Nitrogen-vacancy (NV) centers in diamond have been exploited as reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers: NV0 and NV–, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, the understanding of the dynamics between the different states still remains challenging. Here we show that electron excitation induces the conversion from NV– to NV0 through electron-induced carrier generation. We present for the first time ultrafast pump-probe cathodoluminescence spectroscopy, with electron pulses as pump, and laser pulses as probe, to prepare and read out the NV states. The experimental data is explained with a model considering carrier dynamics (0.8 ns), NV0 spontaneous emission (20 ns) and NV0NV– back transfer (500 ms). Our results provide new insights into the NV–NV0 conversion dynamics, and into the use of pump-probe cathodoluminescence as a nanoscale NV characterization tool.
Nitrogen-vacancy (NV) centers in diamond have been exploited as reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers: NV0 and NV–, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, the understanding of the dynamics between the different states still remains challenging. Here we show that electron excitation induces the conversion from NV– to NV0 through electron-induced carrier generation. We present for the first time ultrafast pump-probe cathodoluminescence spectroscopy, with electron pulses as pump, and laser pulses as probe, to prepare and read out the NV states. The experimental data is explained with a model considering carrier dynamics (0.8 ns), NV0 spontaneous emission (20 ns) and NV0NV– back transfer (500 ms). Our results provide new insights into the NV–NV0 conversion dynamics, and into the use of pump-probe cathodoluminescence as a nanoscale NV characterization tool.
Abstract Nitrogen-vacancy (NV) centers in diamond are reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers, NV0 and NV–, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, an understanding of the dynamics between the different states still remains challenging. Here, conversion from NV– to NV0 due to electron-induced carrier generation is shown. Ultrafast pump–probe cathodoluminescence spectroscopy is presented for the first time, with electron pulses as pump and laser pulses as probe, to prepare and read out the NV states. The experimental data are explained with a model considering carrier dynamics (0.8 ns), NV0 spontaneous emission (20 ns), and NV0 → NV– back transfer (500 ms). The results provide new insights into the NV– → NV0 conversion dynamics and into the use of pump–probe cathodoluminescence as a nanoscale NV characterization tool.
Ultrafast conversion dynamics between the NV 0 and NV – charge states in diamond is crucial for spin-state manipulation and readout. However, the underlying mechanism of the conversion, including the effective excitation wavelength, the time scales of the conversion, and the influencing factors, is still unclear. Here, we proposed a method to probe the ultrafast conversion of the two charge states via two-photon excitation with femtosecond laser pulses separated by 12.5 ns. We found that the highest conversion efficiency occurs at the excitation wavelength of around 532 nm, and the efficiency increases with temperature as well. The conversion time from NV 0 to NV – is obtained to be around 75 ps at 300 K. These findings advance the understanding of NV center charge-state dynamics and provide insights for high-speed spin readout in quantum information applications.
The charge state stability of nitrogen-vacancy (NV) centers critically affects their application as quantum sensors and qubits. Understanding charge state conversion and equilibration is important not only for NV centers in diamond but also for defects and impurities in wide-bandgap materials in general. The mechanisms by which these centers change charge state upon optical or electronic excitation without the presence of mobile carriers remain unclear. Here, we elucidate this issue for the case of photoionization of NV center ensembles. Using pump-probe spectroscopy, we ionize negatively charged NV centers and monitor the recovery of NV^{-} on timescales of up to several seconds. We find that the recovery rate depends strongly on the concentration of surrounding nitrogen donors. Remarkably, the equilibration dynamics exhibit no discernible dependence on temperature, ruling out thermally activated processes. We develop a multiphonon-assisted electron-tunneling model, supported by density-functional calculations, that explains the measurements and identifies tunneling as the equilibration mechanism. Because tunneling rates depend exponentially on donor separation, the random distribution of nitrogen donors spreads recovery times from nanoseconds to hours or longer.
Abstract Nitrogen-vacancy (NV) and silicon-vacancy (SiV) color defects in diamond are promising systems for applications in quantum technology. The NV and SiV centers have multiple charge states, and their charge states have different electronic, optical and spin properties. For the NV centers, most investigations for quantum sensing applications are targeted on the negatively charged NV (NV−), and it is important for the NV centers to be in the NV− state. However, it is known that the NV centers are converted to the neutrally charged state (NV0) under laser excitation. An energetically favorable charge state for the NV and SiV centers depends on their local environments. It is essential to understand and control the charge state dynamics for their quantum applications. In this work, we discuss the charge state dynamics of NV and SiV centers under high-voltage nanosecond pulse discharges. The NV and SiV centers coexist in the diamond crystal. The high-voltage pulses enable manipulating the charge states efficiently. These voltage-induced changes in charge states are probed by their photoluminescence spectral analysis. The analysis result from the present experiment shows that the high-voltage nanosecond pulses cause shifts of the chemical potential and can convert the charge states of NV and SiV centers with the transition rates of ∼MHz. This result also indicates that the major population of the SiV centers in the sample is the doubly negatively charged state (SiV2−), which is often overlooked because of its non-fluorescent and non-magnetic nature. This demonstration paves a path for a method of rapid manipulation of the NV and SiV charge states in the future.
In this letter, the photon-induced charge conversion dynamics of a single Nitrogen-Vacancy (NV) center in nanodiamond between two charge states, negative (NV−) and neutral (NV0), is studied by the auto-correlation function. It is observed that the ionization of NV− converts to NV0, which is regarded as the dark state of the NV−, leading to fluorescence intermittency in single NV centers. A new method, based on the auto-correlation calculation of the time-course fluorescence intensity from NV centers, was developed to quantify the transition kinetics and yielded the calculation of transition rates from NV− to NV0 (ionization) and from NV0 to NV− (recharging). Based on our experimental investigation, we found that the NV−-NV0 transition is wavelength-dependent, and more frequent transitions were observed when short-wavelength illumination was used. From the analysis of the auto-correlation curve, it is found that the transition time of NV− to NV0 (ionization) is around 0.1 μs, but the transition time of NV0 to NV− (recharging) is around 20 ms. Power-dependent measurements reveal that the ionization rate increases linearly with the laser power, while the recharging rate has a quadratic increase with the laser power. This difference suggests that the ionization in the NV center is a one-photon process, while the recharging of NV0 to NV− is a two-photon process. This work, which offers theoretical and experimental explanations of the emission property of a single NV center, is expected to help the utilization of the NV center for quantum information science, quantum communication, and quantum bioimaging.
Nitrogen-vacancy (NV) centers in single-crystal CVD diamond are promising candidates for quantum sensing due to their remarkable optical and spin properties [1]. These defects exhibit stable photoluminescence (PL), long spin coherence times, and high sensitivity to external fields [2]. In this study, we present a room-temperature PL characterization of NV centers excited with a 532 nm laser. The setup was optimized for high signal-to-noise ratio and spectral resolution. Key parameters analyzed include emission intensity, zero-phonon line (ZPL) at ~637 nm, phonon sidebands, and the charge state distribution between NV⁰ and NV⁻. The NV⁻ state, crucial for spin-based sensing, is evaluated to understand its stability under different nitrogen doping conditions [3]. The relative intensities of NV⁰ and NV⁻ provide insights into nitrogen incorporation and vacancy formation. These results contribute to optimizing synthesis conditions for enhanced NV⁻ concentration, supporting the advancement of diamond-based quantum sensing technologies.