Method of manufacturing a luminescent sulfide

In the method of manufacturing a luminescent sulfide of at least one of the elements selected from the group consisting of zinc and cadmium, said luminescent sulfide being self-activated or activated by at least one element selected from the group consisting of silver, copper and gold and coactivated by at least one element selected from the group consisting of aluminum, gallium, indium, scandium and the rare earth metals comprising introducing into a reaction vessel a reaction mixture comprising at least one compound selected from the group consisting of zinc sulfide and cadmium sulfide and the desired quantities of compounds of the coactivator and activator elements and a mixture of carbon and sulfur, said mixture being capable upon heating of producing carbon disulfide, closing said vessel and heating said vessel to a temperature between 950.degree. and 1250.degree.C, the improvement wherein said carbon is separated from said reaction mixture by a gas permeable partition and the carbon disulfide produced by the reaction of said carbon and sulfur at said temperature is transported to the reaction mixture by diffusion through said gas permeable partition while in the gaseous state.