Origin of Exciton-Polariton Interactions and Decoupled Dark States Dynamics in 2D Hybrid Perovskite Quantum Wells.

The realization of efficient optical devices depends on the ability to harness strong nonlinearities, which are challenging to achieve with standard photonic systems. Exciton-polaritons formed in hybrid organic-inorganic perovskites offer a promising alternative, exhibiting strong interactions at room temperature (RT). Despite recent demonstrations showcasing a robust nonlinear response, further progress is hindered by an incomplete understanding of the microscopic mechanisms governing polariton interactions in perovskite-based strongly coupled systems. Here, we investigate the nonlinear properties of quasi-2D dodecylammonium lead iodide perovskite (n3-C12) crystals embedded in a planar microcavity. Polarization-resolved pump-probe measurements reveal the contribution of indirect exchange interactions assisted by dark states formation. Additionally, we identify a strong dependence of the unique spin-dependent interaction of polaritons on sample detuning. The results are pivotal for the advancement of polaritonics, and the tunability of the robust spin-dependent anisotropic interaction in n3-C12 perovskites makes this material a powerful choice for the realization of polaritonic circuits.

Strongly enhanced light-matter coupling of monolayer WS2 from a bound state in the continuum.

Exciton-polaritons derived from the strong light-matter interaction of an optical bound state in the continuum with an excitonic resonance can inherit an ultralong radiative lifetime and significant nonlinearities, but their realization in two-dimensional semiconductors remains challenging at room temperature. Here we show strong light-matter interaction enhancement and large exciton-polariton nonlinearities at room temperature by coupling monolayer tungsten disulfide excitons to a topologically protected bound state in the continuum moulded by a one-dimensional photonic crystal, and optimizing for the electric-field strength at the monolayer position through Bloch surface wave confinement. By a structured optimization approach, the coupling with the active material is maximized here in a fully open architecture, allowing to achieve a 100 meV photonic bandgap with the bound state in the continuum in a local energy minimum and a Rabi splitting of 70 meV, which results in very high cooperativity. Our architecture paves the way to a class of polariton devices based on topologically protected and highly interacting bound states in the continuum.

Colloidal Bismuth Chalcohalide Nanocrystals.

Here we present a colloidal approach to synthesize bismuth chalcohalide nanocrystals (BiEX NCs, in which E=S, Se and X=Cl, Br, I). Our method yields orthorhombic elongated BiEX NCs, with BiSCl crystallizing in a previously unknown polymorph. The BiEX NCs display a composition-dependent band gap spanning the visible spectral range and absorption coefficients exceeding 105  cm-1 . The BiEX NCs show chemical stability at standard laboratory conditions and form colloidal inks in different solvents. These features enable the solution processing of the NCs into robust solid films yielding stable photoelectrochemical current densities under solar-simulated irradiation. Overall, our versatile synthetic protocol may prove valuable in accessing colloidal metal chalcohalide nanomaterials at large and contributes to establish metal chalcohalides as a promising complement to metal chalcogenides and halides for applied nanotechnology.

Pseudocapacitive behaviour in sol-gel derived electrochromic titania nanostructures.

Nanostructured thin films are widely investigated for application in multifunctional devices thanks to their peculiar optoelectronic properties. In this work anatase TiO2 nanoparticles (average diameter 10 nm) synthesised by a green aqueous sol-gel route are exploited to fabricate optically active electrodes for pseudocapacitive-electrochromic devices. In our approach, highly transparent and homogeneous thin films having a good electronic coupling between nanoparticles are prepared. These electrodes present a spongy-like nanostructure in which the dimension of native nanoparticles is preserved, resulting in a huge surface area. Cyclic voltammetry studies reveal that there are significant contributions to the total stored charge from both intercalation capacitance and pseudocapacitance, with a remarkable 50% of the total charge deriving from this second effect. Fast and reversible colouration occurs, with an optical modulation of ∼60% in the range of 315-1660 nm, and a colouration efficiency of 25.1 cm2 C-1 at 550 nm. This combination of pseudocapacitance and electrochromism makes the sol-gel derived titania thin films promising candidates for multifunctional 'smart windows'.

Electrochromic evaluation of airbrushed water-dispersible W18O49nanorods obtained by microwave-assisted synthesis.

