Color Centers in CsCl-Type Alkali Halides

Abstract

A study of x-ray-induced color centers in the CsCl-type alkali halides has been made at room, liquid nitrogen, and liquid helium temperatures. The gross features of this coloration are similar to those observed in NaCl-type alkali halides, namely a principal absorption band in the visible portion of the spectrum with other absorptions at both longer and shorter wavelengths. The absorption spectra observed vary with the temperature of irradiation; the bands show characteristic thermal shifting and broadening, bleach under both thermal and optical excitation, and demonstrate much of the usual color-center behavior. At the same time some characteristics of the cesium halides appear to be unique, in particular the multiplicity in structure which makes its appearance in the principal absorption bands of CsCl and CsBr at liquid helium temperature. Since the principal absorption gives every evidence of being associated with the $F$ center, one possible explanation of the component structure is that it arises from higher excited states of the $F$ center.