Low-Field Electroluminescence in Insulating Crystals of Cadmium Sulfide

Green electroluminescence can be obtained from insulating crystals of CdS at low dc fields. The wavelength of the emitted light corresponds to the energy of the gap between the valence and conduction bands. The emission band and the optical absorption edge shift together with temperature. The emission of light is correlated with an abrupt increase in current through the crystal, and the intensity is proportional to it. The measured electric field in the region of the crystal where light is generated is ~1000 volts/cm. The pattern of the electroluminescence (beams) is deflected by an 8000-gauss magnetic field. The experiments can be explained by the hypothesis that conduction occurs because of injection of free carriers into the insulator by the electric field, electrons from the cathode and holes from the anode. The luminescence results from the recombination of the injected holes and electrons which have drifted into the bulk of the crystal.