Defects in inorganic photorefractive materials and their investigations

Abstract

We have spread out the rich field of defects in most of the inorganic photorefractive materials investigated at present. The aim is to contribute to the improvement of their performance in their various applications. Emphasis was therefore first on the elucidation of the identity of the defects and their microscopic defect structures. Studies by EPR and related methods, such as ODMR and ENDOR, are unsurpassed for this goal. Second, in order to connect these data to the photorefractive effect, close links to the optical defect phenomena have been established where possible. Here a strong tool is ODMR via the MCD of a defect. Furthermore, it is seen that the analysis of the changes of optical absorption, EPR, and MCD in photochromic materials under varying pumplight illuminations can furnish a systematic approach to the identification of defects and the paths of light-induced charge transfers between them. Also, a quantitative assessment of the photorefractive performance of a material can be derived from this method. It applies to all defects, independent of whether they are identified by EPR or not. While the results presented in this chapter are more of a basic nature, it is anticipated that they will establish a foundation on which the further chapters in the book, focusing on the details of the photorefractive effect in most of the materials treated here, can be linked to the microscopic origins of the phenomena.