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The $N_2V$ color center: a ubiquitous visible and near-infrared-II quantum emitter in nitrogen-doped diamond

T0 review · 2 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash

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Pith's one-line read N2V defect is a ubiquitous NIR-II emitter in nitrogen-doped diamond

desk verdict Solid spectroscopy on a known defect; first N2V- lifetime and commercial-sample survey are useful, but the DND NIR-II attribution is circumstantial and the modeling is fitted, not predictive. read the letter →

arxiv 2412.11054 v2 pith:O2JGVUJE submitted 2024-12-15 cond-mat.mes-hall

Brett C. Johnson , Mitchell O. de Vries , Alexander J. Healey , Marco Capelli , Anjay Manian , Giannis Thalassinos , Amanda N. Abraham , Harini Hapuarachchi
show 8 more authors
Tingpeng Luo Vadym Mochalin Jan Jeske Jared H. Cole Salvy Russo Brant C. Gibson Alastair Stacey Philipp Reineck
This is my paper · ORCID
classification cond-mat.mes-hall
keywords N2VcolorcenternitrogenvacancydiamondNIR-IIphotoluminescencedetonationnanodiamondquantumemitterlifetimehigh-pressurehigh-temperature
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper argues that the nitrogen-vacancy-nitrogen (N2V) defect—two nitrogen atoms flanking a vacancy—is far more common than previously appreciated, appearing in as-synthesized HPHT diamond from bulk crystals down to 1 µm particles, in CVD diamond including commercial NV sensing chips, and most likely in detonation nanodiamonds. Its neutral charge state N2V0 emits green light around 540 nm, while the negative charge state N2V- emits in the NIR-II window (950–1400 nm), a spectral region useful for deep-tissue imaging and telecom. The paper reports the first measured PL lifetime of N2V-, 0.323 ± 0.002 ns, and shows that the PL intensity of both charge states rises with substitutional nitrogen concentration. It also demonstrates NIR-II imaging of detonation nanodiamonds inside skin cells. If the ubiquity claim holds, N2V- is a ready-made NIR-II emitter already present in commercial diamond materials.

What carries the argument

The carrying object is the N2V color center itself, a defect consisting of a pair of nitrogen atoms separated by a single carbon vacancy (also called H3 and H2 for the neutral and negative charge states). Its two charge states have well-separated emission bands—N2V0 in the visible near 540 nm with a 503 nm zero-phonon line, N2V- in the NIR-II with a ~986 nm zero-phonon line and phonon sidebands at ~1035 nm and ~1191 nm—which lets the paper track both charge states independently by photoluminescence. Supporting mechanisms include: the donor level of substitutional nitrogen (Ns0/Ns+ at ~3.6 eV above the valence band) that can convert N2V0 to N2V-, DFT charge-transition levels that place N2V-/0 below Ns0/+, the FTIR absorption at 1130 cm-1 used to quantify Ns0, and the ODMR linewidth of NV centers used as a nitrogen-content proxy in microparticles. A phenomenological quantum optical model with vibronic ground states and a fitted dephasing rate, together with a DFT calculation on a hydrogen-terminated 118-carbon nanocrystal, reproduces the measured cryogenic N2V- spectrum.

What would settle it

Measure the photoluminescence lifetime and power dependence of the NIR-II emission from a single detonation nanodiamond after aggressive oxidative purification: N2V- should show a ~0.3 ns single-exponential lifetime and a ZPL (broadened but recoverable at 5 K), while carbon-dot-like emission would show ns–µs multi-exponential decay, excitation-wavelength-dependent spectra, and bleaching. Alternatively, if a 986 nm zero-phonon line can be resolved in 5 K spectra of well-purified DNDs, the assignment is confirmed.

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Extended reading notes

Core claim

The central claim is that N2V is a ubiquitous fluorescent color center in nitrogen-doped diamond: both N2V0 and N2V- are present as-synthesized, without any deliberate defect-engineering, across a wide range of commercial and laboratory samples—HPHT bulk plates and particles from 10 µm down to 0.5 µm, CVD films with as little as 10 ppm substitutional nitrogen, and detonation nanodiamonds. The two charge states are spectrally separated by more than 300 nm at room temperature (N2V0 ZPL at 503 nm; N2V- ZPL at ~986 nm), which allows their separate identification. The PL intensity of both charge states increases with Ns0 concentration in HPHT diamond, the N2V- lifetime is 0.323 ± 0.002 ns, and 5 K spectra are reproduced by a quantum optical model and qualitatively by DFT. The paper further attributes the stable NIR-II emission of detonation nanodiamonds to N2V-, and uses it to image nanodiamonds inside skin cells in the NIR-II window.

