Effect of temperature on optical properties and thermal conductivity of vanadate crystals doped with thulium and erbium

Influence of temperature on spectroscopic and thermal properties of Tm3+ and Er3+ -doped GdVO4 and LuVO4 crystals was examined. Polarized absorption and emission spectra as well as excited state luminescence lifetimes have been measured and analyzed especially at cryogenic temperatures in the 1.5-1.6 μm and 1.8-1.9 μm spectral ranges to assess laser qualities of these materials. The emission cross sections for 4I132→4I15/2 (Er) and 3F4→3H6 (Tm) transitions at T = 77 K were determined and confronted to the results obtained at room temperature. Effective emission cross sections estimated for aforementioned erbium and thulium transitions indicate that effective laser operation at cryogenic temperatures can be achieved in the gadolinium and lutetium vanadate crystals. Efficiency of laser material depends on its ability to heat distribution upon high-power energy pumping process. Accordingly, it has been found that the anisotropy of thermal conductivity for the undoped crystals is weakly influenced by the temperature albeit conductivity values for the GdVO4 are higher than those for LuVO4 at all temperatures. Incorporation of erbium or thulium ions results in a decrease of thermal conductivity in the two vanadate crystals and an anomalous temperature dependence of thermal conductivity in the LuVO4 was observed. Anisotropy of temperature dependence of thermal conductivity was found for the LuVO4:3.2 at%Tm3+ crystal. In this case the thermal conductivity along c-axis is inferior to that along a-axis of the crystal.