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); Sohag University, Faculty of Sciences, Zoology Department, 82524-Campus, Sohag (Egypt); Demir, Esref [Akdeniz University, Faculty of Sciences, Department of Biology, 07058-Campus, Antalya (Turkey); Hernández, Alba [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain); Marcos, Ricard, E-mail: ricard.marcos@uab.es [Grup de Mutagènesi, Departament de Genètica i de Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Cerdanyola del Vallès (Spain); CIBER Epidemiología y Salud Pública, ISCIII, Madrid (Spain)

    2015-10-15

    Since CdSe QDs are increasingly used in medical and pharmaceutical sciences careful and systematic studies to determine their biosafety are needed. Since in vivo studies produce relevant information complementing in vitro data, we promote the use of Drosophila melanogaster as a suitable in vivo model to detect toxic and genotoxic effects associated with CdSe QD exposure. Taking into account the potential release of cadmium ions, QD effects were compared with those obtained with CdCl{sub 2}. Results showed that CdSe QDs penetrate the intestinal barrier of the larvae reaching the hemolymph, interacting with hemocytes, and inducing dose/time dependent significant genotoxic effects, as determined by the comet assay. Elevated ROS production, QD biodegradation, and significant disturbance in the conserved Hsps, antioxidant and p53 genes were also observed. Overall, QD effects were milder than those induced by CdCl{sub 2} suggesting the role of Cd released ions in the observed harmful effects of Cd based QDs. To reduce the observed side-effects of Cd based QDs biocompatible coats would be required to avoid cadmium's undesirable effects. - Highlights: • CdSe QDs were able to cross the intestinal barrier of Drosophila. • Elevated ROS induction was detected in larval hemocytes. • Changes in the expression of Hsps and p53 genes were observed. • Primary DNA damage was induced by CdSe QDs in hemocytes. • Overall, CdSe QD effects were milder than those induced by CdCl{sub 2}.

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

    Science.gov (United States)

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

    2016-07-01

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

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

    Science.gov (United States)

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2016-05-01

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

  14. The influence of surface coating on the properties of water-soluble CdSe and CdSe/ZnS quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Coto-Garcia, Ana Maria; Fernandez-Argueelles, Maria T., E-mail: fernandezteresa@uniovi.es; Costa-Fernandez, Jose M.; Sanz-Medel, Alfredo, E-mail: asm@uniovi.es [University of Oviedo, Department of Physical and Analytical Chemistry (Spain); Valledor, Marta; Campo, Juan C.; Ferrero, Francisco J. [University of Oviedo, Department of Electric and Electronic Engineering (Spain)

    2013-01-15

    It is well-known that ligands coating the surface of luminescent semiconductor nanocrystals (quantum dots [QDs]) play an important role in the preparation, stability and physical properties of the colloidal QDs in both organic and aqueous media. Here we report on the synthesis and characterization of core (CdSe QDs) and core-shell structured QDs (CdSe/ZnS QDs), both of them stabilized in aqueous medium through different mechanisms of modification of their surface chemistry. The approaches evaluated for QDs transfer to aqueous media were ligand exchange and polymer coating. Experiments were performed using two typical thioalkyl acids as ligands, namely mercaptoacetic acid (QDs-MAA) and 2-mercaptoethanesulphonic acid (QDs-MES), and an amphiphilic polymer (PQDs) based on poly(maleic anhydride) functional groups. The effects of pH (buffer solution), illumination and the presence of ions in the QD environment on the spectroscopic properties of the different synthesized QDs are reported. The stability of the prepared QDs has been comparatively evaluated aimed to elucidate which surface chemistry provides the suitable properties to be employed as fluorescence labels in distinct types of applications. The experimental results and conclusions will be useful for the development of sensitive sensors or assays adopting QDs as fluorescence labels.

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

    Science.gov (United States)

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

    2016-07-01

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

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

    International Nuclear Information System (INIS)

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

  17. Hole transport in organic field-effect transistors with active poly(3-hexylthiophene) layer containing CdSe quantum dots

    Czech Academy of Sciences Publication Activity Database

    Bielecka, Urszula; Lutsyk, P.; Nyk, M.; Janus, K.; Samoć, M.; Bartkowiak, W.; Nešpůrek, Stanislav

    2013-01-01

    Roč. 31, č. 2 (2013), s. 288-297. ISSN 2083-1331 EU Projects: European Commission(XE) 35859 - BIMORE Institutional research plan: CEZ:AV0Z40500505 Keywords : organic transistor * poly(3-hexylthiophene) * CdSe Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.327, year: 2013

  18. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    International Nuclear Information System (INIS)

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at TG=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at TGD=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

  19. Formation and properties of epitaxial CdSe, ZnSe quantum dots. Conventional molecular beam epitaxy and related techniques

    Energy Technology Data Exchange (ETDEWEB)

    Mahapatra, Suddhasatta

    2008-01-16

    This thesis systematically investigates three such alternative approaches, along with conventional MBE, with emphasis on the formation-mechanism of QDs, and optimization of their morphological and optical attributes. it is shown here that no distinct 3D islands are formed in MBE growth of CdSe on ZnSe. While CdSe heteroepitaxy occurs in the multilayer-mode at T{sub G}=300 C, a reentrant recovery of the layer-by-layer mode is reported in this thesis, for growth at T{sub G}<{proportional_to}240 C. In the second variant technique, formation of large and distinct islands is demonstrated by deposition of amorphous selenium (a-Se) onto a 2D CdSe epilayer at room temperature and its subsequent desorption at a higher temperature (T{sub D}=230 C). The process steps of the third variant technique, developed in course of this work, are very similar to those of the previous one-the only alteration being the substitution of selenium with tellurium as the cap-forming-material. (orig.)

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

    Science.gov (United States)

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

    2015-04-01

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

  1. Composition-dependent trap distributions in CdSe and InP quantum dots probed using photoluminescence blinking dynamics

    Science.gov (United States)

    Chung, Heejae; Cho, Kyung-Sang; Koh, Weon-Kyu; Kim, Dongho; Kim, Jiwon

    2016-07-01

    Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization efficiencies which are determined by analyses of photoluminescence blinking dynamics. This result suggests that the composition of encapsulated QDs is closely associated with the charge trapping processes, and also provides an insight into the development of more environmentally friendly QD-based devices.Although Group II-VI quantum dots (QDs) have attracted much attention due to their wide range of applications in QD-based devices, the presence of toxic ions in II-VI QDs raises environmental concerns. To fulfill the demands of nontoxic QDs, synthetic routes for III-V QDs have been developed. However, only a few comparative analyses on optical properties of III-V QDs have been performed. In this study, the composition-related energetic trap distributions have been explored by using three different types of core/multishell QDs: CdSe-CdS (CdSe/CdS/ZnS), InP-ZnSe (InP/ZnSe/ZnS), and InP-GaP (InP/GaP/ZnS). It was shown that CdSe-CdS QDs have much larger trap densities than InP-shell QDs at higher energy states (at least 1Eg (band gap energy) above the lowest conduction band edge) based on probability density plots and Auger ionization

  2. Ameliorating effects of extracellular polymeric substances excreted by Thalassiosira pseudonana on algal toxicity of CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Saijin, E-mail: zhangs@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Jiang Yuelu, E-mail: jyuelu@gmail.com [Department of Marine Biology, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Chen, Chi-Shuo, E-mail: chen.chishuo@gmail.com [School of Engineering, University of California - Merced, Merced, CA 95344 (United States); Creeley, Danielle [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Schwehr, Kathleen A., E-mail: schwerhk@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Quigg, Antonietta, E-mail: quigga@tamug.edu [Department of Marine Biology, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Department of Oceanography, Texas A and M University, College Station, TX 77843 (United States); Chin, Wei-Chun, E-mail: wchin2@ucmerced.edu [School of Engineering, University of California - Merced, Merced, CA 95344 (United States); Santschi, Peter H., E-mail: santschi@tamug.edu [Department of Marine Science, Texas A and M University at Galveston, 200 Seawolf Parkway, Galveston, TX 77553 (United States); Department of Oceanography, Texas A and M University, College Station, TX 77843 (United States)

    2013-01-15

    Quantum dots (QDs) are engineered nanoparticles (ENs) that have found increasing applications and shown great potential in drug delivery, biological imaging and industrial products. Knowledge of their stability, fate and transport in the aquatic environment is still lacking, including details of how these nanomaterials interact with marine phytoplankton. Here, we examined the toxicity of functionalized CdSe/ZnS QDs (amine- and carboxyl-) by exposing them for five days to Thalassiosira pseudonana (marine diatom) grown under different nutrient-conditions (enriched versus nitrogen-limited media). The released polysaccharides and proteins, the major components of extracellular polymeric substances (EPS), were measured to assess their potential effects on the interactions between QDs and T. pseudonana. The partitioning of QDs was analyzed by monitoring the concentration of Cd in different size fractions of the cultures (i.e., filtrate, <0.22 {mu}m and permeate, <3 kDa). We found that the Cd release of QDs in the T. pseudonana culture was dependent on the nutrient conditions and nature of QDs' surface coating. Both amine- and carboxyl-functionalized QDs exhibited higher rates of Cd release in N-limited cultures than in nutrient enriched cultures. The results also showed that amine-functionalized QDs aggregate with minimal Cd release, independent of nutrient conditions. Laser scanning confocal microscopy images confirmed that aggregates are composed of QDs and the culture matrix (EPS). In addition, both types of QDs showed limited toxicity to T. pseudonana. The increasing production of proteins induced by QDs suggests that extracellular proteins might be involved in the detoxification of QDs to T. pseudonana via the Cd release of QDs. Our results here demonstrated that EPS can play an ameliorating role in QD toxicity, fate and transport in the aquatic environment.

  3. CdSe量子点的合成及其对潜指纹的荧光显现研究%Synthesis of CdSe Quantum Dots and Their Applications for Labeling of Latent Fingerprints

    Institute of Scientific and Technical Information of China (English)

    许尊炼; 伊魁宇; 马子宁; 王猛; 刘显峰

    2013-01-01

    Thioglycolic acid (TGA) capped water-soluble CdSe quantum dots (QDs) was synthesized via a hy-drothermal synthesis method. The as-prepared QDs were characterized and purified. Thioglycolic acid ( TGA) capped water-soluble CdSe quantum dots emitted strong yellow-green light under the irradiation of UV light at the wavelength of 365 nm, and the PL emission peak is at about 528 nm. Finally, the prepared thioglycolic acid capped CdSe quantum dots were applied in the fluorescent labeling of latent fingerprints on the surface of smooth objects. It is found the fingerprint details on the surface of smooth objects were clearly developed, detail characteristic is obvious, and the bright yellow-green fluorescence fingerprint was developed clearly. It has very high practical value and the value of identification.%以水热法在水相中直接合成了巯基乙酸修饰的CdSe量子点,并将合成的CdSe量子点进行表征、纯化.在波长365 nm紫外光的激发下,CdSe量子点发射出明亮的黄绿色荧光,荧光发射峰约位于528nm,将得到的CdSe量子点纳米发光材料应用于非渗透性客体上潜指纹的荧光标记成像研究,发现CdSe量子点溶液显现的手印纹线流畅,显现细节特征明显,呈现明亮的黄绿色荧光指纹,具有很高的实用价值和鉴定价值.

  4. CdSe quantum dot in vertical ZnSe nanowire and photonic wire for efficient single-photon emission

    DEFF Research Database (Denmark)

    Cremel, Thibault; Bellet-Amalric, Edith; Cagnon, Laurent;

    obtained conformal dielectric coating of Al2O3 on the NW-QDs using Atomic Layer Deposition so that a photonic wire is formed with the CdSe QD deterministically positioned on its axis. The collection enhancement effect is studied by measuring the emission (with pulse excitation, at saturation intensity) of...... a single photon source. We have grown vertically oriented ZnSe NWs (with typical diameter of 10 nm) by molecular beam epitaxy on a ZnSe(111)B buffer layer. The growth of a ZnMgSe passivating shell increases the (otherwise weak) ZnSe near-band-edge luminescence by two orders of magnitude. This has...

  5. Chemical stability of CdSe quantum dots in seawater and their effects on a marine microalga

    International Nuclear Information System (INIS)

    With the increasing use of nanotechnologies, it is expected that nanomaterials end up in natural aquatic systems, from freshwater to the sea. In this work we studied the chemical behaviour of water-soluble CdSe QDs in seawater and their effects on the marine diatom Phaeodactylum tricornutum, as a model of a biological receptor in the marine environment. We evaluated QD toxicity in terms of growth rate inhibition, oxidative stress and ROS accumulation. In addition, we used the synthesis of phytochelatins (PCs) as a biomarker of the presence of free Cd2+ ions released from QDs. The optical and chemical characterization demonstrated the propensity of QDs to aggregate after dispersion in raw seawater. In addition, bare CdSe QDs, lacking the ZnS shell, underwent a salinity-dependent degradation process. Short-term exposure experiments showed that the ease of degradation of QDs in seawater correlated with the synthesis of PCs in P. tricornutum cells. Long-term exposure experiments, carried out with the most stable CdSe/ZnS QDs, showed that algae accumulated Cd, but synthesized negligible amounts of PCs. Since the production of PCs is a specific signal of the presence of bioavailable metal ions, our findings suggest that QDs, associated to P. tricornutum cells, did not release PC-inducing metal species. Our data also showed a gradual decrease in algal growth rate at concentrations of QDs higher than 0.5 nM. Measurements of the activity of the antioxidant enzymes showed that superoxide dismutase (SOD) and catalase (CAT) activities were increased by exposure to [QDs] ≥ 0.5 nM, whereas ascorbate peroxidase (APX) and glutathione reductase (GR) activities were not significantly affected. The increase in SOD and CAT activity can be considered a symptom of oxidative stress induced by an enhanced production of ROS. This hypothesis was confirmed by the concomitant increase in the intracellular ROS concentration.

  6. Effect of rutile-type content on nanostructured anatase-type TiO2 electrode sensitized with CdSe quantum dots characterized with photoacoustic and photoelectrochemical current spectroscopies

    International Nuclear Information System (INIS)

    Two types of nanostructured TiO2 electrodes were prepared without rutile-type (100% anatase-type) and with rutile-type (12%) content. CdSe quantum dots (QDs) were adsorbed onto each of the two types of TiO2 electrodes using a chemical deposition (CD) technique. Optical absorption and photoelectrochemical properties were characterized with photoacoustic (PA) and photoelectrochemical current (PEC) methods. The redshift of the PA and PEC spectra with increasing CdSe sizes were clearly observed, indicating quantum confinement effects and photosensitization. It was found that the PA and PEC spectra in the visible region were different for the two types of TiO2 electrodes for the same deposition time. The PA and PEC intensities of TiO2 electrodes with rutile-type content were larger than those without rutile-type content, indicating that adsorbed CdSe QDs in the TiO2 electrodes with rutile-type content might be higher than those without rutile-type content. Moreover, the transport properties in the TiO2 electrodes with rutile-type content might be improved. These results suggest that the rutile-type content is advantageous to increase the photoelectrochemical properties of TiO2 electrodes

  7. Quantum kinetic exciton-LO-phonon interaction in CdSe

    DEFF Research Database (Denmark)

    Woggon, Ulrike; Gindele, Frank; Langbein, Wolfgang; Hvam, Jørn Märcher

    2000-01-01

    Oscillations with a period of similar to 150 fs are observed in the four-wave mixing (FWM) signal of bulk CdSe and interpreted in terms of non-Markovian exciton-LO-phonon scattering. The experiments show evidence of phonon quantum kinetics in semiconductors of strong polar coupling strength and...... high exciton binding energy. By comparison of the spectral and temporal response of the FWM signal in bulk CdSe and CdSe quantum dots, we demonstrate the influence of continuum states on the interference of electron-hole pair polarizations coupled via an LO phonon....

  8. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jing [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Hu, Rui [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Jianwei [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Zhang, Butian; Wang, Yucheng [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Liu, Xin [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Law, Wing-Cheung [Department of Industrial and System Engineering, The Hang Kong Polytechnic University, Hung Hom (Hong Kong); Liu, Liwei [School of Science, Changchun University of Science and Technology, Changchun 130022 (China); Ye, Ling, E-mail: lye_301@163.com [Institute of Gerontology and Geriatrics & Beijing Key Lab of Aging and Geriatrics, Chinese PLA General Hospital, Beijing 100853 (China); Yong, Ken-Tye, E-mail: ktyong@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

    2015-12-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  9. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

    International Nuclear Information System (INIS)

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive

  10. Optical studies of capped quantum dots

    OpenAIRE

    Wuister, S.F.

    2005-01-01

    This thesis describes the synthesis and spectroscopy of CdSe and CdTe semiconductor quantum dots (QDs). The first chapter gives an introduction into the unique size dependent properties of semiconductor quantum dots. Highly luminescent QDs of CdSe and CdTe were prepared via a high temperature method in a glovebox. These QDs are soluble in organics but can be transferred into water or ethanol after exchange of the surfactants by various thiols (HS-R). For CdTe the exchange with thiols has a be...

  11. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    Semiconductor quantum dots ("solid-state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra. Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dot states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...

  12. Quantum dot spectroscopy

    DEFF Research Database (Denmark)

    Leosson, Kristjan

    1999-01-01

    Semiconductor quantum dots ("solid state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra.Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dots states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...

  13. Optical absorption and ultrafast carrier dynamics characterization of CdSe quantum dots deposited on different morphologies of nanostructured TiO2 films

    International Nuclear Information System (INIS)

    In this study, CdSe QDs were chemically adsorbed onto the inverse opal TiO2 film as well as the common nanocrystalline TiO2 film. The optical absorption studied by using photoacoustic (PA) spectroscopy implies the growing and larger amount of CdSe QDs onto inverse opal TiO2 by increasing deposition time. For the same deposition time, the growth of CdSe QD size are independent on TiO2 matrixes, but largely deposited on the common nanocrystalline TiO2 film than the inverse opal TiO2. Ultrafast carrier dynamics shows a fast (hole) decay process and a slow (electron) decay process with lifetimes of a few ps and a few tens to hundreds ps, respectively. With increasing deposition time, regarding larger size and amount of CdSe QDs, the time constant of these two processes become longer for CdSe deposited inverse opal TiO2 samples. However, for the same deposition time, CdSe deposited inverse opal TiO2 have the shorter lifetime of both hole and electron decay processes compared to one on nanocrystalline TiO2, showing that the amount of CdSe QDs, the interfaces between CdSe QDs, play important role in carrier relaxation

  14. Ultrafast characterization of the electron injection from CdSe quantum dots and dye N719 co-sensitizers into TiO2 using sulfide based ionic liquid for enhanced long term stability

    International Nuclear Information System (INIS)

    Combination of inorganic quantum dots (QDs) and organic/metallorganic dyes as supracollectors nanocomposites could have an important role on the development of efficient photovoltaic devices based on the synergistic action of the hybrid-sensitizers. Here we have analyzed the combination of CdSe QDs and polypyridil N719 ruthenium dye. By ultrafast transient grating measurements we show that the cascading structure (type II) of this system takes full advantage to augment electron injection and hole regeneration efficiencies. Co-sensitized TiO2 electrodes lead to an improvement in charge separation, increasing the number of injected electrons from the CdSe QDs to the TiO2 as a consequence of the suppression of back reaction, by fast regeneration of holes by the dye action. The potentiality of this supracollector system has been verified in a complete cell configuration. Sulfide/polysulfide based ionic liquid in which both sensitizers (QD and dye) are stable has been employed as hole conducting media. In spite of the limited efficiencies of the analyzed cells, the higher photocurrents measured for CdSe/N719 co-sensitization compared to the cells sensitized using a single sensitizer constitutes a valid proof of the concept. Impedance spectroscopy unveiled the recombination limitation of the analyzed cells. On the other hand, ionic liquid exhibits an enhanced cell stability maintaining cell efficiency after one week and keeping it at 80% after 21 days. The reported results highlight a huge potential of the synergetic combination of QD and dyes for improving solar cell performance and of novel sulfide/polysulfide ionic liquid-based electrolytes for enhancing long term stability and sustainability of QD sensitizers

  15. Sensitive and selective determining ascorbic acid and activity of alkaline phosphatase based on electrochemiluminescence of dual-stabilizers-capped CdSe quantum dots in carbon nanotube-nafion composite.

    Science.gov (United States)

    Ma, Xiaolong; Zhang, Xin; Guo, Xinli; Kang, Qi; Shen, Dazhong; Zou, Guizheng

    2016-07-01

    Sensitive and selective determining bio-related molecule and enzyme play an important role in designing novel procedure for biological sensing and clinical diagnosis. Herein, we found that dual-stabilizers-capped CdSe quantum dots (QDs) in composite film of multi-walled carbon nanotubes (CNTs) and Nafion, displaying eye-visible monochromatic electrochemiluminescence (ECL) with fwhm of 37nm, which offers promising ECL signal for detecting ascorbic acid (AA) as well as the activity of alkaline phosphatase (ALP) in biological samples. It was also shown that the dual-stabilizers-capped CdSe QDs can preserve their highly passivated surface states with prolonged lifetime of excited states in Nafion mixtures, and facilitate electron-transfer ability of Nafion film along with CNTs. Compared with the QDs/GCE, the ECL intensity is enhanced 1.8 times and triggering potential shifted to lower energy by 0.12V on the CdSe-CNTs-Nafion/GCE. The ECL quenching degree increases with increasing concentration of AA in the range of 0.01-30nM with a limit of detection (LOD) of 5pM. The activity of ALP was determined indirectly according to the concentration of AA, generated in the hydrolysis reaction of l-ascorbic acid 2-phosphate sesquimagnesium (AA-P) in the presence of ALP as a catalyst, with an LOD of 1μU/L. The proposed strategy is favorable for developing simple ECL sensor or device with high sensitivity, spectral resolution and less electrochemical interference. PMID:27154663

  16. Biodistribution and stability of CdSe core quantum dots in mouse digestive tract following per os administration: Advantages of double polymer/silica coated nanocrystals

    International Nuclear Information System (INIS)

    Highlights: ► New QDs coated with combination of polythiol ligands and silica shell were synthesized. ► We examine the QDs stability in digestive tract of mice after per os administration. ► The polymer/silica shell prevents QDs degradation and fluorescence quenching in vivo. -- Abstract: CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT–APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT–APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials – mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) – are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT–APS) are suitable for biological and biomedical applications in the gastrointestinal tract.

  17. Exciton-Phonon Scattering in CdSe/ZnSe Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    张立功; 申德振; 范希武; 吕少哲

    2002-01-01

    A temperature-dependent photoluminescence measurement is performed in CdSe/ZnSe quantum dots with a ZnCdSe quantum well. We deduce the temperature dependence of the exciton linewidth and peak energy of the zero-dimensional exciton in the quantum dots and two-dimensional exciton in the CdSe wetting layer. The experimental data reveal a reduction of homogeneous broadening of the exciton line in the quantum dots in comparison with that in the two-dimensional wetting layer, which indicates the decrease of exciton and optical phonon coupling in the CdSe quantum dots.

  18. Highly sensitive electroluminescence immunoassay for Hg(II) ions based on the use of CdSe quantum dots, the methylmercury-6-mercaptonicotinic acid-ovalbumin conjugate, and a specific monoclonal antibody

    International Nuclear Information System (INIS)

    We have designed a rapid and ultrasensitive electrochemiluminescent (ECL) competitive immunoassay for the determination of mercury(II) ion. It is based on the use of CdSe quantum dots (QDs), methylmercury-6-mercaptonicotinic acid-ovalbumin as coating antigen and specific monoclonal antibodies (mAbs) against Hg(II). The latter is quite selective for Hg(II). The coating antigen was immobilized on the surface of a gold electrode via reaction between the functional groups of cysteamine and glutaraldehyde. The mercury(II) ions in a sample and the coating antigen compete for binding sites of QD-labeled monoclonal antibody which binds specifically to Hg(II) ions. The ECL of the system decreases with increasing concentration of Hg(II) because less QD-labeled mAbs are present on the surface of the electrode. Under optimal conditions, the decrease of ECL intensity is linearly related to the logarithm of the Hg(II) concentration in the range from 0.02 to 100 ng mL−1, with a detection limit of 6.2 pg mL−1. As far as we know, this is the first report on an ECL immunoassay for Hg(II) based on a specific monoclonal antibody. The favorable results obtained when this method was applied to real samples indicate that this detection scheme can widely enlarge the applicability of detecting heavy metal ions by exploiting the ECL of QDs for immunoassays. (author)

  19. Structural and optical characterization of electrodeposited CdSe in mesoporous anatase TiO2 for regenerative quantum-dot-sensitized solar cells

    International Nuclear Information System (INIS)

    We investigated CdSe-sensitized TiO2 solar cells by means of electrodeposition under galvanostatic control. The electrodeposition of CdSe within the mesoporous film of TiO2 gives rise to a uniform, thickness controlled, conformal layer of nanostructured CdSe particles intimately wrapping the anatase TiO2 nanoparticles. This technique has the advantage of providing not only a fast method for sensitization ( 2–CdSe core–shell structure followed by the growth of an assembly of CdSe nanoparticles resembling cauliflowers. This assembly exhibits at its core a mosaic texture with crystallites of about 3 nm in size, in contrast to a shell composed of well-crystallized single crystals between 5 and 10 nm in size. Preliminary results on the photovoltaic performance of such a nanostructured composite of TiO2 and CdSe show 0.8% power conversion efficiency under A.M.1.5 G conditions—100 mW cm−2 in association with a new regenerative redox couple based on cobalt(+III/+II) polypyridil complex (Voc = 485 mV, Jsc = 4.26 mA cm −2, ff=0.37). (paper)

  20. A Rapid and Cost-Effective Laser Based Synthesis of High Purity Cadmium Selenide Quantum Dots.

    Science.gov (United States)

    Gondall, M A; Qahtan, Talal F; Dastageer, M A; Yamani, Z H; Anjum, D H

    2016-01-01

    A rapid and cost effective method is developed to synthesize high purity cadmium Selenide (CdSe) quantum dots in acetone medium using second harmonic of Nd:YAG nanosecond pulsed laser of 532 nm wavelength. The thermal agglomeration due the nanosecond pulse duration of the laser was successfully eliminated by using unfocussed laser beam and thereby providing a favorable conditions for the synthesis of quantum dots having the grain size of 3 nm. The morphological and optical characterizations like XRD, HRTEM, optical absorption of the synthesized CdSe quantum dots, reveal that the material possesses the similar characteristics of the one synthesized through cumbersome wet chemical methods. Relative to the CdSe bulk material, the synthesized CdSe quantum dots showed a blue shift in the measured band gap energy from near infrared spectral region to visible region, making this material very attractive for many solar energy harvesting applications like photo-catalysis and solar cells. PMID:27398538

  1. 水相中合成CdSe量子点的研究%Synthesis of CdSe Quantum Dots (QDs) in the Water

    Institute of Scientific and Technical Information of China (English)

    田红叶; 贺蓉; 高峰; 古宏晨

    2005-01-01

    分别用Na2SeSO3和NaHSe为前驱体在水相中合成了CdSe半导体量子点(Quantum Dots, QDs)材料.通过紫外吸收光谱(UV-VIS)、荧光发射光谱(PL)、透射电子显微镜(TEM)等手段对制备的样品进行了表征.实验结果表明:选用同一前驱体,紫外吸收峰、荧光发射峰随反应时间的延长有明显红移,即粒径在不断长大;随反应时间延长荧光发射谱的半峰宽逐渐变宽.选用不同的前驱体,反应相同的时间,可以得到不同粒径的量子点材料.量子点水溶液Zeta电位基本不受前驱体和pH值的影响,始终为负值.

  2. Quantum Dots: Theory

    Energy Technology Data Exchange (ETDEWEB)

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

  3. Ultrasmall silicon quantum dots

    NARCIS (Netherlands)

    Zwanenburg, F.A.; Van Loon, A.A.; Steele, G.A.; Rijmenam, C.E.W.M.; Balder, T.; Fang, Y.; Lieber, C.M.; Kouwenhoven, L.P.

    2009-01-01

    We report the realization of extremely small single quantum dots in p-type silicon nanowires, defined by Schottky tunnel barriers with Ni and NiSi contacts. Despite their ultrasmall size the NiSi–Si–NiSi nanowire quantum dots readily allow spectroscopy of at least ten consecutive holes, and addition

  4. Quantum Dots: Theory

    OpenAIRE

    Vukmirovic, Nenad

    2010-01-01

    This review covers the description of the methodologies typically used for the calculation of the electronic structure of self-assembled and colloidal quantum dots. These are illustrated by the results of their application to a selected set of physical effects in quantum dots.

