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arXiv:2508.08565 · Annalen der Physik

Nitrogen‐Vacancy Emission from Nanodiamond: Size, Depth, and Surroundings

Harini Hapuarachchi, Francesco Campaioli, Jared H. Cole, Andrew D. Greentree, Qiang Sun

Published Dec 8, 2025• 3 citations
arXivHTMLPDF

Abstract

ABSTRACT The negatively charged nitrogen‐vacancy (NV) center in diamond is a leading solid‐state quantum emitter, offering spin‐photon interfaces over a wide temperature range with applications from electromagnetic sensing to bioimaging. While NV centers in bulk diamond are well understood, embedding them in nanodiamond (ND) introduces complexities from size, NV location, and NV polarizations. NVs in ND show altered fluorescence properties, including longer lifetimes, lower quantum efficiency, and higher sensitivity to dielectric surroundings, which arise from radiative suppression, surface‐induced non‐radiative decay, and escape inefficiency at the diamond‐background interface. Prior models typically addressed isolated aspects, such as dielectric contrast or surface quenching, without integrating full quantum‐optical NV behavior with classical electrodynamics. We present a hybrid framework coupling rigorous electromagnetic simulations with a quantum‐optical NV model including phonon sideband dynamics. NV emission is found to depend strongly on ND size, NV position, and surrounding refractive index. Our results explain observations such as shallow NVs in water‐coated ND appearing brighter than deeper ones in air. This integrated model provides a unified framework for realistic NV in ND emission scenarios and informs the design of efficient NV‐based sensors and quantum devices, advancing understanding of quantum emitter photophysics in nanoscale crystals.

