Electron-Nuclear Double Resonance ofFCenters in MgO

Abstract

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 ${\mathrm{Mg}}^{25}$ nucleus are obtained with high precision. We find: For the isotropic hyperfine-interaction constant, $\frac{A}{h}=11.03\mathrm{}\pm 0.02$ MHz; for the dipolar interaction constant, $\frac{B}{h}=1.33\mathrm{}\pm 0.02$ MHz; for the quadrupole interaction constant, $\frac{e^2\mathrm{qQ}}{h}=5.64\mathrm{}\pm 0.01$ 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 $e^2\mathrm{qQ}$ for ${\mathrm{Sr}}^{87}$ leads to similar conclusions regarding the relaxation of nearest-neighbor nuclei of the $F$ center in SrO.