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Creation of uniformly dispersed nitrogen-vacancy centers in nano-diamonds by low energy ion-irradiation

The inability of the fabrication of uniformly distributed Nitrogen-vacancy (NV) centers in Nano diamonds (NDs) puts serious limitation on their application in bio-medical, sensing and nano-photonics applications. Asymmetry in the concentration of NV centers is mainly due to vacancy generation by single energy ion-irradiation. We report the fabrication of uniform and high concentration of NV centers in NDs using different low energy He+ ion irradiation. The He+ ion-irradiation was carried out at different energy range between 10 to 50 keV based on the SRIM simulation for the creation of vacancies. The ion implantation was not found detrimental to the crystallinity of NDs. No sign of intra-crystallite defect patches was found as revealed by x-ray diffraction (XRD). Emission spectra reveal that particular irradiation energy range (40–50 keV) leads to maximum emission intensity from NV centers. Further emission contrast in ZPL of NV−/NVo becomes ∼2 fold for this energy range. The emission from NV centers (570–670 nm) is relatively uniform and well dispersed for 40–50 keV as revealed by confocal microscopy. This suggests that ion irradiation at 40–50 keV is the optimized ion dose for the fabrication of uniformly dispersed high concentration of NV− centers in NDs.