Thermoluminescence of Tb doped Gd2O2S phosphor

Thermoluminescence (TL) of gadolinium oxysulfide activated with terbium (Gd2O2S:Tb) is investigated. The glow curves of Gd2O2S:Tb phosphor recorded in the temperature range of 93-500 K with a heating rate of 0.52 K s-1 shows five prominent glow peaks. Comparison of the glow curves exhibited by different samples prepared with varying firing conditions reveals some interesting results. In this phosphor capture centers are mainly formed due to variable valency activators, trace impurities and point defects, which create defects in the sub-lattice. The observed TL spectra suggest a multiplicity of electron and hole traps. The main peak that observed at 150 K is attributed to point defects arising out of sulfur vacancies. These vacancies give rise to electron traps, which are found to be associated with terbium centers. This is confirmed by the monochromatic glow curves observed at wavelengths corresponding to the characteristic terbium emission (5D3-7Fn, 5D4-7Fn). Removal of this glow peak under H2S firing indicates the localized character of the concerned centers