  5. Transmission electron microscopy investigations of the CdSe based quantum structures

    Energy Technology Data Exchange (ETDEWEB)

    Roventa, E.

    2006-09-22

    In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)

  6. Transmission electron microscopy investigations of the CdSe based quantum structures

    International Nuclear Information System (INIS)

    In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)

  7. Quadra-Quantum Dots and Related Patterns of Quantum Dot Molecules: Basic Nanostructures for Quantum Dot Cellular Automata Application

    OpenAIRE

    Somsak Panyakeow

    2010-01-01

    Laterally close-packed quantum dots (QDs) called quantum dot molecules (QDMs) are grown by modified molecular beam epitaxy (MBE). Quantum dots could be aligned and cross hatched. Quantum rings (QRs) created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs) and quantum dot rings (QDRs). Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA) is late...

  8. Ratiometric optical fiber dissolved oxygen sensor based on metalloporphyrin and CdSe quantum dots embedded in sol–gel matrix

    International Nuclear Information System (INIS)

    A simple, low cost technique to fabricate a ratiometric optical fiber dissolved oxygen sensor has been presented. The ratiometric optical fiber dissolved oxygen sensor comprising a plastic optical fiber coated at one end with Pd(II)/CdSe QDs or Pt(II)/CdSe QDs embedded in sol–gel matrix. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the oxygen-sensitive dye (PdTFPP, PdTCPP, PtTFPP and PtOEP) and the reference CdSe QDs have no spectral overlap and therefore permit the dissolved oxygen concentration to be measured using a ratiometric-based method. The sensitivity of optical fiber dissolved oxygen sensor is quantified in terms of the ratio I0/I100, where I0 and I100 represent the detected luminescence intensities in fully-deoxygenated and fully-oxygenated water, respectively. The experimental results show that the sensitivities of the ratiometric optical fiber dissolved oxygen sensors are estimated to be 21.7 for PdTFPP-doped sensor, 7.4 for PdTCPP-doped sensor, 6.5 for PtTFPP-doped sensor and 9.2 for PtOEP-doped sensor. The ratiometric sensing approach presented in this study has the advantage of suppressing the effects of spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optic fiber. - Highlights: • A simple, low cost technique to fabricate a ratiometric optical fiber DO sensor. • Optical fiber coated with Pd(II) or Pt(II)/CdSe QDs embedded in sol-gel matrix. • Using an LED with a central wavelength of 405 nm as an excitation source. • Suppressing the effects of spurious fluctuations in the intensity

  9. Ratiometric optical fiber dissolved oxygen sensor based on metalloporphyrin and CdSe quantum dots embedded in sol–gel matrix

    Energy Technology Data Exchange (ETDEWEB)

    Chu, Cheng-Shane, E-mail: cschu@mail.mcut.edu.tw; Chuang, Chih-Yung

    2015-11-15

    A simple, low cost technique to fabricate a ratiometric optical fiber dissolved oxygen sensor has been presented. The ratiometric optical fiber dissolved oxygen sensor comprising a plastic optical fiber coated at one end with Pd(II)/CdSe QDs or Pt(II)/CdSe QDs embedded in sol–gel matrix. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the oxygen-sensitive dye (PdTFPP, PdTCPP, PtTFPP and PtOEP) and the reference CdSe QDs have no spectral overlap and therefore permit the dissolved oxygen concentration to be measured using a ratiometric-based method. The sensitivity of optical fiber dissolved oxygen sensor is quantified in terms of the ratio I{sub 0}/I{sub 100}, where I{sub 0} and I{sub 100} represent the detected luminescence intensities in fully-deoxygenated and fully-oxygenated water, respectively. The experimental results show that the sensitivities of the ratiometric optical fiber dissolved oxygen sensors are estimated to be 21.7 for PdTFPP-doped sensor, 7.4 for PdTCPP-doped sensor, 6.5 for PtTFPP-doped sensor and 9.2 for PtOEP-doped sensor. The ratiometric sensing approach presented in this study has the advantage of suppressing the effects of spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optic fiber. - Highlights: • A simple, low cost technique to fabricate a ratiometric optical fiber DO sensor. • Optical fiber coated with Pd(II) or Pt(II)/CdSe QDs embedded in sol-gel matrix. • Using an LED with a central wavelength of 405 nm as an excitation source. • Suppressing the effects of spurious fluctuations in the intensity.

  10. Photophysical and structural characterisation of in situ formed quantum dots.

    Science.gov (United States)

    Bansal, A K; Antolini, F; Sajjad, M T; Stroea, L; Mazzaro, R; Ramkumar, S G; Kass, K-J; Allard, S; Scherf, U; Samuel, I D W

    2014-05-28

    Conjugated polymer-semiconductor quantum dot (QD) composites are attracting increasing attention due to the complementary properties of the two classes of materials. We report a convenient method for in situ formation of QDs, and explore the conditions required for light emission of nanocomposite blends. In particular we explore the properties of nanocomposites of the blue emitting polymer poly[9,9-bis(3,5-di-tert-butylphenyl)-9H-fluorene] together with cadmium sulphide (CdS) and cadmium selenide (CdSe) precursors. We show the formation of emissive quantum dots of CdSe from thermally decomposed precursor. The dots are formed inside the polymer matrix and have a photoluminescence quantum yield of 7.5%. Our results show the importance of appropriate energy level alignment, and are relevant to the application of organic-inorganic systems in optoelectronic devices. PMID:24727793

  11. Anisotropy in CdSe quantum rods

    Energy Technology Data Exchange (ETDEWEB)

    Li, Liang-shi

    2003-09-01

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

  12. Quantum Dots for Biophotonics

    OpenAIRE

    Ken-Tye Yong

    2012-01-01

    This theme issue provides an excellent collection of reviews and original research articles on the study of various bioconjugated quantum dot formulations for diagnostics and therapy applications using biophotonic imaging and sensing approaches.

  13. Graphene quantum dots

    CERN Document Server

    Güçlü, Alev Devrim; Korkusinski, Marek; Hawrylak, Pawel

    2014-01-01

    This book reflects the current status of theoretical and experimental research of graphene based nanostructures, in particular quantum dots, at a level accessible to young researchers, graduate students, experimentalists and theorists. It presents the current state of research of graphene quantum dots, a single or few monolayer thick islands of graphene. It introduces the reader to the electronic and optical properties of graphite, intercalated graphite and graphene, including Dirac fermions, Berry's phase associated with sublattices and valley degeneracy, covers single particle properties of

  14. Optical properties of charged semiconductor quantum dots

    Science.gov (United States)

    Jha, Praket P.

    The effect of n-type doping on the luminescence properties of II-VI quantum dots is studied. The addition of two shells of CdS on CdSe quantum dots prevents the creation of surface traps and makes the system stable under reducing environment. The injection of electrons into films of quantum dots leads to lower photoluminescence (PL) efficiency, with the extent of quenching dependent on both the number and the quantum states of the spectator charges in the nanocrystal. It is found that a 1Pe electron is an eightfold better PL quencher than the 1Se electron. Reduced threshold for stimulated emission is also observed in doped CdSe/CdS films. Time resolved photoluminescence measurements are used to extract the recombination rates of a charged exciton, called trion. It is observed that the negative trion has a radiative rate ˜2.2 +/- 0.4x faster than a neutral exciton, while its non-radiative recombination rate is slower than the biexciton non-radiative recombination rate by a factor of 7.5 +/- 1.7. The knowledge of the recombination rates of the trion enables us to calculate the quantum yield of a negative trion to be ˜10% for the nanocrystals investigated in our work. This is larger than the off state quantum yield from a single quantum dot photoluminescence trajectory and eliminates the formation of negative trion as the possible reason for the PL blinking of single quantum dots. Single quantum dot electrochemistry has also been achieved. It is shown that by varying the Fermi level of the system electrons can be reversibly injected into and extracted out of single CdSe/CdS and CdSe/ZnS nanoparticles to modulate the photoluminescence.

  15. Scalable Quantum Computing with "Enhancement" Quantum Dots

    CERN Document Server

    Lyanda-Geller, Y B; Yang, M J

    2005-01-01

    We propose a novel scheme of solid state realization of a quantum computer based on single spin "enhancement mode" quantum dots as building blocks. In the enhancement quantum dots, just one electron can be brought into initially empty dot, in contrast to depletion mode dots based on expelling of electrons from multi-electron dots by gates. The quantum computer architectures based on depletion dots are confronted by several challenges making scalability difficult. These challenges can be successfully met by the approach based on ehnancement mode, capable of producing square array of dots with versatile functionalities. These functionalities allow transportation of qubits, including teleportation, and error correction based on straightforward one- and two-qubit operations. We describe physical properties and demonstrate experimental characteristics of enhancement quantum dots and single-electron transistors based on InAs/GaSb composite quantum wells. We discuss the materials aspects of quantum dot quantum compu...

  16. Quantum dot solar cells

    CERN Document Server

    Wu, Jiang

    2013-01-01

    The third generation of solar cells includes those based on semiconductor quantum dots. This sophisticated technology applies nanotechnology and quantum mechanics theory to enhance the performance of ordinary solar cells. Although a practical application of quantum dot solar cells has yet to be achieved, a large number of theoretical calculations and experimental studies have confirmed the potential for meeting the requirement for ultra-high conversion efficiency. In this book, high-profile scientists have contributed tutorial chapters that outline the methods used in and the results of variou

  17. Empirical pseudo-potential studies on electronic structure of semiconducting quantum dots

    Indian Academy of Sciences (India)

    Anjali Kshirsagar; Neelesh Kumbhojkar

    2008-06-01

    Theoretical investigations of electronic structure of quantum dots is of current interest in nanophase materials. Empirical theories such as effective mass approximation, tight binding methods and empirical pseudo-potential method are capable of explaining the experimentally observed optical properties. We employ the empirical pseudo-potential to calculate the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) as a function of shape and size of the quantum dots. Our studies explain the building up of the bulk band structure when the size of the dot is much larger than the bulk Bohr exciton radius. We present our investigations of HOMO–LUMO gap variation with size, for CdSe, ZnSe and GaAs quantum dots. The calculated excitonic energies are sensitive to the shape and size of quantum dots and are in good agreement with experimental HOMO–LUMO gaps for CdSe quantum dots. The agreement improves as experimentally observed lattice contraction is incorporated in pseudo-potential calculations for ZnSe quantum dots. Electronic structure evolution, as the size of quantum dot increases, is presented for CdSe, ZnSe and GaAs quantum dots.

  18. Spintronics and Quantum Computing with Quantum Dots

    OpenAIRE

    Recher, P.; Loss, D.; Levy, J

    2000-01-01

    The creation, coherent manipulation, and measurement of spins in nanostructures open up completely new possibilities for electronics and information processing, among them quantum computing and quantum communication. We review our theoretical proposal for using electron spins in quantum dots as quantum bits. We present single- and two qubit gate mechanisms in laterally as well as vertically coupled quantum dots and discuss the possibility to couple spins in quantum dots via superexchange. We ...

  19. Quantum dot cascade laser

    OpenAIRE

    Zhuo, Ning; Liu, Feng Qi; Zhang, Jin Chuan; Wang, Li Jun; Liu, Jun Qi; Zhai, Shen Qiang; Wang, Zhan Guo

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up...

  20. Using quantum dot photoluminescence for load detection

    Science.gov (United States)

    Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

    2016-08-01

    We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

  1. Quantum-dot based nanothermometry in optical plasmonic recording media

    Energy Technology Data Exchange (ETDEWEB)

    Maestro, Laura Martinez [Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Autónoma de Madrid, Madrid 28049 (Spain); Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia); Zhang, Qiming; Li, Xiangping; Gu, Min [Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia); Jaque, Daniel [Fluorescence Imaging Group, Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Autónoma de Madrid, Madrid 28049 (Spain)

    2014-11-03

    We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media.

  2. Quantum-dot based nanothermometry in optical plasmonic recording media

    International Nuclear Information System (INIS)

    We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media

  3. Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity

    Science.gov (United States)

    Kaur, Gurvir; Tripathi, S. K.

    2015-01-01

    The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent.

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

    Science.gov (United States)

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

    2016-01-25

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

  5. Time-Resolved Photoluminescence Spectroscopy: A Novel Technique for Determination of Luminescence of Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    ZHENG Zhu-Hong; SHEN De-Zhen

    2007-01-01

    @@ The time-resolved photoluminescence (PL) spectroscopy measured by the gradually increasing start delay time is utilized as a tool for the determination of the luminescence of quantum dots (QDs). The luminescence evolution of self-assembled CdSe QDs during the luminescence decay is fully revealed in terms of the experiment technique.The characteristic narrow luminescence lines of self-assembled CdSe QDs are obtained with increasing start delay time.

  6. Colloidal Double Quantum Dots

    Science.gov (United States)

    2016-01-01

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

  7. Colloidal Double Quantum Dots.

    Science.gov (United States)

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

    2016-05-17

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

  8. Quantum Phase Transitions in Quantum Dots

    OpenAIRE

    Rau, I. G.; Amasha, S.; Oreg, Y.; Goldhaber-Gordon, D.

    2013-01-01

    This review article describes theoretical and experimental advances in using quantum dots as a system for studying impurity quantum phase transitions and the non-Fermi liquid behavior at the quantum critical point.

  9. Quantum Dot Sensitized Photoelectrodes

    OpenAIRE

    Thomas Nann; Thomas J. Macdonald

    2011-01-01

    Quantum Dots (QDs) are promising alternatives to organic dyes as sensitisers for photocatalytic electrodes. This review article provides an overview of the current state of the art in this area. More specifically, different types of QDs with a special focus on heavy-metal free QDs and the methods for preparation and adsorption onto metal oxide electrodes (especially titania and zinc oxide) are discussed. Eventually, the key areas of necessary improvements are identified and assessed.

  10. Quantum Dot Sensitized Photoelectrodes

    Directory of Open Access Journals (Sweden)

    Thomas Nann

    2011-11-01

    Full Text Available Quantum Dots (QDs are promising alternatives to organic dyes as sensitisers for photocatalytic electrodes. This review article provides an overview of the current state of the art in this area. More specifically, different types of QDs with a special focus on heavy-metal free QDs and the methods for preparation and adsorption onto metal oxide electrodes (especially titania and zinc oxide are discussed. Eventually, the key areas of necessary improvements are identified and assessed.

  11. Plasmonic fluorescent quantum dots

    OpenAIRE

    Jin, Yongdong; Gao, Xiaohu

    2009-01-01

    Combining multiple discrete components into a single multifunctional nanoparticle could be useful in a variety of applications. Retaining the unique optical and electrical properties of each component after nanoscale integration is, however, a long-standing problem1,2. It is particularly difficult when trying to combine fluorophores such as semiconductor quantum dots with plasmonic materials such as gold, because gold and other metals can quench the fluorescence3,4. So far, the combination of...

  12. Quantum dots in graphene

    OpenAIRE

    Silvestrov, P.G.; Efetov, K. B.

    2006-01-01

    We suggest a way of confining quasiparticles by an external potential in a small region of a graphene strip. Transversal electron motion plays a crucial role in this confinement. Properties of thus obtained graphene quantum dots are investigated theoretically for different types of the boundary conditions at the edges of the strip. The (quasi)bound states exist in all systems considered. At the same time, the dependence of the conductance on the gate voltage carries an information about the s...

  13. Quantum dot nanostructures

    Directory of Open Access Journals (Sweden)

    Mohamed Henini

    2002-06-01

    These sophisticated technologies for the growth of high quality epitaxial layers of compound semiconductor materials on single crystal semiconductor substrates are becoming increasingly important for the development of the semiconductor electronics industry. This article is intended to convey the flavor of the subject by focusing on the technology and applications of self-assembled quantum dots (QDs and to give an introduction to some of the essential characteristics.

  14. Electrochromic nanocrystal quantum dots.

    Science.gov (United States)

    Wang, C; Shim, M; Guyot-Sionnest, P

    2001-03-23

    Incorporating nanocrystals into future electronic or optoelectronic devices will require a means of controlling charge-injection processes and an understanding of how the injected charges affect the properties of nanocrystals. We show that the optical properties of colloidal semiconductor nanocrystal quantum dots can be tuned by an electrochemical potential. The injection of electrons into the quantum-confined states of the nanocrystal leads to an electrochromic response, including a strong, size-tunable, midinfrared absorption corresponding to an intraband transition, a bleach of the visible interband exciton transitions, and a quench of the narrow band-edge photoluminescence. PMID:11264530

  15. Quantum dot solar cell

    International Nuclear Information System (INIS)

    Full text: The much awaited desire of replacing fossil fuel with photovoltaic will remain a fairy tale if the myriad of issues facing solar cell development are marginalized. Foremost in the list is the issue of cost. Silicon has reached a stage where its use on large scale can no longer be lavishly depended upon. The demand for high grade silicon from the microelectronics and solar industries has soared leading to scarcity. New approach has to be sought. Notable is the increased attention on thin films such as cadmium telluride, copper indium gallium diselenide, amorphous silicon, and the not so thin non-crystalline family of silicon. While efforts to address the issues of stability, toxicity and efficiency of these systems are ongoing, another novel approach is quietly making its appearance - quantum dots. Quantum dots seem to be promising candidates for solar cells because of the opportunity to manipulate their energy levels allowing absorption of a wider solar spectrum. Utilization of minute quantity of these nano structures is enough to bring the cost of solar cell down and to ascertain sustainable supply of useful material. The paper outlines the progress that has been made on quantum dot solar cells. (author)

  16. Effect of cadmium selenide quantum dots on the dielectric and physical parameters of ferroelectric liquid crystal

    International Nuclear Information System (INIS)

    The effect of cadmium selenide quantum dots (CdSe QDs) on the dielectric relaxation and material constants of a ferroelectric liquid crystal (FLC) has been investigated. Along with the characteristic Goldstone mode, a new relaxation mode has been induced in the FLC material due to the presence of CdSe QDs. This new relaxation mode is strongly dependent on the concentration of CdSe QDs but is found to be independent of the external bias voltage and temperature. The material constants have also been modified remarkably due to the presence of CdSe QDs. The appearance of this new relaxation phenomenon has been attributed to the concentration dependent interaction between CdSe QDs and FLC molecules.

  17. Electron correlations in quantum dots

    CERN Document Server

    Tipton, D L J

    2001-01-01

    Quantum dot structures confine electrons in a small region of space. Some properties of semiconductor quantum dots, such as the discrete energy levels and shell filling effects visible in addition spectra, have analogies to those of atoms and indeed dots are sometimes referred to as 'artificial atoms'. However, atoms and dots show some fundamental differences due to electron correlations. For real atoms, the kinetic energy of electrons dominates over their mutual Coulomb repulsion energy and for this reason the independent electron approximation works well. For quantum dots the confining potential may be shallower than that of real atoms leading to lower electron densities and a dominance of mutual Coulomb repulsion over kinetic energy. In this strongly correlated regime the independent electron picture leads to qualitatively incorrect results. This thesis concentrates on few-electron quantum dots in the strongly correlated regime both for quasi-one-dimensional and two-dimensional dots in a square confining p...

  18. Improved performance of nanowire-quantum-dot-polymer solar cells by chemical treatment of the quantum dot with ligand and solvent materials

    Science.gov (United States)

    Nadarajah, A.; Smith, T.; Könenkamp, R.

    2012-12-01

    We report a nanowire-quantum-dot-polymer solar cell consisting of a chemically treated CdSe quantum dot film deposited on n-type ZnO nanowires. The electron and hole collecting contacts are a fluorine-doped tin-oxide/zinc oxide layer and a P3HT/Au layer. This device architecture allows for enhanced light absorption and an efficient collection of photogenerated carriers. A detailed analysis of the chemical treatment of the quantum dots, their deposition, and the necessary annealing processes are discussed. We find that the surface treatment of CdSe quantum dots with pyridine, and the use of 1,2-ethanedithiol (EDT) ligands, critically improves the device performance. Annealing at 380 °C for 2 h is found to cause a structural conversion of the CdSe from its initial isolated quantum dot arrangement into a polycrystalline film with excellent surface conformality, thereby resulting in a further enhancement of device performance. Moreover, long-term annealing of 24 h leads to additional increases in device efficiency. Our best conversion efficiency reached for this type of cell is 3.4% under 85 mW cm-2 illumination.

  19. Quantum dot cascade laser

    Science.gov (United States)

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up to 400 K. Moreover, our materials show the strong perpendicular mid-infrared response at about 1,900 cm-1. These results are very promising for extending the present laser concept to terahertz quantum cascade laser, which would lead to room temperature operation. PACS 42.55.Px; 78.55.Cr; 78.67.Hc PMID:24666965

  20. Surface structure and optical property of amorphous carbon nanotubes hybridized with cadmium selenide quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Kim Han, E-mail: kimhan8419@gmail.com; Johan, Mohd Rafie [University of Malaya, Nanomaterials Engineering Research Group, Advanced Materials Research Laboratory, Department of Mechanical Engineering (Malaysia)

    2013-09-15

    Amorphous carbon nanotubes ({alpha}-CNTs) were synthesized by a chemical reaction between ferrocene and ammonium chloride at low temperature. The as-synthesized {alpha}-CNTs were then hybridized with cadmium selenide quantum dots (CdSe QDs) through a simple chemical process. Raman spectra reveal the amorphous nature of the {alpha}-CNTs surface. X-ray diffraction pattern confirmed the amorphous phase of carbon and the formation of CdSe QDs crystalline phase. Field emission scanning electron microscopy and transmission electron microscopy (TEM and HRTEM) indicate that the successfully formed hybridized {alpha}-CNTs-CdSe QDs possess an average outer diameter in the range of 110-130 nm. The CdSe QDs fall in the size range of 15-40 nm. UV-visible spectroscopy showed quantum confinement effect due to the attachment of CdSe QDs on the surface of {alpha}-CNTs.

  1. Observation of room temperature negative differential resistance in multi-layer heterostructures of quantum dots and conducting polymers

    International Nuclear Information System (INIS)

    Multi-layer heterostructure negative differential resistance devices based on poly-[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conducting polymer and CdSe quantum dots is reported. The conducting polymer MEH-PPV acts as a barrier while CdSe quantum dots form the well layer. The devices exhibit negative differential resistance (NDR) at low voltages. For these devices, strong negative differential resistance is observed at room temperature. A maximum value of 51 for the peak-to-valley ratio of current is reported. Tunneling of electrons through the discrete quantum confined states in the CdSe quantum dots is believed to be responsible for the multiple peaks observed in the I-V measurement. Depending on the observed NDR signature, operating mechanisms are explored based on resonant tunneling and Coulomb blockade effects.

  2. Quadra-Quantum Dots and Related Patterns of Quantum Dot Molecules: Basic Nanostructures for Quantum Dot Cellular Automata Application

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

    Full Text Available Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called 'Droplet Epitaxy' has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390'C with a droplet growth rate of 1ML/s. Arsenic flux (7'8'10-6Torr is then exposed for InGaAs crystallization at 200'C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or, which are preferable crystallographic directions of quantum dot alignment in general.

  3. Quantum dots: Rethinking the electronics

    Science.gov (United States)

    Bishnoi, Dimple

    2016-05-01

    In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including "waste heat" from the sun's energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.

  4. Exciton-LO phonon interaction in II-VI self-assembled quantum dots

    International Nuclear Information System (INIS)

    We study the exciton-LO phonon interaction in CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots (QDs) by means of resonantly excited PL spectroscopy. We find that in the case of large (∝8-10 nm in diameter) CdSe QDs the strength of the exciton-LO phonon coupling is nearly independent of the dot size (e.g. emission energy). In contrast, for CdTe dots (significantly smaller than the CdSe dots) the exciton-LO phonon coupling increases strongly for QDs with higher emission energy (smaller size). Finally, we show for annealed CdTe QDs that, the exciton-LO phonon interaction again becomes independent of emission energy, consistent with the larger dot sizes created by the annealing. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

    Science.gov (United States)

    Kikkawa, J. M.; Turk, M. E.; Vora, P. M.; Fafarman, A. T.; Diroll, B. T.; Murray, C. B.; Kagan, C. R.

    2015-03-01

    We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature (10 K) optical properties of CdSe quantum dot (QD) solids with different ligand and annealing preparation. Close-packed CdSe quantum dot solids are prepared with native aliphatic ligands and with thiocyanate with and without thermal annealing. Using sub-picosecond, broadband time-resolved photoluminescence and absorption, we find that ligand exchange increases the rate of carrier surface trapping. We further determine that holes within the QD core, rather than electrons, can bleach the band-edge transition in these samples at low temperature, a finding that comes as a surprise given what is known about the surface treatment in these QDs. We find that our ligand treatments lead to faster electron trapping to the quantum dot surface, a greater proportion of surface photoluminescence, and an increased rate of nonradiative decay due to enhanced interparticle coupling upon exchange and annealing. All aspects of this work supported by the U.S. Department of Energy Office of Basic Energy Sciences, Division of Materials Science and Engineering, under Award No. DE-SC0002158.

  6. Carrier relaxation processes in magnetic semiconductor quantum-dot systems

    International Nuclear Information System (INIS)

    The energy relaxation process of CdSe/ZnMnSe quantum dots (QDs) was investigated using polarization-selective magneto-photoluminescence (PL). Peaks from the Mn2+ internal transition, the CdSe QDs, and the ZnMnSe barrier were observed in the system. The CdSe QD peak was relatively weak while the intensity of the Mn2+ transition was strong in the spectrum taken at zero magnetic field. However, the peaks intensities changed significantly when a magnetic field was applied, and the situation became reversed (i.e., the CdSe QD peak become stronger than the peak due to the Mn2+ internal transition, specifically for σ+ polarization). The opposite intensity behavior was observed in the peak from the Mn2+ ions and in the PL of the CdSe QDs and revealed that these two carrier capture centers competed with each other for carriers excited in the ZnMnSe barrier. The variation in the Mn2+ internal transition with the magnetic field was well described by using a model developed under an angular momentum selection rule. This suggests that competition between the two energy transfer processes in the CdSe/ZnMnSe QD system is responsible for the observed PL intensity behavior.

  7. Spin pumping through quantum dots

    OpenAIRE

    Rojek, Stephan; Governale, Michele; König, Jürgen

    2013-01-01

    We propose schemes for generating spin currents into a semiconductor by adiabatic or non-adiabatic pumping of electrons through interacting quantum dots. The appeal of such schemes lies in the possibility to tune the pumping characteristics via gate voltages that control the properties of the quantum dot. The calculations are based on a systematic perturbation expansion in the tunnel-coupling strength and the pumping frequency, expressed within a diagrammatic real-time technique. Special focu...

  8. Photonics of shungite quantum dots

    OpenAIRE

    Razbirin, Boris S.; Rozhkova, Natalia N.; Sheka, Elena F.

    2014-01-01

    Shungite quantum dots are associated with nanosize fragments of reduced graphene oxide similarly to synthetic graphene quantum dots thus forming a common class of GQDs. Colloidal dispersions of powdered shungite in water, carbon tetrachloride, and toluene form the ground for the GQD photonic peculiarities manifestation. Morphological study shows a steady trend of GQDs to form fractals and a drastic change in the colloids fractal structure caused by solvent was reliably established. Spectral s...

  9. One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels

    OpenAIRE

    Huang Hai; Wu Yulian; Zhai Chuanxin; Zhang Hui; Du Ning; Chen Bingdi; Yang Deren

    2011-01-01

    Abstract We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs) was used for passivating the defect emission (650 nm) and enhancing the ...

  10. Photoluminescence intermittency of semiconductor quantum dots in dielectric environments

    Energy Technology Data Exchange (ETDEWEB)

    Isaac, A.

    2006-08-11

    The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. (orig.)

  11. Optical enhancement of photoluminescence with colloidal quantum dots

    Science.gov (United States)

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

    2015-08-01

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

  12. Room temperature excitation spectroscopy of single quantum dots

    Directory of Open Access Journals (Sweden)

    Christian Blum

    2011-08-01

    Full Text Available We report a single molecule detection scheme to investigate excitation spectra of single emitters at room temperature. We demonstrate the potential of single emitter photoluminescence excitation spectroscopy by recording excitation spectra of single CdSe nanocrystals over a wide spectral range of 100 nm. The spectra exhibit emission intermittency, characteristic of single emitters. We observe large variations in the spectra close to the band edge, which represent the individual heterogeneity of the observed quantum dots. We also find specific excitation wavelengths for which the single quantum dots analyzed show an increased propensity for a transition to a long-lived dark state. We expect that the additional capability of recording excitation spectra at room temperature from single emitters will enable insights into the photophysics of emitters that so far have remained inaccessible.

