Mössbauer absorption and emission experiments in CaF2(57Fe): relaxation and after-effect study

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Abstract
The entire Mössbauer absorption spectrum of 57Fe impurities in CaF2 and the main part of the emission spectrum of a CaF 2 (57Co) powder sample originate from substitutional Fe 2+ ions in cubic sites. A weak Fe1+ (3d7) charge state contribution is also detected in the emission spectra, but no Fe 3+ contribution is observed. Two long-lived excited electronic level contributions are evidenced out of the thermal equilibrium in the low temperature emission spectra of the cubic site Fe2+ ions. The first originates from the low energy spin-orbit triplet 5E - Γ4 (E ≃ 16 cm-1), whose relaxation properties are also analysed by absorption spectroscopy, and the second probably originates from the highly excited level 5T2 - Γ5g (E ≃ 5 000 cm-1)