基于MEH-PPV/ZnSe纳米复合器件的电致发光特性的研究

以巯基乙酸作为稳定剂在水相中制备了ZnSe纳米晶,用X射线粉末衍射(XRD)和X射线光电子能谱(XPS)对其进行了表征。用表面活性剂将ZnSe纳米晶从水相中转移到有机相中,使其与聚合物MEH-PPV复合作为发光层,制备了多层电致发光器件Glass/ITO/MEH-PPV∶ZnSe/BCP/Alq₃。对ZnSe纳米晶和MEH-PPV薄膜的光致发光谱及其吸收光谱的比较表明ZnSe纳米晶和MEH-PPV之间存在着能量传递,这是导致纳米复合薄膜的光致发光光谱和电致发光光谱存在差异的原因之一。文章对其在光激发和载流子注入条件下的不同发光机制进行了讨论。通过对器件的光电特性进行研究,发现ZnSe纳米晶发光的比例随着外加电压的增加而增加,而且器件的I-V特性基本上符合二极管的特性。     

ZnSe(ZnS)纳米晶与MEH-PPV的共掺有机电致发光器件

采用水相法合成核壳结构ZnSe/ZnS 纳米晶,经X射线衍射(XRD)分析和透射电子显微镜(TEM)表征,证实所制备的样品为立方晶型闪锌矿结构ZnSe/ZnS量子点。按照一定的质量比将ZnSe/ZnS 纳米晶和有机聚合物MEH-PPV(poly ) 共掺并将其作为发光层,分别制备单层和多层有机电致发光器件,结构为ITO/MEH-PPV∶ZnSe(ZnS)(50 nm)/Al和 ITO/PEDOT∶PSS(70 nm)/ MEH-PPV∶ZnSe(ZnS)(50 nm)/BCP(15 nm)/Alq₃(12 nm) /LiF(0.5 nm)/Al。实验结果表明,多层发光器件的发光特性与单层器件不同,工作电压的增大使其发光峰发生了明显的蓝移。     

MEH-PPV/ZnO纳米晶无机有机复合电致发光器件的研究

以Ⅱ一Ⅵ族无机半导体ZnO纳米颗粒为电子传输层,MEH-PPV为空穴传输层兼发光层,得到的电致发光器件比单层MEH-PPV器件的发光亮度和效率都明显提高。器件结构为ITO／MEH-PPV／ZnO／Al的电致发光光谱同单层PPV器件的光谱出现了不同,在620nm处出现了一个小的发光峰,应该是ZnO的发光。另外,双层结构器件的启亮电压由单层器件的9V降到了4V左右。由I-V曲线及发光光谱可判断出发光区域应在MEH-PPV／ZnO界面处,并且复合区域可能随着电压的变化而变化。     

银纳米片等离子体效应增强有机太阳能电池及其性能优化研究

将银纳米片引入有机太阳能电池,增强了器件的光吸收及光电转换效率。制备得到了具有不同等离子共振吸收特性的银纳米片。当银纳米片的等离子共振吸收与活性层的吸收相匹配时,器件的光电流显著增强。通过改变银纳米片与活性层之间的距离,研究了等离子体共振增强电磁场的传递特性。两者的距离越近则耦合入活性层的电磁场越强,器件的光电流越高。经优化后,以P3HT∶PCBM为活性层的有机太阳能电池的光电转换效率由3.04%增长到3.82%,提高了26%。     

多环类苝四甲酸二酐插入层对ZnO纳米棒和聚合物复合太阳电池性能的影响

以ZnO纳米棒和聚[2-甲氧基-5-(2-乙基-己氧基)-1,4-苯撑乙烯撑](MEH-PPV)的复合体系作为光敏层制备了太阳电池.为了增大电池的光吸收,在ZnO纳米棒与MEH-PPV之间插入了有机n型小分子多环类苝四甲酸二酐(PTCDA),制备了不同厚度的PTCDA、结构为ITO/ZnO纳米棒/PTCDA/MEH-PPV/Au的太阳电池.实验发现,插入PTCDA后,电池在可见光区的吸收增强,光生激子数量增大,光电流密度增大.当蒸镀的PTCDA厚度为40 nm时,薄膜的粗糙度适中,表面形貌较为平滑,器件性 关键词： 有机太阳电池 ZnO纳米棒 聚合物     

