Optical absorption and lattice defects induced by neutron irradiation and heat treatment in ZnS crystals

Measurements are made on optical absorption from 350 to 2500 nm at 77 °K of ZnS crystals irradiated by fast neutrons at room temperature and of those fired in a zinc or sulfur vapour at 1100 °C. It has been found that neutron irradiation produces photoinsensitive 2.7 and 1.75 eV bands in addition to the 3.5, 3.2, 2.9, and 2.3 eV bands reported previously, and that the firing in zinc vapour produces new photosensitive 3.2, 2.7, and 1.75 eV bands. All of the six bands produced by neutron irradiation are also produced by the firing in zinc vapour. However these bands can not be produced by the firing in sulfur vapour, which produces four bands different from those induced by the zinc firing. It is proposed that the 3.5, 3.2, 2.7, and 1.75 eV bands are related with sulfur vacancies and that the 2.7 and 1.75 eV bands are due to hole transitions.