The F centre in MgF2. I. EPR and ENDOR

The magnetic resonance absorption at g=2 in irradiated MgF 2 is positively identified in this paper as arising from F-centres. EPR and ENDOR investigations have determined the hyperfine constants and tensor axis orientations for the first six fluorine shells. These agree in detail with the interactions expected from an electron trapped at a negative ion vacancy. The large nearest neighbour interaction (A/sub ///=382.83 MHz, A perpendicular to =288.23 MHz) coupled with the smaller second and third neighbour interactions have been used to reconstruct in detail the resolved EPR spectra when H 0 is parallel to the crystal symmetry axes. A semiempirical wavefunction obtained from the observed contact interactions for all six shells predicts that neighbour cation ENDOR transitions for the 10% abundant 25 Mg nuclei should be observed near the first neighbour fluorine transitions.