It was recalled that the vacancy model for impurity vacancy defects in semiconductors assumed that the ground and low-energy excited states could be derived from the four sp3 hybrid orbitals on atoms which bordered the vacancy. It was pointed out that there were many cases where this model worked, but a counter-example was described here which concerned the lowest excited state of the [V-N3] defect in diamond. It was shown that a shallow electron trap, localized outside the vacancy, was involved in the first excited state and was responsible for the N2 and N4 optical bands which were associated with the defect.

R.Jones, J.P.Goss, P.R.Briddon, S.Oberg: Physical Review B, 1997, 56[4], R1654-6