Parameters of light-induced charge transfer processes in photorefractive crystals

A method is outlined by which the parameters governing light-induced charge transfer processes in photorefractive crystals can be determined. The system BaTiO₃:Rh is treated as an example. EPR is used to obtain information on the EPR-active defect charge states. Through simultaneous observation of light-induced EPR-and optical absorption changes, the corresponding optical absorption bands are established as fingerprints of the defect charge states. Consistency arguments make it possible to label EPR-silent absorption bands in this way also, significantly extending the scope of EPR-based defect studies. On this basis, the charge transfer paths taking place under illumination are identified. Quantitatively, the defect concentrations are directly or indirectly derived from the available EPR signals. In addition, the kinetics of the light-induced changes of the densities of the occurring defect charge states are studied. In conjunction with the defect concentrations, this makes it possible to deduce the responsible transfer parameters.