The Blackening of Zinc Sulfide Phosphors

Abstract

The process of blackening of zinc and cadmium sulfide phosphors is studied experimentally and theoretically. A survey of the principal experimental facts is given and several new experiments are described. It is suggested that the blackening of the sulfide salts is a two-quantum process in which both positive and negative charges are released from the interior; these charges move to the surface and there produce electrolysis in a film of moisture that is present on the surface when the specimen is in damp air. This picture will explain the known experimental facts concerning the blackening process. The important differences between the blackening of sulfides and the print-out effect in photographic emulsions are discussed.