A technique employing a monochromator to select the incident photon energy and a spectrometer to analyze the low temperature photoluminescence of CdS crystals has proven to be valuable, both in analyzing the usual photoluminescent spectra and in obtaining new information on excited states of bound excitons and excited states of neutral donors in the crystal. An accurate measurement of the donor energy levels and the donor binding energy gave a binding energy for the Cl donor in CdS of 33.0 ± 0.2 meV. Energies of excited states of the bound exciton complexes were also measured and for the bound exciton – neutral donor complex (I2 complex) some seven excited state levels were found. One type of radiative decay observed for this I2 complex is a radiative Auger process. This has important consequences in interpreting photoconductivity spectra.