Strong Coupling of Carbon Quantum Dots in Plasmonic Nanocavities

Wet-spinning fluorescent alginate fibres achieved by doping PEI modified CPDs for multiple anti-counterfeiting

Carbonized polymer dots (CPDs) with satisfactory excitation-dependent-emission and biocompatibility had great potential in anti-counterfeiting fibres field. However, it was difficult for CPDs to combined into the fibres due to the unstable interaction between CPDs and spinnable polymer matrix. Polyethyleneimine (PEI) was used to modify CPDs (namely PEI-CPDs) for achieving stable interactions with sodium alginate (SA) by a simple method, which including the physical interaction between the amino groups of PEI-CPDs and carboxyl groups of SA and the chain entanglement between two types of polymer chains. Then alginate fibres based on PEI-CPDs (PEI-CPDs/CaALG fibres) were successfully prepared by wet-spinning for the first time with less loss of PEI-CPDs. The high mechanical strength, excellent thermal stability and good biocompatibility achieved by PEI-CPDs/CaALG fibres. Furthermore, the fibres exhibited the excitation-dependent-emission property. Anti-counterfeiting of the fibres was conducted on both textile and papers, which showed higher security than the existing anti-counterfeiting fibres.

Toward a New Era of SERS and TERS at the Nanometer Scale: From Fundamentals to Innovative Applications

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) have opened a variety of exciting research fields. However, although a vast number of applications have been proposed since the two techniques were first reported, none has been applied to real practical use. This calls for an update in the recent fundamental and application studies of SERS and TERS. Thus, the goals and scope of this review are to report new directions and perspectives of SERS and TERS, mainly from the viewpoint of combining their mechanism and application studies. Regarding the recent progress in SERS and TERS, this review discusses four main topics: (1) nanometer to subnanometer plasmonic hotspots for SERS; (2) Ångström resolved TERS; (3) chemical mechanisms, i.e., charge-transfer mechanism of SERS and semiconductor-enhanced Raman scattering; and (4) the creation of a strong bridge between the mechanism studies and applications.

Red-Emissive Sulfur-Doped Carbon Dots for Selective and Sensitive Detection of Mercury (II) Ion and Glutathione

Carbon dots (CDs) show great potential in bioimaging and biosensing because of their good biocompatibility and excellent optical properties. However, CDs with intense red emissions for sensitive and selective detection are rarely reported. Herein, we prepared the red-emissive carbon dots (RCDs) through a facile hydrothermal method using tetra (4-carboxyphenyl) porphyrin (TCPP) and thiourea as starting materials. The obtained RCDs were characterized by TEM, XRD, and XPS. RCDs exhibited high water solubility and strong red emission (λ_em = 650 nm), with the fluorescence quantum yield as high as 26.7%, which was greatly higher than that of TCPP. Moreover, the as-prepared RCDs could be acted as a highly selective and sensitive probe for the detection of Hg²⁺ and glutathione (GSH) through the fluorometric titration method. The detection limits of Hg²⁺ and GSH were calculated to be 1.73 and 1.6 nM, respectively. The cellular experiments demonstrated the good biocompatibility of RCDs and their feasibility in bioimaging. Thus, this work provided a simple strategy to design and synthesize the highly red-emissive carbon dots, which showed promising application in biological and environmental assays.

Principle and Applications of Multimode Strong Coupling Based on Surface Plasmons

In the past decade, strong coupling between light and matter has transitioned from a theoretical idea to an experimental reality. This represents a new field of quantum light–matter interaction, which makes the coupling strength comparable to the transition frequencies in the system. In addition, the achievement of multimode strong coupling has led to such applications as quantum information processing, lasers, and quantum sensors. This paper introduces the theoretical principle of multimode strong coupling based on surface plasmons and reviews the research related to the multimode interactions between light and matter. Perspectives on the future development of plasmonic multimode coupling are also discussed.

Plasmon enhanced light-matter interaction of rice-like nanorods by a cube-plate nanocavity

Plasmonic nanocavity is widely used for enhancing light-matter interaction. Here, an efficient plasmonic nanocavity of the cube-plate system is constructed for the fluorescence enhancement of rice-like CdSe/CdS nanorods (NRs) with tunable emission wavelength. Over ten thousand times fluorescence enhancement is achieved with the assistance of the plasmonic nanocavity. Additionally, a small splitting effect is observed in both photoluminescence and scattering spectra of the NRs in the nanocavity owing to the intermediate coupling effect between the NRs and plasmonic nanocavity, which provides a potential application for optical signal enhancement and strong light-matter interaction.

