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arXiv:2505.11240

Nitrogen-vacancy centre in lonsdaleite: a novel nanoscale sensor?

Anjay Manian, M. de Vries, Daniel Stavrevski, Qiang Sun, Salvy P. Russo, Andrew D. Greentree

Published May 16, 2025• 0 citations
arXivHTMLPDF

Abstract

Hexagonal diamond, often called lonsdaleite, is an exotic allotrope of carbon, predicted to be harder than cubic (conventional) diamond with a wider bandgap. Due to its pure sp$^3$ bonded lattice, it should be expected to host sub-bandgap defect centres (colour centres). Here we perform \textit{ab initio} modeling of nitrogen-vacancy (NV) colour centres in hexagonal diamond nanocrystals; for both the neutral and negatively charged species (NV$^0$ and NV$^-$). We identify three distinct configurations for the NV center: two of which are analogous to NV in diamond, and one which is a configuration that can only exist in the hexagonal form. The diamond-like NV systems comprise three symmetry equivalent centers which reside on the same carbon plane, and one defect that is split across two planes and replaces a carbon-carbon bond. There is an additional NV centre where the N and V each have four nearest neighbour carbon atoms. The presence of this latter configuration would provide an unambiguous determination of the hexagonal nature of lonsdaleite. Quantum chemical analysis show all derivatives to be thermochemically stable, and each with their own unique photophysical properties, spectral profiles, and magneto-optical characteristics. By assuming that the ground state properties of the NV$^-$ in hexagonal diamond are comparable to those of NV$^-$ in cubic diamond, albeit with increased strain, we predict ground state fine structure splitting for two of the centres of 2.74~GHz and 4.56~MHz, compared with 2.87~GHz for cubic diamond. The possibility of optically detected magnetic resonance with NV$^-$ in lonsdaleite would provide a new carbon-based quantum sensing system, and an unambiguous method to resolve outstanding issues around the structure of lonsdaleite as hexagonal diamond.