有机/无机复合结构光电导型器件的光激发机制

制备了PVK/ZnS有机无机复合的光电导型器件 ,器件结构分别为Glass/ITO/PVK/Al;Glass/ITO/ZnS/Al;Glass/ITO/ZnS/PVK/Al。通过研究此复合器件在外加电场作用下的稳态光电导激发谱 ,得到了基本光激发过程。把PVK/ZnS的吸收谱和器件的光电导谱进行比较 ,知道虽然两者的吸收对器件光电流都有贡献 ,但有效部分在PVK和ZnS的界面处。最大光电流对外加电场的依赖性与器件的暗电流和光电流谱为此提供了证据     

基于CdSe纳米晶发光器件的电致发光特性的研究

以巯基乙酸为稳定剂,在水溶液中制备了硒化镉(CdSe)纳米晶。用X射线光电子能谱(XPS)及其在水溶液中的紫外可见吸收光谱对其进行了表征。又以CdSe为发光材料制备了两种结构的电致发光器件,并对它们的光致发光和电致发光特性进行了研究。在两个器件的电致发光中都得到了CdSe纳米晶的发光,说明CdSe纳米晶是主要的发光中心而聚乙烯咔唑(PVK)只是空穴注入和传输的媒介。在电致发光光谱中还出现了一个不同于CdSe纳米晶和PVK的发光峰值,它是CdSe/BCP(2,9-二甲基-4,7-二苯基-1,10-菲咯啉)界面处的电致发光激基复合物的发光。     

CdSe:Nd纳米晶及CdSe:Nd@SiO2核壳结构的合成及发光性能

利用有机相法合成Nd³⁺掺杂CdSe纳米晶（CdSe∶Nd）,通过X射线粉末衍射（XRD）、透射电镜（TEM）、紫外吸收光光谱及荧光光谱表征,证明Nd³⁺已经成功掺入到CdSe的晶格中。与纯CdSe纳米晶相比,CdSe∶Nd纳米晶的结构仍为立方晶型,且形貌近似球形,均匀分散,粒径约为2~4 nm。紫外吸收峰和荧光发射峰都发生红移,而且掺杂后的CdSe∶Nd纳米晶量子产率也提高,这可能是由于掺杂Nd³⁺引入了新的杂质能级,带隙减小。为了实现CdSe∶Nd纳米晶的可加工性和功能性,通过微乳法合成SiO₂壳包覆的CdSe∶Nd纳米球（CdSe∶Nd@SiO₂纳米球）,CdSe∶Nd@SiO₂纳米球呈均匀球形,直径约为100~115 nm,并且包壳后的CdSe∶Nd@SiO₂纳米球发射峰（581 nm）与CdSe∶Nd纳米晶（598 nm）相比,发光强度提高且发射峰蓝移,蓝移约为17 nm,可能是因为SiO₂壳可以减少纳米晶表面的非辐射跃迁以及改善表面缺陷导致的。     

CdSe/CdS核/壳型纳米晶的光谱特性

以巯基乙酸为稳定剂制备了CdSe/CdS核／壳型纳米晶。用光吸收谱（Abs)、光致发光谱（PL）及光致发光激发谱（PLE）研究了CdS壳层对CdSe纳米晶电子结构，从而对其吸收和发光性能的影响。根据PL和PLE的结果以及带边激子精细结构的计算结果，我们用尺寸很小的纳米晶中所形成的基激缔合物解释了PL光谱与吸收边之间较大的Stokes位移。     

