Color centers and nanodefects in LiF crystals irradiated with 150 MeV Kr ions

The modifications of structure, optical and nano-mechanical properties of LiF crystals after irradiation with 150-MeV Kr+14 ions at a fluence of 6 × 1012 ions cm−2 have been studied using optical absorption spectroscopy, scanning electron and atomic force microscopy, and nanoindentation. Optical spectroscopy shows the saturation of F centers and a comparatively high number of Fn centers. AFM and SEM imaging reveals a nanostructured region with columnar nanocrystallites (size 30–90 nm). Nanostructuring occurs in depths up to 10 μm, where the ion energy loss surpasses a critical threshold of about 10 keV/nm. At a lower energy loss a zone enriched with dislocations is observed. Structural changes are accompanied by a substantial increase of hardness. The recovery processes of structure and properties under annealing have been studied.