Neutron diffraction studies were made of 2 single crystals, doped with 6 or 12mol%UF3. This revealed anionic vacancies on the normal F− ion site and excess anions on an interstitial site, F″. The ratio of F″ sites to anionic vacancies and to U3+ dopant cations indicated that the cluster was of the 1:0:n (n = 2, 3) type that was found in LaF3–doped solid solutions. Electron paramagnetic resonance measurements of isolated U3+ ions (<0.05%) showed that they were at a tetragonal site, where the trivalent U3+ ion replaced a divalent Ca2+ ion; with a charge-compensating F− ion situated along the <100>-axis. The local modes of vibration of H− ions in crystals of CaF2:UF3, that were double-doped with H− ions, revealed clusters at intermediate U3+ dopant concentrations (0.1 to 10mol%). At very low concentrations, electron–phonon splitting (0.6/cm) of the xy vibration of the H− ion was evident.

The Defect Structure of CaF2:U3+. J.A.Campbell, J.P.Laval, M.T.Fernandez-Diaz, M.Foster: Journal of Alloys and Compounds, 2001, 323-324, 111-4