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Inspired by nature, this work presents a scalable method to produce opalescent 3D printing filaments with angle‐dependent structural color. Compared to conventional colorants, these colors provide a more vivid appearance, possess the ability to dynamically change in response to alterations of illumination, and may feature superior longevity as well as durability. Particle synthesis via emulsion polymerization in starved‐feed mode is utilized to achieve a tailored core–shell particle architecture. During processing, the thermoplastic polyacrylate‐based shells form a continuous matrix, wherein the pristine polystyrene cores self‐assemble. The colloidal ordered structure thus formed selectively scatters light according to Bragg's law. Adjusting particle size makes the perceived colors easily tunable over the visible spectrum. The filaments are printable on entry‐level printers with comparable settings to commercial filaments and state‐of‐the‐art print quality. With this work, sustainable 3D printing of iridescent objects with a novel and superior coloration strategy becomes possible for everyone – from hobbyists over customized goods and industrial prototypes to serial production. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) broadband active photonic materials play a crucial role in various domains such as optical communication, phototherapy, and medical imaging. However, the construction of NIR photonic materials with tunable optical response still remains a great challenge. This manuscript proposes a topological structure engineering strategy in Bi‐activated glass for the realization of the controllable NIR emission. By manipulating the topological structure of glass, the Bi cluster configuration can be precisely control, with the cluster size from 2.78 to 1.64 nm. Correspondingly, various optical properties including broadband emission, excited state absorption (ESA), and even unsaturable loss (UL) can be rationally switched. Based on the above findings, Bi cluster‐activated bulk glasses, optical fibers, and the derived NIR active devices with notably improved performance can be successfully fabricated. Their application potentials in optical communication and NIR imaging are also demonstrated. The study highlights the promise of Bi cluster‐activated materials in advancing NIR photonic materials and devices. Furthermore, the topological‐mediated cluster regulation strategy may also provide new insights into the fundamental science and cutting technology of other cluster‐activated materials. [ABSTRACT FROM AUTHOR]

Commercial production of integrated photonic devices is limited by scalability of desirable material platforms. We explore a relatively new photonic material, AlScN, for its use in electro-optic phase shifting and modulation. Its CMOS-compatibility could facilitate large-scale production of integrated photonic modulators, and it exhibits an enhanced second-order optical nonlinearity compared to intrinsic AlN, indicating the possibility for efficient modulation. Here, we measure the electro-optic effect in Al0.80Sc0.20N-based phase shifters. We utilized the TM0 mode, allowing use of the r 33 electro-optic coefficient, and demonstrated V π L around 750 V cm. Since the electro-optic response is smaller than expected, we discuss potential causes for the reduced response and future outlook for AlScN-based photonics.

Abstract Structural colors arise from selective light interaction with (nano)structures, which give them advantages over pigmented colors such as resistance to fading and possibility to be fabricated out of traditional low-cost and non-toxic materials. Since the color arises from the photonic (nano)structures, different structural features can impact their photonic response and thus, their color. Therefore, the detailed characterization of their structural features is crucial for further improvement of structural colors. In this work, we present a detailed multi-scale structural characterization of ceramic-based photonic glasses by using a combination of high-resolution ptychographic X-ray computed tomography and small angle X-ray scattering. Our results uncover the structure-processing-properties’ relationships of such nanoparticles-based photonic glasses and point out to the need of a review of the structural features used in simulation models concomitantly with the need for further investigations by experimentalists, where we point out exactly which structural features need to be improved.

The recent outbreak of coronavirus disease 2019 (COVID‐19) highlights the critical need for rapid, sensitive, and accurate virus detection methods to prevent and manage pandemics. Among the available sensing methods, photonic biosensors have emerged as a forefront technology, characterized by their high sensitivity, minimal analyte requirements, and suitability for miniaturization, making them ideal for point‐of‐care applications in virus detection. This review comprehensively summarizes the recent progress of photonic biosensor technologies, focusing on wavelength shift and luminescence‐based mechanisms. Their operational principles, general configurations, and the challenges associated with these technologies are looked into. An overview of the material developments used in photonic biosensors, encompassing organic, inorganic, and hybrid composite‐based materials is further presented. The discussion extends to surface functionalization using biorecognition elements, including DNA/RNA, aptamers, and antibodies, to craft the specificity of the photonic biosensors for viruses. Ultimately, the importance of a multidisciplinary approach is emphasized in developing new materials architecture, biological receptors, and modifications to photonic methods, aiming to realize better biosensors for virus detection with ultra‐high sensitivity, rapid response, and excellent selectivity. [ABSTRACT FROM AUTHOR]

Structural colors arise from selective light interaction with (nano)structures, which give them advantages over pigmented colors such as resistance to fading and possibility to be fabricated out of traditional low-cost and non-toxic materials. Since the color arises from the photonic (nano)structures, different structural features can impact their photonic response and thus, their color. Therefore, the detailed characterization of their structural features is crucial for further improvement of structural colors. In this work, we present a detailed multi-scale structural characterization of ceramic-based photonic glasses by using a combination of high-resolution ptychographic X-ray computed tomography and small angle X-ray scattering. Our results uncover the structure-processing-properties' relationships of such nanoparticles-based photonic glasses and point out to the need of a review of the structural features used in simulation models concomitantly with the need for further investigations by experimentalists, where we point out exactly which structural features need to be improved. [ABSTRACT FROM AUTHOR]

