Point defects in BaS:Bi phosphors

Abstract

For this study in phosphorescence, thermoluminescence(TL), thermally stimulated conductivity (TSC) and dielectric constant ( k'), samples of polycrystalline barium sulphide phosphors doped with Bi were prepared. These samples were studied after exciting them with UV, X-rays, γ-rays and low-energy electrons. It has been observed that the phosphorescence of these phosphors exhibits a two-stage exponential decay. Complex TL patterns with overlapping glow peaks are obtained and the magnitude of TL output for X-ray irradiated samples is the biggest when compared with that for other ionizing radiations. The TL emission in each peak observed in the 350 to 600 nm wavelength range consists of three overlapping bands. These samples exhibit high dielectric constants in the frequency range 10 2–10 5 Hz and at RT (30 °C). It is noticed that k' decreases with increase in temperature up to 150°C, but increases thereafter with further increase in temperature. Trap depth ( E) and frequency factor( S) are calculated from the experimental data. Attempts have been made to explain these results with impurity complex formation.