Infrared-to-visible conversion of radiation in YVO 4 crystals doped with Yb 3+ and Tm 3+ ions

Abstract

Up-conversion processes in Yb 3+ and Tm 3+ doped YVO 4 crystals have been investigated upon continuous wave and short pulse excitation around 975 nm. The energy transfer efficiency from Yb 3+ to Tm 3+ has been experimentally assessed, using results of pulsed laser excitation. Infrared emission originating in the 3H 4 level and a considerably weaker blue emission originating in the 1G 4 level of Tm 3+ 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 3H 4 emission and a three-step excitation one of the 1G 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 YVO 4: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 3H 4– 3H 6 transition of Tm 3+ may offer a laser potential.