For ion-assisted deposition of thin MgF2 and YbF3 films a gridless end-Hall ion source has been used. The effects of ion energy, ion current and different working gases on the optical and mechanical properties of the single layers, deposited at ambient temperatures, have been investigated. For both materials, IAD with xenon proved to be superior to argon and argon-oxygen mixture, respectively. Compared to hot conventional films, the refractive indices of single layers deposited with optimized parameters could be increased. No significant absorption was observed in the vis spectral range for these layers, in the UV spectral range low absorption for IAD-coatings was achieved. With respect to the mechanical properties, the optimized IAD-MgF2-films were comparable to conventional coatings, and the durability of YbF3-films could be clearly enhanced by the applied IAD-process.