Radiolysis of alkaline-earth fluorides

Alkaline-earth fluorides have been irradiated at temperatures between 4 and 300 K using electrons of energy 70 keV, 300 keV and 1 MeV. The coloration produced has been investigated by both EPR and optical methods. At 77 K and lower temperatures, a rapid first-stage coloration occurs which saturates and is followed by a slower second-stage coloration. The first stage is characterized by perturbed F centres and compensating V K centres. It seems that the perturbed F centres are associated with nearby interstitial fluorine ions but impurities may also be directly involved. The second stage is characterized by the production of isolated F centres and compensating H centres and appears to be the result of intrinsic radiolysis. Thermally induced annealing of the first- and second-stage coloration is investigated. The first stage coloration of BaF 2 is described in some detail in an Appendix.