LASER-EXCITATION EFFECT ON OPTICAL ABSORPTION BAND DUE TO METAL-CLUSTERS IN IONIC CRYSTAL AFTER ELECTRON IRRADIATION

本文主要研究了强电子脉冲辐照和热处理后在NaCl单晶中形成的钠团簇（胶体）。NaCl中的Na团簇在2.10eV处有一个特征的光学吸收带，由于团簇的大小不同，认为它是由许多组分组成的。本工作的目的是对激光强激发后的2.10eV波段进行检测，以获得该波段的组成信息。本研究按以下程序进行：(1)在NaCl中采用电子辐照和热处理法制备Na簇。(2)通过光学吸收测量分析Na簇的形成。(3)建立光激发系统和光谱测量系统。(4)激光激发后2.10eV波段的研究。对于第(1)项和第(2)项，使用大阪大学ISIR的LINAC进行电子辐照，每次处理后样品在…More 100K下测量光吸收光谱。根据光谱各分量高斯峰的详细分析，揭示了Na簇可能是由4个F中心在（111）平面上聚集形成的络合物（称为N_1中心），并且2.10eV波段在形成初期由两个波段组成。对于第(3)项和第(4)项，采用Nd:YAG和DYE激光器建立了强激发系统。利用单色仪和CCD线性传感器对光吸收光谱进行了时间分辨观察。通过改变条件进行测量；激发光强度，从激发到测量的延迟时间等。结果总是否定的。这些结果使我们得出结论，强光激发对Na团簇的吸收带没有影响。这可能说明了一个显著的结果，即自由电子对吸收带的强烈激发效应与局域激发效应完全不同，因为电子辐照后未经热处理的NaCl单晶在相同体系下观察到饱和效应。少

This work is mainly focussed on sodium clusters (colloids) formed in NaCl single crystal after intense electron pulse irradiation and subsequent heat treatment. The Na cluster in NaCl gives a characteristic optical absorption band peaking at 2.10eV, which is believed to be composed of a number of component due to clusters of various sizes. The purpose of this work is to examine the 2.10eV band after intense excitation with laserlight in order to get an information of the components of the band. The work has been carried out according to the following program:(1) Production of Na clusters in NaCl with electron irradiation and heat treatment.(2) Analysis of Na cluster formation through optical absorption measurement.(3) Setup of optical excitation system and spectrum measuring one.(4) Investigation of the 2.10eV band after laser excitation.As for terms (1) and (2), electron irradiation was carried out using a LINAC at ISIR, Osaka university and optical absorption spectrum was measured at … More 100K after each treatment of the sample. Detailed analysis on the basis of Gaussian peak of each component of the spectrum has revealed new facts that the Na clusters may be formed from a complex of four F centers aggregation in a (111) plane (so called N_1 center), and the 2.10eV band is composed of two bands at the initial stage of the formation.As for terms (3) and (4), setup of intense excitation system was made with a Nd:YAG and DYE laser. Optical absorption spectrum was observed with time resolved method using a monochromator coupled with a CCD linear sensor. Measurements were carried out by changing the conditions; the exciting light intensity, the delay time from the excitation to the measurement, etc. The results were always negative. These results lead us to the conclusion that no effect of intense optical excition can be observed on the absorption band due to the Na clusters. This may indicate a remarkable result that the intense excitation effect on the absorption band due to the free electron is completely different from that to the localized ones, since saturation effect is observed with the same system for electron irradiated NaCl single crystal without heat treatment. Less