Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Strong light-matter coupling has garnered significant attention for its potential to optimize optoelectronic responses. In this study, we designed open cavities featuring nonlocal metasurfaces composed of aluminum nanoparticle arrays. The surface lattice resonances in these metasurfaces exhibit electronic strong coupling with the boron difluoride curcuminoid derivative, which is known for its highly efficient thermally activated delayed fluorescence in the near-infrared. Our results show that delayed fluorescence induced by triplet-triplet annihilation can be enhanced by a factor of 2.0-2.6 in metasurfaces that are either tuned or detuned to the molecular electronic transition. We demonstrate that delayed fluorescence enhancements in these systems primarily stem from increased absorption in the organic layer caused by the nanoparticle array, while strong coupling has negligible effects on reverse intersystem crossing rates, aligning with previous studies. We support these findings with finite-difference-time-domain simulations. This study elucidates how light-matter interactions affect delayed fluorescence, highlighting the potential applications in optoelectronic devices.

DOI： 10.1021/acsphotonics.5c00124

PubMed

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Abstract

Metasurface stickers, where the periodic array of nanoparticles is embedded in an elastomer film, can be attached to and detached from the surface of target materials and work as metasurface to control light. The stickers can be fabricated by lithographic and etching/lift-off processes, followed by a transfer process. To transfer, a sacrifice layer, typically water-soluble and oil-insoluble organic polymers, is required to separate the substrate from the metasurface. Although they fulfill the prerequisite as a sacrifice layer, organic polymers cannot be heated above 300 °C, and are often damaged during exposure to reactive gases in the dry etching processes. In this study, we introduced an alternative amorphous germanium dioxide (GeO₂), an inorganic material with high water solubility, as the transfer sacrificial layer. The amorphous GeO₂, made by mist chemical vapor deposition in this study, is stable and maintains the amorphous state under heat treatment up to 750 °C. Upon exposure to water, amorphous GeO₂ is readily nano-crystallized and dissolved while it is unsolved in organic solvents used in the nanofabrication processes. Using this sacrificial layer, we fabricated a TiO₂ metasurface sticker via nanoimprinting of a Ti film followed by thermal oxidation. We demonstrate a photoluminescence outcoupling by placing a sticker on the phosphor plate: the emission pattern is modulated both spatially and spectrally in a way defined by the structure of the metasurface sticker.

DOI： 10.35848/1347-4065/adb164

CiNii Research

Other URL： https://iopscience.iop.org/article/10.35848/1347-4065/adb164/pdf

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Abstract

We fabricated a periodic SiC nanovoid array embedded in the flexible polymer, which is applicable as a sticker to stick to any clean surfaces to control light. Starting from the epitaxial 3C-SiC thin films on Si substrates, the nanovoid array was fabricated by combining nanoimprint lithography and dry etching. After coating the nanovoid with a polydimethylsiloxane (PDMS) film, the Si substrate on the backside was etched away to obtain the free-standing SiC nanovoid array embedded in the PDMS film. The optical measurements show that the resultant nanovoid array sticker supports wave-guiding modes in the SiC layer about 650 nm thick. Photoluminescence enhancement was demonstrated by depositing the luminous layer on top of the nanovoid array. Compared to the same luminous layer on the structure-less flat substrate, the photoluminescence intensity on the nanovoid array was enhanced up to about 8 times. The present method is applicable to fabricate various optical devices using SiC.

DOI： 10.35848/1347-4065/adaecc

Other URL： https://iopscience.iop.org/article/10.35848/1347-4065/adaecc/pdf

Authorship：Lead author,　Last author,　Corresponding author  

The Purcell effect describes the enhancement of the spontaneous emission rate of an emitter near a resonant structure. However, evaluating the Purcell factor quantitatively and empirically is difficult due to the difficulties in measuring the electromagnetic near field of an optical resonance for calculation of the exact effective modal volume, especially with non-Hermitian resonators. Therefore, we propose an analytical approach to circumvent the need to measure the near field and predict the Purcell enhancement with spectral parameters, which can be directly measured in the far field or fitted from such spectral measurements. Our proposed model predicts the averaged Purcell enhancement by metasurfaces on a photoluminescent medium, and is verified with experimental measurements and numerical simulations of nanoparticle arrays coupled to a fluorescent thin film. The model directly analyzes the photoluminescence enhancement and extraction efficiency of the metasurface, and can be generalized to work with an arbitrarily shaped photoluminescent medium that is coupled to a resonator. This discovery provides a practical and accessible way to understand the underlying mechanisms of photoluminescence enhancement and will facilitate optimization of metasurfaces for efficient extraction of the enhanced luminescence.

