Optical absorption and luminescence of 14-MeV neutron-irradiated CaF2 single crystals

The effects of 14-MeV neutron irradiation (1.1 × 1019 n/m2) on crystalline CaF2 have been examined by optical absorption and luminescence techniques to evaluate its suitability as a window material for fusion energy applications. For comparison, similar studies were done on unirradiated and X-irradiated samples. It is confirmed that pristine CaF2 exhibits excellent optical transmission in the spectral region 200–1000 nm. X and neutron irradiation induce similar optical absorption spectra with maximum absorption coefficients approximately 1.6 and 0.8 cm−1, respectively. Thermally stimulated luminescence glow curves are induced by X-ray (11.55 kGy) and neutron exposures; peaks occur at 423, 534, 596 and 479, 550, 605 K, respectively. Thermal annealing experiments show that the major absorption peaks decay in concert with appearance of the first glow peak, which is attributed to an electron trap. Thus, the major absorption bands are associated with F and F-aggregate centers. The relative ease with which these centers are produced strongly suggests that CaF2 is not a good final optic window material for fusion energy applications.