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 4f^7 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 4f^7 state.