Abstract
In 1980, a single LiF crystal was irradiated by thermal neutrons up to the exposition dose 1019 n/cm2 at the Salaspils nuclear reactor. The crystal has been kept at room temperature for 29 years. Samples in size of 5×4×1 mm3 were cut from the crystal and some of them annealed at 920 K for 30 min. To study photoluminescence, measurements with a confocal laser scanning microscope Leica TCS SP5 were performed, during which 3D-defects of size of ~1μm3 were revealed. Photoluminescence was observed in the red spectral region with the peak of ~ 655 nm when excited with an argon laser (Δ = 458 nm).