Abstract: A device for absorption of selected radiation wavelengths, such as solar radiation, for producing heat energy, consists essentially of a single film or layer of a mixture of metal particles and a dielectric material which are coated on a supporting substrate of either metal or glass. The metal and dielectric concentration varies in a gradual transition from a major portion, up to 100%, of metal at one boundary surface to a major portion, up to 100%, of dielectric at the opposite boundary surface. There are no interior boundaries in the film; the film composition is inhomogeneous between the boundary surfaces and substantially homogeneous in planes generally parallel to the boundary surfaces. Dielectric materials and metals are disclosed in combinations adapted for solar radiation absorption over a broad band of wavelengths, on the order of from 0.35 to 1.