The preparation and d.c. electroluminescent properties of two types of powder phosphor are described. The first type is prepared by a slurrying technique in which the activators are added to pre-fired ZnS powder (post activation), and the second type involves the addition of the activators during the precipitation of the ZnS (simultaneous activation). Both types may subsequently be copper coated to give high-brightness panels, which exhibit an electrochemical forming process. The measurement of absolute luminance and efficiency is described in detail and the relationships between the characteristics and the impurity additions are discussed. Quantum efficiencies of greater than unity have been observed on slurried phosphors, and a luminance in the 1000 ft lambert region has been achieved with simultaneously activated, copper-coated phosphors. Temperature experiments on slurried phosphors indicate a maximum efficiency at room temperature and a five-orders drop in luminance to 120°K. A description of the forming process includes the fabrication of a gap-cell device, and a mechanism involving copper diffusion is put forward. Preliminary deterioration experiments have shown a half life of 900 h at 10 ft lamberts for constant-voltage operation. Direct collision excitation of manganese centres is believed to be the dominant mechanism.
