Stable ensemble brightness from nitrogen vacancy centers in nanodiamonds through optimized surface composition

Abstract

Stable ensemble emission from nitrogen vacancy (NV) centers in nanodiamonds (NDs) is highly desirable for diverse areas ranging from bio-imaging to quantum optics. The uniqueness of NV centers lies in their opto-spin properties like energy level structure, emission range (620-850 nm) and optical spin polarization. The host matrix (NDs), however, put some limitation on the photo-physical properties of these color centers. One of the major issues is surface proximity (where high concentration of defects are present) of NV centers. The NV centers being highly sensitive to the neighboring environment are unstable in such circumstances. The surface of NDs mainly exhibit non-diamond carbon which is well-known quencher of emission due to NV centers. The surface composition for desirable photo-physical properties of NV centers is still unknown. Here, we have systemically studied the effect of oxidation time at low oxidation temperature (450 ^oC) on the selective removal of sp² carbon, aqueous dispersion of NDs and emission collection due to NV centers at ensemble level. Among different air oxidations, heat treatment at 450 ^oC at residual time of 8 hours has been found to be suitable air oxidation conditions for the enhancement of brightness and ensemble photo-stability of NV centers.