Photoluminescence from ZnS1-xTex alloys under hydrostatic pressure

ZnS1-xTex (0.02less than or equal toxless than or equal to0.3) alloys are studied by photoluminescence under hydrostatic pressure at room temperature. Only a wide emission band is observed for each sample. Its peak energy is much lower than the corresponding band gap of alloys. These bands are ascribed to the radiative annihilation of excitons bound at Te-n(ngreater than or equal to2) isoelectronic centers. The pressure coefficients of the emission bands are smaller than those of alloy band gaps from 48% to 7%. The difference of the pressure coefficient of the emission band and the band gap increases when the binding energy of Te-n centers decreases. It seems contrary to our expectation and needs further analysis. The integrated intensities of emission bands decrease with increasing pressure due to the decreasing of the absorption coefficient associated with the Te-n centers under pressure. According to this model the Stokes shifts between the emission and absorption bands of the Te-n centers are calculated, which decrease with the increasing Te composition in alloys.

Optical properties of nanocrystalline silicon embedded in SiO2

Nanocrystalline silicon embedded SiO2 matrix has been formed by annealing the a-SiOx films fabricated by plasma enhanced chemical vapor deposition technique. Absorption and photoluminescence spectra of, the films have been studied in conjunction with micro-Raman scattering spectra. It is found that absorption presents an exponential dependence of absorption coefficient to photon energy in the range of 1.5-3.0 eV, and a sub-band appears in the range of 1.0-1.5 eV. The exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrystallites, while the sub-band absorption is ascribed to transitions between surfaces and/or defect states of the silicon nanocrystallites. The existence of Stokes shift between absorption and photoluminescence suggests that the phonon-assisted luminescence would he enhanced due to the quantum confinement effects.

Si-based optoelectronic devices and their attractive applications

The semiconductor photonics and optoelectronics which have a great significance in the development of advanced high technology of information systems will be discussed in this paper. The emphasis will be put on the recent research carried out in our laboratory in enhanced luminescence from low dimensional materials such as SiGe/Si and Er-doped Si-rich SiO2/Si and Er-doped SixNy/Si. A ring shape waveguide structure, used to promote the effective absorption coefficient in PIN photodetector for 1.3 mu m wavelength and a resonant cavity enhanced structure, used to improve the quantum efficiency and response in heterostructure photo-transistor (HPT), are also proposed in this paper.

Improved diphasic nc-si/a-si : H I-layer materials using PECVD

Two series of films has been prepared by using a new regime of plasma enhanced chemical vapor deposition (PECVD) in the region adjacent to the phase transition from amorphous to crystalline state. The photoelectronic properties of the films have been investigated as a function of crystalline fraction. In comparison with typical a-Si:H, these diphasic films with a crystalline fraction less than 0.3 show a similar optical absorption coefficient, higher mobility life-time product ( LT) and higher stability upon light soaking. By using the diphasic nc-Si/a-Si films as the intrinsic layer, a p-i-n junction solar cell has been prepared with an initial efficiency of 9. 10 % and a stabilized efficiency of 8.56 % (AM 1.5, 100 mW/cm(2)).

Optical image processing using the photoinduced anisotropy of pyrrylfulgide

A synthesized photochromic compound-pyrrylfulgide-is prepared as a thin film doped in a polymethylmethacrylate (PMMA) matrix. Under irradiation by UV light, the film converts from the bleached state into a colored state that has a maximum absorption at 635 nm and is thermally stable at room temperature. When the colored state is irradiated by a linearly polarized 650 nm laser, the film returns to the bleached state; photoinduced anisotropy is produced during this process. Application of optical image processing methods using the photoinduced anisotropy of the pyrrylfulgide/PMMA film is described. Examples in non-Fourier optical image processing, such as contrast reversal and image subtraction and summation, as well as in Fourier optical image processing, such as low-pass filtering and edge enhancement, are presented. (c) 2006 Optical Society of America.

