Electron-irradiation-induced defects in BaLiF3 crystals

We report preliminary results on the production of colour centres in BaLiF3 crystals, subjected to electron irradiation. The dependence of the colour-centre creation on the temperature and dose of the irradiation, as well as on the direction of crystal growth, was studied. Our experimental results concerning absorption, emission and excitation spectra measurements show that defect formation in BaLiF3 crystals depends strongly on the conditions of crystal growth and preparation of the samples. By comparing BaLiF3 with KMgF3 and LiF crystals, we were able to attribute the absorption bands at 260, 420, 632, 386 and 480 nm to F, F2, F2+, F3 and F3+ centres. Theoretical evaluations of the absorption energies for these defects were made, and they supported these assignments. Room temperature electron irradiation of crystals grown in <100> and <111> directions favours the formation of different kinds of F-aggregate centre for each of these two cases. In particular, for <100> crystals we were able to observe the formation of F2+ centres with one absorption band at 632 nm and a corresponding emission at 702 nm. (author)