Optical absorption of F_Acentres in mixed ionic crystals

Abstract

The shift with concentration variation of the optical absorption FA band in KCl-KBr mixed crystals, with Li impurities is studied by means of the method of Bartram et al. (1968). The distortion around the FA centre is calculated considering the change in the repulsive and polarisation energies due to the impurity. The energy due to this distortion is obtained by a perturbative method. This correction gives good agreement with the experiment values for one of the two absorption bands of the FA centre, but not for the other. Calculations using several types of wavefunction are in approximate agreement with the experimental observations of Asami and Ishiguro (1986).