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6CCVD Research

Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-03-01
JournalNew Journal of Physics
AuthorsMarco Capelli, Lukas Lindner, Tingpeng Luo, Jan Jeske, Hiroshi Abe
InstitutionsThe University of Melbourne, Fraunhofer Institute for Applied Solid State Physics
Citations19
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study quantifies the detrimental effect of proximal nitrogen impurities on the performance of Nitrogen-Vacancy (NV) centers in diamond, critical for solid-state quantum systems.

  • Core Finding: Neutral substitutional nitrogen (Ns0) defects significantly quench the fluorescence quantum yield (FQY) of negatively charged NV centers (NV-).
  • Mechanism: The reduction in FQY is attributed to increased non-radiative electron tunneling (ktunnel) within the excited N+-NV- pair, causing relaxation without photon emission.
  • Quantified Reduction: Increasing Ns0 density from 88 ppm to 380 ppm caused the relative FQY to drop sharply from 77.4% to 32%.
  • Lifetime Correlation: Fluorescence lifetime decreased from 13.9 ns (low N) to 4.4 ns (high N, 380 ppm), confirming the dominance of the non-radiative decay pathway.
  • Engineering Threshold: To maintain a high relative FQY (above 90%), the concentration of Ns0 defects must be strictly limited to less than 35.5 ppm.
  • Material Implications: Results highlight the variability and limitations of high-nitrogen HPHT diamonds and emphasize the need for nitrogen-doped CVD diamonds with precisely controlled, low Ns0 concentrations for optimal device performance.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Ns0 Concentration Limit< 35.5ppmRequired to maintain relative FQY >90%
Relative FQY (High N)32 ± 7%Measured at 380 ppm Ns0
Relative FQY (Low N HPHT)77.4 ± 0.9%Measured at 88 ppm Ns0
Fluorescence Lifetime (Low N)13.90 ± 0.08nsMeasured at 1.81 ppm Ns0
Fluorescence Lifetime (High N)4.4nsMeasured at 380 ppm Ns0
Radiative Decay Rate (k0)72.0 ± 0.4MHzCalculated from low-nitrogen data points
Zero-Distance Tunnelling Rate (A)185 ± 87MHzMaximum rate obtained from exponential fit
Electron Irradiation Energy2MeVUsed for vacancy creation
Irradiation Fluence Range0.5x1018 to 5x1018cm-2Range used for HPHT Batch 3 samples
Annealing Temperature900 or 1000°CUsed for NV center formation (2 hours)
NV0 Emission Contribution< 0.3%Measured under 725 nm long-pass filter
Ns0 Absorption Signature1130cm-1Used for FTIR concentration calculation
NV- Absorption Signature532nmUsed for UV-Vis concentration calculation

Key Methodologies

Section titled “Key Methodologies”

The study characterized the photodynamics of NV ensembles in synthetic diamond samples (CVD IIa and HPHT Ib) with Ns0 concentrations ranging from 2 ppm up to 400 ppm.

  1. Sample Preparation:

    • CVD IIa (Batch 1) and HPHT Ib (Batches 2 & 3) single crystals were used. HPHT samples were selected based on distinct growth sectors exhibiting varying Ns0 concentrations.
    • NV centers were created via 2 MeV electron irradiation, followed by high-temperature annealing (900°C or 1000°C for 2 hours).

  2. Defect Concentration Characterization:

    • Ns0 Concentration: Determined using Fourier-Transform Infrared (FTIR) spectroscopy, analyzing the absorption coefficient at 1130 cm-1.
    • NV- Concentration: Determined using visible absorption spectroscopy, analyzing the absorption coefficient at 532 nm.

  3. Fluorescence Measurement:

    • A custom confocal microscope was used with a picosecond-pulsed tuneable laser (520 nm excitation, 10 MHz repetition rate).
    • Emission was filtered using a 532 nm long-pass filter and a 725 nm long-pass filter to minimize collection of the neutral NV0 state.

  4. Photodynamics Analysis:

    • Brightness: Calculated from the slope of the linear relationship between emission intensity and excitation power (kept below saturation).
    • Lifetime (τ): Measured using time-tagging correlation. Ensemble decay curves were fitted using a stretched exponential function, I0 exp[−(t/τ0)ÎČ], to account for the continuous distribution of decay rates.
    • Tunnelling Rate (ktunnel): Calculated from the measured average lifetime (τ) using the relationship: ktunnel = (1/τ) - k0, where k0 is the constant decay rate measured at the lowest Ns0 concentration.

  5. Model Development:

    • The average distance between NV- and its closest Ns0 defect was calculated from the Ns0 concentration (ρN).
    • The calculated ktunnel was fitted against the average N-NV distance using an exponential decay model (A exp[-2αd]) to derive the zero-distance tunnelling rate (A) and the decay constant (α).

Commercial Applications

Section titled “Commercial Applications”

The findings provide critical material specifications for optimizing diamond-based quantum technologies, particularly those relying on high-density NV ensembles.

  • Quantum Sensing (Magnetometry/Thermometry):

    • Sensitivity Optimization: The total sensitivity (ηens) of NV ensembles is limited by both coherence time (T2) and FQY (Δ). By limiting Ns0 to <35.5 ppm, manufacturers can prevent FQY collapse, thereby maximizing the signal-to-noise ratio and overall sensor performance.
    • Material Selection: Informs the selection of diamond growth sectors (e.g., in HPHT) or the use of nitrogen-doped CVD diamonds to ensure uniform, high-performance material.

  • Fluorescent Nanodiamonds (Biolabeling):

    • Bright Emitters: Essential for creating nanodiamonds with high brightness per unit mass, making them competitive with other fluorescent biolabels for bioimaging and diagnostics.
    • Uniformity: Addresses the origin of inhomogeneities observed in high-density NV ensembles within nanodiamonds, allowing for better quality control.

  • Quantum Information Processing:

    • Single Photon Sources: High FQY is necessary for efficient single-photon emission, supporting applications in quantum computing and single photon communication systems.

  • Diamond Manufacturing:

    • Process Control: Provides a quantitative target (Ns0 < 35.5 ppm) for diamond growth processes (HPHT or CVD) and post-processing (irradiation/annealing) to ensure the resulting material meets the required optical specifications for quantum devices.
View Original Abstract

Abstract The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4% to 32% with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2013 - The nitrogen-vacancy colour centre in diamond [Crossref]
  2. 2014 - Nitrogen-vacancy centers in diamond: nanoscale sensors for physics and biology [Crossref]
  3. 2007 - Nanometer-sized diamond particle as a probe for biolabeling [Crossref]
  4. 2009 - Diamond standard in diagnostics: nanodiamond biolabels make their mark [Crossref]
  5. 2019 - A perspective on fluorescent nanodiamond bioimaging [Crossref]
  6. 2014 - Magnetometry with nitrogen-vacancy defects in diamond [Crossref]
  7. 2010 - Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond [Crossref]
  8. 2018 - Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window [Crossref]
  9. 2008 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
  10. 2020 - Sensitivity optimization for NV-diamond magnetometry [Crossref]

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