Thermoresponsive Lamellar Hydrogels with Tunable Turbidity, Structural Color, and Anisotropic Swelling.

We report a thermoresponsive anisotropic photonic hydrogel: poly(dodecyl glyceryl itaconate)/polyacrylamide-poly(N-isopropylacrylamide) hydrogel (PDGI/PAAm-PNIPAM hydrogel). Hydrogels with uniaxially aligned lamellar bilayers possess bright structural color and swelling anisotropy, while PNIPAM-based hydrogels exhibit distinct thermoresponsive properties around a lower critical solution temperature (LCST). Hybridization of thermoresponsive PNIPAM with the lamellar hydrogel can give the anisotropic photonic hydrogel various fascinating thermoresponsive properties, such as structural color/turbid transition, thermoresponsive structural color, and anisotropic deswelling/reswelling behavior by temperature stimuli. The temperature-induced changes in turbidity, structural color, and anisotropic swelling of the gel around the LCST can be tuned by controlling the incorporated PNIPAM density. PNIPAM can be regioselectively incorporated into the specific region of the lamellar hydrogels by photomasking during UV polymerization. The PDGI/PAAm-PNIPAM hydrogel can find diverse promising applications such as smart windows and smart displays.

Approaching Theoretical Haze of Highly Transparent All-Cellulose Composite Films.

A highly transparent cellulose film with a high built-in haze is emerging as a green photonic material for optoelectronics. Unfortunately, attaining its theoretical haze still remains a challenge. Here, we demonstrate an all-cellulose composite film with a 90.1% transmittance and a maximal transmission haze of 95.2% close to the theoretical limit (∼100%), in which the entangled network of softwood cellulose fibers works as strong light scattering sources and regenerated cellulose (RC) with undissolved fibril bundles functions as a matrix to simultaneously improve the optical transparency and transmission haze. The underlying mechanism for the ultrahigh haze is attributed to microsized irregularities in the refractive index, arising primarily from the crystalline structure of softwood fibers, undissolved nanofibril bundles in RC, and a small number of internal cavities. Moreover, the resulting composite film presents a folding resistance of over 3500 times and good water resistance, and its application in a perovskite solar cell as an advanced light management layer is demonstrated. This work sheds light on the design of a highly transparent cellulose film with a haze approaching the theoretical limit for optoelectronics and brings us a step further toward its industrial production.

Photonic Crystal Characterization of the Cuticles of Chrysina chrysargyrea and Chrysina optima Jewel Scarab Beetles.

A unified description involving structural morphology and composition, dispersion of optical constants, modeled and measured reflection spectra and photonic crystal characterization is devised. Light reflection spectra by the cuticles of scarab beetles (Chrysina chrysargyrea and Chrysina optima), measured in the wavelength range 300-1000 nm, show spectrally structured broad bands. Scanning electron microscopy analysis shows that the pitches of the twisted structures responsible for the left-handed circularly polarized reflected light change monotonically with depth through the cuticles, making it possible to obtain the explicit depth-dependence for each cuticle arrangement considered. This variation is a key aspect, and it will be introduced in the context of Berreman's formalism, which allows us to evaluate reflection spectra whose main features coincide in those displayed in measurements. Through the dispersion relation obtained from the Helmholtz's equation satisfied by the circular components of the propagating fields, the presence of a photonic band gap is established for each case considered. These band gaps depend on depth through the cuticle, and their spectral positions change with depth. This explains the presence of broad bands in the reflection spectra, and their spectral features correlate with details in the variation of the pitch with depth. The twisted structures consist of chitin nanofibrils whose optical anisotropy is not large enough so as to be approached from modeling the measured reflection spectra. The presence of a high birefringence substance embedded in the chitin matrix is required. In this sense, the presence of uric acid crystallites through the cuticle is strongly suggested by frustrated attenuated total reflection and Raman spectroscopy analysis. The complete optical modeling is performed incorporating the wavelength-dependent optical constants of chitin and uric acid.

Rapid and Energy-Saving Microwave-Assisted Solid-State Synthesis of Pr(3+)-, Eu(3+)-, or Tb(3+)-Doped Lu2O3 Persistent Luminescence Materials.

Persistent luminescence materials Lu2O3:R(3+),M (Pr,Hf(IV); Eu; or Tb,Ca(2+)) were successfully and rapidly (22 min) prepared by microwave-assisted solid-state synthesis (MASS) using a carbon microwave susceptor and H3BO3 as flux. Reaction times are reduced by up to 93% over previous synthetic methods, without special gases application and using a domestic microwave oven. All materials prepared with H3BO3 flux exhibit LuBO3 impurities that were quantified by Rietveld refinement from synchrotron radiation X-ray powder diffraction patterns. The flux does not considerably affect the crystalline structure of the C-Lu2O3, however. Scanning electron micrographs suggest low surface area when H3BO3 flux is used in the materials' synthesis, decreasing the amount of surface hydroxyl groups in Lu2O3 and improving the luminescence intensity of the phosphors. The carbon used as the susceptor generates CO gas, leading to complete reduction of Tb(IV) to Tb(3+) and partial conversion of Pr(IV) to Pr(3+) present in the Tb4O7 and Pr6O11 precursors, as indicated by X-ray absorption near-edge structure data. Persistent luminescence spectra of the materials show the red/near-IR, reddish orange, and green emission colors assigned to the 4f(n) → 4f(n) transitions characteristics of Pr(3+), Eu(3+), and Tb(3+) ions, respectively. Differences between the UV-excited and persistent luminescence spectra can be explained by the preferential persistent luminescence emission of R(3+) ion in the S6 site rather than R(3+) in the C2 site. In addition, inclusion of Hf(IV) and Ca(2+) codopants in the Lu2O3 host increases the emission intensity and duration of persistent luminescence due to generation of traps caused by charge compensation in the lattice. Photonic materials prepared by MASS with H3BO3 flux show higher persistent luminescence performance than those prepared by the ceramic method or MASS without flux. Color tuning of persistent luminescence in Lu2O3:R(3+),M provides potential applications in bioimaging as well as in solar cell sensitizers.

Organic printed photonics: From microring lasers to integrated circuits.

A photonic integrated circuit (PIC) is the optical analogy of an electronic loop in which photons are signal carriers with high transport speed and parallel processing capability. Besides the most frequently demonstrated silicon-based circuits, PICs require a variety of materials for light generation, processing, modulation, and detection. With their diversity and flexibility, organic molecular materials provide an alternative platform for photonics; however, the versatile fabrication of organic integrated circuits with the desired photonic performance remains a big challenge. The rapid development of flexible electronics has shown that a solution printing technique has considerable potential for the large-scale fabrication and integration of microsized/nanosized devices. We propose the idea of soft photonics and demonstrate the function-directed fabrication of high-quality organic photonic devices and circuits. We prepared size-tunable and reproducible polymer microring resonators on a wafer-scale transparent and flexible chip using a solution printing technique. The printed optical resonator showed a quality (Q) factor higher than 4 × 10(5), which is comparable to that of silicon-based resonators. The high material compatibility of this printed photonic chip enabled us to realize low-threshold microlasers by doping organic functional molecules into a typical photonic device. On an identical chip, this construction strategy allowed us to design a complex assembly of one-dimensional waveguide and resonator components for light signal filtering and optical storage toward the large-scale on-chip integration of microscopic photonic units. Thus, we have developed a scheme for soft photonic integration that may motivate further studies on organic photonic materials and devices.