CdSe纳米晶／MEH—PPV复合型光电池研究

采用单前驱体热解法、高温微乳液法合成了高质量的CdSe纳米晶,将CdSe纳米晶按照一定比例与聚苯乙烯撑（MEH—PPV）共混制成光电池,利用TEM、XRD等研究了纳米晶的形貌结构特征,结果显示,所合成的半导体CdSe纳米晶为闪锌矿结构,直径在3-5nm之间,复合光电池最好的器件能量转化达到0．85％,     

闪锌矿CdSe纳米晶的可控合成及其与MEH-PPV共混光电池的器件性能研究

采用溶剂热方法制备了闪锌矿CdSe纳米颗粒,利用TEM、XRD、荧光分析仪对其形貌、结构及光学性能进行了表征.结果表明,纳米颗粒的直径在3～5nm左右,为闪锌矿结构;其吸收峰在600nm左右,并与合成CdSe纳米晶所用的羧酸盐的链长略有差别;将CdSe与MEH-PPV(聚苯乙烯撑)共混,发现有明显的荧光淬灭现象;共混材料制成光电池器件,在模拟太阳光照射下获得了0.85%的能量转化效率.     

巯基包覆CdSe和CdSe/CdS核壳纳米晶的水相合成与表征

利用水相合成的方法制备了巯基包覆的具有较高荧光量子产率的CdSe和CdSe／CdS纳米晶．水相合成方法的优点是原料低廉、安全可靠和重复性高，缺点是纳米晶的尺寸分布较宽，发光效率不是很高．采用X-射线粉末衍射、吸收和荧光等光谱手段对纳米晶的平均尺度、粒径分布、晶体结构及发光特性进行了表征。在77K到300K的温度范围内，随着温度降低，CdSe纳米晶的发光峰逐渐蓝移，而CdSe／Cds纳米晶发光峰位基本不随温度变化而变化．此外，在325nm激光辐照下，CdSe／CdS纳米晶的荧光寿命比CdSe纳米晶延长了6倍左右，稳定性大幅度提高．以上结果表明，核壳结构的CdSe／CdS纳米晶具有较高的发光效率和良好的稳定性，具有广阔的应用前景．     

不同晶型 CdSe纳米棒的制备及光电性能研究

采用水热法制备了不同晶型CdSe纳米棒,并用TEM、SEM、XRD、TGA-DTA对其进行了表征.结果显示反应温度为240℃生成纤锌矿型CdSe纳米棒,反应温度为200℃生成闪锌矿型CdSe纳米棒.并对纳米棒进行了光电性能测定,纤锌矿型CdSe纳米棒膜电极的光电转换效率（IP.CE）优于闪锌矿型CdSe纳米棒膜电极的IPCE.CdSe/PMeT复合膜电极在具有最大光电转换效率时的波长发生了红移.     

不同形貌CdSe纳米晶的合成及其形成机理研究

采用水热反应法,通过调节反应时间制备得到了不同形貌的CdSe纳米晶材料,并用TEM、XRD、EDS、XPS等分析手段对其形貌结构进行表征。研究表明,在反应温度为180℃的条件下,所得产物均为六方晶相的CdSe纳米晶,形貌随着反应时间的改变而发生变化:当控制反应时间为2h、5h、10h时,得到的CdSe纳米晶的形貌分别为树枝状、由树枝状到棒状过渡的簇状及棒状。分析了CdSe纳米晶形成的化学反应原理,并运用结晶学原理和相关模型理论对CdSe纳米晶的形成机理及其形貌变化进行了探讨。     

CdSe纳米棒的制备及光电性能研究

采用水热法制备了CdSe纳米棒,并用TEM、SEM、XRD、TGA-DTA对其进行了表征.结果表明,纳米棒直径在100nm左右,长度约300nm;纳米棒具有闪锌矿的结构;将CdSe纳米棒均匀涂在导电玻璃的导电面上,在400℃下煅烧30min后制备成纳米棒膜电极,并进行了光电化学研究,纳米棒膜结构电极最高单色光的光电转换效率(IPCE)可达74%.     

Ⅱ－Ⅵ族纳米半导体材料的研究（Ⅰ）苯基硒化镉的合成及其热分解

报道了苯基硒化镉合成及其在４－乙基吡啶溶剂中热分解制备纳米ＣｄＳｅ的方法。用红外光谱，紫外可见吸收光谱及电子显微镜分别对上述反应产物进行了分析。紫外可见吸收光谱跟踪热分解过程表明，随着时间的延长，生成的超细ＣｄＳｅ粒子的紫外吸收边有明显的红移现象。电子显微镜分析表明所制备的ＣｄＳｅ粒子尺寸为３～４ｎｍ。     

