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-ban d photoemission. This systematic study includes all five Ln elements f or which the tetravalent state has been stabilized so far. The observe d multi-peaked spectra reflect the correlated electronic structure of these materials, which is characterized by strong 4f/ligand-p hybridiz ation. A description of the Ln core-level spectra on the basis of a si mplified Anderson single-impurity model reveals that the strength of t he 4f/ligand-p hybridization increases in the sequence 7-->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.