  13. Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications

    OpenAIRE

    Xu Hengyi; Dixon JohnDavid; Aguilar Zoraida; Wang Andrew; Xu Jian; Su Huaipeng; Gao Shuai; Wang Jingkang

    2010-01-01

    Abstract We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs) overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resultin...

  14. Femtosecond Cooling of Hot Electrons in CdSe Quantum-Well Platelets

    NARCIS (Netherlands)

    Sippel, Philipp; Albrecht, Wiebke; van der Bok, Johanna C.; Moes, Relinde; Hannappel, Thomas; Eichberger, Rainer; Vanmaekelbergh, Daniel

    2015-01-01

    Semiconductor quantum wells are ubiquitous in high-performance optoelectronic devices such as solar cells and lasers. Understanding and controlling of the (hot) carrier dynamics is essential to optimize their performance. Here, we study hot electron cooling in colloidal CdSe quantum-well nanoplatele

  15. Synthesis of CdSe/CdS core/shell quantum dots for biological sensing applications

    Science.gov (United States)

    Xu, Yang; Mariam, Poojitha; Sethi, Varun; Jones, Mason; Meehan, Kathleen

    2006-02-01

    A simple, room temperature, one-pot method to produce biocompatible CdSe/CdS quantum dots (QDs) in aqueous solution is presented. CdCl II and NaSeSO 3 are the precursors for the CdSe core where gelatin is used as an inhibitor. A CdS shell is grown by injecting H IIS gas, generated by a reaction between sulfuric and sodium sulfide, into the solution. This fast, low cost synthesis approach is simple for scale-up production of QDs. Transmission electron microscopy shows that the bare CdSe quantum dots were 2-3 nm in diameter. The emission peak from the CdSe can be tuned over most of the visible wavelength (from 520nm to 600 nm) as the diameter of the QDs is allowed to increase before growth of the CdS shell. The core/shell structure was confirmed via UV-Vis absorption spectroscopy, PL studies, and structural characterization (XRD). The higher band gap CdS coatings significantly enhanced the photoluminescence (PL) of CdSe quantum dots by a factor of 2-3. However, the large lattice mismatch between the CdS coating and the CdSe core results in eventually quenched luminescence from CdSe with thicker CdS coatings. To increase the photochemical stability and biocompatibility of the CdSe/CdS QDs, a silica coating is grown directly on the QDs. Preliminary data indicates that the PL from CdSe/CdS QDs post-growth is affected as the applied electric field is altered. Efforts to functionalize the QDs with DNA and antibodies have begun. Studies have been initiated to demonstrate the feasibility of microinjecting the QDs into Xenopus embryo with minimal post-synthesis processing.

  16. Quantum dot quantum cascade infrared photodetector

    International Nuclear Information System (INIS)

    We demonstrate an InAs quantum dot quantum cascade infrared photodetector operating at room temperature with a peak detection wavelength of 4.3 μm. The detector shows sensitive photoresponse for normal-incidence light, which is attributed to an intraband transition of the quantum dots and the following transfer of excited electrons on a cascade of quantum levels. The InAs quantum dots for the infrared absorption were formed by making use of self-assembled quantum dots in the Stranski–Krastanov growth mode and two-step strain-compensation design based on InAs/GaAs/InGaAs/InAlAs heterostructure, while the following extraction quantum stairs formed by LO-phonon energy are based on a strain-compensated InGaAs/InAlAs chirped superlattice. Johnson noise limited detectivities of 3.64 × 1011 and 4.83 × 106 Jones at zero bias were obtained at 80 K and room temperature, respectively. Due to the low dark current and distinct photoresponse up to room temperature, this device can form high temperature imaging

  17. Synthesis and optical properties of cadmium selenide quantum dots for white light-emitting diode application

    International Nuclear Information System (INIS)

    Highlights: ► Stable CdSe QDs were synthesized by the one-step and two-level process respectively. ► The fabricated white LEDs show good white balance. ► CdSe QDs present well green to yellow band luminescence. ► CdSe QDs displayed a broad excitation band. - Abstract: Yellow light-emitting cadmium selenide quantum dots were synthesized using one-step and two-step methods in an aqueous medium. The structural luminescent properties of these quantum dots were investigated. The obtained cadmium selenide quantum dots displayed a broad excitation band suitable for blue or near-ultraviolet light-emitting diode applications. White light-emitting diodes were fabricated by coating the cadmium selenide samples onto a 460 nm-emitting indium gallium nitrite chip. Both samples exhibited good white balance. Under a 20 mA working current, the white light-emitting diode fabricated via the one-step and two-step methods showed Commission Internationale de l’Éclairage coordinates at (0.27, 0.23) and (0.27, 0.33), respectively, and a color rendering index equal to 41 and 37, respectively. The one-step approach was simpler, greener, and more effective than the two-step approach. The one-step approach can be enhanced by combining cadmium selenide quantum dots with proper phosphors

  18. Effect of capping agents on optical and antibacterial properties of cadmium selenide quantum dots

    Indian Academy of Sciences (India)

    Deepika; Rakesh Dhar; Suman Singh; Atul Kumar

    2015-09-01

    Cadmium selenide quantum dots (CdSe QDs) were synthesized in aqueous phase by the freezing temperature injection technique using different capping agents (viz. thioglycolic acid, 1-thioglycerol, L-cysteine). Absorption spectra of CdSe QDs exhibited a blue shift as compared to its bulk counterpart, which is an indication of quantum confinement effect. The photoluminescence spectra of CdSe QDs confirmed that the particles are poly-dispersed and possess enhanced luminescent property, depending upon the chemical nature of capping agents. The QDs have been characterized by Fourier-transform infrared spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. Further, antimicrobial activity of as-prepared QDs has also been investigated using the disk diffusion method.

  19. Quadra-quantum Dots and Related Patterns of Quantum Dot Molecules:

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2010-10-01

    Full Text Available Abstract Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called ‘‘Droplet Epitaxy” has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390°C with a droplet growth rate of 1ML/s. Arsenic flux (7–8×10-6Torr is then exposed for InGaAs crystallization at 200°C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or , which are preferable crystallographic directions of quantum dot alignment in general.

  20. Quantum dot field effect transistors

    Directory of Open Access Journals (Sweden)

    Frederik Hetsch

    2013-09-01

    Full Text Available Solution processed colloidal semiconductor quantum dots offer a high potential for decreasing costs and expanding versatility of many electronic and optoelectronic devices. Initially used as a research tool to study charge carrier mobilities in closely packed quantum dot thin films, field effect transistors with quantum dots as the active layer have recently experienced a breakthrough in performance (achievement of mobilities higher than 30 cm2 V−1 s−1 as a result of a proper choice of surface ligands and/or improved chemical treatment of the nanoparticle films during device processing. Here we review these innovative developments and the continuing work that may soon lead to commercial grade electronic components.

  1. CdSe量子点与对氨基苯磺酸偶联反应研究%Coupling reaction of CdSe quantum dots with aminobenzene sulfonic acid

    Institute of Scientific and Technical Information of China (English)

    王伟杰; 俞英; 林碧霞; 梁耀珍

    2011-01-01

    The water soluble CdSe QDs, which were prepared by wrapping nanoparticles of the CdSe QD's with mercapto-propionic acid ( M PA) , were covalently conjugated with ami-nobenzene sulfonic acid ( ABSA) by linker EDC and NHS. The CdSe/MPA/ABSA was characterized using transmission electron microscopy, UV-vis spectrometry, fluorescence spec-trometry, fluorescence decay spectrometry, IR spectrometry, Capillary electrophoregrams. The coupled complex of CdSe QDs with ABSA was proved to be successfully. The results show that CdSe/MPA/ABSA possess fine optical properties.%以巯基丙酸为修饰剂合成水溶性硒化镉量子点(CdSe/MPA),利用碳化二亚胺(EDC)和琥珀酰亚胺(NHS)两种偶联剂,将对氨基苯磺酸与硒化镉量子点进行偶联以制备量子点-对氨基苯磺酸偶合物.通过透射电子显微镜、紫外-可见光谱、荧光光谱、荧光寿命、红外光谱、毛细管电泳对偶合物进行了表征.结果表明:量子点和对氨基苯磺酸偶联成功,该偶合物基本保持了量子点的荧光性能,可以作为研究植物病理的荧光探针.

  2. A colloidal quantum dot spectrometer

    Science.gov (United States)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

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

  3. Quantum features of semiconductor quantum dots

    International Nuclear Information System (INIS)

    The exact solutions of the two-dimensional Schrodinger equation with the position-dependent mass for the square well potential in the semiconductor quantum dots system are obtained. The eigenvalues, which are closely related to the position-dependent masses μ1 and μ2, the potential well depth V0 and the radius of the quantum dots r0, can be calculated from two boundary conditions. We generalize this quantum system to three-dimensional case. The special cases for the angular momentum quantum number l=0, 1, 2 are studied in some detail. We find that the energy levels are proportional to the parameters μ2, V0 and r0 for l=0. The relations between them for l=1, 2 become very complicated. The scattering states of this quantum system are mentioned briefly

  4. Beer's law in semiconductor quantum dots

    CERN Document Server

    Adamashvili, G T

    2010-01-01

    The propagation of a coherent optical linear wave in an ensemble of semiconductor quantum dots is considered. It is shown that a distribution of transition dipole moments of the quantum dots changes significantly the polarization and Beer's absorption length of the ensemble of quantum dots. Explicit analytical expressions for these quantities are presented.

  5. Quantum-dot emitters in photonic nanostructures

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    The spontaneous emission from self-assembled semiconductor quantum dots is strongly influenced by the environment in which they are placed. This can be used to determine fundamental optical properties of the quantum dots as well as to manipulate and control the quantum-dot emission itself....

  6. Quantum dots: promises and accomplishments

    Directory of Open Access Journals (Sweden)

    Dieter Bimberg

    2011-09-01

    Full Text Available Exploration of the Stranski-Krastanow growth of strained semiconductor heterostructures marked the major breakthrough for easy fabrication of defect-free quantum dots (QDs. For the first time, single QDs are facilitating the development of electrically operated emitters of single polarized or entangled photons on demand: an essential component for quantum communication systems. QDs inserted in quantum wells, stacked in planes upon each other, have led to semiconductor lasers that can operate at wavelengths that were previously impossible, or at least difficult to reach, for a given semiconductor family. These lasers show excellent temperature stability, large radiation resistance, and excellent temporal and spatial stability. In this review we discuss recent progress in the field of quantum dot devices.

  7. CdSe量子点/PVK复合电双稳器件的制备及载流子输运性能研究%Fabrication of Hybrid Bi-Stable Device Based on CdSe Quantum Dots/Poly(N-Vinylecarbasole) Composite and Its Carrier Transport

    Institute of Scientific and Technical Information of China (English)

    谢剑星; 李福山; 辛琦; 吴朝兴; 张永志; 张蓓蓓; 徐胜; 郭太良

    2013-01-01

    A novel type of the organic/inorganic hybrid bi-stable device has been successfully fabricated with the CdSe quantum dots (QDs) embedded in poly(N-vinylecaibasole) (PVK) as the nano-composite material, hi the newly-developed device, the reversible transition between the high and low resistance states,corresponding to the write and erase processes of a digital memory device,can be realized at room temperature by applying a positive and/or negative pulsed bias.Moreover,the device has survived the high repetition of read-erase-read-write tests.The current-voltage and capacitance-voltage characteristics of the device were evaluated to understand the possible mechanisms responsible for the capture and release of the carriers in reversible transitions.%报道一种基于CdSe量子点/聚乙烯基咔唑有机无机复合电双稳器件,通过对量子点浓度的控制使器件在室温下可以通过正向偏压和负向偏压脉冲激励下实现高阻态与低阻态的相互转变,相当于存储器件的写入功能与擦除功能,并且可实现重复的“读-擦-读-写”操作.对电流-电压曲线和电容-电压曲线展开讨论,验证器件的载流子捕获与释放机制,阐述载流子在该器件的输运机制.

  8. Spin storage in quantum dot ensembles and single quantum dots

    International Nuclear Information System (INIS)

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T1=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T1∝B-5 has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T1∝T-1. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T1h in the microsecond range, therefore, comparable with electron spin

  9. Spin storage in quantum dot ensembles and single quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Heiss, Dominik

    2009-10-15

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h

  10. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids

    NARCIS (Netherlands)

    Boehme, Simon C.; Walvis, T. Ardaan; Infante, Ivan; Grozema, Ferdinand C.; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J.

    2014-01-01

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We fi

  11. Covalent Linking Greatly Enhances Photoinduced Electron Transfer in Fullerene-Quantum Dot Nanocomposites: Time-Domain Ab Initio Study

    DEFF Research Database (Denmark)

    Chaban, Vitaly V.; Prezhdo, Victor; Prezhdo, Oleg

    2013-01-01

    Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process...

  12. Silicon quantum dot sensors for an explosive taggant, 2,3-dimethyl-2,3-dinitrobutane (DMNB).

    Science.gov (United States)

    Kim, Jin Soo; Cho, Bomin; Cho, Soo Gyeong; Sohn, Honglae

    2016-07-01

    Silicon quantum dots obtained by the reaction of magnesium silicide with ethylenediamine dihydrochloride were utilized to investigate the sensing mechanism and sensitivity for DMNB detection applications. Sensing DMNB provided us with evidence that Si QDs with a higher lying conduction band have better sensitivity compared to CdSe QDs. PMID:27188402

  13. Toxicity of carbon group quantum dots

    Science.gov (United States)

    Hanada, Sanshiro; Fujioka, Kouki; Hoshino, Akiyoshi; Manabe, Noriyoshi; Hirakuri, Kenji; Yamamoto, Kenji

    2009-02-01

    Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for HeLa cells in culture and thereby detected the cellular toxicity by administration of high concentration of Si-QD (>1000 μg/mL), while we detected the high toxicity by administration of over 100 μg/mL of CdSe-QDs. As a hypothesis for the cause of the cellular toxicity, we measured oxy-radical generation from the QDs by means of luminol reaction method. We detected generation of oxy-radicals from the Si-QDs and those were decreased by radical scavenger such as superoxide dismutase (SOD) and N-acetyl cysteine (NAC). We concluded that the Si-QD application to cultured cells in high concentration led cell membrane damage by oxy-radicals and combination usage with radical scavenger is one of the answers.

  14. On triaxial ellipsoidal quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Voon, L C Lew Yan; Willatzen, M [Mads Clausen Institute, University of Southern Denmark, Grundtvigs Alle 150, DK-6400 Soenderborg (Denmark)

    2004-02-25

    The bound-state problem for triaxial ellipsoidal infinite-barrier quantum dots has been solved. It is exactly solvable in terms of ellipsoidal coordinates and the eigenmodes are written in terms of Lame wavefunctions. The need for all eight types of functions is shown. This presents a generalization over previous work on spheres and spheroids. Splitting of degeneracy and level crossing are obtained.

  15. Quantum dot photonic crystal lasers

    OpenAIRE

    Yoshie, T.; Shchekin, O. B.; Chen, H.; Deppe, D. G.; Scherer, A.

    2002-01-01

    Coupled cavity designs on two-dimensional square lattice photonic crystal slabs were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimised photonic crystals.

  16. Optical Fiber Sensing Using Quantum Dots

    OpenAIRE

    Faramarz Farahi; José Luís Santos; Tito Trindade; Manuel António Martins; Pedro Jorge

    2007-01-01

    Recent advances in the application of semiconductor nanocrystals, or quantum dots, as biochemical sensors are reviewed. Quantum dots have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based bioanalytical techniques. An overview of the more relevant progresses in the application of quantum dots as biochemical probes is addressed. Special focus will be given to configurations where the sensing dots are incorporated in sol...

  17. Quantum chaos in open quantum dot arrays

    International Nuclear Information System (INIS)

    Full text: The discovery of chaos in macro-scale physical systems led to the emergence of a new understanding of laws in nature. Chaos should not exist at all in quantum systems - as laws of quantum mechanics actually forbid it. We will show in this work the footprints of quantum chaos in the dynamics of electron transport by studying ballistic open quantum dot arrays. We will apply quantum mechanical calculations and classical calculations in order to explain the low field magneto-transport through open quantum dots. To characterize the quantum/classical correspondence in this system and to understand the transport, it is necessary to invoke dynamical tunneling, a quantum-mechanical mechanism which allows tunneling of electrons between chaotic and regular regions in the phase space, a process which is classically forbidden. The relevant conclusions regarding dynamical tunneling are drawn by using Husimi representations. By comparing the classical trajectories with the electron probability density high accordance is achieved. The Husimi plots are used to visualize the wave function distribution in the vx-x-plane of the Poincare section. We show in the Husimi plots that the wave function has weight on the regular and chaotic regions alike. This represents a distribution in the phase space that cannot be generated by classical dynamics and supports the interpretation including dynamical tunneling. (author)

  18. Coherent control of quantum dots

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Lodahl, Peter; Hvam, Jørn Märcher

    In recent years much effort has been devoted to the use of semiconductor quantum dotsystems as building blocks for solid-state-based quantum logic devices. One importantparameter for such devices is the coherence time, which determines the number ofpossible quantum operations. From earlier...... measurements the coherence time of the selfassembledquantum dots (QDs) has been reported to be limited by the spontaneousemission rate at cryogenic temperatures1.In this project we propose to alter the coherence time of QDs by taking advantage of arecent technique on modifying spontaneous emission rates with...

  19. Semiconductor double quantum dot micromaser.

    Science.gov (United States)

    Liu, Y-Y; Stehlik, J; Eichler, C; Gullans, M J; Taylor, J M; Petta, J R

    2015-01-16

    The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from terahertz sources to quantum communication. Here we demonstrate a maser that is driven by single-electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside a high-quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. PMID:25593187

  20. Performance Study of CdS/Co-Doped-CdSe Quantum Dot Sensitized Solar Cells

    Directory of Open Access Journals (Sweden)

    Xiaoping Zou

    2014-01-01

    Full Text Available In order to optimize the charge transfer path in quantum dot sensitized solar cells (QDSCs, we employed successive ionic layer adsorption and reaction method to dope CdSe with Co for fabricating CdS/Co-doped-CdSe QDSCs constructed with CdS/Co-doped-CdSe deposited on mesoscopic TiO2 film as photoanode, Pt counter electrode, and sulfide/polysulfide electrolyte. After Co doping, the bandgap of CdSe quantum dot decreases, and the conduction band and valence band all improve, forming a cascade energy level which is more conducive to charge transport inside the solar cell and reducing the recombination of electron-hole thus improving the photocurrent and ultimately improving the power conversion efficiency. This work has not been found in the literature.

  1. Quantum-dot computing

    International Nuclear Information System (INIS)

    A quantum computer would put the latest PC to shame. Not only would such a device be faster than a conventional computer, but by exploiting the quantum-mechanical principle of superposition it could change the way we think about information processing. However, two key goals need to be met before a quantum computer becomes reality. The first is to be able to control the state of a single quantum bit (or 'qubit') and the second is to build a two-qubit gate that can produce 'entanglement' between the qubit states. (U.K.)

  2. Quantum-dot computing

    Energy Technology Data Exchange (ETDEWEB)

    Milburn, Gerard

    2003-10-01

    A quantum computer would put the latest PC to shame. Not only would such a device be faster than a conventional computer, but by exploiting the quantum-mechanical principle of superposition it could change the way we think about information processing. However, two key goals need to be met before a quantum computer becomes reality. The first is to be able to control the state of a single quantum bit (or 'qubit') and the second is to build a two-qubit gate that can produce 'entanglement' between the qubit states. (U.K.)

  3. Semiconductor quantum-dot lasers and amplifiers

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Borri, Paola; Ledentsov, N. N.;

    2002-01-01

    We have produced GaAs-based quantum-dot edge-emitting lasers operating at 1.16 mu m with record-low transparency current, high output power, and high internal quantum efficiencies. We have also realized GaAs-based quantum-dot lasers emitting at 1.3 mu m, both high-power edge emitters and low-power...... biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...... surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier is...

  4. Chaos and Interactions in Quantum Dots

    OpenAIRE

    Alhassid, Y.

    2001-01-01

    Quantum dots are small conducting devices containing up to several thousand electrons. We focus here on closed dots whose single-electron dynamics are mostly chaotic. The mesoscopic fluctuations of the conduction properties of such dots reveal the effects of one-body chaos, quantum coherence and electron-electron interactions.

  5. Resonant electron transfer between quantum dots

    OpenAIRE

    Openov, Leonid A.

    1999-01-01

    An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposition of electron s...

  6. Co-sensitized quantum dot solar cell based on ZnO nanowire

    International Nuclear Information System (INIS)

    An efficient photoelectrode is fabricated by sequentially assembled CdS and CdSe quantum dots (QDs) onto a ZnO-nanowire film. As revealed by UV-vis absorption spectrum and scanning electron microscopy (SEM), CdS and CdSe QDs can be effectively adsorbed on ZnO-nanowire array. Electrochemical impedance spectroscopy (EIS) measured demonstrates that the electron lifetime for ZnO/CdS/CdSe (13.8 ms) is calculated longer than that of ZnO/CdS device (6.2 ms), which indicates that interface charge recombination rate is reduced by sensitizing CdSe QDs. With broader light absorption range and longer electron lifetime, a power conversion efficiency of 1.42% is achieved for ZnO based CdS/CdSe co-sensitized solar cell under the illumination of one Sun (AM 1.5G, 100 mW cm-2).

  7. Quantum Computer Using Coupled Quantum Dot Molecules

    CERN Document Server

    Wu, N J; Natori, A; Yasunaga, H; Wu*, Nan-Jian

    1999-01-01

    We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can...

  8. Lanthanide modification of CdSe/ZnS core/shell quantum dots

    DEFF Research Database (Denmark)

    Dethlefsen, Johannes Rytter; Mikhailovsky, Alexander A.; Burks, Peter T.;

    2012-01-01

    Lanthanide-modified CdSe quantum dots (CdSe(Ln) QDs) have been prepared by heating a solution of Cd(oleate)(2), SeO2, and Ln(bipy)(S2CNEt2)(3) (bipy = 2,2'-bipyridine) to 180-190 degrees C for 10-15 min. The elemental compositions of the resulting CdSe(Ln) cores and CdSe(Ln)/ZnS core/shell QDs show...

  9. Cytocompatibility of direct water synthesized cadmium selenide quantum dots in colo-205 cells

    OpenAIRE

    Rodriguez-Torres, Marcos R.; Velez, Christian; Zayas, Beatriz; Rivera, Osvaldo; Arslan, Zikri; Gonzalez-Vega, Maxine N.; Diaz-Diestra, Daysi; Beltran-Huarac, Juan; Morell, Gerardo; Primera-Pedrozo, Oliva M.

    2015-01-01

    Cadmium selenide quantum dots (CdSe QDs), inorganic semiconducting nanocrystals, are alluring increased attraction due to their highly refined chemistry, availability, and super tunable optical properties suitable for many applications in different research areas, such as photovoltaics, light-emitting devices, environmental sciences, and nanomedicine. Specifically, they are being widely used in bio-imaging in contrast to organic dyes due to their high brightness and improved photo-stability, ...

  10. Optical Waveguide Lightmode Spectroscopy (OWLS) as a Sensor for Thin Film and Quantum Dot Corrosion

    OpenAIRE

    Jinke Tang; Qilin Dai; Wenyong Wang; Hao Yu; Eggleston, Carrick M; Jiajun Chen

    2012-01-01

    Optical waveguide lightmode spectroscopy (OWLS) is usually applied as a biosensor system to the sorption-desorption of proteins to waveguide surfaces. Here, we show that OWLS can be used to monitor the quality of oxide thin film materials and of coatings of pulsed laser deposition synthesized CdSe quantum dots (QDs) intended for solar energy applications. In addition to changes in data treatment and experimental procedure, oxide- or QD-coated waveguide sensors must be synthesized. We synthesi...

  11. Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots

    Directory of Open Access Journals (Sweden)

    Sai Li-Man

    2011-01-01

    Full Text Available Abstract A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

  12. Ex situ formation of metal selenide quantum dots using bacterially derived selenide precursors

    International Nuclear Information System (INIS)

    Luminescent quantum dots were synthesized using bacterially derived selenide (SeII−) as the precursor. Biogenic SeII− was produced by the reduction of SeIV by Veillonella atypica and compared directly against borohydride-reduced SeIV for the production of glutathione-stabilized CdSe and β-mercaptoethanol-stabilized ZnSe nanoparticles by aqueous synthesis. Biological SeII− formed smaller, narrower size distributed QDs under the same conditions. The growth kinetics of biologically sourced CdSe phases were slower. The proteins isolated from filter sterilized biogenic SeII− included a methylmalonyl-CoA decarboxylase previously characterized in the closely related Veillonella parvula. XAS analysis of the glutathione-capped CdSe at the S K-edge suggested that sulfur from the glutathione was structurally incorporated within the CdSe. A novel synchrotron based XAS technique was also developed to follow the nucleation of biological and inorganic selenide phases, and showed that biogenic SeII− is more stable and more resistant to beam-induced oxidative damage than its inorganic counterpart. The bacterial production of quantum dot precursors offers an alternative, ‘green’ synthesis technique that negates the requirement of expensive, toxic chemicals and suggests a possible link to the exploitation of selenium contaminated waste streams. (paper)

  13. Thermoelectric energy harvesting with quantum dots

    International Nuclear Information System (INIS)

    We review recent theoretical work on thermoelectric energy harvesting in multi-terminal quantum-dot setups. We first discuss several examples of nanoscale heat engines based on Coulomb-coupled conductors. In particular, we focus on quantum dots in the Coulomb-blockade regime, chaotic cavities and resonant tunneling through quantum dots and wells. We then turn toward quantum-dot heat engines that are driven by bosonic degrees of freedom such as phonons, magnons and microwave photons. These systems provide interesting connections to spin caloritronics and circuit quantum electrodynamics. (topical review)

  14. Charging graphene nanoribbon quantum dots

    OpenAIRE

    Żebrowski, D. P.; B. Szafran

    2015-01-01

    We describe charging a quantum dot induced electrostatically within a semiconducting graphene nanoribbon by electrons or holes. The applied model is based on a tight-binding approach with the electron-electron interaction introduced by a mean field local spin density approximation. The numerical approach accounts for the charge of all the $p_z$ electrons and screening of external potentials by states near the charge neutrality point. Both a homogenous ribbon and a graphene flake embedded with...

  15. FRET sensor with quantum dot

    Czech Academy of Sciences Publication Activity Database

    Datinská, Vladimíra; Klepárník, Karel; Belšánová, Barbora; Minárik, M.; Foret, František

    Veszprém: PANNON Egyetem, 2015 - (Mizsey, P.), s. 20-23 ISBN 978-963-396-072-1. [Műszaki Kémiai Napok 2015. Veszprém (HU), 21.04.2015-23.04.2015] R&D Projects: GA ČR(CZ) GA14-28254S; GA TA ČR(CZ) TA02010672 Institutional support: RVO:68081715 Keywords : FRET * quantum dot * sensor Subject RIV: CB - Analytical Chemistry, Separation

  16. FRET sensor with quantum dot

    Czech Academy of Sciences Publication Activity Database

    Datinská, Vladimíra; Klepárník, Karel; Belšánová, Barbora; Minárik, M.; Foret, František

    Veszprém : PANNON Egyetem, 2015 - (Mizsey, P.), s. 20-23 ISBN 978-963-396-072-1. [Műszaki Kémiai Napok 2015. Veszprém (HU), 21.04.2015-23.04.2015] R&D Projects: GA ČR(CZ) GA14-28254S; GA TA ČR(CZ) TA02010672 Institutional support: RVO:68081715 Keywords : FRET * quantum dot * sensor Subject RIV: CB - Analytical Chemistry, Separation

  17. Photoactivation of silicon quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Lockwood, R., E-mail: rossl@ualberta.c [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); McFarlane, S. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); Rodriguez Nunez, J.R. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Wang, X.Y. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada); Veinot, J.G.C. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Meldrum, A. [Department of Physics, University of Alberta, Edmonton, Alberta, T6G 2G7 (Canada)

    2011-07-15

    We show that free-standing silicon quantum dots (QDs) can be photoactivated by blue or UV optical irradiation. The luminescence intensity increases by an order of magnitude for irradiation times of several minutes under moderate optical power. The cut-off energy for photoactivation is between 2.1 and 2.4 eV, not very different from the activation energy for hydrogen dissociation from bulk silicon surfaces. We propose the mechanism for this effect is associated with silicon-hydride bond breaking and the subsequent oxidation of dangling bonds. This phenomenon could be used to 'write' luminescent quantum dots into pre-determined arrays. - Research highlights: {yields}Laser light causes increased photoluminescence intensity in silicon quantum dots. {yields} The photoactivation process is effective for wavelengths of 514 nm and shorter. {yields} Hydrogen bound to the Si-QDs is replaced by oxygen in a two-step process. {yields} Patterning is possible but limited by physical dispersion of Si-QDs.

