A theoretical and experimental investigation of inhomogeneous CeO2-MgF2 and ZnS-Na3AIF6 anti-reflection coatings for the visible spectrai region has been made. By a proper choice of the refractive index profile, the reflectance may be considerably reduced. In the infrared region, Ge-MgF2 films on Ge substrates are shown to give a low reflectance with a small wavelength dependence.
Roland Jacobsson and John Olof Måensson, "Evaporated Inhomogeneous Thin Films," Appl. Opt. 5, 29-34 (1966)