Host material induced hyperfine structure of F⁺ centres EPR spectra in CaS

The hyperfine structure (HFS) of F⁺ centres in CaS single crystals due to the interaction with ³³S and ⁴³Ca nuclei was observed in EPR spectra for the first time. Angular variations of the HFS were measured for rotation of magnetic field in {100} and {110} crystallographic planes. Using measured orientation-dependent EPR spectra and the EPR NMR program, the parameters of the spin Hamiltonian were determined. In case of ³³S nucleus there is a strong dependence of the F⁺ centre EPR spectrum on the quadrupole term whereas for ⁴³Ca nucleus this dependence is insignificant.