  18. Ultrasmall colloidal PbS quantum dots

    International Nuclear Information System (INIS)

    Ultrasmall colloidal lead sulfide quantum dots can increase the open circuit voltages of quantum-dot-based solar cells because of their large energy gap. Their small size and visible or near infrared light-emitting property make them attractive to the applications of biological fluorescence labeling. Through a modified organometallic route, we can synthesize lead sulfide quantum dots as small as 1.6 nm in diameter. The low reaction temperature and the addition of a chloroalkane cosolvent decrease the reaction rate, making it possible to obtain the ultrasmall quantum dots. - Highlights: • Ultrasmall colloidal PbS quantum dots as small as 1.6 nm in diameter are synthesized. • The quantum dots emit red light with photoluminescence peak at 760 nm. • The growth temperature is as low as 50 °C. • Addition of cosolvent 1,2-dichloroethane in the reaction decreases the reaction rate

  19. Charge State Hysteresis in Semiconductor Quantum Dots

    OpenAIRE

    Yang, C. H.; Rossi, A; Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A.S.

    2014-01-01

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which acc...

  20. Multiple Energy Exciton Shelves in Quantum-Dot-DNA Nanobioelectronics.

    Science.gov (United States)

    Goodman, Samuel M; Singh, Vivek; Ribot, Josep Casamada; Chatterjee, Anushree; Nagpal, Prashant

    2014-11-01

    Quantum dots (QDs) are semiconductor nanocrystallites with multiple size-dependent quantum-confined states that are being explored for utilizing broadband radiation. While DNA has been used for the self-assembly of nanocrystals, it has not been investigated for the formation of simultaneous conduction pathways for transporting multiple energy charges or excitons. These exciton shelves can be formed by coupling the conduction band, valence band, and hot-carrier states in QDs with different HOMO-LUMO levels of DNA nucleobases, resulting from varying degrees of conjugation in the nucleobases. Here we present studies on the electronic density of states in four naturally occurring nucleobases (guanine, thymine, cytosine, and adenine), which energetically couple to quantized states in semiconductor QDs. Using scanning tunneling spectroscopy of single nanoparticle-DNA constructs, we demonstrate composite DOS of chemically coupled DNA oligonucleotides and cadmium chalcogenide QDs (CdS, CdSe, CdTe). While perfectly aligned CdTe QD-DNA states lead to exciton shelves for multiple energy charge transport, mismatched energy levels in CdSe QD-DNA introduce intrabandgap states that can lead to charge trapping and recombination. Although further investigations are required to study the rates of charge transfer, recombination, and back-electron transfer, these results can have important implications for the development of a new class of nanobioelectronics and biological transducers. PMID:26278768

  1. The quantum Hall effect in quantum dot systems

    International Nuclear Information System (INIS)

    It is proposed to use quantum dots in order to increase the temperatures suitable for observation of the integer quantum Hall effect. A simple estimation using Fock-Darwin spectrum of a quantum dot shows that good part of carriers localized in quantum dots generate the intervals of plateaus robust against elevated temperatures. Numerical calculations employing local trigonometric basis and highly efficient kernel polynomial method adopted for computing the Hall conductivity reveal that quantum dots may enhance peak temperature for the effect by an order of magnitude, possibly above 77 K. Requirements to potentials, quality and arrangement of the quantum dots essential for practical realization of such enhancement are indicated. Comparison of our theoretical results with the quantum Hall measurements in InAs quantum dot systems from two experimental groups is also given

  2. Activation of silicon quantum dots for emission

    Institute of Scientific and Technical Information of China (English)

    Huang Wei-Qi; Miao Xin-Jian; Huang Zhong-Mei; Liu Shi-Rong; Qin Chao-Jian

    2012-01-01

    The emission of silicon quantum dots is weak when their surface is passivated well. Oxygen or nitrogen on the surface of silicon quantum dots can break the passivation to form localized electronic states in the band gap to generate active centers where stronger emission occurs.From this point of view,we can build up radiative matter for emission.Emissions of various wavelengths can be obtained by controlling the surface bonds of silicon quantum dots.Our experimental results demonstrate that annealing is important in the treatment of the activation,and stimulated emissions at about 600 and 700 nm take place on active silicon quantum dots.

  3. Improved performance of nanowire–quantum-dot–polymer solar cells by chemical treatment of the quantum dot with ligand and solvent materials

    International Nuclear Information System (INIS)

    We report a nanowire–quantum-dot–polymer solar cell consisting of a chemically treated CdSe quantum dot film deposited on n-type ZnO nanowires. The electron and hole collecting contacts are a fluorine-doped tin-oxide/zinc oxide layer and a P3HT/Au layer. This device architecture allows for enhanced light absorption and an efficient collection of photogenerated carriers. A detailed analysis of the chemical treatment of the quantum dots, their deposition, and the necessary annealing processes are discussed. We find that the surface treatment of CdSe quantum dots with pyridine, and the use of 1,2-ethanedithiol (EDT) ligands, critically improves the device performance. Annealing at 380 °C for 2 h is found to cause a structural conversion of the CdSe from its initial isolated quantum dot arrangement into a polycrystalline film with excellent surface conformality, thereby resulting in a further enhancement of device performance. Moreover, long-term annealing of 24 h leads to additional increases in device efficiency. Our best conversion efficiency reached for this type of cell is 3.4% under 85 mW cm−2 illumination. (paper)

  4. Organic-Inorganic Nanocomposites via Directly Grafting Conjugated Polymers onto Quantum Dots

    Science.gov (United States)

    Lin, Zhiqun; Xu, Jun; Wang, Jun; Mitchell, Mike; Mukherjee, Prasun; Jeffries-El, Malika; Petrich, Jacob W.

    2008-03-01

    Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by directly grafting vinyl terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5-nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites.

  5. Photoinduced charge separation in organic-inorganic hybrid system: C60-containing electropolymer / CdSe-quantum dots

    International Nuclear Information System (INIS)

    Graphical Abstract: Display Omitted -- Highlights: •Modified ethylenedioxythiophene allows the formation of an electropolymer holding C60. •Polymer decoration with CdSe QDs produces a photoactive organic-inorganic interface. •Photoinduced electron transfers were analyzed by surface photovoltage. •The interface is a potential structure for the development of optoelectronic devices. -- Abstract: A photoactive interface is formed between an electrochemical generated organic polymer film and CdSe quantum dots. The specifically designed and synthesized 3,4 ethylenedioxythiophene electroactive monomer, holding C60 buckminsterfullerene, allows the formation of thin films containing both, electron acceptor and hole transport moieties. The generation of photoinduced heterogeneous charge transfer in CdSe quantum dots-electropolymer system was characterized by time resolved and spectral dependent surface photovoltage. In films containing C60 moieties whose surface was modified with 5 nm CdSe quantum dots, the illumination generated photovoltage values around twenty times larger than those obtained without nanoparticles decoration. The results show that this organic-inorganic hybrid interface is a potential structure for the development of optoelectronic devices

  6. Photoluminescence and structural properties of CdSe quantum dot–gelatin composite films

    International Nuclear Information System (INIS)

    Optical and structural properties of composite films of CdSe quantum dots (QDs) embedded in gelatin matrix have been investigated by photoluminescence (PL), optical absorption and X-ray diffraction (XRD) methods. The optical absorption of the composite in the visible spectral range is found to be determined mainly by light absorption in the QDs. The decrease of the film transparency and the shift of the absorption edge to lower energies observed upon thermal annealing of the films at 140–160 °C are ascribed to the formation of chromophore groups in gelatin matrix. XRD patterns of the composite revealed helix to coil transition in gelatin matrix under thermal annealing of the composite at 100–160 °C. It is found that PL spectra of the composite are dominated by exciton and defect-related emission of the QDs and also contain weak emission of gelatin matrix. It is found that thermal annealing of the composite at 100–160 °C changes PL intensity and produces the shift of the PL bands to lower energies. As the annealed composite was kept in air for several months, the shift of exciton-related PL band position restored partially and the PL intensity increased. It is proposed that the increase of the PL intensity upon the thermal annealing of composite at 140 °C can be used for enhancement of the QD-related PL. Changes that occurred in the PL spectra of composite are ascribed to structural and chemical transformations in gelatin matrix and at the QD/gelatin interface

  7. Photoluminescence and structural properties of CdSe quantum dot–gelatin composite films

    Energy Technology Data Exchange (ETDEWEB)

    Borkovska, L., E-mail: bork@isp.kiev.ua [V. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, Pr. Nauky 41, 03028 Kyiv (Ukraine); Korsunska, N.; Stara, T.; Gudymenko, O.; Kladko, V. [V. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, Pr. Nauky 41, 03028 Kyiv (Ukraine); Stroyuk, O.; Raevskaya, A. [L. Pysarzhevsky Institute of Physical Chemistry of NAS of Ukraine, Pr. Nauky 31, 03028 Kyiv (Ukraine); Kryshtab, T. [Instituto Politécnico Nacional – ESFM, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F. (Mexico)

    2014-11-15

    Optical and structural properties of composite films of CdSe quantum dots (QDs) embedded in gelatin matrix have been investigated by photoluminescence (PL), optical absorption and X-ray diffraction (XRD) methods. The optical absorption of the composite in the visible spectral range is found to be determined mainly by light absorption in the QDs. The decrease of the film transparency and the shift of the absorption edge to lower energies observed upon thermal annealing of the films at 140–160 °C are ascribed to the formation of chromophore groups in gelatin matrix. XRD patterns of the composite revealed helix to coil transition in gelatin matrix under thermal annealing of the composite at 100–160 °C. It is found that PL spectra of the composite are dominated by exciton and defect-related emission of the QDs and also contain weak emission of gelatin matrix. It is found that thermal annealing of the composite at 100–160 °C changes PL intensity and produces the shift of the PL bands to lower energies. As the annealed composite was kept in air for several months, the shift of exciton-related PL band position restored partially and the PL intensity increased. It is proposed that the increase of the PL intensity upon the thermal annealing of composite at 140 °C can be used for enhancement of the QD-related PL. Changes that occurred in the PL spectra of composite are ascribed to structural and chemical transformations in gelatin matrix and at the QD/gelatin interface.

  8. 倒置器件结构及局域等离子体效应对CdSe量子点LED发光性能的改进%Improvement of Performance for CdSe Quantum Dot LEDs by Using An Inverted Device Structure and Localized Surface Plasmon Resonance

    Institute of Scientific and Technical Information of China (English)

    陈肖慧; 赵家龙

    2012-01-01

    The improvement of the performance for CdSe quantum dot light emitting diodes ( QD-LEDs) was studied by using the inverted device structure and localized surface plasmon resonant (LSPR) coupling of Au nanoparticles with the QDs. We fabricated inverted QD-LEDs with TiO2 as the electron injection/transport layer. The current density-voltage characteristics of electron-only device were studied. The electron-injection current from the top Al electrode with the forward-bias voltage (Al was used as the cathode) was symmetrical with that of the bottom ITO electrode with reverse-bias voltage (ITO was used as the cathode), indicating the electron injection from ITO to TiO2 is facilitated like the case from Al cathode. It was noticed that the efficiency of QD-LEDs with Au nanoparticles was enhanced while the drop rate of the efficiency was clearly reduced with increasing the current density. A significant enhancement of 42% for current efficiency of the LEDs was achieved under high current density of 200 mA/cm.%研究了倒置器件结构以及CdSe量子点发光材料与金属纳米粒子之间的相互作用对量子点的电致发光性能的影响.利用TiO2作为电子传输/注入层,成功地制备了倒置结构的量子点电致发光器件.通过对单载流子器件电压-电流特性的分析,证明了ITO作为阴极到TiO2的电子注入特性与Al作为阴极时的效果几乎相同.观察到金属纳米粒子产生的局域等离子体效应提高了器件的效率,使得效率随电流增大而降低的速度明显减小.在电流密度为200 mA/cm2时,电致发光器件的效率大约提高了42%.

  9. Few-electron quantum dots

    International Nuclear Information System (INIS)

    We review some electron transport experiments on few-electron, vertical quantum dot devices. The measurement of current versus source-drain voltage and gate voltage is used as a spectroscopic tool to investigate the energy characteristics of interacting electrons confined to a small region in a semiconducting material. Three energy scales are distinguished: the single-particle states, which are discrete due to the confinement involved; the direct Coulomb interaction between electron charges on the dot; and the exchange interaction between electrons with parallel spins. To disentangle these energies, a magnetic field is used to reorganize the occupation of electrons over the single-particle states and to induce changes in the spin states. We discuss the interactions between small numbers of electrons (between 1 and 20) using the simplest possible models. Nevertheless, these models consistently describe a large set of experiments. Some of the observations resemble similar phenomena in atomic physics, such as shell structure and periodic table characteristics, Hund's rule, and spin singlet and triplet states. The experimental control, however, is much larger than for atoms: with one device all the artificial elements can be studied by adding electrons to the quantum dot when changing the gate voltage. (author)

  10. Quantum Optics with Quantum Dots in Photonic Nanowires

    DEFF Research Database (Denmark)

    Gérard, J.-M.; Claudon, J.; Bleuse, J.;

    2011-01-01

    We review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices.......We review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices....

  11. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    We will review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices.......We will review recent studies performed on InAs quantum dots embedded in GaAs photonic wires, which highlight the strong interest of the photonic wire geometry for quantum optics experiments and quantum optoelectronic devices....

  12. Quantum dot cosensitized solar cell based on PMOT@CdSe@ZnO core shell nanostructures with dual emission

    Science.gov (United States)

    Sehgal, Preeti; Narula, Anudeep Kumar

    2016-01-01

    Quantum dot sensitized solar cell based on poly(3-methoxythiophene) (PMOT)@CdSe@ZnO core shell nanostructure were synthesized where PMOT serves as hole transport material, CdSe acts as a photosensitizer which enhances visible range absorption and also helps in injection of electrons from PMOT to ZnO where ZnO provides channel for efficient electron transport. The properties of the device were assessed with and without CdSe quantum dots and effect of annealing was also observed on the device. After the addition of CdSe QDs, the visible light absorption of PMOT@ZnO was enhanced due to increase in surface area. PMOT@CdSe@ZnO exhibited dual emission, where CdSe and ZnO exhibited visible and UV emission respectively. The interface formed between PMOT and CdSe improves the charge separation. The better photovoltaic measurement of PMOT@CdSe@ZnO over CdSe@ZnO indicates that PMOT efficiently dissociate excitons at interface and suppress the interfacial charge recombination. A power conversion efficiency of 0.989% was attained for the device PMOT@CdSe@ZnO with Voc=0.56 V and Jsc=2.5 mA/cm2. Upon annealing, the efficiency of the device was enhanced to 1.1609% with Voc=0.58, Jsc=3.2 mA/cm2.

  13. Colloidal quantum dot photodetectors

    KAUST Repository

    Konstantatos, Gerasimos

    2011-05-01

    We review recent progress in light sensors based on solution-processed materials. Spin-coated semiconductors can readily be integrated with many substrates including as a post-process atop CMOS silicon and flexible electronics. We focus in particular on visible-, near-infrared, and short-wavelength infrared photodetectors based on size-effect-tuned semiconductor nanoparticles made using quantum-confined PbS, PbSe, Bi 2S3, and In2S3. These devices have in recent years achieved room-temperature D values above 1013 Jones, while fully-depleted photodiodes based on these same materials have achieved MHz response combined with 1012 Jones sensitivities. We discuss the nanoparticle synthesis, the materials processing, integrability, temperature stability, physical operation, and applied performance of this class of devices. © 2010 Elsevier Ltd. All rights reserved.

  14. Quantum Dot Spectrum Converters for Enhanced High Efficiency Photovoltaics Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This research proposes to enhance solar cell efficiency, radiation resistance and affordability. The Quantum Dot Spectrum Converter (QDSC) disperses quantum dots...

  15. Adiabatic pumping through quantum dots

    International Nuclear Information System (INIS)

    A finite charge can be pumped through a mesoscopic system in the absence of an applied bias voltage by changing periodically in time some parameters of the system. If these parameters change slowly with respect to all internal time scales of the system, pumping is adiabatic. The scope of this work is to investigate adiabatic pumping through a quantum dot, in particular the influence of Coulomb interaction between electrons in the dot on the pumped charge. On one hand we develop a formalism based on Green's functions, in order to calculate the pumped charge from the weak-tunnel-coupling regime down to the Kondo regime. We extend our calculations to a system with a superconducting contact. On the other hand we use a systematic perturbation expansion for the calculation of the pumped charge, giving us the possibility to analyze processes which contribute to charge pumping and to highlight the important role of interaction-induced level renormalization. (orig.)

  16. Photoluminescence of a quantum-dot molecule

    International Nuclear Information System (INIS)

    The coherent coupling of quantum dots is a sensitive indicator of the energy and phase relaxation processes taking place in the nanostructure components. We formulate a theory of low-temperature, stationary photoluminescence from a quantum-dot molecule composed of two spherical quantum dots whose electronic subsystems are resonantly coupled via the Coulomb interaction. We show that the coupling leads to the hybridization of the first excited states of the quantum dots, manifesting itself as a pair of photoluminescence peaks with intensities and spectral positions strongly dependent on the geometric, material, and relaxation parameters of the quantum-dot molecule. These parameters are explicitly contained in the analytical expression for the photoluminescence differential cross section derived in the paper. The developed theory and expression obtained are essential in interpreting and analyzing spectroscopic data on the secondary emission of coherently coupled quantum systems

  17. Electroluminescent hybrid organic/inorganic quantum dot devices

    International Nuclear Information System (INIS)

    The synthesis of PbS crystallites in aqueous solution in the presence of ethylenediaminetetraacetic acid (EDTA) has been investigated. Nanocrystalline material exhibiting charge confinement effects have been observed. The factors affecting crystallite growth, and hence the optical properties of the ultimately synthesised sample have been studied. A simple analytical model of the linear optical properties of quantum dots of finite size distribution has been developed. The model has been used in conjunction with the effective mass approximation (EMA) in order to model the optical properties of the synthesised PbS with a great deal of success. The EMA is found to limit the applicability of the optical model to samples of quantum dots consisting of larger crystallites as one would expect. Size-quantised CdSe particles have also been synthesised in aqueous solution. The same optical model successfully models the absorption spectra of these quantum dots, subject to the constraints of the EMA. Excessive scattering of light in solutions containing flocculated and/or bulk material is also found to limit the applicability of the model. The incorporation of colloidally suspended quantum dots into optoelectronic device structures has been considered. Energy level offsets between the quantum dots and host matrices have been studied and have been found to be unfavourable to the injection of electronic charge from the matrix into the dots. Alternative electroluminescent device structures in which the quantum dots are incorporated into electroluminescent host matrices which optically pump the quantum dots have therefore been proposed. Such devices have proved difficult to fabricate, eventual luminescence from quantum dot surface states having been obtained, but luminescence from the quantum dot effective bandgap not having been obtained. The scope of the project has extended to the investigation of charge injection into the quantum dot matrix materials themselves from the device

  18. Quantum dot cascade laser: Arguments in favor

    OpenAIRE

    Dmitriev, I. A.; Suris, R. A.

    2007-01-01

    Quantum cascade lasers are recognized as propitious candidates for future terahertz optoelectronics. Here we demonstrate several definite advantages of quantum dot cascade structures over quantum well devices, which suffer fundamental performance limitations owing to continuous carrier spectrum. The discrete spectrum of quantum dots opens an opportunity to control the non-radiative relaxation and optical loss and also provides for more flexibility in the choice of an optical and electrical de...

  19. Silicon quantum dots: surface matters

    International Nuclear Information System (INIS)

    Silicon quantum dots (SiQDs) hold great promise for many future technologies. Silicon is already at the core of photovoltaics and microelectronics, and SiQDs are capable of efficient light emission and amplification. This is crucial for the development of the next technological frontiers—silicon photonics and optoelectronics. Unlike any other quantum dots (QDs), SiQDs are made of non-toxic and abundant material, offering one of the spectrally broadest emission tunabilities accessible with semiconductor QDs and allowing for tailored radiative rates over many orders of magnitude. This extraordinary flexibility of optical properties is achieved via a combination of the spatial confinement of carriers and the strong influence of surface chemistry. The complex physics of this material, which is still being unraveled, leads to new effects, opening up new opportunities for applications. In this review we summarize the latest progress in this fascinating research field, with special attention given to surface-induced effects, such as the emergence of direct bandgap transitions, and collective effects in densely packed QDs, such as space separated quantum cutting. (topical review)

  20. Dynamic Trap Formation and Elimination in Colloidal Quantum Dots

    KAUST Repository

    Voznyy, O.

    2013-03-21

    Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers\\' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping. © 2013 American Chemical Society.

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

    Science.gov (United States)

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

    2016-09-01

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

  2. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    OpenAIRE

    Sreeram Cingarapu; Zhiqiang Yang; Sorensen, Christopher M.; Kenneth J. Klabunde

    2012-01-01

    We report synthesis of CdSe and CdTe quantum dots (QDs) from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD) technique and refined digestive ripening. The outcomes of this new process are (1) the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO) and oleylamine (OA)) as capping agent as well as digestive ripening solvent, (2) ability to tune the photoluminescence (PL) from 410 nm to 670 nm, (...

  3. Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell) Quantum Dots by Ligand Exchange

    OpenAIRE

    Huaping Zhu; Michael Z. Hu; Lei Shao; Kui Yu; Reza Dabestani; Md. Badruz Zaman; Shijun Liao

    2014-01-01

    The colloidal photoluminescent quantum dots (QDs) of CdSe (core) and CdSe/ZnS (core/shell) were synthesized at different temperatures with different growth periods. Optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra) of the resulting QDs were investigated. The shell-protected CdSe/ZnS QDs exhibited higher photoluminescent (PL) efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the i...

  4. Photoluminescence of hybrid quantum dots

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Bratislava: Slovak Expert Group of Solid State Chemistry and Physics , 2013 - (Koman, M.; Jorík, V.; Kožíšek, Z.). s. 28-28 ISBN 978-80-970896-5-8. [Joint Seminar – Development of materials science in research and education /23./. 09.09.2013-13.09.2013, Kežmarské Žľaby] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : energy transfer * quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism; JA - Electronics ; Optoelectronics, Electrical Engineering (UMCH-V)

  5. Quantum Wires and Quantum Dots for Neutral Atoms

    OpenAIRE

    Schmiedmayer, Joerg

    1998-01-01

    By placing changeable nanofabricated structures (wires, dots, etc.) on an atom mirror one can design guiding and trapping potentials for atoms. These potentials are similar to the electrostatic potentials which trap and guide electrons in semiconductor quantum devices like quantum wires and quantum dots. This technique will allow the fabrication of nanoscale atom optical devices.

  6. Thick-shell nanocrystal quantum dots

    Science.gov (United States)

    Hollingsworth, Jennifer A.; Chen, Yongfen; Klimov, Victor I.; Htoon, Han; Vela, Javier

    2011-05-03

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  7. Quantum Dots-based Reverse Phase Protein Microarray

    Energy Technology Data Exchange (ETDEWEB)

    Shingyoji, Masato; Gerion, Daniele; Pinkel, Dan; Gray, Joe W.; Chen, Fanqing

    2005-07-15

    CdSe nanocrystals, also called quantum dots (Qdots) are a novel class of fluorophores, which have a diameter of a few nanometers and possess high quantum yield, tunable emission wavelength and photostability. They are an attractive alternative to conventional fluorescent dyes. Quantum dots can be silanized to be soluble in aqueous solution under biological conditions, and thus be used in bio-detection. In this study, we established a novel Qdot-based technology platform that can perform accurate and reproducible quantification of protein concentration in a crude cell lysate background. Protein lysates have been spiked with a target protein, and a dilution series of the cell lysate with a dynamic range of three orders of magnitude has been used for this proof-of-concept study. The dilution series has been spotted in microarray format, and protein detection has been achieved with a sensitivity that is at least comparable to standard commercial assays, which are based on horseradish peroxidase (HRP) catalyzed diaminobenzidine (DAB) chromogenesis. The data obtained through the Qdot method has shown a close linear correlation between relative fluorescence unit and relative protein concentration. The Qdot results are in almost complete agreement with data we obtained with the well-established HRP-DAB colorimetric array (R{sup 2} = 0.986). This suggests that Qdots can be used for protein quantification in microarray format, using the platform presented here.

  8. PREFACE: Quantum dots as probes in biology

    Science.gov (United States)

    Cieplak, Marek

    2013-05-01

    The recent availability of nanostructured materials has resulted in an explosion of research focused on their unique optical, thermal, mechanical and magnetic properties. Optical imagining, magnetic enhancement of contrast and drug delivery capabilities make the nanoparticles of special interest in biomedical applications. These materials have been involved in the development of theranostics—a new field of medicine that is focused on personalized tests and treatment. It is likely that multimodal nanomaterials will be responsible for future diagnostic advances in medicine. Quantum dots (QD) are nanoparticles which exhibit luminescence either through the formation of three-dimensional excitons or excitations of the impurities. The excitonic luminescence can be tuned by changing the size (the smaller the size, the higher the frequency). QDs are usually made of semiconducting materials. Unlike fluorescent proteins and organic dyes, QDs resist photobleaching, allow for multi-wavelength excitations and have narrow emission spectra. The techniques to make QDs are cheap and surface modifications and functionalizations can be implemented. Importantly, QDs could be synthesized to exhibit useful optomagnetic properties and, upon functionalization with an appropriate biomolecule, directed towards a pre-selected target for diagnostic imaging and photodynamic therapy. This special issue on Quantum dots in Biology is focused on recent research in this area. It starts with a topical review by Sreenivasan et al on various physical mechanisms that lead to the QD luminescence and on using wavelength shifts for an improvement in imaging. The next paper by Szczepaniak et al discusses nanohybrids involving QDs made of CdSe coated by ZnS and combined covalently with a photosynthetic enzyme. These nanohybrids are shown to maintain the enzymatic activity, however the enzyme properties depend on the size of a QD. They are proposed as tools to study photosynthesis in isolated

  9. Multi-color single particle tracking with quantum dots.

    Directory of Open Access Journals (Sweden)

    Eva C Arnspang

    Full Text Available Quantum dots (QDs have long promised to revolutionize fluorescence detection to include even applications requiring simultaneous multi-species detection at single molecule sensitivity. Despite the early promise, the unique optical properties of QDs have not yet been fully exploited in e. g. multiplex single molecule sensitivity applications such as single particle tracking (SPT. In order to fully optimize single molecule multiplex application with QDs, we have in this work performed a comprehensive quantitative investigation of the fluorescence intensities, fluorescence intensity fluctuations, and hydrodynamic radii of eight types of commercially available water soluble QDs. In this study, we show that the fluorescence intensity of CdSe core QDs increases as the emission of the QDs shifts towards the red but that hybrid CdSe/CdTe core QDs are less bright than the furthest red-shifted CdSe QDs. We further show that there is only a small size advantage in using blue-shifted QDs in biological applications because of the additional size of the water-stabilizing surface coat. Extending previous work, we finally also show that parallel four color multicolor (MC-SPT with QDs is possible at an image acquisition rate of at least 25 Hz. We demonstrate the technique by measuring the lateral dynamics of a lipid, biotin-cap-DPPE, in the cellular plasma membrane of live cells using four different colors of QDs; QD565, QD605, QD655, and QD705 as labels.

  10. Introduction to the physics of quantum dots

    International Nuclear Information System (INIS)

    Quantum dots contain only a few well-defined energy levels for electron and/or holes as a result of the confinement of charge in all three spatial dimensions. Here, we describe both the application of photoluminescence spectroscopy and transport measurements to the characterisation of quantum dots and the novel phenomena that they exhibit. These include the Coulomb blockade, single electron tunneling and single photon detection. The impact of quantum dots on future electronics and directions for future research, such as in quantum computing and cryptography, are discussed. (author)

  11. Electron transport in quantum dots

    CERN Document Server

    2003-01-01

    When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the...

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

    OpenAIRE

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

    2013-01-01

    Ultrafast time-resolved absorption spectroscopy is used to investigate exciton dynamics in CdSe nanocrystal films. The effects of morphology, quantum-dot versus quantum-rod, and preparation of nanocrystals in a thin film form are investigated. The measurements revealed longer intraband exciton relaxation in quantum-rods than in quantum-dots. The slowed relaxation in quantum-rods is due to mitigation of the Auger-relaxation mechanism from elongating the nanocrystal. In addition, the nanocrysta...

