Some Optical Properties of Zinc Sulfide Crystals

Abstract

The study of zinc sulfide single crystals, prepared by a vapor phase reaction method and doped with various amounts of impurities, has been made concerning optical transmission, photoconductivity, luminescence, thermal quenching and infrared quenching. The crystals grown through the bromine vapor process show blue luminescence, while these crystals, when doped further with copper of 1×10⁻⁶∼1×10⁻⁴ and 1×10⁻⁴∼1×10⁻³g atom per mol, emit green luminescence and dark blue one respectively.
Based on the experimental results, the models of these luminescence centers have been proposed. It is concluded that the blue emission is due to the recombinations of nearly free trapped electrons with trapped holes, the green emission is due to the recombinations of free electrons with trapped holes, and the dark blue emission is due to the transitions of trapped electrons to the valence band or to the levels near the band. From the optical transmission measurements of thin ZnS crystals with a light polarized parallel to and perpendicular to the c-axis of the crystal, it is found that the optical band gaps are 3.680 eV and 3.704 eV respectively, and that the value of the spin-orbit splitting of the valence band is 0.024 eV. The temperature dependence of the absorption edge is measured to be −4.86×10⁻⁴ eV/°C.