Studies on the ultraviolet-light-induced absorption changes in congruent LiNbO3:Mg

By measuring the ultraviolet-light-induced absorption coefficient changes and the ultraviolet-light-gated two-color recording sensitivity at 633 nm, we found that the ultraviolet-light-induced absorption coefficient changes in congruent LiNbO3:Mg has a threshold effect with respect to the Mg-doping concentration. It is only when the concentration of Mg is more than 3.0 mol.% that the ultraviolet-light-induced absorption coefficient changes can be observed. This threshold value is lower than the well-known damage-resistant threshold value of 4.6 mol.% for Mg in congruent LiNbO3:Mg. We attribute the appearance of the ultraviolet-light-induced absorption coefficient changes to the elimination of the antisite defect NbLi and the formation of O−where a hole is trapped at a O2− site near a negatively charged center.