  13. Semiconductor quantum dots enhanced graphene/CdTe heterostructure solar cells by photo-induced doping

    OpenAIRE

    Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian; Lin, Shisheng

    2015-01-01

    We report a type of solar cells based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is one-atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.1%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by transport, photoluminescence and quantum efficiency measurements. This work demonstrates a feasible way of de...

  14. Semiconductor quantum dots enhanced graphene/CdTe heterostructure solar cells by photo-induced doping

    CERN Document Server

    Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian; Lin, Shisheng

    2015-01-01

    Photo-induced doping is employed into graphene based solar cell through designing of a novel type of solar cell based on graphene/CdTe Schottky heterostructure. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the performance of the graphene/CdTe solar cell is improved by about 50%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by resistance, photoluminescence and quantum efficiency measurements. This work demonstrates a general and feasible way of designing novel type of solar cells based on two dimensional materials/semiconductor heterostructures.

  15. Temperature-dependent photoluminescence of water-soluble quantum dots for a bioprobe

    International Nuclear Information System (INIS)

    The photoluminescence of water-soluble CdSe/ZnS core/shell quantum dots is found to be temperature-dependent: as temperature arising from 280 K to 351 K, the photoluminescence declines with emission peak shifting towards the red at a rate of ∼0.11 nm K-1. And the studies show that the photoluminescence of water-soluble CdSe/ZnS quantum dots with core capped by a thinner ZnS shell is more sensitive to temperature than that of ones with core capped by a thicker one. That is, with 50% decrement of the quantum yield the temperature of the former need to arise from 280 K to 295 K, while the latter requires much higher temperature (315.6 K), which means that the integrality of shell coverage is a very important factor on temperature-sensitivity to for the photoluminescence of water-soluble CdSe/ZnS quantum dots. Moreover, it is found that the water-soluble CdSe quantum dots with different core sizes, whose cores are capped by thicker ZnS shells, possess almost the same sensitivity to the temperature. All of the studies about photoluminescence temperature-dependence of water-soluble CdSe/ZnS core/shell quantum dots show an indispensable proof for their applications in life science

  16. Application of Quantum-Dot Conjugates for Detection and Subspecies Differentiation of Vibrio cholerae by Optical Methods

    Science.gov (United States)

    Erohin, P. S.; Utkin, D. V.; Kouklev, V. E.; Ossina, N. A.; Miheeva, E. A.; Alenkina, T. V.

    2016-03-01

    The application of bioconjugates of specific antibodies and CdSe quantum dots to identify two serovariants of Vibrio cholerae using fluorescence microscopy and optical spectroscopy is considered. It is found that a mixture of different bioconjugates with different emission maxima can be used without affecting the specificity of the method. Different V. cholerae serovariants are colored differently in fl uorescence microscopy (bright green and bright yellow), thereby allowing subspecies differentiation. The absorption spectrum of the bacterial suspension changed with homologous antigens in the sample and did not change with heterologous antigens. It is shown that the quantum-dot bioconjugates can serve as an alternative to the traditional fluorescence and agglutination diagnostics.

  17. Quantum dot devices for optical communications

    DEFF Research Database (Denmark)

    Mørk, Jesper

    2005-01-01

    record-low threshold currents and amplifiers with record-high power levels. In this tutorial we will review the basic properties of quantum dots, emphasizing the properties which are important for laser and amplifier applications, as well as devices for all-optical signal processing. The high....... The main property of semiconductor quantum dots compared to bulk material or even quantum well structures is the discrete nature of the allowed states, which means that inversion of the medium can be obtained for very low electron densities. This has led to the fabrication of quantum dot lasers with......Semiconductor quantum dots are often described as "artificial atoms": They are small nanometre-sized structures in which electrons only are allowed to exist at certain discrete levels due to size quantization, thus allowing the engineering of fundamental properties such as the coupling to light...

  18. Large quantum dots with small oscillator strength

    DEFF Research Database (Denmark)

    Stobbe, Søren; Schlereth, T.W.; Höfling, S.;

    2010-01-01

    We have measured the oscillator strength and quantum efficiency of excitons confined in large InGaAs quantum dots by recording the spontaneous emission decay rate while systematically varying the distance between the quantum dots and a semiconductor-air interface. The size of the quantum dots is...... measured by in-plane transmission electron microscopy and we find average in-plane diameters of 40 nm. We have calculated the oscillator strength of excitons of that size assuming a quantum-dot confinement given by a parabolic in-plane potential and a hard-wall vertical potential and predict a very large...... oscillator strength due to Coulomb effects. This is in stark contrast to the measured oscillator strength, which turns out to be so small that it can be described by excitons in the strong confinement regime. We attribute these findings to exciton localization in local potential minima arising from alloy...

  19. Time-bin Entanglement from Quantum Dots

    CERN Document Server

    Weihs, Gregor; Predojević, Ana

    2016-01-01

    The desire to have a source of single entangled photon pairs can be satisfied using single quantum dots as emitters. However, we are not bound to pursue only polarization entanglement, but can also exploit other degrees of freedom. In this chapter we focus on the time degree of freedom, to achieve so-called time-bin entanglement. This requires that we prepare the quantum dot coherently into the biexciton state and also build special interferometers for analysis. Finally this technique can be extended to achieve time-bin and polarization hyper-entanglement from a suitable quantum dot.

  20. Magnon-driven quantum dot refrigerators

    Science.gov (United States)

    Wang, Yuan; Huang, Chuankun; Liao, Tianjun; Chen, Jincan

    2015-12-01

    A new model of refrigerator consisting of a spin-splitting quantum dot coupled with two ferromagnetic reservoirs and a ferromagnetic insulator is proposed. The rate equation is used to calculate the occupation probabilities of the quantum dot. The expressions of the electron and magnon currents are obtained. The region that the system can work in as a refrigerator is determined. The cooling power and coefficient of performance (COP) of the refrigerator are derived. The influences of the magnetic field, applied voltage, and polarization of two leads on the performance are discussed. The performances of two different magnon-driven quantum dot refrigerators are compared.

  1. Ultrafast coherent terahertz spectroscopy in high magnetic fields and directed energy flows in quantum dot assemblies

    International Nuclear Information System (INIS)

    We describe the design, construction and use of fiber-coupled terahertz antennas for performing ultrafast coherent THz spectroscopy directly in the cryogenic bore of high-field magnets. With the aim towards measuring the high-frequency (100 GHz - 2000 GHz) complex conductivity of correlated electron materials in the regime of low temperatures and high magnetic fields, these miniature THz emitters and receivers are demonstrated to work down to 1.5 and up to 18 T, for eventual use in higher-field magnets. Results from a variety of semiconducting and superconducting samples are presented. This paper also describes a separate effort towards achieving coupling between colloidal semiconductor nanocrystal quantum dots, wherein we realize and study inter-dot communication via resonant (Foerster) energy transfer. We present studies of the dynamics of resonant energy transfer in monodisperse and energy gradient (layered) assemblies of CdSe nanocrystal quantum dots. Time- and spectrally-resolved photoluminescence data directly reveal the energy-dependent transfer rate of excitons from smaller to larger dots. Results from layered nanocrystal quantum dot assemblies demonstrate unidirectional energy flows, a first step towards artificial light-harvesting structures. Lastly, time-resolved studies at milikelvin temperatures elucidate the nature of ground-state 'dark' excitons in these quantum dots. (author)

  2. Structural and optical characterization of Si/Ge quantum dots

    OpenAIRE

    Wigblad, Dan

    2008-01-01

    In this study silicon-germanium quantum dots grown on silicon have been investigated. The aim of the work was to find quantum dots suitable for use as a thermistor material. The quantum dots were produced at KTH, Stockholm, using a RPCVD reactor that is designed for industrial production. The techniques used to study the quantum dots were: HRSEM, AFM, HRXRD, FTPL, and Raman spectroscopy. Quantum dots have been produced in single and multilayer structures. As a result of this work a multilayer...

  3. Accurate analysis of electron transfer from quantum dots to metal oxides in quantum dot sensitized solar cells

    Science.gov (United States)

    Javad Fahimi, Mohammad; Fathi, Davood; Ansari-Rad, Mehdi

    2015-09-01

    Electron transfer rate from quantum dot (QD) to metal oxide (MO) in quantum dot sensitized solar cells (QDSSCs) has an important role in the efficiency. In this work, we analyse the electron transfer rate from CdSe, CdS and CdTe QDs to TiO2, ZnO and SnO2 MOs by extending the related equations with considering various effects, based on the Marcus theory. In this regard, the effects of QD diameter, QD-MO spacing, the crystalline defects, temperature, and the reorganizational energy, on the electron transfer rate are investigated. The results show that, the maximum electron transfer rate is achieved for CdTe QD with the mentioned three MOs. Moreover, in order to direct the designer to reach the appropriate QDs-MOs combinations for obtaining the maximum electron transfer rate, the average electron transfer rate for various combinations is calculated. For the verification of simulation method, a part of work has been compared with the previous experimental and theoretical results, which indicates the correctness of our simulation algorithm.

  4. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    International Nuclear Information System (INIS)

    We report synthesis of CdSe and CdTe quantum dots (QDs) from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD) technique and refined digestive ripening. The outcomes of this new process are (1) the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO) and oleylamine (OA)) as capping agent as well as digestive ripening solvent, (2) ability to tune the photoluminescence (PL) from 410 nm to 670 nm, (3) demonstrate the ability of SMAD synthesis technique for other semiconductors (CdTe), (4) direct comparison of CdSe QDs growth with CdTe QDs growth based on digestive ripening times, and (5) enhanced PL quantum yield (QY) of CdSe QDs and CdTe QDs upon covering with a ZnS shell. Further, the merit of this synthesis is the use of bulk CdSe and CdTe as the starting materials, which avoids usage of toxic organometallic compounds, eliminates the hot injection procedure, and size selective precipitation processes. It also allows the possibility of scale up. These QDs were characterized by UV-vis, photoluminescence (PL), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and powder XRD.

  5. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    Directory of Open Access Journals (Sweden)

    Sreeram Cingarapu

    2012-01-01

    Full Text Available We report synthesis of CdSe and CdTe quantum dots (QDs from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD technique and refined digestive ripening. The outcomes of this new process are (1 the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO and oleylamine (OA as capping agent as well as digestive ripening solvent, (2 ability to tune the photoluminescence (PL from 410 nm to 670 nm, (3 demonstrate the ability of SMAD synthesis technique for other semiconductors (CdTe, (4 direct comparison of CdSe QDs growth with CdTe QDs growth based on digestive ripening times, and (5 enhanced PL quantum yield (QY of CdSe QDs and CdTe QDs upon covering with a ZnS shell. Further, the merit of this synthesis is the use of bulk CdSe and CdTe as the starting materials, which avoids usage of toxic organometallic compounds, eliminates the hot injection procedure, and size selective precipitation processes. It also allows the possibility of scale up. These QDs were characterized by UV-vis, photoluminescence (PL, transmission electron microscopy (TEM, high-resolution transmission electron microscopy (HRTEM, X-ray photoelectron spectroscopy (XPS, and powder XRD.

  6. Optical Fiber Sensing Using Quantum Dots

    Directory of Open Access Journals (Sweden)

    Faramarz Farahi

    2007-12-01

    Full Text Available Recent advances in the application of semiconductor nanocrystals, or quantumdots, as biochemical sensors are reviewed. Quantum dots have unique optical properties thatmake them promising alternatives to traditional dyes in many luminescence basedbioanalytical techniques. An overview of the more relevant progresses in the application ofquantum dots as biochemical probes is addressed. Special focus will be given toconfigurations where the sensing dots are incorporated in solid membranes and immobilizedin optical fibers or planar waveguide platforms.

  7. Tunable Quantum Dot Solids: Impact of Interparticle Interactions on Bulk Properties

    Energy Technology Data Exchange (ETDEWEB)

    Sinclair, Michael B. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Fan, Hongyou [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Brener, Igal [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Liu, Sheng [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Luk, Ting S. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Li, Binsong [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    QD-solids comprising self-assembled semiconductor nanocrystals such as CdSe are currently under investigation for use in a wide array of applications including light emitting diodes, solar cells, field effect transistors, photodetectors, and biosensors. The goal of this LDRD project was develop a fundamental understanding of the relationship between nanoparticle interactions and the different regimes of charge and energy transport in semiconductor quantum dot (QD) solids. Interparticle spacing was tuned through the application of hydrostatic pressure in a diamond anvil cell, and the impact on interparticle interactions was probed using x-ray scattering and a variety of static and transient optical spectroscopies. During the course of this LDRD, we discovered a new, previously unknown, route to synthesize semiconductor quantum wires using high pressure sintering of self-assembled quantum dot crystals. We believe that this new, pressure driven synthesis approach holds great potential as a new tool for nanomaterials synthesis and engineering.

  8. Optical anisotropy in vertically coupled quantum dots

    DEFF Research Database (Denmark)

    Yu, Ping; Langbein, Wolfgang Werner; Leosson, Kristjan;

    1999-01-01

    We have studied the polarization of surface and edge-emitted photoluminescence (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found to be strongly dependent on the number of stacked layers. While single...... number due to increasing dot size....

  9. Double Acceptor Interaction in Semimagnetic Quantum Dot

    Directory of Open Access Journals (Sweden)

    A. Merwyn Jasper D. Reuben

    2011-01-01

    Full Text Available The effect of geometry of the semimagnetic Quantum Dot on the Interaction energy of a double acceptor is computed in the effective mass approximation using the variational principle. A peak is observed at the lower dot sizes as a magnetic field is increased which is attributed to the reduction in confinement.

  10. Ge Quantum Dot Infrared Imaging Camera Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Luna Innovations Incorporated proposes to develop a high performance Ge quantum dots-based infrared (IR) imaging camera on Si substrate. The high sensitivity, large...

  11. Submonolayer Quantum Dot Infrared Photodetector

    Science.gov (United States)

    Ting, David Z.; Bandara, Sumith V.; Gunapala, Sarath D.; Chang, Yia-Chang

    2010-01-01

    A method has been developed for inserting submonolayer (SML) quantum dots (QDs) or SML QD stacks, instead of conventional Stranski-Krastanov (S-K) QDs, into the active region of intersubband photodetectors. A typical configuration would be InAs SML QDs embedded in thin layers of GaAs, surrounded by AlGaAs barriers. Here, the GaAs and the AlGaAs have nearly the same lattice constant, while InAs has a larger lattice constant. In QD infrared photodetector, the important quantization directions are in the plane perpendicular to the normal incidence radiation. In-plane quantization is what enables the absorption of normal incidence radiation. The height of the S-K QD controls the positions of the quantized energy levels, but is not critically important to the desired normal incidence absorption properties. The SML QD or SML QD stack configurations give more control of the structure grown, retains normal incidence absorption properties, and decreases the strain build-up to allow thicker active layers for higher quantum efficiency.

  12. Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    Guan-xin Yao; Zai-xi Fu; Xian-yi Zhang; Xian-feng Zheng; Xue-han Ji; Zhi-feng Cui; Hong Zhang

    2011-01-01

    The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique.By selectively exciting the core and shell carrier,the dynamics are studied in detail.Carrier relaxation is found faster in the conduction band of the CdS shell (about 130 fs) than that in the conduction band of the CdSe core (about 400 fs).From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell,indicating that ultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.

  13. Semiconductor nanocrystals inside spherical microcavities: A case of quantum dots in photonic dots

    OpenAIRE

    Artemyev, M. V.

    2003-01-01

    Quantum dots in photonic dots, a new type of microstructures involving highly luminescent II-VI semiconductor nanocrystals has been proposed and realized by incorporating nanocrystals (quantum dots) into glass and polymeric microspheres. The high quality micron-size microspheres represent simplest fully three-dimensional microcavities (photonic dots). Coupling of discrete electron states of quantum dots and photon states inside photonic dots strongly affects onto both stationary and dynamic p...

  14. Positioning of quantum dots on metallic nanostructures

    International Nuclear Information System (INIS)

    The capability to position individual emitters, such as quantum dots, near metallic nanostructures is highly desirable for constructing active optical devices that can manipulate light at the single photon level. The emergence of the field of plasmonics as a means to confine light now introduces a need for high precision and reliability in positioning any source of emission, which has thus far been elusive. Placing an emission source within the influence of plasmonic structures now requires accuracy approaching molecular length scales. In this paper we report the ability to reliably position nanoscale functional objects, specifically quantum dots, with sub-100-nm accuracy, which is several times smaller than the diffraction limit of a quantum dot's emission light. Electron beam lithography-defined masks on metallic surfaces and a series of surface chemical functionalization processes allow the programmed assembly of DNA-linked colloidal quantum dots. The quantum dots are successfully functionalized to areas as small as (100 nm)2 using the specific binding of thiolated DNA to Au/Ag, and exploiting the streptavidin-biotin interaction. An analysis of the reproducibility of the process for various pattern sizes shows that this technique is potentially scalable to the single quantum dot level with 50 nm accuracy accompanied by a moderate reduction in yield.

  15. Time dependent quantum transport through Kondo correlated quantum dots

    OpenAIRE

    Goker, Ali; Gedik, Elif

    2013-01-01

    In this article, we review recent work about time dependent quantum transport through a quantum dot in Kondo regime. This represents a major step towards designing next generation transistors that are expected to replace current MOSFET's in a few years. We first discuss the effects of the density of states of gold contacts on the instantaneous conductance of an asymmetrically coupled quantum dot that is abruptly moved into Kondo regime via a gate voltage. Next, we investigate the effect of st...

  16. Magnetic quantum dots and magnetic edge states

    International Nuclear Information System (INIS)

    Starting with defining the magnetic edge state in a magnetic quantum dot, which becomes quite popular nowadays conjunction with a possible candidate for a high density memory device or spintronic materials, various magnetic nano-quantum structures are reviewed in detail. We study the magnetic edge states of the two dimensional electron gas in strong perpendicular magnetic fields. We find that magnetic edge states are formed along the boundary of the magnetic dot, which is formed by a nonuniform distribution of magnetic fields. These magnetic edge states circulate either clockwise or counterclockwise, depending on the number of missing flux quanta, and exhibit quite different properties, as compared to the conventional ones which are induced by electrostatic confinements in the quantum Hall system. We also find that a close relation between the quantum mechanical eigenstates and the classical trajectories in the magnetic dot. When a magnetic dot is located inside a quantum wire, the edge-channel scattering mechanism by the magnetic quantum dot is very different from that by electrostatic dots. Here, the magnetic dot is formed by two different magnetic fields inside and outside the dot. We study the ballistic edge-channel transport and magnetic edge states in this situation. When the inner field is parallel to the outer one, the two-terminal conductance is quantized and shows the features of a transmission barrier and a resonator. On the other hand, when the inner field is reversed, the conductance is not quantized and all channels can be completely reflected in some energy ranges. The difference between the above two cases results from the distinct magnetic confinements. We also describe successfully the edge states of magnetic quantum rings and others in detail

  17. Quantum phase transition in trigonal triple quantum dots: The case of quantum dots deviated from particle–hole symmetric point

    International Nuclear Information System (INIS)

    We consider a triple quantum dot system in a triangular geometry with one of the dots connected to metallic leads. We investigate quantum phase transition between local moment phase and Kondo screened strong coupling phase in triple quantum dots where energy levels of dots are deviated from the particle–hole symmetric point. The effect of on-site energy of dots on quantum phase transition between local moment phase and Kondo screened strong coupling phase in triple quantum dots is studied based on the analytical arguments and the numerical renormalization group method. The results show that the critical value of tunnel coupling between side dots decreases when the energy level of embedded dot rises up from the symmetric point to the Fermi level and the critical value increases when the energy levels of two side dots rise up. The study of the influence of on-site-energy changes on the quantum phase transitions in triple quantum dots has the importance for clarifying the mechanism of Kondo screening in triple quantum dots where energy levels of dots are deviated from the particle–hole symmetric point

  18. Inter-dot coupling effects on transport through correlated parallel coupled quantum dots

    Indian Academy of Sciences (India)

    Shyam Chand; G Rajput; K C Sharma; P K Ahluwalia

    2009-05-01

    Transport through symmetric parallel coupled quantum dot system has been studied, using non-equilibrium Green function formalism. The inter-dot tunnelling with on-dot and inter-dot Coulomb repulsion is included. The transmission coefficient and Landaur–Buttiker like current formula are shown in terms of internal states of quantum dots. The effect of inter-dot tunnelling on transport properties has been explored. Results, in intermediate inter-dot coupling regime show signatures of merger of two dots to form a single composite dot and in strong coupling regime the behaviour of the system resembles the two decoupled dots.

  19. Quantum-dot-in-perovskite solids

    KAUST Repository

    Ning, Zhijun

    2015-07-15

    © 2015 Macmillan Publishers Limited. All rights reserved. Heteroepitaxy - atomically aligned growth of a crystalline film atop a different crystalline substrate - is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned \\'dots-in-a-matrix\\' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

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

    Energy Technology Data Exchange (ETDEWEB)

    Vitukhnovskii, A. G., E-mail: alexei@sci.lebedev.ru; Vaschenko, A. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Bychkovskii, D. N. [OOO Optogan-OLS (Russian Federation); Dirin, D. N.; Tananaev, P. N.; Vakshtein, M. S. [OOO RTTC Nanotech-Dubna (Russian Federation); Korzhonov, D. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    2013-12-15

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

  1. (In,Mn)As multilayer quantum dot structures

    International Nuclear Information System (INIS)

    (In,Mn)As multilayer quantum dots structures were grown by molecular beam epitaxy using a Mn selective doping of the central parts of quantum dots. The study of the structural and magneto-optical properties of the samples with three and five layers of (In,Mn)As quantum dots has shown that during the quantum dots assembly, the out-diffusion of Mn from the layers with (In,Mn)As quantum dots can occur resulting in the formation of the extended defects. To produce a high quality structures using the elaborated technique of selective doping, the number of (In,Mn)As quantum dot layers should not exceed three

  2. Optically controlled spins in semiconductor quantum dots

    Science.gov (United States)

    Economou, Sophia

    2010-03-01

    Spins in charged semiconductor quantum dots are currently generating much interest, both from a fundamental physics standpoint, as well as for their potential technological relevance. Being naturally a two-level quantum system, each of these spins can encode a bit of quantum information. Optically controlled spins in quantum dots possess several desirable properties: their spin coherence times are long, they allow for all-optical manipulation---which translates into fast logic gates---and their coupling to photons offers a straightforward route to exchange of quantum information between spatially separated sites. Designing the laser fields to achieve the unprecedented amount of control required for quantum information tasks is a challenging goal, towards which there has been recent progress. Special properties of hyperbolic secant optical pulses enabled the design of single qubit rotations, initially developed about the growth axis z [1], and later about an arbitrary direction [2]. Recently we demonstrated our theoretical proposal [1] in an ensemble of InAs/GaAs quantum dots by implementing ultrafast rotations about the z axis by an arbitrary angle [3], with the angle of rotation as a function of the optical detuning in excellent agreement with the theoretical prediction. We also developed two-qubit conditional control in a quantum dot `molecule' using the electron-hole exchange interaction [4]. In addition to its importance in quantum dot-based quantum computation, our two-qubit gate can also play an important role in photonic cluster state generation for measurement-based quantum computing [5]. [1] S. E. Economou, L. J. Sham, Y. Wu, D. S. Steel, Phys. Rev. 74, 205415 (2006) [2] S. E. Economou and T. L. Reinecke, Phys. Rev. Lett., 99, 217401 (2007) [3] A. Greilich, S. E. Economou et al, Nature Phys. 5, 262 (2009) [4] S. E. Economou and T. L. Reinecke, Phys. Rev. B, 78, 115306 (2008) [5] S. E. Economou, N. H. Lindner, and T. Rudolph, in preparation

  3. Engineered Quantum Dot Single Photon Sources

    CERN Document Server

    Buckley, Sonia; Vuckovic, Jelena

    2012-01-01

    Fast, high efficiency, and low error single photon sources are required for implementation of a number of quantum information processing applications. The fastest triggered single photon sources to date have been demonstrated using epitaxially grown semiconductor quantum dots (QDs), which can be conveniently integrated with optical microcavities. Recent advances in QD technology, including demonstrations of high temperature and telecommunications wavelength single photon emission, have made QD single photon sources more practical. Here we discuss the applications of single photon sources and their various requirements, before reviewing the progress made on a quantum dot platform in meeting these requirements.

  4. Origins and optimization of entanglement in plasmonically coupled quantum dots

    Science.gov (United States)

    Otten, Matthew; Larson, Jeffrey; Min, Misun; Wild, Stefan M.; Pelton, Matthew; Gray, Stephen K.

    2016-08-01

    A system of two or more quantum dots interacting with a dissipative plasmonic nanostructure is investigated in detail by using a cavity quantum electrodynamics approach with a model Hamiltonian. We focus on determining and understanding system configurations that generate multiple bipartite quantum entanglements between the occupation states of the quantum dots. These configurations include allowing for the quantum dots to be asymmetrically coupled to the plasmonic system. Analytical solution of a simplified limit for an arbitrary number of quantum dots and numerical simulations and optimization for the two- and three-dot cases are used to develop guidelines for maximizing the bipartite entanglements. For any number of quantum dots, we show that through simple starting states and parameter guidelines, one quantum dot can be made to share a strong amount of bipartite entanglement with all other quantum dots in the system, while entangling all other pairs to a lesser degree.

  5. Quantum dot optoelectronic devices: lasers, photodetectors and solar cells

    International Nuclear Information System (INIS)

    Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells. (topical review)

  6. Dot-in-Well Quantum-Dot Infrared Photodetectors

    Science.gov (United States)

    Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

  7. Quantum Dots in Photonic Crystal Waveguides

    DEFF Research Database (Denmark)

    Sollner, Immo Nathanael

    This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the...... chiral quantum-dot-waveguide coupling. Such a structure is ideally suited for a number of applications in quantum information processing and among others we propose an on-chip spin-photon interface, a single photon transistor, and a deterministic cNOT gate.......This Thesis is focused on the study of quantum electrodynamics in photonic crystal waveguides. We investigate the interplay between a single quantum dot and the fundamental mode of the photonic crystal waveguide. We demonstrate experimental coupling eciencies for the spontaneous emission into the...... mode exceeding 98% for emitters spectrally close to the band-edge of the waveguide mode. In addition we illustrate the broadband nature of the underlying eects, by obtaining coupling eciencies above 90% for quantum dots detuned from the band edge by as far as 20nm. These values are in good agreement...

  8. Colloidal Quantum dot photovoltaics: Tuning optoelectronic properties

    International Nuclear Information System (INIS)

    Full text: Colloidal quantum dots combine processing from the solution phase with tunability of the bandgap. Via the size-effect the optical properties can be matched to the solar spectrum for a wide-range photon harvesting. To engineer photovoltaic devices, quantum dots are compressed from their colloidal form into a close-packed nanocrystal matrix, while undergoing a systematic layer-by-layer process. The resulting quantum dot solid is treated as semiconductor medium - one having electron-hole mobilites, free carrier densities and a dielectric constant. While the size-effect determined the band-gap before, it is now the nature of ligand and the treatment route, that influences mentioned electronic parameters. We took the view on the processing steps and found a concept for analysing trap states, moblility and device performance in real quantum dot solids. Our findings emphasize the interplay of mobility and trap-distribution with routes that take special care on the nanocrystal surface and hence conserve optoelectronic qualities of quantum dots for efficient photovoltaic cells. (author)

  9. Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells

    Science.gov (United States)

    Mahmoud, Samadpour; Azam Iraji, zad; Mehdi, Molaei

    2014-04-01

    TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained just by tuning the photoanode structure without further treatments, which will make this system a promising nanostructure for efficient quantum dot sensitized solar cells.

  10. Bound states in continuum: Quantum dots in a quantum well

    International Nuclear Information System (INIS)

    We report on the existence of a bound state in the continuum (BIC) of quantum rods (QR). QRs are novel elongated InGaAs quantum dot nanostructures embedded in the shallower InGaAs quantum well. BIC appears as an excited confined dot state and energetically above the bottom of a well subband continuum. We prove that high height-to-diameter QR aspect ratio and the presence of a quantum well are indispensable conditions for accommodating the BIC. QRs are unique semiconductor nanostructures, exhibiting this mathematical curiosity predicted 83 years ago by Wigner and von Neumann.

  11. Faraday Rotation Spectroscopy of Quantum-Dot Quantum Wells

    OpenAIRE

    Meier, Florian; Awschalom, David D.

