A series of fluorescence spectra (between 10°K and 300°K) and thermoluminescence measurements have been performed on self-activated cubic ZnS crystals prepared by two different methods. The vacuum-grown crystals (type I) show two series of edge emission lines ($A$ and $B$) and a broad-band blue emission (self-activated). Thermoluminescence results indicate the presence of three traps. Crystals grown in ${\mathrm{H}}_2$S-HCl atmosphere (type II) show only the long-wavelength series of edge emission lines ($B$), the same blue emission and, at low temperature, a weaker broad-band emission at an intermediate wavelength. The thermoluminescence results indicate the presence of only one trap.

Using only the defects known to be present (Cl substituted at S sites, S vacancies, and Zn vacancies) and the decay of excitons, a model is proposed to account for the observed luminescent processes.

• Received 5 September 1961

DOI:https://doi.org/10.1103/PhysRev.125.901