Electron-Nuclear Double Resonance of the Self-Trapped Hole in CaF2and BaF2

The results of an electron-nuclear double-resonance (ENDOR) study of the $V_K$ center (self-trapped hole) in Ca${\mathrm{F}}_2$ and Ba${\mathrm{F}}_2$ are reported. In addition to reporting the ENDOR hyperfine constants, some interesting features of ENDOR spectra due to the glide-reflection symmetry of the fluorite lattice are discussed. Also, the large ${\mathrm{Ba}}^{++}$ion produces effects on the fluorine hyperfine constants that are not observed in the ENDOR spectra of the $V_K$ center in Ca${\mathrm{F}}_2$, LiF, or NaF.