Motivated by the technological relevance of tungsten oxide nanostructures as valuable materials for energy saving technology, electrochemical and electrochromic characteristics of greener processed nanostructured W18O49-based electrodes are discussed in this work. For the purpose, microwave-assisted water-dispersible W18O49nanorods have been synthesized and processed into nanostructured electrodes. An airbrushing technique has been adopted as a cost-effective large-area scalable methodology to deposit the W18O49nanorods onto conductive glass. This approach preserves the morphological and crystallographic habit of native nanorods and allows highly homogeneous transparent coating where good electronic coupling between nanowires is ensured by a mild thermal treatment (250 °C, 30 min). Morphological and structural characteristics of active material were investigated from the synthesis to the nanocrystal deposition process by transmission and scanning electron microscopy, x-ray diffraction, atomic force microscopy and Raman spectroscopy. The as-obtained nanostructured film exhibited good reversible electrochemical features through several intercalation-deintercalation cycles. The electrochromic properties were evaluated on the basis of spectro-electrochemical measurements and showed significant optical contrast in the near-infrared region and high coloration efficiency at 550 nm.

Exploiting Photo- and Electroluminescence Properties of FIrpic Organic Crystals.

In this work, we investigate the optical and structural properties of the well-known triplet emitter bis(4',6'-difluorophenylpyridinato)-iridium(III) picolinate (FIrpic), showing that its ability to pack in two different ordered crystal structures promotes attractive photophysical properties that are useful for solid-state lighting applications. This approach allows the detrimental effects of the nonradiative pathways on the luminescence performance in highly concentrated organic active materials to be weakened. The remarkable electro-optical behavior of sky-blue phosphorescent organic light-emitting diodes incorporating crystal domains of FIrpic, dispersed into an appropriate matrix as an active layer, has also been reported as well as the X-ray diffraction, nuclear magnetic resonance, electro-ionization mass spectrometry, and scanning electron microscopy analyses of the crystalline samples. We consider this result as a crucial starting point for further research aimed at the use of a crystal triplet emitter in optoelectronic devices to overcome the long-standing issue of luminescence self-quenching.

Thermochromic Printable and Multicolor Polymeric Composite Based on Hybrid Organic-Inorganic Perovskite.

Hybrid organic-inorganic perovskites (PVKs) are among the most promising materials for optoelectronic applications thanks to their outstanding photophysical properties and easy synthesis. Herein, a new PVK-based thermochromic composite is demonstrated. It can reversibly switch from a transparent state (transmittance > 80%) at room temperature to a colored state (transmittance < 10%) at high temperature, with very fast kinetics, taking only a few seconds to go from the bleached to the colored state (and vice versa). X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calometry, rheological, and optical measurements carried out during heating/cooling cycles reveal that thermochromism in the material is based on a reversible process of PVK disassembly/assembly mediated by intercalating polymeric chains, through the formation and breaking of hydrogen bonds between polymer and perovskite. Therefore, differently from other thermochromic perovskites, that generally work with the adsorption/desorption of volatile molecules, the system is able to perform several heating/cooling cycles regardless of environmental conditions. The color and transition temperature (from 70 to 120 °C) can be tuned depending on the type of perovskite. Moreover, this thermochromic material is printable and can be deposited by cheap techniques, paving the way for a new class of smart coatings with an unprecedented range of colors.

Collagen Membrane as Water-Based Gel Electrolyte for Electrochromic Devices.

Bio-based polymers are attracting great interest due to their potential for several applications in place of conventional polymers. In the field of electrochemical devices, the electrolyte is a fundamental element that determines their performance, and polymers represent good candidates for developing solid-state and gel-based electrolytes toward the development of full-solid-state devices. In this context, the fabrication and characterization of uncrosslinked and physically cross-linked collagen membranes are reported to test their potential as a polymeric matrix for the development of a gel electrolyte. The evaluation of the membrane's stability in water and aqueous electrolyte and the mechanical characterization demonstrated that cross-linked samples showed a good compromise in terms of water absorption capability and resistance. The optical characteristics and the ionic conductivity of the cross-linked membrane, after overnight dipping in sulfuric acid solution, demonstrated the potential of the reported membrane as an electrolyte for electrochromic devices. As proof of concept, an electrochromic device was fabricated by sandwiching the membrane (after sulfuric acid dipping) between a glass/ITO/PEDOT:PSS substrate and a glass/ITO/SnO2 substrate. The results in terms of optical modulation and kinetic performance of such a device demonstrated that the reported cross-linked collagen membrane could represent a valid candidate as a water-based gel and bio-based electrolyte for full-solid-state electrochromic devices.

