Plasmon-exciton Coupling Research Articles

Tuning nanoscale plasmon-exciton coupling via chemical interface damping.

Understanding the exact role of each plasmon decay channel in the plasmon-exciton interaction is essential for realizing the translational potential of nanoscale plexciton hybrids. Here, using single-particle spectroscopy, we demonstrate how a particular decay channel, chemical interface damping (CID), influences the nanoscale plasmon-exciton coupling. We investigate the interaction between cyanine dye J-aggregates and gold nanorods in the presence and absence of CID. The CID effect is introduced via surface modification of the nanorods with 4-nitrothiophenol. The relative contribution of CID is systematically tuned by varying the diameter of the nanorods, while maintaining the aspect ratio constant. We show that the incorporation of the CID channel, in addition to other plasmon decay channels, reduces the plasmon-exciton coupling strength. Nanorods' diameter-dependency measurements reveal that in the absence of CID contribution, the plasmon mode-volume factor gradually dominates over the plasmon decoherence effects as the diameter of the nanorods decreases, resulting in an increase in the plasmon-exciton coupling strength. However, the situation is entirely different when the CID channel is active: plasmon dephasing determines the plasmon-exciton coupling strength by outweighing the influence of even a very small plasmon mode-volume. Most importantly, our findings indicate that CID can be used to controllably tune the plasmon-exciton coupling strength for a given plexciton system by modifying the nanoparticle's surface with suitable adsorbates without the need for altering either the plasmonic or excitonic systems. Thus, judicious exploitation of CID can be tremendously beneficial in tailoring the optical characteristics of plexciton hybrid systems to suit any targeted application.

Plexcitonics: plasmon-exciton coupling for enhancing spectroscopy, optical chirality, and nonlinearity.

Plexcitonics is a rapidly developing interdisciplinary field that holds immense potential for the creation of innovative optical technologies and devices. This field focuses on investigating the interactions between plasmons and excitons in hybrid systems. In this review, we provide an overview of the fundamental principles of plasmonics and plexcitonics and discuss the latest advancements in plexcitonics. Specifically, we highlight the ability to manipulate plasmon-exciton interactions, the emerging field of tip-enhanced spectroscopy, and advancements in optical chirality and nonlinearity. These recent developments have spurred further research in the field of plexcitonics and offer inspiration for the design of advanced materials and devices with enhanced optical properties and functionalities.

Plasmon-exciton couplings in the MoS2/AuNP plasmonic hybrid structure

The understanding and engineering of the plasmon-exciton coupling are necessary to control the innovative optoelectronic device platform. In this study, we investigated the intertwined mechanism of each plasmon-exciton couplings in monolayer molybdenum disulfide (MoS2) and plasmonic hybrid structure. The results of absorption, simulation, electrostatics, and emission spectra show that interaction between photoexcited carrier and exciton modes are successfully coupled by energy transfer and exciton recombination processes. Especially, neutral exciton, trion, and biexciton can be selectively enhanced by designing the plasmonic hybrid platform. All of these results imply that there is another degree of freedom to control the individual enhancement of each exciton mode in the development of nano optoelectronic devices.

Plasmon-Exciton Interaction in Perspective Hetero-Systems

Surface plasmons and excitons have been widely studied experimentally and theoretically for various material systems. However, a number of aspects require further deeper study and understanding, among which the connection of these quasi-particles occupies an important place. New physical effects arise when plasmons and excitons in nanostructures begin to be localized at certain small distances, as a result, we can talk about their coupling. Complex systems containing the excitation of plasmons and excitons, as well as their coupling, show interesting optical properties that they cannot exhibit individually. In this type of system, the plasmon enhances the coupling between the system and the external field, and the exciton controls certain spectral properties, which opens up new possibilities for tuning their optical response. The transferred energy between plasmons and excitons becomes an important factor affecting their interaction when the resonance frequency of the localized plasmon is very close to the molecular energy transition frequency. Two types of coupling can occur depending on the ratio between the strength of the coupling and the energy losses of individual components in the system, namely strong and weak. In addition to the mutual coupling between the plasmon and the exciton, their different linewidths and ability to couple to an external field provide a variety of means to tune the optical properties of hybrid systems. Thus, it enables precise control of light at the nanometer scale, opening up possibilities for new electronics and photonics applications. In this review, we highlight the features of weak and strong modes of plasmon-exciton coupling, modern trends, and perspectives in the study of hetero-systems semiconductor–metal, metal–2D material, semiconductor–molecule, etc. Semiconductor-metal hybrid nanostructures open up exciting opportunities for the study of quantum phenomena, optical processes, and multiparticle interactions and confidently lead to application in new photonics devices.

