Electron spin resonance, photoconductivity, thermally stimulated conductivity, photoluminescence and thermoluminescence measurements were made of single crystals at 4.2 to 290K. Two sorts of O– shallow hole center were revealed which were responsible for 2 temperature regions of photoluminescence and photoconductivity enhancement: below 70K and 100 to 150K. Both O– centers were identified by their electron spin resonance spectra. At low temperatures, the photoluminescence and photoconductivity did not depend essentially upon the crystal type or quality. At 100 to 150K, both quantities depended strongly upon the defect content and vanished in well-oxidized crystals. It was shown that O– centers served as radiative electron–hole recombination centers with energy levels at 0.08 and 0.16eV above the top of the valence band. Because electrons were mobile in KTaO3, the thermally stimulated conductivity and thermoluminescence were both attributed to thermal ionization of the same shallow donor centers; which were related to isolated O vacancies.

Light-Induced Defects in KTaO3. V.V.Laguta, M.D.Glinchuk, I.P.Bykov, A.Cremona, P.Galinetto, E.Giulotto, L.Jastrabik, J.Rosa: Journal of Applied Physics, 2003, 93[10], 6056-64