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Optical control is achieved on the excited state energy transfer between spatially separated donor and acceptor molecules, both coupled to the same optical mode of a cavity. The energy transfer occurs through the formed hybrid polaritons and can be switched on and off by means of ultraviolet and visible light. The control mechanism relies on a photochromic component used as donor, whose absorption and emission properties can be varied reversibly through light irradiation, whereas in-cavity hybridization with acceptors through polariton states enables a 6-fold enhancement of acceptor/donor contribution to the emission intensity with respect to a reference multilayer. These results pave the way for synthesizing effective gating systems for the transport of energy by light, relevant for light-harvesting and light-emitting devices, and for photovoltaic cells., Comment: 54 pages, 41 Figures, Nanophotonics 2024

Photonic components responsive to external optical stimuli are attracting increasing interest, because their properties can be manipulated by light with fast switching times, high spatial definition, and potentially remote control. These aspects can be further enhanced by novel architectures, which have been recently enabled by the availability of 3D printing and additive manufacturing technologies. However, current methods are still limited to passive optical materials, whereas photo-responsive materials would require the development of 3D printing techniques able to preserve the optical properties of photoactive compounds and to achieve high spatial resolution to precisely control the propagation of light. Also, optical losses in 3D printed materials are an issue to be addressed. Here we report on advanced additive manufacturing technologies, specifically designed to embed photo-responsive compounds in 3D optical devices. The properties of 3D printed devices can be controlled by external UV and visible light beams, with characteristic switching times in the range 1-10 s., Comment: 7 pages, 3 Figures

3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials., Comment: 8 pages, 3 figures

We report on a comprehensive study of the unique adhesive properties of mats of polymethylmethacrylate (PMMA) nanofibers produced by electrospinning. Fibers are deposited on glass, varying the diameter and the relative orientation of the polymer filaments (random vs aligned configuration). While no significant variation is observed in the static contact angle (about 130{\deg}) of deposited water drops upon changing the average fiber diameter up to the micrometer scale, fibers are found to exhibit unequalled water adhesion. Placed vertically, they can hold up water drops as large as 60 microL, more than twice the values typically obtained with hairy surfaces prepared by different methods. For aligned fibers with anisotropic wetting behavior, the maximum volume measured in the direction perpendicular to the fibers goes up to 90 {\mu}L. This work suggests new routes to tailor the wetting behavior on extended areas by nanofiber coatings, with possible applications in adsorbing and catalytic surfaces, microfluidic devices, and filtration technologies., Comment: 17 pages, 5 figures, 2 tables

Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic assembly of fibers as well as their functional properties. Light-emitting or other active polymer nanofibers, made of conjugated polymers or of blends embedding chromophores or other functional dopants, are suitable for various applications in advanced photonics and sensing technologies. In particular, their almost one-dimensional geometry and finely tunable composition make them interesting materials for developing novel lasing devices. However, electrospinning techniques rely on a large variety of parameters and possible experimental geometries, and they need to be carefully optimized in order to obtain suitable topographical and photonic properties in the resulting nanostructures. Targeted features include smooth and uniform fiber surface, dimensional control, as well as filament alignment, enhanced light emission, and stimulated emission. We here present various optimization strategies for electrospinning methods which have been implemented and developed by us for the realization of lasing architectures based on polymer nanofibers. The geometry of the resulting nanowires leads to peculiar light-scattering from spun filaments, and to controllable lasing characteristics., Comment: Comments: 7 pages, 4 figures, 20 references. Invited contribution. Copyright (2016) Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a wide variety of fields, including optoelectronics, photonics, energy harvesting, nanoelectronics, and microelectromechanical systems. Realizing nanocomposite nanofibers is especially interesting in this respect. In particular, methods suitable for embedding inorganic nanocrystals in electrified jets and then in active fiber systems allow for controlling light-scattering and refractive index properties in the realized fibrous materials. We here report on the design, realization, and morphological and spectroscopic characterization of new species of active, composite nanowires and nanofibers for nanophotonics. We focus on the properties of light-confinement and photon transport along the nanowire longitudinal axis, and on how these depend on nanoparticle incorporation. Optical losses mechanisms and their influence on device design and performances are also presented and discussed., Comment: 7 pages, 3 figures, 29 references. Invited contribution. Copyright (2016) Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments., Comment: 29 pages, 9 figures, 1 Table