Engineering Water Stable Perovskite and Plasmonic‐Perovskite Nanocomposites: A Step toward Unleashing the True Potential of Perovskite Catalysis

AbstractDespite garnering so much research interest, the potential technological developments of perovskites are limited due to the instability of perovskites in polar solvents. Here, it is discovered that upon exposure to ethanol, the initial cubic cesium lead bromide nanocrystals (CsPbBr3 NCs) undergo a phase transformation from the cubic phase to the orthorhombic phase. Further exposure of the orthorhombic phase to water leads to the formation of CsPbBr3 perovskite nanoaggregates, which shows higher stability in water compared to pristine CsPbBr3 NCs. A systematic investigation of the interfaces using various spectroscopic techniques demonstrating the self‐assembly process and phase transformation is presented. The increased stability of ethanol‐treated CsPbBr3 NCs is attributed to the ethoxide ions adsorption on the CsPbBr3 interface, owing to strong affinity of alkoxide ions to Pb2+. Effective surface passivation leads to enhanced charge‐carrier separation, a prerequisite to an effective photocatalyst. Ethoxide‐stabilized CsPbBr3 in water is utilized to reduce Au3+ to Au0 to synthesize water‐stable Au‐CsPbBr3 nanocomposites. The formation of hybrid plasmonic metal‐perovskites nanocomposite influences the perovskite's excited state charge carrier dynamics. This opens the possibilities of utilizing the synergistic effects of the light‐harvesting properties of plasmonic nanomaterials with the catalytic attributes of perovskite materials and controlling the interface properties by tuning plasmon–exciton coupling.

Enhanced amplified spontaneous emission of CsPbBr3 quantum dots via gold nanorods-induced localized surface plasmon resonance

Incorporating metallic nanostructures into a cesium lead halide [CsPbX3 (X = Cl, Br, I)] perovskite system has attracted considerable attention for improving the performance of amplified spontaneous emission (ASE) and lasing. However, the ASE/lasing threshold is normally quite high since the photophysical properties of pristine CsPbX3 quantum dots (QDs) are limited and the traditionally utilized metal nanoparticles suffer from a weak localized surface plasmon resonance within a narrow spectral range. Herein, a configuration of a silica coated CsPbBr3 QDs (CsPbBr3@SiO2 QDs) film incorporated with the deposition of gold nanorods (AuNRs) underneath has been proposed for high-performance ASE. In this configuration, SiO2 coating not only serves as an insulation layer to avoid the large Ohmic loss between CsPbBr3 and Au but also contributes to improved photoluminescence quantum yield and stability against water, heat, and ultraviolet light compared to the counterparts of pristine CsPbBr3 QDs. As a result, the fabricated CsPbBr3@SiO2-AuNRs hybrid film yields a low-threshold ASE (23.6 μJ/cm2) with excellent photostability owing to efficient exciton–plasmon coupling effect, which is only 23% of the pristine CsPbBr3 QDs film (102 μJ/cm2). The demonstration of metallic NRs coupled perovskite QDs not only provides a strategy for realizing strong light–matter interactions but also paves the way for improving the performance of perovskite-based optoelectronic devices.

Plasmon–exciton coupling in a dimer cavity revisited: effect of excitonic dipole orientation

We revisit plasmon–exciton coupling of a single emitter in a dimer cavity, featuring the analysis of how the excitonic dipole orientation influences the coupling behaviour from both the spectral and temporal aspects. Results demonstrate that the dipolar mode could be suppressed to vanish while the magnitude of the pseudomode could only be suppressed to half of the maximum value. The temporal analysis gives further evidence of this effect on the dipolar mode and pseudomode. The analysis might have potential significance on the experimental community as the excitonic dipole orientation could be precisely measured and has a rather important impact on the experiments.

Polarized Photoluminescence Enhancement of Monolayer MoS2 Coupled with Plasmonic Salisbury‐Type Absorber (Laser Photonics Rev. 16(10)/2022)

Photoluminescence Enhancement In article number 2200008, Wei Li, Ming Xin, Baoli Liu, and colleagues employ the metal-insulator-metal (MIM) Salisbury-type perfect absorber with a symmetry-breaking metallic metasurface to construct an exciton–plasmon coupling system. Fully utilizing the unique property of maximum in-plane electric field of the Salisbury-type absorber in a designed direction, large photoluminescence enhancement and the high degree of linear polarization of photoluminescence independent of the excitation polarization are achieved in monolayer MoS2.

