Photorefractive Response in a Crystal with Three-Valence-States Impurity-Centers and Shallow Traps

We show that specific features of holographic recording such as a non-monotonic behavior of diffraction efficiency and the development of a latent image observing in some photorefractive crystals can be explained on the base of the band-transport model including deep donor centers (that allow double ionization) and shallow traps. It is shown that the cause of the some observing effects of the enhancement and the development of the photorefractive gratings is a spatial shift of charge gratings relative to one another without changing their amplitudes.