Thin-Film Elucidation of the Electroluminescence Process

Abstract

Very thin sulfide films emit light only on alternate half-cycles of the voltage sine wave, whereas the emission of thicker films and phosphor powders is quite symmetrical with polarity. This asymmetry of emission, together with clipping or dc bias of the applied voltage, is used to confirm unambiguously that the excitation and recombination steps in electroluminescence are separable and occur sequentially and under different field configurations, and that the recombination is field-driven.

Electroluminescence of Lead-Containing Zinc Sulfide Films

“…On the other hand, a positive d-c bias also causes a new peak in phase with the a-c voltage although it is so small that it is hardly distinguished from peaks P~ and PI' even at a much higher bias-voltage than in the case of the negative bias. Neither positive nor negative bias gives any drastic influence on the height and on the phase of P1 and PI', contrary to the result in the above reference (9). A small pulse superposed on a-c voltage also gives a pronounced influence on the peak P2.…”

“…In some other cases the emission at the negative polarity is also detectable b u t rather weak. Asymmetric brightness waveforms were observed also by Thornton (9) in a ZnS:Cu,C1 film, which, together with clipping or d-c bias of the applied voltage, was used to confirm separability of ex- citation and recombination steps in EL. In this work, a small pulse superposed on the sinusoidal voltage was used to confirm this separation, which technique is familiar to workers in this field (10).…”