An EPR study of rare-earth impurities in single crystals of the zircon-structure orthophosphates ScPO4, YPO4, and LuPO4 a)

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Abstract
Ceramic materials based on the lanthanide orthophosphate series of compounds are known to be highly stable both chemically and physically. These characteristics have recently led to an extensive evaluation of these substances as potential primary containment media for the disposal of high‐level radioactive wastes. Since one important class of high‐level nuclear waste (i.e., reprocessed light water reactor spent fuel) contains a relatively high concentration of various lanthanides, the solid state chemical properties of the mixed rare‐earth and actinide‐doped orthophosphates are of considerable practical interest. The Kramers’ ions Ce3+, Nd3+, Dy3+, Er3+, Yb3+, and U3+ have been incorporated in single crystals of the tetragonal symmetry hosts ScPO4, YPO4, and LuPO4, and EPR spectroscopy has been used to verify the substitutional behavior of these ions and to investigate their electronic ground state properties. Principal axial spectroscopic splitting factors and hyperfine parameters were determined. These results are compared to those obtained for the same paramagnetic ions in other hosts characterized by crystal fields with tetragonal symmetry at the impurity‐ion site.