纳米MEH-PPV阵列的光致发光

以多孔氧化铝为模板,将可溶性发光聚合物聚（2-甲氧基-5-（2’-乙基己氧基）-1,4-对苯乙炔）（MEH-PPV）镶嵌在纳米孔中,制备出高发光效率的纳米发光聚合物阵列,其光学特性与MEH-PPV薄膜显著不同。纳米孔内的MEH-PPV分子链形成链束,链束中的分子链数目依赖于制备纳米MEH-PPV阵列所用溶液的浓度。相对于稀溶液,在由浓溶液制备的纳米MEH-PPV阵列中,MEH—PPV链束的分子链数目较多,链间作用使MEH-PPV的能带展宽,能隙减小,因而浓溶液获得的纳米MEH—PPV阵列的光致发光峰红移。热处理纳米MEH-PPV阵列的PL谱表明,纳米孔内的聚合物分子链的弛豫运动受到限制。     

Sensitivity enhancement in optical waveguide sensors using metamaterials

In this paper, we show negative differential resistance (NDR) in CdSe quantum dot/MEH-PPV based nanocomposite multi-layer heterostructures at room temperature. The four-layer structure exhibited a maximum peak-to-valley ratio of current of 1190 at room temperature, while two-layer structures show a value of 4. Two-, three- and four-layer structures are studied. Each device configuration exhibits different kind of negative differential resistance. The possible mechanism is explained on the basis of tunneling phenomena.     

The optical properties of the blends of CdSe nanocrystals and poly(N-vinylcarbazole)

The CdSe nanocrystals with different sizes were synthesized in aqueous solution through water-sol method using l-cysteine hydrochloride as the stabilizer. The pH-dependent optical properties of the CdSe nanocrystals were investigated. Furthermore, the CdSe nanocrystals were dispersed into chloroform by using a cationic surfactant, and mixed with poly(N-vinylcarbazole) (PVK) in different mass ratios. The investigation of the photoluminescence (PL) and absorption spectra of the CdSe:PVK blends suggested that energy transfer from the PVK excited states to the CdSe nanocrystals, and it is more efficient for the smaller size nanocrystals. In the meantime, it was found that the relative emission intensity of the CdSe nanocrystals to PVK in the blends depended on the mass ratios, and the emission from the CdSe nanocrystals was the strongest as the mass ratio of CdSe to PVK was 2:1.     

氨基酸稳定的CdSe纳米晶对溶菌酶进行荧光标记

利用氨基酸中惟一带有巯基的L-半胱氨酸盐酸盐(L-Cys)作为稳定剂在水相体系中合成CdSe纳米晶,通过表面包覆的L-Cys与生物试剂溶菌酶进行结合,实现CdSe纳米晶对溶菌酶的荧光标记.利用TEM、荧光光谱仪及荧光显微镜等多种手段对样品的结构、形貌及光学性能进行表征.试验结果表明,利用L-Cys为稳定剂合成的CdSe纳米晶具有较强的生物活性,L-Cys本身所带的氨基和羧基可以和多种生物试剂通过不同途径进行结合.对溶菌酶(Lys)标记前后,CdSe纳米晶的发射光谱的峰位发生微小红移,大约为2nm,半峰全宽基本保持不变,在40~50nm之间,荧光强度随所标记的Lys浓度的不同均发生明显增强.所有特性均表明实验所合成的CdSe纳米晶在生物标记方面具有很好的实用价值.     

The temporal evolution of the structure and luminescence properties of CdSe semiconductor quantum dots grown at low temperatures

Mono-dispersed CdSe quantum dots have been prepared by water based route using 2-mercaptoethanol at low temperatures. The structures of the CdSe nanocrystals were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The XRD pattern showed that the prepared CdSe has a cubic phase with zinc blende structure. The temporal evolution of the absorption and photoluminescence spectra was used to follow the reaction process and to characterize the optical properties of the prepared CdSe quantum dots. The results exhibited clear exciton peaks in the absorption spectra. The influence of the temperature and/or time of reaction on the properties of the CdSe nanocrystals were investigated. It is found that the size of CdSe nanoparticles increases, as the reaction temperature and/or time are increased. The results showed that the Stokes shift between photoluminescence emission peak and absorption peaks is increased with the increase of the reaction temperature.     