Optical Introduction and Manipulation of Plasmon–Exciton–Trion Coupling in a Si/WS2/Au Nanocavity

Strong plasmon-exciton coupling, which has potential applications in nanophotonics, plasmonics, and quantum electrodynamics, has been successfully demonstrated by using metallic nanocavities and two-dimensional materials. Dynamical control of plasmon-exciton coupling strength, especially by using optical methods, remains a big challenge although it is highly desirable. Here, we report the optical introduction and manipulation of plasmon-exciton-trion coupling realized in a dielectric-metal hybrid nanocavity, which is composed of a silicon (Si) nanoparticle and a thin gold (Au) film, with an embedded tungsten disulfide (WS2) monolayer. We employ scattering and photoluminescence spectra to characterize the coupling strength between plasmons and excitons in Si/WS2/Au nanocavities constructed by using Si nanoparticles with different diameters. We enhance the plasmon-exciton and plasmon-trion coupling strength by injecting excitons and trions into the WS2 monolayer with a 488 nm laser beam. It is revealed that the emission intensities of excitons and trions with respect to the reference WS2 monolayer can be modified through the change in the coupling strength induced by the laser light. Interestingly, the coupling strength between the plasmons and the excitons/trions can be manipulated from weak to strong coupling regime by simply increasing the laser power, which is clearly resolved in the scattering spectra of Si/WS2/Au nanocavities. More importantly, the plasmon-exciton-trion coupling induced by the laser light is confirmed by the energy exchange between excitons and trions. Our findings indicate the possibility for optically manipulating plasmon-exciton interaction and suggest the practical applications of dielectric-metal hybrid nanocavities in nanoscale plasmonic devices.

Enhancing Raman spectra by coupling plasmons and excitons for large area MoS2 monolayers

Surface-enhanced Raman spectroscopy (SERS) has been applied to analyze 2D materials with plasmonic enhancement at hotspots, localized at gaps or junctions. However, the SERS technique strongly demands hotspots at excitation laser wavelengths to achieve energy confinement at the excitation wavelength. In this study, we report the enhancement of Raman signals by the plasmon-exciton coupling between large-area monolayer MoS2 and plasmonic nanogrooves (NGs). The plasmon-exciton coupling enhances Raman signal instead of SERS enhancement at an excitation wavelength. In addition, spectrally tunable plasmonic NGs are utilized to investigate coupled and de-coupled enhancements. The enhancement performance is further examined through electromagnetic field enhancement. We demonstrate that the proposed nanostructures integrated with atomically thin 2D materials, showing highly uniform Raman signals, are applicable for broad applications in materials science and nanophotonic.

Plexciton modes guided by an exciton slab in a columnar thin film

In this study, we reported the plasmon-exciton coupling for excitation of the surface plexciton wave in columnar thin film with a central exciton slab using the transfer matrix method in Turbadar–Kretschmann–Raether configuration. The optical absorptance spectra for surface plasmon polariton, surface exciton and surface plexciton was investigated at different structural parameters in proposed structure. The characteristics of surface optical modes were analyzed and there was an anticrossing behavior between polariton branches of plexciton spectra. Localization of surface modes on interfaces and hybridization between plasmons and excitons at both interfaces of exciton slab were proved by the time-averaged Poynting vector. We found that the types of coupling regimes between plasmons and excitons from weak to strong could be achieved. We obtained a high Rabi splitting energy 840 meV corresponding to the time period 5 fs which indicates to the fast energy transfer between surface plasmon polaritons and surface excitons.

Ultrafast resonant exciton-plasmon coupling for enhanced emission in lead halide perovskite with metallic Ag nanostructures.

Integrating metal halide perovskites onto plasmonic nanostructures has recently become a trending method of enabling superior emissive performance of perovskite nanophotonic devices. In this work, we present an in-depth study on the spontaneous emission properties of hybrid systems comprising CsPbBr3 nanocrystals and silver nanostructures. Specifically, a 5.7-fold increment of the photoluminescence (PL) intensity and a 1.65-fold enhancement of the PL relaxation rate is attained when the transition energy of CsPbBr3 is spectrally resonant with the oscillational frequency of Ag nanodisks (NDs), which is attributed to the intense exciton-plasmon coupling-induced Purcell effect. Furthermore, a 540-fs ultrafast energy transfer from the CsPbBr3 excitons to Ag plasmons is revealed by femtosecond pump-probe experiments, suggesting the key mechanism responsible for the Purcell-enhanced radiative emission. Our finding offers a unique understanding of the enhanced emissive behavior in the plasmon-coupled perovskite system and paves the way for further applications.

