Further effects of high temperature annealing on the photoluminescence of an ultra high pure ZnS crystal

Abstract

If an ultra high pure ZnS crystal is annealed at 1200°C and afterwards slowly or rapidly cooled down to room temperature, one obtains reversible and irreversible changes of the photoluminescence in the visible part of the spectrum. Besides two different reversible blue-green conversions, violet and orange fluorescence bands are reversibly created and annihilated. The blue-blue conversion produced by a variation of the cooling rate after annealing at 1000°C is irrecoverably destroyed if the crystal is only once warmed up to 1200°C. High temperature annealing affects luminescence and thermoluminescence in the same direction. Etching the crystals after annealing at 1000°C has no influence on the reversible behaviour of the fluorescence bands. The experimental results indicate that the structure of the deep centers in ZnS has to be discussed from a more uniform aspect.