Inverse photoemission of mixed-valence compounds and4finner-well stability

Abstract

We present the inverse photoemission spectra of compounds which unambiguously display either homogeneous or inhomogeneous mixed valence, TmSe, and oxidized SmS. The spectra show two $4f$ peaks, ${4f}^n$ and ${4f}^{n+1\mathrm{}}$, arising from the ${4f}^{n-1\mathrm{}}$ and ${4f}^n$ ground-state configurations. These data, along with inverse photoemission spectra on clean SmS, show that the $4f$ inner potential well is stable enough to contain one more $4f$ electron than in the divalent, atomic ground state. The valence deduced from the TmSe bremsstrahlung isochromat spectrum agrees well with that obtained from other spectroscopic studies.