空穴传输材料对CdSe核壳量子点的荧光影响

用稳态光谱和时间分辨光谱技术研究了空穴传输材料对CdSe/ZnSe 与CdSe/ZnS核壳量子点的荧光影响。结果表明,空穴传输材料对量子点有较强的猝灭作用,随空穴传输材料分子浓度的增加,量子点的荧光强度明显地被猝灭,同时量子点的荧光寿命也被减短。两种不同空穴传输分子对CdSe/ZnSe量子点的荧光猝灭明显不同。在与相同空穴传输分子相互作用时,包覆ZnS壳层的CdSe核壳量子点荧光猝灭效率明显低于包覆ZnSe壳层的CdSe核壳量子点。量子点的荧光猝灭过程可以解释为静态猝灭和动态猝灭过程,其中静态猝灭来源于量子点表面与空穴传输材料间相互作用,而动态猝灭则主要来源于量子点到空穴传输材料的空穴转移过程。实验结果表明空穴传输材料的种类以及核壳量子点的壳层结构都对其荧光猝灭效应起关键作用。     

Photoluminescence properties of Mn-doped II–VI semiconductor nanocrystals

Our recent photoluminescence studies on ZnS:Mn²⁺- and CdS:Mn²⁺-nanocrystals dispersed in polyvinyl alcohol polymer films are reviewed. Both nanocrystal samples show Mn²⁺ 3d intrashell luminescence with high quantum efficiencies of about 20% at room temperature under the interband excitation. Noticeable characteristics of our nanocrystal samples are that the luminescence involving some trap state is much weaker than the Mn²⁺ luminescence, unlike other reports, and that thermal quenching of the Mn²⁺ luminescence is remarkably weak, compared with the corresponding bulky crystal powder. These two characteristics lead to the above high quantum efficiencies of the Mn²⁺ luminescence at room temperature. In addition, we examine the dominant excitation mechanism of Mn²⁺ in the nanocrystals under the interband excitation and the validity of the sp–d mixing model proposed previously to explain the high luminescence quantum efficiency.     

Patterning of polypyrrole using a fluoropolymer as an adsorption-protecting molecule

Patterning of the conducting polymer polypyrrole (PPy) was achieved using perfluoropolyether (PFPE) as a mask material. The fluoropolymer PFPE has both hydrophobic and oleophobic properties that allowed the generation of passivated patterns against PPy deposition. We exploited these properties to achieve the selective micropattern deposition of PPy, by simple chemical oxidation in an aqueous solution. Using a microcontact printing method, circle patterns with exposed carboxyl groups were prepared, while other region was protected by PFPE. Chemical oxidation of PPy on the patterned substrate resulted in selective deposition of PPy onto only the carboxylate-terminated regions, with little deposition on the PFPE layer. Cross-sectional analysis of the pattern revealed that the PFPE layer would form a hole-like structure around the carboxylate-terminated surfaces, with PPy deposition only in the holes. The PFPE layer had little influence on surface smoothness, compared to other self-assembled monolayers. These results suggest that PFPE can be used as a protective material for the surface modification and patterning of various materials.     

Photoluminescence of the layered compound CdInGaS4

Summary The photoluminescence of the layered compound CdInGaS₄ was measured and analysed. The broad emission band at about 1.95 eV was found to be composed of three bands peaking at 2.16, 1.98 and 1.76 eV at 4.8K. These bands are due to free-to-bound or donor-to-acceptor transitions. We have found a new emission band peaking at 2.38 eV. This band shows that peak intensity markedly depends on the position in the crystal and is related to localized centres. The origin of the centres is discussed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Properties of electropolymerised polypyrrole thin film on silver

This paper reports the properties of electropolymerised polypyrrole thin film on silver. The transmission, reflection, conductivity and dielectric behavior of polypyrrole coated silver has been studied in the 8-12 GHz frequency range of the electromagnetic spectrum. The polypyrrole thin film makes silver a better conductor for microwaves. The microwave conductivity is larger than the DC conductivity by many orders of magnitude. The real and imaginary part of dielectric constant increases in magnitude with increasing doping level and also it decreases in magnitude with increasing frequency.     

Photoluminescence polarization of semiconductor nanocrystals

We review the polarization properties of photoluminescence (PL) in nanocrystals (NCs) from both theoretical and experimental points of view. We show that, under linearly polarized excitation, NCs emit partly polarized light owing to their uniaxial structure or their anisotropic shape. In elongated NCs, the anisotropy may have two origins, the electronic confinement or the effect of depolarizing field created by the light-induced charges on the interfaces. Results of polarization studies in porous silicon are presented. They are explained by the shape of the Si NCs. Experiments in CdSe NCs reveal the fine structure of the excitonic levels and show evidence of the enhancement of the electron-hole exchange energy with decreasing NC size. Spin orientation in wurtzite-type NCs is achieved by optical pumping with circularly polarized light. The effect of a magnetic field on the degree of circular polarization and the mechanisms of spin relaxation are discussed. Results in large-size NCs are presented.     