Given the ever‐increasing demand for transmission capacity in optical fiber communication systems, there is a growing focus on developing active fibers and devices with an optical response across a wider spectrum. Bismuth (Bi)‐doped photonic glasses have attracted significant interest for their exceptional ultra‐broadband optical response, particularly within telecommunication bands. However, developing advanced Bi‐activated materials with robust optical response, high compatibility with commercial transmission systems, and low processing temperature remains a huge challenge. Herein, an anion hybridization strategy is proposed to overcome the aforementioned limitations. The anion hybridization significantly enhances the broadband optical response (≈10 times) of the Bi center following the introduction of fluorine ions, and reduces the transition temperature of the photonic glass (≈200 °C). Moreover, the near‐infrared optical response bandwidth experiences significant broadening, a result attributed to the larger inhomogeneous broadening. Furthermore, successful fabrication of the anion‐hybridized Bi‐activated glass fiber is achieved, demonstrating excellent compatibility with commercial transmission fibers. Additionally, the fabricated fiber exhibits an amplified spontaneous emission and on‐off gain across a broad waveband, further validating its efficacy. These results indicate that anion hybridization offers an effective strategy to optimize the optical and thermal properties of photonic materials to develop novel advanced photonic devices. [ABSTRACT FROM AUTHOR]

We present a comprehensive review of recent developments in Spin Orbit Interactions (SOIs) of light in photonic materials. In particular, we highlight progress on detection of Spin Hall Effect (SHE) of light in hyperbolic metamaterials and metasurfaces. Moreover, we outline some fascinating future directions for emergent applications of SOIs of light in photonic devices of the upcoming generation. [ABSTRACT FROM AUTHOR]

This comprehensive optical study analyzes field manipulations of bands in infrared (IR) spectra of thin films and functional surfaces for varying measurement and sample conditions. Band variations related to the materials dielectric functions, the measurement geometry, the film thickness as well as the direction dependence of the probing electromagnetic fields are demonstrated. Examples are discussed for isotropic polymer films (≈200 nm polymethylmethacrylate [PMMA]) on gold and silicon as well as an anisotropic hydrogen monolayer on a Si(111) surface, characterized by IR–attenuated total reflection, IR microscopy, and incidence‐angle‐dependent IR polarimetry. Even for fixed optical material properties, significant manipulations of band frequency and shape (shifts up to ≈14 cm−1 for PMMA, up to ≈3 cm−1 for H–Si) occur in not only polarization‐dependent but also unpolarized spectra. The shown data underline that polarimetric measurements and optical analyses are essential for a detailed interpretation of band shapes. [ABSTRACT FROM AUTHOR]

This comprehensive optical study analyzes field manipulations of bands in infrared (IR) spectra of thin films and functional surfaces for varying measurement and sample conditions. Band variations related to the materials dielectric functions, the measurement geometry, the film thickness as well as the direction dependence of the probing electromagnetic fields are demonstrated. Examples are discussed for isotropic polymer films (≈200 nm polymethylmethacrylate [PMMA]) on gold and silicon as well as an anisotropic hydrogen monolayer on a Si(111) surface, characterized by IR–attenuated total reflection, IR microscopy, and incidence‐angle‐dependent IR polarimetry. Even for fixed optical material properties, significant manipulations of band frequency and shape (shifts up to ≈14 cm−1 for PMMA, up to ≈3 cm−1 for H–Si) occur in not only polarization‐dependent but also unpolarized spectra. The shown data underline that polarimetric measurements and optical analyses are essential for a detailed interpretation of band shapes.

Plastic pollution has caused numerous environmental issues in recent decades. As one of the most commonly used packaging materials, aluminum‐plastic laminates (APL) are particularly challenging for recycling purposes due to their sophisticated materials components. This work reveals a new strategy to upcycle such post‐consumer APL packaging waste, e.g., chips‐bags, for passive daytime cooling applications. This opens an attractive route to reuse APLs while at the same time reducing global energy consumption and carbon emissions. The mirror‐like appearance of the APLs possesses a strong solar reflection, up to 86%. By coating, this reflective layer of the APL waste with a high emissive polydimethylsiloxane layer, a simple but effective passive daytime cooling foil is constructed, which shows promising passive cooling performance theoretically and practically. More importantly, the passive cooling foil based on APL waste is flexible and can be applied to any target object, protecting it from harsh sunlight. The low‐cost APL waste‐based passive cooling foil proposed in this work will significantly contribute to both energy and environmental issues that humans face today. [ABSTRACT FROM AUTHOR]

