Solid solutions of prepared by firing in sealed silica tubes are cubic in structure. With suitable additions of Cu and a coactivator, photo‐luminescence and electroluminescence are obtained. The coactivators used were halides, Ga, or In. The electroluminescence in the red consists of two emission bands which do not appear to be analogous to the blue and green emission bands of Cu, Cl in . The quantum efficiency is of the same order of magnitude as that of , but the emission bandwidth is about twice as large and the red electroluminescence consists of emission located to a large extent in the infrared. tends to retain the cubic structure of ternary systems provided that the ratio does not exceed certain limits; until this is so, the introduction of Cd causes increased electroluminescence.