Growth and spectroscopic properties of Er:Yb:KGd(PO_3)_4 crystal as a promising 155 μm laser gain medium

An Er:Yb:KGd(PO3)4 crystal doped with 1.83 at.% Er3+ and 3.98 at.% Yb3+ was grown by the top seeded solution method, and polarized spectroscopic properties of the crystal were investigated at room temperature. Fluorescence lifetimes of the 4I11/2 and 4I13/2 multiplets of Er3+ were measured to be about 1.54 μs and 6.32 ms, respectively. Fluorescence quantum efficiency of the 4I13/2 multiplet of Er3+ and energy transfer efficiency from Yb3+ to Er3+ were estimated to be 60% and 62%, respectively. The results indicate that the spectroscopic properties of the Er:Yb:KGd(PO3)4 crystal related to 1.55 μm laser operation are comparable to those of the commercial Er:Yb:phosphate glass and the crystal is a promising gain medium for the eye-safe 1.55 μm laser.