High-resolution nonresonant x-ray Raman scattering study on rare earth phosphate nanoparticles

Abstract

We report high-resolution x-ray Raman scattering studies of high-order multipole spectra of rare earth 4d -> 4f excitations (the N-4,N-5 absorption edge) in nanoparticles of the phosphates LaPO4, CePO4, PrPO4, and NdPO4. We also present corresponding data for La 5p -> 5d excitations (the O-2,O-3 edge) in LaPO4. The results are compared with those from calculations by atomic multiplet theory and for the dipole contribution to the La 4d -> 4f transition from a calculation using time-dependent density functional theory (TDLDA). Agreement with the atomic multiplet calculations for the highorder multiplet spectra is remarkable in the case of the N-4,N-5 spectra. In contrast, we find that the shallow O-2,O-3 semicore excitations in LaPO4 manifest a relatively broad band and an apparent quenching of 5p spin-orbit splitting. The more sophisticated TDLDA, which has earlier been found to explain dipolar spectra well in Ba compounds, is less satisfactory here in the case of La.