Strong Linearly Polarized Emission from Monolayer WS2 Coupled with Plasmonic Nanocavity Array

AbstractAs an indispensable component of optoelectronic system, an on‐chip light source with well‐defined polarization is desirable in optical communication, signal processing and display applications. The emerging atomically thin transition metal dichalcogenides (TMDCs), due to their high quantum yield and robust valley coherence, provide an unprecedented platform to realize the high‐efficient linearly polarized light emission. Although the valley‐related optical selection rules suggest that valley coherence should be possible, extreme conditions such as cryogenic temperatures are required, which is a long‐term challenge for their practical applications. In this paper, the strongly enhanced linearly polarized emission is realized by integrating WS2 monolayers with a delicate designed plasmonic nanocavity. It is demonstrated that strong plasmon–exciton coupling gives rise to the plasmon–exciton polariton. The polariton valley coherence results in a linear polarization up to 0.32 at room temperature and contributes to 52% of the total linear polarization. Enhancement of linear polarization through polariton valley coherence can be understood as the consequence of the extra relaxation channel introduced by its plasmonic counterpart. The potential of 2D TMDC‐plasmon hybrid structure appears to be high and of significant technological interest, as well as inspires new perspectives on quantum manipulations in 2D solid‐state systems.

Strong coupling with directional scattering features of metal nanoshells with monolayer WS2 heterostructures

Realizing and manipulating strong light–matter coupling in 2D monolayer semiconductors are of the utmost importance in the development of photonic devices. Hollow nanostructures of noble metals are particularly interesting because of their stronger local electromagnetic field compared with solid nanoparticles, which facilitate the strong coupling of single metal nanostructures. Here, the tunable single nanocavity plasmon–exciton coupling was demonstrated at room temperature in hybrid systems consisting of Ag@Au hollow nanocubes (HNCs) and monolayer WS2 underneath, where a large vacuum Rabi splitting of 131.3 meV was observed. Mode splitting can be clearly observed from the dark-field scattering spectrum of the single hybrid nanocavity, which is ascribed to the strong coupling between the nanocavity mode and the excitonic mode. Then, we used the finite difference time domain method to simulate these hybrid systems. By changing the thickness of the shell of the Ag@Au HNC, we can tune the surface plasmon resonance peak position of HNCs to match the exciton energy of the monolayer WS2. The strong couplings were realized via the calculated scattering spectra. The calculated results were consistent with the experimental results. Furthermore, the mode volume of different nanostructures was discussed, and the mode volume of HNCs is smaller than other solid ones at the same plasmonic resonance wavelength, which also indicates that its ability to restrict an electromagnetic field is stronger. This study provides an ideal platform for the strong coupling of a single nanocavity at room temperature and has broad application prospects in the field of single-photon devices.

Relevance of Rabi splitting effect for tunable enhancement of Raman scattering in self-assembled silver – Fullerene nanocomposite films

We report on detection of plasmon-enhanced Raman scattering (PERS) in self-assembled AgxC60 nanocomposite films and on evolution of this effect with increase of the Ag concentration, x, in the interval of 2<x < 25. Optical absorption spectra show that origin of the PERS effect is closely related with dipolar plasmonic mode generated by uniform 3D-ensemble of Ag nanoparticles, which arise in the C60-based matrix during the film deposition. Careful analysis of the absorption spectra designates features of strong coupling between dipolar plasmon mode and the C60 low-energy exciton suggesting energy exchange between the arisen high- and low-energy polaritonic states. Evaluation of dispersion spectra of the polaritons revealed anti-crossing effect as a sign of the strong plasmon-exciton coupling with Rabi splitting energy of about 300 meV. In frames of the recently-reported quantum-electrodynamics model, the detected PERS effect was ascribed to abundant population of the low-energy polaritonic states caused by asymmetric transitions between the low- and high-energy polaritons. The obtained PERS-spectra display sensitivity of the C60 vibrational modes to the x-driven plasmonic field strength, which demonstrates some reduction at higher x due to charge transfer through C60 molecular junctions. The evident tunability of PERS suggests an emerging potential of the self-assembled AgxC60 films for their application in molecular electronics and molecular photochemistry.

Interfacial engineering of plasmonic nanoparticle metasurfaces

SignificanceMolecules interacting with metallic nanostructures can show tunable exciton-plasmon coupling, ranging from weak to strong. One factor that influences the interactions is the spatial organization of the molecules relative to the localized plasmon-enhanced electromagnetic fields. In this work, we show that the arrangement of aromatic dye molecules can be tuned within plasmonic hotspots by interfacial engineering of nanoparticle surfaces. By controlling the local chemical and physical interactions, we could modulate lasing thresholds. Surface-functionalized plasmonic metasurfaces open prospects for programmable light-matter interactions at the nanoscale.

