Advances in Processing of Transparent Lutetia-Based Ceramics for High Power Laser Applications

Abstract

Conventional and scalable methods of green-body formation of powder compacts, along with temperature/pressure processing methods, were optimized to sinter Lu2O3 powder compacts to relative densities of 97-98%, with micrometer-sized grains. Post-HIPing at or below sintering temperatures yielded theoretically dense ceramics. A key development was the use of LiF vapor produced adjacent to the compact in the furnace environment, which physisorbed onto particle surfaces of the pre-sintered compact. Lowering grain boundary energy, it acted as a grain growth inhibitor and hence a remarkable sintering aid. An important focus of the work was processing steps which mitigated gap retention between spray dried granules in powder compacts, which ultimately negatively affected transparency. Optical transparency up to 99.1% of theoretical transparency at 1100 nm was achieved. The optimized processing parameters from the undoped work translated well to the development of Yb3+-doped lutetia ceramics. Dopant concentrations of up to 16-mol% Yb3+ were studied. Fully miscible solid-solution of the ytterbia and lutetia were confirmed at all studied dopant concentrations. Transmittance of optimally processed specimens approached theoretical limits and was especially good at the highest doping levels. Photoluminescence measurements implied quenching effects at higher doping levels, which were attenuated after sample thinning.