Growth, microstructure and optical characteristics of doped LiNbO3:Gd and LiNbO3:Cu:Gd lithium niobate crystals

Double- and single-doped lithium niobate (LN) crystals were grown by Czochralski at air from platinum crucibles: sample 1 ([Cu] = 0.57, [Gd] = 0.07 wt%), sample 2 ([Cu] = 0.041, [Gd] = 0.076 wt%), sample 3 ([Gd] = 0.003 wt%), sample 4 ([Gd] = 0.01 wt%), sample 5 ([Gd] = 0.05 wt%) and sample 6 ([Gd] = 0.26 wt%). Macro- and microstructure of as-grown LiNbO3:Cu:Gd and LiNbO3:Gd crystals have been studied by optical microscopy. Laser conoscopy, photoinduced light scattering (PILS) and optical spectroscopy have studied optical transmission, optical uniformity and photorefraction in LN crystals. Such a composition have been determined for a four-component system Li2O–Nb2O5–CuO—Gd2O3, at which a highly compositionally and optically uniform LiNbO3:Cu:Gd crystal (sample 2, [Cu] = 0.041, [Gd] = 0.076 wt%) can be grown. Raman spectra in 180-grade scattering geometry have determined conditions for the excitation of transverse and longitudinal polar modes during Raman scattering in LiNbO3:Cu:Gd crystals. A great increase in 175 and 603 cm−1 Raman bands intensities has been detected at an increase in copper concentration; it has been explained as a manifestation of photorefractive effect.