Gold coated Cicada wings: Anti-reflective micro-environment for plasmonic enhancement of fluorescence from upconversion nanoparticles

Dual-Mode Circularly Polarized Light Emission and Metal-Enhanced Fluorescence Realized by the Luminophore-Chiral Cellulose Nanocrystal Interfaces

Circularly polarized (CP) light has attracted wide attention for its great potential in broad applications. However, it remains a challenge to generate left-handed and right-handed circularly polarized (LCP and RCP) light from cellulose nanocrystal (CNC)-based materials only with an intrinsic left-handed chiral structure, owing to the pattern of CP light emission primarily based on the chirality of materials. Herein, a separation structure of luminophore layers and chiral CNCs was provided to achieve dual-mode CP light emission by building a luminophore-chiral CNC interface. By directly exciting the back and front of two-layer films, LCP and RCP light could be easily emitted without any assisting means and specific setting angles. In addition, owing to the formation of the luminophore-chiral CNC interface, metal-enhanced fluorescence (MEF) was achieved to offset the brightness loss caused by circular polarization. By incorporating gold triangular nanoprisms in CNC chiral layers, the fluorescence enhancement of the ensemble was as high as 6.5-fold. The decisive role of the luminophore-chiral CNC interface in enhancing luminescence and dual-mode CP light emission was carefully investigated by contrasting the systems with and without luminophore-chiral CNC interfaces in this study. We believe that this dual-mode CP light emission film with MEF enables a promising approach to extending the application of CP light materials.

Broader-Band and Flexible Antireflective Films with the Window-like Structures Inspired by the Backside of Butterfly Wing Scales

Antireflective performance is critical for most optical devices, such as the efficient solar energy utilization in photovoltaic cells of an aerospace craft and optical displays of scientific precise equipment. Therein, outstanding broad-band antireflection is one of the most crucial properties for antireflection films (ARFs). Unfortunately, it is still a challenging work to realize perfect "broader-band" antireflection because both the low refractive indices materials and time-consuming nanotexturing technologies are required in the fabricating process. Even in this case, a broader-band and flexible ARF with hierarchical structures is successfully developed, which is inspired by butterfly wing scales. First, the butterfly wings surface is treated with acid and stuck on a clean glass. Now, all the scales on the wings will form a strong adhesion with the glass substrate. Then, the wings are removed and the scales are left on the glass slide. Now the backside of scales is facing outward, the backside structures of the scales are coincidentally used as the template. Finally, the structure is replicated and the ARF with a controllable thickness is successfully fabricated by rotating PDMS on the biological template. In this work, the bionic ARFs realize the transmission of nearly 90% and more than 90% in the visible light and infrared region. It enhanced transmission to 13% under standard illumination compared with flat PDMS films of the same thickness. Furthermore, the ARF is flexible enough that it could bend nearly 180° to meet the special antireflection requirements in some extreme conditions. It is expected that this bioinspired AR film could revolutionize the technologies of broader-band antireflective materials and impact numerous applications from glass displays to optoelectronic devices.

Reversibly Erasable Broadband Omnidirectional Antireflection Coatings Inspired by Inclined Conical Structures on Blue-Tailed Forest Hawk Dragonfly Wings

Blue-tailed forest hawk dragonfly (Orthetrum triangulare) wings, covered with inclined conical structures, are studied for their high transparency and low reflectance for large viewing angles. However, limited by existing technologies, the exquisite inclined structures are not replicated easily or applied adequately. Here, we combine a shear-induced self-assembly approach and a colloidal lithography technology to create omnidirectional antireflection structures that are inspired by dragonfly wings. Nonclose-packed colloid crystals are spin-coated and serve as structural templates in a plasma etching procedure to pattern subwavelength inclined conical structures directly on shape memory polymer-coated substrates. The dependence of the antireflection functionality on the shape and inclination of conical structures is systematically investigated in this research. Compared with a featureless substrate, the structure-covered substrate can display an approximately 8% higher average transmittance in the visible wavelength range at normal incidence and even approximately 23% higher average transmittance as the incident angle increases to 75°. Moreover, the reconfigurable structures composed of shape memory polymers can be repeatedly deformed and recovered as a result of external stimuli at ambient conditions, and the corresponding broadband omnidirectional antireflection functionality is therefore reversibly erased and restored.