Interstitial halogen centers in X-irradiated CsBr

Abstract

Interstitial halogen centers in CsBr produced by X-irradiation at liquid helium and liquid nitrogen temperatures are studied and the assignment of several absorption bands associated with these centers is made. The most prominent bands formed by X-irradiation at liquid helium temperature are the F and H bands. Besides the known two σ-polarized absorption bands associated with the H center, another weakly π-polarized band at 1062 nm is found. The next prominent bands formed at liquid helium temperature are the α and I bands whose peak positions are at 205 and 236 nm, respectively. X-irradiation at liquid helium temperature also causes an absorption band at 324 nm due to H′ center. It is shown that the height of H′ band is proportional to the square of the height of the H band, suggesting that the centers associated with the H′ band are di- H-centers. Optical and thermal bleaching of the H bands causes the increase in H′ band. The study of the thermal annealing properties of H′ band suggests the composite nature of the band. After the H bands are thermally bleached three absorption bands at 425, 502 and 1060 nm are found to grow whose source might be the interstitial atom associated with an impurity. X-irradiation at liquid nitrogen temperature has produced the F and V 4 centers, the latter of which has absorption band at 276 nm. The V 4 center has 〈100〉 orientation. The formation and thermal bleaching properties of the H′ and V 4 bands are compared.