CdSe与CdSe/ZnS量子点合成及稀土掺杂

在LSS(liquid-solid-solution)多相体系中制得了CdSe、CdSe/ZnS量子点和Eu掺杂的量子点。利用TEM、XRD、PL、EDS对产物进行了表征。TEM结果显示所得的量子点形貌规则、尺寸均匀。XRD结果显示CdSe/ZnS量子点呈六方晶系。PL结果对比表明,合适厚度壳层ZnS包覆后的CdSe量子点发光效率明显提高,发光峰的半高宽有大幅度提高,并分析了所得的结果。掺杂稀土元素Eu后,CdSe(Eu)量子点在红光区域产生了新的发光峰;而CdSe(Eu)/ZnS量子点在红光区域内没有出现发光峰,并阐明了这种现象的原因。     

CdSe胶质量子点的电致发光特性研究

采用胶体化学法合成硒化镉(CdSe)胶质量子点, 在此基础上制成了以CdSe胶质量子点为有源层, 结构为ITO/ZnS/CdSe/ZnS/Al的电致发光(EL)器件. 透射电镜测量表明量子点的尺寸为4.3 nm, 扫描电子显微镜测量ZnS薄膜和Al薄膜结果显示表面均较为平整, 由器件结构的X射线衍射分析观察到了CdSe(111)、ZnS(111)等晶面的衍射, 表明器件中包含了CdSe量子点和ZnS绝缘层材料. 光致发光谱表征胶质量子点的室温发光峰位于614 nm, 电致发光测量得到器件在室温下的发光波长位于450 ~ 850 nm, 峰值在800 nm附近. 本文对电致发光机制及其与光致发光谱的区别进行了讨论.     

CdS量子点的制备和光学性质

以醋酸镉、硫粉为原料制备CdS量子点,研究了硫的加入量对其光学性质的影响,结果表明:合成的CdS量子点粒径均匀,分散性较好,随着硫加入量的增加CdS量子点的粒径增大;反应中过量的硫能有效地填补硫空位,从而抑制表面态发光,同时,ODA的修饰也能有效地钝化表面态,减小表面态的发光强度.     

石墨烯量子点/CdS/CdSe共敏化太阳能电池

以三维锐钛矿TiO₂微球为上层光散射层材料, 以商业纳米TiO₂为下层连接材料, 采用刮刀法制备了一种新颖的双层TiO₂薄膜, 并应用于量子点敏化太阳能电池(QDSSC)。其中, 石墨烯量子点(GQDs)采用滴液法引入, CdS/CdSe量子点采用连续离子层吸附法(SILAR)制备。采用场发射扫描电镜、透射电镜、X射线衍射、紫外-可见漫反射光谱及荧光光谱对样品进行表征。实验还制备了CdS/CdSe量子点敏化及石墨烯量子点/CdS/CdSe共敏化太阳能电池, 并研究了石墨烯量子点及CdS不同敏化周期及对电池性能影响。研究结果表明, 石墨烯量子点及CdS不同敏化周期对薄膜的光学性质、电子传输及载流子复合均有较大影响。优选条件下, TiO₂/QGDs/CdS(4)/CdSe电池的光电转换效率为1.24%, 光电流密度为9.47 mA/cm², 显著高于TiO₂/CdS(4)/CdSe电池的这些参数(0.59%与6.22 mA/cm²)。这主要是由于TiO₂表层吸附石墨烯量子点后增强了电子的传输, 减少了载流子的复合。     

羧基CdSe荧光量子点的制备及其荧光特性研究

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。     

不同温度下硒化镉(CdSe)量子点的生长及荧光性研究

研究了以氧化镉（CdO）和硒（Se）粉为前驱体,在三辛基膦（TOP）和油酸中合成无机半导体量子点（quantum dots, QDs）CdSe.研究了在不同的反应温度下粒子的生长,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）等手段跟踪反应过程并对样品性能进行了表征.实验结果表明,反应温度和反应时间对量子点的生长和荧光性能有很大的影响.     

