Thermoluminescence in ZnS Crystals Fired in Zinc or Sulfur Vapor

Abstract

Photoluminescence spectra, glow curves of blue and green emissions and the thermal bleaching of the 2.3eV absorption band (due to a single-negatively charged sulfur vacancy) have been measured on ZnS crystals heated in sulfur or zinc vapor. It has been found that the as-grown specimens show the self-activated blue emission (470 nm) and a weak green emission. The specimens heated in zinc or sulfur vapor show mainly the copper blue (452 nm) and the copper green (545 nm) emissions. The temperatures of glow peak maxima are obtained as 133,165,207 and 235K with a heating speed of 1 deg·sec⁻¹. The emission of the 133 K glow peak consists of the copper blue emission and the others of the self-activated blue or the copper green emission. The 2.3 eV band is bleached thermally accompanied by the 133K glow emission. It is concluded that the 133 K glow peak is due to positive holes released from hole trapping centers while the others due to electrons from electron trapping centers.