Mixed valence of Yb 3S 4

Abstract

Reflectivity and photoemission spectra of a mixed-valence semiconductor, Yb 3S 4, were measured for the investigation of the electronic structure and the mean valence. The mean valence was determined to be 2.67 by the 4f and 5p photoemission spectra. The energy gap was recognized to be 0.4 eV by the optical conductivity spectrum, but the absorption coefficient is small. The energy gap is considered to consist of the occupied S-3p and the unoccupied Yb 3+ -4f states.