As contamination and environmental degradation increase nowadays, there is a huge demand for new eco-friendly materials. Despite its use for thousands of years, cellulose and its derivatives have gained renewed interest as favourable alternatives to conventional plastics, due to their abundance and lower environmental impact. We report the fabrication of photonic and plasmonic structures by moulding hydroxypropyl cellulose into sub-micrometric periodic lattices, using soft lithography. This is an alternative way to achieve structural colour in this material which is usually obtained exploiting its chiral nematic phase. Cellulose based photonic crystals are biocompatible and can be dissolved in water or not depending on the derivative employed. Patterned cellulose membranes exhibit tuneable colours and may be used to boost the photoluminescence of a host organic dye. Furthermore, we show how metal coating these cellulose photonic architectures leads to plasmonic crystals with excellent optical properties acting as disposable surface enhanced Raman spectroscopy substrates.

516 wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.depreparation of compression sensitive inverse opals which allow the mechanical tuning of the photonic stopgap position. [ 18 ] Elastomers have also played a fundamental role for studying color tunable photonic crystals (PCs), [ 19,20 ] whose lattice parameter might be controlled by deformation (mechanochromic effect) or elastomer swelling. [ 21 ] An equivalent approach was proposed for the development of tunable phononic crystals. [ 22 ] Another active area of research concerns fl exible systems implemented, for instance, as UV-fi lters [ 23 ] and light emitting diodes or displays. [ 24 ] The present work addresses the fabrication of periodic nanofeatures with SME by using a replica molding approach for imprinting a 2D photonic nanostructure on the surface of a shape-memory elastomer. Structural and optical characterization of the as-produced system allowed to demonstrate its shape-memory functionality for confi guring the lattice parameter or erasing the nanopattern. This property might be very attractive, for example, for the development of reusable or self-healing photonic elements with adaptive properties.Polydiolcitrates (PDCs), fi rst described by Ameer and colleagues in 2004, [ 25 ] have been recently identifi ed as thermoresponsive elastomers presenting SME. [ 26 ] However, as far as we know, their applicability in the accomplishment of photonic nanostructured systems has not been reported in the literature yet. The synthesized polyester networks were obtained upon:(1) increase of the mol ratio of hydroxyl to carboxyl groups in the reaction mixture (4:3 in hydroxyl-dominant PDCs versus 1:1 in the original ones) and (2) the use of a more hydrophobic diol (e.g., 1,12-dodecanediol, DD). These polymers include covalent netpoints responsible for the permanent shape and hydrophobic micro-domains (either pre-polymer or DD-rich domains) physically cross-linked by intermolecular hydrophobic interactions as switch structures to fi x the temporary shape. To investigate the SME of these polymers for potential photonic applications, we followed the general procedure depicted in Figure 1 . The fi rst step consisted of the synthesis of the pre-polymer solution composed of DD and citric acid. 1 H nuclear magnetic resonance ( 1 H-NMR) confi rmed the mol ratio expected for both components (1.5) and the beginning of the condensation reaction (e.g., multiplicity of peaks at 2.6-2.9 ppm) (see Supporting Information (SI), Figure S7). Nanopatterning of the elastomer surface was achieved by using an approach inspired in soft-lithography [ 27 ] and, more specifi cally, in replica molding (Figure 1 a). [ 28,29 ] Briefl y, the pre-polymer solution was spread over the template, in our case a colloidal monolayer composed of polystyrene (PS) spheres of 870 nm in diameter ( d ). After curing at 90 °C for 12 h, the resulting cross-linked poly mer (PDDC-HD) was peeled off from the monolayer. When evaluating the cross-linking degree of the so-produced elast...

Bio-polymer based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties. In this composite, CNCs provide an intense structural coloration and improve the overall mechanical cohesion, while the elastomer drastically reduces the intrinsic brittleness of the photonic cellulose film and enables the shape memory effect. The fabricated samples are characterized by polarized optical microscopy, scanning electron microscopy and thermomechanical programming. The obtained results demonstrate that this hybrid material retains its chiral nematic structure and performs shape recovery in thermomechanical experiments thus widening the functionality of the independent components. Keywords cellulose nanocrystals; cholesteric; polydiolcitrates; shape memory; biomimetic Plastics are key materials in many aspects of daily life, ranging from packaging, to construction, to medical applications. The replacement of conventional plastics with biocompatible and biodegradable ones enables to exploit the versatility of polymeric materials with the advantage of using sustainable fabrication approaches. Within this context, photonic materials produced by self-assembly of biopolymers are receiving growing interest in the materials community.1-3 Many photonic structures with diverse optical responses have been produced using a large variety of biomaterials and fabrication methods. *Corresponding Authors: C.L.: c.lopez@csic.es; S.V.: sv319@cam.ac.uk. 1 Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Científicas, Carrer dels Til·lers S/N, Campus de la UAB, 08193 Bellaterra, Barcelona, Spain. Author ContributionsThe manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts 4-6 However, there are limitations on the different functionalities that can be achieved using only sustainable and biocompatible polymers. As an example, cellulose-based photonic structures can provide strong, intense colorations but they are generally very brittle.7 The addition of organic and inorganic matrices to such cellulose structures improves their mechanical properties but either comports the loss of the photonic effect or reduces the fully biocompatibility of the final composite.8Here we present a hybrid cellulose-based photonic structure exhibiting shape memory, fabricated by combining cellulose nanocrystals (CNCs) photonic films with a polydiolcitrate elastomer.9 In particular, we directly impregnate and embed colored CNC films with hydroxyl-dominant poly(dodecanediol-co-citrate) (PDDC-HD).10 The CNCs contribute both to the structural coloration of the film and to its overall mechanical cohesion, while the PDDC-HD provides both flexibil...