Load-bearing premise

The weakest link is the identification of N2V- in detonation nanodiamonds, which is based on spectral shape, photostability, excitation-wavelength independence, and high nitrogen/vacancy content, without a directly observed zero-phonon line at 5 K; if that emission actually comes from non-diamond carbon or another defect, the 'ubiquitous' claim for DNDs would be undermined.

Editorial extensions

If this is right

  • Because N2V is present in as-synthesized commercial HPHT and CVD diamond, any optical measurement on nitrogen-rich diamond—including NV-based quantum sensing—must account for N2V photoluminescence and possible photoionization cross-talk.
  • The first reported N2V- lifetime of 0.323 ± 0.002 ns enables quantitative modeling of N2V- emission and its contributions to diamond photoluminescence.
  • The positive correlation between N2V PL and substitutional nitrogen concentration provides a simple route to engineer N2V brightness by choosing nitrogen-doped diamond with higher Ns0 content.
  • Detonation nanodiamonds, already produced at scale and taken up by cells, can serve as NIR-II photostable bioimaging labels without additional defect-creation processing.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If N2V- is indeed ubiquitous in commercial diamond, then NV-based quantum sensors and computers may already be suffering from N2V-induced photoabsorption around 700 nm and non-radiative electron-transfer pathways; a controlled experiment comparing NV PL quantum yield in diamond with and without N2V would quantify this.
  • The 0.3 ns lifetime implies a very fast emission rate; if the quantum yield turns out to be high, N2V- could be useful for super-resolution or high-speed imaging where rapid photon turnover matters.
  • The NIR-II emission falling in the telecom O-band (1260–1360 nm) suggests N2V- could be developed as a waveguide-coupled single-photon source in silicon photonics, but that would require demonstrating single-photon emission from N2V-, which has not been reported.
  • The apparent absence of a ZPL in DNDs could be turned into a diagnostic: systematic measurement of ZPL broadening as a function of particle size and strain might provide a quantitative probe of surface- and size-related strain in nanodiamonds.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

2 major / 5 minor

Summary. This manuscript reports an experimental survey of the nitrogen-vacancy-nitrogen (N2V) color center in nitrogen-doped diamond samples from multiple commercial suppliers. The authors identify the characteristic zero-phonon lines of N2V0 (503 nm) and N2V- (986 nm) in bulk and micron-sized HPHT diamonds, observe that both charge states scale with substitutional nitrogen concentration, show N2V0 in CVD-grown samples, measure a 0.323 ns lifetime for N2V-, compare 5 K and 300 K spectra with a quantum-optical model and a DFT model, and attribute stable NIR-II photoluminescence from detonation nanodiamonds to N2V-, using that emission for cellular imaging. The central claim is that N2V is a ubiquitous visible and NIR-II emitter in nitrogen-doped diamond from bulk samples down to nanodiamond particles.

Significance. If the results hold, the paper establishes a common, commercially available NIR-II emitter in diamond that is relevant for bioimaging and telecom-wavelength quantum photonics, and it reports the first N2V- lifetime measurement. The experimental core is well documented: a multi-supplier sample table, FTIR nitrogen quantification, growth-sector control, ODMR linewidth correlations, and a carefully deconvolved time-resolved measurement. The weakest link is the DND attribution, which is circumstantial and is explicitly acknowledged as uncertain in the text. The model comparisons are useful but are consistency checks rather than independent predictions. Overall the manuscript deserves publication after the DND claim is either substantiated or appropriately qualified.