沉积电位对CdSe纳米晶薄膜的结构、形貌和光学性质的影响

使用电化学法在ITO玻璃上制备了CdSe纳米晶薄膜.研究了沉积电位对薄膜晶体结构、表面形貌及光学性质的影响,并讨论了所得样品禁带宽度与晶粒尺寸的关系.X-ray衍射结果表明:沉积电位在-600～-700mV之间均可得到立方相CdSe,晶粒尺寸随沉积电位降低而增大.原子力显微镜观察表明,沉积电位较高时,粒子聚集为块状或柱状,沉积电位较低时,粒子呈现不均匀团聚.透射光谱测试显示:在350～850nm波段范围内,随沉积电位降低,透过率降低,吸收边红移.所得样品的禁带宽度均比体相CdSe大,且随晶粒尺寸的增大而减小,表现出明显的量子尺寸效应.     

CdSe/ZnSe量子点的制备及电化学发光性能

利用ZnSe半导体纳米材料晶体结构与CdSe相似、带隙更宽的特点,采用水热法合成了核-壳型CdSe/ZnSe量子点。结果表明：温度在70~160℃时,ZnSe壳逐渐包裹在CdSe核上,反应时间在0~4 h时,内壳在核上是均匀包裹的,当核壳摩尔比为1∶3时,CdSe/ZnSe QDs的电化学发光性能最强,其电化学发光强度是CdSe量子点的6倍,且发光信号稳定。     

尺寸分布和界面混合对InAs/GaAs量子点光学性质的影响

研究了自组织生长模式(S-K modes)下量子点尺寸的不均匀分布对量子点发光性质的影响,对其光致发光峰进行了拟合计算.研究发现,量子点尺寸的不均匀分布导致了量子点发光峰的展宽以及发光峰位的红移.另一方面,后处理工艺中的退火及质子注入引起的界面混合导致了量子点PL谱发光峰的蓝移及半高宽的减小.     

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

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.     

CdSe量子点的制备及荧光性能改善

主要讨论了CdSe量子点的制备及荧光性能的改善.采用水相合成方法制备了CdSe量子点,并用X射线粉末衍射仪对所合成的量子点进行表征,用荧光分光光度计研究了量子点的荧光性质.结果表明,采用样品处理温度的调节和ZnS壳层的包覆能在一定程度上改善CdSe量子点的荧光性能.     

CdSe and CdSe/ZnS quantum dots for the detection of C-reactive protein

In this study, a method for the detection of C-reactive protein (CRP) using CdSe and CdSe/ZnS quantum dots (QDs) is proposed. CdSe and CdSe/ZnS core-shell QDs are synthesised by using 2-mercaptosuccinic acid (MSA) as a capping agent. These QDs were then subjected to various characterisation studies, namely X-ray diffraction and transmission electron microscope for size and structure, Fourier transform infrared spectroscopy for the confirmation of functional groups, ultraviolet–visible absorption and fluorescence spectroscopy for optical characteristics and dynamic light scattering for hydrodynamic changes of QDs. Two biochemical mixtures were developed: one by mixing blood serum containing CRP and CdSe-phosphorylethanolamine (PEA) and the other by mixing blood serum with CdSe/ZnS-PEA. When these mixtures are observed for fluorescence due to interaction of QDs with CRP, a correlation between changes in fluorescence for different concentrations of CRP is noted. The result demonstrates that CRP can be detected with the help of QDs without using any antibodies.     

CdSe／CdS核壳量子点拉曼光谱的表面模分析

研究了不同壳层厚度(0～5.5ML)的CdSe/CdS核壳量子点的一次和高次拉曼散射,具体分析了CdSe和CdS的表面模随着壳层厚度的变化情况.结果表明,随着壳层厚度的增加,CdSe表面模(SO1)从198cm-1频移到185cm-1,CdS的表面模(SO2)从275cm-1频移到267cm-1,并且SO1和SO2试验结果与由介电连续模型得到的理论值很接近.此外,根据CdSe表面模的频移,对随着CdS壳层厚度的增加而引起的核层(CdSe)的介电常数随环境的变化做出了修正.     

Two-fold emission from the S-shell of PbSe/CdSe core/shell quantum dots

The optical properties of PbSe/CdSe core/shell quantum dots with core sizes smaller than 4 nm in the 5-300 K range are reported. The photoluminescence spectra show two peaks, which become increasingly separated in energy as the core diameter is reduced below 4 nm. It is shown that these peaks are due to intrinsic exciton transitions in each quantum dot, rather than emission from different quantum dot sub-ensembles. Most likely, the energy separation between the peaks is due to inter-valley coupling between the L-points of PbSe. The temperature dependence of the relative intensities of the peaks implies that the two emitting states are not in thermal equilibrium and that dark exciton states must play an important role.     

