Electron spin resonance and thermoluminescence studies in CaSO4: Dy,Ag phosphor

Abstract

The defect centres formed in the thermoluminescence (TL) phosphor CaSO4 : Dy,Ag are studied using the technique of electron spin resonance (ESR). The Ag co-doped phosphor exhibits three glow peaks around 130°C, 220°C and 375°C, in contrast to the two glow peaks observed in the CaSO4 : Dy phosphor at 130°C and 220°C, at gamma ray dose of 1 Gy when the TL measurements were carried out in the spectral region 300–650 nm. ESR studies show that the additional peak at 375°C correlates with a Ag2+ centre formed owing to γ-irradiation and observable 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 375°C; this radical is characterized by the g-values g‖ = 2.0023 and g⊥ = 2.0038 and is assigned to the radical. It is observed that there is more incorporation of Ag in the CaSO4 : Dy system as compared with that in the pure CaSO4 system. The variation of Ag2 + ESR intensity with Ag concentration as well as with dose in the range 0.3–120 kGy is studied. The Ag2 + ESR signal and TL saturate at 2 × 104 Gy, but the intensity of the radical continues to increase up to the studied dose of 1.2 × 105 Gy. The intensity of the radical decreases with Ag concentration in CaSO4 : Dy,Ag, in agreement with the TL model proposed in this work.