Engineering Nitrogen-Vacancy Centers in Nano-diamonds for Single Photon Emission

Defects in diamond have evolved as unique object for their potential application for Optical imaging and Nano-photonics. High pressure high temperature (HPHT) grown type-Ib diamond particles were milled down to the size of ~ 80 nm and purified to remove iron & graphitic carbon impurities and irradiated with 35 KeV He+ ions to create vacancies in the diamond lattice. Vacancies diffuse close to substitutional nitrogen impurities of nano-diamond particles upon thermal treatment. Characteristic sharp emission of NV centers were observed at 575.5 nm and 637.9 nm corresponding to NV° and NV− charged states in addition to a broad emission in the range 550-750 nm. Structural and photo-physical behavior of these fluorescent diamonds was found to depend on the method of purification adopted. Samples purified through acid reflux were found suitable for bio-imaging applications while, sample purified through air oxidation shows properties desirable for Nano-photonic applications. Photon-correlation measurements of emission from individual diamond nanoparticles using Hanbury Brown and Twiss interferometer (HBT) shows anti-bunching curve with g2(t)= 0 confirming their suitability as single photon source. Such sources of indistinguishable photons are highly desirable for quantum computation and quantum optics applications.