Molecule‐based micro/nanocrystal heterojunctions (MMHs) have attracted much attention in the fields of information security, optical sensors, photonic communications, crystal laser media, and miniaturized white‐light device. Although several types of MMHs materials are designed and synthesized, some challenges still need to be recognized and solved, such as in‐depth understanding on the formation–growth mechanisms of low‐dimensional micro/nanostructures and the realization of their practical applications. In this review, recent development of MMHs materials, including basic concepts (i.e., binding force, lattice match, nucleation rate, and crystal interfacial energy), materials classification (from single‐component to multicomponent heterojunctions), preparation methods, together with representative photonic applications, is systematically summarized. This review not only introduces state‐of‐the‐art advances of MMHs systems, but also presents their current issues and future trends, which are favorable to provide new ideas and guidance for expanding the understanding and promoting the evolution of MMHs for advanced optical applications. [ABSTRACT FROM AUTHOR]

Implementing compact, efficient, and reliable passive pulsed lasers at visible wavelengths is attractive. This paper systematically investigated the thickness-dependent optical absorption characteristics of two-dimensional materials, including graphene, transition-metal dichalcogenides, and dye films at the 532 nm wavelength band, and revealed the effects of thickness on different optical absorption parameters. The results suggested that dye films are more suitable for loss-sensitive pulsed lasers and graphene is more suitable for modulation depth-sensitive pulsed lasers, while transition-metal dichalcogenide samples have intermediate performance. It can provide guidance for the rational selection of saturable absorbers in pulsed all-fiber lasers to optimize the optical pulse performance in the visible-wavelength band. [ABSTRACT FROM AUTHOR]

The synthesis of upconversion nanoparticles (UCNPs) by flame aerosol is of great significance to realize industrial large-scale production of UCNPs and develop nanotechnology further. Here, for the first time, we successfully fabricated the ultrasmall Y2O3:Yb3+/Ho3+ UCNPs by a self-build swirl flame spray pyrolysis (SFSP) method with a high production rate of ∼40 g$ \cdot $ h−1. These flame-made UCNPs are all pure cubic phases with an average ultrasmall size of ∼14 nm. Excited by 980 nm laser, the synthesized UCNPs show bright green (2F4, 5S2 → 5I8) and relatively weak red (5F5 → 5I8) upconversion luminescence (UCL). Based on the UCL spectra of Y2O3:Yb3+/Ho3+ UCNPs, the optimal doping concentrations of 6 mol% Yb3+ and 0.1 mol% Ho3+ were determined to reach the most intense UCL. The dependence of UCL intensity and pump power was further analyzed, and it indicated that the green and red UCL are two-photon processes. In addition, the UCL properties with different synthesized conditions were also demonstrated. The UCL mechanism of these flame-made Y2O3:Yb3+/Ho3+ UCNPs were illustrated in detail. Our results prove that industrial large-scale production of continuous one-step synthesis of UCNPs by flame aerosol technology is completely feasible and deserves further study.

Micro/nanogels are unique materials that exhibit the properties of both colloids and hydrogels, i.e. being colloids they exhibit a large specific surface area, while they are hydrophilic and porous allowing them to swell to a great degree with water. Engineering micro/nanogels, through the rational design of various polymer compositions and/or optical structures, can enable them to respond to a myriad of stimuli, e.g. temperature, pH, biomolecules, CO2, light, and electricity. These multi-responsive micro/nanogels and their assemblies, are capable of recognizing and transducing analyte signals into changes in optical properties observable spectroscopically or via the naked eye, allowing their use as optical sensors. In this review, we have highlighted recent state-of-the-art examples of stimuli-responsive micro/nanogel-based systems for optical sensors.

In this study, core–shell-hairy-type melanin particles surface modified with a polydopamine shell layer and a polymer brush hairy layer were fabricated and assembled to readily obtain bright structural color films. The hot pressing of freeze-dried samples of melanin particles decorated with a hydrophilic, low glass transition temperature polymer brush results in films that exhibit an angle-dependent structural color due to a highly periodic microstructure, with increased regularity in the arrangement of the particle array due to the fluidity of the particles. Flexible, self-supporting, and easy-to-cut and process structural color films are obtained, and their flexibility and robustness are demonstrated using compression tests. This method of obtaining highly visible structural color films using melanin particles as a single component will have a significant impact on practical materials and applications. [ABSTRACT FROM AUTHOR]

Blending multiple polymers together to form the so-called "high-entropy polymers (HEPs)" can generate the effects of molecular dispersion in addition to suppressing polymer phase separation. We embedded a semiconducting polymer (conjugated polymers, CPs) in an optically inert matrix composed of n polymer species and found that a molecule-level dispersion is attained in HEPs defined as n ≥ 5. In the regime of dilute CP concentrations, the photonic properties vary widely in the n = 1 matrices owing to diverse solubility parameters, but the distribution narrows with n , and the CP starts to exhibit behaviors of molecule-level dispersion at n ≥ 5, where the matrix polymers compete with each other to exert direct influences on the embedded CP. Specifically, for MEH-PPV, increasing n reduces the fluorescence redshift and spectral width from diminishing aggregation. For the rigid PFO molecules, increasing n creates a dilution effect facilitating formation of the low-energy planar β-phase. For the flexible regioregular P3HT-rr, HEPs offer well-dispersed amorphous chains highly susceptible to chain environments, thus influencing η R 's in the quasi-fixed amorphous-crystalline energy transfer landscape. The HEP effects continue for greater CP concentrations, consistent with the matrix dispersing behaviors in the dilute regime. This work demonstrates a molecular-level dispersion by HEPs, offering a method of molecular tailoring for polymer research and applications via simple mixing.

