The absorption spectrum of KBr:Sn2+

Abstract

Thorough annealing on crystals of KBr.Sn2+ results in significant changes in their absorption spectra. These changes have been interpreted as the effect of the annealing on the relative concentration of different types of Sn2+ centres: isolated Sn2+ substitutional ions ("cubic" centres) and Sn2+–cation vacancy complexes ("tetragonal" and "rhombic" centres). The line shape of the optical absorption has been calculated theoretically, by diagonalizing the complete 12 × 12 Hamiltonian matrix, for cubic centres only, for tetragonal centres only, and for different relative concentrations of cubic and tetragonal centres. The experimental absorption spectra of KBr:Sn2+ crystals that have undergone various annealing treatments are in good agreement with theoretical spectra calculated for appropriate mixtures of the above centres. These results confirm that thorough annealing increases the fraction of isolated Sn2+ substitutional ions at the expense of the Sn2+–cation vacancy complexes. The consistency of the theoretical model is demonstrated by the agreement of the calculated moments of the absorption bands of KBr:Sn2+ with the experimentally derived values.