Structural characterization, defect evolution and luminescence properties of natural CaF2 under 10 MeV electron irradiation.

Present study investigates the response of various coloured variants of natural fluorite (CaF 2) to 10 MeV electron beam irradiation at accumulated dose of 5–10 MGy. The fluorite specimens did not show any post irradiation radioactivity. However, after irradiation the specimens developed purple colouration of different shades depending on the dose. In-depth characterization of the as-received and irradiated specimens using XPS and Raman spectroscopy confirm the relocation of fluorine (F) anions at interstitial sites and formation of metallic calcium (Ca). The calculated displacement cross sections for F and Ca indicate that it is easier to form fluorine anion interstitials within lattice structure. However, the estimated lower fraction of interstitial fluorine (∼14%) as compared to metallic Ca (>50%) is attributed to their surface diffusion and desorption. Electron irradiation was found to cause photoluminescence quenching in all the CaF 2 specimens that is likely caused by a radiation-induced formation of competing recombination channels. • Cationic and anionic sub-lattice defects in the co-located natural CaF 2 under 10 MeV electron irradiation were studied. • Increase in metallic Ca fraction was higher than the increase in F-ions displaced from their lattice sites. • Mechanism for radiation damage is proposed. • Effect of irradiation on luminescence properties is elucidated. [ABSTRACT FROM AUTHOR]