Luminescent defects in hexagonal boron nitride (h-BN) have recently emerged as a promising platform for non-classical light emission. On-chip solutions, however, require techniques for controllable in-situ manipulation of quantum light. Here, we demonstrate the dynamic spectral and temporal tuning of the optical emission from h-BN via moving acoustomechanical modulation induced by stimulated phonons. When perturbed by the propagating acoustic phonon, the optically probed radiative h-BN defects are periodically strained and their sharp emission lines are modulated by the deformation potential coupling. This results in an acoustically driven spectral tuning within a 2.5-meV bandwidth. Our findings, supported by first-principles theoretical calculations, reveal exceptionally high elasto-optic coupling in h-BN of~50 meV/%. Temporal control of the emitted photons is achieved by combining the acoustically mediated fine-spectral tuning with spectral detection filtering. This study opens the door to the use of sound for scalable integration of h-BN emitters in nanophotonic and quantum information technologies.

A method to produce photonic glasses (disordered dielectric structures built from monodisperse spheres) composed of silica is discussed. This method is capable of dispensing samples in a few minutes with the help of a uniaxial press. An analytical model that accounts for the most relevant features and explains how Mie scattering is the leading phenomenon is developed.

Although enormous advances are accomplished using shape memory polymers (SMPs) and their derived composites, the application of these media in optics and photonics is still restricted to a few systems. The present work addresses the fabrication and characterization of novel composites based on polydiolcitrates doped with titania nanoparticles, aiming at expanding the capabilities of the original elastomer. They constitute advanced photonic white paints, which incorporate the shape memory effect as an additional functionality. In these materials, light propagation is diffusive and it is possible to tailor its transport mean free path by acting on the titania fillers concentration. Optical gain is introduced by additionally doping the composites with organic dyes. This allows the shape recovery process to be monitored by luminescence and, conversely, the composites can perform as configurable shape active media. Their application in nonresonant feedback random lasers is demonstrated by systematic photoluminescence studies. The threshold for stimulated emission is shown to depend on both the fillers and dye concentrations. The so‐obtained multifunctional composites are promising candidates for establishing synergies between applications from the domain of SMPs with those typically restricted to random photonic media, leading to novel self‐reporting sensors/actuators or responsive illumination devices, for example.

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly (in which a silica precursor, tetraethyl orthosilicate (TEOS), is added to the base colloid) with confined growth in a wedge-shaped cell, while profiting from the advantages of both techniques. Using this method, it is possible to fabricate the composite monolayer in a single growth step. A systematic study of the influence of TEOS concentration in the initial colloid was performed in order to improve the quality of the two-dimensional crystals produced. Thus, it was demonstrated that the two methods are compatible. Furthermore, the composites were then subjected to thermal treatment so that the polymer is removed to reveal the inverse structure. After the calcination the membranes still present very good quality and so the proposed approach is effective for the fabrication of porous membranes. A comparison of reflectance spectra, between composite monolayers fabricated using this method and composites achieved by infiltrating polystyrene bare opals with silica chemical vapor deposition, is also established. The procedure presented is expected to establish the route for an easier and quicker fabrication of inverse monolayers of high refractive index materials with applications in light control.

Inspired by geometrically frustrated magnetic systems, we present the optical response of three cases of hexagonal lattices of plasmonic nanoelements. All of them were designed using a metal-insulator-metal configuration to enhance absorption of light, with elements in close proximity to exploit near-field coupling, and with triangular symmetry to induce frustration of the dipolar polarization in the gaps between neighboring structures. Both simulations and experimental results demonstrate that these systems behave as perfect absorbers in the visible and/or the near infrared. Besides, the numerical study of the time evolution shows that they exhibit a relatively extended time response over which the system fluctuates between localized and collective modes. It is of particular interest the echoed excitation of surface lattice resonance modes, which are still present at long times because of the geometric frustration inherent to the triangular lattice. It is worth noting that the excitation of collective modes is also enhanced in other types of arrays where dipolar excitations of the nanoelements are hampered by the symmetry of the array. However, we would like to emphasize that the enhancement in triangular arrays can be significantly larger because of the inherent geometric incompatibility of dipolar excitations and three-fold symmetry axes.