DOI： 10.1103/physreva.111.013511

CiNii Research

Authorship：Lead author,　Last author,　Corresponding author  

DOI： 10.1117/12.3055231

Authorship：Lead author,　Last author,　Corresponding author  

Authorship：Lead author,　Last author,　Corresponding author  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

We report the formation of polariton condensates from strongly coupled molecules to bound states in the continuum with quadrupolar character in a metasurface of silicon nanoparticles. Our experiments demonstrate a strong dependence of the condensation threshold on the excitation spot size. The condensation threshold decreases as the excitation spot size increases, achieving thresholds below 3 μm cm-2 for spot sizes of around 1 mm2 and condensate lifetimes exceeding 20 ps. The strong dependence of the condensation threshold on the spot size is caused by the long propagation length of the polaritons. We reproduce this dependence in simulations by including a term for the ballistic transport of exciton-polaritons in the rate equations describing the condensation. These results illustrate the critical role that polariton transport plays in condensation and highlight the relevance of considering the size of the excitation in condensation experiments.

DOI： 10.1021/acsnano.4c09970

PubMed

CiNii Research

Authorship：Lead author,　Last author,　Corresponding author  

<jats:p>We investigate the chiral emission from non-chiral molecules coupled to metasurfaces with a unit cell formed by dimers of detuned and displaced Si nanodisks. The detuning and displacement lead to the formation of narrow modes, known as quasi-bound states in the continuum (Q-BICs), with different electric and magnetic characteristics. The dispersion and character of the modes are explained by using the guided-mode expansion method and finite-element simulations. The coupling between these modes leads to an extrinsic chiral response with large circular dichroism for defined energies and wavevectors. When the lattice constant of the metasurface is changed, the dispersion of the extrinsic chiral Q-BICs can be tuned and the emission properties of a thin film of dye molecules on top of the metasurface are modified. In particular, we observe strongly directional and circularly polarized emission from the achiral dye molecules with a degree of circular polarization reaching 0.8 at the wavelengths defined by the dispersion of the Q-BICs. These results could enable the realization of compact light sources with a large degree of circular polarization for applications in displays, optical recording, or optical communication.</jats:p>

DOI： 10.1364/prj.528976

CiNii Research

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Fluorescent dye films on transparent substrates are essential for OLEDs, flexible displays, X-ray detection, and wireless optical communications. However, their efficiency is often hampered by fluorescence trapping due to total internal reflection (TIR) and waveguiding. This study tackles this longstanding challenge by reconceptualizing the integration of dye films with nanoantenna metasurfaces. Traditional methods involve directly spin-coating films onto c-Si metasurfaces on quartz substrates, resulting in edge luminescence and weak inner signals. We present a straightforward, adjustable approach by integrating dye films on the opposite side of quartz substrates, reaching a 2.5-fold photoluminescence enhancement and improving the uniformity of the emission compared to the conventional methods. These gains stem from redirecting a significant portion of leaked fluorescence light trapped inside the substrate into free space, surpassing TIR conditions through in-plane diffraction orders of the metasurfaces across the full RGB spectrum. Our findings facilitate the design of more efficient luminescent devices.

DOI： 10.1021/acs.nanolett.4c03294

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adpr.202400050

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<p>We investigated the changes in shape and extinction intensity of Au nanorod arrays by rapid thermal annealing (RTA). RTA was performed at 400~800°C for 3 min in an N₂ atmosphere using a halogen lamp as a heater. With increasing annealing temperature, the surface roughness of the rod decreases, the long axis of the rod shrinks while the short axis inflates, and finally some rods split. The wavelength and intensity of localized surface plasmon resonance varied with the rods shape. In particular, annealing at 800°C shifts the high-order (3<i>λ</i>/2) mode along the long axis from the near infrared to the visible region. Also surface lattice resonance is observed, showing that the periodicity of the array is retained even after annealing at 800°C.</p>

DOI： 10.2497/jjspm.23-00054

CiNii Research

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

This work presents a bulk refractive index sensor based on quasi-bound states in the continuum (BICs) induced by broken symmetries in metasurfaces. The symmetry is broken by detuning the size and position of silicon particles periodically arranged in an array, resulting in multiple quasi-BIC resonances. We investigate the sensing characteristics of each of the resonances by measuring the spectral shift in response to changes in the refractive index of the surrounding medium. In addition, we reveal the sensing range of the different resonances through simulations involving a layer of deviating refractive index of increasing thickness. Interestingly, the resonances show very different responses, which we describe via the analysis of the near-field. This work contributes to the development of highly sensitive and selective BIC-based sensors that can be used for a wide range of applications.

DOI： 10.1364/OE.514787

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

H-type supramolecular polymers with preferred helicity and highly efficient emission have been prepared from the self-assembly of chiral tetraphenylene-based monomers. Implementation of the one-dimensional fibers into dielectric nanoparticle arrays allows for a significant reshaping of fluorescence due to weak light-matter coupling.

DOI： 10.1039/d3cc05877h

PubMed

Authorship：Lead author,　Last author,　Corresponding author  

Authorship：Lead author,　Last author,　Corresponding author  

Authorship：Lead author,　Last author,　Corresponding author  

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