An investigation of the effects of X-rays on undoped and on hydrogen doped alkaline earth fluorides

Abstract

We have investigated, using e.p.r. methods, the effects of X-rays on undoped and hydrogendoped alkaline earth fluorides. We find that irradiation of undoped CaF 2 at any temperature does not produce F centres in observable concentration. Irradiation of undoped SrF 2 and BaF 2 at 77 °K produces V k centres and trapped electron centres which anneal out below room temperature. The undoped SrF 2 and BaF 2 crystals are extremely difficult to colour with room temperature X-irradiation due, apparently, to recombination of electrons and holes. Irradiation of SrF 2 :H and BaF 2 :H crystals at 77 °K produces hydrogen atoms in fluorine sites (Hg centres) and trapped electron centres. The rate of introduction of the electron centres into the crystals is greater by a factor of about 3 than in the undoped crystals. Irradiation of CaF 2 :H at 77 °K also produces Hg centres and trapped electron centres but the rate of generation of the electron centres in these crystals is greater than in undoped CaF 2 by a factor of at least 25. The origin of this difference in the behaviour of CaF 2 :H and the behaviour of SrF 2 :H and BaF 2 :H and the nature of the response of alkaline earth fluorides to X-rays are discussed. The use of polarized bleaching light to extract information from the optical absorption spectrum of irradiated CaF 2 :H is described in an appendix.