Color Centers Induced by Neutron Irradiation in ZnS Single Crystals

Correlations among the changes in optical density due to illumination with uv, 425-, or 540-mµ light have been examined of the uv, 390-, 425-, and 540-mµ bands introduced by neutron irradiation in ZnS single crystals. The photosensitive behavior before and after isochronal annealing of the samples and the analysis of the intensity distribution of the 425- and 540-mµ bands reveal that the 425-mµ band consists of a broad and narrow bands, and that this broad band and the 540-mµ band may have the same origin of absorption, The narrow 425-mµ band and the 390-mµ band disappear by isochronal annealing up to 340° and 480°C, respectively. The photosensitive uv band and the other visible bands begin to disappear from the step at 520°C. Activation energy for the defects responsible for 540-mµ band has been estimated to be 2.2 eV. A reasonable placement of the energy levels has been made of these absorption centers.