Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

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.

Novel Hybrid SiO2/ZnS Coated CdTe/CdS Quantum Dots and Their Bioapplications

Novel CdTe/CdS quantum dots(QDs)coated with a hybrid of SiO_2 and ZnS were fabricated through a simple two-step approach.The hybrid SiO_2/ZnS coated CdTe/CdS quantum dots was characterized by transmission electron microscopy(TEM),UV and fluorescence spectrometer.Results indicated that the core-shell structure gave the QDs outstanding photoluminescence properties,includinganarrowphotoluminescencespectrum,high photoluminescence(PL)quantum yield and long emission lifetime(average PL lifetime of increased from 26.4 ns to 49.1 ns).Cellular studies showed the QDs had good cytocompatibility with Hela cells as determined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide(MTT)assay after coating SiO_2/ZnS,and also proved the feasibility of using the hybrid SiO_2/ZnS coated QDs as optical probes for in vitro cell imaging.The synthesis method of QDs is highly promising for the production of robust and functional optical probes for bio-imaging and sensing applications.

氢氟酸处理InP/GaP/ZnS量子点的光学性能及其发光二极管应用

采用氢氟酸(HF)原位注入法制备了InP/GaP/ZnS量子点。通过紫外/可见/近红外光谱、光致发光光谱、透射电镜、球差校正透射电镜、X射线衍射、X射线光电子能谱等测试手段分析了HF对InP量子点的发光性能影响。实验结果表明,HF刻蚀减少了量子点表面氧化缺陷状态,有效控制了InP核表面的氧化,并且原子配体形式的F-钝化了量子点表面的悬挂键,显著提升了量子点的光学性能。HF处理的InP/GaP/ZnS量子点具有最佳的发光性能,PLQY高达96%。此外,用HF处理InP/GaP/ZnS量子点制备的发光二极管,其发光的电流效率为6.63 cd/A,最佳外量子效率(EQE)为3.83%。

Synthesis and characterization of ZnS-based quantum dots to trace low concentration of ammonia

In the present work,a solution-based co-precipitation method has been adopted to synthesize pure and cobalt-doped ZnS quantum dots and characterized by XRD,SEM,TEM with EDX,FTIR and gas sensing properties.XRD analysis has shown a single phase of ZnS quantum dots having a zinc blend structure.TEM and XRD line broadening indicated that the average crystallite size in the sample is in the range of 2 to 5 nm.SEM micrographs show spherical-shaped quantum dots.FTIR studies show that cobalt has been successfully doped into the ZnS cubic lattice.EDX spectra have analyzed the elemental presence in the samples and it is evident that the spectra confirmed the presence of cobalt(Co),zinc(Zn),oxygen(O),and sulphur(S)elements only and no other impurities are observed.The ZnS-based quantum dot sensors reveal high sensitivity towards 50 ppm of ammonia vapors at an operating temperature of 70℃.Hence,ZnS-based quantum dots can be a promising and quick traceable sensor towards ammonia sensing applications with good response and recovery time.

CdTe/ZnS核壳结构半导体量子点的荧光特性研究

纳米技术研究体系中量子点是重要的研究模块之一,量子点尺寸非常小,具有独特的光物理特性。该文旨通过实验进行分析,实验过程选择99%纯度硼氢化钠、99%纯度硫酸锌、S212恒速搅拌器、TG16-WS高速离心机、0.310 mL巯基乙酸等,制备0.4565 g CdCl_(2)·2.5H_(2)O混合液,当样本溶液呈现橙色时,表明CdTe核已制备完成。实验结果显示:单脉冲能量增加时,τ_(-rise)与τ_(2)有所降低,τ_(1)数值增加,τ_(-rise)与壳层厚度呈正比关系。通过对量子点荧光特性的分析,有利于促进核壳结构量子点的制备。

Large-scale control of enhancement and quenching of photoluminescence for ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution

We investigated the optical properties of hybrid exciton–plasmon coupling ensembles composed of ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution. We modulated their average interval by changing the ratio of quantum dots and Ag nanoparticles. The transition from dramatic PL enhancement to PL quenching state was experimentally observed, according to the continuous decrease of the PL lifetime. The PL enhancement rate exceeded 10, with the Purcell factor of 3.5. Meanwhile, the proportion of fast decay increased from 0.3 to 0.6, corresponding to the proportion of slow decay decreased from 0.7 to 0.4. Our experiment is important for the hybrid exciton–plasmon coupling system to be practicable in optoelectronic application.

