Optical Absorption of an Interstitial Alkali‐Earth Cation in an Alkali‐Halide Crystal

Using both the concepts of the polaron model of the electron‐excess color center and the valence‐electron model of atoms introduced in this paper, we have formulated a method to compute the optical absorption energy of an interstitial alkali‐earth cation contained in an alkali‐halide crystal. The numerical results are given for the interstitial ion Ca+ in KCl and KBr. The possibility of Kojima's model for the Z2 and Z3 bands is also discussed in this work.