A new analysis of hole burning and magnetic circular dichroism observations of the fine structure of the excited 3E state in the N-vacancy centre showed that the effective spin-orbit contribution was much smaller than had previously been estimated. This implied that spin-spin interactions determined the fine structure in centres with strain splittings of greater than 0.5/cm. It was suggested that this result was more consistent with the observed weak strain-dependence of hole-burning features than were earlier calculations, and that they supported the 6-electron model for the centre.

Fine Structure of Excited 3E State in Nitrogen-Vacancy Centre of Diamond. J.P.D.Martin: Journal of Luminescence, 1999, 81[4], 237-47