Photo Dissociation of Blue-Light-Induced VIS-Centers in SBN:Ce, Cr and in BCT:Fe into Small Polarons at Low Temperatures

Abstract

The promising photorefractive single crystal systems SrxBa1-xNb2O6 (SBN, congruent composition x = 0.61) [1] and Ba1-yCayTiO3 (BCT, congruent y = 0.23) [2], can be doped with polyvalent ions like Fe, Cr, Ce to enhance and optimize their photorefractive properties. Illumination with blue Ar+-laser light at low temperature creates light-induced NIR and VIS absorption bands [3, 4]. The NIR absorption has been identified as being due to electron polarons (Nb4+ in SBN, Ti3+ in BCT) and their properties have been investigated in some detail [3, 4]. The VIS-Centers (at about 2 eV) are less well understood and their nature is still under discussion [5]. We could show that illumination with red Kr+-laser light (647 nm) leads to a dissociation of the VIS-Centers and a simultaneous build-up of a transient NIR-polaron absorption [5]. These features give new insight into the dynamic nature of these VIS-Centers.