Modelling the radioluminescence of Sm²⁺ and Sm³⁺ in the dosimeter material NaMgF₃:Sm

Photoluminescence (PL) and radioluminescence (RL) measurements were made on NaMgF₃:Sm before, during and after exposure to high doses of ionising radiation. Magnetic measurements prior to irradiation showed that approximately 10% of the total Sm concentration was in the divalent state. The RL from Sm³⁺ was found to increase while the Sm²⁺ RL decreased with increasing x-ray dose before reaching steady-state values for high doses. This behaviour is opposite to that previously reported for Sm³⁺ and Sm²⁺ PL. We show that this apparent discrepancy can be accounted for by a RL model where there is a hole trap, an electron trap, and direct x-ray induced carrier recombination at Sm²⁺ and Sm³⁺. Furthermore, a good fit to the dose-dependence of all of the Sm RL emissions can be obtained by assuming that the relevant electron and hole traps are close to Sm³⁺. Our model accounts for F₃-centre production during irradiation that affects some of the Sm³⁺ RL emissions via reabsorption of the RL by the F₃-centres. Thus, the rate of F₃-centre production can be conveniently monitored by the RL intensity ratio, I _RL(567 nm)/I _RL(650 nm). Additionally, the Sm²⁺ RL emissions may be expressed as [1.94  ×  I _RL(721 nm)]  -  I _RL(695 nm) to determine the real-time dose rate, independent of dose history.