Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1811.01972 · Physical Review Applied

Microwave-Assisted Spectroscopy Technique for Studying Charge State in Nitrogen-Vacancy Ensembles in Diamond

D.P.L. Aude Craik, Pauli Kehayias, Andrew S. Greenspon, X. Zhang, M.J. Turner, Jennifer M. Schloss, E. Bauch, C.A. Hart, E.L. Hu, R.L. Walsworth

Published Jul 6, 2020• 34 citations
arXivHTMLPDF

Abstract

We introduce a microwave-assisted spectroscopy technique to determine the relative ratio of fluorescence emitted by nitrogen-vacancy (N-$V$) centers in diamond that are negatively charged ($\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$) and neutrally charged ($\mathrm{N}\text{\ensuremath{-}}{V}^{0}$) and present its application to studying spin-dependent ionization in N-$V$ ensembles and enhancing N-$V$-magnetometer sensitivity. Our technique is based on selectively modulating the $\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$ fluorescence with a spin-state-resonant microwave drive to isolate, in situ, the spectral shape of the $\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$ and $\mathrm{N}\text{\ensuremath{-}}{V}^{0}$ contributions to an N-$V$-ensemble sample's fluorescence. As well as serving as a reliable means to characterize the charge state, the method can be used as a tool to study spin-dependent ionization in N-$V$ ensembles. As an example, we apply the microwave technique to a high-N-$V$-density diamond sample and find evidence for an additional spin-dependent ionization pathway, which we present here alongside a rate-equation model of the data. We further show that our method can be used to enhance the contrast of optically detected magnetic resonance (ODMR) on N-$V$ ensembles and may lead to significant sensitivity gains in N-$V$ magnetometers dominated by technical noise sources, especially where the $\mathrm{N}\text{\ensuremath{-}}{V}^{0}$ population is large. With the high-N-$V$-density diamond sample investigated here, we demonstrate an up to 4.8-fold enhancement in the ODMR contrast. We also propose a second postprocessing method of increasing the ODMR contrast in shot-noise-limited applications. The techniques presented here may also be applied to other solid-state defects, as long as their fluorescence can be selectively modulated by means of a microwave drive. We demonstrate this utility by applying our method to isolate room-temperature spectral signatures of the V2-type silicon vacancy from an ensemble of V1 and V2 silicon vacancies in $4H$ silicon carbide.

DOI
10.1103/physrevapplied.14.014009

Related papers

Characterizing the nitrogen-vacancy center singlet transition and its phonon sideband for absorption-based room-temperature magnetometry

Tobias Probst, Florian Schall, Sebastian Heuft +9 more

Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV$^-$ triplet fluorescence. The absorption techniques rely on magnetic-field-dependent absorption at the NV$^-$ singlet zero phonon line at 1042$\,$nm and its phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050$\,$nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected magnetic resonance (ODMR) contrast. The highest contrast is found at 1042$\,$nm, but multiple points of high contrast are found at the peaks of the phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80$\,\%$ are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire phonon sideband. We determine the absorption cross section at 1042$\,$nm to be $σ^{\,\bigstar}_{1042}=(0.89\pm0.14)\cdot 10^{-21}\,\text{m}^2$ or $σ^{\,\blacktriangle}_{1042}=(2.9\pm0.5)\cdot 10^{-21}\,\text{m}^2$. depending on the employed 532$\,$nm NV$^-$ absorption cross section.

quant-pharXiv:2608.02060•Aug 4, 2026•0 citations

Creation of ensembles of nitrogen-vacancy centers in diamond by neutron and electron irradiation

Tobias Nöbauer, K. Buczak, Andreas Angerer +7 more

We created dense ensembles of negatively charged nitrogen-vacancy (NV-) centers in diamond by neutron and electron irradiation for applications in hybrid quantum systems and magnetometry. We characterize fluorescence intensity, optical and coherence properties of the resulting defects by confocal microscopy, UV/Vis and FTIR spectroscopy, optically detected magnetic resonance and small angle X-ray scattering. We find the highest densities of NV- at neutron fluences on the order of 10^17 cm^-2 and electron doses of 10^18 cm^-2, with spin resonance linewidths of 6 MHz. Lower electron energies increase the ratio of centers in the desired negative charge state to those in the neutral one. Annealing at 900 °C during the irradiation reduces the spin resonance linewidth. Electron irradiation furthermore results in substantially higher optical transparency compared to neutron irradiation.

