Effect Of Mg Concentration On Structtur And Properties Of Mg, Mn Lithium Niobate

Mg:Mn:LiNbO₃ crystal series are grown by Czochralski method at the first time, and the crystals have no macroscopic defect and exhibit good optical homogeneity. Appropriate parameters (temperature gradient, pulling speed and rotating speed) are chosen during the crystal growth process to maintain the flat solid-liquid interface. The structures and properties of the crystals are analyzed by using infrared absorption spectrum, UV-Visible absorption spectra, XRD and two wave coupling methods.O-H absorption peak of Mg(6mol%):Mn:LiNbO₃ crystal shifts to 3537 cm^-1 compared with that of other crystals doped with lower Mg concentration 3484 cm^-1, which indicates that Mg doping concentration of 6mol% is over the threshold.With the increase of Mg doping amount, the absorption edge in ultraviolet-visible absorption spectra of Mg:Mn:LiNbO₃ crystal shifts to the violet and then inversely to the red when Mg doping concentration is up to the threshold. For the same specimen, the absorption edge shifts to the violet with the treatments of oxidization and reduction compared with as grown.XRD results show shat, with the increase of Mg doping amount, the lattice defect of Mg:Mn:LiNbO₃ crystals are increase and then decrease when Mg doping amount is up to the threshold. For the same specimen, the lattice defect is increase with the treatments from oxidization to as grown to reduction.The location of the doped ions in the crystals are analyzed by combining the measurement results of infrared absorption spectrum, UV-Vis absorption spectra, and XRD. The results show that the doped Mg, Mn ions can replace Li⁺,NbLi_<sup>4+ or Nb⁵⁺. Mn ions locate normal Li⁺ sites and then Nb⁵⁺ sites when Mg ions concentration is up to the threshold in the LiNbO₃ crystal. Mg ions entering LiNbO₃ crystal firstly substitute NbLi⁴⁺ and then occupied normal Li+ and Nb5+ sites when their concentration is up to the threshold.The photorefractive and photorefractive resistance properties are measured by two wave coupling and facula distortion method. The results show shat, with the increase of Mg doping amount, the diffraction efficiency decrease and the...