Exciton-Photonics: From Fundamental Science to Applications

Semiconductors in all dimensionalities ranging from 0D quantum dots and molecules to 3D bulk crystals support bound electron-hole pair quasiparticles termed excitons. Over the past two decades, the emergence of a variety of low-dimensional semiconductors that support excitons combined with advances in nano-optics and photonics has burgeoned an advanced area of research that focuses on engineering, imaging, and modulating the coupling between excitons and photons, resulting in the formation of hybrid quasiparticles termed exciton-polaritons. This advanced area has the potential to bring about a paradigm shift in quantum optics, as well as classical optoelectronic devices. Here, we present a review on the coupling of light in excitonic semiconductors and previous investigations of the optical properties of these hybrid quasiparticles via both far-field and near-field imaging and spectroscopy techniques. Special emphasis is given to recent advances with critical evaluation of the bottlenecks that plague various materials toward practical device implementations including quantum light sources. Our review highlights a growing need for excitonic material development together with optical engineering and imaging techniques to harness the utility of excitons and their host materials for a variety of applications.

Water-Wettable Open Plasmonic Nanocavities for Ultrasensitive Molecular Detections in Multiple Phases

Plasmonic nanocavities between metal nanoparticles on metal films are either hydrophobic or fully occupied by nonmetallic spacers, preventing molecular diffusion into electromagnetic hotspots. Here we realize water-wettable open plasmonic cavities by devising gold nanoparticle with site-selectively grown ultrathin dielectric layer-on-gold film structures. We directly confirm that hydrophilic dielectric layers of SiO₂ or TiO₂, which are formed only at the tips of gold nanorod via precise temperature control, render sub-10 nm cavities open to the surroundings and completely water-wettable. Simulations reveal that spontaneous wetting in our cavities is driven by the presence of tip-selective hydrophilic layer and tendency of minimizing high energy air/water interface inside the cavities. Our plasmonic cavities show significant Raman enhancement of up to 4 orders of magnitude higher than those of conventional ones for molecules in various media. Our findings will offer new opportunities for sensing applications of plasmonic nanocavities and have huge impacts on cavity plasmonics.

Novel nano-architectured carbon quantum dots (CQDs) with phosphorous acid tags as an efficient catalyst for the synthesis of multisubstituted 4H-pyran with indole moieties under mild conditions

In this work, a new nano-structured catalyst with phosphorus acid moieties, synthesized by the reaction of carbon quantum dots (CQDs) and phosphorus acid under refluxing EtOH. The structure and morphology of CQDs–N(CH₂PO₃H₂)₂ were fully characterized using various techniques such as Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG) analysis, fluorescence and X-ray diffraction (XRD) measurements. The new CQDs–N(CH₂PO₃H₂)₂ catalyst was successfully used for the synthesis of 2-amino-6-(2-methyl-1H-indol-3-yl)-4-phenyl-4H-pyran-3,5-dicarbonitriles by the one-pot reaction of various aromatic aldehydes, 3-(1H-indol-3-yl)-3-oxopropanenitrile derivatives and malononitrile in refluxing EtOH and/or ultrasonic irradiation conditions.

A new nano-structured catalyst with phosphorus acid moieties, synthesized by the reaction of carbon quantum dots (CQDs) and phosphorus acid under refluxing EtOH.

Optical-Cavity Manipulation of Conical Intersections and Singlet Fission in Pentacene Dimers

We demonstrate how the singlet fission process in pentacene dimers mediated by a conical intersection is controlled by coupling the molecule to a confined optical cavity photon mode. By following the polariton quantum dynamics of a conical intersection coupled to a cavity mode taking into account vibrational relaxation and cavity loss, we find that the singlet fission can be significantly suppressed because the polaritonic conical intersection is pushed away from the initial Franck-Condon excitation region.

Recent advances in plasmonic nanocavities for single-molecule spectroscopy

Plasmonic nanocavities are able to engineer and confine electromagnetic fields to subwavelength volumes. In the past decade, they have enabled a large set of applications, in particular for sensing, optical trapping, and the investigation of physical and chemical phenomena at a few or single-molecule levels. This extreme sensitivity is possible thanks to the highly confined local field intensity enhancement, which depends on the geometry of plasmonic nanocavities. Indeed, suitably designed structures providing engineered local optical fields lead to enhanced optical sensing based on different phenomena such as surface enhanced Raman scattering, fluorescence, and Förster resonance energy transfer. In this mini-review, we illustrate the most recent results on plasmonic nanocavities, with specific emphasis on the detection of single molecules.

Plasmon-Induced Trap State Emission from Single Quantum Dots

Charge carriers trapped at localized surface defects play a crucial role in quantum dot (QD) photophysics. Surface traps offer longer lifetimes than band-edge emission, expanding the potential of QDs as nanoscale light-emitting excitons and qubits. Here, we demonstrate that a nonradiative plasmon mode drives the transfer from two-photon-excited excitons to trap states. In plasmonic cavities, trap emission dominates while the band-edge recombination is completely suppressed. The induced pathways for excitonic recombination not only shed light on the fundamental interactions of excitonic spins, but also open new avenues in manipulating QD emission, for optoelectronics and nanophotonics applications.