BISTABLE DEFECT SYSTEMS IN CDF2-M3+ (M=AL, GA, IN) AND THEIR PHOTOREFRACTIVE PROPERTIES

On the basis of the method recently used in the study of the trivalent impurity state in CdF2:M3+ (M: In, Ga, Sc and Y), the structure of th e electron trapped at an Al3+ centre in CdF2 is determined. Although a bistable system is obtained, due to the locally soft lattice around t he Al3+ ion the localized compact state has higher energy than the del ocalized state. The excited p-like states and the oscillator strengths for the optical transition between the sand p-like states in the thre e bistable systems (with Al, Ga, In) are evaluated. The changes in the refractive index as the systems change from localized to delocalized states are estimated, and the results are discussed in the context of the recently reported data on the photorefractive properties of In and Ga centres in CdF2.