Hydrothermal Single-Crystal Growth of Lu2O3 and Lanthanide-Doped Lu2O3

The hydrothermal growth of bulk single crystals of lutetium oxide (Lu2O3) is reported. Crystals were grown at 600-650 degrees C at 2 kbar in water with high concentrations (10-20 M) of KOH as a mineralizer. Under these conditions crystals formed spontaneously and could also be transported to suitable seeds to form large (3-8 mm/edge) single crystals. Experiments were done to optimize transport conditions and the quality of the crystals for the first time. The crystals were doped with trivalent laser active ions such as Er3+ and Yb3+. Absorption spectra of the doped materials were determined. Thermal conductivities of the pure single crystals as well as of the Yb-doped crystals were determined between room temperature and 77 K. The conductivity of the pure crystals increases significantly at lower temperatures as expected, and is significantly greater than that of YAG. The Yb-doped crystals have a thermal conductivity almost unchanged from the pure host, which is promising for use in high-energy laser applications.