The effect of Mn concentration on the luminescence properties of NaMgF3:Mn: Defect/Mn complex photoluminescence, radioluminescence, and optically stimulated luminescence for radiation dose monitoring

Abstract

Luminescence measurements were made on NaMgF3:Mn before and after irradiation with X-rays over a wide Mn concentration range from x = 0.1%–5%. Photoluminescence (PL) is seen from distorted Mn2+ sites that saturate for x ≥ 1% and non-distorted Mn2+ sites. The non-distorted Mn2+ crystal field parameter and crystal field splitting are independent of Mn concentration and they are B = 779 ± 14 cm−1 and 10Dq = 9250 ± 160 cm−1. F-centre/Mn complexes are seen for all concentrations with a PL emission at ∼670 nm. The complexes have perturbed Mn2+ energy levels that shift by less than 1630 cm−1 in the 320 nm–570 nm wavelength range. There is also a PL emission at ∼730 nm that is likely to arise from F3-centres perturbed by nearby Mn. The PL from these two perturbed centres is linear in dose up to 3.8 kGy when probed in the 550 nm–650 nm region and it can be repeatedly probed without bleaching. Optically stimulated luminescence (OSL) occurs for all Mn concentrations from the non-distorted Mn2+ site after X-ray irradiation. The OSL intensity is linear up to ∼270 Gy for 0.5% Mn and the trapped carriers can be selectively bleached. Radioluminescence (RL) is also observed in all samples from both Mn2+ sites. Not all Mn2+ displays RL and a larger fraction of distorted Mn2+ sites do not display RL, which may be due to a higher concentration of nearby non-radiative recombination sites. The ratio of the RL of the non-distorted Mn2+ to the distorted Mn2+ is nearly dose-history-independent after an initial predose for 0.1% Mn, and it is linear in dose up to 9.6 kGy for 5% Mn. Our results show that NaMgF3:Mn has great potential for real-time and total dose measurements where there are complementary methods available to obtain the dose rate, the dose-history, the dose after each irradiation, and the cumulative dose up to very high doses.