Ultraviolet photorefractivity features in doped lithium niobate crystals

In this work we studied photorefractive effect of lithium niobate (LiNbO₃) doped with Zn, In, and Na at ultraviolet (UV) wavelength down to 3510.3em0exnm. It is found that the UV photorefraction of LiNbO₃ doped with Zn, In, or Na was enhanced significantly as compared to that of the nominally pure LiNbO₃. Our results show that the statement that the property of resistance against photorefraction in highly Zn and In doped LiNbO₃ is correct only in visible light range. By contrary, these crystals exhibit as excellent photorefractive characteristics in UV. We also find that there are doping concentration threshold values of Zn and In for the disappearance of the light-induced lens-like effect both in visible and in UV, but such concentration threshold values are not found for UV photorefraction within the highest doping concentrations we used. In highly Zn or In doped LiNbO₃ crystals, diffusion dominates over photovoltaic effect and electrons are determined to be the dominant charge carriers in UV photorefraction. The results are of interest to the study on the defect structure of LiNbO₃. Further investigation on this field is greatly urgent.