The effect of Mg²⁺ ions in Er³⁺,Tm ³⁺-codoped LiNbO₃ single crystal

Absorption, photoluminescence (PL), and PL excitation (PLE) spectra are studied for LiNbO₃ (LNO) single crystal doped with Er (0.2 wt%), Tm (0.3 wt%), and Mg (2.6 wt%), LNO crystal doped with Er (0.3 wt%), and LNO crystal doped with Tm (0.2 wt%). The same absorption and PL bands due to Er ³⁺ and Tm³⁺ as observed in the singly doped LNOs are observed in the Mg-codoped LNO. Additional PL and absorption bands are not observed in the Mg-codoped LNO, indicating that the energy states of Er and Tm are not changed by Mg even if Mg ions are located close to Er and Tm ions. It is found that the wavelengths of the PL band peaks due to Tm (also Er) are not changed in the Mg-codoped LNO but the intensity ratio among the Tm (Er) emission components is changed. These results are understood by the energy transfer between Tm and Er or by the Mg doping effect. It is concluded that Mg does not influence the electronic states of Er and Tm in LNO, but it influences the emission spectra of Er and Tm.