arXiv:1309.0453•Sep 2, 2013•14 citations

Investigation of artificial diamonds for optical sensing with ensemble of nitrogen-vacancy centres

Marco Capelli

The fluorescence of the nitrogen-vacancy (NV) centre in artificial diamond has been widely studied for applications such as quantum communication protocols, quantum computation, fluorescence-based biolabelling, and optical sensing. Optical sensing by itself encompasses a wide range of possible applications: from magnetic and electric field sensing to temperature sensing and enabling, for example, the detection of paramagnetic ions and the identification of molecules by nuclear magnetic resonance. Compared to many other systems capable of optical sensing, the NV centre works at room temperature, and its spin-dependent fluorescence emission is the key property to achieve a high sensitivity to the surrounding environment. Additionally, the NV centre emission is highly photostable, has a relatively short lifetime (~ 12ns) and spans a broad wavelength range, from the red to the near-infrared region of the electromagnetic spectrum (600 - 800nm). While the common denominator of all mentioned applications is the NV centre, the properties of the artificial diamond surrounding the NV centre have a significant impact on its sensing performance. At present, the processing of artificial diamond has not been fully optimised, and research and development towards the realisation of the `best¿ diamond sample for optical sensing is far from over. Specifically, the role of other defects in diamond and their effects on the photo-physical properties of the NV centres are not entirely understood. In this thesis, I will discuss the potential benefits of a novel processing technique to create ensembles of NV centres, and the importance that surrounding nitrogen defects has on the achievable magnetic field sensitivity. Additionally, I will show both theoretical and experimental investigations of the NV centres photo-physical processes, with focus on magnetic field sensing. I will initially explore a protocol for microwave-free magnetometry. This protocol predicts a theoretical magnetic field sensitivity <10µT/√Hz in the range 0.3 - 30mT and I will demonstrate it experimentally with a maximum sensitivity of 3.6mT/Hz. Following, I will focus on exploring techniques to increase the magnetic field sensitivity by improving the material properties of the diamond samples. I will demonstrate that the simultaneous electron irradiation and annealing improves the creation efficiency of an ensemble of NV centres by up to 117%. Finally, I will investigate how substitutional nitrogen defects in the surrounding lattice affects the charge state of the NV centre, its emission intensity, its lifetime and its magnetic field sensitivity. I will study a sample characterised by multiple regions across its volume, with nitrogen concentration changing between 10ppm and 100ppm in each region. There si an optimal region with ~ 40ppm of substitutional nitrogen which demonstrates the highest fluorescence emission, mainly from the negatively-charged NV centre, and the highest magnetic field sensitivity of 1.6 ± 0.2µT/√Hz. However, both the regions with lower and higher substitutional nitrogen concentration than the optimal region show lower emission intensity and worse magnetic field sensitivity. Following is a summary of the content in each chapter: Chapter 1 will present an introduction to the diamond material and the classification of artificial diamond samples. It will introduce the NV centre, its fluorescence properties and the process to create NV centres in diamond. The chapter will also introduce the concepts around optical magnetometry and the working principle that allows the NV centre to sense magnetic fields as well as other external quantities, such as temperature or pressure. Finally, it will include a brief overview of the defects that are found in artificial diamond or are created during the sample processing. Chapter 2 will describe the working principle of the instruments utilised in this work. I will list the details of each instrument and describe the methods used for the analysis of the data. Chapter 3 will introduce the background of modelling the fluorescence emission from NV centres. I will discuss the implementation of a computational model based on the Lindblad master equation to simulate the photo-physical dynamics of the NV centre. I will demonstrate the successful simulation of the saturation emission, fluorescence lifetime and optically detected magnetic resonance using the theoretical model. Finally, I will explore the theoretically predicted sensitivity of microwave-free magnetometry, based on the NV centre emission intensity change under an external magnetic field. Chapter 4 will demonstrate experimentally the microwave-free magnetometry technique. In relation to the study of microwave-free magnetometry, this chapter will explore an unexpected increase in emission intensity at high magnetic fields > 100mT. Combining the experimental observations and the theoretical simulation developed in the previous chapter, I will identify and discuss a phenomenological decrease in the NV centre transition rate from the triplet state to the singlet state. The chapter will conclude comparing the experimental and theoretical sensitivities associated with the microwave-free magnetometry technique. Chapter 5 will show the characterisation of a diamond sample at each step of the process to create NV centres. I will study the electron irradiation followed by separate annealing on a high-pressure high-temperature diamond sample. I will then characterise the sample employing visible and infrared absorption spectroscopy, as well as measure the fluorescence spectra and lifetime of the defects identified at each step. Chapter 6 will examine an alternative method to create NV centres in diamond. I will compare diamond samples irradiated and annealed separately with samples simultaneously irradiated and annealed (referred to as 'annealing in situ'). To compare the two processes, I will estimate the concentration of nitrogen defects and NV centres and calculate their N-to-NV conversion efficiency. Chapter 7 will discuss the effects of substitutional nitrogen on the properties of the NV centres in diamond. For this discussion, I will use a single-crystal diamond that shows the presence of 4 growth sectors. Each growth sector is characterised by a different nitrogen concentration, as I will demonstrate at the beginning of the chapter. I will focus on 4 main properties affected by the concentration of nitrogen in the different sectors: the balance between the charge states of the NV centre, the overall fluorescence intensity from each sector, the fluorescence lifetime and its relation to non-radiative processes, and the magnetic field sensitivity obtained with the optically detected magnetic resonance technique. Chapter 8 will gather the results and conclusions of the entire body of work. It will also discuss future avenues of research in the topic of diamond processing and characterisations, to improve the existing optical sensing applications.

