Hydrothermal Synthesis and Solid-State Laser Refrigeration of Ytterbium-Doped Potassium-Lutetium-Fluoride (KLF) Microcrystals

Hydrothermal methods are used for the first time to synthesize distinct crystallographic stoichiometries within the potassium-lutetium-fluoride phase diagram for applications in solid-state laser refrigeration. Four crystalline phases were synthesized hydrothermally and doped with 10% Yb(III) ions, namely, orthorhombic K2LuF5 (space group Pnma), trigonal KLuF4 (space group P3(1)21), orthorhombic KLu2F7 (space group Pna2(1)), and cubic KLu3F10 (space group Fm (3) over barm), with each phase exhibiting unique microcrystalline morphologies. Among the four phases, the most significant cooling was observed for the KLuF4 phase, which showed an overall refrigeration of 8.6 +/- 2.1 K below room temperature. Laser refrigeration for KLuF4 was measured by observing both the eigenfrequencies of optomechanical cantilevers in vacuum and also the Brownian dynamics of optically trapped microcrystals in water. Cooling was also observed for the first time for the K2LuF s phase in vacuum based on measurements of the mean luminescence wavelength of Yb(III) ions. Cooling was not observed with the other two phases.

Automated summary

Hydrothermal methods were used to synthesize four distinct crystal phases doped with Yb(III) ions within the potassium-lutetium-fluoride phase diagram, with the KLuF4 phase showing the most significant cooling effect and the K2LuF s phase demonstrating cooling for the first time in vacuum.