It is shown that the ions Cl-, Br-, and I-play an essential part in the blue centers of ZnS.Ag, ZnS.Zn, and ZnS.Cu phosphors. The centers are assumed to be Ag+Cl -, and Cu+Cl -, respectively, (or the corresponding bromides and iodides), and to occupy normal zinc and sulfur sites in the zinc sulfide lattice. The spectral distribution of the fluorescence is the same for the centers containing chlorine or bromine ions; Ag, Zn, and Cu cause bands at slightly different wave lengths.A difference in peak positions for wurtzite and sphalerite is explained by the difference in separation between the upper occupied and the lower empty energy band of the base lattice.

Trivalent bismuth forms fluorescence centers in its own compounds as well as in other systems in which it is present as an activator. The fluorescent emission consists of various bands lying between the ultraviolet and the red end of the spectrum. The relative intensity of these bands depends upon the nature of the host lattice and the temperature of observation.Sulfates and phosphates of the alkaline earth group show predominantly red fluorescence. The red fluorescence of Ca2P2O7:normalBi shows the remarkable feature that its temperature dependence is different for excitation by cathode rays and by x‐rays.

Chemical determinations of the chlorine present in phosphors support a previously enunciated theory of blue centers.

Magnesium germanate activated by manganese may contain the activator in different valencies. When this valency is higher than two, fluorescence excited by ultraviolet occurs in seven narrow bands decaying with the same time constant. The variation of this decay constant and the intensity of fluorescence with temperature is explained by the assumption that the relative contribution of radiative and nonradiative transitions is determined by a Boltzmann equilibrium regulating the population of various excited states.

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