II-VI族半导体量子点的发光特性及其应用研究进展

半导体量子点由于具有独特的发光特性而具有极高的应用价值。结合本实验室的工作介绍了半导体量子点的发光原理和发光特性，在实验中发现核壳结构的CdSe／CdS半导体量子点比没有包覆的CdSe半导体量子点的发光稳定性提高．吸收光谱和发射光谱均发生红移，而且粒径不同．半导体量子点所呈现的颜色也不同，随着粒径的增加吸收光谱和发射光谱向长波方向红移。介绍了半导体量子点在光电子器件和生物医学方面的应用．并对其发展前景进行了展望。     

反应条件对水溶性CdSe量子点光学性能的影响

以巯基乙酸(TGA)为配位剂合成了水溶性CdSe量子点,研究了反应时间、溶液pH值及前驱体溶液中镉元素与硒元素的摩尔比对量子点光学性能的影响。以L-半胱氨酸(L-cys)、巯基乙酸和巯基乙胺(CA)为配位剂在优化的pH值条件下合成了系列水溶性量子点,研究了配位剂的种类对量子点光学性能的影响。结果表明:当以TGA为配位剂时,反应条件对量子点的粒径分布及光学性能有重要的影响;为获得粒径分布窄的量子点溶液,宜采用的最佳反应条件为pH值为10～12,Se与Cd的摩尔配比为2∶3,量子点的粒径随时间延长而增大;此外,利用不同的配位剂可有效改变水溶性量子点的表面物理化学特性,且量子点的尺寸大小因所用配位剂不同依以下顺序递减:巯基乙酸L-半胱氨酸巯基乙胺。     

RGO-CdSe纳米复合材料的制备及其光学非线性吸收特性

通过两相法制备了氧化石墨烯 -硒化镉(GO-CdSe)纳米复合材料,并进一步通过水合肼还原, 制备了还原氧化石墨烯-硒化镉(RGO-CdSe)纳米复合材料。通过透射电镜(TEM)、 X射线衍射仪(XRD)、紫外可见光吸收(UV-Vis)光谱和荧光(PL)光谱对复合材料的 形貌、结 构和光学特性进行了表征。CdSe量子点为闪锌矿结构,粒径在6nm左右,基本均匀的分布在 RGO片上。在波长为532nm、脉冲宽度为30ps 的激光作用下,采用单光束Z扫描 技术,对复合材料的三阶光学非线性吸收性质进行了研究。研究发现,RGO-CdSe纳米复合 材料展现出反饱和吸收的非线性光学特性;相对于未附着CdSe量子点的 RGO,复合材料的光学非线性吸收特性有所增强。RGO-CdSe纳米复合材料的非线性吸收系数 为18.3cm/GW,高于纯RGO的11.2cm/GW。实 验 结果表明,RGO-CdSe纳米复合材料在光限幅器、光开关等光学器件方面有着潜在的应用前 景。     

CdSe/ZnS量子点光纤纤芯基底的研究

量子点光纤正逐渐成为光通信领域的研究热点。首先介绍了CdSe/ZnS量子点掺杂光纤的发展历史,随后给出两种不同纤芯基底材料的CdSe/ZnS量子点掺杂光纤的制备方法,并对它们的光谱特性及发射峰值增益进行了分析比较,最后分析得出适合CdSe/ZnS量子点掺杂光纤的纤芯基底材料。CdSe/ZnS量子点掺杂光纤基底材料的研究对其他量子点光纤的研制具有一定的借鉴作用。     

CdSe@CdTe核壳II型量子点掺杂的薄膜太阳能电池

采用胶体化学法制备了CdSe@CdTe核壳量子点,将其置于CdTe量子点层与CdSe量子点层间构筑了三层结构的全无机薄膜太阳能电池(ITO/CdTe/CdSe@CdTe/CdSe/Al),在电池制备过程中对量子点薄膜进行了退火处理。吸收光谱、荧光光谱及荧光寿命测试结果表明所制备的CdSe@CdTe量子点为典型的II型量子点。其光电转换性能测量结果表明所制太阳能电池具有高达0.48%的能量转换效率,这主要得益于三层量子点间能带能量的差异对电子与空穴的定向传输的促进以及退火工艺对薄膜结晶质量的改善。     

