Model for the Electronic Structure of theKandLBands in Alkali Halides

Abstract

A speculative model is proposed for the origin of the $K$ and $L$ bands in alkali halide crystals. They are assigned to transitions of the ${F_2}^{+}$ center (an anion vacancy pair plus an electron). This is plausible under the assumption that there is a plentiful supply of anion vacancies in the crystal. It is in general qualitative agreement with experiment. In addition, it possesses an advantage over ascribing these bands to transitions of the $F$ center in that it explains the low quantum efficiency for photoconductivity observed in the $L$ region.