Ni^2＋掺杂透明ZnO-Al2O3-SiO2系微晶玻璃的光学性质

采用传统熔融冷却的方法制备了透明Ni^2＋掺杂ZnO-Al2O3-SiO2系玻璃，结合X-射线、吸收和荧光等测试手段，研究了不同热处理温度对Ni^2＋掺杂透明ZnO-Al2O3-SiO2系微晶玻璃光学性质的影响。由X-射线衍射谱鉴定出微晶玻璃中析出的晶相为ZnAl2O4微晶，其尺寸在13nm以下。玻璃中没有发现近红外发光，而在微晶玻璃中存在宽带近红外发光，其可归属为八面体六配位Ni^2＋离子的^3T2g（^3F）激发态向^3A2g（^3F）基态的跃迁。随热处理温度升高发光强度增强，而发射峰位则发生蓝移；荧

不同烧蚀条件下飞秒激光脉冲诱导ZnO纳米结构研究

烧蚀条件对飞秒激光脉冲诱导氧化锌纳米结构有重要影响。研究了800nm,150fs,250kHz的飞秒激光脉冲分别在空气中,去离子水中以及无水乙醇中垂直聚焦于氧化锌晶体表面,诱导形成不同形态的纳米结构。实验结果表明,在空气中利用飞秒激光脉冲辐照样品表面,形成了周期为180nm的纳米线;在去离子水中辐照诱导形成了由氧化锌纳米线聚集而成的"纳米球";在无水乙醇中形成出现分叉结构的纳米线。拉曼光谱分析辐照前后晶体晶相结果表明,形成的纳米结构相对于辐照前特征峰437cm-1强度有所下降,在570cm-1处的峰值则显著增强。分析了在各种烧蚀条件下诱导形成纳米结构的演化过程以及物理机理。

Descoloração e Mineralização de Corantes Reativos por Processo Fotocatalítico Utilizando ZnO e Radiação UV

As indústrias consomem volumes elevados de água e outras substâncias químicas na síntese dos seus produtos e geram grande quantidade de rejeitos. Entre os mais importantes poluentes encontrados nos efluentes dessas indústrias estão os corantes sintéticos que representam um problema, pois não são facilmente destruídos por tratamentos convencionais. A fotocatálise heterogênea tem sido considerada como uma alternativa efetiva no tratamento de efluentes contendo esses corantes. Neste trabalho, estudou-se a cinética de descoloração e o grau de mineralização dos corantes sintéticos reativos Yellow 145, Black 5, Red 4 e Blue 21 através da fotocatálise utilizando ZnO puro e impregnado com íons Fe2+ e Co2+. Testes preliminares foram realizados para otimizar a concentração dos corantes e a massa mínima de catalisador a ser utilizado nos experimentos fotocatalíticos. Além da fotocatálise, experimentos individuais de fotólise e adsorção também foram realizados, porém se mostraram poucos eficientes. Através da espectrofotometria UV-Vis, verificou-se o total descoramento individual dos corantes em aproximadamente 30 minutos de irradiação com ZnO. O grau de mineralização de cada corante foi determinado através de análise de carbono orgânico total (COT), atingindo-se cerca de 70 a 80% de mineralização após 240 minutos de tratamento fotocatalítico. Foram comparadas, ainda, as eficiências de cada fotocatalisador ZnO, Fe/ZnO e Co/ZnO na mineralização de uma solução contendo a mistura dos quatro corantes já mencionados após 240 minutos de reação. A eficiência na mineralização da mistura dos corantes seguiu a seguinte ordem: Co/ZnO (32%), ZnO (78%) e Fe/ZnO (87%). A reação de degradação fotocatalítica do corante Black 5 seguiu uma cinética de primeira ordem, enquanto que os corantes Yellow 145, Red 4 e Blue 21 seguiram uma cinética de ordem zero.

Luminescence properties of electron-hole-droplets in pure and doped germanium

This work contains 4 topics dealing with the properties of the luminescence from Ge.

The temperature, pump-power and time dependences of the photoluminescence spectra of Li-, As-, Ga-, and Sb-doped Ge crystals were studied. For impurity concentrations less than about 10¹⁵cm^-3, emissions due to electron-hole droplets can clearly be identified. For impurity concentrations on the order of 10¹⁶cm^-3, the broad lines in the spectra, which have previously been attributed to the emission from the electron-hole-droplet, were found to possess pump-power and time dependent line shape. These properties show that these broad lines cannot be due to emission of electron-hole-droplets alone. We interpret these lines to be due to a combination of emissions from (1) electron-hole- droplets, (2) broadened multiexciton complexes, (3) broadened bound-exciton, and (4) plasma of electrons and holes. The properties of the electron-hole-droplet in As-doped Ge were shown to agree with theoretical predictions.

The time dependences of the luminescence intensities of the electron-hole-droplet in pure and doped Ge were investigated at 2 and 4.2°K. The decay of the electron-hole-droplet in pure Ge at 4.2°K was found to be pump-power dependent and too slow to be explained by the widely accepted model due to Pokrovskii and Hensel et al. Detailed study of the decay of the electron-hole-droplets in doped Ge were carried out for the first time, and we find no evidence of evaporation of excitons by electron-hole-droplets at 4.2°K. This doped Ge result is unexplained by the model of Pokrovskii and Hensel et al. It is shown that a model based on a cloud of electron-hole-droplets generated in the crystal and incorporating (1) exciton flow among electron-hole-droplets in the cloud and (2) exciton diffusion away from the cloud is capable of explaining the observed results.

It is shown that impurities, introduced during device fabrication, can lead to the previously reported differences of the spectra of laser-excited high-purity Ge and electrically excited Ge double injection devices. By properly choosing the device geometry so as to minimize this Li contamination, it is shown that the Li concentration in double injection devices may be reduced to less than about 10¹⁵cm^-3 and electrically excited luminescence spectra similar to the photoluminescence spectra of pure Ge may be produced. This proves conclusively that electron-hole-droplets may be created in double injection devices by electrical excitation.

The ratio of the LA- to TO-phonon-assisted luminescence intensities of the electron-hole-droplet is demonstrated to be equal to the high temperature limit of the same ratio of the exciton for Ge. This result gives one confidence to determine similar ratios for the electron-hole-droplet from the corresponding exciton ratio in semiconductors in which the ratio for the electron-hole-droplet cannot be determined (e.g., Si and GaP). Knowing the value of this ratio for the electron-hole-droplet, one can obtain accurate values of many parameters of the electron-hole-droplet in these semiconductors spectroscopically.

Theoretical investigation of nonvolatile holographic storage in doubly doped lithium niobate crystals

We have studied theoretically the inherent mechanisms of nonvolatile holographic storage in doubly doped LiNbO3 crystals. The photochromic effect of doubly doped LiNbO3 crystals is discussed, and the criterion for this effect is obtained through the photochromism-bleach factor a = S(21)gamma(1)/S(11)gamma(2) that we define. The two-center recording and fixing processes are analytically discussed with extended Kukhtarev equations, and analytical expressions for recorded and fixed steady-state space-charge fields as well as temporal behavior during the fixing process are obtained. The effects of microphysical quantities, the macrophotochromic effect on fixing efficiency, and recorded and fixed steady-state space-charge fields, are discussed analytically and numerically. (C) 2002 Optical Society of America.