R.M. Montereali, F. Bonfigli, F. Menchini, and M.A. Vincenti, Optical spectroscopy and microscopy of radiationinduced light-emitting point defects in lithium fluoride crystals and films, Low Temp. Phys. 38, (2012) [Fiz. Nizk. Temp. 38, 976-984, (2012)] DOI: https://doi.org/10.1063/1.4740241.