Photorefractive properties with multiple traps and two types of charge carriers in doped KNSBN crystals

Anomalous diffraction behavior is observed, for the first time to our knowledge, in doped KNSBN crystals. The space-charge field increases to its maximum value and then gradually decreases as the incident light intensity increases. Sublinear (x < 1) and superlinear (x > 1) dependence of the response rate on intensity, i.e. tau(-1) proportional to I-x, are obtained. We also find that the total amount of dark decay of the grating becomes even larger and the rate of dark decay of the grating is faster when the above nonlinearity diminished as x approaches to 1 in one of the samples used in experiments. A new model with multiple traps and two types of charge carriers is proposed to explain these results.