Comparative optical study of thulium-dopedYVO4,GdVO4, andLuVO4single crystals

Abstract

$\mathrm{Y}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$ crystals grown by the Czochralski technique and $\mathrm{Gd}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$ and $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$ 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 $6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The crystal-field analysis was performed assuming the ${D}_{2\mathrm{d}}$ site symmetry for ${\mathrm{Tm}}^{3+}$ ions. In this way the missing crystal-field components of the $^{3}H_{6}$ 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 ${\mathrm{Tm}}^{3+}$ follow a general trend diminishing in agreement with the sequence: $\mathrm{Y}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}\ensuremath{\rightarrow}\mathrm{Gd}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}\ensuremath{\rightarrow}\mathrm{Lu}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$. Luminescence lifetimes measured for the systems under study are similar except for the $^{3}F_{4}$ lifetime, which appears to be surprisingly short for $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$. Anisotropy of optical spectra is particularly pronounced in $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$. Peak absorption cross section for the band relevant for optical pumping at about $805\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ is roughly three times higher for $\ensuremath{\pi}$ polarization. Stimulated emission cross sections for the $^{3}F_{4}\text{\ensuremath{-}}^{3}H_{6}$ transition near $1800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were evaluated using the reciprocity method. The diode-pumped continuous wave laser operation in $\mathrm{Gd}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$ with a slope efficiency of up to 40% is demonstrated. In $\mathrm{Lu}\mathrm{V}{\mathrm{O}}_{4}:{\mathrm{Tm}}^{3+}$ the diode-pumped laser oscillation in a pulsed mode was observed.