Green up-conversion of Er3+ in KGd(WO4)2 crystals. Effects of sample orientation and erbium concentration

Abstract.Pumping with infrared light resonant to the energy position of 4I11/2 and 4I9/2 multiplets respectively has excited green up-conversion of Er3+ in KGd(WO4)2 single crystal. At room temperature the maximum green-emission intensity is achieved by pumping with light polarized parallel to the C2 symmetry axis of the crystal (//p) at 981 and 801.5 nm, while pumping with light parallel to the principal m axis (//m) has maximum up-conversion at 978.2, 806 and 800 nm. The emission is weakly polarized. The maximum of the emission peaks at 547.8 nm if the light is analyzed parallel to the C2 axis or at 552.4 nm for light perpendicular to it. The largest emission intensity was achieved with an erbium concentration about 3×1020 cm-3. A schematic model of the up-conversion process is suggested.