Electroluminescent cells are constructed by dispersing a copper-activated zinc sulfo-selenide phosphor powder in a thermoplastic dielectric matrix. The resulting sheet material is observed to glow when an alternating electric field is applied. The light produced is not continuous, but flickers with twice the applied frequency, dropping to zero between flashes.
The electric field in the phosphor particles can be calculated if the particles are assumed to be spheres; however, it is first necessary to determine their dielectric constant. This is done by comparing the dielectric constant of the phosphor-plastic aggregate with that of the clear plastic. The results of these calculations show that, for a variety of plastic matrix materials having different dielectric constants, the brightness of electroluminescence depends only on the electric field in the phosphor particles.
A cell having a matrix of polystyrene was used in studying the brightness of electroluminescence versus temperature. This material has a relatively small temperature coefficient of dielectric constant. Only a small change of brightness was observed in a temperature range from -100°C to +50° C. This fact suggests that the mechanism responsible for electroluminescence does not depend on thermal activation.
SHEPARD ROBERTS, "Field Strength and Temperature Studies of Electroluminescent Powders in Dielectric Media," J. Opt. Soc. Am. 42, 850-851 (1952)