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.