Stability of Color Centers in Alkali Halides

Abstract

Color centers have been formed in alkali halide crystals by exposing them to x‐rays, electron bombardment, and pile irradiation, and their stability with respect to temperature and light bleaching has been investigated. In general such crystals contain centers of non‐uniform stability. The lower the temperature at which the color centers have been produced, the more unstable they are on the average. In the absorption spectra taken at low temperature of crystals irradiated at low temperature new bands appear on the short wave‐length side of the F‐band which are never observed in crystals irradiated at room temperature and which, on warming the crystal to room temperature, vanish together with a part of the F‐centers. It is suggested that the instability of some of the color centers formed at low temperature is connected with the presence of these new absorption bands.