The superhyperfine spectrum of the relaxed excited state of F centers was studied by detecting dips in the quantum efficiency of the F luminescence as a function of magnetic fields of less than 0.31T at 4K. The superhyperfine spectrum depended upon the angle between the magnetic field and the crystalline axis. By analyzing this angular dependence, the isotropic and anisotropic superhyperfine interaction constants of the relaxed excited state were determined, up to the 32nd shell, as a function of the shell distance (from an anion vacancy) - divided by the lattice constant.

N.Akiyama, H.Ohkura: Physical Review B, 1996, 53[16], 10632-40