Electroluminescence at Low Voltages

Electroluminescence occurs in activated ZnS thin films at 1.5 volts rms (peak voltage 2.2 volts) corresponding to electron energies less than the band gap (3.8 electron volts) and less than the mean energy (2.6 electron volts) of the photons emitted. The light emission decreases by ${10}^4$ between 2.0 and 1.5 volts rms and shows no tendency toward a threshold, nor does its spectral character change at low voltage. This behavior suggests that electroluminescence does not depend upon collision ionization but perhaps on carrier injection or free electron temperature.