Defect Formation by N⁺⁺ Ion Bombardment in LiF and NaF

Abstract

The F-light absorption was measured in LiF and NaF single crystals bombarded by 0.7 MeV N⁺⁺ ions from a Van de Graaff accelerator. The growth curves showed a maximum, from which the F-center concentration at the saturation was estimated to be 7.6 and 3.8×10¹⁹ F-centers/cm³ in LiF and NaF, respectively. The rates of production, 3020 and 1210 F-centers/N⁺⁺ ion, and the formation energies of an F-center, 232 and 578 eV, were determined from the initial portions of the growth curves in LiF and NaF, respectively. The formation of metallic film on the bombarded surface and other imperfections as the result of radiation damage are discussed, referring also to the micrographic observations. It is thus concluded that the damage by N⁺⁺ ions is fairly severe; the double charge is possibly responsible for this phenomenon.