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 $4d\to 4f$ excitations (the ${{N}_{4,5}}$ absorption edge) in nanoparticles of the phosphates LaPO _4 , CePO _4 , PrPO _4 , and NdPO _4 . We also present corresponding data for La $5p\to 5d$ excitations (the ${{O}_{2,3}}$ edge) in LaPO _4 . The results are compared with those from calculations by atomic multiplet theory and for the dipole contribution to the La $4d\to 4f$ transition from a calculation using time-dependent density functional theory (TDLDA). Agreement with the atomic multiplet calculations for the high-order multiplet spectra is remarkable in the case of the ${{N}_{4,5}}$ spectra. In contrast, we find that the shallow ${{O}_{2,3}}$ semicore excitations in LaPO _4 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.

Keywords

• inelastic x-ray scattering
• rare earths
• lanthanides
• non-dipole
• x-ray Raman scattering