Photonic crystals, characterized by their periodic structures, have been extensively studied for their ability to manipulate light. Typically, the development of 2D photonic crystals requires either sophisticated equipment or precise orientation of spherical nanoparticles. However, liquid-crystalline (LC) materials offer a promising alternative, facilitating the formation of periodic structures without the need for complex manipulation. Despite this advantage, the development of 2D photonic periodic structures using LC materials is limited to a few colloidal nanodisk liquid crystals. Herein, 2D photonic colloidal liquid crystals composed of biomineral-based nanorods and water is reported. The soft photonic materials with 2D structure by self-assembled LC colloidal nanorods are unique and a new class of photonic materials different from conventional solid 2D photonic materials. These colloids exhibit bright structural colors with high reflectance (>50%) and significant angular dependency. The structural colors are adjusted by controlling the concentration and size of the LC colloidal nanorods. Furthermore, mechanochromic hydrogel thin films with 2D photonic structure are developed. The hydrogels exhibit reversible mechanochromic properties with angular dependency, which can be used for an advanced stimuli responsible sensor., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

A new class of highly efficient nonlinear optical organic salt crystals is reported. In nonlinear optics based on organic materials, it is well known that using two electron‐withdrawing groups (EWGs) onto cationic electron acceptors instead of conventional one EWG remarkably enhances microscopic optical nonlinearity for chromophores. However, the corresponding organic crystals possessing enhanced large macroscopic optical nonlinearity have not been reported yet. Herein, a design strategy is proposed for obtaining highly efficient nonlinear optical crystals based on two EWGs in cationic electron acceptors. Introducing a phenolic electron donor, promoting a head‐to‐tail interionic assembly, along with a two‐EWG N‐pyrimidinyl pyridinium electron acceptor in cationic chromophores results in a preferred non‐centrosymmetric, perfectly parallel alignment of chromophores in crystal. Newly designed OPR (4‐(4‐hydroxystyryl)‐1‐(pyrimidin‐2‐yl)pyridinium) crystals exhibit approximately two times larger effective first hyperpolarizability than that of analogous N‐alkyl OHP (4‐(4‐hydroxystyryl)‐1‐methylpyridinium) crystals based on only one EWG. OPR crystals exhibit comparable second‐order optical nonlinearity to benchmark red‐colored DAST (4‐(4‐(dimethylamino)styryl)‐1‐methylpyridinium 4‐methylbenzenesulfonate) crystals, but a significant blue‐shifted absorption resulting in orange‐color crystals. Therefore, phenolic organic salt crystals using two EWGs are highly promising materials for various nonlinear optical applications.

Implementing compact, efficient, and reliable passive pulsed lasers at visible wavelengths is attractive. This paper systematically investigated the thickness-dependent optical absorption characteristics of two-dimensional materials, including graphene, transition-metal dichalcogenides, and dye films at the 532 nm wavelength band, and revealed the effects of thickness on different optical absorption parameters. The results suggested that dye films are more suitable for loss-sensitive pulsed lasers and graphene is more suitable for modulation depth-sensitive pulsed lasers, while transition-metal dichalcogenide samples have intermediate performance. It can provide guidance for the rational selection of saturable absorbers in pulsed all-fiber lasers to optimize the optical pulse performance in the visible-wavelength band.

Polymer indicators are autonomous responsive materials that provide an optical signal of a specific exposure in time. This review describes the different polymer systems utilized to obtain indicators based on structural color. Structural color originates from the interaction of light with a periodic nanostructured polymer which causes a specific wavelength to be reflected. This reflected light can be used for fabricating battery-free indicators that show visible structural color changes upon exposure to a stimulus or analyte. In this review, the typical structural color response types categorized by stimulus are discussed and compared. Furthermore, the steps toward possible applications of optical indicators based on structural colored polymers are outlined. [ABSTRACT FROM AUTHOR]

Disordered photonic nanostructures have attracted tremendous interest in the past three decades, not only due to the fascinating and complex physics of light transport in random media, but also for peculiar functionalities in a wealth of interesting applications. Recently, the interest in dielectric disordered systems has received new inputs by exploiting the role of long‐range correlation within scatterer configurations. Hyperuniform photonic materials, that share features of photonic crystals and random systems, constitute the archetype of systems where light transport can be tailored from diffusive transport to a regime dominated by light localization due to the presence of photonic band gap. Here, advantage is taken of the combination of the hyperuniform disordered (HuD) design in slab photonics, the use of embedded quantum dots for feeding the HuD resonances, and near‐field hyperspectral imaging with sub‐wavelength resolution in the optical range to explore the transition from localization to diffusive transport. It is shown, theoretically and experimentally, that photonic HuD systems support resonances ranging from strongly localized modes to extended modes. It is demonstrated that Anderson‐like modes with high Q/V are created, with small footprint, intrinsically reproducible and resilient to fabrication‐induced disorder, paving the way for a novel photonic platform for quantum applications. [ABSTRACT FROM AUTHOR]