CdSe／HgSe／CdSe量子点量子阱（QDQW）的HREM研究

我们应用胶体化学合成方法制备出具有核壳结构的CdSe/HgSe/CdSe量子点量子阱(QDQW)纳米晶,由于QDQW中载流子的量子限制效应,其光致发光谱(PL)出现了明显的蓝移现象,谱峰也有明显增强。本文中,我们通过对CdSe/HgSe/CdSe量子点量子阱核壳结构进行HREM的研究,并对包裹层这种异质外延生长及PL谱进行分析,获得了有意义的结论。胶体CdSe纳米晶是在水溶液中加以生长[1]。其化学反应式为:Cd2++2OH-+SeSO32-→CdSe+SO32-+H2O(1)通过改变Cd2+、SeSO32-的浓度及溶液中pH值,对CdSe纳米晶的尺度加以控制,并加入化学稳定剂阻止CdSe纳…     

CdSe/ZnS量子点掺杂聚合物光纤放大器增益特性分析

提出了一种半导体量子点CdSe/ZnS掺杂聚合物光纤放大器。测量了CdSe/ZnS量子点吸收和发射光谱,采用二能级结构和速率方程的方法,全面描述了CdSe/ZnS量子点掺杂聚合物光纤放大器的增益性能。计算了放大器增益随量子点掺杂光纤长度、量子点掺杂浓度和信号光强度的变化,给出了不同泵浦光强条件下的增益谱线及半高全宽。结果表明,在mW量级的泵浦条件下,CdSe/ZnS量子点掺杂聚合物光纤放大器可获得35dB以上的增益,获得相同增益所需泵浦光强度只有同类型染料掺杂聚合物光纤放大器的万分之一。泵浦光强与量子点掺杂浓度之间存在最佳对应关系,单位泵浦功率激发的最佳量子点数为6.33×107/mW。在室温下,CdSe/ZnS量子点掺杂聚合物光纤放大器具有550nm～610nm的带宽,含盖了聚合物光纤的低损窗口。     

CdSe/ZnS和PbSe量子点光纤及光纤放大器研究进展

近年来,纳米晶体(量子点)以及量子点光纤、量子点光纤放大器成为一个研究热点。介绍了CdSe/ZnS和PbSe量子点的光谱特性以及量子点的吸收-辐射截面,表明量子点具有强的吸收和发射。总结了低浓度和较高浓度CdSe/ZnS量子点掺杂光纤、熔融法及溶胶凝胶法制备PbSe量子点光纤材料的最新研究进展,分析了两种方法制备量子点光纤材料的优缺点,概述了PbSe量子点光纤放大器的研究近况,展望了量子点光纤的应用前景。     

CdSe量子点的制备与荧光特性研究

主要讨论了CdSe量子点的制备及荧光特性。CdSe量子点由化学方法制备，通过选择不同的反应时间得到不同尺度的量子点样品。用荧光方法研究了量子点样品在石英衬底和有机溶剂中的荧光特性。实验表明，这些量子点都有良好的荧光特性。还用无限深球方势阱模型分析了量子点样品的电子态，并根据荧光参数估算了量子点的尺度．各样品荧光峰具有一致的半峰宽，表明CdSe量子点的成核过程在反应开始时同时完成。     

CdSe/ZnSe量子点的合成与荧光特性

采用低温成核生长与一步法相结合的方式合成了CdSe/ZnSe核壳结构量子点,并通过吸收光谱、荧光光谱、X射线衍射等分析手段证明了ZnSe壳层包覆成功.对加入空穴传输材料后CdSe/ZnSe量子点的荧光变化情况进行了深入的研究.稳态光谱结果表明.空穴传输材料对量子点发光有较强的淬灭作用;时间分辨光谱结果显示,随着空穴传输材料分子浓度的增加,量子点的荧光寿命明显缩短,其荧光淬灭过程可以解释为静态淬灭和动态淬灭过程.静态淬灭来源于量子点表面与空穴传输材料间的相互作用;而动态淬灭则来源于量子点到空穴传输材料的空穴转移过程.因此,量子点的壳层结构及空穴传输材料的种类对量子点的荧光淬灭起关键作用.     

