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Study of Sodium Colour Centres in Diamond for Quantum Technology Applications

Guilherme Santos

Published Dec 15, 2025• 0 citations
Publisher

Abstract

Colour centres in diamonds represent one of the most actively researched areas in the field of quantum technologies. In this work, we investigate a specific colour centre based on sodium (Na), selected due to promising theoretical predictions suggesting its potential for various quantum applications, despite the current lack of experimental studies. To explore this centre, we conducted two complementary experiments at ISOLDE/CERN. First, we employed the electron emission channeling (EC) technique to determine the most probable lattice sites occupied by sodium in a single-crystal lattice of a diamond implanted with radioactive 24Na. We then used a photoluminescence (PL) set-up to obtain the emission spectrum of a similar sample implanted with stable 23Na. EC measurements revealed that sodium likely adopts a combination of substitutional (S) and bond-centre (BC) sites, maximised after an annealing temperature of 600°C, exhibiting approximately 51% NaV split-vacancy (the highest fraction observed) and 17% substitutional Na (which increases slowly and almost linearly with annealing temperature). However, at higher annealing temperatures, the BC configuration decreases rapidly, and the combined fraction of these two sites also drops, suggesting the emergence of another, yet unidentified, configuration. In the PL experiments, we did not observe a direct optical signal attributable to sodium, but we present the optical characterisation of single-crystal diamond samples fabricated by Element Six and implanted with stable sodium at different annealing temperatures. We found the 3H centre consistently present across nearly all samples followingimplantation and annealing, with its zero-phonon line (ZPL) located around 503 nm.

