Localized-states quantum confinement induced by roughness in CdMnTe/CdTe heterostructures grown on Si(111) substrates

This work shows that despite a lattice mismatch of almost 20%, CdMnTe/CdTe/CdMnTe heterostructures grown directly on Si(111) have surprisingly good optical emission properties. The investigated structures were grown by molecular beam epitaxy and characterized by scanning transmission electron microscopy, macro-and micro-photoluminescence. Low temperature macro-photoluminescence experiments indicate three emission bands which depend on the CdTe layer thickness and have different confinement characteristics. Temperature measurements reveal that the lower energy emission band (at 1.48 eV)is associated to defects and bound exciton states, while the main emission at 1.61 eV has a weak 2D character and the higher energy one at 1.71 eV has a well-defined (zero-dimensional, 0D) 0D nature. Micro-photoluminescence measurements show the existence of sharp and strongly circularly polarized (up to 40%) emission lines which can be related to the presence of Mn in the heterostructure. This result opens the possibility of producing photon sources with the typical spin control of the diluted magnetic semiconductors using the low-cost silicon technology.

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.

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.

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.

Higher open-circuit voltage set by cobalt redox shuttle in SnO_2 nanofibers-sensitized CdTe quantum dot solar cells

In this study, we report an efficient CdTe-SnOquantum dot（QD） solar cell fabricated by heat-assisted drop-casting of hydrothermally synthesized CdTe QDs on electrospun SnOnanofibers. The as-prepared QDs and SnOnanofibers were characterized by dynamic light scattering（DLS）, UV–Vis spectroscopy,photoluminescence（PL） spectra, X-ray diffraction（XRD） and transmission electron microscopy（TEM）. The SnOnanofibers deposited on fluorine-doped tin oxide（SnO） and sensitized with the CdTe QDs were assembled into a solar cell by sandwiching against a platinum（Pt） counter electrode in presence of cobalt electrolyte. The efficiency of cells was investigated by anchoring QDs of varying sizes on SnO. The best photovoltaic performance of an overall power conversion efficiency of 1.10%, an open-circuit voltage（Voc）of 0.80 V, and a photocurrent density（JSC） of 3.70 m A/cmwere obtained for cells with SnOthickness of5–6 μm and cell area of 0.25 cmunder standard 1 Sun illumination（100 m W/cm）. The efficiency was investigated for the same systems under polysulfide electrolyte as well for a comparison.

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.

BINDING ENERGY OF THE SHALLOW DONOR IN （CdTe）_m／（ZnTe）_n STRAINED DOUBLE QUANTUM WELL

In this paper the binding energy of the shallow.donor in CdTe/ZnTe strained double quantum well was calculated.The effect of the finite well potential and strain,resulting from the lattice mismatch,on the binding energy of the impurity is included in a variational framework.The binding energy is obtained as a function of the well width,barrier width,and impurity position in the barrier by using a variational method.The result of the present calculation shows that the variational law of the binding energy is similar to that of unstrained materials.

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.

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.

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.

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.

All-Optical Reconfigurable Metamaterial Employing the Self-Assembly of CdTe Quantum Dots

Positively and negatively charged polyelectrolytes, namely, Poly(diallyldimethylammonium chloride) and Poly(styrene sulfonate), respectively, were employed to disperse and deploy negatively charged quantum dots on an otherwise passive metamaterial structure with a resonant frequency of 0.62 THz, by employing a layer-by-layer, self-assembly scheme. Upon exposure to a UV source with a wavelength of 365 nm the amplitude modulation was observed to increase with increases in the number of deposited bi-layers, until a modulation maximum of 2.68% was recorded enabling an all-optical, dynamically reconfigurable metamaterial geometry. Furthermore, amplitude modulation was subsequently observed to decrease with further increases in the number of layers employed due to quenching and shadowing effects. The experimental observations reported herein will enable the utilization of all-optical reconfigurable THz devices for communication and data transmission applications.

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots（QDs） are fabricated on Si nanowires（NWs） substrates with and without Au nanoparticles（NPs）. The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence（PL） intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.

