Chapter 2 - Light-Induced Charge Transport in Photorefractive Crystals

Abstract

This chapter discusses light-induced charge transport in photorefractive crystals. The well-known one-center, two-center, and three-valence models are developed to describe the transport properties of lithium niobate and lithium tantalate at high light intensities, as well as perovskite, sillenite, and tungsten–bronzetype crystals. The so-called one-center model is developed to explain the transport properties of transition metal-doped LiNbO3 and LiTaO3 crystals at usual continuous-wave laser intensities. But in other cases, the situation is much more complicated. The interpretation of the experimental results for the charge transport requires the assumption of two or more interacting centers and/or of more than two valence states of the centers involved. Light-induced absorption effects and a nonlinear dependence of photoconductivity on light intensity are typical consequences of these models. For LiNbO3 and LiTaO3 at high intensities, the two-center model is applied. The second center is identified as NbLi polaron.