    2004-01-01

    Time-resolved Faraday rotation studies of CdS/CdSe/CdS quantum-dot quantum wells have recently shown that the Faraday rotation angle exhibits several well-defined resonances as a function of probe energy close to the absorption edge. Here, we calculate the Faraday rotation angle from the eigenstates of the quantum-dot quantum well obtained with k.p theory. We show that the large number of narrow resonances with comparable spectral weight observed in experiment is not reproduced by the level s...

  12. Inorganic passivation and doping control in colloidal quantum dot photovoltaics

    KAUST Repository

    Hoogland, Sjoerd H.

    2012-01-01

    We discuss strategies to reduce midgap trap state densities in colloidal quantum dot films and requirements to control doping type and magnitude. We demonstrate that these improvements result in colloidal quantum dot solar cells with certified 7.0% efficiency.

  13. Coherent transport through interacting quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hiltscher, Bastian

    2012-10-05

    The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in

  14. Coherent transport through interacting quantum dots

    International Nuclear Information System (INIS)

    The present thesis is composed of four different works. All deal with coherent transport through interacting quantum dots, which are tunnel-coupled to external leads. There a two main motivations for the use of quantum dots. First, they are an ideal device to study the influence of strong Coulomb repulsion, and second, their discrete energy levels can easily be tuned by external gate electrodes to create different transport regimes. The expression of coherence includes a very wide range of physical correlations and, therefore, the four works are basically independent of each other. Before motivating and introducing the different works in more detail, we remark that in all works a diagrammatic real-time perturbation theory is used. The fermionic degrees of freedom of the leads are traced out and the elements of the resulting reduced density matrix can be treated explicitly by means of a generalized master equation. How this equation is solved, depends on the details of the problem under consideration. In the first of the four works adiabatic pumping through an Aharonov-Bohm interferometer with a quantum dot embedded in each of the two arms is studied. In adiabatic pumping transport is generated by varying two system parameters periodically in time. We consider the two dot levels to be these two pumping parameters. Since they are located in different arms of the interferometer, pumping is a quantum mechanical effect purely relying on coherent superpositions of the dot states. It is very challenging to identify a quantum pumping mechanism in experiments, because a capacitive coupling of the gate electrodes to the leads may yield an undesired AC bias voltage, which is rectified by a time dependent conductance. Therefore, distinguishing features of these two transport mechanisms are required. We find that the dependence on the magnetic field is the key feature. While the pumped charge is an odd function of the magnetic flux, the rectified current is even, at least in

  15. Coherent scattering in a small quantum dot

    International Nuclear Information System (INIS)

    Ballistic transport in an open small (100 nm) three-terminal quantum dot based on the high-mobility two-dimensional electron gas of the AlGaAs/GaAs heterojunction has been analyzed. It has been shown that the gate oscillations of resistance of such a dot arise due to the coherent scattering of electrons on its quasidiscrete levels being suppressed by a weak magnetic field

  16. Implications of orbital hybridization on the electronic properties of doped quantum dots: the case of Cu:CdSe

    Science.gov (United States)

    Wright, Joshua T.; Forsythe, Kyle; Hutchins, Jamie; Meulenberg, Robert W.

    2016-04-01

    This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of these materials. This information provides insights into many of the physical properties of doped QDs, including the highly debated near-infrared photoluminescence in Cu doped CdSe QDs. We show that all our results point to a common theme of orbital hybridization in Cu doped CdSe QDs which leads to optically and electronically active states below the conduction band minimum. Our model is supported from current-voltage measurements of doped and undoped materials, which exhibit Schottky to Ohmic behavior with Cu doping, suggestive of a tuning of the lowest energy states near the Fermi level.This paper investigates how chemical dopants affect the electronic properties of CdSe quantum dots (QDs) and why a model that incorporates the concepts of orbital hybridization must be used to understand these properties. Extended X-ray absorption fine structure spectroscopy measurements show that copper dopants in CdSe QDs occur primarily through a statistical doping mechanism. Ultraviolet photoemission spectroscopy (UPS) experiments provide a detailed insight on the valence band (VB) structure of doped and undoped QDs. Using UPS measurements, we are able to observe photoemission from the Cu d-levels above VB maximum of the QDs which allows a complete picture of the energy band landscape of

  17. Tunneling Processes in Optically Excited Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    LI Xiu-Ping; WEI Hua-Rong; XU Li-Ping; GONG Jian-Ping; YAN Wei-Xian

    2011-01-01

    The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts: the electron and the hole parts, which are analytically obtained in the framework of the Keldysh formalism. The tunneling process is selective tunneling, which results in dark tunneling states. The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states.%The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts:the electron and the hole parts,which are analytically obtained in the framework of the Keldysh formalism.The tunneling process is selective tunneling,which results in dark tunneling states.The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states.Probing the fine-energy structure of the exciton complexes[1-10] in an optically excited quantum dot is an important way of exploring new mechanisms in nanostructures.Single electron tunneling (SET) devices consisting of a central quantum dot (QD) and a tunneling coupled source and drain have become important optoelectronic nano-devices.[11,12

  18. Fibrous CdS/CdSe quantum dot co-sensitized solar cells based on ordered TiO{sub 2} nanotube arrays

    Energy Technology Data Exchange (ETDEWEB)

    Huang Shuqing; Zhang Quanxin; Huang Xiaoming; Guo Xiaozhi; Deng Minghui; Li Dongmei; Luo Yanhong; Meng Qingbo [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, 100190 Beijing (China); Shen Qing; Toyoda, Taro, E-mail: qbmeng@iphy.ac.cn [Department of Engineering Science, Faculty of Informatics and Engineering, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan)

    2010-09-17

    A new kind of fibrous quantum dot sensitized solar cell has been designed and fabricated by using CdS and CdSe co-sensitized TiO{sub 2} nanotubes on Ti wire as the photoanode and highly active Cu{sub 2}S as the counter electrode. By optimizing the CdSe deposition time and the length of the nanotube, a power conversion efficiency of 3.18% has been obtained under AM 1.5 illumination (100 mW cm{sup -2}). The potential application of this kind of solar cell has also been discussed in this paper.

  19. Fibrous CdS/CdSe quantum dot co-sensitized solar cells based on ordered TiO2 nanotube arrays

    International Nuclear Information System (INIS)

    A new kind of fibrous quantum dot sensitized solar cell has been designed and fabricated by using CdS and CdSe co-sensitized TiO2 nanotubes on Ti wire as the photoanode and highly active Cu2S as the counter electrode. By optimizing the CdSe deposition time and the length of the nanotube, a power conversion efficiency of 3.18% has been obtained under AM 1.5 illumination (100 mW cm-2). The potential application of this kind of solar cell has also been discussed in this paper.

  20. Nonvolatile Quantum Dot Gate Memory (NVQDM): Tunneling Rate from Quantum Well Channel to Quantum Dot Gate

    Science.gov (United States)

    Hasaneen, El-Sayed; Heller, Evan; Bansal, Rajeev; Jain, Faquir

    2003-10-01

    In this paper, we compute the tunneling of electrons in a nonvolatile quantum dot memory (NVQDM) cell during the WRITE operation. The transition rate of electrons from a quantum well channel to the quantum dots forming the floating gate is calculated using a recently reported method by Chuang et al.[1]. Tunneling current is computed based on transport of electrons from the channel to the floating quantum dots. The maximum number of electrons on a dot is calculated using surface electric field and break down voltage of the tunneling dielectric material. Comparison of tunneling for silicon oxide and high-k dielectric gate insulators is also described. Capacitance-Voltage characteristics of a NVQDM device are calculated by solving the Schrodinger and Poisson equations self-consistently. In addition, the READ operation of the memory has been investigated analytically. Results for 70 nm channel length Si NVQDMs are presented. Threshold voltage is calculated including the effect of the charge on nanocrystal quantum dots. Current-voltage characteristics are obtained using BSIM3v3 model [2-3]. This work is supported by Office of Navel Research (N00014210883, Dr. D. Purdy, Program Monitor), Connecticut Innovations Inc./TranSwitch (CII # 00Y17), and National Science Foundation (CCR-0210428) grants. [1] S. L. Chuang and N. Holonyak, Appl. Phys. Lett., 80, pp. 1270, 2002. [2] Y. Chen et. al., BSIM3v3 Manual, Elect. Eng. and Comp. Dept., U. California, Berkeley, CA, 1996. [3] W. Liu, MOSFET Models for SPICE Simulation, John Wiley & Sons, Inc., 2001.

  1. Few-quantum-dot lasing in photonic crystal nanocavities

    DEFF Research Database (Denmark)

    Liu, Jin; Ates, Serkan; Stobbe, Søren; Lorke, Michael; Lodahl, Peter

    2012-01-01

    A very smooth lasing transition in photonic crystal nanocavities with embedded quantum dots is observed and compared to the theory. Decay rate measurements reveal that only a few quantum dots are feeding the cavity.......A very smooth lasing transition in photonic crystal nanocavities with embedded quantum dots is observed and compared to the theory. Decay rate measurements reveal that only a few quantum dots are feeding the cavity....

  2. Excitonic Properties in GaAs Parabolic Quantum Dots

    OpenAIRE

    Jaziri, S.; Bennaceur, R.

    1995-01-01

    Certain classes of semiconductor quantum dots being actually fabricated exhibit a nearly parabolic confinement for both the electron and the hole. In undoped quantum dots, excitonic effects are important. In this work, first we present theoretical results on exciton properties in parabolic quantum dots: resonance energy, binding energy and oscillator strength. Then, we investigate the effects of external electric and magnetic fields on exciton in quantum dots.

  3. Quantum well and quantum dot energy harvesting devices

    Science.gov (United States)

    Welser, Roger E.; Sood, Ashok K.; Laboutin, Oleg A.; Guido, Louis J.; Dhar, Nibir K.; Wijewarnasuriya, Priyalal S.

    2011-06-01

    Quantum structured solar cells seek to harness a wide spectrum of photons at high voltages by embedding low energy-gap wells or dots within a high energy-gap matrix. Quantum well and quantum dot solar cells have the potential to deliver ultra-high power conversion efficiencies in single junction devices, efficiencies that in theory can approach 45% in un-concentrated sunlight over a wide range of environmental conditions. In this paper, we will briefly review the theoretical underpinnings of quantum well and quantum dot photovoltaic devices, and summarize recent experimental efforts developing quantum-structured solar cell devices. In a specific example, test devices utilizing radiation-hard, III-V nitride materials have been built using both bulk and multiple quantum well (MQW) structures. Photovoltaic devices with an InGaN MQW structure are shown to outperform devices employing a thicker, bulk InGaN layer. These results, along with the underlying theoretical foundations, suggest that quantum well and quantum dot structures can enhance the performance of photovoltaic devices for a variety of defense applications.

  4. Bright infrared LEDs based on colloidal quantum-dots

    KAUST Repository

    Sun, Liangfeng

    2013-01-01

    Record-brightness infrared LEDs based on colloidal quantum-dots have been achieved through control of the spacing between adjacent quantum-dots. By tuning the size of quantum-dots, the emission wavelengths can be tuned between 900nm and 1650nm. © 2013 Materials Research Society.

  5. Weak localization in arrays of metallic quantum dots

    OpenAIRE

    Golubev, Dmitri S.; Zaikin, Andrei D.

    2006-01-01

    Combining scattering matrix formalism with non-linear $\\sigma$-model technique we analyze weak localization effects in arrays of chaotic quantum dots connected via barriers with arbitrary distribution of channel transmissions. With the aid of our approach we evaluate magnetoconductance of two arbitrarily connected quantum dots as well as of $N\\times M$ arrays of identical quantum dots.

  6. Cadmium telluride quantum dots advances and applications

    CERN Document Server

    Donegan, John

    2013-01-01

    Optical Properties of Bulk and Nanocrystalline Cadmium Telluride, Núñez Fernández and M.I. VasilevskiyAqueous Synthesis of Colloidal CdTe Nanocrystals, V. Lesnyak, N. Gaponik, and A. EychmüllerAssemblies of Thiol-Capped CdTe Nanocrystals, N. GaponikFörster Resonant Energy Transfer in CdTe Nanocrystal Quantum Dot Structures, M. Lunz and A.L. BradleyEmission of CdTe Nanocrystals Coupled to Microcavities, Y.P. Rakovich and J.F. DoneganBiological Applications of Cadmium Telluride Semiconductor Quantum Dots, A. Le Cign

  7. One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels

    Directory of Open Access Journals (Sweden)

    Huang Hai

    2011-01-01

    Full Text Available Abstract We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs using poly(acrylic acid (PAA as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs was used for passivating the defect emission (650 nm and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530–600 nm. Moreover, the PL emission peak of CdSe/CdS core–shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core–shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol-2-diphenyltertrazolium bromide (MTT assay. The results showed the satisfactory (>80% biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.

  8. THz quantum-confined Stark effect in semiconductor quantum dots

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Monozon, Boris S.; Livshits, Daniil A.;

    2012-01-01

    We demonstrate an instantaneous all-optical manipulation of optical absorption at the ground state of InGaAs/GaAs quantum dots (QDs) via a quantum-confined Stark effect (QCSE) induced by the electric field of incident THz pulses with peak electric fields reaching 200 kV/cm in the free space. As a...

  9. Noise enhancement due to quantum coherence in coupled quantum dots

    OpenAIRE

    Kiesslich, G.; Schoell, E.; Brandes, T.; Hohls, F.; Haug, R. J.

    2007-01-01

    We show that the intriguing observation of noise enhancement in the charge transport through two vertically coupled quantum dots can be explained by the interplay of quantum coherence and strong Coulomb blockade. We demonstrate that this novel mechanism for super-Poissonian charge transfer is very sensitive to decoherence caused by electron-phonon scattering as inferred from the measured temperature dependence.

  10. Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

    Indian Academy of Sciences (India)

    P K Ghosh; A Ghosal; D Chattopadhyay

    2009-02-01

    Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

  11. Formation and ordering of epitaxial quantum dots

    Science.gov (United States)

    Atkinson, Paola; Schmidt, Oliver G.; Bremner, Stephen P.; Ritchie, David A.

    2008-10-01

    Single quantum dots (QDs) have great potential as building blocks for quantum information processing devices. However, one of the major difficulties in the fabrication of such devices is the placement of a single dot at a pre-determined position in the device structure, for example, in the centre of a photonic cavity. In this article we review some recent investigations in the site-controlled growth of InAs QDs on GaAs by molecular beam epitaxy. The method we use is ex-situ patterning of the GaAs substrate by electron beam lithography and conventional wet or dry etching techniques to form shallow pits in the surface which then determine the nucleation site of an InAs dot. This method is easily scalable and can be incorporated with marker structures to enable simple post-growth lithographic alignment of devices to each site-controlled dot. We demonstrate good site-control for arrays with up to 10 micron spacing between patterned sites, with no dots nucleating between the sites. We discuss the mechanism and the effect of pattern size, InAs deposition amount and growth conditions on this site-control method. Finally we discuss the photoluminescence from these dots and highlight the remaining challenges for this technique. To cite this article: P. Atkinson et al., C. R. Physique 9 (2008).

  12. Induced quantum dots and wires: electron storage and delivery

    OpenAIRE

    Bednarek, S.; Szafran, B; R. Dudek; Lis, K.

    2007-01-01

    We show that quantum dots and quantum wires are formed underneath metal electrodes deposited on a planar semiconductor heterostructure containing a quantum well. The confinement is due to the self-focusing mechanism of an electron wave packet interacting with the charge induced on the metal surface. Induced quantum wires guide the transfer of electrons along metal paths and induced quantum dots store the electrons in specific locations of the nanostructure. Induced dots and wires can be usefu...

  13. Semiconductor Quantum Dots for Biomedicial Applications

    OpenAIRE

    Lijia Shao; Feng Yan; Yanfang Gao

    2011-01-01

    Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can...

  14. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....

  15. Synthesis of Monodisperse CdSe QDs using Controlled Growth Temperatures

    International Nuclear Information System (INIS)

    The effect of growth temperatures on size of CdSe quantum dots (QDs) has been investigated. CdSe QDs were synthesized using thermolysis of organometallics precursor route using wet chemical method. The growth temperature was varied from 260-310 degree Celsius with growth period fixed at 60 s. As the growth temperature increased, the monodispersed CdSe QDs with diameter in the range 3-7 nm were obtained. Both absorption and PL spectra of the QDs revealed a strong red-shift supporting the increment size of QDs with the rise of growth temperature. (author)

  16. Non-Equilibrium Electron Transport through a Double Quantum Dot System: Study of Two Exchange Coupled Quantum Dots in a 4-Terminal Geometry

    OpenAIRE

    Koerting, Verena

    2007-01-01

    In this thesis we study two exchange-coupled quantum dots with an emphasis on non-equilibrium physics. Assuming a single electron on each quantum dot, the double quantum dot system is characterized by an interplay between the Kondo spin coupling of the dots with the leads and the spin-exchange coupling between the dots. We find that a finite voltage on one quantum dot drives the other quantum dot out of equilibrium.

  17. Coherent control of quantum dots

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Lodahl, Peter; Hvam, Jørn Märcher

    In recent years much effort has been devoted to the use of semiconductor quantum dotsystems as building blocks for solid-state-based quantum logic devices. One importantparameter for such devices is the coherence time, which determines the number ofpossible quantum operations. From earlier...

  18. FRET from core and core–shell quantum dots to laser dye: A comparative investigation

    International Nuclear Information System (INIS)

    A remarkable progress has been made in the recent past in fluorescence resonance energy transfer (FRET) studies using semiconductor quantum dots (QDs) and application of QD-based FRET to probe specific biological processes. Here we report a systematic study of FRET from CdSe (core) and CdSe/ZnS (core–shell) quantum dots (donor) to sulforhodamine B (SRB) dye (acceptor) using steadystate and time resolved fluorescence spectroscopy. The results obtained demonstrate occurrence of efficient energy transfer from QDs to dye and are discussed in the light of the Förster theory. Time resolved decay curves of QDs obtained in the presence and absence of sulforhodamine B dye are analyzed. The values of spectral overlap, Förster distance and transfer efficiency have been determined using steady-state and time-resolved fluorescence spectroscopic data. It is observed that the transfer efficiency does not follow a linear dependence on spectral overlap integral and quantum yield of donor as predicted by the Förster theory for molecules. This nonlinear dependence of transfer efficiency on overlap integral as well as quantum yield of donor; and the possibility of surface states and defect states of QDs causing this are discussed. - Highlights: • FRET from CdSe and CdSe/ZnS QDs to SRB dye using time resolved fluorescence spectroscopy studied. • Fluorescence quantum yields of QDs are measured employing standard method. • FRET efficiency depends nonlinearly on spectral overlap and quantum yield of QD. • Possibility of surface states and defect states of QDs causing non-linear dependency is discussed

  19. Nonlocal quantum cloning via quantum dots trapped in distant cavities

    Institute of Scientific and Technical Information of China (English)

    Yu Tao; Zhu Ai-Dong; Zhang Shou

    2012-01-01

    A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covariant cloning machine,and 1 → 3 economical phase-covariant cloning machine are constructed.The present scheme,which is attainable with current technology,saves two qubits compared with previous cloning machines.

  20. Quantum Mechanics of Semiconductor Quantum Dots and Rings

    OpenAIRE

    I. Filikhin; Matinyan, S. G.; Vlahovic, B.

    2012-01-01

    We consider the several phenomena which are taking place in Quantum Dots (QD) and Quantum Rings (QR): The connection of the Quantum Chaos (QC) with the reflection symmetry of the QD, Disappearance of the QC in the tunnel coupled chaotic QD, electron localization and transition between Double Concentric QR in the transverse magnetic field, transition of electron from QR to the QD located in the center of QR. Basis of this consideration is the effective Schr\\"odinger equation for the correspond...

  1. Nonlocal quantum cloning via quantum dots trapped in distant cavities

    International Nuclear Information System (INIS)

    A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed. By modulating the parameters of the system, the optimal 1 → 2 universal quantum cloning machine, 1 → 2 phase-covariant cloning machine, and 1 → 3 economical phase-covariant cloning machine are constructed. The present scheme, which is attainable with current technology, saves two qubits compared with previous cloning machines. (general)

  2. Ostwald's ripening of nanostructures with quantum dots

    CERN Document Server

    Vengrenovich, R D; Yarema, S V

    2001-01-01

    The scenario of quantum dots shaping during ripening three-dimensional islands obtained by heteroepitaxy in a Stranski-Krastanow mode, is offered. It is shown that throughout the growth of dislocations with their subsequent separation from the island bottom, the size distribution function becomes narrower with noticeable diminishing the dispersion. The possible reasons for signal attenuation of Ostwald's ripening islands are analyzed

  3. Ostwald's ripening of nanostructures with quantum dots

    International Nuclear Information System (INIS)

    The scenario of quantum dots shaping during ripening three-dimensional islands obtained by heteroepitaxy in a Stranski-Krastanow mode, is offered. It is shown that throughout the growth of dislocations with their subsequent separation from the island bottom, the size distribution function becomes narrower with noticeable diminishing the dispersion. The possible reasons for signal attenuation of Ostwald's ripening islands are analyzed

  4. Multiple exciton generation effect in quantum dots

    International Nuclear Information System (INIS)

    Full text: Recently among various investigations in the field of nanophysics a great intensification in studying of multiple exciton generation (MEG) effect in quantum dots at absorption of photons with the energy several times higher than the gap in electronic spectra (hν>>Eg) has been made [1-2]. There have been proposed four theoretical approaches to explain the MEG effect. However, the statistic approach basing on the Fermi theory of multiple pi-mesons generation (1950) is the most adequate related to others. In this work: 1. the results of statistic approach have been generalized; 2. the microscopic mechanism basing on theory of electronic 'shaking' has been proposed; 3. the problem of deviation of mean multiplicity of MEG effect from the Poisson law of fluctuations has been investigated that is a evidence of strong non-linear and non-equilibrium character of exciton generation process; 4. the role of interface electronic states of quantum dot and ligand has been considered by means of perturbation theory of closed states related to surface Tamm electronic states of quantum dot and legend; 5. the problem of size optimization of quantum dot to receive the maximum multiplicity has been studied; 6. the efficiency of MEG effect for the third generation of solar cells has been calculated on the basis of proposed theory. (authors)

  5. Incipient Wigner localization in circular quantum dots

    Science.gov (United States)

    Ghosal, Amit; Güçlü, A. D.; Umrigar, C. J.; Ullmo, Denis; Baranger, Harold U.

    2007-08-01

    We study the development of electron-electron correlations in circular quantum dots as the density is decreased. We consider a wide range of both electron number, N⩽20 , and electron gas parameter, rs≲18 , using the diffusion quantum Monte Carlo technique. Features associated with correlation appear to develop very differently in quantum dots than in bulk. The main reason is that translational symmetry is necessarily broken in a dot, leading to density modulation and inhomogeneity. Electron-electron interactions act to enhance this modulation ultimately leading to localization. This process appears to be completely smooth and occurs over a wide range of density. Thus there is a broad regime of “incipient” Wigner crystallization in these quantum dots. Our specific conclusions are (i) the density develops sharp rings while the pair density shows both radial and angular inhomogeneity; (ii) the spin of the ground state is consistent with Hund’s (first) rule throughout our entire range of rs for all 4⩽N⩽20 ; (iii) the addition energy curve first becomes smoother as interactions strengthen—the mesoscopic fluctuations are damped by correlation—and then starts to show features characteristic of the classical addition energy; (iv) localization effects are stronger for a smaller number of electrons; (v) finally, the gap to certain spin excitations becomes small at the strong interaction (large rs ) side of our regime.

  6. Quantum dot waveguides: ultrafast dynamics and applications

    DEFF Research Database (Denmark)

    Chen, Yaohui; Mørk, Jesper

    2009-01-01

    In this paper we analyze, based on numerical simulations, the dynamics of semiconductor devices incorporating quantum dots (QDs). In particular we emphasize the unique ultrafast carrier dynamics occurring between discrete QD bound states, and its influence on QD semiconductor optical amplifiers...

  7. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...

  8. Decoherence in Nearly-Isolated Quantum Dots

    DEFF Research Database (Denmark)

    Folk, J.; M. Marcus, C.; Harris jr, J.

    2000-01-01

    Decoherence in nearly-isolated GaAs quantum dots is investigated using the change in average Coulomb blockade peak height upon breaking time-reversal symmetry. The normalized change in average peak height approaches the predicted universal value of 1/4 at temperatures well below the single...

  9. Enabling biomedical research with designer quantum dots

    NARCIS (Netherlands)

    Tomczak, N.; Janczewski, D.; Dorokhin, D.V.; Han, M-Y; Vancso, G.J.; Navarro, Melba; Planell, Josep A.

    2012-01-01

    Quantum Dots (QDs) are a new class of semiconductor nanoparticulate luminophores, which are actively researched for novel applications in biology and nanomedicine. In this review, the recent progress in the design and applications of QD labels for in vitro and in vivo imaging of cells is presented.

  10. System and method for making quantum dots

    KAUST Repository

    Bakr, Osman M.

    2015-05-28

    Embodiments of the present disclosure provide for methods of making quantum dots (QDs) (passivated or unpassivated) using a continuous flow process, systems for making QDs using a continuous flow process, and the like. In one or more embodiments, the QDs produced using embodiments of the present disclosure can be used in solar photovoltaic cells, bio-imaging, IR emitters, or LEDs.

  11. Photoluminescence of hybrid quantum dot systems

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    2015-01-01

    Roč. 7, č. 4 (2015), 347-349. ISSN 2164-6627 R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

  12. Producing Quantum Dots by Spray Pyrolysis

    Science.gov (United States)

    Banger, Kulbinder; Jin, Michael H.; Hepp, Aloysius

    2006-01-01

    An improved process for making nanocrystallites, commonly denoted quantum dots (QDs), is based on spray pyrolysis. Unlike the process used heretofore, the improved process is amenable to mass production of either passivated or non-passivated QDs, with computer control to ensure near uniformity of size.

  13. Application of quantum dots as vectors in targeted survivin gene siRNA delivery

    Directory of Open Access Journals (Sweden)

    Zhao JJ

    2013-04-01

    Full Text Available Jianjiang Zhao, Xiaoling Qiu, Zhiping Wang, Jie Pan, Jun Chen, Jiusong Han Department of Surgery, Guangdong Provincial Stomatological Hospital, Southern Medical University, Guangzhou, People's Republic of China Abstract: Gene silencing using short interfering RNA (siRNA is becoming an attractive approach for probing gene function in mammalian cells. This study evaluated the specificity and efficiency of quantum dots (QDs as non-viral gene vectors for delivery of survivin siRNA and downregulation of survivin gene expression in oral squamous cell carcinoma Tca8113 cells. Water-dispersible cationically-modified QDs were electrostatically attached to anionic siRNA molecules and complexed with siRNA for downregulating expression of the survivin gene. Cellular uptake and allocation of QD–siRNA complexes in Tca8113 cells were monitored using confocal laser scanning microscopy. Real-time polymerase chain reaction (PCR was used to quantify survivin messenger RNA (mRNA levels. CdSe QDs were observed with high intensity fluorescence under confocal laser scanning microscopy. Tca8113 cells were successfully transfected by QDs with survivin siRNA, and the red fluorescence from CdSe QDs and green fluorescein amidite fluorescence from siRNA could both be easily observed after 6 hours of incubation. The release of siRNA into the cytoplasm was verified through real-time PCR quantification that showed reduced survivin mRNA levels. In this study, survivin siRNA successfully complexed with water-soluble CdSe QDs and exhibited excellent fluorescent properties and downregulated the expression of the survivin gene in oral squamous cell carcinoma Tca8113 cells. QDs are a novel non-viral gene delivery vector. Keywords: quantum dots, survivin, siRNA delivery, transfection, Tca8113, tongue cancer cells

  14. Luminescence Spectra of a Quantum-Dot Cascade Laser

    OpenAIRE

    Apalkov, Vadim; Chakraborty, Tapash

    2000-01-01

    A quantum cascade laser where the quantum wells in the active regions are replaced by quantum dots with their atom-like discrete energy levels is an interesting system to study novel features in optical spectroscopy. We study structures suitable for diagonal lasing transitions in coupled dots, and vertical lasing transitions in a single dot, in the active regions of the laser device. The luminescence spectra as a function of electron number and dot size show that for diagonal transitions, a s...

  15. Optical properties of a Quantum-Dot Cascade Structure

    OpenAIRE

    Apalkov, V. M.; Chakraborty, Tapash

    2001-01-01

    We report on our theoretical studies of the luminescence spectra of a quantum cascade laser where the quantum wells in the active regions are replaced by parabolic quantum dots. We analyze the influence of shape and size of the dots on the luminescence spectra. The emission spectra have interaction induced blueshift which increases almost linearly with increasing electron number. The blueshift is smaller for larger and non-circular dots. For large dots, shape of the emission line has weak dep...

