Experimental and theoretical evidence is reviewed to determine if edge emission in CdS is due to exciton recombination or is characteristic of a center. New evidence is presented which shows that edge luminescence may be produced in CdS at low temperatures by stimulating with infrared light, and simultaneous measurements have been made on the decay of edge luminescence and conductivity in single crystals at 4°K under this irradiation. It is concluded that emission occurs by recombination of a free hole with an electron shallowly trapped at an imperfection. The atomic nature of the imperfection is examined briefly.

• Received 7 June 1956

DOI:https://doi.org/10.1103/PhysRev.103.1715