Infrared-to-visible conversion of radiation in YVO4 crystals doped with Yb3+ and Tm3+ ions

Up-conversion processes in Yb3+ and Tm3+ doped YVO4 crystals have been investigated upon continuous wave and short pulse excitation around 975 nm. The energy transfer efficiency from Yb3+ to Tm3+ has been experimentally assessed, using results of pulsed laser excitation. Infrared emission originating in the H-3(4) level and a considerably weaker blue emission originating in the (1)G(4) level of Tm3+ has been observed. The ratio of the IR to blue up-converted emission intensities is about 25:1 at room temperature. The dependence of the intensity of both emissions on the excitation power implies a two-step excitation mechanism of the H-3(4) emission and a three-step excitation one of the (1)G(4) emission. Temperature dependencies of IR and blue up-converted emission have been discussed based on optical absorption and emission spectra and lifetimes recorded at several temperatures between 4.2 and 300 K. Up-converted blue emission in YVO4:Yb + Tm is qualitatively similar to that observed in other matrices containing ytterbium and thulium but high intensity of up-converted IR emission associated with the H-3(4)-H-3(6) transition of Tm3+ may offer a laser potential. (C) 2004 Elsevier B.V. All rights reserved.