OH^-和氧离子杂质对BaF_2晶体辐照损伤的影响

Radiation Damage Induced by OH￣- and Oxygen Impurities in BaF_2 Crystal

从理论和实验两方面研究ＯＨ－和氧离子杂质对ＢａＦ２晶体辐照损伤的影响，并对其机理进行讨论．理论上用（ＨＦＳ－ＤＶＭ－Ｘα）局域密度离散变分法计算ＯＨ－和氧离子杂质心在ＢａＦ２中的电子结构，得到ＯＨ－，Ｈｓ－（Ｕ心），Ｏｓ－，Ｏｓ２－和（Ｏｓ２－－Ｆ＋）都可能是引起辐照损伤的源泉．实验发现，ＢａＦ２晶体水解处理后，ＯＨ－和氧离子杂质很容易进入ＢａＦ２，在晶体中的存在形式主要是：ＯＨ－占据阴离子位置，氧离子以Ｏｓ２－的形式占据Ｆ－的晶格位置，并由氟空位（Ｆ＋）作电荷补偿，较大可能以（Ｏｓ２－Ｆ＋）形式存在．γ辐照前后水解处理样品的光吸收谱（ＶＵＶ，ＵＶ，ＩＲ）和电子顺磁共振谱（ＥＰＲ）验证了理论计算的正确性．综合理论和实验，我们认为ＯＨ－氧离子杂质引起ＢａＦ２晶体辐照损伤的主要原因是：ＯＨ－和（Ｏｓ２－Ｆ＋）辐照分解成Ｈｓ－（Ｕ心）和Ｏｓ－．上海硅酸盐研究所在晶体生长工艺中，有意识地对ＯＨ－和氧离子给予特别的注意，在改进辐照损伤上获得较好的效果．

We have investigated the influence of the OH- and oxygen impurities on the radiation resistance of BaF2. The HFS-DVM-Xa method was employed to calculate the electronic structure of OH- and oxygen impurities in BaF2. The results were that the OH- , Hs (U center), Os, Os- and (Os-F+) center would be all the possible sources for the damage in BaF2. The experimente demonstrated that the OH- and oxygen impurities can be easily introduced into BaF2 by heating it under wet conditions and the most likely modes are that the OH- ions substitute for the site of anions and Os2- ions substitute for the fluorine associated with charge-compensating fluorine vacancies (Os2-F+). The VUV, UV, IR absorption and EPR spectra of the hydrolyzed and untreated BaF2 before and after irradiation verified our theoretical calculation. We proposed that the radiation damage observed in BaF2 containing OH- and oxygen can be explained that the OH- and (Os2-F+) are dissociated into Hs(U center) and Os through an irradiation.Great improvement was made in the radiation resistance of BaF2 by the Shanghai Institute of Ceramics when additional attention was put to the OH- and oxygen impurities during the growth of the crystals.