Creation and Stability of Color Centers in BaF₂ Single Crystals Irradiated with Swift ¹³²Xe Ions

It was demonstrated that various defects can be induced in halide crystals by irradiation with swift heavy ions. Here, we irradiated barium fluoride (BaF₂) single crystals with 220 MeV xenon ions at room temperature and performed stepwise thermal annealing up to the temperature of 825 K to study the kinetics of ion-induced defects at different temperatures. Optical spectroscopy was utilized for the measurement of the wide range of absorption spectra from NIR to VUV. A sharp decrease in the F₂ absorption peak was observed for the samples annealed in the temperature range of 400–450 K. This result can be explained by their recombination with anion interstitials during thermal decay of the complex hole centers. The mobile interstitials, those did not recombine with the F₂ centers, increase the absorption peaks in the 9–10 eV region, which can be associated with interstitial aggregates.