飞秒激光流动烧蚀制备ZnSe有机复合量子点

采用飞秒激光流动烧蚀法制备了聚乙烯亚胺(PEI)包覆的ZnSe量子点水相分散液。水相分散液外观呈现亮黄色透明液体状。多个ZnSe有机复合量子点在水中聚集形成球形胶束,通过扫描电子显微镜(SEM)检测发现,胶束粒径为40~100 nm。利用高分辨透射电子显微镜(HRTEM)和X射线衍射(XRD)研究ZnSe晶体学特性变化,结果表明制得的ZnSe量子点保持了块体ZnSe的立方闪锌矿晶型。该ZnSe有机复合量子点的水分散液在365 nm紫外光照射下显示出明亮的绿色荧光,荧光中心波长约在500 nm处。采用光致发光光谱和紫外可见吸收光谱研究了该有机复合量子点的pH值响应特性,结果表明随着分散液中pH值由9降低到4,光致发光光谱显示出蓝移特性,波长最大蓝移量为25 nm。讨论了绿色荧光的来源与荧光波长调谐的可能机理。     

Facile synthesis of high-quality ZnS,CdS, CdZnS,and CdZnS/ZnS core/shell quantum dots: characterization and diffusion mechanism

Binary CdS and ZnS and ternary CdZnS alloy quantum dots (QDs) were synthesized via a simple, inexpensive, and reproducible route using sulfur, cadmium stearate, and zinc stearate as precursors and N-oleoylmorpholine as the reaction medium and solvent. Both binary and ternary QDs exhibited a narrow size distribution and high crystallinity as confirmed TEM and HRTEM images. The alloy QDs exhibited excellent composition-dependent optical properties and a narrow full-width at half maximum of 19–21 nm. UV-visible absorbance and photoluminescence (PL) emission spectra of the CdZnS QDs showed a blue shift during growth, indicating the formation of alloy QDs. ZnS shells were successively coated onto the alloy core via decomposition of zinc diethyldithiocarbamate at a relatively low temperature. The CdZnS/ZnS core/shell QDs obtained showed a significant increase in size and exhibited strong band edge emission with a significant increase in PL quantum yield. XRD patterns revealed that all the QDs had a zinc blende structure. The QD diffraction peaks gradually shifted to higher angle in the order CdS < CdZnS < CdZnS/ZnS < ZnS. The mechanism for the synthesis of CdZnS alloy and CdZnS/ZnS core/shell QDs is discussed.     

Pure and Fe3+-doped ZnS quantum dots as novel and efficient nanophotocatalysts: Synthesis,characterization and use for decolorization of Victoria blue R

Ultra-small pure and iron-doped ZnS quantum dots (QDs) were synthesized using a simple and fast procedure based on chemical precipitation in aqueous solution. The QD size was controlled by adding 2-mercaptoethanol as a capping agent at room temperature. The QDs were characterized by X-ray diffraction (XRD), UV-Vis absorbance, transmission electron microscopy and atomic absorption spectroscopy. XRD analysis revealed that the iron-doped nanoparticles were crystalline with a cubic zinc blende structure and a crystallite size of 17±2 Å. The undoped and Fe³⁺-doped ZnS QDs were used as nanophotocatalysts for decolorization of Victoria blue R as a cationic dye under UV irradiation. The effects of the photocatalyst dose, mole fraction of the dopant, irradiation time, and sample pH on the dye decolorization efficiency were studied.     

Lattice‐Symmetry‐Driven Epitaxy of Hierarchical GaN Nanotripods

Lattice‐symmetry‐driven epitaxy of hierarchical GaN nanotripods is demonstrated. The nanotripods emerge on the top of hexagonal GaN nanowires, which are selectively grown on pillar‐patterned GaN templates using molecular beam epitaxy. High‐resolution transmission electron microscopy confirms that two kinds of lattice‐symmetry, wurtzite (wz) and zinc‐blende (zb), coexist in the GaN nanotripods. Periodical transformation between wz and zb drives the epitaxy of the hierarchical nanotripods with N‐polarity. The zb‐GaN is formed by the poor diffusion of adatoms, and it can be suppressed by improving the ability of the Ga adatoms to migrate as the growth temperature increased. This controllable epitaxy of hierarchical GaN nanotripods allows quantum dots to be located at the phase junctions of the nanotripods and nanowires, suggesting a new recipe for multichannel quantum devices.     