Enantioseparation of chiral phytocannabinoids in medicinal cannabis.

The evaluation of the chiral composition of phytocannabinoids in the cannabis plant is particularly important as the pharmacological effects of the (+) and (-) enantiomers of these compounds are completely different. Chromatographic attempts to assess the presence of the minor (+) enantiomers of the main phytocannabinoids, cannabidiolic acid (CBDA) and trans-Δ9-tetrahydrocannabinolic acid (trans-Δ9-THCA), were carried out on heated plant extracts for the determination of the corresponding decarboxylated species, cannabidiol (CBD) and trans-Δ9-tetrahydrocannabinol (trans-Δ9-THC), respectively. This process produces an altered phytocannabinoid composition with several new and unknown decomposition products. The present work reports for the first time the stereoselective synthesis of the pure (+) enantiomers of the main phytocannabinoids, trans-CBDA, trans-Δ9-THCA, trans-CBD and trans-Δ9-THC, and the development and optimization of an achiral-chiral liquid chromatography method coupled to UV and high-resolution mass spectrometry detection in reversed phase conditions (RP-HPLC-UV-HRMS) for the isolation of the single compounds and evaluation of their actual enantiomeric composition in plant. The isolation of the peaks with the achiral stationary phase ensured the absence of interferences that could potentially co-elute with the analytes of interest in the chiral analysis. The method applied to the Italian medicinal cannabis variety FM2 revealed no trace of the (+) enantiomers for all phytocannabinoids under investigation before and after decarboxylation, thus suggesting that the extraction procedure does not lead to an inversion of configuration.

Rydberg polaritons in ReS2 crystals.

Rhenium disulfide belongs to group VII transition metal dichalcogenides (TMDs) with attractive properties such as exceptionally high refractive index and remarkable oscillator strength, large in-plane birefringence, and good chemical stability. Unlike most other TMDs, the peculiar optical properties of rhenium disulfide persist from bulk to the monolayer, making this material potentially suitable for applications in optical devices. In this work, we demonstrate with unprecedented clarity the strong coupling between cavity modes and excited states, which results in a strong polariton interaction, showing the interest of these materials as a solid-state counterpart of Rydberg atomic systems. Moreover, we definitively clarify the nature of important spectral features, shedding light on some controversial aspects or incomplete interpretations and demonstrating that their origin is due to the interesting combination of the very high refractive index and the large oscillator strength expressed by these TMDs.

Light-Emitting Textiles: Device Architectures, Working Principles, and Applications.

E-textiles represent an emerging technology aiming toward the development of fabric with augmented functionalities, enabling the integration of displays, sensors, and other electronic components into textiles. Healthcare, protective clothing, fashion, and sports are a few examples application areas of e-textiles. Light-emitting textiles can have different applications: sensing, fashion, visual communication, light therapy, etc. Light emission can be integrated with textiles in different ways: fabricating light-emitting fibers and planar light-emitting textiles or employing side-emitting polymer optical fibers (POFs) coupled with light-emitting diodes (LEDs). Different kinds of technology have been investigated: alternating current electroluminescent devices (ACELs), inorganic and organic LEDs, and light-emitting electrochemical cells (LECs). The different device working principles and architectures are discussed in this review, highlighting the most relevant aspects and the possible approaches for their integration with textiles. Regarding POFs, the methodology to obtain side emissions and the critical aspects for their integration into textiles are discussed in this review. The main applications of light-emitting fabrics are illustrated, demonstrating that LEDs, alone or coupled with POFs, represent the most robust technology. On the other hand, OLEDs (Organic LEDs) are very promising for the future of light-emitting fabrics, but some issues still need to be addressed.

Tuning of the Berry curvature in 2D perovskite polaritons.

The engineering of the energy dispersion of polaritons in microcavities through nanofabrication or through the exploitation of intrinsic material and cavity anisotropies has demonstrated many intriguing effects related to topology and emergent gauge fields such as the anomalous quantum Hall and Rashba effects. Here we show how we can obtain different Berry curvature distributions of polariton bands in a strongly coupled organic-inorganic two-dimensional perovskite single-crystal microcavity. The spatial anisotropy of the perovskite crystal combined with photonic spin-orbit coupling produce two Hamilton diabolical points in the dispersion. An external magnetic field breaks time-reversal symmetry owing to the exciton Zeeman splitting and lifts the degeneracy of the diabolical points. As a result, the bands possess non-zero integral Berry curvatures, which we directly measure by state tomography. In addition to the determination of the different Berry curvatures of the multimode microcavity dispersions, we can also modify the Berry curvature distribution, the so-called band geometry, within each band by tuning external parameters, such as temperature, magnetic field and sample thickness.

