Impacts of nitrogen concentration and electron irradiation fluence on the formation of nitrogen-vacancy defects in diamond

Using the diamond samples with different N concentrations and irradiated by 10 MeV electron beam with the fluences varied from 2.5 x 1017 to 1.0 x 1019 cm-2, the formation of negatively-and neutrally-charged nitrogen -vacancy (NV- and NV0) defects is explored by quantitatively characterizing the concentration of NV defects with the absorption coefficient of NV- at the zero phonon line (ZPL). In the samples with high N concentrations ranging from a few dozen to >100 ppm, the NV- centers are predominant as the electron irradiation fluence is 2.5 x 1017 cm-2. With the increase in the irradiation fluence, NV- concentration is almost linearly increased and NV0 starts to appear in the diamond samples. For the samples with a few ppm N or lower, a fluence of 2.5 x 1017 cm-2 is sufficient to lead to co-existence of NV- and NV0 centers, and the concentration of NV0 centers will increase with the increase in the influence while the NV- concentration becomes relatively low. In the formation of NV defects, excessive N and vacancy are suggest to act as the roles of donor and acceptor, respectively, and thus dominate the formation of NV- and NV0 centers. Therefore, the concentrations of NV centers could be controllably fabricated if the N concentration is determined. In addition to NV- and NV0 centers, other irradi-ation defects are observed to be luminescent and in association with N and vacancy concentrations. In the samples with high N concentrations, the ZPL490 line is brighter than ZPL503 and ZPL467 lines. In the samples with low N and irradiated by electron beam with high fluences (>2.5 x 1018 cm-2), however, the ZPL503 and ZPL467 lines are relatively bright, while the ZPL490 line is rather weak, as weak as lower than the detection limit.