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Novel optical sources require fast decay rates, making hyperbolic metamaterials (HMMs) an increasingly attractive option. HMMs are well‐known for their remarkable anisotropy, and leverage hyperbolic dispersion to enhance the decay rate of a fluorophore placed on top of them. This study tackles the complex task of embedding a fluorophore into an HMM, successfully overcoming challenges related to surface roughness, thickness imperfections, and layer washing effects. Specifically, CsPbBr3 perovskite nanocrystals (NCs)‐based HMM are fabricated, by alternating silver/nanocrystals (Ag/NCs) layers. Through a systematic investigation of the photophysical response following the deposition of each bilayer, compelling evidence of the achievement of hyperbolic dispersion is provided. Specifically, the impact of “high‐k” modes is isolated, which is distinctive to the HMM architecture. Therefore, the longstanding debate regarding the number of bilayers needed to achieve hyperbolic dispersion is conclusively resolved. The research demonstrates a nearly twofold increase in the decay rate and a threefold enhancement in photoluminescence intensity. These findings are further supported by theoretical Purcell factor calculations. This study marks a pioneering advancement in the field of bulk dye‐embedded HMMs, laying the groundwork for the development of advanced optical sources such as “resonant gain HMMs”. [ABSTRACT FROM AUTHOR]

Bio‐inspired and biodegradable quantum optics scenarios constitute a pathway toward environmentally friendly front‐end technologies. Such an inspiring perspective necessitates the replacement of classic gain materials with a biological counterpart like photoluminescent bacteria. It is easy to imagine that, in this case, a planar and cell‐viable substitute of classic bulk solid‐states resonators can be highly beneficial. In this paper a micro‐ and nano‐photonic structuration of both a standard and a functionalized version of a typical bacterial growth medium (Luria‐Bertani Agar – LBA) is successfully realized. Three structures belonging to the categories of photonic crystals are replicated, such as quasi‐crystals and meta‐surfaces, demonstrating how the proposed media can be used as templates for high‐end photonic applications. The optical quality of the replicated structures is confirmed by far‐field diffraction measurements. The structured growth media allow for a broad control of the surface wettability by accessing a so‐called Wenzel state, in which the original hydrophilicity of a material is increased due to the photonic structuration. Finally, the suitability of the nano‐structured LBA as a plasmonic platform is evidenced. The proposed micro‐and nano‐structured photonic growth media constitute the first, fundamental step toward quantum optical frameworks from biological media. [ABSTRACT FROM AUTHOR]

The strong coupling of optical resonators results in a mode splitting proportional to the coupling strength, which can be achieved with metal‐dielectric‐metal (MDM) cavities that have similar thickness and refractive index. However, an active control of the mode coupling is challenging. Here, an alternative configuration of an MDM cavity coupled with a Guided‐Mode‐Resonator (GMR) is explored. The GMR grating is fabricated on top of the MDM cavity, such that the coupling can be tuned by the thickness of the central metal. The typical modal anti‐crossing (with a splitting of ≈50–65 meV) detected in the angular dispersion of the GMR‐MDM is observed. Excellent agreement of the experimental reflectance with simulations allows to report the angular dispersion from −50° to 50°. The anisotropy of the GMR modes enables to switch in and out of the strong coupling by changing the polarization of the incident light. Moreover, the asymmetry of the GMR‐MDM architecture induces a side‐dependent response. The MDM cavity is only transparent at its resonances, which leads to a suppression of all modes outside the resonance bands when impinging from the MDM side. These features are highly interesting for optoelectronic applications such as optical switches and multi‐level optical multiplexing. [ABSTRACT FROM AUTHOR]

Strong light–matter interaction is usually achieved by embedding a gain medium in a high‐quality (Q)‐factor cavity made with thick external mirrors. The high reflectivity of the mirrors poses, therefore, a trade‐off between pump radiation coupling efficiency and high Q‐factor, thus preventing the use of optical cavities in photonic contexts where the photosensitive element necessitates to be readily accessible. Here, this long‐standing problem is overcome by engineering "Pseudo‐Cavity Modes" (PCM) in a Metal/Dielectric Open Cavity (MDOC) system that has been commonly thought to be incapable to show resonances. The MDOC system lets the embedded fluorophore exposed to radiation, opening to strong light/matter interaction. To prove this: i) exciton/PCM strong coupling regime, with 160 meV Rabi splitting, ii) photoluminescence enhancement by more than 7 times, and iii) polarized and angle‐dependent spontaneous emission are experimentally and theoretically demonstrated. The proposed system holds great potential envisioning scenarios like cavity‐enhanced photovoltaics, surface‐enhanced Raman scattering, open‐cavity lasers, photoluminescence steering and polarization. [ABSTRACT FROM AUTHOR]

Abstract: The quest for unconventional optical materials finds natural answers in the field of plasmonics. Here, special composites can manifest singularities in their dielectric permittivity. The so‐called epsilon‐near‐zero (εNZ) condition is typically encountered in artificial materials called hyperbolic metamaterials (HMMs). Unfortunately, tuning the HMMs εNZ is still challenging. Here it is demonstrated how the εNZ frequency of an HMM can be reversibly tuned via thermally induced water absorption/desorption. The key element is a dielectric hygroscopic material, consisting of a blend of a polymer, a sol–gel unsintered TiO2, and an organic dye. Due to the hygroscopic nature of unsintered TiO2, an increase of temperature induces a reversible physical contraction of the thickness of the dielectric blend, as well as an increase of refractive index. This causes a remarkable 45 nm shift of the absorption peak of the embedded dye, acting as a chromatic label. When such a blend is embedded in an HMM, a reversible thermal tuning of the overall optical response, as well as an epsilon‐near‐zero wavelength shift by about 25 nm, is induced. The remarkable tuning range shown here, besides obvious HMM‐based temperature sensing applications, paves the way toward a plethora of new functions in which tunable εNZ materials are needed. [ABSTRACT FROM AUTHOR]

Directing and polarizing the emission of a fluorophore is of fundamental importance in the perspective of novel photonic sources based on emerging nanoemitter technologies. These two tasks are usually accomplished by a sophisticated and demanding structuring of the optical environment in which the emitter is immersed, or by nontrivial chemical engineering of its geometry and/or band structure. Here, the wavelength and polarization selective spontaneous emission from a dye‐embedded in a metal/insulator/metal (d‐MIM) nanocavity is demonstrated. A push–pull chromophore with large Stokes shift is embedded in a MIM cavity whose resonances are tuned with the spectral emission band of the chromophore. Angular and polarization resolved spectroscopy experiments reveal that the radiated field is reshaped according to the angular dispersion of the nanocavity, and that its spectrum manifests two bands with different polarization corresponding to the p‐ and s‐polarized resonances of the cavity. The d‐MIM cavities are a highly versatile system for polarization and wavelength division multiplexing applications at the nanoscale, as well as for near‐field focused emission and nanolenses. [ABSTRACT FROM AUTHOR]

Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal structure of their shell. Here, the growth protocol for CdS branched nanocrystals is applied on CdSe nanoplatelet seeds and bone‐shaped heterostructures are obtained with a highly anisotropic shell. Surprisingly, the nanoplatelets withstand the high growth temperature of 350 °C and structures with a CdSe nanoplatelet core that is overcoated by a shell of cubic CdS are obtained, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a band‐edge emission around 657 nm with a photoluminescence quantum yield of ≈42% in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. This work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered. [ABSTRACT FROM AUTHOR]