Photoluminescence of CuGaS2 and heterostructure formation with sputtered ZnS

Summary CuGaS₂ crystals grown by iodine transport exhibit room temperature photoluminescences at 2.45 eV and at 1.44 eV. The spectral distribution of the green emission is shown to be relatively well described by the calculated curve for a direct band-to-band transition withk-selection. The heterojunction formation has been tried between sulfur-treated CuGaS₂ crystals and low-resistivity amorphous ZnS films prepared by sputtering at room temperature. TheI–V characteristic of the diode shows rectifying behaviour, but no injection luminescence has been observed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Photoluminescence properties of a single tapered CuO nanowire

Photoluminescence spectroscopy has been employed in order to explore the optical emission properties of a single CuO nanowire, grown on a copper grid in static air by simple thermal oxidation method. As the diameter of the single tapered CuO nanowire decreases, the green emission of the nanowire gradually shifts towards the higher energy side. A steady blue shift of 20 nm of the photoluminescence (PL) peak has been attributed to nanosize effect. Higher surface to volume ratio and enhanced surface defects along the growth direction of the nanowire might be responsible for the observed PL behavior. In addition, crystallization process along the length of the nanowire during growth to form pure CuO structure from the precursor state may also have some role in observed shift in the PL peak.     

Photoluminescence of ion-implanted phosphors

Ion-implanted phosphors were prepared by implanting Sb in CaS at 25 keV with concentration ranging from 0.05 to 0.2% by weight. Samples of similar concentration were also prepared using the conventional technique. The spectral response under UV excitation of both types of samples is compared.     

SiOx纳米管的制备及其发光特性

以液态金属镓为媒介,利用热蒸发法合成大量非晶SiOx纳米管,这些纳米管管径均匀分布,平均约80 nm,长度大于10μm,且管内外径比例较小．分析发现,在实验过程中,熔入金属镓液滴中的硅元素和氧元素结合并从液滴的表面饱和析出,形成以镓为中心的非晶SiOx纳米管状结构．在室温中,利用260 nm的激发光源激发SiOx纳米管,发现在蓝光波段附近发出强而稳定的PL谱线,这可能与样品中的氧缺陷和空位有关．     

Photoluminescence properties of various CVD-grown ZnO nanostructures

We have studied systematically room-temperature photoluminescence (PL) properties of many nanostructured ZnO samples grown by chemical vapour deposition (CVD). Their PL spectra consist of two emissions peaked in the ultraviolet (UV) and green regions. The relative intensity of these emissions depends on the excitation energy density, size and morphology of ZnO nanostructures. Based on the excitation-density dependence of the integrated intensity ratio of UV-to-green emission, we could classify PL spectra of ZnO nanostructures into three groups characteristic of size and morphology. Our study also reveals that with increasing excitation density, the UV-peak position shifts slightly towards longer wavelengths while the green emission around 514-520 nm is almost unchanged. This green-luminescence emission is dominant when the nanostructure sizes range from 20 to 200 nm, which is related to a large surface-to-volume ratio.     

Photoluminescence ofn-GaAs at transparent Schottky contacts

Near-bandgap photoluminescence at 300 K of a Se-dopedn-GaAs crystal withn=4.8·10¹⁶ cm⁻³ was measured at a transparent CrAu−GaAs Schottky contact. The dependence of the luminescence intensity on the applied reverse voltage was recorded. Both the doping concentration and absorption coefficients above bandgap are determined.     

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.     

一种蓝光发射材料的表征及发光性能研究

8-羟基喹啉铝类有机金属配合物作为一类重要的发光材料广受关注.文章合成并通过真空升华提纯得到了一种高纯度的8-羟基喹啉铝的衍生物-三(2-甲基-8-羟基喹啉)铝,通过红外光谱、核磁共振谱以及元素分析确定了三(2-甲基-8-羟基喹啉)铝的分子结构.通过热重和差示扫描量热分析研究了三(2-甲基-8-羟基喹啉)铝的热稳定性,试验结果表明:此衍生物的结晶转变温度可达158℃,分解温度为357℃;并进一步通过紫外可见吸收光谱和荧光光谱表征了材料的带隙以及能带结构.将吸收边的线性关系延伸到与能量轴相交所得禁带宽度2.85 eV,三(2-甲基-8-羟基喹啉)铝在365 nm紫外光的激发下,在乙醇溶液体系中的荧光发射峰在479 nm处,为蓝色荧光,荧光量子效率高,是一种蓝光发射的优选材料.     

Photoluminescence from colloidal silver nanoparticles

Highly luminescent singles of Ag sol with gradual changes were detected when adjusting the granularity and concentration of particles. It can be deduced that these Ag sols, composed of a large amount of silver nanoparticles and clusters, may have their surface energy bands alterable, which might be caused by the interactions between particles. A model that describes the shift of energy band is proposed, and it can be understood as the hybridization of elementary plasmons when interactions occur between particles. Besides, both hybridization and absorption-rescattering mechanisms were proposed to explain the changeable phenomena of photoluminescence with different concentrations.     

