Photoluminescence decomposition analysis: a technique to characterize NV creation in diamond

Abstract

Treatment of lab-grown diamond by electron irradiation and annealing has enabled quantum sensors based on negatively-charged nitrogen-vacancy (NV${}^{\text{-}}$) centers to demonstrate record sensitivities. \cite{Clevenson2015,Wolf2015,Barry2016,Chatzidrosos2017}. Here we investigate the irradiation and annealing process applied to 28 diamond samples using a new ambient-temperature, all-optical approach. As the presence of the neutrally-charged nitrogen-vacancy (NV${}^{\text{0}}$) center is deleterious to sensor performance, this photoluminescence decomposition analysis (PDA) is first employed to determine the concentration ratio of NV${}^{\text{-}}$ to NV${}^0$ in diamond samples from the measured photoluminescence spectrum. The analysis hinges on (i) isolating each NV charge state's emission spectrum and (ii) measuring the NV${}^{\text{-}}$ to NV${}^0$ emission ratio, which is found to be 2.5$\pm$0.5 under low-intensity 532 nm illumination. Using the PDA method, we measure the effects of irradiation and annealing on conversion of substitutional nitrogen to NV centers. Combining these measurements with a phenomenological model for diamond irradiation and annealing, we extract an estimated monovacancy creation rate of $0.52\pm 0.26$ cm${}^{\text{-1}}$ for 1 MeV electron irradiation and an estimated monovacancy diffusion coefficient of 1.8 nm${}^2$/s at 850~${}^{\circ }$C. Finally we find that irradiation doses $\gtrsim 10^{18}$ e${}^{\text{-}}$/cm${}^2$ deteriorate the NV${}^{\text{-}}$ decoherence time $T_2$ whereas $T_1$ is unaffected up to the the maximum investigated dose of $5\times 10^{18}$ e${}^{\text{-}}$/cm${}^2$.

19 pages, 10 figures