DOI
10.1002/andp.202500367

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•Jan 1, 2018•0 citations
ABSTRACT The negatively charged nitrogen‐vacancy (NV) center in diamond is a leading solid‐state quantum emitter, offering spin‐photon interfaces over a wide temperature range with applications from electromagnetic sensing to bioimaging. While NV centers in bulk diamond are well understood, embedding them in nanodiamond (ND) introduces complexities from size, NV location, and NV polarizations. NVs in ND show altered fluorescence properties, including longer lifetimes, lower quantum efficiency, and higher sensitivity to dielectric surroundings, which arise from radiative suppression, surface‐induced non‐radiative decay, and escape inefficiency at the diamond‐background interface. Prior models typically addressed isolated aspects, such as dielectric contrast or surface quenching, without integrating full quantum‐optical NV behavior with classical electrodynamics. We present a hybrid framework coupling rigorous electromagnetic simulations with a quantum‐optical NV model including phonon sideband dynamics. NV emission is found to depend strongly on ND size, NV position, and surrounding refractive index. Our results explain observations such as shallow NVs in water‐coated ND appearing brighter than deeper ones in air. This integrated model provides a unified framework for realistic NV in ND emission scenarios and informs the design of efficient NV‐based sensors and quantum devices, advancing understanding of quantum emitter photophysics in nanoscale crystals.
The nitrogen vacancy (NV) center is the most widely studied single optical defect in diamond with great potential for applications in quantum technologies. Development of practical single-photon devices requires an understanding of the emission under a range of conditions and environments. In this work, we study the properties of a single NV center in nanodiamonds embedded in an air-like silica aerogel environment which provides a new domain for probing the emission behavior of NV centers in nanoscale environments. In this arrangement, the emission rate is governed primarily by the diamond crystal lattice with negligible contribution from the surrounding environment. This is in contrast to the conventional approach of studying nanodiamonds on a glass coverslip. We observe an increase in the mean lifetime due to the absence of a dielectric interface near the emitting dipoles and a distribution arising from the irregularities in the nanodiamond geometry. Our approach results in the estimation of the mean quantum efficiency (~0.7) of the nanodiamond NV emitters.
Nitrogen–vacancy (NV) centers in diamond are generally recognized as highly promising as indefinitely stable highly efficient single-photon sources. We report an experimental quantification of the brightness, radiative decay rate, nonradiative decay rate and quantum efficiency of single NV centers in diamond nanocrystals. Our experiments show that the commonly observed large spread in fluorescence decay rates of NV centers in nanodiamond is inconsistent with the common explanation of large nanophotonic mode-density variations in the ultra-small high-index crystals at near-unity quantum efficiency. We report that NV centers in 25 nm nanocrystals are essentially insensitive to local density of optical states (LDOS) variations that we induce at a dielectric interface by using liquids to vary the refractive index, and propose that quantum efficiencies in such nanocrystals are widely distributed between 0 and 20%. For single NV centers in larger 100 nm nanocrystals, we show that decay rate changes can be reversibly induced by nanomechanically approaching a mirror to change the LDOS. Using this scanning mirror method, for the first time we report calibrated quantum efficiencies of NV centers, and show that different but nominally identical nanocrystals have widely distributed quantum efficiencies between 10 and 90%. Our measurements imply that nanocrystals that are to be assembled into hybrid photonic structures for cavity QED should first be individually screened to assess fluorescence properties in detail.
With in-built advantages (high quantum efficiency and room temperature photostability1) for deployment in quantum technologies as a bright on-demand source of single photons, the nitrogen vacancy (NV) center is the most widely studied optical defect in diamond. Despite significant success in controlling its spontaneous emission2, the fundamental understanding of its photo-physics in various environments and host material remains incomplete. Studying NV photoemission from nanodiamonds on a glass substrate, we recently pointed out a disparity between the measured and calculated decay rates (assuming near unity quantum efficiency)3. This indicates the presence of some strong nonradiative influences from factors most likely intrinsic to nanodiamond itself. To obtain a clearer picture of the NV emission, here we remove the substrate contributions to the decay rates by embedding our nanodiamonds inside silica aerogel, a substrate-free environment of effective index n ~ 1.05. Nanodiamond doped aerogel samples were fabricated using the “two-step” process4. Time-resolved fluorescence measurement on ~20 centers for both coverslip and aerogel configurations, showed an increase in the mean lifetime (~37%) and narrowing of the distribution width (~40%) in the aerogel environment, which we associate with the absence of a air/cover-glass interface near the radiating dipoles3. Finite difference time domain (FDTD) calculations showed the strong influence of the irregular nanodiamond geometry on the remaining distribution width. Finally a comparison between measurements and calculations provides an estimate of the quantum efficiency of the nanodiamond NV emitters as ~0.7. This value is apparently consistent with recent reports concerning the oscillation of the NV center between negative and neutral charge states5.
Nitrogen vacancy (NV) centers in diamond have been identified over the past few years as promising systems for a variety of applications, ranging from quantum information science to magnetic sensing. This relies on the unique optical and spin properties of the negatively charged NV. Many of these applications require shallow NV centers, i.e., NVs that are close (a few nm) to the diamond surface. In recent years there has been increasing interest in understanding the spin and charge dynamics of NV centers under various illumination conditions, specifically under infrared (IR) excitation, which has been demonstrated to have significant impact on the NV centers' emission and charge state. Nevertheless, a full understanding of all experimental data is still lacking, with further complications arising from potential differences between the photodynamics of bulk and shallow NVs. Here we suggest a generalized quantitative model for NV center spin- and charge-state dynamics under both green and IR excitation. We experimentally extract the relevant transition rates, providing a comprehensive model which reconciles all existing experimental results in the literature, except for highly nonlinear regimes. Moreover, we identify key differences between the photodynamics of bulk and shallow NVs, and use them to significantly enhance the initialization fidelity of shallow NVs to the useful negatively charged state.
The nitrogen vacancy center in diamond in its negative charge state is a promising candidate for quantum optic experiments that require single photon emitters. Important benefits of the NV center are its high brightness and photo-stability, even at room temperature. Engineering the emission properties of NV centers with optical resonators is a widely followed approach to meet the requirements for quantum technological applications, but the effect on non-radiative decay paths is yet to be understood. Here we report on modifying the internal quantum efficiency of a single NV center in a nanodiamond coupled to a 1D photonic crystal cavity. We assess the Purcell enhancement via three independent measurement techniques and perform autocorrelation measurements at elevated excitation powers in confocal microscopy. Employing a three-level model allows us to extract the setup efficiency, individual transition rates and thus the internal quantum efficiency of our system. Combining our results, we find that the enhancement of the radiative decay rate via the Purcell effect results in an internal quantum efficiency of 90 % for cavity-coupled NV centers. Our findings will facilitate the realization of nano-scale single photon sources with near-unity internal quantum efficiencies operating at high repetition rates.
The NV defect center in diamond forms a pseudo-atomic quantum system with discreet optically excitable transitions between ground and excited states in the gap between valence and conduction bands, making the NV center a deep-level defect center in diamond. For the negatively charged NV center (NV-), both the ground and excited states are spin triplets (S=1) and coupling between optical and spin states provides unique opportunities for optical detection of magnetic resonance (ODMR) and quantum metrology under ambient conditions. As an atomically sized point defect that is stable in single nanodiamonds as small as a few nanometers, the NV center enables spin based imaging of temperature, electric fields, magnetic fields and mechanical strain with nanoscale spatial resolution. Made of carbon, nanodiamonds are also ideal nanoparticles for use in biological systems, exhibiting extremely low cytotoxicity, no photo bleaching and exceptional contrast in transmission electron and light microscopy. With the ability to act as both a passive, non perturbing sensor (e.g. a diamagnetic material used for sensing magnetic fields) and a connection point for two way, direct coupling of far field optics to NV−^-− spins and indirectly to the highly localized neighborhood of atoms, electronic states and phonon modes in the local vicinity, NV diamond provides a route to nanoscale field sensing and spin based optical microscopy. These sensors are also stable in nanodiamonds. For nanoparticles, the reduction in particle diameter dramatically enhances the proportion of the material that is surface exposed, enhancing any surface related properties. Nitrogen Vacancy centers in nanodiamonds provide another example of material properties that vary with particle size. In chapter 5, evidence that modulation of nanodiamonds fluorescent emissions by electrical perturbations in their surrouding environment allows transduction of local electrodynamics into a far field optical signal capable of mapping action potentials in cardiomyocytes in presented. The unifying theme for all of the work presented in this dissertation is to enable the use of magnetic resonance signals and interactions for imaging and sensing in previously inaccessible regimes. The specific focus is on methods and techniques to enable nanoscale physical sensing and functional imaging in live tissues, with the ultimate aim to lay the predicate for the combination of both without compromise.