  16. Coherence and dephasing in self-assembled quantum dots

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Leosson, K.; Birkedal, Dan

    We measured dephasing times in InGaAl/As self-assembled quantum dots at low temperature using degenerate four-wave mixing. At 0K, the coherence time of the quantum dots is lifetime limited, whereas at finite temperatures pure dephasing by exciton-phonon interactions governs the quantum dot cohere...... coherence. The inferred homogeneous line widths are significantly smaller than the line widths usually observed in the photoluminescence from single quantum dots indicating an additional inhomogeneours broadening mechanism in the latter.......We measured dephasing times in InGaAl/As self-assembled quantum dots at low temperature using degenerate four-wave mixing. At 0K, the coherence time of the quantum dots is lifetime limited, whereas at finite temperatures pure dephasing by exciton-phonon interactions governs the quantum dot...

  17. Optical Properties of Quantum-Dot-Doped Liquid Scintillators

    CERN Document Server

    Aberle, C; Weiss, S; Winslow, L

    2013-01-01

    Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.

  18. Thermal annealing of selected individual quantum dots

    International Nuclear Information System (INIS)

    Cathodoluminescence spectra of single InAs/GaAs quantum dots were recorded before and after consecutive thermal annealing steps. The annealing process leads to an overall blueshift of the spectra indicating In/Ga interdiffusion. Excitonic fine-structure splitting and binding energies of charged and neutral excitonic complexes were monitored. A drastic reduction of the fine-structure splitting from 170 μeV to less than 20 μeV can be observed accompanied by a change of the character of the biexciton from anti-binding to binding with respect to the exciton. Tailoring the fine-structure splitting is especially important for the use of single quantum dots in opto-electronic devices for quantum key distribution where a degeneracy of the exciton ground state (i.e. a fine-structure splitting below the homogeneous linewidth) is required for the on-demand production of entangled photon pairs

  19. Efficient Luminescence from Perovskite Quantum Dot Solids

    KAUST Repository

    Kim, Younghoon

    2015-11-18

    © 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

  20. Light emission from Si quantum dots

    Directory of Open Access Journals (Sweden)

    Philippe M. Fauchet

    2005-01-01

    Full Text Available Si quantum dots (QDs as small as ∼2 nm in diameter have been synthesized by a variety of techniques. Because of quantum confinement and the elimination of bulk or surface defects, these dots can emit light from the near infrared throughout the visible with quantum efficiencies in excess of 10%. The luminescence wavelength range has been extended to longer wavelengths by the addition of light-emitting rare earths such as erbium (Er. Light-emitting devices (LEDs have been fabricated and their performances are starting to approach those of direct band gap semiconductor or organic LEDs. A search for a Si QD-based laser is even under way. The state-of-the-art in the materials science, physics, and device development of luminescent Si QDs is reviewed and areas of future research are pointed out.

  1. Quantum Dots and Their Multimodal Applications: A Review

    Directory of Open Access Journals (Sweden)

    Paul H. Holloway

    2010-03-01

    Full Text Available Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence or electric field (electroluminescence. In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

  2. High-resolution photoluminescence studies of single semiconductor quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis;

    2000-01-01

    Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has...... developed in the study of single quantum dots, characterized by sharp atomic-like transition lines revealing their zero-dimensional density of states. Substantial information about the fundamental properties of individual quantum dots, as well as their interactions with other dots and the host lattice, can...

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

    Science.gov (United States)

    Melvin David Kumar, M.; Devadason, Suganthi

    2013-06-01

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

  4. Unraveling the mesoscopic character of quantum dots in nanophotonics

    OpenAIRE

    Tighineanu, Petru; Sørensen, Anders Søndberg; Stobbe, Søren; Lodahl, Peter

    2014-01-01

    We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. At the microscopic level the deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, w...

  5. Thermodynamic properties of a quantum Hall anti-dot interferometer

    OpenAIRE

    Schreier, Sarah Levy; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.

    2015-01-01

    We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop....

  6. Inclusion of thiol DAB dendrimer/CdSe quantum dots based in a membrane structure: Surface and bulk membrane modification

    International Nuclear Information System (INIS)

    Highlights: ► Fluorescent nanocomposite based in CdSe quantum dots (QDs) coated by thiol polypropylenimine (DAB). ► Bulk chemical characterization by TEM and EDAX ► Inclusion of the S-DAB-CdSe QDs in a cellulosic support and its characterization by Fluorescence and XPS. ► Electrical characterization by Impedance Spectroscopy of dry and wet samples containing a heavy metal. -- Abstract: The behavior of a fluorescent nanocomposite, obtained by means of a thiol polypropylenimine dendrimer of third generation coated with CdSe quantum dots, and embedded in a hydrophilic cellulosic membrane as support is electrochemically studied in order to evaluate its applicability as a sensor in liquid media. The characterization of the nanocomposite by TEM and EDAX shows uniform nano morphology (size comprised in the range 60–90 nm) and composition, respectively. The analysis of the engineered hybrid cellulose-dendrimer quantum dots material by confocal fluorescence microscopy indicates almost mono-dispersion distribution of the nanocomposite when irradiated under UV light, while its presence on the film surface was determined by X-ray photoelectron spectroscopy. Impedance spectroscopy measurements performed with dry membrane samples show a decrease in the conductivity and dielectric constant of the modified membrane in comparison with the raw support. Electrical changes in the modified film associated to the presence of Cd(II) uptakes from a Cl2Cd solution were also obtained. These results support the possible application of this nanocomposite material as heavy metal sensor in liquid media

  7. Electron and hole spectra in quantum wire with two quantum dots in the electric field

    OpenAIRE

    O.Makhanets; A.Gryschyk; M.Dovganiuk

    2007-01-01

    The energy spectrum of electron and hole is investigated in a complicated nanoheterosystem consisting of two cylindrical semiconductor quantum dots placed into semiconductor quantum wire. Quantum dots are separated by barrier-layer, which is under the action of a constant electric field. The dependencies of electron and hole energies on geometric parameters of quantum dots and electric field intensity are analysed.

  8. Comparison of quantum discord and local quantum uncertainty in a vertical quantum dot

    OpenAIRE

    Faizi, E.; Eftekhari, H.

    2014-01-01

    In this paper, we consider quantum correlations (quantum discord and local quantum uncertainty) in a vertical quantum dot. Their dependencies on magnetic field and temperature are presented in detail. It is noticeable that, quantum discord and local quantum uncertainty behavior is similar to a large extent. In addition, the time evolution of quantum discord and local quantum uncertainty under dephasing and amplitude damping channels is investigated. It has been found that, for some Belldiagon...

  9. Quantum Size- Dependent Third- Order Nonlinear Optical Susceptibility in Semiconductor Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    SUN Ting; XIONG Gui-guang

    2005-01-01

    The density matrix approach has been employed to investigate the optical nonlinear polarization in a single semiconductor quantum dot(QD). Electron states are considered to be confined within a quantum dot with infinite potential barriers. It is shown, by numerical calculation, that the third-order nonlinear optical susceptibilities for a typical Si quantum dot is dependent on the quantum size of the quantum dot and the frequency of incident light.

  10. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

    Science.gov (United States)

    Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

    2014-07-22

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films. PMID:24883930

  11. Identification of Different Donor-Acceptor Structures via Förster Resonance Energy Transfer (FRET) in Quantum-Dot-Perylene Bisimide Assemblies

    OpenAIRE

    Christian von Borczyskowski; Jörg Schuster; Mohamed Abdel-Mottaleb; Nicole Amecke; Danny Kowerko; Stefan Krause

    2009-01-01

    Nanoassemblies are formed via self-assembly of ZnS capped CdSe quantum dots (QD) and perylene bisimide (PBI) dyes. Upon assembly formation the QD photoluminescence is quenched, as can be detected both via single particle detection and ensemble experiments in solution. Quenching has been assigned to FRET and NON-FRET processes. Analysis of FRET allows for a distinction between different geometries of the QD dye assemblies. Time-resolved single molecule spectroscopy reveals intrinsic fluctuatio...

  12. A Fusion-Spliced Near-Field Optical Fiber Probe Using Photonic Crystal Fiber for Nanoscale Thermometry Based on Fluorescence-Lifetime Measurement of Quantum Dots

    OpenAIRE

    Toshiharu Saiki; Yuji Nagasaka; Yoshihiro Taguchi; Takuro Fujii

    2011-01-01

    We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se Quantum Dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a ...

  13. Systematic optimization of quantum junction colloidal quantum dot solar cells

    Science.gov (United States)

    Liu, Huan; Zhitomirsky, David; Hoogland, Sjoerd; Tang, Jiang; Kramer, Illan J.; Ning, Zhijun; Sargent, Edward H.

    2012-10-01

    The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1% under AM1.5 simulated solar illumination.

  14. Charge-tunable indium gallium nitride quantum dots

    Science.gov (United States)

    Zhang, Lei; Teng, Chu-Hsiang; Ku, Pei-Cheng; Deng, Hui

    2016-02-01

    III-Nitride quantum dots have emerged as a new chip-scale system for quantum information science, which combines electrical and optical interfaces on a semiconductor chip that is compatible with noncryogenic operating temperatures. Yet most work has been limited to optical excitations. To enable single-spin-based quantum optical and quantum information research, we demonstrate here quantized charging in optically active, site-controlled III-nitride quantum dots. Single-electron charging was confirmed by the voltage dependence of the energy, dipole moment, fine structures, and polarization properties of the exciton states in the quantum dots. The fundamental energy structures of the quantum dots were identified, including neutral and charged excitons, fine structures of excitons, and A and B excitons. The results lay the ground for coherent control of single charges in III-nitride quantum dots, opening a door to III-nitride-based spintronics and spin-qubit quantum information processing.

  15. Single quantum dots fundamentals, applications, and new concepts

    CERN Document Server

    2003-01-01

    This book reviews recent advances in the exciting and rapid growing field of semiconductor quantum dots by contributions from some of the most prominent researchers in the field. Special focus is given to the optical and electronic properties of single quantum dots due to their potential applications in devices operating with single electrons and/or single photons. This includes quantum dots in electric and magnetic fields, cavity-quantum electrodynamics, nonclassical light generation, and coherent optical control of excitons. Single Quantum Dots also addresses various growth techniques as well as potential device applications such as quantum dot lasers, and new concepts like a single-photon source, and a single quantum dot laser.

  16. Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications

    Science.gov (United States)

    Su, Huaipeng; Xu, Hengyi; Gao, Shuai; Dixon, John David; Aguilar, Zoraida P.; Wang, Andrew Y.; Xu, Jian; Wang, Jingkang

    2010-03-01

    We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs) overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd0.5Zn0.5S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3).

  17. Microwave Synthesis of Nearly Monodisperse Core/Multishell Quantum Dots with Cell Imaging Applications

    Directory of Open Access Journals (Sweden)

    Xu Hengyi

    2010-01-01

    Full Text Available Abstract We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd0.5Zn0.5S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3.

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

    Science.gov (United States)

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

    2006-03-01

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

  19. Barrier Li Quantum Dots in Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    LIUYi-Min; LIXiao-Zhu; YANWen-Hong; BAOCheng-Guang

    2003-01-01

    The methods for the few-body system are introduced to investigate the states of the barrier Li quantum dots (QDs) in an arbitrary strength of magnetic field. The configuration, which consists of a positive ion located on the z-axis at a distaneed from the two-dimensional QD plane (the x-y plane) and three electrons in the dot plane bound by the positive ion, is called a barrier Li center. The system, which consists of three electrons in the dot plane bound by the ion,is called a barrier Li QD. The dependence of energy of the state of the barrier Li QD on an external magnetic field B and the distance d is obtained. The angular momentum L of the ground states is found to jump not only with the variation orB but also with d.

  20. Quantum computation with nuclear spins in quantum dots

    OpenAIRE

    Christ, Henning

    2008-01-01

    In this thesis we present protocols for the polarization of nuclear spins in a quantum dot via the hyperfine interaction with a conduction band electron and give a quantitative solution to the master equation we derive. The collective interference effects limiting the polarization are studied in detail, and ways of mitigating them are proposed. At high polarization levels the electron-nuclear interaction is approximated with simple and practical (quantum optical) models, suggesting the possib...

  1. Linear Kondo conductance in a quantum dot

    International Nuclear Information System (INIS)

    In a tunnelling experiment across a quantum dot it is possible to change the coupling between the dot and the contacts at will, by properly tuning the transparency of the barriers and the temperature. Gate voltages allow for changes of the relative position of the dot addition energies and the Fermi level of the leads. Here we discuss the two limiting cases: weak and strong coupling in the tunnelling Hamiltonian. In the latter case Kondo resonant conductance can emerge at low temperature in a Coulomb blockade valley. We give a pedagogical approach to the single-channel Kondo physics at equilibrium and review the Nozieres scattering picture of the correlated fixed point. We emphasize the effect of an applied magnetic field and show how an orbital Kondo effect can take place in vertical quantum dots tuned both to an even and to an odd number of electrons at a level crossing. We extend the approach to the two-channel overscreened Kondo case and discuss recent proposals for detecting the non-Fermi liquid fixed point which could be reached at strong coupling

  2. Facile labeling of lipoglycans with quantum dots

    International Nuclear Information System (INIS)

    Bacterial endotoxins or lipopolysaccharides (LPS) are among the most potent activators of the innate immune system, yet mechanisms of their action and in particular the role of glycans remain elusive. Efficient non-invasive labeling strategies are necessary for studying interactions of LPS glycans with biological systems. Here we report a new method for labeling LPS and other lipoglycans with luminescent quantum dots. The labeling is achieved by partitioning of hydrophobic quantum dots into the core of various LPS aggregates without disturbing the native LPS structure. The biofunctionality of the LPS-Qdot conjugates is demonstrated by the labeling of mouse monocytes. This simple method should find broad applicability in studies concerned with visualization of LPS biodistribution and identification of LPS binding agents.

  3. Quantum Dot Devices for Optical Signal Processing

    DEFF Research Database (Denmark)

    Chen, Yaohui

    with other semiconductor materials. The understanding of such properties is important in order to improve the performance of existing devices and to trigger the development of new semiconductor devices for dierent optical signal processing functionalities in the future. We present a detailed quantum dot...... and the continuum. Additional to the conventional time-domain modeling scheme, a small-signal perturbation analysis has been used to assist the investigation of harmonic modulation properties. The static properties of quantum dot devices, for example high saturation power, have been quantitatively analyzed....... Additional to the static linear amplication properties, we focus on exploring the gain dynamics on the time scale ranging from sub-picosecond to nanosecond. In terms of optical signals that have been investigated, one is the simple sinusoidally modulated optical carrier with a typical modulation frequency...

  4. Quantum dot/glycol chitosan fluorescent nanoconjugates

    Science.gov (United States)

    Mansur, Alexandra AP; Mansur, Herman S.

    2015-04-01

    In this study, novel carbohydrate-based nanoconjugates combining chemically modified chitosan with semiconductor quantum dots (QDs) were designed and synthesised via single-step aqueous route at room temperature. Glycol chitosan (G-CHI) was used as the capping ligand aiming to improve the water solubility of the nanoconjugates to produce stable and biocompatible colloidal systems. UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were used to characterise the synthesis and the relative stability of biopolymer-capped semiconductor nanocrystals. The results clearly demonstrated that the glycol chitosan derivative was remarkably effective at nucleating and stabilising semiconductor CdS quantum dots in aqueous suspensions under acidic, neutral, and alkaline media with an average size of approximately 2.5 nm and a fluorescent activity in the visible range of the spectra.

  5. Many electron effects in semiconductor quantum dots

    Indian Academy of Sciences (India)

    R K Pandey; Manoj K Harbola; V Ranjan; Vijay A Singh

    2003-01-01

    Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as ‘artificial atoms’ by some, they are much larger (1 100 nm) than real atoms. One can study a variety of manyelectron effects in them, which are otherwise difficult to observe in a real atom. We have treated these effects within the local density approximation (LDA) and the Harbola–Sahni (HS) scheme. HS is free of the selfinteraction error of the LDA. Our calculations have been performed in a three-dimensional quantum dot. We have carried out a study of the size and shape dependence of the level spacing. Scaling laws for the Hubbard ‘’ are established.

  6. Protease-activated quantum dot probes

    Science.gov (United States)

    Chang, Emmanuel; Sun, Jiantang; Miller, Jordan S.; Yu, William W.; Colvin, Vicki L.; West, Jennifer L.; Drezek, Rebekah

    2006-04-01

    We demonstrate a novel quantum dot based probe with inherent signal amplification upon interaction with a targeted proteolytic enzyme. This probe may be useful for imaging in cancer detection and diagnosis. In this system, quantum dots (QDs) are bound to gold nanoparticles (AuNPs) via a proteolytically-degradable peptide sequence to non-radiatively suppress luminescence. A 71% reduction in luminescence was achieved with conjugation of AuNPs to QDs. Peptide cleavage results in release of AuNPs and restores radiative QD photoluminescence. Initial studies observed a 52% rise in luminescence over 47 hours of exposure to 0.2 mg/mL collagenase. These probes can be customized for targeted degradation simply by changing the sequence of the peptide linker.

  7. Magnetoconductance fluctuations in open bismuth quantum dots

    Science.gov (United States)

    Hackens, B.; Minet, J. P.; Farhi, G.; Crahay, A.; Faniel, S.; Gustin, C.; Bayot, V.

    2002-03-01

    We investigate the low temperature (300 mK - 10 K) magnetoconductance of open circular bismuth quantum dots (diameter: 500 nm). The structures are fabricated using a combination of electron beam lithography, lift off and plasma etching techniques on bismuth thin films evaporated on heated SiO2 substrates. We observe reproducible magnetoconductance fluctuations (UCFs) up to 5T, qualitatively similar to conductance fluctuations evidenced in open quantum dots patterned in high mobility semiconductor heterostructures. In our samples, UCFs are superposed on a slowly varying negative magnetoconductance background. We also observe a sharp conductance maximum centered in B=0, which is reminescent of the spin-orbit induced anti-localisation phenomenon. The behavior of UCFs and of the conductance maximum is discussed as a function of the temperature, thickness and degree of cristallinity of the cavity.

  8. Quantum photonics with quantum dots in photonic wires

    DEFF Research Database (Denmark)

    Munsch, Mathieu; Kuhlmann, Andreas; Cadeddu, Davide;

    2016-01-01

    We present results from the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter’s properties with the highest sensitivity. Weperform a...

  9. Quantum transport in a ring of quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Sena Junior, Marcone I.; Macedo, Antonio M.C. [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Dept. de Fisica

    2012-07-01

    Full text: Quantum dots play a central role in the recent technological efforts to build efficient devices to storage, process and transmit information in the quantum regime [1]. One of the reasons for this interest is the relative simplicity with which its control parameters can be changed by experimentalists. Systems with one, two and even arrays of quantum dots have been intensively studied with respect to their efficiency in processing information carried by charge, spin and heat [1]. A particularly useful realization of a quantum dot is a ballistic electron cavity formed by electrostatic potentials in a two-dimensional electron gas. In the chaotic regime, the shape of the dot is statistically irrelevant and the ability to change its form via external gates can be used to generate members of an ensemble of identical systems. From a theoretical point of view, such quantum dots are ideal electron systems in which to study theoretical models combining phase-coherence, chaotic dynamics and Coulomb interactions. In this work, we use the Keldysh non-linear sigma model [2] with a counting field to study electron transport through a ring of four chaotic quantum dots pierced by an Aharonov-Bohm flux. This system is particularly well suited for studying ways to use the weak-localization effect to process quantum information. We derive the quantum circuit equations for this system from the saddle-point condition of the Keldysh action. The results are used to build the action of the corresponding supersymmetric (SUSY) non-linear sigma model. The connection with the random scattering matrix approach is then made via the color-flavor transformation. In the perturbative regime, where weak-localization effects appear, the Keldysh, SUSY and random scattering matrix approaches can be compared by means of independent analytical calculations. We conclude by pointing out the many advantages of our unified approach. [1] For a review, see Yu. V. Nazarov, and Ya. M. Blanter, Quantum

  10. Quantum transport in a ring of quantum dots

    International Nuclear Information System (INIS)

    Full text: Quantum dots play a central role in the recent technological efforts to build efficient devices to storage, process and transmit information in the quantum regime [1]. One of the reasons for this interest is the relative simplicity with which its control parameters can be changed by experimentalists. Systems with one, two and even arrays of quantum dots have been intensively studied with respect to their efficiency in processing information carried by charge, spin and heat [1]. A particularly useful realization of a quantum dot is a ballistic electron cavity formed by electrostatic potentials in a two-dimensional electron gas. In the chaotic regime, the shape of the dot is statistically irrelevant and the ability to change its form via external gates can be used to generate members of an ensemble of identical systems. From a theoretical point of view, such quantum dots are ideal electron systems in which to study theoretical models combining phase-coherence, chaotic dynamics and Coulomb interactions. In this work, we use the Keldysh non-linear sigma model [2] with a counting field to study electron transport through a ring of four chaotic quantum dots pierced by an Aharonov-Bohm flux. This system is particularly well suited for studying ways to use the weak-localization effect to process quantum information. We derive the quantum circuit equations for this system from the saddle-point condition of the Keldysh action. The results are used to build the action of the corresponding supersymmetric (SUSY) non-linear sigma model. The connection with the random scattering matrix approach is then made via the color-flavor transformation. In the perturbative regime, where weak-localization effects appear, the Keldysh, SUSY and random scattering matrix approaches can be compared by means of independent analytical calculations. We conclude by pointing out the many advantages of our unified approach. [1] For a review, see Yu. V. Nazarov, and Ya. M. Blanter, Quantum

  11. SPECTRAL PROPERTIES OF SHUNGITE QUANTUM DOTS

    OpenAIRE

    RAZBIRIN B.S.; ROZHKOVA N.N.; Sheka, E. F.; Nelson, D. K.; Starukhin, A. N.; Goryunov, A. S.

    2014-01-01

    A low-temperature study has been performed for aqueous shungite, carbon tetrachloride, and toluene dispersions. Spectral characteristics for graphene quantum dots (GQDs) of shungite, attributed to individual fragments of reduced graphene oxide (rGO), reveal a dual character of the dispersions emitting centers: individual GQDs are responsible for the spectra position while fractal structure of GQD colloids provides large broadening of the spectra due to structural inhomogeneity of the colloida...

  12. The Silicon:Colloidal Quantum Dot Heterojunction

    KAUST Repository

    Masala, Silvia

    2015-10-13

    A heterojunction between crystalline silicon and colloidal quantum dots (CQDs) is realized. A special interface modification is developed to overcome an inherent energetic band mismatch between the two semiconductors, and realize the efficient collection of infrared photocarriers generated in the CQD film. This junction is used to produce a sensitive near infrared photodetector. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Quantum dot/glycol chitosan fluorescent nanoconjugates

    OpenAIRE

    Mansur, Alexandra AP; Mansur, Herman S.

    2015-01-01

    In this study, novel carbohydrate-based nanoconjugates combining chemically modified chitosan with semiconductor quantum dots (QDs) were designed and synthesised via single-step aqueous route at room temperature. Glycol chitosan (G-CHI) was used as the capping ligand aiming to improve the water solubility of the nanoconjugates to produce stable and biocompatible colloidal systems. UV-visible (UV–vis) spectroscopy, photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR) spec...

  14. Kondo Effect in Mesoscopic Quantum Dots

    OpenAIRE

    Grobis, M.; Rau, I. G.; Potok, R. M.; Goldhaber-Gordon, D.

    2006-01-01

    A dilute concentration of magnetic impurities can dramatically affect the transport properties of an otherwise pure metal. This phenomenon, known as the Kondo effect, originates from the interactions of individual magnetic impurities with the conduction electrons. Nearly a decade ago, the Kondo effect was observed in a new system, in which the magnetic moment stems from a single unpaired spin in a lithographically defined quantum dot, or artificial atom. The discovery of the Kondo effect in a...

  15. Shot noise of coupled semiconductor quantum dots

    OpenAIRE

    Kiesslich, G.; Wacker, A; Schoell, E.

    2003-01-01

    The low-frequency shot noise properties of two electrostatically coupled semiconductor quantum dot states which are connected to emitter/collector contacts are studied. A master equation approach is used to analyze the bias voltage dependence of the Fano factor as a measure of temporal correlations in tunneling current caused by Pauli's exclusion principle and the Coulomb interaction. In particular, the influence of the Coulomb interaction on the shot noise behavior is discussed in detail and...

  16. Quantum dots: synthesis, bioapplications, and toxicity

    OpenAIRE

    Valizadeh, Alireza; Mikaeili, Haleh; Samiei, Mohammad; Farkhani, Samad Mussa; Zarghami, Nosratalah; Kouhi, Mohammad; Akbarzadeh, Abolfazl; Davaran, Soodabeh

    2012-01-01

    This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra...

  17. Depleted Bulk Heterojunction Colloidal Quantum Dot Photovoltaics

    KAUST Repository

    Barkhouse, D. Aaron R.

    2011-05-26

    The first solution-processed depleted bulk heterojunction colloidal quantum dot solar cells are presented. The architecture allows for high absorption with full depletion, thereby breaking the photon absorption/carrier extraction compromise inherent in planar devices. A record power conversion of 5.5% under simulated AM 1.5 illumination conditions is reported. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Ultra-bright alkylated graphene quantum dots

    Science.gov (United States)

    Feng, Lan; Tang, Xing-Yan; Zhong, Yun-Xin; Liu, Yue-Wen; Song, Xue-Huan; Deng, Shun-Liu; Xie, Su-Yuan; Yan, Jia-Wei; Zheng, Lan-Sun

    2014-10-01

    Highly efficient and stable photoluminescence (PL) are urgently desired for graphene quantum dots (GQDs) to facilitate their prospective applications as optical materials. Here, we report the facile and straightforward synthesis of alkylated graphene quantum dots (AGQDs) via the solvothermal reaction of propagatively alkylated graphene sheets (PAGenes). In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with a relative quantum yield of up to 65%. Structural and chemical composition characterization demonstrated that the synthesized AGQDs are nearly oxygen-defect-free with alkyl groups decorated on edges and basal plane, which may contribute to their greatly improved pH tolerance and high quantum efficiency. The photocatalytic performance of AGQDs-P25 nanocomposites was evaluated by the degradation of Rhodamine B under visible light. The photocatalytic rate is ca. 5.9 times higher than that of pure P25, indicating that AGQDs could harness the visible spectrum of sunlight for energy conversion or environmental therapy.Highly efficient and stable photoluminescence (PL) are urgently desired for graphene quantum dots (GQDs) to facilitate their prospective applications as optical materials. Here, we report the facile and straightforward synthesis of alkylated graphene quantum dots (AGQDs) via the solvothermal reaction of propagatively alkylated graphene sheets (PAGenes). In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with a relative quantum yield of up to 65%. Structural and chemical composition characterization demonstrated that the synthesized AGQDs are nearly oxygen-defect-free with alkyl groups decorated on edges and basal plane, which may contribute to their greatly improved pH tolerance and high quantum efficiency. The photocatalytic performance of AGQDs-P25 nanocomposites was evaluated by the degradation of Rhodamine B under visible light. The

  19. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2010-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... determined the oscillator strength, quantum efficiency and spin-flip rates of QD excitons as well as their dependencies on emission wavelength and QD size. Enhancement and inhibition of QD spontaneous emission in photonic crystal membranes (PCMs) is observed. Efficient coupling to PCM waveguides is...

  20. Quantum-dot excitons in nanostructured environments

    DEFF Research Database (Denmark)

    Hvam, Jørn Märcher; Stobbe, Søren; Lodahl, Peter

    2011-01-01

    The interaction between light and quantum-dot (QD) excitons is strongly influenced by the environment in which the QD is placed. We have investigated the interaction by measuring the time-resolved spontaneous-emission rate of QD excitons in different nanostructured environments. Thereby, we have...... determined the oscillator strength, quantum efficiency and spin-flip rates of QD excitons as well as their dependencies on emission wavelength and QD size. Enhancement and inhibition of QD spontaneous emission in photonic crystal membranes (PCMs) is observed. Efficient coupling to PCM waveguides is...

