Green and blue photoluminescence has been observed below 100°K in vacuum‐deposited low‐resistivity CdS films given no post‐deposition treatment. The films were deposited on fused quartz substrates in a heated chamber inside the bell jar on substrates held at temperatures between 140° and 180°C. The CdS evaporant containing a trace of residual chlorine gave polycrystalline films that had resistivities at 300°K in the range of 1–102&OHgr; cm parallel to the substrate. The green luminescence in the films at 77°K was similar to the emission reported in the literature for donor‐doped CdS. The doped‐CdS emission differs from the phonon‐assisted ``edge emission'' starting at 5140 Å when observed in pure CdS in that the emission peak at 5220 Å, corresponding to the emission of onek=0LOphonon, is more intense than the zero phonon peak. The relative peak intensities of the zero phonon and phonon replicas in pure CdS can be described by a Poisson distribution inN¯whereN¯is the mean number of phonons emitted in the transition. These Gaussian‐shaped component peaks also have equal halfwidthsH. For pure CdS at 77°K values found in the literature areN¯≅0.8−1.0 andH≅0.03 eV. For the CdS films good fits could be obtained withN¯=1.1−1.5 andH=0.04−0.06 eV. However, it is also possible that the film luminescence is the superposition of two emission series. The peak position of the green emission spectrum observed at 10°K was close to that at 77°K, and an additional peak at 5040 Å was observed. The decay time of the green emission was less than 1.5 &mgr;sec at 77°K, and thermal quenching of the luminescence began around 100°K, with an activation energy of 0.15–0.17 eV. Baking in saturated cadmium vapor at 500°C quenched the green emission, and for films baked in H2S or H2S+HCl+H2at 600°C, emission similar to that observed in pure CdS was obtained. Optical absorption measurements indicated that the band edge was sharpened by the baking processes. The blue emission peak observed in the films was at 4892 Å at 77°K, which is in the fundamental absorption edge. It shifted to 4875 Å and became more intense and narrower at 10°K. This emission persists to 300°K with the peak position decreasing in energy as the bandgap. The peak is quenched by baking in H2S but not by baking in saturated Cd vapor. The blue emission is probably associated with a shallow donor or Cd excess in the films.