Thermostimulated luminescence, photoluminescence and X-ray-induced luminescence in CaSO 4 : Ce; CaSO 4 : Ce, Na; CaSO 4 : Ce, Mn and CaSO 4 : Ce, Mn, Na phosphors

Abstract

Thermostimulated luminescence (TSL) and photoluminescence (PL) studies were carried out on CaSO 4 : Ce; CaSO 4 : Ce, Na; CaSO 4 : Ce, Mn and CaSO 4 : Ce, Mn, Na phosphors with the aim of studying their PL and TSL processes as well as the energy transfer and the effect of charge compensation. Following γ-irradiation, a drastic reduction in Ce 3+ fluorescence was observed in all these samples. To explain the peculiar nature of the TSL glow curve of CaSO 4 : Ce, the γ-ray-induced oxidation of Ce 3+ ions (i.e., Ce 3+→Ce 4++e −) is proposed as a viable mechanism of hole trap production. Post-irradiation thermal annealing and optical bleaching data shows a coincidence between one of the recovery steps of Ce 3+ fluorescence and the 400°C TSL peak readout. However, dramatically opposing trends were witnessed in the PL and TSL efficiencies of CaSO 4 : Ce 3+ with the co-doping of Na + charge compensator. The presence of Ce 3+ emission in the Mn 2+ induced 92°C peak as well as the differences in the emission spectra of Mn 2+ in the TSL glow peaks and in the PL spectra of Mn 2+ excited via Ce 3+ in CaSO 4 : Ce, Mn indicate the absence of energy transfer from one activator ion to another during TSL. The glow peak temperature-dependent spectral emission of CaSO 4 : Ce, Mn as well as the X-ray-induced luminescence spectral data are however consistent with the energy transfer model proposed by Morgan and Stoebe. Unlike the results reported in literature, the TSL sensitivity of 400°C peak in CaSO 4 : Ce, Mn is found to be less than that in CaSO 4 : Ce.