Abstract The concentration and distribution of negatively charged nitrogen-vacancy color centers (NV−) directly affect the sensitivity and resolution of quantum sensing. In this paper, a simple method is proposed to estimate the concentration of the ensemble of NV− centers with spin coherent manipulation. The stray fluorescence is eliminated by separating the fluorescence near the NV− zero-phonon line. By introducing a single NV− fluorescence quantitative model, the number of NV− centers in the diamond under test can be obtained. The average concentration of the ensemble of NV− centers in the sample can be obtained by combining the detection volume. Compared with the results measured by electron spin resonance, the concentration of NV− centers measured by our method can be verified, and the maximum error between the two methods is less than 4.3%. The results show that the method provides an effective reference for accurately characterizing the concentration distribution characteristics of the NV− ensemble.
Abstract The concentration and distribution of negatively charged nitrogen-vacancy color centers (NV−) directly affect the sensitivity and resolution of quantum sensing. In this paper, a simple method is proposed to estimate the concentration of the ensemble of NV− centers with spin coherent manipulation. The stray fluorescence is eliminated by separating the fluorescence near the NV− zero-phonon line. By introducing a single NV− fluorescence quantitative model, the number of NV− centers in the diamond under test can be obtained. The average concentration of the ensemble of NV− centers in the sample can be obtained by combining the detection volume. Compared with the results measured by electron spin resonance, the concentration of NV− centers measured by our method can be verified, and the maximum error between the two methods is less than 4.3%. The results show that the method provides an effective reference for accurately characterizing the concentration distribution characteristics of the NV− ensemble.
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.
The nitrogen-vacancy (NV) center in diamond enables optical initialization and readout of its electronic spin, forming the basis of a wide range of quantum sensing and metrology applications. A central challenge in such measurements is the coexistence of two charge states, NV- and NV0: While detection protocols rely on the spin-dependent properties of NV-, fluorescence from NV0 does not carry useful contrast and is typically removed as background, reducing the available signal. Here, we show that the origin of NV0 emission depends strongly on the excitation wavelength in nitrogen-containing diamond. Using ensembles of NV centers with varying nitrogen concentrations, we compare excitation at the NV0 zero-phonon line (ZPL) at 575 nm with the commonly used 532 nm. We find that excitation at 575 nm generates NV0 predominantly through spin-selective tunneling from the excited state of NV- to nearby nitrogen donors, such that the NV0 emission follows the spin polarization of NV-. As a result, the NV0 fluorescence contributes to the measurable spin contrast, allowing the full fluorescence signal to be used for detection. This result opens opportunities for improved sensitivity in NV-based sensing applications.
The negatively charged nitrogen−vacancy (NV − ) center ensembles in diamonds offer enormous potential for developing integrated sensors with an improved signal-to-noise ratio (SNR) and high sensitivity. However, the preparation and treatment of diamond samples with suitable NV − concentrations and dephasing time have remained challenging. This work provided insight into the NV − center formation mechanism and reconstruction via a comprehensive analysis of the concentration and dephasing time of a set of diamond samples treated by various parameters. By varying the electron irradiation dose and subsequent annealing duration, the conversion rate of nitrogen to NV − is up to 18.45%, and the corresponding maximum NV − concentration is 3.69 ppm. The dephasing time for all samples varies around 300 ns. The nitrogen-related NV − center ensemble dephasing rate per unit density is 146.4 (ppm·ms) −1 , indicating that the treatment did not substantially alter the paramagnetic spin environment around the NV − center. This study not only offers support to exquisite sensitivities of NV-based sensors but also provides valuable experience for the preparation of unique properties of synthetic diamonds.
Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( T2∗ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.
The ensemble of nitrogen-vacancy (NV) centers is widely used in quantum information transmission, high-precision magnetic field, and temperature sensing due to their advantages of long-lived state and the ability to be pumped by optical cycling. In this study, we investigate the zero-phonon line behavior of the two charge states of NV centers by measuring the photoluminescence of the NV center at 1.6 K-300 K. The results demonstrate a positional redshift, an increase in line width, and a decrease in fluorescence intensity for the ZPL of NV0 and NV- as the temperature increased. In the range of 10 K to 140 K, the peak shift with high concentrations of NV- revealed an anomaly of bandgap reforming. The peak position undergoes a blueshift and then a redshift as temperature increases. Furthermore, the transformation between NV0 and NV- with temperature changes has been obtained in diamonds with different nitrogen concentrations. This study explored the ZPL characteristics of NV centers in various temperatures, and the findings are significant for the development of high-resolution temperature sensing and high-precision magnetic field sensing in ensemble NV centers.
NV- center has been paid attention as a quantum sensor for highly sensitive detection of magnetic field, electric field, temperature and strain, etc.. Electron beam irradiation followed by subsequent thermal annealing is known as the effective procedures to create NV- center in diamond. The electron irradiation generates vacancies in diamond and the annealing enables vacancies to diffuse in the lattice. Then diffused vacancies are captured by nitrogen atoms, and as a result, NV centers are created. In addition, substitutional nitrogen atom at a lattice site (P1 center) also acts as a donor for NV center, the charge state of NV centers changes from neutral (NV0) to NV-. Creation high concentration of ensemble NV- centers is needed to achieve high sensitively sensing. The magnetic sensitivity is proportional to the reciprocal of the number of NV centers and T2 (spin coherence time), i.e., high concentration NV- centers with long T2 increase the sensitivity. P1 center has an important role for being a component of NV- centers and acting as donor to the NV center. But it also plays a role as decoherence source (decrease in magnetic field sensitivity). Therefore, it is important to create high concentration of NV- centers considering the amount of P1 centers. In current study, we investigate irradiation fluence dependence of the creation behavior of NV centers in type-Ib diamonds by using electron spin resonance (ESR) and photo-luminescence (PL) to understand the creation mechanism of NV- center. The values of T2 are also evaluated by Hahn-echo measurement, since it is one of the key parameters for highly sensitive magnetometry. Then, we discuss the creation mechanism of NV centers based on concentrations of defects.