•Sep 24, 2020•2 citations

Microwave saturation spectroscopy of nitrogen-vacancy ensembles in diamond

Pauli Kehayias, Mariusz Mrózek, Víctor M. Acosta +5 more

Negatively charged nitrogen-vacancy (NV${}^{\ensuremath{-}}$) centers in diamond have generated much recent interest for their use in sensing. The sensitivity improves when the NV ground-state microwave transitions are narrow, but these transitions suffer from inhomogeneous broadening, especially in high-density NV ensembles. To better understand and remove the sources of broadening, we demonstrate room-temperature spectral ``hole burning'' of the NV ground-state transitions. We find that hole burning removes the broadening caused by magnetic fields from ${}^{13}$C nuclei and demonstrate that it can be used for magnetic-field-insensitive thermometry.

arXiv:1403.2119•Physical Review B•Jun 3, 2014•55 citations

Spin readout via spin-to-charge conversion in bulk diamond nitrogen-vacancy ensembles

Harishankar Jayakumar, Siddharth Dhomkar, Jacob Henshaw +1 more

We demonstrate the optical readout of ensembles of nitrogen-vacancy (NV) center spins in a bulk diamond sample via spin-to-charge conversion. A high power 594 nm laser is utilized to selectively ionize these paramagnetic defects in the mS=0 spin state with a contrast of up to 12%. In comparison to the conventional 520 nm spin readout, the spin-to-charge-conversion-based readout provides a higher signal-to-noise ratio, with tenfold sensing measurement speedup for millisecond long pulse sequences. This level of performance was achieved for an NV− ionization of only 25%, limited by the ionization and readout laser powers. These observations pave the way to a range of high-sensitivity metrology applications where the use of NV− ensembles in bulk diamond has proven useful, including sensing and imaging of target materials overlaid on the diamond surface.

arXiv:1809.07380•Applied Physics Letters•Sep 17, 2018•26 citations

High temperature spectroscopy of ensembles of nitrogen-vacancy centers in diamond

