Electroluminescence of Zinc Sulfide Single Crystals

Quantitative measurements of the electroluminescent emission from synthetic single crystals of zinc sulfide with silver paint contacts under 60-cycle half-wave voltage excitation have been carried out at several temperatures. Other workers have shown that the emission intensity has two major peaks per cycle, the first coincident with the voltage maximum and the second as the voltage is falling to zero. These peaks have the same color, and both appear to originate throughout the crystals, but they have different voltage dependencies. The second peak is the larger at low-voltage amplitudes, but the first peak grows the more rapidly with increasing voltage amplitude. Emission intensities of the order of ${10}^{12}$ photons per second, with energy efficiency of the order of ${10}^{-5\mathrm{}}$, were obtained. The total current consists of a displacement current which is linear with voltage and a conduction current which is roughly exponential with voltage. No evidence of space-charge polarization was detected. It is tentatively suggested that excitation occurs by impact of conduction electrons accelerated through internal barriers, that the two emission peaks result, respectively, from immediate recombination and from recombination delayed by trapping of the excited electron, and that the electric field tends to hold the electron in the trap state.