Abstract Polymer indicators are autonomous responsive materials that provide an optical signal of a specific exposure in time. This review describes the different polymer systems utilized to obtain indicators based on structural color. Structural color originates from the interaction of light with a periodic nanostructured polymer which causes a specific wavelength to be reflected. This reflected light can be used for fabricating battery‐free indicators that show visible structural color changes upon exposure to a stimulus or analyte. In this review, the typical structural color response types categorized by stimulus are discussed and compared. Furthermore, the steps toward possible applications of optical indicators based on structural colored polymers are outlined.

Iridescent photonic materials have wide‐ranging applications in security printing, and optical devices. While the commonly used photonic materials are based on polymers or inorganic colloidal particles, self‐assembled small molecules are rarely exploited. Herein, a Bodipy (Bodipy‐PE‐2) self‐assembly is reported that forms a layered photonic structure upon thermal annealing, exhibiting angle‐dependent iridescence of green and pink with a luminescence shift from yellow to red. The micro‐ and nano‐periodicity associated with the layered structure and the phase transformation due to the annealing are responsible for the observed properties. The single‐crystal analysis reveals the critical role of weak dispersive interactions (C–H···π, C–H···O, and N–H···F) in the crystal packing and a possible phase change in the formation of the layered structure. A stimuli‐responsive ink prepared with the annealed powder using polyethylene glycol as a vehicle medium exhibits reversible emission change between red and yellow upon heating and solvent exposure, respectively. A composite gel of the annealed Bodipy‐PE‐2 and polystyrene displays angle‐dependent color change and optical waveguiding properties. The self‐assembled Bodipy‐PE‐2 obtained from toluene exhibits active and passive waveguiding properties when excited with 532 and 633 nm laser sources. [ABSTRACT FROM AUTHOR]

Materials of metal–organic frameworks (MOFs) in pure and hybridized forms showing photonic properties have received much attention during past years. Strategies to prepare photonic MOF‐based materials are constantly used as follows: 1) designing of pure MOFs with intrinsic luminescent units such as organic linkers and/or lanthanide ions; 2) designing of hybrid MOF composites through encapsulation of extrinsic luminescent units such as organic dyes and/or inorganic nanospecies; and 3) designing of MOF‐based composites through mixing both intrinsic and extrinsic luminescent units to display synergistic effect. A highly ordered structure with the richness of space groups enable well‐designed MOFs to display second‐harmonic generation. In addition, easy formation of well‐faceted morphology, to serve as optical microresonators in MOF crystals, is beneficial for the exploration of the miniaturization of lasers. Moreover, with the assistance of stepwise coating, devices fabricated by using MOF‐based materials in lighting have been realized. Furthermore, biocompatible nanoscale MOF composites coated by polymers and encapsulated with photo‐absorbing agents in cancer treatment are also discussed. This review provides a summary and discussion of the very recent progress of photonic MOFs in applications of white solid‐state lighting, lasing, nonlinear optics, and phototherapy in cancer treatment. [ABSTRACT FROM AUTHOR]

In this study, core–shell-hairy-type melanin particles surface modified with a polydopamine shell layer and a polymer brush hairy layer were fabricated and assembled to readily obtain bright structural color films. The hot pressing of freeze-dried samples of melanin particles decorated with a hydrophilic, low glass transition temperature polymer brush results in films that exhibit an angle-dependent structural color due to a highly periodic microstructure, with increased regularity in the arrangement of the particle array due to the fluidity of the particles. Flexible, self-supporting, and easy-to-cut and process structural color films are obtained, and their flexibility and robustness are demonstrated using compression tests. This method of obtaining highly visible structural color films using melanin particles as a single component will have a significant impact on practical materials and applications.

Photonic materials featuring simultaneous iridescence and light emission are an attractive alternative for designing novel optical devices. The luminescence study of a new optical material that integrates light emission and iridescence through liquid crystal self-assembly of cellulose nanocrystal-template silica approach is herein presented. These materials containing Rhodamine 6G were obtained as freestanding composite films with a chiral nematic organization. The scanning electron microscopy confirms that the cellulose nanocrystal film structure comprises multi-domain Bragg reflectors and the optical properties of these films can be tuned through changes in the relative content of silica/cellulose nanocrystals. Moreover, the incorporation of the light-emitting compound allows a complementary control of the optical properties. Overall, such findings demonstrated that the photonic structure plays the role of direction-dependent inner-filter, causing selective suppression of the light emitted with angle-dependent detection.