超声化学法合成稀土纳米材料

稀土纳米材料因其独特的光、电、磁和催化等性能，在纳米器件和功能材料等诸多领域具有重要的应用价值。大量研究表明，纳米材料的物理和化学性质与其尺寸、成分、形貌和晶型密切相关。稀土纳米材料的合成方法有许多，然而，要真正实现这类材料的简单可控合成仍然是个艰难的课题。超声化学法由于具有操作简单、合成周期短、反应温度低、成本低廉并且产物均匀、粒径分布窄和纯度高等突出优点，已经在无机纳米材料制备领域中显示出独特的魅力。因此，本论文的工作是运用超声化学法合成有广泛应用前景的稀土纳米材料，对产物的形貌和粒径进行有效的调控，研究和分析其形成机理，并进一步考察其形貌、结构与性能之间的相互关系。 在本论文中，我们研究的体系集中在稀土磷酸盐、稀土氟化物和稀土钒酸盐三类纳米材料。 采用超声化学法得到的CePO4:Tb和CePO4:Tb/LaPO4(核/壳)纳米棒结晶完好，具有CePO4体材料的六方相结构。CePO4:Tb纳米棒直径为10-30 nm，长度为200 nm，CePO4:Tb/LaPO4(核/壳)纳米棒的LaPO4壳的厚度为2-10 nm。CePO4:Tb和CePO4:Tb/LaPO4(核/壳)纳米棒均具有Ce3+ (5d - 4f)和Tb3+ 5D4-7FJ(J = 6-3)的特征发射。与CePO4:Tb纳米棒核相比，CePO4:Tb/LaPO4(核/壳)纳米棒的光谱强度及荧光寿命均有较大的提高，这是由于形成核/壳结构后发光中心镧系金属离子与表面淬灭中心的距离增大，减少了能量传递过程中非辐射复合的路径，使能量淬灭受到抑制。 采用简单、快速、无模板辅助的超声化学法合成了稀土氟化物，并对产物的形貌和粒径进行了有效的调控。通过应用不同氟源(KBF4、NaF和NH4F)选择性合成了具有不同形貌的CeF3纳米材料，如片状、棒状和颗粒状。对具有不同形貌的CeF3样品进行了UV-Vis吸收光谱和荧光光谱测试和比较。研究结果表明不同形貌的样品，它们的光学性质存在很大差异，这说明纳米材料的光学性质与其形貌、粒径、晶体结构等因素有密切的关系。得到的EuF3单晶纳米材料具有三维花状形貌。这些纳米花的外形为球状，平均直径为0.9 μm-1.0 μm，每个花瓣的厚度约为0.14 μm。在其他实验条件不变的情况下，采用搅拌法而不经过超声辐射的对比实验只能得到二维纳米片，这表明超声辐射对花状EuF3的形成起到了至关重要的作用。基于不同反应时间的实验结果，我们提出了这种三维花状EuF3纳米材料可能的形成机理。 采用超声化学法选择性地合成了介孔及棒状CeVO4和纺锤状的YVO4:Eu3+ 纳米材料。CeVO4纳米棒的平均直径为5 nm，长度为150 nm。介孔CeVO4材料的比表面积较高(122 m2•g-1)，孔径分布窄，其催化性能有望得到提高。纺锤状的YVO4:Eu3+ 纳米粒子具有四方相锆石结构，其直径为90-150 nm，长度为250-300 nm。超声辐射对样品的形貌起着关键作用，在其他反应条件不变，未采用超声辐射的情况下只能得到团聚严重的纳米颗粒。荧光测试表明，纺锤状YVO4:Eu样品表现为Eu3+ 5D0-7FJ(J = 1- 4)的特征跃迁，以5D0-7F2电偶极跃迁(614nm)为最强峰，属于红光发射。

Effect of Si-Ge interdiffusion on the waveguide properties of SiGe-Si MQW photodetector

Because of Si-Ge interdiffusion in the Si-SiGe interface during the growth process, the square-wave refractive index distribution of a SiGe-Si multiple-quantum-web (MQW) will become smooth. In order to simulate the actual refractive index profile, a staircase approximation is applied. Based on this approach, the dispersion equation of the MQW waveguide is obtained by using a transfer matrix method, The effects of index changes caused by the interdiffusion on the optical field and the characteristics of the photodetector are evaluated by solving the dispersion equation, It is shown that the Si-Ge interdiffusion can result in a reduction of the effective absorption coefficient and the quantum efficiency.

Characterization of diphasic nc-Si/a-Si : H thin films and solar cells

Hydrogenated silicon films with diphasic structure have been prepared by using a new regime of plasma enhanced chemical vapor deposition (PECVD) in the region adjacent to the phase transition from amorphous to crystal. line state. The photoelectronic and microstructural properties of the films have been characterized by the constant photocurrent method (CPM), Raman scattering and nuclear magnetic resonance (NMR). In comparison with typical hydrogenated amorphous silicon (a-Si:H), these diphasic films with a crystalline fraction less than 0.3 show a similar optical absorption coefficient, lower deep-defect densities and higher stability upon light soaking. By using the diphasic nc-Si/a-Si films a p-i-n junction solar cell has been prepared With an initial efficiency of 8.51 % and a stabilized efficiency of 8.02 % on an area of 0.126 cm(2) (AM1.5, 100 mW/cm(2)).

