Infrared-to-visible conversion of radiation in YVO4 crystals doped with Yb3þ and Tm3þ ions

Up-conversion processes in Yb3þ and Tm3þ doped YVO4 crystals have been investigated upon continuous wave and short pulse excitation around 975 nm. The energy transfer efficiency from Yb3þ to Tm3þ has been experimentally assessed, using results of pulsed laser excitation. Infrared emission originating in the 3H4 level and a considerably weaker blue emission originating in the 1G4 level of Tm3þ 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 3H4 emission and a three-step excitation one of the 1G4 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 þ 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 3H4–3H6 transition of Tm3þ may offer a laser potential. q 2004 Elsevier B.V. All rights reserved.