Phenomenological characterization of photoactive centers in Bi12TiO20 crystals

Abstract

We report optical and electrical measurements contributing for a better characterization of the relevant photoactive center levels in undoped photorefractive Bi12TiO20 (BTO) crystals grown in Brazil. Comparative results for Pb-doped BTO and Bi12GaO20 are also reported. A center responsible for photochromism was identified at 0.42–0.44eV, probably below the conduction band (CB). The main electron and hole donor center is detected at 2.2eV from the CB and the equilibrium Fermi level is pinned at this level. Other localized centers were identified at different positions in the band gap and their relation with the behavior of BTO under different wavelengths and operating conditions is discussed with particular attention to holographic recording.