Synthetic single crystals of CdS, CdSe, and CdTe have been produced by the reaction of cadmium vapor with ${\mathrm{H}}_2$S, ${\mathrm{H}}_2$Se, and ${\mathrm{H}}_2$Te, respectively. These "incomplete phosphors" show no phosphorescence but strongly developed photo-conductivity. Photo-cells made from these crystals are extremely sensitive in the whole region from the infra-red down to the ultraviolet, x-rays, and gamma-rays and for corpuscular rays, alpha- and beta-rays. Two different mechanisms of photo-conductivity occur. The normal photo-conductivity in the region of strong absorption from the blue to the ultraviolet, and the selective photo-conductivity in the region of weak absorption in the visible, x-rays, and corpuscular-rays region. The phenomena observed are in general accordance with the zonal theory of phosphorescence.

• Received 4 June 1947

DOI:https://doi.org/10.1103/PhysRev.72.594