Nanostructuring Iridium Complexes into Crystalline Phosphorescent Nanoparticles: Structural Characterization, Photophysics, and Biological Applications.

One of the key challenges in materials science is to control the properties of a material by directing its supramolecular arrangement. Here we show that iridium complexes, such as FIrpic, Ir-PPY, and Ir-MDQ, can be organized into crystalline and phosphorescent nanoparticles through the nanoprecipitation method, which allows thorough modification of their functional properties. Moreover, we found that it is possible to combine different iridium complexes into a single multicomponent nanostructure, thus creating nanoparticles whose photonic properties derive from the close spatial proximity of the electronic excited states of the different Ir complexes. The morphology of all nanoparticles was fully characterized by microscopic and spectroscopic techniques, and their ordered arrangement was assessed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements. We demonstrate that the nanostructuring of the complexes influences their optical and redox properties-by promoting a fine-tuning of emission, photoluminescence quantum yield, excited state lifetime, HOMO/LUMO energy levels, and energy-transfer processes-as well as their interaction with living cells. Investigations on glioblastoma U-251 MG cells demonstrate that nanostructuring represents an effective tool to regulate the efficiency of cell loading, cell viability, colocalization, and penetration in 3D spheroids.

Thermomechanical and Morphological Studies of CFRP Tested in Different Environmental Conditions.

The present work describes the mechanical characterization combined with the thermal degradation kinetics of Carbon Fiber Reinforced Polymers (CFRP). The thermal degradation kinetics of CFRP have never been studied in the past. In that regard, the present work focuses on studying the thermal degradation kinetics of CFRP tested mechanically at different environmental conditions. Tensile tests were performed on the specimens with different lay-ups at room temperature, elevated temperature (71 °C), and cryogenic conditions (-54 °C), and the same specimens were used for thermal degradation kinetic studies. Mechanical tests show different responses respect to the different environmental conditions and different fibers orientation. On the other hand, the thermogravimetric results, mass loss, and derivative mass loss, show no significant difference in the degradation of CFRP tested at different temperatures. However, the thermal degradation kinetics shows more insight into the degradation pattern of the materials. The activation energy of degradation shows that the degradation of materials subjected to elevated conditions increases rapidly in the later stages of degradation, suggesting the formation of high char yield. The varying activation energy has been related to different degradation mechanisms. Lastly, the morphology of the materials was studied under SEM to understand the structural change in the material after tested in different weather conditions.

Analytical and preparative enantioseparation and main chiroptical properties of Iridium(III) bis(4,6-difluorophenylpyridinato)picolinato.

Almost all Iridium(III) complexes employed both as dopants in PhOLEDs and as pharmaceuticals and fluorescence bioprobes are racemic mixtures. In this study the single enantiomers of the most stable diastereomeric form fac-trans-N-N, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) were separated and analysed. The data obtained showed that the complex can be separated into stable optically active Λ and Δ isomers employing cellulose based chiral stationary phase both in normal and polar phase mode. Their chirality was confirmed and their absolute configuration assigned employing several methods (DFT and TDDFT calculations, CD and VCD). The CPL spectroscopy of the isolated enantiomers of FIrpic was also recorded due to its possible value in the OLEDs field. The chromatographic method was applied for a semipreparative purpose demonstrating that polar organic solvent chromatography (POSC) could be used to avoid the low-solubility issues associated with these Iridium(III) complexes. Finally, the chemical and stereochemical stability of the single isomers was evaluated under thermal stress by liquid chromatography coupled to high-resolution mass spectrometry (LC-QTOF) on both chiral and achiral columns. No racemization and/or isomerization was observed; however, the dissociation of the ancillary ligand was demonstrated employing LC-QTOF.

X-ray excited visible luminescence spectroscopy of organic materials using a portable optical spectrometer.

The use of a portable video telescope, mounted externally to a beamline endstation, to obtain synchrotron-radiation-excited visible luminescence, is described. Real-time video monitoring permits simple and quick alignment, and allows a visual record of the luminescence experiment. The telescope is fibre-optic-coupled to an optical spectrometer. Examples are given of X-ray excited optical spectroscopy from organic materials for light-emitting-diode applications.