纳米晶TiO2的形貌对其荧光性能影响的研究

利用溶剂热合成法成功制备出了形貌为准球形、棒形、球棒混合型和菱形,粒径在50nm以下、尺寸均一的锐钛矿型TiO2纳米晶,对合成出的纳米晶TiO2用荧光光谱,紫外/可见光吸收光谱进行光学性能表征,结果表明,TiO2纳米晶在330 nm的激发光下,分别在345 nm、363nm、380nm和402 nm处存在4个发光峰位。在实验中,首次发现和证实了理论计算出的锐钛矿型TiO2纳米晶的两种直接跃迁发光,分别对应为X（1b）→X（2b）（345 nm）和X（1b）→X（1a）（363 nm）,主要因为油酸改变了TiO2纳米晶的{001}晶面族晶面的表面态。TiO2纳米晶的紫外吸收峰位于229 nm,且与其形貌无关;禁带宽度的计算值接近其理论值3.2 eV。     

水热法合成ZnSe纳米晶及其发光性质的研究

采用水热法在低温下合成了球形的立方相ZnSe纳米晶,研究了水热过程中ZnSe纳米晶的结晶动力学过程。通过在水热反应过程中添加不同量的C17H33COOH,得到了形貌规则、不同粒径的ZnSe纳米晶。水热条件下C17H33COOH能控制纳米晶形貌和分散性的机理为:C17H33COOH分子内部的羧基提升了ZnSe纳米晶的表面完整性,并保护了ZnSe结构内部的非极性烷基,使得ZnSe纳米晶很容易分散在非极性溶剂中,提高了溶液中ZnSe纳米晶的分散性。光谱测试结果表明ZnSe纳米晶的发射光谱随着粒径减小发生蓝移,归因于量子限域效应的增强。     

纳米晶PCT薄膜的合成与表征

纳米材料的制备技术结合Ｓｏｌ－Ｇｅｌ工艺在（１００）单晶硅上制备了粒径在２０￣８０ｎｍ的多晶ＰＬＴ（Ｐｂ１－ｘＬａｘＴｉＯ３）纳米晶膜，并用ＩＲ、ＴＧＡ、ＸＲＤ、ＳＥＭ等对膜的制备过程及结果进行了研究。结果表明，所制备的ＰＬＴ纳米晶膜属多晶钙钛矿结构，薄膜表面平整致密，厚度均匀，约为１ｕ，颗粒为球形或椭球形，粒度呈对称分布。     

Colloidal PbS nanocrystals with narrow photoluminescence spectra

Luminescent PbS nanocrystals have been synthesized by the colloidal method. PVA has been employed to modify the surface of prepared PbS nanocrystals and improve their optical properties. Optical and morphological characteristics of lead sulfide nanocrystals have been studied by high resolution electron microscopy and spectrophotometer. Optical absorption and photoluminescence (PL) studies of the PbS nanocrystals have shown the strong quantum confinement effects. For the first time, the prepared lead sulfide nanocrystals have emitted at 608 nm wavelength with narrow band width (21 nm) and high Stokes shift. Experimental results have shown that the surface charge traps have higher contribution to the optical properties of colloidal PbS nanocrystals and in our sample photoluminescence was due to hole relaxation. These properties made them a material with potential application in nanophotonics.     

Temperature-controlled synthesis of CdSe nanocrystals with narrow size distribution

CdSe quantum dots (QDs) with narrow size distribution and fine crystallinity were synthesized in paraffin liquid through temperature-control method. TEM, HRTEM, SEAD, XRD, PL and UV-VIS spectra were used to characterize the size, crystal structure and photoluminescence (PL) properties of CdSe nanocrystals. The PL spectra and TEM results revealed that the monodispersed and uniformed CdSe QDs with narrow size distribution were synthesized at a certain reaction temperature. HRTEM images combined with selected area electron diffraction (SAED) and XRD patterns illustrated that CdSe QDs showed near-perfect zinc-blende and wurtzite crystallinity at different temperatures. The Gibbs-Thomson calculation provided a thermodynamic explanation for obtaining the CdSe nanocrystals with narrow size distribution by temperature-control method.     

Study on the photoluminescence character of water-soluble CdSe nanocrystals under ambient conditions

Water soluble, thioglycolic acid (TGA) modified CdSe nanocrystals (NCs) have been prepared in aqueous media by the reaction between Cd2+ and NaHSe. Although initially these quantum dots (QDs) display photoluminescence (PL) with very low quantum yields (QY), upon prolonged exposure to ambient light, a strong PL enhancement by illumination is observed which leads to water soluble QDs with high luminescence. This result may have important application potential in biological or other fields. The primary reason for the luminescence enhancement is concluded to be the incorporation of sulfide ions from TGA into the lattice of CdSe NCs and the subsequent formation of alloy structures. Moreover, the CdSe/CdS core-shell structured QDs synthesized in aqueous solutions also consolidate this conclusion.     

Reduced photo-instability of luminescence spectrum of core-shell CdSe/CdS nanocrystals

Coated CdSe/CdS nanocrystals have been synthesized through a new reaction routine in micelle solution. High resolution transmission electron microscope image demonstrated the monodispersity and core-shell structure of CdSe/CdS nanocrystals. Photooxidation experiments shown that by coating with a wider bandgap material CdS, the surface states of CdSe cores could be decreased and the photo-instability of their luminescence spectrum could be reduced. This phenomena were temporary interpreted that lack of carriers at the outlayer surface reduced photooxidation degradation of CdSe/CdS nanocrystals.     