Si-based optoelectronic devices and their attractive applications

The semiconductor photonics and optoelectronics which have a great significance in the development of advanced high technology of information systems will be discussed in this paper. The emphasis will be put on the recent research carried out in our laboratory in enhanced luminescence from low dimensional materials such as SiGe/Si and Er-doped Si-rich SiO2/Si and Er-doped SixNy/Si. A ring shape waveguide structure, used to promote the effective absorption coefficient in PIN photodetector for 1.3 mu m wavelength and a resonant cavity enhanced structure, used to improve the quantum efficiency and response in heterostructure photo-transistor (HPT), are also proposed in this paper.

Dynamics of excited OCS investigated by resonance-enhanced multiphoton ionization

The predissociation decay behavior of molecule carbonyl sulfide (OCS) has been investigated by resonance-enhanced multiphoton ionization spectroscopy using the pump-probe technique of dichroic femtosecond lasers in real time. The lifetime of excited OCS around 74 720 cm(-1) by two-photon absorption of 268 nm, corresponding to upsilon(1)=1 of the Rydberg state [(2)Pi(1/2)]4ppi((1)Sigma(+)), is directly determined to be tau(D)=1071+/-11 fs. This picosecond decay process indicates that the excited state is predissociative. The temporal information of dissociation enriches the knowledge of the potential-energy surface of the associative excited state.

Preparation and characteristics of nonflammable polyimide materials

The thermal and flame-retardant properties of homo- and copolyimides were evaluated. Those containing sulfone linkages in the backbone were found to be more flame retardant. Both properties were dependent on the composition. A polyimide/silica nanocomposite was obtained through sol-gel processing. The effects of the addition of silica an the dispersion, interfacial adhesion, fire resistance, mechanical properties, and thermal stability of the composites were investigated. SEM analysis showed a good dispersion of silica with a diameter of 50-300 nm in the organic matrices. The addition of silica increased the fire retardancy and mechanical properties of the composites. (C) 2000 John Wiley & Sons, Inc.

Two-dimensional beta-NaLuF4 hexagonal microplates

A simple hydrothermal method has been developed to synthesize monodisperse beta-NaLuF4 microplates in a large scale. The microcrystals have a perfect hexagonal shape with a diameter of about 5.2 mu m and a thickness of 300 nm. Trisodium citrate (Cit(3-)), which is introduced into the reaction mixture and acts as the chelating agent and shape modifier, plays a key role in fine-tuning the microstructures. The dominant adsorption of Cit(3-) onto the {0001} facets lowers the surface energy of these facets.

"Sandglass"-shaped self-assembly of coil-rod-coil triblock copolymer containing rigid aniline-pentamer

The amphiphilic PEG1 500-b-EM AP-b-PEG1 500 (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline-pentamer (EM AP) in its concentrated solution can self-assemble into a special shape like "sandglass", as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This "sandglass"- shaped assembly is composed of several "rods" aggregated in the middle, with every "rod" being about 8 VLrn in length and 300 nm in diameter.

Electroactive Aniline Pentamer Cross-Linking Chitosan for Stimulation Growth of Electrically Sensitive Cells

A new kind of electroactive polymers was synthesized by using aniline pentamer (AP) cross-linking chitosan (CS) in acetic acid/DMSO/DMF solution. UV-vis and CV confirmed the electroactivity of polymers in acidic aqueous solution. The amphiphilic polymers self-assembled into 200-300 nm micelles by dialysis against deionized water from the acetic acid buffer solution. Three samples with different weight percentages of AP were used to identify the relationship between the content of AP and the differentiation of rat neuronal pheochromocytoma PC-12 cells without external stimulation.

Highly Uniform Gd(OH)(3) and Gd2O3:Eu3+ Nanotubes: Facile Synthesis and Luminescence Properties

Uniform Gd(OH)(3) nanotubes have been prepared via a simple wet-chemical route at ambient pressure and low temperature, without any catalysts, templates, or substrates, in which Gd(NO3)(3) was used as the gallium source and ammonia as the alkali. SEM and TEM images indicate that the as-obtained Gd(OH)3 entirely consists of uniform nanotubes in high yield with diameters of about 40 nm and lengths of 200-300 nm. The temperature-dependent morphological evolution and the formation mechanism of the Gd(OH)(3) nanotubes were investigated in detail. Furthermore, the Gd2O3 and Eu3+-doped Gd2O3 nanotubes, which inherit their parents' morphology, were obtained during a direct annealing process in air. The corresponding Gd2O3:Eu3+ nanotubes exhibit the strong red emission corresponding to the D-5(0)-F-7(2), transition of the Eu3+ ions under UV light or low-voltage electron beam excitation, which might find potential applications in the fields such as light-emitting phosphors, advanced flat panel displays, or biological labeling.