Shallow and deep impurity levels in undoped Rh- and Ce-doped photorefractive BaTiO3

The shallow and deep impurity levels in undoped, Rh- and Ce- doped as-grown BaTiO3 crystals were investigated. We have found two shallow impurity levels in all the crystals by light-induced absorption spectrum studies, and have determined their thermal depths. We identified that one of the shallow levels has the same defect origins in al the crystals, while the other shallow level has the same defect origins in the undoped and Ce-doped crystals. Thermo-induced absorption spectra in these crystals were studied for the first time and proved to be a useful method for observing the absorption peaks of deep impurity levels in photorefractive crystals. The thermal depths of the deep levels in these crystals were determined by studies of grating dark-decay. The thermal levels and corresponding optical transitions in the crystals were given.