Cholesteric liquid crystals (CLCs) are chiral photonic materials reflecting only circularly polarized light with the same handedness as the helical polymer structure. Concurrent shape and color changes can be achieved using CLCs, but the fabrication of CLCs with switchable 3D shape, structural color, and hyper‐reflectivity, that is, reflecting both left‐ and right‐handed circularly polarized light simultaneously, has not yet been achieved. Here, CLC elastomer (CLCE) actuators are reported to reflect equal amounts of left‐ and right‐handed circularly polarized light. Hyper‐reflectivity is achieved by uniaxially stretching the partially crosslinked film to induce helix deformation which is then fully crosslinked to fix the deformed helical structure. The shape, structural color, and hyper‐reflectivity of the polymer film are switchable with temperature. At high temperatures, only right‐handed circularly polarized light is reflected and the color is redshifted. The film can be shaped in three dimensions: a structural colored 3D shaped beetle is fabricated using molding, which reflects both left‐ and right‐handed circularly polarized light and shows reversible, temperature responsive structural color and 3D shape changes. Hence, 4D engineered bioinspired multifunctional materials are fabricated, which are interesting for applications ranging from sensing actuators to switchable hyper‐reflective films and objects. [ABSTRACT FROM AUTHOR]

The urban heat island is increasing the temperature of cities up to 10 °C and has a very important impact on energy, environmental quality and health. Materials used in the building and urban fabric affect the urban thermal balance and contribute highly to urban overheating. The article presents the progress achieved on the design, development and implementation of mitigation materials presenting a low and very low surface temperature. The recent technological progress and developments concerning natural, light colour, IR reflective, PCM doped, thermochromic, fluorescent, photonic and plasmonic materials is presented. Experimental results on the cooling capacity and the thermal performance of conventional and advanced materials are described in a comparative way. It is demonstrated that innovative materials can exhibit sub-ambient surface temperatures and contribute highly to mitigate urban overheating. • New innovative mitigation materials are recently developed. • Innovative advanced materials present a superior performance. • New materials contribute to counterbalance urban overheating. • Super cool materials operate under sub ambient surface temperatures. [ABSTRACT FROM AUTHOR]

Blue phase liquid crystal films are quite useful in reflective displays, flexible photonic devices, and optical sensors. However, the effects of refractive index properties of refilled liquid crystals and environment temperature on reflection properties of blue phase liquid crystal films are far from fully exploration. Herein, we demonstrate blue phase liquid crystal films refilled with different nematic liquid crystals. The effects of birefringence and average refractive index of refilled nematic liquid crystals on the reflection properties such as reflectance, central wavelength, and linewidth of photonic band have been studies. The temperature effect on reflectance and central wavelength has been studied. A narrow linewidth (19.4 nm) and temperature insensitivity blue phase liquid crystal film has been fabricated by refilling liquid crystals of DYX8013 with small birefringence. The narrow linewidth and excellent temperature insensitivity properties of BPLC film can be applied in color reflective display and flexible photonic devices.

Reported herein is the novel achievement of uniform and tunable interference colors of nanocomposite films containing organized cellulose nanocrystals (CNCs) from dynamic hydrogel precursors. Homogeneous and amendable interference colors with broad range are obtained either by stacking the nanocomposite films to adjust the amount of CNCs in the propagation pathway of light or by regulating the rotation angles between the individual films to alter the relative organization of CNCs within the system. Moreover, the precise and controllable patterned CNC composite films with multicolors in one film are facilely fabricated for the first time from the patterned hydrogel precursors. Based on this stacking/rotation‐method, these patterned nanocomposite films with tunable interference colors can be further applied as fundamental elements for optical encryption by establishing a ternary‐coded decimal system with encoded decimal numerals, paving the way for the development of photonic functional materials based on CNCs. [ABSTRACT FROM AUTHOR]

Living tissues, heterogeneous at the microscale, usually scatter light. Strong scattering is responsible for the whiteness of bones, teeth, and brain and is known to limit severely the performances of biomedical optical imaging. Transparency is also found within collagen-based extracellular tissues such as decalcified ivory, fish scales, or cornea. However, its physical origin is still poorly understood. Here, we unveil the presence of a gap of transparency in scattering fibrillar collagen matrices within a narrow range of concentration in the phase diagram. This precholesteric phase presents a three-dimensional (3D) orientational order biomimetic of that in natural tissues. By quantitatively studying the relation between the 3D fibrillar network and the optical and mechanical properties of the macroscopic matrices, we show that transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The striking similarities between synthetic and natural materials provide insights for better understanding the occurring transparency. [ABSTRACT FROM AUTHOR]

