Crystalline perfection, Raman, UV-VIS-NIR and prism coupler investigations on Cz-grown pure and Zn-doped LiNbO3 single crystals

Abstract

Pure and Zn-doped (1 mol%) LiNbO₃ single crystals have been grown by the Czochralski technique. From powder X-ray diffraction analysis, the crystal structure and the lattice strains have been evaluated. The crystalline perfection analysis by high resolution X-ray diffraction revealed that the pure crystal is free from structural grain boundaries and contains predominantly vacancy defects whereas the doped crystal contains low angle structural grain boundaries. The Raman spectral studies indicate no variation in lattice vibrations with slight changes in the peak width and intensity. The Zn doping in crystals leads to an enhancement in optical transparency over the entire visible and near-infrared wavelength range and optical band gap. The prism coupler, refractive indices and birefringence measurements infer that the doped crystal is suitable for photorefractive applications in the ultraviolet wavelength region. The evaluated Li concentration by Raman and UV, as well as birefringence depicts that the grown crystals are congruent in nature with a slight deviation from stoichiometry.