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

本工作主要研究了经强电子脉冲辐照和随后的热处理后，在氯化钠单晶中形成的钠团簇(胶体)。NaC l中的Na团簇在2.10 eV处有一个特征光吸收带，由于团簇的大小不同，认为该吸收带由多个组分组成。本工作的目的是对激光强激发后的2.10 eV能带进行检测，以获得该能带的组成信息。(1)电子辐照和热处理在氯化钠溶液中产生Na团簇。(2)通过光学吸收测量分析Na团簇的形成。(3)光激发系统的建立和光谱测量。(4)激光激发后2.10 eV波段的研究。关于(1)和(2)项，在大阪大学ISIR用直线加速器进行电子辐照，在…上测量光吸收光谱每次处理样品后超过100K。对光谱各分量的高斯峰进行了详细的分析，发现Na团簇可能是由四个F中心聚集在(111)面上的复合体(即N1中心)形成的，而2.10 eV谱带在形成初期由两个谱带组成。利用单色仪与线阵CCD线性传感器的耦合，用时间分辨的方法观测了光吸收光谱。通过改变激发光强度、从激发到测量的延迟时间等条件进行测量，结果总是否定的。这些结果使我们得出结论：由于Na团簇的存在，强光激发不会对吸收带产生影响。这可能表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电子对吸收带的强烈激发效应完全不同，因为在同一系统中，电子辐照未经热处理的氯化钠单晶也观察到了饱和效应。较少

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