In this work, light and temperature responsive, brush‐painted photonic coatings exhibiting three different colored and surface topographical states are reported. The different states arise from the use of cholesteric liquid‐crystalline micrometer‐sized polymer particles as shape‐memory photonic pigments that are dispersed in a shape‐memory binder. The first temporal state is induced by compressing the photonic particles at high temperature, resulting in blueshift of the structural color. The second temporal state is obtained by embossing a diffractive grating on the surface at an intermediate temperature leading to a relief topography and a rainbow optical effect. Both optical and surface topographical changes coexist and are stable at room temperature until they are reverted independently either by heating or locally by light illumination. Multicolored paints that reflect selectively left‐handed or right‐handed polarized light are developed to create arbitrary polarization‐dependent multicolor and topographical brush‐painted patterns. These temperature and light responsive triple shape‐memory photonic paints have potential applications as battery‐free optical sensors, responsive decoration, and smart adhesives. [ABSTRACT FROM AUTHOR]

We develop a bistable smart window based on mixture of negative dielectric nematic liquid crystal, chiral dopant, and chiral ionic liquid (CIL). The developed smart window is driven by dual-frequency modulation, where the transparent state is turned on under an electric field with high frequency (4 kHz), and the scattering state is switched on by an electric field with low frequency (20 Hz). The dual-frequency characteristics of the proposed smart window have been extensively investigated. This smart window has intrinsic features including dual-frequency modulation, simple fabrication process, and excellent stability. This smart window is capable of practical use in modern life as a building wall, sunroof, and curtain-free window.

Fabricating materials with specific refractive indices, which do not naturally exist in the nature, has always been an issue. This paper presents a method for fabricating SiOx films with specified refractive index. It is well known that the refractive index of reactively sputtered SiOx films depends on its deposition conditions; in this paper, this fact was employed to fabricate films with arbitrary refractive indices. A statistical study and a Genetic Algorithm are implemented that can determine the deposition conditions (including oxygen partial flow and pressure) for fabricating a film with an arbitrary refractive index in the range of 1.4-4.2. The method was experimentally shown to correctly determine the deposition conditions. The functionality of using the proposed method in fabricating optical components was further evaluated by fabricating a distributed Bragg reflector (DBR) consisting of 4.5 pairs, whose refractive indices of the layers were determined by the proposed method. The DBR featured a high 95% reflection in a bandwidth of more than 270 nm, which can be categorized as a high-quality DBR. The advance of the proposed method is that the films are made from a single target source without making any physical changes in the target or substrate positions.

We demonstrated all-optical intensity modulator based on polarization-dependent graphene-covered microfiber (GMF) waveguide. By controlling the polarization mode of incident light, a greatly adjustable enhanced interaction between the propagating light and the graphene can be obtained via the evanescent field of the microfiber. By employing 980-nm pump light and 1550-nm signal light in continuous wave, the strong light–graphene interaction enables a maximum modulation depth of ∼20.86 dB, and by pumping 980 nm wave pulses, we obtained the temporal response characteristics of signal light with modulation rate of 5.13 kHz. This all-optical intensity modulator is compatible with optical fiber systems, and features with ease of fabrication, and steerable high modulation depth, which show potential in graphene's applications such as all-optical switching and all-optical communications.

While stimuli-responsive structural colors are commonly found in nature, mimicking these in artificial materials is challenging. Dynamically switchable and tunable coloration, however, is in high demand in widespread fields of applications, including advanced display and monitoring technologies, smart sensing, and anticounterfeiting. This work reports a scalable protocol for the synthesis of tailor-made core-shell particles and subsequent processing to opal films with iridescent, pH-responsive, and mechanochromic structural color. Novel monodisperse core-shell architectures based on hard polystyrene core particles are synthesized via stepwise emulsion polymerization in a starved-feed mode. The incorporation of 4-vinylpyridine and methacrylic acid as functional comonomers in the soft particle shell facilitates pH-responsive swelling and deswelling. Mechanically stable and well-ordered colloidal crystal films are obtained by the self-assembly of the particles during processing with the powerful melt-shear organization technique. Thereby obtained opal films show Bragg-scattering at the colloidal crystalline structure and exhibit brilliant green-turquoise to blue-violet reflection colors, dependent on the angle of view and illumination. Upon changes in the pH value or mechanical deformation, the reflected wavelength shifts by more than 100 nm, leading to intriguing changes in the visible structural color. Excellent reversibility is achieved by the subsequent application of a convenient UV cross-linking strategy, corroborating the high application potential of these advanced functional materials.

The structural support of plant cells is provided by the cell wall, which major load-bearing component is an array of hierarchical orientedhierarchical-oriented cellulose nano-, micro- and meso-structures of cellulose microfibrils. Cellulosic structures can respond to humidity changes by expanding or shrinking and this allows, for example, the dispersion of seeds. Previous studies have shown that nanorods, extracted from cell walls, can generate lyotropic liquid crystals that are at the origin of solid cholesteric-like arrangements. Not only photonic films, but also right and left helical filaments, anisotropic films with the ability to bend back and forth under the action of a moisture gradient at room temperature, are some of the materials that were produced from cellulose liquid crystal systems. This work is a review that focus on liquid crystalline-based structures obtained from cellulosic materials and how small perturbations on their structures affect significantly the response to external stimulus and interactions with the environment. Special emphasis is given to cholesteric-like organization of cellulose structures existing in plants, which are an inspiration for the production of the next generation of soft interactive materials. [ABSTRACT FROM AUTHOR]