major comments (2)
  1. [Figure 4c,d and the paragraph beginning 'One remaining question...'] The attribution of DND NIR-II photoluminescence to N2V- is not directly established. In Figure 4c, DNDs show no 986 nm zero-phonon line even at 5 K, unlike all HPHT samples. The explanation relies on an exponential extrapolation of the ZPL width versus particle size from approximately 0.5 µm down to roughly 5 nm, spanning two orders of magnitude with no DND-scale data point. The supporting observations, namely spectral shape similarity, photostability, excitation-wavelength independence, and high nitrogen/vacancy content, are consistent with N2V- but do not exclude non-diamond carbon or another defect. The text itself concedes that the shorter-wavelength shoulder in SI Figure S19 implies 'either some non-diamond carbon PL is present or that another color center is more efficiently excited.' Because the abstract's 'ubiquitous ... from bulk samples to nanoparticles' claim and the cellular imaging demonstration rest on this assignment, the manuscript must either provide an unambiguous N2V- signature in DNDs (for example, matching lifetime, charge-state switching, or EPR) or explicitly reframe the DND assignment as a tentative hypothesis rather than an established conclusion.
  2. [SI Table S2 and the quantum optical model discussion following Figure 4a] The quantum-optical model comparison is presented as a validation, but it is actually a consistency check. The ground-state energies, optical decay rates, vibronic decay rates, and dephasing rates in SI Table S2 are all fitted to the 5 K and 300 K experimental spectra, and the measured 0.3 ns lifetime is used as an input to constrain the band decay rates. The statement that 'the phenomenological quantum optical model ... captures the dominant physics of the N2V- center' is therefore too strong; the agreement in Figure 4b and SI Figure S16 does not independently confirm the model because the parameters are derived from the data being reproduced. The authors should explicitly label this as a fitted consistency check. This concern does not undermine the experimental lifetime or spectral measurements, but it prevents overinterpretation of the model agreement.
minor comments (5)
  1. [Caption of Figure 4c] The caption refers to a ZPL at 968 nm, whereas the text and Figure 4b report 984.7 nm at 5 K and 986.5 nm at 300 K; this appears to be a typo and should be corrected.
  2. [Figure 2a,b caption and text] The sentence stating that the solid lines are 'linear fits ... and a are to the eye only' is grammatically incomplete; it should read 'the fits are to guide the eye only.'
  3. [DFT comparison, Figure 4b and accompanying text] The DFT spectrum is only compared after an ad hoc 175 nm blue-shift, and the authors note that the phonon sideband is strongly suppressed by the small nanocrystal size and hydrogen termination; this limitation should be stated directly in the main text so that readers do not infer independent predictive confirmation of the spectral position.
  4. [SI computational details] The red absorption cross-section used to estimate the incoherent excitation rate is taken from the NV- center; this is an approximation that should be acknowledged in the main text where the excitation-rate input to the quantum optical model is introduced.
  5. [Title and Introduction] The term 'quantum emitter' is applied to N2V- even though single-photon emission has not been demonstrated for this charge state; consider qualifying the usage to avoid overstating the quantum-optical credentials of the N2V- center.

Circularity Check

1 steps flagged · score 5.0 of 10

Quantum-optical 'prediction' is a fit to the same spectra with the measured lifetime as input; the core experimental ubiquity claim remains independent.

  1. fitted input called prediction [Figure 4 b; SI 'Phenomenological quantum optical model for the N2V- center' and Table S2]
    "Comparing the phenomenological quantum optical model with the measured spectrum at 5 K, we obtain reasonable estimates for the possible PSB peaks, rates of optical decay through each emission band (the summation of which results in the total rate of 1/0.3 ns), rates of fast vibronic decay between adjacent ground levels and dephasing, as tabulated in the SI Table S2. ... Thus, we find that the phenomenological quantum optical model, together with the predicted parameters, captures the dominant physics of the N2V- center from the ZPL up to ~1350 nm."

    The apparent validation of the quantum-optical model is by construction: the per-band optical decay rates are fit outputs from the same 5 K/300 K spectra that the model is then said to reproduce, and the measured 0.323 ns lifetime is imposed as the constraint that fixes the sum of these rates ('the summation of which results in the total rate of 1/0.3 ns'). Calling the fitted values 'predicted parameters' and concluding that the model 'captures the dominant physics' converts a fit into a prediction. This does not compromise the independent experimental claims (spectral identification, lifetime determination, ubiquity across samples), but the model-agreement claim itself reduces to a consistency check.

full rationale

The experimental backbone of the paper—N2V0/N2V- PL signatures (503 nm and 986 nm ZPLs) in HPHT, CVD, and commercial NV chips; the FTIR-correlated increase of PL with Ns0; the ODMR linewidth correlation; the 0.323 ns lifetime; and the cellular NIR-II imaging of DNDs—is independent of the theoretical models and is not circular. The one genuine reduction is in the model section: the quantum-optical rates in SI Table S2 are fitted to the very 5 K and 300 K spectra they are then used to 'reproduce', and the measured lifetime is used as a constraint on the sum of decay rates, so the claim that the model 'captures the dominant physics' is a consistency check rather than a prediction. The DFT comparison is disclosed as requiring a 175 nm ad hoc blue-shift to overlay the ZPL; that weakens the comparison but is transparent rather than circular. The DND NIR-II attribution is explicitly flagged as an open question: no 986 nm ZPL is observed at 5 K, and the argument relies on spectral similarity, photostability, excitation-wavelength independence, and a two-order-of-magnitude size extrapolation of ZPL broadening. These are reasonable but circumstantial inferences, not a reduction of the attribution to its own inputs, and the paper's own wording ('suggest', 'One remaining question') stops short of claiming proof. Overall, the central experimental claims stand independently; the model 'prediction' reduces to a fit, so a moderate score is appropriate.

