Correlation of EPR and electro-optical measurements in ZnS

A recent publication(1) by one of us describes an optically stimulated e.p.r. spectrum in ZnS doped with various amounts of Al. On the basis of the experimentally observed decrease in the optical energy required to excite the e.p.r. spectrum, which was due to Al2+, with increasing aluminum, a model was proposed. The model involved two major assumptions: (1) increasing association of aluminum ions and zinc vacancies with increasing aluminum concentration and (2) a direct, optically induced transfer of charge between these two centers. The present work describes measurements of luminescence and d.c. photoconductivity in these same powder samples which are in disagreement with this model. A second model involving a doubly ionizable center and indirect optical transfer of charge from this center to the Al2+ via the conduction band is proposed which is in agreement with all of the available data. © 1963.