The invention is a method of vacuum evaporation of a multi-element sulfur bearing thin film compositions onto a substrate. The method comprises targeting a source of gas or vapour sulfur species at one or more source materials that make up at least part of the thin film composition during evaporation of the source materials. The sulfur species is heated to a high temperature as it reaches the one or more source materials and there is a chemical interaction of the sulfur species with evaporant from the one or more source materials during deposition of said thin film composition. The method is particularly useful for the deposition of phosphors for full colour ac electroluminescent displays employing thick film dielectric layers with a high dielectric constant.