Crystal field theory treatment of S2 ion impurity centres with Oh, D4h, C4v and C2v symmetry in alkali halides

The effect of impurity anions on the electron transitions in alkali halide phosphors has been studied. The energies of electron transitions have been calculated for O_h, D_4h, C_4v and C_2v symmetries in the cases of strong and weak fields. The theoretical model has been shown to agree satisfactorily with experimental data assuming the formation of higher symmetry impurity centres to be more probable.