ESR and TL mechanism in CaSO4 : Ag co-doped phosphors

Abstract

Thermoluminescence (TL) studies have been carried out on CaSO4 : Mn, CaSO4 : Ag,Mn, CaSO4 : Ag,Nd, CaSO4 : Ag,Mn,Nd, CaSO4 : Ag,Zr and CaSO4 : Ag,Mn,Zr phosphors. It is found that TL at 360 °C in CaSO4 : Ag,Mn,Nd is about 40 times that of CaSO4 : Ag,Mn and about 170 times that of CaSO4 : Ag,Nd. This shows that the presence of an efficient luminescent centre (Mn2+) as well as a trivalent impurity (such as Nd3+ or Y3+) is important for enhancement of TL at 360 °C in the CaSO4 : Ag,Mn,Nd phosphor system. Electron spin resonance (ESR) studies show that the peak at 360 °C correlates with an Ag2+ centre formed due to γ-irradiation and observable only below −170 °C. The Ag2+ centre is characterized by an axial g-tensor with principal values g|| = 2.38 and g⊥ = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (−170 °C) appears to act as the recombination centre for the TL peak at 360 °C. The low temperature centre is characterized by the g-values g|| = 2.0023 and g⊥ = 2.0038 and is assigned to the radical.