Divalent admixtures to the trivalent ground-state configurations of Pr and Nd in transition-metal compounds

Resonant photoemission spectra at the 3→d4f absorption threshold are presented for some Pr and Nd transition-metal compounds. It is shown that the shape of spectra varies strongly with the composition of the compounds. Hybridization of the $4f$ electrons with valence-band states can lead to giant effects resulting in energy splittings of $4f$ emission by several electron volts. The phenomena are described quantitatively in the framework of a single-impurity Anderson model. Large splittings of the $4f$ emission are obtained if the energy position of the bare $4f$ state coincides with maxima of the valence-band density of states. For the 4fⁿ ground states, admixtures of 4fⁿ⁺¹ states of the order of some percent are obtained. Contributions of valence states to the resonant photoemission process are discussed.