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Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor
B C Bhatt1, Bhushan Dhabekar, Rajesh Kumar
1Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India. bcbhatt2003@yahoo.com
Radiation Protection Dosimetry
|May 20, 2006
Summary
Electron Spin Resonance (ESR) reveals a new defect center in silver-co-doped calcium sulfate dysprosium (CaSO4:Dy,Ag) phosphors. This center, a silver (Ag2+) ion, is responsible for an additional thermoluminescence (TL) glow peak at 375°C.
Area of Science:
- Solid State Physics
- Materials Science
- Luminescence and Spectroscopy
Background:
- Thermoluminescence (TL) phosphors are crucial for radiation dosimetry.
- Calcium sulfate doped with dysprosium (CaSO4:Dy) is a well-established TL material.
- Co-doping with other elements can modify TL properties.
Purpose of the Study:
- To investigate defect centers in silver (Ag) co-doped CaSO4:Dy phosphors.
- To understand the origin of an additional thermoluminescence glow peak.
- To characterize the defect centers using Electron Spin Resonance (ESR).
Main Methods:
- Electron Spin Resonance (ESR) spectroscopy.
- Thermoluminescence (TL) measurements.
- Gamma ray irradiation.
Main Results:
- Ag co-doped CaSO4:Dy exhibits three glow peaks (130°C, 220°C, 375°C) vs. two in CaSO4:Dy (130°C, 220°C) after 1Gy gamma irradiation.
- The 375°C TL peak correlates with a gamma-induced Ag2+ center, observable below -170°C, characterized by an axial g-tensor (g∥=2.38, g⊥=2.41).
- A precursor radical, assigned to SO3- (g∥=2.0023, g⊥=2.0038), acts as the recombination center for the 375°C TL peak.
Conclusions:
- Silver co-doping introduces a new defect center (Ag2+) responsible for the high-temperature TL peak at 375°C in CaSO4:Dy.
- The Ag2+ center and the SO3- radical are key to understanding the thermoluminescent mechanism at 375°C.
- Enhanced incorporation of Ag is observed in CaSO4:Dy compared to pure CaSO4.