On the basis of new spectroscopic information, retrieved from experiments on individual N–vacancy (NV) defect centers, a 5-level photo-physical model for the center was introduced and its applicability in consistently describing various experiments on single NV centers was demonstrated. The model took account of the triplet–triplet character of the optical transition, 3A–3E (637nm), of the center and of the presence of a metastable singlet state 1A. By supposing the optical excitation rates, BT, from the spin sub-states (T = X, Y, Z) of the ground 3A state as well as the fluorescence emission rates, AT, to these sub-states to be different (with BZ/BX equal to about 11, BX = BY and AZ/AX equal to about 18, AX = AY), it was possible to fit consistently the experimental data obtained for green-laser excited single NV centers at room-temperature. These data were the lineshapes of fluorescence-detected magnetic resonance at 2.88GHz in the ground 3A state and their changes due to the strains in the diamond crystal, fluorescence saturation and photon anti-bunching/bunching in the fluorescence light emitted by a single NV center.

Modeling Fluorescence of Single Nitrogen–Vacancy Defect Centers in Diamond. A.P.Nizovtsev, S.Y.Kilin, C.Tietz, F.Jelezko, J.Wrachtrup: Physica B, 2001, 308-310, 608-11