Influence of Lattice Vibrations on the Hyperfine Structure Constants of VK‐ and VF‐Centres in Earth Alkaline Fluorides

The ESR spectra of diatomic F molecules of the type V K and V F in CaF 2 , SrF 2 , and BaF 2 show temperature‐dependent hyperfine structure constants. This temperature dependence results from a vibration with sharp frequency ω, coupling to the hfs. It can be described by A ( T ) = A 0 + α coth (ħ ω/2 kT ). The frequencies ω for the V K ‐ and V F ‐ centres are determined from the experimental data. Molecular vibrations of the centre or lattice vibrations may produce change of the hfs‐constants. The frequencies of such vibrations are calculated. From the comparison with the measured ones it is concluded that the change of the hfs‐constants results from a lattice vibration of the cation sublattice in [110] direction with k at the vicinity of the edge of the Brillouin zone.