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

At a Glance

Metadata	Details
Publication Date	2022-03-01
Journal	New Journal of Physics
Authors	Marco Capelli, Lukas Lindner, Tingpeng Luo, Jan Jeske, Hiroshi Abe
Institutions	RMIT University, Fraunhofer Institute for Applied Solid State Physics
Citations	19
Analysis	Full AI Review Included

Technical Analysis: Optimizing NV Center Quantum Yield in MPCVD Diamond

This document analyzes the findings of the research paper “Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond” and details how 6CCVD’s advanced Microwave Plasma Chemical Vapor Deposition (MPCVD) diamond materials directly address the challenges identified, providing superior solutions for quantum sensing and computing applications.

Executive Summary

The research confirms that the performance of nitrogen-vacancy (NV¯) centers—critical for quantum sensing and computing—is severely limited by the concentration of proximal neutral substitutional nitrogen (N$_{s}^{0}$) defects.

Core Finding: N$_{s}^{0}$ defects quench NV¯ fluorescence quantum yield (QY) via non-radiative electron tunneling, leading to reduced brightness and sensitivity.
Performance Degradation: Samples with high N$_{s}^{0}$ concentration (380 ppm, typical of HPHT Ib diamond) exhibited a drastic QY drop from 77.4% down to 32%, and fluorescence lifetime reduction from 13.9 ns to 4.4 ns.
Material Requirement: To maintain a relative QY above 90%, the N$_{s}^{0}$ concentration must be strictly limited to less than 35.5 ppm.
Inhomogeneity Issue: HPHT samples showed significant variability in N$_{s}^{0}$ concentration across different growth sectors, leading to non-uniform device performance.
6CCVD Solution: High-purity, low-nitrogen MPCVD Single Crystal Diamond (SCD) from 6CCVD routinely achieves nitrogen concentrations in the low parts-per-billion (ppb) range, ensuring optimal QY (>90%) and maximum sensitivity for NV ensemble applications.
Application Impact: These results are crucial for optimizing diamond materials used in high-precision sensing, metrology, and single-photon communication devices.

Technical Specifications

The following table extracts key quantitative data points and experimental parameters from the study, highlighting the relationship between nitrogen concentration and NV center photodynamics.

Parameter	Value	Unit	Context
Lowest N$_{s}^{0}$ Concentration Investigated	1.81	ppm	CVD IIa sample (Batch 1)
Highest N$_{s}^{0}$ Concentration Investigated	380 ± 10	ppm	HPHT Ib sample (Batch 2)
Maximum Average Fluorescence Lifetime (τ)	13.90 ± 0.08	ns	Observed at 1.81 ppm N$_{s}^{0}$
Minimum Average Fluorescence Lifetime (τ)	4.4	ns	Observed at 380 ppm N$_{s}^{0}$
Highest Relative Quantum Yield (ε_rel)	77.4 ± 0.9	%	Observed at 88 ± 2 ppm N$_{s}^{0}$
Lowest Relative Quantum Yield (ε_rel)	32 ± 7	%	Observed at 380 ± 10 ppm N$_{s}^{0}$
Target N$_{s}^{0}$ Concentration for QY > 90%	< 35.5	ppm	Derived from best-fit model (6.2×10^-3 nm^-3)
Electron Irradiation Energy	2	MeV	Used for vacancy creation
Annealing Temperature Range	900 to 1000	°C	Used for NV center formation
Radiative Decay Rate (k₀)	72.0 ± 0.4	MHz	Baseline decay rate (low N)
Zero-Distance Tunnelling Rate (A)	185 ± 87	MHz	Fitted non-radiative rate parameter

Key Methodologies

The study employed a rigorous combination of material synthesis, defect creation, and advanced optical characterization techniques:

Sample Preparation: Used both low-nitrogen CVD IIa diamond (Fraunhofer IAF) and high-nitrogen HPHT Ib diamond (ElementSix, Sumitomo Electric). HPHT samples were selected based on distinct growth sectors to access a wide range of intrinsic N$_{s}^{0}$ concentrations (2 ppm to 400 ppm).
Defect Creation: Samples were irradiated using a 2 MeV electron beam at varying total fluences (0.5×10¹⁸ cm^-2 to 5×10¹⁸ cm^-2) to introduce vacancies.
Thermal Processing: Subsequent annealing was performed at 900 °C or 1000 °C for 2 hours to facilitate vacancy migration and NV center formation.
Nitrogen Concentration Measurement: N$_{s}^{0}$ concentration was quantified using Fourier-Transform Infrared (FTIR) absorption spectroscopy, specifically measuring the absorption coefficient at 1130 cm^-1.
NV Concentration Measurement: NV¯ concentration was estimated using visible absorption spectroscopy at 532 nm.
Photodynamics Characterization: A custom-built fluorescence confocal microscope was used, employing a picosecond-pulsed tuneable laser (520 nm excitation) and a 725 nm long-pass filter to minimize NV$^{0}$ emission collection.
Lifetime Analysis: Fluorescence decay curves were measured and fitted using a stretched exponential function to accurately determine the average fluorescence lifetime (τ) of the NV ensemble.

6CCVD Solutions & Capabilities

The research clearly demonstrates that material purity—specifically the control of N$_{s}^{0}$ concentration—is the primary limiting factor for high-performance NV ensemble devices. 6CCVD specializes in producing the high-purity MPCVD diamond required to overcome these limitations.

Research Requirement/Finding	6CCVD Solution & Capability	Technical Advantage & Sales Driver
Requirement for N$_{s}^{0}$ < 35.5 ppm (for QY > 90%)	Optical Grade Single Crystal Diamond (SCD): Our MPCVD growth process inherently yields ultra-low nitrogen concentrations, typically in the low ppb range (well below the 1.81 ppm benchmark).	Maximum Quantum Yield: Eliminates non-radiative tunneling pathways (k_tunnel), guaranteeing the highest possible fluorescence QY and brightness for NV ensemble sensing applications.
Need for Uniformity & Reproducibility	Large-Area PCD & SCD Wafers: We offer plates up to 125 mm (PCD) and large-area SCD, grown under highly controlled conditions, ensuring uniform defect incorporation across the entire substrate.	Eliminates Growth Sector Variability: Unlike HPHT, 6CCVD materials provide highly homogeneous N concentration, ensuring consistent NV performance across all fabricated devices.
Need for Precise NV Layer Engineering	Custom Thickness Control: SCD and PCD plates available from 0.1 µm to 500 µm thickness, and substrates up to 10 mm.	Optimized Implantation: Allows engineers to precisely control the depth and density of the NV ensemble layer for optimal coupling into optical systems and waveguides.
Surface Quality for Optical Integration	Advanced Polishing Services: SCD polished to Ra < 1 nm; inch-size PCD polished to Ra < 5 nm.	Reduced Surface Quenching: Minimizes surface defects and scattering losses, which are known to reduce QY for shallow NV centers (as discussed in the literature cited by the paper).
Need for Charge State Stabilization	Boron-Doped Diamond (BDD): We offer custom BDD films (SCD or PCD) to precisely tune the Fermi level, ensuring the NV centers remain predominantly in the desired negatively charged state (NV¯).	Enhanced Signal-to-Noise: Maximizes the concentration of the spin-dependent NV¯ state, crucial for high-sensitivity magnetometry and sensing.
Custom Device Integration	In-House Metalization: Capabilities include Au, Pt, Pd, Ti, W, and Cu deposition.	Seamless Integration: Allows researchers to immediately integrate NV-containing diamond chips into microelectronic or microwave structures without external processing delays.

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers specializes in defect engineering and material optimization for solid-state quantum systems. We provide comprehensive consultation on material selection, post-processing parameters (irradiation fluence, annealing temperature), and surface preparation to maximize NV¯ coherence time (T$_{2}$) and fluorescence quantum yield for similar high-density ensemble projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of high-purity diamond solutions worldwide.

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

Original Source

DOI: https://doi.org/10.1088/1367-2630/ac5ca9

References

2013 - The nitrogen-vacancy colour centre in diamond [Crossref]
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2019 - A perspective on fluorescent nanodiamond bioimaging [Crossref]
2014 - Magnetometry with nitrogen-vacancy defects in diamond [Crossref]
2010 - Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond [Crossref]
2018 - Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window [Crossref]
2008 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
2020 - Sensitivity optimization for NV-diamond magnetometry [Crossref]