Assumptions & free parameters 5 free parameters · 8 assumptions · 0 invented entities

The paper relies on prior structural and spectroscopic assignments of N2V, literature calibrations for FTIR and ODMR nitrogen quantification, and theoretical models that require fitting. No new particles or forces are introduced.

free parameters (5)
  • DFT spectral blue-shift = 175 nm
    DFT predicted ZPL about 175 nm red-shifted from experiment; the spectrum was blue-shifted to coincide with the experimental ZPL in Figure 4b.
  • Quantum optical model ground state energies (14 values) = 0 to 293.8 meV (Table S2)
    Fitted to reproduce the 5 K and 300 K PL spectra.
  • Quantum optical model optical decay rates (14 values) = 24.1 to 502.8 MHz (Table S2)
    Fitted to the experimental spectra; the total rate is constrained by the measured 0.3 ns lifetime.
  • Quantum optical model vibronic decay rates (13 values) = 0 to 67.2 THz at T=0 (Table S2)
    Fitted to sideband widths; temperature dependence assumed via Bose factors.
  • Dephasing rates (5 K and 300 K) = ~1.0 THz and ~15.0 THz
    Adjusted to match the ZPL width at each temperature.
assumptions (8)
  • domain assumption Charge state transition levels of Ns, N2V, and NV from prior DFT calculations (Deak et al.) are accurate enough to argue that Ns donates electrons to N2V0 and that N2V- can donate to NV.
    Used in the discussion of charge state coexistence and to argue all N2V should be negative if only transition levels mattered.
  • domain assumption The FTIR absorption at 1130 cm-1 can be converted to Ns0 concentration using the published calibration.
    Underlies the PL versus Ns0 concentration correlation in Figure 2.
  • domain assumption ODMR linewidth increases by about 10 MHz per 100 ppm Ns0, following the Bauch et al. calibration.
    Used to infer relative Ns0 content of individual 5 micrometer particles from ODMR FWHM.
  • ad hoc to paper The quantum optical model level structure, one excited state and 14 ground vibronic states, is sufficient to describe N2V- emission.
    Introduced for this paper; there is no independent validation that 14 levels capture the physics.
  • domain assumption The DFT method (PBE0, def2-SV(P), vertical gradient) on a 118-carbon hydrogen-terminated nanocrystal captures bulk N2V- emission qualitatively.
    Used for the predicted spectrum; the 175 nm error and suppressed phonon sideband show the approximation is rough.
  • domain assumption Detonation nanodiamonds contain high nitrogen (over 10,000 ppm) and vacancies (over 1,000 ppm) as reported in the literature, making N2V formation feasible.
    Supports the DND attribution to N2V-.
  • domain assumption Non-diamond carbon PL in DNDs is photobleachable and shifts with excitation wavelength, while color center PL is stable and fixed, based on prior work.
    Used to argue that DND NIR-II PL is not from carbon.
  • domain assumption The ZPL at 986 nm is characteristic of N2V- as established by prior EPR and PL work.
    Identification of the emitter in HPHT samples rests on prior assignments.

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Cite this review

Pith. "Pith review of The $N_2V$ color center: a ubiquitous visible and near-infrared-II quantum emitter in nitrogen-doped diamond." pith.science (2026). https://pith.science/paper/O2JGVUJE

@misc{pith2026241211054,
  author       = {Pith},
  title        = {Pith review of: The $N_2V$ color center: a ubiquitous visible and near-infrared-II quantum emitter in nitrogen-doped diamond},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/O2JGVUJE}},
  note         = {Machine review of arXiv:2412.11054}
}
abstract

Photoluminescent defects in diamond, like the nitrogen-vacancy (NV) color center, are at the forefront of emerging optical quantum technologies. Most emit in the visible and near-infrared spectral region below 1000 nm (NIR-I), limiting their applications in photonics, fiber communications, and biology. Here, we show that the nitrogen-vacancy-nitrogen ($N_2V$) center, which emits in the visible and near-infrared-II (NIR-II, 1000-1700 nm), is ubiquitous in as-synthesized and processed nitrogen-doped diamond from bulk samples to nanoparticles. We demonstrate that $N_2V$ is also present in commercially available state-of-the-art NV diamond sensing chips made via chemical vapor deposition (CVD). In high-pressure high-temperature (HPHT) diamonds, the photoluminescence (PL) intensity of both $N_2V$ charge states, $N_2V^0$ in the visible and $N_2V^-$ in the NIR-II, increases with increasing substitutional nitrogen concentration. We determine the PL lifetime of $N_2V^-$ to be 0.3 ns and compare a quantum optical and density functional theory model of the $N_2V^-$ with experimental PL spectra. Finally, we show that detonation nanodiamonds (DND) show stable PL in the NIR-II, which we attribute to the $N_2V$ color center, and use this NIR-II PL to image DNDs inside skin cells. Our results will contribute to the scientific and technological exploration and development of the $N_2V$ color center and inspire more research into its effect on other color centers in diamond.

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Works this paper leans on

3 extracted references · 2 canonical work pages

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