Infrared optical characterization and energy transfer of Na5Lu9F32 single crystals co-doped with Er3+/Tm3+ grown by Bridgman method

This paper reported on successful preparation of Na5Lu9F32 single crystals co-doped with ∼2 mol% Er3+ and various Tm3+ concentrations from 0.7 mol% to 3.2 mol% by Bridgman method. The J-O intensity parameters of Er3+ were calculated and analyzed according to the absorption spectra. The fluorescence decay curve at Er3+:4I13/2 level was measured to investigate the luminescent properties of the Er3+/Tm3+ co-doped Na5Lu9F32, and the energy transfer process between Er3+ and Tm3+. An intense 2.7 μm emission was achieved with Tm3+ ions sensitizing Er3+ ions under the 800 nm LD pumping. The maximum emission intensity at 2.7 μm was obtained at about 3.2 mol% doping concentration of Tm3+ when the concentration of Er3+ ions was fixed at ∼2 mol% in the current research. The calculated maximum value of emission cross section at 2.7 μm was 2.22 × 10−20 cm2, and energy transfer efficiency from Er3+:4I13/2 to Tm3+:3F4 was 78%. The electric dipole-dipole interaction was dominant for the energy transfer from Er3+ to Tm3+ ions by using Inokuti-Hirayama's model.