Monitoring Dark-State Dynamics of a Single Nitrogen-Vacancy Center in Nanodiamond by Auto-Correlation Spectroscopy - Photonionization and Recharging

At a Glance

Metadata	Details
Publication Date	2021-04-10
Journal	Nanomaterials
Authors	Mengdi Zhang, Bai‐Yan Li, Jing Liu
Institutions	University of Indianapolis, Indiana University – Purdue University Indianapolis
Citations	5
Analysis	Full AI Review Included

Technical Analysis: NV Center Dark-State Dynamics via Auto-Correlation Spectroscopy

This document analyzes the research paper “Monitoring Dark-State Dynamics of a Single Nitrogen-Vacancy Center in Nanodiamond by Auto-Correlation Spectroscopy: Photonionization and Recharging” (Nanomaterials 2021, 11, 979). The findings are critical for engineers developing next-generation quantum sensors, quantum communication devices, and advanced bioimaging platforms utilizing diamond Nitrogen-Vacancy (NV) centers.

Executive Summary

This study successfully quantifies the ultrafast transition kinetics between the negative (NV⁻, “bright”) and neutral (NV⁰, “dark”) charge states in single NV centers using Auto-Correlation Spectroscopy (ACS).

Core Achievement: Developed a robust ACS method to measure transition rates in the sub-microsecond to millisecond range, overcoming limitations of traditional ON/OFF histograms.
Ionization Mechanism (NV⁻ to NV⁰): Identified as a fast, one-photon absorption process. The transition time is approximately 0.1 µs (100 ns range), and the rate increases linearly (P^1.0) with laser power.
Recharging Mechanism (NV⁰ to NV⁻): Identified as a slow, sequential two-photon process. The transition time is significantly longer, around 20 ms, and the rate exhibits a quasi-quadratic dependence (P^1.85) on laser power.
Wavelength Dependence: Strong charge conversion intermittency is observed under 532 nm (green) excitation, while 633 nm (red) excitation suppresses ionization, leading to stable mono-state emission.
Application Relevance: Precise control and understanding of these charge state dynamics are essential for optimizing NV centers for quantum information science, quantum communication, and high-resolution quantum bioimaging.

Technical Specifications

The following hard data points were extracted from the time-resolved spectroscopy and auto-correlation analysis:

Parameter	Value	Unit	Context
Excitation Wavelength (Intermittency)	532	nm	Induces strong NV⁻/NV⁰ charge conversion
Excitation Wavelength (Mono-state)	633	nm	Photon energy too low to induce ionization
NV⁻ (“ON” State) Lifetime	11.88	ns	Measured via Time-Correlated Single Photon Counting (TCSPC)
NV⁰ (“OFF” State) Lifetime	6.14	ns	Measured via TCSPC
Ionization Transition Time (NV⁻ → NV⁰)	~0.1	µs	Fast component, one-photon process
Recharging Transition Time (NV⁰ → NV⁻)	~20	ms	Slow component, two-photon process
Ionization Rate Power Dependence (k₁₂)	Linear (P^1.0)	N/A	Confirms one-photon absorption
Recharging Rate Power Dependence (k₂₀)	Quasi-Quadratic (P^1.85)	N/A	Confirms sequential two-photon absorption
Ionization Rate Range (532 nm)	5.33 to 160.26	ms⁻¹	Measured across 0.02 mW to 1.5 mW excitation power
Nanodiamond Nominal Size	50	nm	Host material for NV centers

Key Methodologies

The experiment relied on high-purity material preparation and advanced time-resolved single molecule spectroscopy:

Nanodiamond Cleaning: Commercial 50 nm nanodiamonds (0.5% w/v) were subjected to five cycles of centrifugation (5000 rpm) and supernatant replacement (80% volume fraction) to eliminate small particles and impurities.
Sample Preparation: The cleaned nanodiamond suspension was spin-coated onto a MgO substrate at 2000 rpm.
Immobilization Layer: A 60-nm-thick layer of Polyvinyl Alcohol (PVA, 1.5% w/v) was applied to immobilize the nanodiamonds and protect them from surface oxidation effects.
Excitation Source: A picosecond-pulsed laser (532 nm) with a tunable repetition frequency (10/20 MHz) was used for excitation.
Detection Setup: A customized scanning confocal microscope utilizing a water-immersion objective (NA 1.2) collected fluorescence, which was filtered (685-70 band pass) and split 50/50 into two single photon avalanche photodiodes (SPADs) in a Hanbury Brown-Twiss (HBT) geometry.
Data Analysis: Fluorescence lifetime was obtained via TCSPC fitting. Auto-correlation analysis of the intensity fluctuations was performed to extract the transition rates (k₁₂ and k₂₀) and dark-state lifetime (T_D).

