Enhanced red emissions and higher quenching temperature based on the intervalence charge transfer in Pr3+ doped LiNbO3 with Mg2+ incorporation

For investigating the effect of exceeding Mg2+ doping on optical properties and luminescent mechanism, detailed spectroscopic characterizations of Pr3+ (1 mol%) and Mg2+ (0 and 5mol%) doped congruent LiNbO3 (CLN) single crystals were studied. The exceeding Mg2+ doping of 5mol% was found to enhance the dominant red emissions (1D2→3H4) under 360nm excitation with a larger population of 1D2 via the Pr3+-Nb5+ intervalence charge transfer (IVCT). Quenching of blue-green emissions in Pr3+ doped CLNs was ascribed to the depopulation of 3P0 via IVCT state. The lifetimes related to 1D2→3H4 were significantly increased with Mg2+ incorporation at a temperature range from 20K to 430K. As the temperature rises, the progressively thermal quenching of the red emission and lifetime was observed, which was interpreted with the thermally activated energy transfer from the IVCT state to ground level 3H4. More importantly, exceeding Mg2+ doping led to a displacement of the IVCT state in the configuration coordinate diagram, resulting in larger quenching activation energy and higher quenching temperature (310K→370K) in Pr:Mg:CLN. The emission enhancement and quenching temperature increase at exceeding Mg2+ concentration were considered to be of practical value in luminescent and laser applications.