Copper-Activated Zinc Sulfide Phosphors with Trivalent Substituents

With increasing concentrations of Cu and Al in ‐fired phosphors, the emission spectrum is shifted from green to orange under 3650 Å excitation. The emission of these triple Sulfides consists of three sub‐bands of such relative intensities that the presence of a single band is simulated. The bands have different temperature, decay, and excitation characteristics. Among other substituents, the elements Sc, Ce, Pr, and Nd are of interest, as they produce infrared stimulability even with high activator concentrations. When fired in with oxide additions, the phosphors with Al emit only green light and become strongly electroluminescent. The green emission persists at all frequencies from 60 to 15000 cps. Phosphors prepared with 0.1 to 0.4 per cent Cu and with 0.25 to 2.5 moles Al/mole Cu are nearly equally bright. The mole ratio Cu:Al in the brightest ‐washed phosphors is near 1:1. The results lend strong support to Kroeger's theory of charge compensation. The complexity of the emission spectra leads to the conclusion that several species of Cu atoms must be present in the phosphors. The electroluminescent response is attributed to oxide barriers in, or on, the phosphors.