Charge transfer processes and dynamic equilibrium of electronic state occupancies in optically excited SrTiO3:Cr crystals

Spectral and kinetic measurements of (2)E --> (4)A(2) photoluminescence (PL) in SrTiO3 crystals containing small amounts of Cr were performed and a strong effect of IR illumination on the PL was observed. The dominant photoionization mechanism of Cr-3 + PL excitation was established. The locations in the SrTiO3 band gap of Cr3+ donor levels (1.85 eV below the bottom of the conduction band) and of Cr4+ acceptor levels (1.4 eV above the top of the valence band) were found. A new mechanism of optical erasing of burnt spectral holes of the R lines in SrTiO3:Cr was determined.