Photoluminescence, radioluminescence and optically stimulated luminescence in nanoparticle and bulk KMgF3(Eu)

Photoluminescence (PL) and radioluminescence (RL) were observed in both bulk polycrystalline and nanoparticle KMgF3(Eu). Eu2+ and Eu3+ emissions were detected in the PL of both samples. The nanoparticles had more Eu3+, more distorted Eu3+ sites, and a higher PL quantum efficiency when compared to the bulk compound. X-ray-induced valence conversion of Eu2+ to Eu3+ was observed in the bulk, while Eu3+ to Eu2+ was found for nanoparticles. The valence conversion was reversed for the bulk compound by UV bleaching (254 nm) and partially reversed in the nanoparticles by 330 nm stimulation. F2 and F3-centre PL was observed in the bulk after X-ray irradiation but was absent in the nanoparticles. PL from other point defects occurred in both samples that is likely to be oxygen related. The PL from one of these defects in the nanoparticles changed with X-ray irradiation or UV illumination and the PL slowly recovered at room temperature. We propose this may be due to charge-transfer in O2--F+ pairs where this defect could potentially be used in a solar UV dosimeter. Optically stimulated luminescence was observed only from Eu2+ in the bulk material that can be used for dose monitoring after irradiation. It was absent in the nanoparticles, which may be due to the absence of fluorine related point defects. The bulk RL from Eu2+ and Eu3+ had significant dose-history dependence that could be corrected for. The nanoparticles had RL that was independent of dose history after ~ 4 kGy. Thus, bulk and nanoparticle KMgF3(Eu) may have potential application as an RL dosimeter.