The negatively charged diamond nitrogen‐vacancy () center plays a central role in many quantum sensing applications, though much is still unknown about the energy levels in this system. The ionization energy of the singlet state in the center has only recently been measured to be between 2.25 and 2.33 eV. In this work, we reduce this uncertainty by measuring the ionization energy as a function of excitation laser wavelength and diamond temperature via magnetically mediated spin‐selective photoluminescence (PL) quenching that transfers population from the in the into the neutral charge configuration. Measurements are performed for excitation wavelengths between 450 and 470 nm, and between 540 and 566 nm in increments of 2 nm, and for temperatures ranging from about 50 to 150 K in 5 K increments. We determine the ionization energy to be between 2.29 and 2.33 eV, which provides about a twofold reduction in uncertainty of this quantity. Distribution level: A. Approved for public release; distribution unlimited.
The negatively charged diamond nitrogen‐vacancy () center plays a central role in many quantum sensing applications, though much is still unknown about the energy levels in this system. The ionization energy of the singlet state in the center has only recently been measured to be between 2.25 and 2.33 eV. In this work, we reduce this uncertainty by measuring the ionization energy as a function of excitation laser wavelength and diamond temperature via magnetically mediated spin‐selective photoluminescence (PL) quenching that transfers population from the in the into the neutral charge configuration. Measurements are performed for excitation wavelengths between 450 and 470 nm, and between 540 and 566 nm in increments of 2 nm, and for temperatures ranging from about 50 to 150 K in 5 K increments. We determine the ionization energy to be between 2.29 and 2.33 eV, which provides about a twofold reduction in uncertainty of this quantity. Distribution level: A. Approved for public release; distribution unlimited.
The 1E--1A1 singlet manifold of the negatively charged nitrogen vacancy ($\mathrm{N}{V}^{\ensuremath{-}}$) center in diamond plays a central role in its quantum-information and quantum-sensing applications. However, the energy gap between the 1E singlet state and diamond band edges or the 3A2--3E triplet manifold has not been measured directly. Using the magnetic-field quenching effect on the $\mathrm{N}{V}^{\ensuremath{-}}$ photoluminescence (PL) spectra, we measure these energy gaps as a function of temperature, applied magnetic field, excitation wavelength, and excitation power in a heavily nitrogen-doped sample. Increased PL and decreased zero-phonon line width from the NV0 center were observed in the presence of an applied magnetic field, indicating ionization from the long-lived 1E singlet state. A temperature-dependent ionization threshold between 532 and 550 nm was found, locating the singlet states within the diamond band gap.
Spectroscopy of photoionization from the 1E singlet state in nitrogen−vacancy centers in diamond
The 1E−1A1 singlet manifold of the negatively charged nitrogen vacancy (NV−) center in diamond plays a central role in the quantum information and quantum sensing applications of the NV− center. However, the energy of this manifold within the diamond bandgap and with respect to the 3A2−3E triplet manifold has not been measured directly. Using field-quenching effects on photoluminescence (PL) spectra, we report on the energy gap between the 1E−1A1 singlet manifold and the 3A2 and 3E ground and excited triplet states of the NV− as a function of excitation wavelength and power, temperature, and applied magnetic field in a heavily nitrogen-doped sample. Increased PL and decreased zero-phonon line width from the NV0 were observed in the presence of an applied magnetic field, indicating ionization from the long-lived 1E singlet state. A temperature-dependent ionization threshold between 532 nm and 550 nm was found, locating the singlet states within the diamond band gap.
The singlet states of the negatively charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be in the range 1.91--2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and nitrogen-vacancy charge state differentiation, along with simulations based on the nitrogen-vacancy's master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved readout methods.
The nitrogen–vacancy centre (NV) has drawn much attention for over a decade, yet detailed knowledge of the photophysics needs to be established. Under typical conditions, the NV can have two stable charge states, negative (NV − ) or neutral (NV 0 ), with photo-induced interconversion of these two states. Here, we present detailed studies of the ionization dynamics of single NV centres in bulk diamond at room temperature during illumination and its dependence on the excitation wavelength and power. We apply a recent method which allows us to directly measure the charge state of a single NV centre, and observe its temporal evolution. We find that the steady-state NV − population is always ⩽75% for 450–610 nm excitation wavelength. In combination with saturation measurements, we show that the optimal excitation wavelength is around 510–540 nm. Furthermore, the relative absorption cross-section of NV − is determined for 540–610 nm, revealing a double-peak structure. Finally, the energy of the NV − ground state of 2.6 eV below the conduction band is measured. These results reveal new insights into the charge state dynamics of the NV centre.
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 negatively charged nitrogen vacancy center in diamond is widely used for quantum sensing due to the sensitivity of the spin triplet in the electronic ground state to external perturbations such as strain and electromagnetic fields, which makes it an excellent probe for changes in these perturbations. The spin state can be measured through optically detected magnetic resonance, which is most commonly achieved by detecting the photoluminescence after exciting the spin-triplet transition. Recently, methods have been proposed and demonstrated that use the absorption of the infrared singlet transition at 1042 nm instead. These methods, however, require cryogenic temperatures or external cavities to enhance the absorption signal. Here, we report on our efforts to optimize the magnetometer sensitivity at room temperature and without cavities. We reach a sensitivity of 18 pT / Hz , surpassing previously reported values, and a calculated shot-noise limit of 5 pT / Hz . We also report on a defect that is native to diamond grown by chemical vapor deposition and thus absent in high-pressure high-temperature diamond, the excitation of which impacts the measured singlet absorption signal.