Hole-burning Stark spectroscopy of the 5770 AA colour centre in NaF

Laser-induced spectral hole burning in the presence of applied electric and magnetic fields has been used to determine the symmetry and electronic character of the colour centre in X-irradiated NaF whose zero-phonon line is at 5770 AA. The centre is found to have Cs symmetry, perturbed only slightly from trigonal. The authors speculate that it, and other centres in this special region, may arise from F3+ centres perturbed by structural or chemical defects.