MEASURING ON THIN-FILM ELECTROLUMINESCENT DEVICES

The measurement of the light generation efficiency of thin film electroluminescent devices needs besides the light power the electric power input to be determined. The usual way of analog integration over the dissipated current in each half-period of the applied voltage, giving the transferred charge Q, and multiplying it by the threshold voltage U(th) for the electroluminescence relies on the so-called back-to-back Zener model. It is proven to be correct, if the model is applicable. This is not the case for samples with trailing edge currents, mainly occurring in alkaline earth sulfide based devices. In those cases Q(approximately)U(th), with Q(approximately) being the leading edge current integral, excluding the trailing edge, is shown to be a much better approximation of the concisely determined electric input.