DOI
10.17181/x3svz-5bw49

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Colour centres in diamonds represent one of the most actively researched areas in the field of quantum technologies. In this work, we investigate a specific colour centre based on sodium (Na), selected due to promising theoretical predictions suggesting its potential for various quantum applications, despite the current lack of experimental studies. To explore this centre, we conducted two complementary experiments at ISOLDE/CERN. First, we employed the electron emission channeling (EC) technique to determine the most probable lattice sites occupied by sodium in a single-crystal lattice of a diamond implanted with radioactive 24Na. We then used a photoluminescence (PL) set-up to obtain the emission spectrum of a similar sample implanted with stable 23Na. EC measurements revealed that sodium likely adopts a combination of substitutional (S) and bond-centre (BC) sites, maximised after an annealing temperature of 600°C, exhibiting approximately 51% NaV split-vacancy (the highest fraction observed) and 17% substitutional Na (which increases slowly and almost linearly with annealing temperature). However, at higher annealing temperatures, the BC configuration decreases rapidly, and the combined fraction of these two sites also drops, suggesting the emergence of another, yet unidentified, configuration. In the PL experiments, we did not observe a direct optical signal attributable to sodium, but we present the optical characterisation of single-crystal diamond samples fabricated by Element Six and implanted with stable sodium at different annealing temperatures. We found the 3H centre consistently present across nearly all samples followingimplantation and annealing, with its zero-phonon line (ZPL) located around 503 nm.
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Single-photon sources are a fundamental element for developing quantum technologies, and sources based on colour centres in diamonds are among the most promising candidates. The well-known nitrogen vacancy centres are characterized by several limitations, and thus few other defects have recently been considered. In the present work, we characterize, in detail, native efficient single colour centres emitting in the near infra-red ( λ = 740–780 nm) in both standard IIa single-crystal and electronic-grade polycrystalline commercial chemical vapour deposited (CVD) diamond samples. In the former case, a high-temperature ( T > 1000 °C) annealing process in vacuum is necessary to induce the formation/activation of luminescent centres with good emission properties, while in the latter case the annealing process has marginally beneficial effects on the number and performance of native centres in commercially available samples. Although displaying significant variability in several photo-physical properties (emission wavelength, emission rate instabilities, saturation behaviours), these centres generally display appealing photophysical properties for applications as single photon sources: short lifetimes (0.7–3 ns), high emission rates (∼50–500 × 10 3 photons s −1 ) and strongly (>95%) polarized light. The native centres are tentatively attributed to impurities incorporated in the diamond crystal during the CVD growth of high-quality type-IIa samples, and offer promising perspectives in diamond-based photonics.
We provide the first systematic characterization of the structural and photoluminescence properties of optically active centers fabricated upon implantation of 30–100 keV Mg + ions in synthetic diamond. The structural configurations of Mg-related defects were studied by the electron emission channeling technique for short-lived, radioactive 27 Mg implantations at the CERN-ISOLDE facility, performed both at room temperature and 800 °C, which allowed the identification of a major fraction of Mg atoms (∼30 to 42%) in sites which are compatible with the split-vacancy structure of the MgV complex. A smaller fraction of Mg atoms (∼13 to 17%) was found on substitutional sites. The photoluminescence emission was investigated both at the ensemble and individual defect level in the 5–300 K temperature range, offering a detailed picture of the MgV-related emission properties and revealing the occurrence of previously unreported spectral features. The optical excitability of the MgV center was also studied as a function of the optical excitation wavelength to identify the optimal conditions for photostable and intense emission. The results are discussed in the context of the preliminary experimental data and the theoretical models available in the literature, with appealing perspectives for the utilization of the tunable properties of the MgV center for quantum information processing applications.
Abstract We report on the creation and characterization of Pb-related color centers in diamond upon ion implantation and subsequent thermal annealing. Their optical emission in the photoluminescence (PL) regime consists of an articulated spectrum with intense emission peaks at 552.1 and 556.8 nm, accompanied by a set of additional lines in the 535–700 nm range. The attribution of the PL emission to stable Pb-based defects is corroborated by the correlation of its intensity with the implantation fluence of Pb ions. PL measurements performed as a function of sample temperature (in the 143–300 K range) and under different excitation wavelengths (i.e., 532, 514, 405 nm) suggest that the complex spectral features observed in Pb-implanted diamond might be related to a variety of different defects and/or charge states. The emission of the 552.1 and 556.8 nm lines is reported at the single-photon emitter level, demonstrating that they originate from the same individual defect. This work follows from previous reports on optically active centers in diamond based on group-IV impurities, such as Si, Ge, and Sn. In perspective, a comprehensive study of this set of defect complexes could bring significant insight on the common features involved in their formation and opto-physical properties, thus offering a basis for the development of a new generation of quantum-optical devices.
Silicon-vacancy (SiV) centers in diamond are gaining an increased interest for application, such as in quantum technologies and sensing. Due to the strong luminescence concentrated in its sharp zero-phonon line at room temperature, SiV centers are being investigated as single-photon sources for quantum communication, and also as temperature probes for sensing. Here, we discussed strategies for the fabrication of SiV centers in diamond based on Si-ion implantation followed by thermal activation. SiV color centers in high-quality single crystals have the best optical properties, but polycrystalline micro and nanostructures are interesting for applications in nano-optics. Moreover, we discuss the photoluminescence properties of SiV centers in phosphorous-doped diamond, which are relevant for the creation of electroluminescent devices, and nanophotonics strategies to improve the emission characteristics of the SiV centers. Finally, the optical properties of such centers at room and high temperatures show the robustness of the center and give perspectives for temperature-sensing applications.
Tin-Vacancy (Sn-V) colour centres in diamond have a spin coherence time in the millisecond range at temperatures of 2 K, so they are promising to be used in diamond-based quantum optical devices. However, the incorporation of large Sn atoms into a dense diamond lattice is a non-trivial problem. The objective of our work is to use microwave plasma-assisted chemical vapour deposition (CVD) to grow Sn-doped diamond with submicron SnO 2 particles as a solid-state source of impurity. Well-faceted diamond microcrystals with sizes of a few micrometres were formed on AlN substrates. The photoluminescence (PL) signal with zero-phonon line (ZPL) peak for Sn-V centre at ≈620 nm was measured at room temperature (RT) and at 7 K. The peak width (full width at half-maximum) was measured to be 1.1–1.7 nm at RT and ≈0.05 nm at 7 K. The observed variations of ZPL shape and position, in particular, narrowing of PL peak at RT and formation of single-line fine structure at low- T , are attributed to strain in the crystallites. The diamond doping with Sn via CVD process offers a new route to from Sn-V colour centre in the bulk of the diamond crystallites. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.