Light induced charge transfer processes in Cr doped Bi 12GeO 20 and Bi 12SiO 20 single crystals

Abstract

Optical absorption and ESR spectra of Bi 12GeO 20 doped with Cr were measured before and after illumination with visible light. It was found that Cr 4+ ions in tetrahedral position are responsible for light induced ESR and optical spectra. The g-factor of the center is 1.945 ± 0.002. Crystal field parameters for the Cr 4+ center are D q = 820 cm −1 and B = 429cm −1. The photochromic effect is explained in terms of a Cr 5+−Cr 4+ charge transfer process.