Experiments indicated that the perfect KMgF3 crystal exhibited no absorption in the visible range. However, electron irradiation introduced a complex absorption spectrum. The absorption spectra could be decomposed into five Gaussian bands peaking at 2.5eV (488nm), 3.4eV (359nm), 4.2eV (295nm), 4.6eV (270nm) and 5.2eV (239nm), respectively. The purpose here was to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF3 or for KMgF3: VF+ with electrical neutrality were studied by using a density functional theory code with the lattice structure optimized. The calculation results predicate that KMgF3: VF+ also exhibited five absorption bands caused by the existence of the fluorine ion vacancy VF+ and the five absorption bands well concided with the experimental results. It was believable that the five absorption bands were related to VF+ in KMgF3 crystal produced by the electron irradiation.

First Principle Studies on the Electronic Structures and Absorption Spectra in KMgF3 Crystal with Fluorine Vacancy. F.Cheng, T.Liu, Q.Zhang, H.Qiao, X.Zhou: Nuclear Instruments and Methods in Physics Research B, 2010, 268[15], 2403-7