DOI
10.48550/arxiv.2505.11240

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Hexagonal diamond, often called lonsdaleite, is an exotic allotrope of carbon, predicted to be harder than cubic (conventional) diamond with a wider bandgap. Due to its pure sp3^33 bonded lattice, it should be expected to host sub-bandgap defect centres (colour centres). Here we perform \textit{ab initio} modeling of nitrogen-vacancy (NV) colour centres in hexagonal diamond nanocrystals; for both the neutral and negatively charged species (NV0^00 and NV−^-−). We identify three distinct configurations for the NV center: two of which are analogous to NV in diamond, and one which is a configuration that can only exist in the hexagonal form. The diamond-like NV systems comprise three symmetry equivalent centers which reside on the same carbon plane, and one defect that is split across two planes and replaces a carbon-carbon bond. There is an additional NV centre where the N and V each have four nearest neighbour carbon atoms. The presence of this latter configuration would provide an unambiguous determination of the hexagonal nature of lonsdaleite. Quantum chemical analysis show all derivatives to be thermochemically stable, and each with their own unique photophysical properties, spectral profiles, and magneto-optical characteristics. By assuming that the ground state properties of the NV−^-− in hexagonal diamond are comparable to those of NV−^-− in cubic diamond, albeit with increased strain, we predict ground state fine structure splitting for two of the centres of 2.74GHz and 4.56MHz, compared with 2.87~GHz for cubic diamond. The possibility of optically detected magnetic resonance with NV−^-− in lonsdaleite would provide a new carbon-based quantum sensing system, and an unambiguous method to resolve outstanding issues around the structure of lonsdaleite as hexagonal diamond.
We show that negatively charged nitrogen-vacancy (NV) centers in the hexagonal diamond polymorph lonsdaleite offer a route to spin qubits with enhanced coherence relative to their cubic-diamond counterparts. Using first-principles calculations, we examine two distinct defect configurations, AA, with the same symmetry as in cubic diamond and AB, with reduced symmetry. We find that the AB configuration of the NV center exhibits a finite transverse zero-field splitting, giving rise to an approximate fourfold enhancement of the Hahn-echo coherence time T2T_2T2​ at zero magnetic field. The AA configuration, by contrast, closely reproduces the electronic structure and coherence properties of the cubic NV center. We further characterize the many-body electronic structure, vertical excitation energies, and photoluminescence spectra of both configurations, providing spectral fingerprints for their experimental identification. Our results establish symmetry-broken NV centers in lonsdaleite as promising candidates for quantum sensing and information science applications.
The nitrogen-vacancy (NV) colour centre in diamond is an important physical system for emergent quantum technologies, including quantum metrology, information processing and communications, as well as for various nanotechnologies, such as biological and sub-diffraction limit imaging, and for tests of entanglement in quantum mechanics. Given this array of existing and potential applications and the almost 50 years of NV research, one would expect that the physics of the centre is well understood, however, the study of the NV centre has proved challenging, with many early assertions now believed false and many remaining issues yet to be resolved. This review represents the first time that the key empirical and ab initio results have been extracted from the extensive NV literature and assembled into one consistent picture of the current understanding of the centre. As a result, the key unresolved issues concerning the NV centre are identified and the possible avenues for their resolution are examined.
One of the most common impurities in synthetic diamond is single substitutional nitrogen, which is incorporated in the diamond lattice substituting a carbon atom. If the nitrogen is adjacent to a vacancy in the diamond lattice, it forms the nitrogen-vacancy (NV) colour centre (CC). The negatively charged state of this CC, NV-, is particularly well studied since its quantum properties are suitable for applications such as quantum information processing, single-photon sources and optical magnetometry. NV CCs in the neutral state (NV0) are less widely studied. This CC exhibits broadband luminescence at slightly shorter wavelengths than NV-, and hence is also potentially of interest for tuneable and ultrafast visible laser applications. In this report, we present a detailed study of the laser-related spectroscopic properties of a diamond containing NV0 and NV-CCs.
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.
When the word diamond comes up, the majority of people thinks about engagement rings or gemstones. In fact, it is additionally, one of the most promising host materials for the implementation of advanced technology, exploiting the nature of quantum physics. Such quantum technologies have disruptive potential, ones the quantum effects can be applied in macroscopic, commercial products. The nitrogen-vacancy (NV) centre in diamond is a promising candidate to perform such tasks in the fields of quantum computation, quantum cryptography or metrology. Especially in the field of quantum sensing, the NV sensor impresses with nano-scale spatial resolution paired with high sensitivity. The electronic spin of the atomic-sized point defect can be initialised, manipulated and read-out at ambient conditions and coherence lifetimes are comparably long. Diamond magnetometers based on negatively charged NV centres have shown to be very attractive, and the sensitivity goes down to the single-atom level. In order to exploit such a high sensitivity level for sensing prospects, in this thesis, the NV centres are fabricated well confined in a certain distance to the diamond surface, since the detectable field usually decays with the third power of the distance between sensor and target. The surface depicts a fracture of the spin wise protecting diamond lattice and charge fluctuations affect the stability of NV centres, which are overcome by diamond surface termination. In order to improve the sensitivity further, the sensor density, measurement contrast and interaction time are increased. The nitrogen doping technique, which is applied during a plasma-enhanced chemical vapour deposition (PECVD) diamond growth process is used to fabricate NV centre ensembles aligned along one diamond crystal axis, thereby improving the measurement contrast by a factor up to four. The interaction time limiting spin bath is analysed using the sensor capabilities of the NVs, which leads to enhanced growth strategies and the fabrication of sensitivity optimised NV centre ensembles for magnetometry applications.
Abstract Nitrogen-vacancy (NV) defect centers in diamond are key to applications in quantum sensing and quantum computing. They create localized electronic states in the diamond lattice with distinct population relaxation pathways following photoexcitation that ultimately enable its unique properties. The defect is known to exist in two charge states: neutral and negative, with respectively one and two known optically-active electronic transitions. Here, we report on the observation of a large number of hitherto undiscovered excited electronic states in both charge states as evidenced by distinct optical transitions in the infrared to ultraviolet part of the spectrum. These transitions are observed by monitoring the electronic relaxation of NV centers after photoexcitation using transient absorption spectroscopy, directly probing transient phenomena occurring on timescales from femtoseconds to microseconds. We also for the first time probed the electron transfer dynamics from the 3 E state of NV− to nearby single-substitutional nitrogen defects (N s ) that leads to the well-known effect of NV photoluminescence quenching.