[Paper Review] Diamond particles as nanoantennas for nitrogen-vacancy color centers

Jean‐Jacques Greffet, Jean‐Paul Hugonin+4 more|arXiv (Cornell University)|Jul 3, 2011

Diamond and Carbon-based Materials Research2 references18 citations

TL;DR

This paper demonstrates that diamond nanoparticles act as dielectric nanoantennas that mediate the optical response of nitrogen-vacancy (NV) centers, explaining size-dependent emission properties such as lifetime fluctuations and reduced resolution in STED microscopy. The key contribution is a unified model showing that sub-wavelength particles suppress emission via dielectric screening, while larger particles support Mie resonances, with STED resolution fundamentally limited by particle size due to uniform excitation of dipolar modes.

ABSTRACT

The photoluminescence of nitrogen-vacancy (NV) centers in diamond nanoparticles exhibits specific properties as compared to NV centers in bulk diamond. For instance large fluctuations of lifetime and brightness from particle to particle have been reported. It has also been observed that for nanocrystals much smaller than the mean luminescence wavelength, the particle size sets a lower threshold for resolution in Stimulated Emission Depletion (STED) microscopy. We show that all these features can be quantitatively understood by realizing that the absorption-emission of light by the NV center is mediated by the diamond nanoparticle which behaves as a dielectric nanoantenna.

Motivation & Objective

• To understand the origin of large fluctuations in NV center photoluminescence lifetime and brightness in nanodiamonds compared to bulk diamond.
• To resolve the paradox that STED microscopy fails to achieve sub-10 nm resolution on NV centers in 40 nm nanodiamonds despite success in bulk diamond.
• To establish a theoretical framework linking NV optical properties to the dielectric nanoantenna behavior of nanodiamonds.
• To quantify how particle size and environment affect the local density of states (LDOS) and emission rate of NV centers.

Proposed method

• Modeling the NV center as a point-like electric dipole in a dielectric sphere using Mie theory to compute the normalized emission rate (Purcell factor) relative to bulk diamond.
• Applying the reciprocity theorem to relate far-field radiation to the internal field distribution under plane-wave illumination.
• Using finite element simulations to account for the effect of a dielectric substrate on the Purcell factor, particularly for particles on silica coverslips.
• Simulating the excitation of nanodiamonds by structured STED beams to analyze spatial field distribution and mode coupling.
• Computing the local density of states (LDOS) ratio (Purcell factor) as a function of particle radius and wavelength to identify electrostatic and Mie regimes.
• Analyzing angular emission patterns and field distributions to show that sub-wavelength particles support only dipolar modes with uniform field profiles.

Experimental results

Research questions

• RQ1 Why do NV centers in nanodiamonds exhibit broad distributions in photoluminescence lifetime and brightness despite similar intrinsic properties?
• RQ2 How does the dielectric environment of a nanodiamond alter the emission rate of an embedded NV center compared to bulk diamond?
• RQ3 Why does STED microscopy fail to resolve individual NV centers within nanodiamonds smaller than the emission wavelength?
• RQ4 What role do Mie resonances play in modifying the optical response of NV centers in larger nanodiamonds?
• RQ5 To what extent does the presence of a substrate influence the emission properties of NV centers in nanodiamonds?

Key findings

• The Purcell factor for a NV center at the center of a spherical nanodiamond is less than 1 in the electrostatic regime (a ≪ λ), indicating reduced emission rate due to dielectric screening.
• For particles with radius a ≈ λ/n, the Purcell factor increases and exhibits oscillations due to Mie resonances, indicating enhanced emission at specific sizes.
• The maximum Purcell factor for a 45 nm nanodiamond on a silica substrate is approximately 0.39 for a dipole parallel to the interface, in good agreement with the experimental value of ~0.47.
• Sub-wavelength nanodiamonds (e.g., 50 nm) support only a uniform dipolar mode, which causes the structured STED beam's spatial pattern to be lost inside the particle.
• The STED resolution is fundamentally limited by the particle size because the dipolar mode excites the NV center uniformly regardless of position, preventing sub-particle resolution.
• Simulations confirm that the STED-depleted field structure does not penetrate uniformly into sub-wavelength particles, leading to delocalized excitation and blurred imaging.