Electron Paramagnetic Resonance Studies of the ZnS-A and -B Centers

Abstract

Two photosensitive electron paramagnetic resonance signals A and B are found in self‐activated ZnS phosphors of polycrystalline form. Both these signals appear at 77°K when illuminated with uv light, and can be quenched with visible light of longer wavelength. The center responsible for the A signal is a hole trap and is found to be the luminescent center of the self‐activated emission. The atomic structure of this center is concluded to be an associate of zinc‐ion vacancy and a coactivator ion at one of the nearest possible sites. The center responsible for the B signal is an electron trap. A simple sulfur vacancy is proposed to be the structure of this center. In one case, the A signal was traced using a crude single crystal. Owing to the crudeness of the crystal, the result is not complete, but is found to be sufficient enough to substantiate the accuracy of the powder pattern analysis. Also described in this report are the results of investigating the effects of oxygen incorporated into ZnS by both the electron paramagnetic resonance and the thermoluminescence techniques. One of the observed effects is that the incorporation of oxygen leads to formation of self‐activated luminescent centers whose coactivator ions are not at the nearest possible sites.