Photoemission studies of the electronic structure of EuO, EuS, EuSe, and GdS

Photoemission measurements on the magnetic semiconductors EuO, EuS, and EuSe show emission from 4f7 states which lie in the gap above the top of ∼2- to 3-eV-wide valence bands. These measurements, together with optical data, indicate semiconductor energy gaps of 4.3, 3.1, and 3.1 eV for EuO, EuS, and EuSe (all ±0.4 eV). Metallic GdS shows a narrow occupied conduction band at the Fermi level, in addition to a filled valence band and 4f7 state. © 1969 The American Physical Society.