Mechanisms of writing and decay of holographic gratings in semiconducting CdF2:Ga

We consider the mechanisms responsible for the photoinduced change in the optical properties of semiconducting ${\mathrm{CdF}}_{\mathrm{2}}$ crystals with metastable Ga impurities forming DX centers. Unlike the case of compound semiconductors with DX centers (GaAlAs:Si, GaAlAs:Te, CdZnTe:Cl), this change is caused not by free electrons but by a redistribution of electrons between deep and shallow localized states. The resulting modification of the refractive index of the crystal allows writing of persistent holographic gratings at temperatures up to 200 K, high for this class of holographic materials. Holographic characteristics of ${\mathrm{CdF}}_{\mathrm{2}}\mathrm{:Ga}$ crystals such as refractive index change, sensitivity, and grating decay are described.