Optimal vacancy concentrations to maximize the N-V yield in nanodiamonds

In recent years fluorescent diamond nanoparticles have begun to fill the need for optically bright and stable, non-toxic probes for a growing range of biomedical applications. Significant attention has been given to finding ways of obtaining small particles with a higher yield of the optically active N-V defects, on-demand, by processing mass produced samples post defacto. While it has been established that a combination of irradiation (to introduce an abundance of vacancies) and annealing (to increase vacancy mobility) can achieve these goals, it is desirable to know how many vacancies to introduce a priori. In this paper a numerical model is developed to predict and compare the yield of different nitrogen/vacancy complexes in nanodiamond, as a function of the individual nitrogen and vacancy concentrations, the particle size and annealing temperature. The results reveal that, irrespective of the temperature and nitrogen content, this processing strategy is unlikely to work for detonation nanodiamond, but tuning these concentrations can promote the formation of N-V or H3 defects over similar to 20 nm.