We demonstrate the strong coupling of direct transition excitons in tungsten disulfide (WS2) with collective plasmonic resonances at room temperature. We use open plasmonic cavities formed by periodic arrays of metallic nanoparticles. We show clear anticrossings with monolayer, bilayer and thicker multilayer WS2 on top of the nanoparticle array.The Rabi energy of such hybrid system varies from 50 to 110 meV from monolayer to sixteen layers, while it does not scale with the square root of the number of layers as expected for collective strong coupling. We prove that out-of-plane coupling components can be disregarded since the normal field is screened due to the high refractive index contrast of the dielectric layers. Even though the in-plane dipole moments of the excitons decrease beyond monolayers, the strong in-plane field distributed in the flake can still enhance the coupling strength with multilayers. However, the screened out-of-plane field leads to the saturation of the Rabi energy.The achieved coherent coupling of TMD multilayers with open cavities could be exploited for

Key in the application of plasmonics is the realization of low loss or high quality (Q) factor resonances. Nanoparticle arrays are systems capable of sustaining remarkably high Q‐factor resonances through the hybridization of plasmonic and photonic modes, known as surface lattice resonances (SLRs). SLRs result from the coupling of localized surface plasmon resonances (LSPRs) to in‐plane orders of diffraction known as Rayleigh anomalies (RAs). To date, the highest Q‐factors have been achieved with the (±1, 0) diffraction orders. However, these Q‐factors are highly sensitive to the angle of excitation. Here, a strategy is presented to generate high Q‐factor SLRs with low dispersion by coupling LSPRs to the (0, ±1) diffraction orders. 2D arrays of silver nanoparticles are investigated experimentally and numerically, and it is shown that the Q‐factor of SLRs critically depends on the quality of the metal film, the detuning between RAs and LSPRs, and the absorption of adhesive layer used between the substrate and the metallic nanoparticles. These silver nanoparticle arrays can achieve Q‐factors higher than 330 in the visible range. These extraordinarily high Q‐factors could be increased to values above 1500 if no adhesive layer is used, which could significantly improve sensors and enhance nonlinearities in plasmonic systems.

An enhanced delayed fluorescence is demonstrated experimentally in tetracene single crystals strongly coupled to optical modes in open cavities formed by arrays of plasmonic nanoparticles. Hybridization of singlet excitons with collective plasmonic resonances in the arrays leads to the splitting of the material dispersion into a lower and an upper polariton band. This splitting significantly modifies the dynamics of the photoexcited tetracene crystal, resulting in an increase of the delayed fluorescence by a factor of 4. The enhanced delayed fluorescence is attributed to the emergence of an additional radiative decay channel, where the lower polariton band harvests long-lived triplet states. There is also an increase in total emission, which is wavelength dependent, and can be explained by the direct emission from the lower polariton band, the more efficient light out-coupling, and the enhancement of the excitation intensity. The observed enhanced fluorescence opens the possibility of efficient radiative triplet harvesting in open optical cavities, to improve the performance of organic light emitting diodes. and organic photovoltaics (OPV). The performance of these devices is determined by properties such as absorption and emission cross-section, chemical reactivity, and excited state dynamics, arising from the potential energy surface of the molecules. [1,2] Hence, controlling the energy surface can provide a remarkable impact on photophysical processes involved in these devices. Tuning of the properties of organic materials is usually done through chemical synthesis. However, changing the molecular composition might also affect the processability and morphology of thin films fabricated from the molecules, which may be detrimental for the performance.Recently, an alternative method has emerged to modify the energy surfaces of molecules and to alter their properties without changing the molecular composition: strong light-matter coupling. Theoretical developments continue to uncover the physics underpinning changes to the potential energy surfaces of molecules in this regime, [3][4][5] with tremendous implications for the photophysical properties of organic materials. Strong coupling between photons in optical cavities and excitons in semiconductors results in hybrid quasi-particles called exciton-polaritons. The strong coupling leads to an avoided crossing between the dispersions of cavity photons and excitons at the energy and momentum at which they would overlap. This coupling leads to the splitting in energy of the dispersion into the lower polariton band (LPB) and the upper polariton band (UPB). The width of the splitting between these bands is determined by the coupling strength and is called the Rabi energy. The properties of these hybrid quasi-particles are a combination of the properties of the two uncoupled states (bare states). [6] This remarkable consequence of strong coupling has led to the possibility of tuning the properties of materials, such as exciton transport, [7][8][9][10] conductivity, [11] ...

The advent of metamaterials more than 15 years ago has offered extraordinary new ways of manipulating electromagnetic waves. Yet, progress in this field has been unequal across the electromagnetic spectrum, especially when it comes to finding applications for such artificial media. Optical metamaterials, in particular, are less compatible with active functionalities than their counterparts developed at lower frequencies. One crucial roadblock in the path to devices is the fact that active optical metamaterials are so far controlled by light rather than electricity, preventing them from being integrated in larger electronic systems. Here we introduce electroluminescent metamaterials based on metal nano-inclusions hybridized with colloidal quantum dots. We show that each of these miniature blocks can be individually tuned to exhibit independent optoelectronic properties (both in terms of electrical characteristics, polarization, colour and brightness), illustrate their capabilities by weaving complex light-emitting surfaces and finally discuss their potential for displays and sensors.