Copper‐Activated Zinc Sulfide Phosphors with Yellow and Red Emission

Abstract

Hexagonal, phosphors prepared with 0.05 to 1 per cent Cu are characterized by a yellow‐red luminescent emission obtained with ultraviolet, cathode ray, x‐ray, and electroluminescent excitation as well as with infrared stimulation. Peaked at 6500 Å, the emission is shown to consist of two bands, a strong red band at 6700 Å and a weaker yellow band at 5800 Å. The intensity of the yellow band declines toward zero at −196°C, while the red band increases in intensity and moves toward longer wave lengths. With electroluminescent excitation, the yellow‐red emission persists without changing to blue over the frequency range of 60 to 15000 cps.Washed with solution to remove excess free copper sulfide, the phosphors retain only a certain percentage of the amount of Cu originally added. The amount of retained Cu is one or two orders of magnitude larger than in conventional phosphors, indicating a limit of solubility near 0.3 per cent Cu. The incorporation of Cu into the lattice must be explained without benefit of charge compensating ions. To account for the double band emission and the infrared stimulability, the presence of two species of Cu atoms may be assumed.