Detection of zinc blende phase by the pulsed laser photoacoustic technique in ZnO thin films deposited via pulsed laser deposition

Pulsed laser deposition (PLD) was used to grow ZnO thin films on corning glass and silicon substrates at different oxygen pressures (1 y 10 mTorr). The structural analysis of the films was performed by X-ray diffraction and pulsed laser photoacoustic (PLPA) techniques. Both methods were employed to identify the minority zinc blende phase in the films. The relative difference between the structural changes detected in the films with the temperature increases was statistically analyzed. It was found that regardless of the substrate and the oxygen pressure used for the growth, the films exhibit a phase transition at 310 °C, which corresponds to the transformation of zinc blende structure to hexagonal wurtzite. The results demonstrate that the zinc blende phase in the films is present not only on cubic substrates but also on glass, and confirm that PLPA technique is a very sensitive method for the detection of minority phase changes.     

Effects of annealing on the structural and optical properties of zinc sulfide thin films deposited by ion beam sputtering

We report the structural and optical properties of ZnS thin films fabricated by ion-beam sputtering. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed a polycrystalline ZnS film with zinc blende phase as manifested by diffraction from the (111), (220) and (311) planes. Annealing resulted in the appearance of a metastable wurtzite phase with a concentration up to 26.6%. An energy bandgap, estimated from absorption spectra, was found to vary between 3.32 and 3.40 eV. The lower energy of this bandgap, as compared to bulk ZnS, is associated with the structural point defects along with mixed zinc blende and wurtzite phases of the polycrystalline ZnS films. Ion beam sputtering deposition can be used to tune the optical bandgap for potential applications in optoelectronic materials.     

Band‐Edge Photoluminescence Recovery from Zinc‐Blende CdSe Nanocrystals Synthesized at Room Temperature

Low‐cost, large‐scale production of highly photoluminescent semiconductor nanocrystals (NCs) is desirable for a variety of applications. In this paper we report the realization of highly photoluminescent zinc‐blende CdSe nanocrystals from room‐temperature water‐phase synthesis, followed by low‐temperature (80 ± 5 °C) chemical etching in a solution of 3‐amino‐1‐propanol/H₂O (v/v = 10/1). X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data indicate that these CdSe NCs exhibit a cubic, zinc‐blende crystal structure. After etching, these CdSe nanocrystals show strong band‐edge photoluminescence (with quantum efficiency as high as 50 %) and lack of deep‐trap emissions. A high‐resolution TEM investigation suggests that this etching not only removes surface irregularities, but also attacks grain boundaries. Moreover, the size distribution reduces upon progressive etching to allow photoluminescence full‐width‐at‐half‐maximum (FWHM) values as low as 30 nm.     

A real-time quantitative assessment of self-assembled quantum dots by reflection high-energy electron diffraction

A method for in-situ quantitative characterization of quantum dots during growth is provided using the readily available reflection high-energy electron diffraction (RHEED). RHEED patterns of uncapped self-assembled InAs/GaAs quantum dots are investigated theoretically and experimentally. Previously predicted intensity fringes along chevron tails of quantum dot's RHEED diffraction spots are observed experimentally. Post-growth atomic force microscopic images and theoretical RHEED images of the same are obtained parallel to experimental data. The bounding facets of the quantum dots are determined using the angle between the chevrons. The size (height) of the quantum dots is determined using the periodicity of intensity fringes along the chevrons during growth.     

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 aver-age crystallite size in the sample is in the range of 2 to 5 nm.SEM micrographs show spherical-shaped quantum dots.FTIR stud-ies show that cobalt has been successfully doped into the ZnS cubic lattice.EDX spectra have analyzed the elemental pres-ence 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.