Valence photoelectron spectroscopy of Gd silicides

${\mathrm{Gd}}_3$ ${\mathrm{Si}}_5$, GdSi, and ${\mathrm{Gd}}_5$ ${\mathrm{Si}}_3$ were investigated with photoemission spectroscopy in the photon-energy range 40.8–149 eV by exploiting the energy dependence of the photoemission cross sections and the valence resonance at the crossing of the Gd 4d-4f threshold. The modification of the spectra versus photon energy, along with their stoichiometry dependence, show the relevance of covalent mixed Gd 5d–Si 3sp states in the formation of the chemical bond. In the region close to the Fermi level an increase of the d contribution is observed. These points are discussed in connection with the existing models of the silicide bond.