Electron spin resonance (ESR) and dc-magnetization experiments have been performed in Gd-doped amorphous (a-)silicon films. The films were deposited by the cosputtering technique following different conditions rendering samples with varying Gd and hydrogen concentrations. In addition to films with different contents of impurities and, in order to probe the inuence of the atomic structure on the magnetic properties of the Gd species, the films were also submitted to laser-induced crystallization processing. Both ESR and dc-magnetization results show that Gd is incorporated as a trivalent ion (Gd3+) in the Si host. ESR data indicate a strong dependence between the Gd concentration and the density of Si dangling bonds. Moreover, the Gd3+ local environment is nearly insensitive to the Gd and H content, as well as to the atomic structure of the Si host. Along with gadolinium, other rare-earth species have been investigated and the main results are discussed.