Interpretation of the Properties of Zinc Sulphide Phosphors

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Abstract
The properties of pure and copper activated zinc sulfide phosphors are described, and an attempt is made to interpret these properties following the plan of a previous paper on alkali halide phosphors activated by thallium. It is pointed out, as has been done by previous workers, that the combination of photoconductivity and bimolecular decay law of phosphorescence implies that an ionization process accompanies the excitation of zinc sulfide phosphors. By applying the ideas of the quantum theory of solids, it is shown that this ionization process does not correspond to the freeing of an electron from the Zn++ or S—— ions of the lattice. It is concluded that the pure ZnS phosphor probably contains neutral interstitial zinc atoms, and that these are responsible for the luminescence and photoconductivity. By analogous reasoning, it is concluded that the copper activated phosphor contains interstitial copper atoms. The relative stability of interstitial copper atoms and substitutional copper ions is discussed in terms of the Schottky‐Wagner theory of deviations from stochiometrical proportions. It is concluded that the interstitial copper atoms probably are in a metastable condition.
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