4f-ligand hybridization inCeF4andTbF4probed by core-level spectroscopies

X-ray absorption spectroscopy (XAS) at the 3d and 2p thresholds as well as 3d core-level photoemission (XPS) were used to investigate the electronic structure of ${\mathrm{CeF}}_4$ and ${\mathrm{TbF}}_4$. From non- atomic 4f-related spectral features in the 3d XAS spectra, 4f-ligand hybridization is clearly visible in the case of ${\mathrm{CeF}}_4$ and—less pronounced—in ${\mathrm{TbF}}_4$. For the latter compound, $L_3$-edge XAS data support the view of a finite 4f admixture to the Tb-F bonding orbitals, while the $L_1$-edge spectrum reflects more explicitly tetravalency. From 3d XPS measurements, an estimate of ≃12 eV is obtained for the core-hole–4f Coulomb interaction in ${\mathrm{TbF}}_4$. The high-energy spectra characterize both fluorine compounds as tetravalent insulators with covalent bonding and clearly show a decrease in 4f-ligand mixing, i.e., an increase in 4f localization, with respect to the corresponding dioxides.