Does Progressive Nitrogen Doping Intensify Negatively Charged Nitrogen Vacancy Emission from e-Beam-Irradiated Ib Type High-Pressure–High-Temperature Diamonds?

Micron-sized samples of Ib type high-pressure–high-temperature diamonds synthesized with low and high substitutional nitrogen content and high energy e-beam irradiated to form luminescent negatively charged nitrogen-vacancy (NV–) centers are studied by X-band electron paramagnetic resonance (EPR), photoluminescence (PL), and Raman techniques. High nitrogen doping leads to the appearance of paramagnetic centers characterized by strong interactions between unpaired spins of substitutional nitrogen defects. Actual concentrations of paramagnetic substitutional nitrogen and NV– centers were obtained by EPR. The intensity of the PL emission from NV– centers was analyzed as a function of the content of NV– centers. We report that the NV– PL intensity is controlled by both the content of NV– centers and the presence of nitrogen-related crystal defects/imperfections. Increasing the nitrogen content increases the structural imperfections, which are responsible for the appearance of additional nonradiative recombination centers and significant intensification of PL quenching. It is suggested that PL intensity may be optimized by the appropriate choice of nitrogen doping and irradiation fluence.