Mohammed Attrash, Oleg Shtempluck, Eyal Buks

We study the spectroscopy of an ensemble of negatively charged nitrogen-vacancy centers in diamond at high temperatures between room temperature and 700K under high vacuum conditions. Spin resonances are studied using optical detection of magnetic resonance (ODMR), and optical spectroscopy is employed to study radiative transitions. Upon increasing the temperature, the intensity of radiative decay in visible and infrared decreased. In addition, the ODMR resonance frequencies were decreased, and the phonon line emission shifted to higher wavelengths. Density functional theory calculation of the zero-field splitting parameter (D) revealed that thermal expansion is not enough to explain the shift in the ODMR frequencies. Fitting the measured intensity of photo-luminescence with the theoretical predictions of the Mott–Seitz model yields the value of 0.22eV for the energy barrier associated with nonradiative decay.

arXiv:2209.12558•Journal of Applied Physics•Mar 1, 2023•11 citations
We introduce a microwave-assisted spectroscopy technique to determine the relative ratio of fluorescence emitted by nitrogen-vacancy (N-VVV) centers in diamond that are negatively charged (N\ensuremath-V\ensuremath−\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}N\ensuremath-V\ensuremath−) and neutrally charged (N\ensuremath-V0\mathrm{N}\text{\ensuremath{-}}{V}^{0}N\ensuremath-V0) and present its application to studying spin-dependent ionization in N-VVV ensembles and enhancing N-VVV-magnetometer sensitivity. Our technique is based on selectively modulating the N\ensuremath-V\ensuremath−\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}N\ensuremath-V\ensuremath− fluorescence with a spin-state-resonant microwave drive to isolate, in situ, the spectral shape of the N\ensuremath-V\ensuremath−\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}N\ensuremath-V\ensuremath− and N\ensuremath-V0\mathrm{N}\text{\ensuremath{-}}{V}^{0}N\ensuremath-V0 contributions to an N-VVV-ensemble sample's fluorescence. As well as serving as a reliable means to characterize the charge state, the method can be used as a tool to study spin-dependent ionization in N-VVV ensembles. As an example, we apply the microwave technique to a high-N-VVV-density diamond sample and find evidence for an additional spin-dependent ionization pathway, which we present here alongside a rate-equation model of the data. We further show that our method can be used to enhance the contrast of optically detected magnetic resonance (ODMR) on N-VVV ensembles and may lead to significant sensitivity gains in N-VVV magnetometers dominated by technical noise sources, especially where the N\ensuremath-V0\mathrm{N}\text{\ensuremath{-}}{V}^{0}N\ensuremath-V0 population is large. With the high-N-VVV-density diamond sample investigated here, we demonstrate an up to 4.8-fold enhancement in the ODMR contrast. We also propose a second postprocessing method of increasing the ODMR contrast in shot-noise-limited applications. The techniques presented here may also be applied to other solid-state defects, as long as their fluorescence can be selectively modulated by means of a microwave drive. We demonstrate this utility by applying our method to isolate room-temperature spectral signatures of the V2-type silicon vacancy from an ensemble of V1 and V2 silicon vacancies in 4H4H4H silicon carbide.
Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV−^-− triplet fluorescence. The absorption techniques rely on magnetic-field-dependent absorption at the NV−^-− singlet zero phonon line at 1042 \,nm and its phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050 \,nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected magnetic resonance (ODMR) contrast. The highest contrast is found at 1042 \,nm, but multiple points of high contrast are found at the peaks of the phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80 %\,\%% are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire phonon sideband. We determine the absorption cross section at 1042 \,nm to be σ1042 ★=(0.89±0.14)⋅10−21 m2σ^{\,\bigstar}_{1042}=(0.89\pm0.14)\cdot 10^{-21}\,\text{m}^2σ1042★​=(0.89±0.14)⋅10−21m2 or σ1042 ▲=(2.9±0.5)⋅10−21 m2σ^{\,\blacktriangle}_{1042}=(2.9\pm0.5)\cdot 10^{-21}\,\text{m}^2σ1042▲​=(2.9±0.5)⋅10−21m2. depending on the employed 532 \,nm NV−^-− absorption cross section.
We created dense ensembles of negatively charged nitrogen-vacancy (NV-) centers in diamond by neutron and electron irradiation for applications in hybrid quantum systems and magnetometry. We characterize fluorescence intensity, optical and coherence properties of the resulting defects by confocal microscopy, UV/Vis and FTIR spectroscopy, optically detected magnetic resonance and small angle X-ray scattering. We find the highest densities of NV- at neutron fluences on the order of 10^17 cm^-2 and electron doses of 10^18 cm^-2, with spin resonance linewidths of 6 MHz. Lower electron energies increase the ratio of centers in the desired negative charge state to those in the neutral one. Annealing at 900 °C during the irradiation reduces the spin resonance linewidth. Electron irradiation furthermore results in substantially higher optical transparency compared to neutron irradiation.