Temperature dependence of the photoluminescence of MnS/ZnS core–shell quantum dots

The temperature dependence of the photoluminescence（PL） from Mn S/Zn S core–shell quantum dots is investigated in a temperature range of 8 K–300 K. The orange emission from the ^4T1→^6A1transition of Mn^2＋ions and the blue emission related to the trapped surface state are observed in the Mn S/Zn S core–shell quantum dots. As the temperature increases, the orange emission is shifted toward a shorter wavelength while the blue emission is shifted towards the longer wavelength. Both the orange and blue emissions reduce their intensities with the increase of temperature but the blue emission is quenched faster. The temperature-dependent luminescence intensities of the two emissions are well explained by the thermal quenching theory.

Water-soluble CdSe/ZnS quantum dots passivated by poly(glycino amino acid) phosphazenes

Poly(organophosphazenes) have potential applications in making water-soluble and biocompatible quantum dots (QDs) due to their wide variety of properties. The CdSe QDs of green emission and the core-shell CdSe/ZnS QDs of red emission were prepared. Subsequently the trioctylphosphine oxide-stabilized CdSe/ZnS QDs were transferred from chloroform into water through a ligand exchange process with poly(glycino amino acid)phosphazenes, which can be obtained from the saponification of poly (glycino amino ester)phosphazenes at room temperature. The resulting QDs-polymer nanocomposite particles can form colloidally stable suspensions in water and exhibit good photostability.

In-situ Synthesis of SnO2 Quantum Dots/ZnS Nanosheets Heterojunction as a Visible-light-driven Photocatalyst for Degradation of Rhodamine B,Potassium Dichromate and Tetracycline

The SnO2 quantum dots(SnO2QDs)/ZnS nanosheets(ZnSNs)heterojunction was fabricated via an in-situ synthetic method at room temperature.Rhodamine B,potassium dichromate,and tetracycline were used to discuss the photocatalytic activities of the as-prepared samples under the visible light illumination.The photocatalytic mechanism of the as-prepared samples was also proposed.The experimental results indicate that the degradation efficiency of the as-prepared SnO2QDs/ZnSNs heterojunction first increases and then decreases with increasing the usage of ZnSNs.When the mass ratio of SnO2QDs to ZnSNs is 1:2 in 180 min,the as-prepared samples have the highest degradation efficiency of 89.1%for rhodamine B,97.7%for potassium dichromate,and 83.8%for tetracycline,which are much higher than 51.7%,26.8%,and 0.9%of pure SnO2QDs as well as 37.9%,87.1%,and 19.1%of pure ZnSNs,respectively.After it is repeatedly degraded for 3 times,it possesses the degradation efficiency of 62.5%for rhodamine B,which increases by 200.5%in comparison with 20.8%of the pure SnO2QDs.Moreover,the enhanced photocatalytic performances of the as-prepared hybrids are attributed to the formation of heterojunction between the SnO2QDs and ZnSNs.In addition,hydroxyl radicals and superoxide anion radicals play major roles during the photocatalytic degradation process,while holes play a minor role.

Effect of gamma irradiation on optical properties of CdSe/ZnS quantum dots embedded in PDMS

The optical properties of CdSe/ZnS quantum dots(QDs)embedded in polydimethylsiloxane(PDMS)flexible materials after irradiated withγ-rays were studied.As an embedding matrix,PDMS exhibits the advantage of high radiation hardness.The luminescence spectra and fluorescence lifetime of the irradiated and unirradiated samples were tested.The fluorescence intensity of QDs decreases with the increase of the irradiation dose according to the result of luminescence spectra.The fluorescence intensity of the QDs decreases by 80%after irradiation with a dose of 1 kGy,but the position of the emission peak and the spectral shape of the QDs remain consistent before and after irradiation.In addition,the fluorescence lifetime of QDs is shortened after irradiation.Based on the fluorescence response of QDs to the irradiation ofγ-rays and combined with flexible materials,our work provides a theoretical basis for the application of QDs as a new wearable dosimeter.

Investigation of ultrafast dynamics of CdTe quantum dots by femtosecond fluorescence up-conversion spectroscopy

The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.

