LAUSR

Abstract Here we study the homogeneity of Eu 3+ -doped La 1-x Gd x PO 4 (x = 0, 0.11, 0.33, 0.55, 0.75, 0.92, 1) monazite-type solid solutions by a combination of Raman and time-resolved laser fluorescence spectroscopies (TRLFS) with complementary quasi-random structure-based atomistic modeling studies. For the intermediate La 0.45 Gd 0.55 PO 4 composition we detected a significant broadening of the Raman bands corresponding to the lattice vibrations of the LnO 9 polyhedron, indicating much stronger distortion of the lanthanide cation site than the PO 4 tetrahedron. A distortion of the crystal lattice around the dopant site was also confirmed in our TRLFS measurements of Eu 3+ doped samples, where both the half width (FWHM) of the excitation peaks and the 7 F 2 / 7 F 1 ratio derived from the emission spectra increase for intermediate solid-solution compositions. The observed variation in FWHM correlates well with the simulated distribution of Eu···O bond distances within the investigated monazites. The combined results imply that homogenous Eu 3+ -doped La 1-x Gd x PO 4 monazite-type solid solutions are formed over the entire composition range, which is of importance in the context of using these ceramics for immobilization of radionuclides.