The performance of a powder direct current electroluminescent (DCEL) device depends on the conductivity of its copper-coated ZnS phosphor, but little effort has been spent on the study of this problem. We report a series of experiments the results of which are used to analyze the forming and aging behavior in a DCEL device. Factors affecting the conductivity of a copper-coated DCEL phosphor are found to be its temperature, coating solution temperature, and gaseous atmosphere. Based on these results, new theories about forming and the effect of a gaseous atmosphere on a DCEL device, as well as how to produce a long lifetime DCEL phosphor are discussed.