High frequency study of electropolymerised conducting polypyrrole thin film

The polypyrrole (PPY) thin films were synthesized by electropolymerisation in potassium nitrate solution. The substrate used was stainless steel. DC conductivity, microwave reflection, microwave conductivity and microwave dielectric constant of the conducting PPY thin films are reported. DC conductivity was between 1.6 × 10⁻² S/cm and 42.3 × 10⁻² S/cm. Microwave conductivity was between 10 S/cm and 160 S/cm. The ?′ generally decreases as frequency increases similarly ?″ also decreases with increases in frequency. The measurements have been carried over the frequency range 8.2-12 GHz. These polypyrrole thin films were characterized by FTIR. The polypyrrole thin film increases the reflectivity of the stainless steel.     

Tb掺杂Si纳米线的光致发光特性

以金属Au-Al为催化剂,在温度为1 100 ℃,N₂气流量为1 500 sccm、生长时间为30 min,从Si(100)衬底上直接生长了直径约为50～120 nm、长度为数百纳米的高密度、大面积的Si纳米线。然后,利用Tb₂O₃在不同温度(1 000～1 200 ℃)、掺杂时间(30～90 min)和N₂气流量(0～1 000 sccm)等工艺条件下对Si纳米线进行了Tb掺杂。最后,对Si(100)衬底进行了Tb掺杂对比。室温下,利用荧光分光光度计(Hitachi F-4600) 测试了Tb掺杂Si纳米线的光致发光特性。实验研究了不同掺杂工艺参数(温度、时间和N₂气流量)对Tb3+绿光发射的影响。根据Tb3+能级结构和跃迁特性对样品的发射光谱进行了分析。结果表明,在温度为1 100 ℃,N₂气流量为1 500 sccm、时间为30 min等条件下制备的Si纳米线为掺杂基质,Tb掺杂温度为1 100 ℃,N₂气流量为1 000 sccm、光激发波长为243 nm时,获得了最强荧光发射,其波长为554 nm(5D₄→7F₅),同时还出现强度相对较弱的494 nm(5D₄→7F₆),593 nm(5D₄→7F₄)和628 nm(5D₄→7F₃)三条谱带。Tb掺杂的体Si衬底在波长554 nm处仅有极其微弱的光致发光峰。     

Photoluminescence quenching of CdTe/CdS core-shell quantum dots in aqueous solution by ZnO nanocrystals

Photoluminescence (PL) properties of 3-mercaptopropionic acid (MPA) coated CdTe/CdS core-shell quantum dots (QDs) in aqueous solution in the presence of ZnO colloidal nanocrystals were studied by steady-state and time-resolved PL spectroscopy. The PL quenching of CdTe/CdS core-shell QDs with addition of purified ZnO nanocrystals resulted in a decrease in PL lifetime and a small red shift of the PL band. It was found that CdTe(1.5 nm)/CdS type II core-shell QDs exhibited higher efficiency of PL quenching than the CdTe(3.0 nm)/CdS type I core-shell QDs, indicating an electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals. The experimental results indicated that the efficient electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals could be controlled by changing the CdTe core size on the basis of the quantum confinement effect.     

Self-assembly Drives Quantum Dot Photoluminescence

Engineering the spectral properties of quantum dots can be achieved by a control of the quantum dots organization on a substrate. Indeed, many applications of quantum dots as LEDs are based on the realization of a 3D architecture of quantum dots. In this contribution, we present a systematic study of the quantum dot organization obtained on different chemically modified substrates. By varying the chemical affinity between the quantum dots and the substrate, the quantum dot organization is strongly modified from the 2D monolayer to the 3D aggregates. Then the photoluminescence of the different obtained samples has been systematically studied and correlated with the quantum dot film organization. We clearly show that the interaction between the substrate and the quantum dot must be stronger than the quantum dot–quantum dot interaction to avoid 3D aggregation and that these organization strongly modified the photoluminescence of the film rather than intrinsic changes of the quantum dot induced by pure surface chemistry.     

脉冲激光退火纳米碳化硅的光致发光

采用XeCl准分子脉冲激光退火技术制备了纳米晶态碳化硅薄膜(nc-SiC),并对薄膜的光致发光(PL)特性进行了分析。结果表明,纳米SiC薄膜的光致发光表现为300～600 nm范围内的较宽发光谱带,随退火激光能量密度的增加,nc-SiC薄膜398 nm附近的发光峰相对强度增加,而470 nm附近发光峰相对减小。根据nc-SiC薄膜的结构特性变化, 认为这两个发光峰分别来源于6H-SiC导带到价带间的复合发光和缺陷态发光,并且这两种发光过程存在竞争。