Adaption of Au Nanoparticles and CdTe Quantum Dots in DNA Detection

A DNA fluorescence probe system based on fluorescence resonance energy transfer （FRET） from CdTe quantum dot （QD） donors to Au nanoparticle （AuNP） acceptors is presented. CdTe QDs, 2.5nm in diameter, as energy donors, were prepared in water. Au nanoparticles, 16nm in diameter, as energy acceptors, were prepared from gold chloride by reduction. CdTe QDs were linked to 5＇-NH2-DNA through 1-ethyl-3-（dimethylaminopropyl）car- bodiimide hydrochloride （EDC） as a linker, and the 3＇-SH-DNA was self-assembled onto the surface of AuNPs. The hybridization of complementary double stranded DNA （dsDNA） bound to the QDs and AuNPs （CdTe-dsDNA-Au） determined the FRET distance of CdTe QDs and Au nanoparticles. Compared to the fluorescence of CdTe-DNA, the fluorescence of CdTe-DNA-Au conjugates decreased extremely, which indicated that the FRET occurred between CdTe QDs and Au nanoparticles. The fluorescence change of this conjugate depended on the ratio of Au-DNA to CdTe-DNA. When the AuNPs-DNA to QD-DNA ratio was 10：1, the FRET efficiency reached a maximum. The probe system would have a certain degree of fluorescence recovery when a complementary single stranded DNA was introduced into this system, which showed that the distance between CdTe QDs and Au nanoparticles was increased.

Using capillary electrophoresis mobility shift assay to study the interaction of CdTe quantum dots with bovine serum albumin

In this work, the capillary electrophoresis mobility shift assay （CEMSA） was first adopted to study the interaction of protein with quantum dots （QDs）. In this study, bovine serum albumin （BSA） and CdTe QDs were used as model samples. We observed that BSA was facilely adsorbed to CdTe QDs surface, and the QD-BSA complex was formed by a 1：1 stoichiometric ratio. A value of 2.17 4-0.27 × 10^6 mol^-1 L^-1 （at 25 ℃） for the association constant was obtained by CEMSA.

Ultrasensitive Detection of Glyphosate Using CdTe Quantum Dots in Sol-Gel-Derived Silica Spheres Coated with Calix[6]arene as Fluorescent Probes

We have developed a simple method for the preparation of highly fluorescent and stable, water-soluble CdTe quantum dots in sol-gel-derived composite silica spheres which were coated with calix[6]arene. The resulting nanoparticles (NPs) were characterized in terms of UV, fluorescence and FT-IR spectroscopy and TEM. The results show that the new NPs display more intense fluorescence intensity and are more stable than its precursors of the type SiO2/CdTe. Under the optimum, the novel NPs exhibit a higher selectivity and ultrasensitive fluorescence probes for the determination of gly-phosate over other pesticides, the fluorescence intensity increase with the concentration of glyphosate in the range from 1.0 to 25.0 nmol/L and the detection limit is low to 0.0725 nmol/L. A mechanism is suggested to explain the inclusion process by a Langmuir binding isotherm.

Interaction of CdTe/CdS quantum dots with antibodies

In the study, we observed the strong adsorption of CdTe/CdS QDs to antibodies and the formation of QDs-antibodies conjugates. Capillary electrophoresis with laser-induced fluorescence detection （CE-LIF）, fluorescence spectrometry and fluorescence correlation spectroscopy （FCS） were used to characterize the QDs conjugates with antibody. We found that the QDs-antibody conjugates possessed high fluorescence, small hydrodynamic radii and good stability in aqueous solution. 2009 Ji Cun Ren. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Cytotoxicity and DNA Damage Effect of TGA-capped CdTe Quantum Dots

The cytotoxicity and DNA damage caused by thioglycolic acid（TGA）-capped cadmium telluride（CdTe） quantum dots（QDs） to hepatocyte line HL-7702 were investigated.Cell viability was measured by 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide（MTT） assay;DNA damage was detected by single cell gel electrophoresis（SCGE）;the change of cell cycle progression was examined by propidium iodide（PI）-flow cytometry（FCM）;apoptosis was measured by acridine orange/ethidium bromide（AO/EB） assay and Annexin V-FITC/PI-FCM（FITC：fluorescein isothiocyanate）.The results show that the cytotoxicity induced by CdTe QDs was increased in a dose-dependent and time-dependent manner;after exposure to QDs for 24 h,as the exposure dose increased,the rate of DNA damage was significantly increased（P0.05）,and the degree of DNA damage was elevated.As the dose of CdTe QDs increased,the percentage of G 0 /G 1 phase cells was significantly decreased（P0.001）,while the percenttages of S and G 2 /M phases cells were significantly increased（P0.001）.In AO/EB assay,apoptotic cells could be observed under a fluorescence microscope,and apoptotic rate was increased as exposure dose increased.In Annexin V-FITC/PI-FCM assay,the apoptotic rates of CdTe QDs treated groups were significantly increased compared with that of control group（P0.05）.Our studies indicate that CdTe QDs could influence cell viability,and induce DNA damage,the S and G2 /M phases arrest and apoptosis of HL-7702.

