Modelling of photoluminescence from F2 and F3+ colour centres in lithium fluoride irradiated at high doses by low-energy proton beams

Lithium fluoride (LiF) crystals were irradiated with a proton beam. With nominal beam energies of 3 and 7 MeV, several irradiations were performed which delivered doses ranging from 10(3) to 10(7) Gy. The ionisation produced by the protons in the LiF samples induced the stable formation in the crystalline lattice of colour centres, two types of which, the F-2 and F-3(+) ones, possess broad photoluminescence bands in the red and green, respectively, when optically pumped in the blue at wavelengths close to 450 nm. At both proton energies, measurements of the distinct F-2 and F-3(+) contributions to the emission spectra showed a decrease of the F-3(+) integrated photoluminescence intensity at large doses, say from similar to 10(6)-10(7) Gy on. We try to explain such a behaviour by assuming the formation of absorption and/or quenching centres, and compare the predictions of an ad hoc developed model with experimental data.