Electron-Nuclear Double Resonance of F Centers in MgO

Electron-nuclear double-resonance measurements on F centers in MgO are reported. From these measurements, the magnetic and electric hyperfine interaction constants for sites with one nearest-neighbor Mg²⁵ nucleus are obtained with high precision. We find: For the isotropic hyperfine-interaction constant, A/h=11.03±0.02 MHz; for the dipolar interaction constant, B/h=1.33±0.02 MHz; for the quadrupole interaction constant, e²qQh=5.64±0.01 MHz. From the quadrupole interaction constant, it is shown that the Mg nuclei relax outward from the vacancy by an amount between 0.04 and 0.08 times the Mg-O distance. The value of e²qQ for Sr⁸⁷ leads to similar conclusions regarding the relaxation of nearest-neighbor nuclei of the F center in SrO.