Copper produces two emission bands in all and all phosphors. Both bands shift monotonically to lower or higher quantum energies, if the Zn/Cd ratio is varied, so that their differences to the also varying energy of the band gap remain constant. In contrast, the positions of the emission bands in , , and depend relatively little on the S/Se or Se/Te ratio, respectively, except for a pronounced, and as yet not understood, discontinuity near 100% . Otherwise, the behavior can be understood qualitatively by assuming predominantly ionic crystal bonding, with the Schön‐Klasens model of luminescence, and with Fonger's model of term‐splitting in all cases where the activator is surrounded by different kinds of anions.