N‐V‐related fluorescence of the monoenergetic high‐energy electron‐irradiated diamond nanoparticles

Fluorescent diamond nanoparticles (FND) have recently been introduced as promising luminescent probes for bioimaging to compete with more commonly used fluorophores and quantum dots. In this work, we investigate the formation of NV color centers in diamond nanocrystallites using monoenergetic electrons. A large quantity (1.4 g) of FNDs has been irradiated in the cyclic relativistic electron accelerator (Microtron) with the surface charge up to 3C/cm2 using collimated accelerated electrons extracted with monochromatic energies 6−25 MeV. The nitrogen-vacancy (NV) color centers have been activated by the high temperature vacuum annealing followed by the oxidation and sonification to remove sp2 carbon from the surface and to form stable colloid solutions with the concentration 1 mg/ml and the electro-kinetic (zeta) potential about −35 mV. The steady state fluorescence spectra show that the fluorescence yield increases linearly with the surface charge irradiation.