Photoluminescence Spectroscopy of Doped and Undoped BaTiO3

Despite the many important potential applications for photorefractive BaTiO31, the precise nature and the depth of the photorefractive trapping centers has yet to be positively identified. In one study2, a correlation was noted between the iron concentration as measured with EPR, the photorefractive trap density determined by two-beam coupling versus grating wavevector measurements, and the optical absorption coefficient. This tentatively identified iron as the photorefractive center in commercially-grown, nominally undoped crystals. More recently, high photorefractive gains were reported in nominally iron-free BaTiO3 crystals3, and evidence was presented3,4 that, in purposely iron-doped crystals, the most common valence states for iron are Fe+3 and Fe+4.