6CCVD Solutions & Capabilities

The research highlights the critical need for high-purity, structurally controlled diamond materials to achieve predictable NV center performance. While this study used nanodiamonds, scaling this research into robust quantum devices requires high-quality bulk or thin-film MPCVD diamond. 6CCVD is uniquely positioned to supply the foundational materials and customization services necessary to replicate and advance this work.

Applicable Materials

To achieve the highest coherence and stability required for quantum applications, researchers should transition from stochastic nanodiamonds to engineered Single Crystal Diamond (SCD) substrates.

Optical Grade Single Crystal Diamond (SCD): Essential for creating highly stable, isolated NV centers via controlled nitrogen incorporation or ion implantation. Our SCD features extremely low native nitrogen content (< 1 ppb), maximizing NV⁻ stability and minimizing spectral diffusion.
Polycrystalline Diamond (PCD) Substrates: Available in large formats (up to 125mm diameter) for scalable integration of NV-based sensors or integrated photonics.
Boron-Doped Diamond (BDD): Available for applications requiring conductive diamond electrodes or specific charge state manipulation near the surface.

Customization Potential

6CCVD’s in-house manufacturing capabilities directly address the needs of advanced quantum research and device fabrication:

Research Requirement/Challenge	6CCVD Solution & Capability	Technical Advantage
Need for Scalable Substrates	Custom Dimensions up to 125mm (PCD)	Enables the fabrication of large-area NV sensor arrays or integrated quantum photonic circuits, moving beyond small, spin-coated samples.
Precise NV Depth Control	SCD Thickness Control (0.1µm - 500µm)	Critical for optimizing NV center depth, whether for shallow sensing (0.1 µm) or deep bulk coherence measurements (500 µm).
High-Fidelity Optical Interface	Ultra-Polishing (Ra < 1nm for SCD)	Our superior polishing minimizes surface defects and scattering, ensuring high-quality optical coupling necessary for precise ACS and TCSPC measurements.
Integrated Device Contacting	Custom Metalization (Au, Pt, Pd, Ti, W, Cu)	We offer internal metalization services, allowing researchers to define electrodes directly on the diamond surface for electrical control over the NV charge state, a key factor in controlling the NV⁻/NV⁰ transition kinetics.
Material Purity and Consistency	High-Purity MPCVD Growth	Provides consistent material properties across batches, ensuring reliable replication of complex kinetic studies like those involving power-dependent two-photon processes.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond quantum defects. We provide expert consultation on:

Optimizing nitrogen concentration and NV creation methods (e.g., implantation dose and annealing recipes) to maximize the yield of stable NV⁻ centers.
Selecting the appropriate diamond grade and surface termination to minimize the charge state blinking observed in this research, thereby improving quantum coherence.
Designing custom diamond structures (e.g., thin films or membranes) for integration into optical cavities or waveguides for enhanced photon collection efficiency.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this letter, the photon-induced charge conversion dynamics of a single Nitrogen-Vacancy (NV) center in nanodiamond between two charge states, negative (NV−) and neutral (NV0), is studied by the auto-correlation function. It is observed that the ionization of NV− converts to NV0, which is regarded as the dark state of the NV−, leading to fluorescence intermittency in single NV centers. A new method, based on the auto-correlation calculation of the time-course fluorescence intensity from NV centers, was developed to quantify the transition kinetics and yielded the calculation of transition rates from NV− to NV0 (ionization) and from NV0 to NV− (recharging). Based on our experimental investigation, we found that the NV−-NV0 transition is wavelength-dependent, and more frequent transitions were observed when short-wavelength illumination was used. From the analysis of the auto-correlation curve, it is found that the transition time of NV− to NV0 (ionization) is around 0.1 μs, but the transition time of NV0 to NV− (recharging) is around 20 ms. Power-dependent measurements reveal that the ionization rate increases linearly with the laser power, while the recharging rate has a quadratic increase with the laser power. This difference suggests that the ionization in the NV center is a one-photon process, while the recharging of NV0 to NV− is a two-photon process. This work, which offers theoretical and experimental explanations of the emission property of a single NV center, is expected to help the utilization of the NV center for quantum information science, quantum communication, and quantum bioimaging.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano11040979

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