Electron paramagnetic resonance and thermally stimulated luminescence studies of uranyl doped calcium sulphate

Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted onγ-irradiated CaSO₄:UO ₂ ²⁺ to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain the trap parameters (trap depth and frequency factor). Intense TSL glow peaks around 140, 375, 400 and 438±2K are observed and their spectral characteristics have shown that UO ₂ ²⁺ and UO ₆ ⁶⁻ act as luminescent centres. EPR studies have shown the peaks at 140 and 400/438K to be associated with the thermal destruction of O⁻ and SO ₄ ⁻ radical ion in two stages respectively. The maximum rate of thermal destruction of SO ₄ ⁻ ions (as seen by EPR) in various alkaline earth sulphate matrices investigated in our laboratory is also summarized. The activation energy which characterizes the electron transfer reaction between SO ₄ ⁻ and the dopant ion lies in the range of (0.95±0.15 eV). This value is independent of the dopant and therefore seems to be characteristic of the binding energy of hole in the SO ₄ ⁻ radical ion.