The intensity of the time-average output of the steady-state electroluminescence of powdered zinc sulfide phosphors in an intense alternating electric field is characterized by a dynamic equilibrium between the monomolecular collision excitation process and the bimolecular recombination process. This equilibrium condition permits predictions of the dependence of the emission intensity, the efficiency, and other properties on several parameters such as the voltage, the temperature, and the concentrations of electron traps and activator centers. These predictions are compared with experimental results.
WILLI LEHMANN, "Electroluminescence of Zinc Sulfide Phosphors as an Equilibrium Process," J. Opt. Soc. Am. 48, 647-652 (1958)