Surface control of CdSe nanocrystals by UV-exposure in air and successive thermal treatment under ultra high vacuum

Colloidal CdSe nanocrystals were synthesized through a solution process. The CdSe nanocrystals coated on Si(1 0 0) wafers were UV-exposed in either an air or argon atmosphere to distinguish the effect of generated ozone from UV-radiation at 365 nm on the removal of surface capping pyridine molecules. The pyridine on the CdSe nanocrystal's surface could be effectively removed by the ozone generated during UV-exposure with an accompanying highly oxidized surface state of the CdSe nanocrystals. For the removal of surface oxides of CdSe nanocrystals, a successive thermal treatment under ultra high vacuum (UHV) was adopted. The optical energy bandgap measured by using UV-vis absorption spectroscopy showed a red shift with treatment with an increase of annealing temperature. The electronic energy structure of UHV-annealed CdSe nanocrystals film was analyzed in situ using X-ray absorption and photoelectron spectroscopy. A great resemblance was found between the values of the optical and electron energy bandgaps of effectively surface-treated CdSe nanocrystals film after UHV-annealing at 400 °C.     

Preparation of pure CdSe nanocrystals through mechanical alloying

Pure CdSe nanocrystals have been successfully synthesized by mechanical alloying Cd and Se elemental powders. XRD results show that pure CdSe compound in wurtzite structure has been fabricated after mechanical alloying the elemental powders for 130 min. All the diffraction peaks from elemental Cd and Se disappeared completely in those XRD patterns of as-milled CdSe nanocrystals for more than 3 h. When the mechanical alloying process was carried out for 40 h, typical zinc blende structure diffraction mode was exhibited in the XRD pattern. Structural evolution of CdSe nanocrystal with ball milling time has been discussed in detail. A phase transformation from wurtzite to zinc blende structure took place when the mechanical alloying process prolonged to 40 h. HRTEM images of the individual as-milled CdSe nanocrystals confirmed such phase transformation. The grain size of the as-milled CdSe nanocrystals ranges from 2 to 30 nm, with majority being distributed within the range from 2 to 8 nm.     

Formation and spectroscopic characterization of mono-dispersed CdSe nanocrystals

In this article, mono-dispersed hexagonal structure CdSe nanocrystals with polyhedron shape were prepared by an open solvent thermal reaction. They show a discrete excitonic transition structure in the absorption spectra and the minimal photoluminescence （PL） peak full-width at half-maximum of 19nm. The PL quantum yield is about 60%. Transmission electron micrographs, high-resolution transmission electron micrographs, x-ray powder diffraction patterns, UV-vis absorption spectra and PL spectra were obtained for the as-prepared CdSe nanocrystals. The size of the CdSe nanocrystals can be tuned by changing the reaction temperature or time. Due to the improved synthesis method, a different growth mechanism of the CdSe nanocrystals is discussed.     

Luminescent CdSe and CdSe/CdS core-shell nanocrystals synthesized via a combination of solvothermal and two-phase thermal routes

A new solvothermal route has been developed for synthesizing the size-controlled CdSe nanocrystals with relatively narrow size distribution, and the photoluminescence (PL) quantum yields (QYs) of the nanocrystals can reach 5-10%. Then the obtained CdSe nanocrystals served as cores to prepare the core/shell CdSe/CdS nanocrystals via a two-phase thermal approach, which exhibited much higher PL QYs (up to 18-40%) than the CdSe core nanocrystals. The nanocrystal samples were characterized by ultraviolet-visible (UV-vis) absorption spectra, PL spectra, wide-angle X-ray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).