Enhanced photoluminescence of F2 and F3+ colour centres in lithium fluoride film-based detectors for proton beams

Abstract In recent years, lithium fluoride (LiF) detectors based on the optical reading of photoluminescence emitted by radiation-induced F2 and F3+ colour centres have been successfully used for advanced diagnostics of proton beams. In this work, the visible photoluminescence response of LiF film-based radiation detectors of three different thicknesses, grown by thermal evaporation on glass and Si(100) substrates and irradiated with 27 MeV proton beams at doses in the range between 4.2 × 103 and 1.7 × 105 Gy, was carefully investigated by fluorescence optical microscopy. Before irradiation, the structural and morphological properties of LiF films were investigated by atomic force microscopy and X-ray diffraction techniques. Substrate-enhanced photoluminescence response up to 48% was observed in LiF film-based detectors grown on Si(100) substrates with respect to those deposited on glass in the same deposition run and irradiated in the same conditions. This photoluminescence enhancement can be mainly ascribed to the reflective properties of the Si substrate in the visible spectral range, where the emission bands of F2 and F3+ colour centres are located, combined with the proper choice of the film thickness. Other complex effects related to the polycrystalline nature of the LiF films cannot be excluded.