A novel method for the preparation of water-soluble and small-size CdSe quantum dots

A novel method for the preparation of water-soluble and small-size CdSe quantum dots has been reported under high-intensity ultrasonic irradiation. The as-prepared products have been characterized by absorption spectra, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM).     

Surface modification of CdSe quantum dots for biosensing applications: Role of ligands

For an optimum performance of colloidal nanocrystal devices for a variety of applications such as photonic devices, solar cells and biological labelling, the determining factors are the nanocrystal surface and size. In this work, these two factors have been tuned via wet chemistry to tailor the material properties: The absorption and emission spectra have been tailored by choice of the nanocrystal size; nanocrystal shape by surface modification and photoluminescence (PL) efficiency determined by surface traps, has been tuned via appropriate selection of the nanocrystal capping ligands. Here, we have shown that through ligand-exchange process, the surface of the CdSe quantum dots (QDs) can be modified by replacing the longer-chain ligands of conventional trioctyl phosphine oxide (TOPO) or oleic acid (OA) with shorter-chain ligand of butyl amine. This imparts colloidal stability and water solubility to CdSe QDs for its potential applications in biosensors and biological imaging. It is conjectured that crystallite sizes, oxidation potential of CdSe QDs and stereochemical compatibility of ligands (TOPO, oleic acid and butyl amine) greatly influences the photophysics and photochemistry of CdSe QDs.     

Shell distribution on colloidal CdSe/ZnS quantum dots

Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the chemical distribution of semiconductor shell material around colloidal core-shell CdSe/ZnS quantum dots (QDs). EELS signals from positions around the QD indicate a well-defined shell of ZnS surrounding the CdSe core, but the distribution of the shell material is highly anisotropic. This nonuniformity may reflect the differences in chemical activity of the crystal faces of the core QD and implies a nonoptimal QD surface passivation.     

Studies of interaction of amines with TOPO/TOP capped CdSe quantum dots: Role of crystallite size and oxidation potential

This work reports the interaction of aliphatic (triethyl amine, butyl amine) and aromatic amines (PPD, aniline) with CdSe quantum dots of varied sizes. The emission properties and lifetime values of CdSe quantum dots were found to be dependent on the oxidation potential of amines and crystallite sizes. Smaller CdSe quantum dots (size 5 nm) ensure better surface coverage of amines and hence higher quenching efficiency of amines could be realized as compared to larger CdSe quantum dots (size 14 nm). Heterogeneous quenching of amines due to the presence of accessible and inaccessible set of CdSe fluorophores is indicated. PPD owing to its lowest oxidation potential (0.26 V) has been found to have higher quenching efficiency as compared to other amines TEA and aniline having oxidation potentials 0.66 and >1.0 V, respectively. Butyl amine on the other hand, plays a dual role: its post-addition acts as a quencher for smaller and enhances emission for larger CdSe quantum dots, respectively. The beneficial effect of butyl amine in enhancing emission intensity could be attributed to enhance capping effect and better passivation of surface-traps.     

Light-controlled bioelectrochemical sensor based on CdSe/ZnS quantum dots

This study reports on the oxygen sensitivity of quantum dot electrodes modified with CdSe/ZnS nanocrystals. The photocurrent behavior is analyzed for dependence on pH and applied potential by potentiostatic and potentiodynamic measurements. On the basis of the influence of the oxygen content in solution on the photocurrent generation, the enzymatic activity of glucose oxidase is evaluated in solution. In order to construct a photobioelectrochemical sensor which can be read out by illuminating the respective electrode area, two different immobilization methods for the fixation of the biocatalyst have been investigated. Both covalent cross-linking and layer-by-layer deposition of GOD by means of the polyelectrolyte polyallylamine hydrochloride show that a sensor construction is possible. The sensing properties of this type of electrode are drastically influenced by the amount and density of the enzyme on top of the quantum dot layer, which can be advantageously adjusted by the layer-by-layer technique. By depositing four bilayers [GOD/PAH](4) on the CdSe/ZnS electrode, a fast-responding sensor for the concentration range of 0.1-5 mM glucose can be prepared. This study opens the door to multianalyte detection with a nonstructured sensing electrode, localized enzymes, and spatial read-out by light.