The fluorescence of the nitrogen-vacancy (NV) centre in artificial diamond has been widely studied for applications such as quantum communication protocols, quantum computation, fluorescence-based biolabelling, and optical sensing. Optical sensing by itself encompasses a wide range of possible applications: from magnetic and electric field sensing to temperature sensing and enabling, for example, the detection of paramagnetic ions and the identification of molecules by nuclear magnetic resonance. Compared to many other systems capable of optical sensing, the NV centre works at room temperature, and its spin-dependent fluorescence emission is the key property to achieve a high sensitivity to the surrounding environment. Additionally, the NV centre emission is highly photostable, has a relatively short lifetime (~ 12ns) and spans a broad wavelength range, from the red to the near-infrared region of the electromagnetic spectrum (600 - 800nm). While the common denominator of all mentioned applications is the NV centre, the properties of the artificial diamond surrounding the NV centre have a significant impact on its sensing performance. At present, the processing of artificial diamond has not been fully optimised, and research and development towards the realisation of the `best¿ diamond sample for optical sensing is far from over. Specifically, the role of other defects in diamond and their effects on the photo-physical properties of the NV centres are not entirely understood. In this thesis, I will discuss the potential benefits of a novel processing technique to create ensembles of NV centres, and the importance that surrounding nitrogen defects has on the achievable magnetic field sensitivity. Additionally, I will show both theoretical and experimental investigations of the NV centres photo-physical processes, with focus on magnetic field sensing. I will initially explore a protocol for microwave-free magnetometry. This protocol predicts a theoretical magnetic field sensitivity <10µT/√Hz in the range 0.3 - 30mT and I will demonstrate it experimentally with a maximum sensitivity of 3.6mT/Hz. Following, I will focus on exploring techniques to increase the magnetic field sensitivity by improving the material properties of the diamond samples. I will demonstrate that the simultaneous electron irradiation and annealing improves the creation efficiency of an ensemble of NV centres by up to 117%. Finally, I will investigate how substitutional nitrogen defects in the surrounding lattice affects the charge state of the NV centre, its emission intensity, its lifetime and its magnetic field sensitivity. I will study a sample characterised by multiple regions across its volume, with nitrogen concentration changing between 10ppm and 100ppm in each region. There si an optimal region with ~ 40ppm of substitutional nitrogen which demonstrates the highest fluorescence emission, mainly from the negatively-charged NV centre, and the highest magnetic field sensitivity of 1.6 ± 0.2µT/√Hz. However, both the regions with lower and higher substitutional nitrogen concentration than the optimal region show lower emission intensity and worse magnetic field sensitivity. Following is a summary of the content in each chapter: Chapter 1 will present an introduction to the diamond material and the classification of artificial diamond samples. It will introduce the NV centre, its fluorescence properties and the process to create NV centres in diamond. The chapter will also introduce the concepts around optical magnetometry and the working principle that allows the NV centre to sense magnetic fields as well as other external quantities, such as temperature or pressure. Finally, it will include a brief overview of the defects that are found in artificial diamond or are created during the sample processing. Chapter 2 will describe the working principle of the instruments utilised in this work. I will list the details of each instrument and describe the methods used for the analysis of the data. Chapter 3 will introduce the background of modelling the fluorescence emission from NV centres. I will discuss the implementation of a computational model based on the Lindblad master equation to simulate the photo-physical dynamics of the NV centre. I will demonstrate the successful simulation of the saturation emission, fluorescence lifetime and optically detected magnetic resonance using the theoretical model. Finally, I will explore the theoretically predicted sensitivity of microwave-free magnetometry, based