EPR investigations of Gd3+ in single crystals and powders of the zircon–structure orthophosphates YPO4, ScPO4, and LuPO4

The tetragonal xenotime (YPO4) and monoclinic monazite (CePO4) orthophosphates are known to be chemically and physically stable in geological environments and are also radiation resistant. For these reasons, materials of this type are currently candidates for the primary containment of radioactive actinide solid wastes. Single crystals of the tetragonal orthophosphates YPO4, ScPO4, and LuPO4 doped with Gd3+ were grown by slowly cooling a Pb2P2O7 flux. Finely divided (<0.1 μ), rare-earth-doped powders of these materials were also prepared using a technique of precipitation in molten urea. Electron paramagnetic resonance investigations have shown that the Gd3+ impurities occupy identical substitutional sites in both single crystal and powder specimens of the tetragonal-symmetry orthophosphates. These results provide a basis for future investigations of the effects of heavy-particle radiation damage in the lanthanide orthophosphates.