Fig. 1

Emission properties of NV color centers in diamond. a Atomic configuration of NV color defect in diamond. One nitrogen (blue) and three carbons (green) are adjacent to a vacancy site. The NV center can exist in two charge configurations, the neutrally charge NV0 center and the negatively charged NV− center. b Two level model of the electronic transitions of the NV− color center. c Emission spectrum of nanodiamonds. The spectrum shows a zero phonon line at 575 nm for the NV0 center and at 637 nm for the NV− center. Both centers show a broad phonon side band