Enhanced emission of Tm3+:3F4 → 3H6 transition by backward energy transfer from Yb3+ in Y2O3 for mid-infrared applications

Tm3+ doped luminescence materials have attracted great attention owing to their potential for achieving 2 μm laser. Here, we report that the 2 μm emission intensity of Tm3+:3F4 → 3H6 transition can be enhanced by as large as 1.8 times through introducing Yb3+ into Tm3+ doped Y2O3 upon 782 nm excitation, where the population of Tm3+:3F4 level is increased by backward energy transfer from Yb3+ following the forward energy transfer from the upper level Tm3+:3H4 to an intermediate level Yb3+:2F5/2. In addition, the efficiencies of Yb3+ to Tm3+ backward energy transfer are determined based on the analysis of emission spectra and fluorescence time profiles. It is found that the Yb3+ to Tm3+ backward energy transfer upon Tm3+ excitation at 782 nm is more efficient than the Yb3+ to Tm3+ energy transfer upon Yb3+ direct excitation at 980 nm, which is explained by the preferential excitation of Yb3+ with a nearby Tm3+ in the forward energy transfer from Tm3+ to Yb3+ upon Tm3+ excitation. Our results demonstrate that codoping Yb3+ into Tm3+ activated materials offers a promising approach to obtain efficient 2 μm laser, and the efficient backward energy transfer may play a key role in other rare earth ions doped luminescence materials.