Pump-intensity- and shell-thickness-dependent evolution of photoluminescence blinking in individual core/shell CdSe/CdS nanocrystals

We report a systematic study of photoluminescence (PL) intensity and lifetime fluctuations in individual CdSe/CdS core/shell nanocrystal quantum dots (NQDs) as a function of shell thickness. We show that while at low pump intensities PL blinking in thin-shell (4-7 monolayers, MLs) NQDs can be described by random switching between two states of high (ON) and low (OFF) emissivities, it changes to the regime with a continuous distribution of ON intensity levels at high pump powers. A similar behavior is observed in samples with a medium shell thickness (10-12 MLs) without, however, the PL intensity ever switching to a complete "OFF" state and maintaining ca. 30% emissivity ("gray" state). Further, our data indicate that highly stable, blinking-free PL of thick-shell (15-19 MLs) NQDs ("giant" or g-NQDs) is characterized by nearly perfect Poisson statistics, corresponding to a narrow, shot-noise limited PL intensity distribution. Interestingly, in this case the PL lifetime shortens with increasing pump power and the PL decay may deviate from monoexponential. However, the PL intensity distribution remains shot-noise limited, indicating the absence of significant quantum yield fluctuations at a given pump power intensity during the experimental time window.     

Symmetry considerations in CdSe nanocrystals

Semiconductor nanocrystals or quantum dots show a wide range of physical properties depending on their size or shape. In this paper, we show that symmetry is also an important characteristic that can lead to different electronic and optical properties. We use pseudopotential density-functional theory, within a real space approach, and address the sensitivity of electronic and optical properties with respect to the symmetry point groups associated to CdSe nanocrystals.     

Preparation of copper-doped CdSe nanocrystals

Sols of stabilized copper-doped CdSe nanocrystals in a nonpolar high-boiling solvent have been synthesized using cadmium oleate, copper stearate, and trioctylphosphine selenide as starting reagents. The average size of the nanocrystals is 2.8–2.9 nm, with a 10% variance, as evaluated from their absorption spectra. The samples show excitonic luminescence and bright near-IR (700–900 nm) luminescence with a lifetime on the order of 0.5–1 μs. The luminescence spectroscopy data are consistent with the assumption that the copper distribution over the nanocrystals follows Poisson’s law. The average copper content of the samples is 0.1–2 atoms per nanocrystal.     

Reversible and hierarchical composite gels with CdSe nanocrystals

To synthesize composite solid materials of metal salt and CdSe nanocrystals by a simple one-step method has been described. These solids can form stable gel in some organic solvent, such as benzene, cyclohexane and 1-butanol, especial in n-decane even below 0.1 wt/vol.%. Furthermore, these gels appear strong fluorescence which can be easily adjusted by the gel concentration. Temperature-dependent fluorescence spectra of composite gels suggested that the CdSe NCs aggregate together in gel state which would induce the energy transfer between nanocrystals and these aggregates could be reversibly disintegrated when gel was heated to form sol. TEM observations provided the further evidence of the energy transfer and suggested that the CdSe NCs were enchased regularly not only on the surface of self assembly of metal salt, but also embedded inside of self assembly in composite gel with small size nanocrystals. In contrast, in composite organogel with large nanocrystals they were only enchased on the edge of self assembly.     

Electronic impurity doping in CdSe nanocrystals

We dope CdSe nanocrystals with Ag impurities and investigate their optical and electrical properties. Doping leads not only to dramatic changes but surprising complexity. The addition of just a few Ag atoms per nanocrystal causes a large enhancement in the fluorescence, reaching efficiencies comparable to core-shell nanocrystals. While Ag was expected to be a substitutional acceptor, nonmonotonic trends in the fluorescence and Fermi level suggest that Ag changes from an interstitial (n-type) to a substitutional (p-type) impurity with increased doping.     

Multi-wavelength intermittent photoluminescence of single CdSe quantum dots

A single chromophore detection using video-microscopy is one of the latest methodologies to reveal unique characteristics, which could not be obtained from ensemble measurements. Among many kinds of subjects, dynamic optical properties observed in colloidal semiconductor nanoparticles are attractive and important not only for the basis of photo-physics but also for application studies, e.g. biological labeling, electronic devices. In this study, fluorescence video-microscopy was performed on cadmium selenide (CdSe) quantum dots (QDs) spin-coated on a glass substrate. From single CdSe QDs detection, emissions at wavelengths separated over 60 nm were observed for the first time. This spectral feature was attributed to the existence of double-emissive relaxation processes in CdSe QDs. Photoluminescence intermittency was also observed both from relaxation processes. Fluorescence video-microscopy, which was advanced in biology, can be applicable for the real-time monitoring of dynamic properties in semiconductor photo-physics.