Polarization of the Edge Emission in CdS

The edge emission spectra of CdS has been examined in the temperature range 70°-150°K. In this interval the ratio of the intensity of the light emitted whose plane of polarization is perpendicular to the $c$ axis of the crystal to that parallel to the $c$ axis was determined. The ratio $\frac{I_{\perp }}{I_{\mathrm{II}}}$ decreased with increasing temperature. In agreement with an earlier paper assigning the emission as the recombination of a trapped hole and free electron an interpretation is offered in terms of the splitting of the ground state of the center. The splitting is caused by the presence of the crystal field in a manner similar to that observed for the valence band. However, from the present experiment alone an equally satisfactory explanation can be offered in terms of the recombination of a trapped electron with holes possessing a thermal distribution among the valence band levels. In either case a splitting of $\Delta E=0.014\mathrm{}$ ev is obtained.