Observation of in-plane exciton–polaritons in monolayer WSe2 driven by plasmonic nanofingers

Abstract The transition metal dichalcogenides (TMDs) have drawn great research attention, motivated by the derived remarkable optoelectronic properties and the potentials for high-efficient excitonic devices. The plasmonic nanocavity, integrating deep-sub wavelength confinement of optical mode with dramatic localized field enhancement, provides a practical platform to manipulate light–matter interaction. In order to obtain strong exciton–plasmon coupling effects, it’s crucial to match the vibration direction of exciton to the available strong localized in-plane electric field. Herein, we demonstrate the coupling effect of in-plane exciton in monolayer tungsten diselenide (WSe2) to deterministic gap-plasmon field which is produced by nanometrically gapped collapsed nanofingers. The gap-plasmon field which is completely parallel to the in-plane excitons in WSe2 will drive a strong exciton–plasmon coupling at room temperature. More interestingly, it is experimentally observed that the luminescence of exciton–polariton cannot be influenced by the temperature in the range from 77 K to 300 K due to the presence of nanofingers. According to the theoretical analysis results, we attribute this finding to the dielectric screening effect arising from the extremely strong localized electric field of plasmonic nanofingers. This work proposes a feasible way to harness and manipulate the exciton of low-dimensional semiconductor, which might be potential for quantum optoelectronics.

Unified Scattering and Photoluminescence Spectra for Strong Plasmon-Exciton Coupling.

The strong coupling between excitons and single plasmonic nanocavities enables plexcitonic states in nanoscale systems at room temperature. Here we demonstrate the strong coupling of surface plasmon modes of metal nanowires and excitons in monolayer semiconductors, with Rabi splitting manifested in both scattering and photoluminescence (PL) spectra. By utilizing the propagation properties of surface plasmons on the nanowires, the PL emitted through the scattering of plasmon-exciton hybrid modes is extracted. The analytically calculated scattering and PL spectra well reproduce the experimental results. These findings unify the scattering and PL spectra in the plexcitonic system and eliminate the ambiguities of PL emission, shedding new light on understanding the rich spectral phenomena in the plasmon-exciton strong coupling regime.

State-selective exciton–plasmon interplay in a hybrid WSe2/CuFeS2 nanosystem

The integration of confined exciton and localized surface plasmon in a hybrid nanostructure has recently stimulated extensive interests. The mechanistic insights into the elusive exciton–plasmon interplay at the nanoscale are of both fundamental and applicable values. Herein, by taking a hybrid WSe2/CuFeS2 system as a prototype, in which the excitonic semiconductor WSe2 nanosheets are interfaced with the plasmonic semiconductor CuFeS2 nanocrystals to form a heterostructure, we design and perform an ultrafast dynamics study to glean information in this regard. Specifically, the band-alignment relationship between the two components enables the contrasting case studies in which the excitonic excited states of WSe2 are pre-selected to be on-/off-resonant with the plasmon band of CuFeS2. As revealed by the joint observations from steady-state absorption and photoexcitation-dependent/temperature-dependent femtosecond time-resolved transient absorption (fs-TA) spectroscopy, an effective energy transfer process occurs in this exciton–plasmon system where the energy donor (acceptor) is the excitonic WSe2 (plasmonic CuFeS2) and its efficiency is modulated by the exciton–plasmon coupling strength. Furthermore, as inferred from the temperature-dependent fs-TA analysis, the opening of such an energy-transfer channel turns out to take place during the early phase of plasmon decay (∼1 ps). In addition, the activation energy of energy transfer for a specific exciton-state-selected case is estimated (∼200 meV). This work provides a dynamics perspective to the plasmon semiconductor-involved exciton–plasmon interplay that features excited-state selectivity of exciton band and, hence, would be of guiding value for rational design and optimization of relevant applications based on exciton–plasmon manipulation.

Local Plasmon Phase Delay Effect in Plasmon–Exciton Coupling

AbstractManipulating plasmon–exciton coupling is a pivotal desire for many potential applications. Here, it is found that the plasmonic phase delay can modulate the interference‐induced asymmetrical spectrum line shape of the plasmon–exciton coupling system considerably. The phase effect in a hybrid system consisting of monolayer WSe2 and an individual gold nanorod is demonstrated. The phase delay can modulate the relative intensities of the coupling modes but not the splitting energy, effective in both weak and strong coupling regimes. There is an excellent agreement between the numerical calculations and the experimental results. The findings reveal that the local phase delay can act as an effective way to manipulate plasmon−exciton coupling properties at the nanoscale.