Alloyed CdTe_0.6S_0.4Quantum Dots Sensitized TiO₂Electrodes for Photovoltaic Applications

The photovoltaic performance of alloyed CdTe0.6S0.4 quantum dot sensitized solar cells (QDSSCs) is investigated. Fluorine doped Tin Oxide (FTO) substrates were coated with 20 nm-diameter TiO2 nanoparticles (NPs). Presynthesized colloidal solution of alloyed CdTe0.6S0.4 quantum dots (QDs) of 4.2 nm was deposited onto TiO2 NPs substrates using direct adsorption (DA) technique, by dipping for different times at ambient conditions. The FTO counter electrodes were coated with platinum, while the electrolyte containing I-/I-3 redox species was sandwiched between the two electrodes. Compared to pure CdTe QDs and CdS QDs, CdTe0.6S0.4 QDs showed better photovoltaic performance. The J-V characteristic curves of the assembled QDSSCs were measured at AM 1.5 simulated sunlight. The short current density (Jsc) and efficiency (η) increase with dipping time. At 24 h dipping time, the open-circuit photovoltage Voc, Jsc, fill factor (FF), and η were 0.46 volts, 1.54 mA/cm2, 0.43% and 0.31%, respectively.

Surface Quantum-Dimensional Photocarrier Recombination in CdTe Microcrystals

The scope of the study is the spectra of low-temperature (T = 2K) photoluminescence of a p-CdTe/n-CdS film heterostructure comprising a monolayer of CdTe microcrystals, where a single microcrystalline particle is typically one micron in size. Focus is made on the dominant band of “super-hot” emission appearing in the spectral region located in energy above the fundamental absorption edge of a CdTe bulk crystal. A theoretical model has been developed that assumes the existence of a space-charge layer inside a microcrystal, which leads to the formation of a triangular potential well for an electron near the surface. The anomalous emission band arises as a result of the optical transitions of electrons from near-surface levels of spatial quantization to valence band states.

基于CdTe量子点荧光探针对稀土元素铕的快速检测

铕(Eu)作为地球储备较少的稀土元素之一,在很多领域都有重要作用。本文通过一锅法合成了巯基乙酸修饰的CdTe量子点作为荧光探针,并基于稀土元素铕离子对于荧光探针的特异性猝灭作用,建立了水环境中对稀土元素铕离子的快速检测。在最佳条件下,在49.97nmol·L^(-1)~1088.03nmol·L^(-1)的浓度的范围内,CdTe荧光探针猝灭强度与Eu^(3+)浓度呈现良好的线性关系,检出限为36.47nmol·L^(-1),相关系数为0.9992。该方法对水环境中Eu^(3+)检测中回收率为108.2%~112.4%,具有响应速度快、简单、特异性强、灵敏度高等突出优点。

CdTe/ZnSe核壳量子点免疫层析试纸条检测克伦特罗的研究

采用巯基丁二酸作为表面修饰剂,水相法合成水溶性的CdTe/ZnSe核壳量子点,然后在N-羟基琥珀酰亚胺(NHS)的作用下,将CdTe/ZnSe核壳量子点与抗克伦特罗多克隆抗体(Anti-CLE pAb)连接。通过凝胶电泳和斑点杂交实验,验证CdTe/ZnSe核壳量子点与Anti-CLE pAb连接成功,并且CdTe/ZnSe-Anti-CLE pAb偶联物能识别克伦特罗-BSA抗原(CLE-BSA)。光谱分析表明,量子点与抗体连接后荧光增强,荧光峰位从628nm红移至635nm。将合成的CdTe/ZnSe-Anti-CLE pAb偶联物作为指示克伦特罗(CLE)分子的荧光标记物,制备出一种用于检测CLE的免疫层析试纸条,其最低检测量可达1μg/L。与ELISA法的对比实验表明,此试纸条能应用于CLE残留的快速检测。

CdTe／CdS量子点的Ⅰ-Ⅱ型结构转变与荧光性质

制备了壳层厚度可以精确控制的CdTe/CdS核壳量子点,利用紫外-可见吸收光谱、光致发光光谱、透射电镜和时间分辨光谱等技术,分析了CdS壳层厚度对CdTe量子点的荧光量子产率和光谱结构的影响规律.发现了不同于CdSe/CdS,CdSe/ZnS,CdTe/ZnS等核壳量子点的荧光峰展宽、大幅度红移以及荧光寿命大幅度增加现象.根据能带的位置关系,随着CdS厚度的增加,CdTe从Ⅰ型结构逐渐过渡到Ⅱ型核壳结构.对于Ⅱ型CdTe/CdS核壳量子点,不仅存在CdTe核区导带电子与价带空穴间的直接复合,还存在CdS壳层导带电子与CdTe核价带空穴界面处的间接复合,发光机制的变化导致荧光峰的展宽、明显红移和荧光寿命的增加.当壳层过厚时,壳层表面新引入的缺陷会阻碍荧光寿命和量子产率的进一步提高.