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.
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