Core-level spectroscopy of the tetravalent lanthanide compounds M(3)LnF(7) (with M=Cs, Rb; Ln=Ce, Pr, Nd, Tb, Dy)

The series of tetravalent lanthanide (Ln) fluorides, M(3)LnF(7) (M=Cs, Rb; Ln=Ce, Pr, Nd, Tb, Dy), was investigated by X-ray absorption near-edge-structure (XANES) spectroscopy at the Ln-L(III), Ln-M(IV,V), and F-K absorption thresholds as well as by 3d core-level and valence-band photoemission. This systematic study includes all five Ln elements for which the tetravalent state has been stabilized so far. The observed multi-peaked spectra reflect the correlated electronic structure of these materials, which is characterized by strong 4f/ligand-p hybridization. A description of the Ln core-level spectra on the basis of a simplified Anderson single-impurity model reveals that the strength of the 4f/ligand-p hybridization increases in the sequence Cs2RbTbF7-->Cs2RbDyF7-->Cs2RbCeF7-->Cs2RbPrF7-->Cs2RbNdF7. XANES spectra at the F-K threshold were also studied as a direct monitor of holes in the ligand-p shell caused by covalent hybridization.