The characteristics of two types of d.c. electroluminescent powder phosphors in the ZnS (Mn, Cu) system are described. The first shows a quantum efficiency (photons/electron) of over 100% at a luminance of 0·5 ft lamberts. The second yields over 103 ft lamberts with a quantum efficiency of 5% at room temperature. The power efficiencies are 0·33 and 0·05% respectively. Typical current-voltage-luminance relationships are shown.

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.

This review deals mainly with direct current electroluminescence (dcel) in manganese and copper activated ZnS. The preparative techniques and dcel observations on powders, thin films and single crystals are described. The basic mechanisms are outlined and possible future developments are discussed.

A study of the materials preparation of zinc sulfide powders activated by manganese and copper has yielded direct‐current electroluminescent cells with considerably improved performance. Investigation of the forming process has led to new cell configurations which are described. Some low‐voltage characteristics are illustrated, 0.5 ft‐L being obtained at 20V. The main problem of deterioration is discussed.

Direct current electroluminescent (dcel) powder phosphors in the zinc sulphide: manganese, copper, system can now be readily prepared giving a luminance of 250 ft lamberts at 100 V and 5 mA cm−2. Under continuous constant voltage operation at 100 V, the luminance falls to 100 ft lamberts in about 5 hours, and subsequently to 50 ft lamberts in about 25 hours. With constant power input a luminance of 100 ft lamberts has been maintained for a period of 400 hours. dcel has also been obtained in zinc selenide: manganese, copper powder phosphors. In addition to the yellow/orange emission due to manganese, green dcel emission has been observed in erbium activated zinc sulphide.