Photoluminescence and patricualarities of defective structure of congruent and near-stoichiometric lithium niobate crystals obtained by different technologies

Photoluminescence was studied in the volume of congruent and near-stoichiometric lithium niobate crystals obtained by different technologies. Luminescence intensity in near-stoichiometric crystals was found to be lower than that in a congruent crystal. We have shown that not only basic centers (caused by point defects Nb$_{Li}$, $V_{Li}$) contribute to luminescence, but also complex defects caused by existence of OH-groups.