  1. Relaxation dynamics in correlated quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Andergassen, S. [Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Schuricht, D.; Pletyukhov, M.; Schoeller, H. [Institute for Theory of Statistical Physics, RWTH Aachen University and JARA-Fundamentals of Future Information Technology, 52056 Aachen (Germany)

    2014-12-04

    We study quantum many-body effects on the real-time evolution of the current through quantum dots. By using a non-equilibrium renormalization group approach, we provide analytic results for the relaxation dynamics into the stationary state and identify the microscopic cutoff scales that determine the transport rates. We find rich non-equilibrium physics induced by the interplay of the different energy scales. While the short-time limit is governed by universal dynamics, the long-time behavior features characteristic oscillations as well as an interplay of exponential and power-law decay.

  2. The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

    International Nuclear Information System (INIS)

    InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelength infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states

  3. Electrically addressing a single self-assembled quantum dot

    CERN Document Server

    Ellis, D J P; Atkinson, P; Ritchie, D A; Shields, A J

    2006-01-01

    We report on the use of an aperture in an aluminum oxide layer to restrict current injection into a single self-assembled InAs quantum dot, from an ensemble of such dots within a large mesa. The insulating aperture is formed through the wet-oxidation of a layer of AlAs. Under photoluminescence we observe that only one quantum dot in the ensemble exhibits a Stark shift, and that the same single dot is visible under electroluminescence. Autocorrelation measurements performed on the electroluminescence confirm that we are observing emission from a single quantum dot.

  4. Reconfigurable quadruple quantum dots in a silicon nanowire transistor

    OpenAIRE

    Betz, A. C.; Tagliaferri, M. L. V.; Vinet, M.; Broström, M.; Sanquer, M.; Ferguson, A.J.; Gonzalez-Zalba, M. F.

    2016-01-01

    We present a novel reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consist of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired...

  5. Hybrid YAG/CdSe quantum dots phosphors for white light-emitting diodes.

    Science.gov (United States)

    Chung, Shu-Ru; Wang, Kuan-Wen; Wang, Ming-Wei

    2013-06-01

    CdSe quantum dots (QDs) with the emission wavelength of 577 nm, full width at half maximum (FWHM) of 28 nm, quantum yield (QY) of 40% and average particle size of 3.7 +/- 0.5 nm are prepared. 1, 3 and 5 wt% of CdSe QDs is blended with commercial YAG:Ce phosphor (called as composite phosphor) and the device performance of YAG-based and composite phosphor-based white light-emitting diode (WLED) is investigated. The color rendering index (CRI) and luminous efficiency could be improved simultaneous for composite phosphor-based WLED. As the applied current increases, the correlated color temperature (CCT), Commission International d'Eclairage (CIE) chromaticity coordinates and CRI of both WLEDs are almost the same when compared with standard condition (20 mA), while the luminous efficiency of both WLEDs decreases with increasing applied current. It is interesting to find that there is a positive effect of QDs on the luminous efficiency and CRI value. This result also reveals that adding a small amount of yellow emitting QDs can not only reduce the scattering of light effectively but increase utilization efficiency of reflection and refraction light, thereby enhancing the efficiency of composite phosphor-based WLED. Moreover, the emission wavelength of 577 nm QDs is longer than that of YAG, it redound to extends emission range resulting in increase the CRI of devices. PMID:23862503

  6. Polarization-insensitive quantum-dot coupled quantum-well semiconductor optical amplifier

    International Nuclear Information System (INIS)

    The optical gain of a quantum-dot semiconductor optical amplifier is usually seriously dependent on polarization; we propose a quantum-dot coupled tensile-strained quantum-well structure to obtain polarization insensitivity. The tensile-strained quantum well not only serves as a carrier injection layer of quantum dots but also offers gain to the transverse-magnetic mode. Based on the polarization-dependent coupled carrier rate-equation model, we study carrier competition among quantum well and quantum dots, and study the polarization dependence of the quantum-dot coupled quantum-well semiconductor optical amplifier. We also analyze polarization-dependent photon-mediated carrier distribution among quantum well and quantum dots. It is shown that polarization-insensitive gain can be realized by optimal design

  7. Quantum optics with quantum dots in photonic nanowires

    DEFF Research Database (Denmark)

    Claudon, Julien; Munsch, Matthieu; Bleuse, Joel;

    2012-01-01

    Besides microcavities and photonic crystals, photonic nanowires have recently emerged as a novel resource for solidstate quantum optics. We will review recent studies which demonstrate an excellent control over the spontaneous emission of InAs quantum dots (QDs) embedded in single-mode Ga...... quantum optoelectronic devices. Quite amazingly, this approach has for instance permitted (unlike microcavity-based approaches) to combine for the first time a record-high efficiency (72%) and a negligible g(2) in a QD single photon source....

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

    Science.gov (United States)

    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

  9. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals

    International Nuclear Information System (INIS)

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure

  10. Second-harmonic imaging of semiconductor quantum dots

    DEFF Research Database (Denmark)

    Østergaard, John Erland; Bozhevolnyi, Sergey I.; Pedersen, Kjeld;

    2000-01-01

    Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maxim...... further observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. (C) 2000 American Institute of Physics....

  11. Core–shell quantum dots: Properties and applications

    International Nuclear Information System (INIS)

    Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core–shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis

  12. Mode Competition in Dual-Mode Quantum Dots Semiconductor Microlaser

    OpenAIRE

    Chusseau, Laurent; Philippe, Fabrice; Viktorovitch, Pierre; Letartre, Xavier

    2013-01-01

    This paper describes the modeling of quantum dots lasers with the aim of assessing the conditions for stable cw dual-mode operation when the mode separation lies in the THz range. Several possible models suited for InAs quantum dots in InP barriers are analytically evaluated, in particular quantum dots electrically coupled through a direct exchange of excitation by the wetting layer or quantum dots optically coupled through the homogeneous broadening of their optical gain. A stable dual-mode ...

  13. Core–shell quantum dots: Properties and applications

    Energy Technology Data Exchange (ETDEWEB)

    Vasudevan, D., E-mail: vasudevand@rediffmail.com [Electrodics and electrocatalysis division, CSIR-CECRI, Karaikudi 630006 (India); Gaddam, Rohit Ranganathan [Amity Institute of Nanotechnology, Amity University, Noida 201301 (India); Trinchi, Adrian; Cole, Ivan [CSIRO Materials Science and Engineering, Clayton South MDC, 3169 (Australia)

    2015-07-05

    Fluorescent quantum dots (QDs) are semiconducting nanocrystals (NCs) that find numerous applications in areas, such as bio labelling, sensors, lasers, light emitting diodes and medicine. Core–shell quantum dots were developed to improve the photoluminescence efficiency of single quantum dots. Capping their surface with organic ligands as well as their extraction into aqueous media enables their use in sensing applications. The current review highlights the importance and applications of core shell quantum dots as well as their surface modifications and applications in the field of medicine and as sensors for chemical and biochemical analysis.

  14. Polarized quantum dot emission in electrohydrodynamic jet printed photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    See, Gloria G. [Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 208 North Wright Street, Urbana, Illinois 61801 (United States); Xu, Lu; Nuzzo, Ralph G. [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States); Sutanto, Erick; Alleyne, Andrew G. [Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, 154 Mechanical Engineering Building, Urbana, Illinois 61801 (United States); Cunningham, Brian T. [Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 208 North Wright Street, Urbana, Illinois 61801 (United States); Department of Bioengineering, University of Illinois at Urbana-Champaign, 1270 Digital Computer Laboratory, MC-278, Urbana, Illinois 61801 (United States)

    2015-08-03

    Tailored optical output, such as color purity and efficient optical intensity, are critical considerations for displays, particularly in mobile applications. To this end, we demonstrate a replica molded photonic crystal structure with embedded quantum dots. Electrohydrodynamic jet printing is used to control the position of the quantum dots within the device structure. This results in significantly less waste of the quantum dot material than application through drop-casting or spin coating. In addition, the targeted placement of the quantum dots minimizes any emission outside of the resonant enhancement field, which enables an 8× output enhancement and highly polarized emission from the photonic crystal structure.

  15. Silicon quantum dots: fine-tuning to maturity.

    Science.gov (United States)

    Morello, Andrea

    2015-12-18

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science. PMID:26584678

  16. Silicon quantum dots: fine-tuning to maturity

    Science.gov (United States)

    Morello, Andrea

    2015-12-01

    Quantum dots in semiconductor heterostructures provide one of the most flexible platforms for the study of quantum phenomena at the nanoscale. The surging interest in using quantum dots for quantum computation is forcing researchers to rethink fabrication and operation methods, to obtain highly tunable dots in spin-free host materials, such as silicon. Borselli and colleagues report in Nanotechnology the fabrication of a novel Si/SiGe double quantum dot device, which combines an ultra-low disorder Si/SiGe accumulation-mode heterostructure with a stack of overlapping control gates, ensuring tight confining potentials and exquisite tunability. This work signals the technological maturity of silicon quantum dots, and their readiness to be applied to challenging projects in quantum information science.

  17. The quantum dot nanoconjugate tool box (Invited Paper)

    Science.gov (United States)

    Tomlinson, I. D.; Wright, D. W.; Giorgio, T. D.; Blakely, R. D.; Pennycook, S. J.; Hercules, D.; Bentzen, L.; Smith, R. A.; McBride, J.; Vergne, M. J.; Rosenthal, S.

    2005-04-01

    The surface coating of quantum dots has been characterised using Z-stem. Quantum dots have been pegylated to increase stability in aqueous solution. The fluorescence intensity of the quantum dots was modulated pegylation. PEG was coupled using different ratios of EDC, PEG and NHS. Optimum coupling conditions were found to occur when 2000 equivalents of PEG were reacted with 1 equivalent of dot in the presence of 1500 equivalents of NHS and EDC. Angiotensin II was also conjugated to quantum dots and these conjugates were shown to be biologically active. Quantum dots have also been surface functionalised with other peptides such as NGR with subsequent demonstration of cell surface binding and can be characterized by flow cytometry.

  18. Modified magnetic quantum dot with electric confining potentials

    International Nuclear Information System (INIS)

    The electronic properties of a modified magnetic quantum dot are studied. The modified magnetic quantum dot is a quantum structure that is formed by spatially inhomogeneous distributions of magnetic fields. Electrons are magnetically confined to the plane where the magnetic fields inside and outside the dot are different from each other. The energy spectrum exhibits quite different features depending on the directions of the magnetic fields inside and outside the dot. In particular, the case of opposite directions of the fields is more interesting than that of the same direction. An electrostatic potential is introduced to the system to study the effects of an electric confining potential on the eigenenergy of a single electron in the modified magnetic quantum dot. The additional potential raises the whole energy spectrum and changes its shape. The ground-state angular momentum transitions occurring in a bare modified magnetic quantum dot disappear on introduction of the additional parabolic potential

  19. Quantum dot spin cellular automata for realizing a quantum processor

    International Nuclear Information System (INIS)

    We show how single quantum dots, each hosting a singlet–triplet qubit, can be placed in arrays to build a spin quantum cellular automaton. A fast (∼10 ns) deterministic coherent singlet–triplet filtering, as opposed to current incoherent tunneling/slow-adiabatic based quantum gates (operation time ∼300 ns), can be employed to produce a two-qubit gate through capacitive (electrostatic) couplings that can operate over significant distances. This is the coherent version of the widely discussed charge and nano-magnet cellular automata, and would increase speed, reduce dissipation, and perform quantum computation while interfacing smoothly with its classical counterpart. This combines the best of two worlds—the coherence of spin pairs known from quantum technologies, and the strength and range of electrostatic couplings from the charge-based classical cellular automata. Significantly our system has zero electric dipole moment during the whole operation process, thereby increasing its charge dephasing time. (paper)

  20. Hybrid passivated colloidal quantum dot solids

    KAUST Repository

    Ip, Alex

    2012-07-29

    Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electrong-"hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device. © 2012 Macmillan Publishers Limited. All rights reserved.

  1. Synthesis, biological targeting and photophysics of quantum dots

    Science.gov (United States)

    Clarke, Samuel Jon

    Quantum dots (QDs) are inorganic nanoparticles that have exceptional optical properties. Currently, QDs have failed to reach their potential as fluorescent probes in live cells, due to the nontrivial requirements for biological interfacing. The goal of this thesis is to address technical hurdles related to the reproducible synthesis of QDs, strategies for the specific targeting of QDs to biological cells and to understanding and exploitation of the photophysical properties. High quality QDs of varying composition (CdSe, CdTe and core/shell CdSe/ZnS) were synthesized with an organometallic method. To prepare biocompatible QDs, three strategies were used. The simplest strategy used small mercaptocarboxylic acids, while performance improvements were realized with engineered-peptide and lipid-micelle coatings. For specific biological targeting of the QDs, conjugation strategies were devised to attach biomolecules, while spectroscopic characterization methods were developed to assess conjugation efficiencies. To target gram-negative bacterial cells, an electrostatic self-assembly method was used to attach an antibiotic selective for this class of bacteria, polymyxin B. To target dopamine neurotransmitter receptor, a covalent conjugation method was used to attach dopamine, the endogenous ligand for that receptor. It was shown that dopamine molecule enabled electron transfer to QDs and the photophysics was studied in detail. A novel conjugation and targeting strategy was explored to enable the selective binding of QDs to polyhistidine epitopes on membrane proteins. Epifluorescence microscopy was used to evaluate the biological activity of the three QD probes. Combined, they add to the QD 'toolkit' for live-cell imaging. Finally, due to its negative implications in biological imaging, the fluorescent intermittency (blinking) of CdTe QDs was investigated. It was shown that mercaptocarboxylic acids contribute to the blinking suppression of the QDs, results that may aid in

  2. Quantum optics and cavity QED with quantum dots in photonic crystals

    CERN Document Server

    Vuckovic, Jelena

    2014-01-01

    This chapter will primarily focus on the studies of quantum optics with semiconductor, epitaxially grown quantum dots embedded in photonic crystal cavities. We will start by giving brief introductions into photonic crystals and quantum dots, then proceed with the introduction to cavity quantum electrodynamics (QED) effects, with a particular emphasis on the demonstration of these effects on the quantum dot-photonic crystal platform. Finally, we will focus on the applications of such cavity QED effects.

  3. Quantum optics and cavity QED with quantum dots in photonic crystals

    OpenAIRE

    Vuckovic, Jelena

    2014-01-01

    This chapter will primarily focus on the studies of quantum optics with semiconductor, epitaxially grown quantum dots embedded in photonic crystal cavities. We will start by giving brief introductions into photonic crystals and quantum dots, then proceed with the introduction to cavity quantum electrodynamics (QED) effects, with a particular emphasis on the demonstration of these effects on the quantum dot-photonic crystal platform. Finally, we will focus on the applications of such cavity QE...

  4. Mapping between quantum dot and quantum well lasers: From conventional to spin lasers

    OpenAIRE

    Lee, JeongSu; Oszwałdowski, Rafał; Gøthgen, Christian; Žutić, Igor

    2012-01-01

    We explore similarities between the quantum wells and quantum dots used as optical gain media in semiconductor lasers. We formulate a mapping procedure which allows a simpler, often analytical, description of quantum well lasers to study more complex lasers based on quantum dots. The key observation in relating the two classes of laser is that the influence of a finite capture time on the operation of quantum dot lasers can be approximated well by a suitable choice of the gain compression fac...

  5. White light emission from quantum well structured quantum dots

    International Nuclear Information System (INIS)

    Highlights: • CdS/ZnS/CdS/ZnS quantum well quantum dot prepared via reverse micelle process. • White light emission achieved by this type of QWQDs. • Tunable emission spectra of QWQDs with varied water-to-surfactant ratios. • Enhanced PL efficiency by suppressing Auger recombination with QWQD structure. - Abstract: Four-layer quantum well quantum dots (QWQDs) with structure of CdS/ZnS/CdS/ZnS were synthesized using a reverse micelle process. White light emission can be achieved by this type of QWQD, as the blue and green/orange emission components were originated from CdS core and ZnS inner shell, respectively. The emission spectra of QWQDs can be adjusted by varying the water-to-surfactant ratios in the reverse micelle process which controls the particle size and core/shell nanostructure of QWQDs. Efficient luminescence with PL quantum yield up to 30% can be achieved, due to the effective suppression of non-radiative relaxations from the Auger recombination with the quantum well structure

  6. Trajectory phases of a quantum dot model

    International Nuclear Information System (INIS)

    We present a thermodynamic formalism to study the trajectories of charge transport through a quantum dot coupled to two leads in the resonant-level model. We show that a close analogue of equilibrium phase transitions exists for the statistics of transferred charge; by tuning an appropriate ‘counting field’, crossovers to different trajectory phases are possible. Our description reveals a mapping between the statistics of a given device and current measurements over a range of devices with different dot–lead coupling strengths. Furthermore insight into features of the trajectory phases are found by studying the occupation of the dot conditioned on the transported charge between the leads; this is calculated from first principles using a trajectory biased two-point projective measurement scheme. (paper)

  7. Resonance fluorescence from a telecom-wavelength quantum dot

    CERN Document Server

    Al-Khuzheyri, R; Huwer, J; Santana, T S; Szymanska, J Skiba-; Felle, M; Ward, M B; Stevenson, R M; Farrer, I; Tanner, M G; Hadfield, R H; Ritchie, D A; Shields, A J; Gerardot, B D

    2016-01-01

    We report on resonance fluorescence from a single quantum dot emitting at telecom wavelengths. We perform high-resolution spectroscopy and observe the Mollow triplet in the Rabi regime--a hallmark of resonance fluorescence. The measured resonance-fluorescence spectra allow us to rule out pure dephasing as a significant decoherence mechanism in these quantum dots. Combined with numerical simulations, the experimental results provide robust characterisation of charge noise in the environment of the quantum dot. Resonant control of the quantum dot opens up new possibilities for on-demand generation of indistinguishable single photons at telecom wavelengths as well as quantum optics experiments and direct manipulation of solid-state qubits in telecom-wavelength quantum dots.

  8. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    future challenge for the droplet-epitaxy technique. A multipolar theory of spontaneous emission from quantum dots is developed to explain the recent observation that In(Ga)As quantum dots break the dipole theory. The analysis yields a large mesoscopic moment, which contains magnetic-dipole and electric......-quadrupole contributions and may compete with the dipole moment in light-matter interactions. A theory for the quantum-dot wavefunctions is developed showing that the mesoscopic moment originates from distortions in the underlying crystal lattice. The resulting quantum-mechanical current density is curved leading to light......-matter interaction of both electric and magnetic character. Our study demonstrates that In(Ga)As quantum dots lack parity symmetry and, as consequence, can be employed for locally probing the parity symmetry of complex photonic nanostructures. This opens the prospect for interfacing quantum dots with optical...

  9. Microscopic Theory of Cation Exchange in CdSe Nanocrystals

    OpenAIRE

    Ott, Florian D.; Spiegel, Leo L.; Norris, David J.; Erwin, Steven C.

    2014-01-01

    Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We used density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key...

  10. Correlated Coulomb drag in capacitively coupled quantum-dot structures

    DEFF Research Database (Denmark)

    Kaasbjerg, Kristen; Jauho, Antti-Pekka

    2016-01-01

    We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach which accounts for higher-order tunneling (cotunneli...

  11. Cytocompatibility of direct water synthesized cadmium selenide quantum dots in colo-205 cells

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Torres, Marcos R. [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Velez, Christian; Zayas, Beatriz [Universidad Metropolitana, ChemTox Laboratory, School of Environmental Affairs (United States); Rivera, Osvaldo [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Arslan, Zikri [Jackson State University, Department of Chemistry (United States); Gonzalez-Vega, Maxine N. [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States); Diaz-Diestra, Daysi; Beltran-Huarac, Juan; Morell, Gerardo [University of Puerto Rico, Molecular Science Research Center (United States); Primera-Pedrozo, Oliva M., E-mail: oprimera1@suagm.edu [Universidad Metropolitana, Nanomaterials Science Laboratory, School of Science and Technology (United States)

    2015-06-15

    Cadmium selenide quantum dots (CdSe QDs), inorganic semiconducting nanocrystals, are alluring increased attraction due to their highly refined chemistry, availability, and super tunable optical properties suitable for many applications in different research areas, such as photovoltaics, light-emitting devices, environmental sciences, and nanomedicine. Specifically, they are being widely used in bio-imaging in contrast to organic dyes due to their high brightness and improved photo-stability, and their ability to tune their absorption and emission spectra upon changing the crystal size. The production of CdSe QDs is mostly assisted by trioctylphosphine oxide compound, which acts as solvent or solubilizing agent and renders the QDs soluble in organic compounds (such as toluene, chloroform, and hexane) that are highly toxic. To circumvent the toxicity-related factor in CdSe QDs, we report the synthesis of CdSe QDs capped with thioglycolic acid (TGA) in an aqueous medium, and their biocompatibility in colo-205 cancer cells. In this study, the [Cd{sup 2+}]/[TGA] ratio was adjusted to 11:1 and the Se concentration (10 and 15 mM) was monitored in order to evaluate its influence on the optical properties and cytocompatibility. QDs resulted to be quite stable in water (after purification) and RPMI cell medium and no precipitation was observed for long contact times, making them appealing for in vitro experiments. The spectroscopy analysis, advanced electron microscopy, and X-ray diffractometry studies indicate that the final products were successfully formed exhibiting an improved optical response. Colo-205 cells being exposed to different concentrations of TGA-capped CdSe QDs for 12, 24, and 48 h with doses ranging from 0.5 to 2.0 mM show high tolerance reaching cell viabilities as high as 93 %. No evidence of cellular apoptotic pathways was observed as pointed out by our Annexin V assays at higher concentrations. Moreover, confocal microscopy analysis conducted to

  12. Cytocompatibility of direct water synthesized cadmium selenide quantum dots in colo-205 cells

    International Nuclear Information System (INIS)

    Cadmium selenide quantum dots (CdSe QDs), inorganic semiconducting nanocrystals, are alluring increased attraction due to their highly refined chemistry, availability, and super tunable optical properties suitable for many applications in different research areas, such as photovoltaics, light-emitting devices, environmental sciences, and nanomedicine. Specifically, they are being widely used in bio-imaging in contrast to organic dyes due to their high brightness and improved photo-stability, and their ability to tune their absorption and emission spectra upon changing the crystal size. The production of CdSe QDs is mostly assisted by trioctylphosphine oxide compound, which acts as solvent or solubilizing agent and renders the QDs soluble in organic compounds (such as toluene, chloroform, and hexane) that are highly toxic. To circumvent the toxicity-related factor in CdSe QDs, we report the synthesis of CdSe QDs capped with thioglycolic acid (TGA) in an aqueous medium, and their biocompatibility in colo-205 cancer cells. In this study, the [Cd2+]/[TGA] ratio was adjusted to 11:1 and the Se concentration (10 and 15 mM) was monitored in order to evaluate its influence on the optical properties and cytocompatibility. QDs resulted to be quite stable in water (after purification) and RPMI cell medium and no precipitation was observed for long contact times, making them appealing for in vitro experiments. The spectroscopy analysis, advanced electron microscopy, and X-ray diffractometry studies indicate that the final products were successfully formed exhibiting an improved optical response. Colo-205 cells being exposed to different concentrations of TGA-capped CdSe QDs for 12, 24, and 48 h with doses ranging from 0.5 to 2.0 mM show high tolerance reaching cell viabilities as high as 93 %. No evidence of cellular apoptotic pathways was observed as pointed out by our Annexin V assays at higher concentrations. Moreover, confocal microscopy analysis conducted to evaluate

  13. Electrostatically defined silicon quantum dots with counted antimony donor implants

    Energy Technology Data Exchange (ETDEWEB)

    Singh, M., E-mail: msingh@sandia.gov; Luhman, D. R.; Lilly, M. P. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87175 (United States); Pacheco, J. L.; Perry, D.; Garratt, E.; Ten Eyck, G.; Bishop, N. C.; Wendt, J. R.; Manginell, R. P.; Dominguez, J.; Pluym, T.; Bielejec, E.; Carroll, M. S. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

    2016-02-08

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

  14. Electrostatically defined silicon quantum dots with counted antimony donor implants

    International Nuclear Information System (INIS)

    Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors in 100 nm × 150 nm windows straddling quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular Coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants

  15. Lateral excitonic switching in vertically stacked quantum dots

    Science.gov (United States)

    Jarzynka, Jarosław R.; McDonald, Peter G.; Shumway, John; Galbraith, Ian

    2016-06-01

    We show that the application of a vertical electric field to the Coulomb interacting system in stacked quantum dots leads to a 90° in-plane switching of charge probability distribution in contrast to a single dot, where no such switching exists. Results are obtained using path integral quantum Monte Carlo with realistic dot geometry, alloy composition, and piezo-electric potential profiles. The origin of the switching lies in the strain interactions between the stacked dots hence the need for more than one layer of dots. The lateral polarization and electric field dependence of the radiative lifetimes of the excitonic switch are also discussed.

  16. Direct Interband Light Absorption in Conical Quantum Dot

    OpenAIRE

    Hayrapetyan, D. B.; Chalyan, A. V.; Kazaryan, E. M.; H. A. Sarkisyan

    2015-01-01

    In the framework of the adiabatic approximation, the energy states of electron as well as the direct light absorption are investigated in conical quantum dot. Analytical expressions for particle energy spectrum are obtained. The dependence of the absorption edge on geometrical parameters of conical quantum dot is obtained. Selection rules are revealed for transitions between levels with different quantum numbers. In particular, it is shown that for the radial quantum number transitions are al...

  17. Colloidal Quantum Dot Photovoltaics: A Path Forward

    KAUST Repository

    Kramer, Illan J.

    2011-11-22

    Colloidal quantum dots (CQDs) offer a path toward high-efficiency photovoltaics based on low-cost materials and processes. Spectral tunability via the quantum size effect facilitates absorption of specific wavelengths from across the sun\\'s broad spectrum. CQD materials\\' ease of processing derives from their synthesis, storage, and processing in solution. Rapid advances have brought colloidal quantum dot photovoltaic solar power conversion efficiencies of 6% in the latest reports. These achievements represent important first steps toward commercially compelling performance. Here we review advances in device architecture and materials science. We diagnose the principal phenomenon-electronic states within the CQD film band gap that limit both current and voltage in devices-that must be cured for CQD PV devices to fulfill their promise. We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field. © 2011 American Chemical Society.

  18. Nano-laser on silicon quantum dots

    Science.gov (United States)

    Huang, Wei-Qi; Liu, Shi-Rong; Qin, Chao-Jian; Lü, Quan; Xu, Li

    2011-04-01

    A new conception of nano-laser is proposed in which depending on the size of nano-clusters (silicon quantum dots (QD)), the pumping level of laser can be tuned by the quantum confinement (QC) effect, and the population inversion can be formed between the valence band and the localized states in gap produced from the surface bonds of nano-clusters. Here we report the experimental demonstration of nano-laser on silicon quantum dots fabricated by nanosecond pulse laser. The peaks of stimulated emission are observed at 605 nm and 693 nm. Through the micro-cavity of nano-laser, a full width at half maximum of the peak at 693 nm can reach to 0.5 nm. The theoretical model and the experimental results indicate that it is a necessary condition for setting up nano-laser that the smaller size of QD (d nano-laser will be limited in the range of 1.7-2.3 eV generally due to the position of the localized states in gap, which is in good agreement between the experiments and the theory.

  19. Quantum Gates Between Two Spins in a Triple Dot System with an Empty Dot

    CERN Document Server

    Coello, Jose Garcia

    2011-01-01

    We propose a scheme for implementing quantum gates and entanglement between spin qubits in the outer dots of a triple-dot system with an empty central dot. The voltage applied to the central dot can be tuned to realize the gate. Our scheme exemplifies the possibility of quantum gates outside the regime where each dot has an electron, so that spin-spin exchange interaction is not the only relevant mechanism. Analytic treatment is possible by mapping the problem to a t-J model. The fidelity of the entangling quantum gate between the spins is analyzed in the presence of decoherence stemming from a bath of nuclear spins, as well as from charge fluctuations. Our scheme provides an avenue for extending the scope of two qubit gate experiments to triple-dots, while requiring minimal control, namely that of the potential of a single dot, and may enhance the qubit separation to ease differential addressability.

  20. Optical properties of multicoated CdSe/CdS/ZnS quantum dots for multiphoton applications

    International Nuclear Information System (INIS)

    CdSe-core CdS/Cd0.5Zn0.5S/ZnS multishell quantum dots (QDs) were synthesized by using the successive ion layer adsorption and reaction method, and their optical properties were characterized experimentally. Based on probability calculations of the time-dependent Schroedinger equation, a kinetic Monte Carlo method was used to simulate and analyse the absorption and spontaneous emission spectra of multiphoton-excited QDs. It has been shown that the blue shift of the photoluminescence peak of the core CdSe QD after coating is most probably due to the Zn diffusion during the synthesis of the ZnS coating layer