Lutetium is used in phosphors (Rare earth activated lutetium oxysulfide phosphor for direct x-ray detection (2005)), and scintillators for X-ray detection (Lutetium Oxide-Based Transparent Ceramic Scintillators (2013)).
The performance of NdYAG laser crystals can be enhanced by substituting yttrium ions in the host lattice by smaller lutetium ions which subsequently allows a larger proportion of Nd dopant: Lutetium Neodymium Doped Yttrium Aluminum Garnet (1972).
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All patent information has been obtained from Espacenet (European Patent Office).