Electron irradiation-induced paramagnetic and fluorescent defects in type Ib high pressure-high temperature microcrystalline diamonds and their evolution upon annealing

Defects introduced to synthetic type Ib diamond micrometer-size particles by electron-beam irradiation were studied by electron paramagnetic resonance and photoluminescence (PL) spectroscopy as a function of e-beam fluence and post-irradiation thermal annealing. Increasing electron-beam fluence causes a substantial reduction of the substitutional nitrogen (P1) content, accompanied by progressively higher concentrations of paramagnetic negatively charged vacancies (V-) and triplet interstitials (R1/R2). Annealing results in a drastic decrease in the V- and R1/R2 content and an increase in the negatively charged nitrogen-vacancies (NV- or W15). Analysis of PL spectra allows for identification of color centers in the irradiated diamond samples and following their evolution after annealing. These data facilitate understanding of different factors contributing to the formation of color centers in diamond and promote efforts toward controlled engineering of optical centers in fluorescent diamond particles.