Study on OH~- Absorption Spectra in Highly Mg-doped Lithium Niobate Crystals at Low Temperature

The infrared absorption spectra of lithium niobate crystals and highly Mg-doped lithium niobate were measured at low temperature,and the change with the temperature was observed.It was found that the OH- absorption peak of pure lithium niobate crystals don' t changed with temperature but the peak position of OH- absorption spectra in highly magnesium-doped lithium niobate crystals moves to the high wavenumber with the temperature decreasing.From the analysis of the defect model in two types of crystals and the location of H+ there,the above observations were explained.In contrast with the case of pure lithium niobate crystals,the H+ directly participant in defect complex and distribute very near the highly-charged impurity defects in highly magnesium-doped lithium niobate crystals,which causes the OH- absorption peak varies with changing temperature.The increasing interaction between defects in complex is suggested to be the origin of the blue shift of OH- absorption peak with the decrease of the temperature.