Hyperfine Interaction Constants of theF-Center Electron with the Lattice in Alkali Halides (with NaCl Structure)

Abstract

On the basis of the de Boer model for the $F$ center, one can obtain expressions for the coupling constants in the hyperfine interaction of the $F$ electron with a nucleus of the lattice. These constants can be determined experimently by means of "electron nuclear double resonance." The comparison of the theoretical expressions and the empirical values permits an estimate of the importance of the several factors determining these coupling constants. The formal similarity between the magnetic dipole-dipole constants and the contribution of the $F$ electron to the electric quadrupole coupling constants is exploited. The measured magnetic constants are used in the discussion of the quadrupole constants. It is shown that the polarization of the lattice, as a result of the displacement of the ions in the first few shells around the negative-ion vacancy, is important in determining the electric quadrupole coupling constant. This conclusion is in qualitative agreement with Kojima's calculations in LiF. It also explains the fact that while the magnetic interaction shows negligible deviation for "axial" symmetry at sites of lower symmetry, this is not true for the electric quadrupole interaction.