The Eu—transition-metal compounds Eu${\mathrm{Ag}}_5$, Eu${\mathrm{Rh}}_2$, Eu${\mathrm{Pt}}_5$, and Eu${\mathrm{Pd}}_5$ were studied by resonant $4d\to 4f$ photoemission techniques. In divalent Eu${\mathrm{Ag}}_5$, a surface core-level shift of the final-state $4f^6$ multiplet components of 0.75 eV is found. For the trivalent Eu compounds Eu${\mathrm{Pt}}_5$ and Eu${\mathrm{Pd}}_5$ as well as for the mixed-valence compound Eu${\mathrm{Rh}}_2$, a surface valence change to the lower-valence state is observed. For Eu${\mathrm{Pt}}_5$, an inhomogeneously mixed-valence surface is noticed, pointing to a strong coordination dependence of the surface valence transition. The energy position of the final-state $4f$ screening orbital is discussed on the basis of $4d$ photoemission and photoabsorption threshold energies.

• Received 24 March 1983

DOI:https://doi.org/10.1103/PhysRevB.28.2017