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 Sr_xBa_1-xNb₂O₆ (SBN, congruent composition x = 0.61) [1] and Ba_1-yCa_yTiO₃ (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.

Keywords:

• Light-induced absorption
• small polarons
• barium-calcium titanate (BCT)
• strontium-barium niobate (SBN)
• photo-dissociation

Acknowledgements

Support by DFG (Grad. College 695), by NATO (PST.CLG 977348) is gratefully acknowledged.