Excited States of Cesium Halide Crystals

A model of the conduction band structure of cesium halide crystals is suggested. It combines the features of two earlier electron-transfer models by Fischer and Hilsch and by Klick and Kabler into one which, in the language of effective mass theory, amounts to requiring several, but at least three, separate conduction bands having a splitting of the order of 0.1 eV. On the basis of this model, both the fine structure of the cesium halide $F$ bands and the unusually high multiplicity of cesium halide exciton bands can be consistently understood. Further implications of the model are discussed.