Photonic materials use photons as information carriers and offer the potential for unprecedented applications in optical and optoelectronic devices. In this study, we introduce a new strategy for photonic materials using metal–organic frameworks (MOFs) as the host for the rational construction of donor–acceptor (D–A) heterostructure crystals. We have engineered a rich library of heterostructure crystals using the MOF NKU‐111 as a host. NKU‐111 is based upon an electron‐deficient tridentate ligand (acceptor) that can bind to various electron‐rich guests (donors). The resulting heterocrystals exhibit spatially segregated multi‐color emission resulting from the guest‐dependent charge‐transfer (CT) emission. Spatially effective mono‐directional energy transfer results from tuning the energy gradient between adjacent domains through the selection of donor guest molecules, which suggests potential applications in integrated optical circuit devices, for example, photonic diodes, on‐chip signal processing, optical logic gates. [ABSTRACT FROM AUTHOR]

Vertical convective self‐assembly has been extensively used for the preparation of direct photonic crystals, which can be later infiltrated with a more stable material, such as oxide ceramics, by atomic layer deposition. However, the relationship between the self‐assembly parameters of the direct photonic crystals and the optical properties of the inverse opal photonic crystals remains elusive. In this work, the effect of different experimental parameters on the 3D structure and the density of defects of polystyrene direct photonic crystals produced by vertical convective self‐assembly was assessed. Self‐assembly was investigated using deionized water as media with polymer particles' concentrations up to 2 mg/mL; temperatures of 40, 50, and 80°C; and relative humidity of 45%, 70%, and 90%. The 3D structure of the resultant direct photonic materials was characterized by the combination of scanning electron microscopy and image analysis, and their optical properties were assessed by reflectance measurements. These results were correlated with the performance of oxide‐based inverse opal photonic crystals produced by the controlled infiltration of the former direct photonic crystals by atomic layer deposition (ALD). It was found that the thickness increased with the concentration of polystyrene particles, while the photonic structure ordering is dependent on the synergy between humidity and temperature. Results also showed higher defects population with increasing evaporation temperature and decreasing relative humidity. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we report on a new photonic behavior based on a series of photoluminescence and mechanoluminescence experiments conducted on Strontium aluminate (SrAl 2 O 4) (SAO) co-doped with lanthanide ions such as Eu2+ (europium ion) and Dy3+ (dysprosium ion) (SAOED). It was observed that the increase of the dislocation density in SAOED decreased its stress-free afterglow while increasing its mechanoluminescence (ML). The dissimilar behavior between these two properties is yet to be reported in literature. We observed that as the lattice strain increased, the light intensity change ratio (LICR) during an applied exogenous tensile force increased while the stress-free afterglow decreased. As the crystallite size decreased, the LICR increased while the stress-free afterglow decreased. All the aforementioned observations resulted in the introduction of a newly joint stress-free afterglow-ML mechanism where the interstitial vacancy in the SAO host lattice should be taken in consideration. Based on the trap-depth reduction model, we derived a LICR expression and predicted the current ML behavior as well for other photonic materials. The fundamental findings presented in this work will drastically change the paradigm of mechanoluminescent material design and pave the way for the full development of this technology. [ABSTRACT FROM AUTHOR]

Blue phase liquid crystal films are quite useful in reflective displays, flexible photonic devices, and optical sensors. However, the effects of refractive index properties of refilled liquid crystals and environment temperature on reflection properties of blue phase liquid crystal films are far from fully exploration. Herein, we demonstrate blue phase liquid crystal films refilled with different nematic liquid crystals. The effects of birefringence and average refractive index of refilled nematic liquid crystals on the reflection properties such as reflectance, central wavelength, and linewidth of photonic band have been studies. The temperature effect on reflectance and central wavelength has been studied. A narrow linewidth (19.4 nm) and temperature insensitivity blue phase liquid crystal film has been fabricated by refilling liquid crystals of DYX8013 with small birefringence. The narrow linewidth and excellent temperature insensitivity properties of BPLC film can be applied in color reflective display and flexible photonic devices. [ABSTRACT FROM AUTHOR]

The directed self-assembly of liquid crystal polymers enables significantly enhanced optical properties compared to conventional isotropic optical materials. The transmissive properties of these thin polymeric films have been extensively studied, but the exploration of reflective liquid crystalline polymeric materials films has received little attention due to challenges in producing large, high-quality self-assembled films. We explore here for the first time stacked polymer cholesteric liquid crystal thin films as a pathway to generate reflective diffractive optics that act on both hands of circularly polarized light independently. We present 3 unique exemplar cases with increasing design complexity to communicate the widespread potential of these unique thin polymer films. [Display omitted] • Directed self-assembly of liquid crystal polymers enables new optical physics. • Reflective geo-phase polymers require two types of directed self-assembly. • Stacked polymeric cholesteric films can generate reflective diffractive optics. • Three unique exemplar cases with increasing design complexity are presented. [ABSTRACT FROM AUTHOR]