on the NV centre emission intensity change under an external magnetic field. Chapter 4 will demonstrate experimentally the microwave-free magnetometry technique. In relation to the study of microwave-free magnetometry, this chapter will explore an unexpected increase in emission intensity at high magnetic fields > 100mT. Combining the experimental observations and the theoretical simulation developed in the previous chapter, I will identify and discuss a phenomenological decrease in the NV centre transition rate from the triplet state to the singlet state. The chapter will conclude comparing the experimental and theoretical sensitivities associated with the microwave-free magnetometry technique. Chapter 5 will show the characterisation of a diamond sample at each step of the process to create NV centres. I will study the electron irradiation followed by separate annealing on a high-pressure high-temperature diamond sample. I will then characterise the sample employing visible and infrared absorption spectroscopy, as well as measure the fluorescence spectra and lifetime of the defects identified at each step. Chapter 6 will examine an alternative method to create NV centres in diamond. I will compare diamond samples irradiated and annealed separately with samples simultaneously irradiated and annealed (referred to as 'annealing in situ'). To compare the two processes, I will estimate the concentration of nitrogen defects and NV centres and calculate their N-to-NV conversion efficiency. Chapter 7 will discuss the effects of substitutional nitrogen on the properties of the NV centres in diamond. For this discussion, I will use a single-crystal diamond that shows the presence of 4 growth sectors. Each growth sector is characterised by a different nitrogen concentration, as I will demonstrate at the beginning of the chapter. I will focus on 4 main properties affected by the concentration of nitrogen in the different sectors: the balance between the charge states of the NV centre, the overall fluorescence intensity from each sector, the fluorescence lifetime and its relation to non-radiative processes, and the magnetic field sensitivity obtained with the optically detected magnetic resonance technique. Chapter 8 will gather the results and conclusions of the entire body of work. It will also discuss future avenues of research in the topic of diamond processing and characterisations, to improve the existing optical sensing applications.
Negatively charged nitrogen-vacancy (NV${}^{\ensuremath{-}}$) centers in diamond have generated much recent interest for their use in sensing. The sensitivity improves when the NV ground-state microwave transitions are narrow, but these transitions suffer from inhomogeneous broadening, especially in high-density NV ensembles. To better understand and remove the sources of broadening, we demonstrate room-temperature spectral ``hole burning'' of the NV ground-state transitions. We find that hole burning removes the broadening caused by magnetic fields from 13{}^{13}13C nuclei and demonstrate that it can be used for magnetic-field-insensitive thermometry.
We demonstrate the optical readout of ensembles of nitrogen-vacancy (NV) center spins in a bulk diamond sample via spin-to-charge conversion. A high power 594 nm laser is utilized to selectively ionize these paramagnetic defects in the mS=0 spin state with a contrast of up to 12%. In comparison to the conventional 520 nm spin readout, the spin-to-charge-conversion-based readout provides a higher signal-to-noise ratio, with tenfold sensing measurement speedup for millisecond long pulse sequences. This level of performance was achieved for an NV− ionization of only 25%, limited by the ionization and readout laser powers. These observations pave the way to a range of high-sensitivity metrology applications where the use of NV− ensembles in bulk diamond has proven useful, including sensing and imaging of target materials overlaid on the diamond surface.
We study the spectroscopy of an ensemble of negatively charged nitrogen-vacancy centers in diamond at high temperatures between room temperature and 700K under high vacuum conditions. Spin resonances are studied using optical detection of magnetic resonance (ODMR), and optical spectroscopy is employed to study radiative transitions. Upon increasing the temperature, the intensity of radiative decay in visible and infrared decreased. In addition, the ODMR resonance frequencies were decreased, and the phonon line emission shifted to higher wavelengths. Density functional theory calculation of the zero-field splitting parameter (D) revealed that thermal expansion is not enough to explain the shift in the ODMR frequencies. Fitting the measured intensity of photo-luminescence with the theoretical predictions of the Mott–Seitz model yields the value of 0.22eV for the energy barrier associated with nonradiative decay.