Attempts were made to obtain well-defined and simple singly activated strontium sulfide phosphors. This paper is concerned with the effect of strontium oxide, an unavoidable constituent of strontium sulfide phosphors, on copper- or bismuth-activated strontium sulfide phosphors with strontium chloride as flux. Two different phenomena are encountered with variation in concentration of strontium oxide. One, observed with both copper and bismuth activation, is a gradual shift in emission. The other, obtained with bismuth-activated phosphors, is a surprisingly abrupt change of the emission band. In each case the effect of various oxide concentrations was found to depend upon the concentration of the strontium chloride flux. The distribution coefficient of the activators between strontium sulfide and strontium oxide, the solubility of strontium oxide in strontium chloride, and other solubility relationships largely determine the changes in the emission characteristics.
In the continued search for simple luminescent systems, the investigation was extended to strontium oxide phosphors. Anionic impurities and flux can be avoided and at least some of these phosphors exhibit the essential characteristics of the complex Lenard phosphors. Copper was found to act as an activator only if present in the univalent state.
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