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

Pumping with infrared light resonant to the energy position of I-4(11/2) an d I-4(11/2) multiplets respectively has excited green up-conversion of Er3 in KGd(WO4)(2) single crystal. At room temperature the maximum green-emiss ion intensity is achieved by pumping with light polarized parallel to the C -2 symmetry axis of the crystal (//p) at 981 and 801.5 nm, while pumping wi th light parallel to the principal m axis (//m) has maximum up-conversion a t 978.2, 806 and 800 nm. The emission is weakly polarized. The maximum of t he emission peaks at 547.8 nm if the light is analyzed parallel to the C-2 axis or at 552.4 nm for light perpendicular to it. The largest emission int ensity was achieved with an erbium concentration about 3 x 10(20) cm(-3). A schematic model of the up-conversion process is suggested.