Effect of point defects on the STE luminescence of CaF₂ single crystals

The study is devoted to the radiation defects created in the calcium fluoride single crystals with reactor irradiation to the fluence of 3.7 × 10¹⁷ thermal and 4.6 × 10¹⁷ fast (E_n > 1 MeV) neutrons per cm², and their effect on the luminescence of the crystals. UV–VIS absorption spectroscopy revealed the formation of point defects, mainly F and F₂ centers. From the comparison of the annealing behavior of the absorption and the ion-beam-induced luminescence (IBIL), we conclude that the color centers are responsible for a non-radiation decay of self-trapped excitons (STEs) and thus cause the luminescence quenching. In addition, the Raman analysis revealed a disorder of about 44% and a stress formation in the material after the neutron irradiation. Annealing at 100 °C reduces the disorder to 13% and eliminates the stress.