RESUMEN
The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV(-) into the neutral state NV(0) under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV(0), and the population of an ensemble of centres can be shifted from NV(0) to NV(-). Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV(+).
RESUMEN
This article reports stable photoluminescence and high-contrast optically detected electron spin resonance (ODESR) from single nitrogen-vacancy (NV) defect centers created within ultrasmall, disperse nanodiamonds of radius less than 4 nm. Unexpectedly, the efficiency for the production of NV fluorescent defects by electron irradiation is found to be independent of the size of the nanocrystals. Fluorescence lifetime imaging shows lifetimes with a mean value of around 17 ns, only slightly longer than the bulk value of the defects. After proper surface cleaning, the dephasing times of the electron spin resonance in the nanocrystals approach values of some microseconds, which is typical for the type Ib diamond from which the nanoparticle is made. We conclude that despite the tiny size of these nanodiamonds the photoactive nitrogen-vacancy color centers retain their bulk properties to the benefit of numerous exciting potential applications in photonics, biomedical labeling, and imaging.