LIGHT-INDUCED CHARGE-TRANSPORT IN BATIO3 VIA 3 CHARGE STATES OF RHODIUM

By combined studies of electron spin resonance and optical absorption at low temperatures, the charge-transfer bands of Rh5+ and Rh4+ are identified to be peaked near 1.6 and 1.9 eV, respectively. On this basis, the light-induced charge-transfer processes in BaTiO3:Rh are unraveled at room temperature. It is shown that three charge states of Rh are involved, leading to two levels: the shallow Rh-4+/5+ and the deeper Rh-3+/4+ level. The optical behaviour of these two levels corresponds to those expected from a 'two-center' model. The present paper represents the first atomic-scale identification of three charge states of one element leading to optical 'two-level' response.