Exploring Feasibility for Application of Luminescent CdTe Quantum Dots Prepared in Aqueous Phase to Live Cell Imaging

This paper explored the feasibility for the application of luminescent CdTe quantum dots prepared in aqueous phase to live cell imaging. The highly luminescent CdTe quantum dots （QDs） were first prepared in aqueous phase, and then were covalentiy coupled to a plant lectin （UEA-1）, as a fluorescent probe. After incubating with of human umbilical vein endothelial cells （HUVECs）, the QD probe with UEA-1 was able to specifically bind the corresponding cell receptor. The good cell images were obtained in live cells using laser confocal scanning microscopy. We predict that QDs prepared in water phase will probably become an attractive alternative probe in cellular imaging and bio-labeling.

Luminescent properties dependence of water-soluble CdTe quantum dots on stabilizing agents and reaction time

The influence of stabilizing agents and reaction time on the luminescent properties of water-soluble CdTe quantum dots(QDs) was discussed.The thioglycolic acid(TGA)-CdTe ODs were characterized by TEM,XRD and FTIR.It is found that larger-size QDs can be synthesized more easily when L-cysteine(Cys) or golutathione(GSH) is chosen as stabilizing agent and TGA is proper to prepare highly luminescent QDs because of the effect between Cd2+ and sulfhydryl group.Furthermore,the absorption wavelength,full width at half maximum(FWHM),stokes shift,photoluminescence(PL) quantum yield and PL stability of TGA-CdTe are strongly dependent on reaction time,in which the absorption wavelength changes against reaction time with an exponential function.The TGA-CdTe QDs prepared at 2 h possess more excellent luminescent properties.

Direct Synthesis of Zn_(1-x)Cd_xS (0≤x≤1) Quantum Dots in Aqueous Solution and Application in Biology

A simple procedure was presented to directly synthesize Zn1_xCdxS （0 ≤x≤1） quantum dots （QDs） in aqueous solution. QDs＇ structures and properties were characterized by TEM （transmission electron microscopy）, XRD （X-ray diffraction） and fluorescence microscopy. For those as-synthesized Zn1_xCdxS QDs, when the molar ratio between Zn and Cd changed from 1 to 0, its photoluminescence （PL） emission peak shifted from 430 nm to 675 nm. PL emission quantum efficiency was up to 15%. The experiment results demonstrated that those alloyed QDs showed a good biocompatibility and could be used as labelling materials in cell biology.

MTT Detection of the Toxicity on CdTe Quantum Dots

Objective: The quantum dots are the useful materials in microelectronics and biomedical research. However its toxicity has to be considered. We studied the effect of cell inhibition with ZnS core quantum dots and CdTe quantum dots modified with Thioglycolic acid or Cysteine functional group (TGA-CdTe, TGA-CdTe/ZnS, Cys-CdTe, Cys-CdTe/ZnS) on Caco-2 cell proliferation. Methods: We studied the effect of cell inhibition with ZnS core QDs and CdTe QDs modified with functional group on Caco-2 cell proliferation by MTT assay at 0, 12.5, 25, 50, 100 μg/ml and 6, 24, 48 h. Result: Our results showed that all QDs have inhibited cell proliferation and reached maximum 79.21%. The inhibition rate of Cys-modified QDs increased with the increase of concentration and reached maximum 66.72%. The inhibition rate of TGA-modified QDs increased with the increase of time. The ratios of Cys-modified to TGA-modified were less than 1 at all concentrations and three exposure times (P ≤ 0.01). The average ratios of Cys-CdTe/ZnS to Cys-CdTe reached 1.11 only for 48 h (P ≤ 0.05). The ratios of TGA-CdTe/ZnS to TGA-CdTe were closed to 1 at all concentrations and exposure times. Conclusion: The regularity of QDs modified with functional group is that inhibition of TGA-modified higher than Cys-modified. Inhibition exhibited dose-dependent for Cys-modified while exhibited time-dependent for TGA-modified. The regularity of CdTe-QDs with ZnS or not is that the inhibition of Cys-CdTe/ZnS was higher than Cys-CdTe while TGA-CdTe/ZnS and TGA-CdTe were consistent.