Diffused p - n junctions in CdTe have been shown to emit efficient electroluminescence under forward bias at 77°K. Capacitance measurements, current - voltage characteristics, photovoltaic measurements, and the shift of the emitted photon energies with current and temperature are consistent with a space-charge recombination controlled current. The dependence of the quantum efficiency on temperature and current is consistent with a simple, Schön - Klasens-type model of thermal quenching and with limitations imposed by the second law of thermodynamics. The low average concentration of majority carriers at the junction (∼1016 cm-3) that characterizes these devices is a major limitation in obtaining high efficiencies of electroluminescence at 300°K, even at high current densities. © 1966 The American Institute of Physics.