PHOTOLUMINESCENCE OF NOMINALLY PURE LITHIUM NIOBATE SINGLE CRYSTALS PRODUCED BY VARIOUS TECHNOLOGIES

Abstract

Volume and surface photoluminescence of congruent and stoichiometric lithium niobate crystals obtained with different technologies was studied. It was found that luminescence intensity in stoichiometric crystal was lower than in congruent one. Luminescence in the crystal volume is mainly caused by Nb_Li defects, while for the near-surface layer, luminescence quenching is observed in the long-wave ( ˃ 500 nm) region of the spectrum due to energy scattering on the crystal lattice vibrations and an increase in the luminescence intensity of the Nb_Nb⁴⁺-O^–-pair. It is shown that the luminescence bands with maxima at 426 and 446 nm are caused by the complex defects in the form of electron-hole pairs Nb_Nb⁴⁺-O^–, in which the niobium atom is bound to the oxygen atoms by a covalent and electrostatic bond. An increase in the Li/Nb ratio leads to a shift of the luminescence bands to the short-wave spectral region and to a change of the fundamental absorption edge of the studied crystals.