Shake-up excitations and core-hole screening in Eu systems

X-ray photoemission (XPS) spectra of the Eu $3d$ and Eu $4d$ core levels in Eu metal and in divalent and trivalent Eu compounds exhibit splittings into two components, caused by the occurrence of $4f^6$ and $4f^7$ final-state configurations. The observed phenomena are described in terms of final-state shake-up and shake-down processes accompanied by a decrease, respectively, increase of the $4f$ occupation number. An extension of the Kotani-Toyozawa model to $f$ and $d$ states gives a consistent description of both processes.