Comparative optical study of thulium-doped YVO4, GdVO4, and LuVO4 single crystals

YVO4:Tm3+ crystals grown by the Czochralski technique and GdVO4:Tm3+ and LuVO4:Tm3+ crystals grown by the floating-zone technique were investigated using methods of optical spectroscopy. Polarized absorption and emission spectra were recorded at room temperature and at 6 K. The crystal-field analysis was performed assuming the D-2d site symmetry for Tm3+ ions. In this way the missing crystal-field components of the H-3(6) ground multiplet were located. Room temperature absorption spectra were analyzed in the framework of the Judd-Ofelt theory. Evaluated radiative lifetimes of luminescent levels of Tm3+ follow a general trend diminishing in agreement with the sequence: YVO4:Tm3+-> GdVO4:Tm3+-> LuVO4:Tm3+. Luminescence lifetimes measured for the systems under study are similar except for the F-3(4) lifetime, which appears to be surprisingly short for LuVO4:Tm3+. Anisotropy of optical spectra is particularly pronounced in LuVO4:Tm3+. Peak absorption cross section for the band relevant for optical pumping at about 805 nm is roughly three times higher for pi polarization. Stimulated emission cross sections for the F-3(4)-H-3(6) transition near 1800 nm were evaluated using the reciprocity method. The diode-pumped continuous wave laser operation in GdVO4:Tm3+ with a slope efficiency of up to 40% is demonstrated. In LuVO4:Tm3+ the diode-pumped laser oscillation in a pulsed mode was observed.