Vivid structural colors from long-range ordered and carbon-integrated colloidal photonic crystals

Bio-Inspired Highly Brilliant Structural Colors and Derived Photonic Superstructures for Information Encryption and Fluorescence Enhancement

Inspired by the brilliant and tunable structural colors based on the large refractive index contrast (Δn) and non-close-packing structures of chameleon skins, ZnS-silica photonic crystals (PCs) with highly saturated and adjustable colors are fabricated. Due to the large Δn and non-close-packing structure, ZnS-silica PCs show 1) intense reflectance (maximal: 90%), wide photonic bandgaps, and large peak areas, 2.6-7.6, 1.6, and 4.0 times higher than those of silica PCs, respectively; 2) tunable colors by simply adjusting the volume fraction of particles with the same size, more convenient than the conventional way of altering particle sizes; and 3) a relatively low threshold of PC's thickness (57 µm) possessing maximal reflectance compared to that (>200 µm) of the silica PCs. Benefiting from the core-shell structure of the particles, various derived photonic superstructures are fabricated by co-assembling ZnS-silica and silica particles into PCs or by selectively etching silica or ZnS of ZnS-silica/silica and ZnS-silica PCs. A new information encryption technique is developed based on the unique reversible "disorder-order" switch of water-responsive photonic superstructures. Additionally, ZnS-silica PCs are ideal candidates for enhancing fluorescence (approximately tenfold), approximately six times higher than that of silica PC.

Artificial Chameleon Skin with Super-Sensitive Thermal and Mechanochromic Response

Both the nonclose-packed structure and the large refractive index contrast of guanine nanocrystals and cytosols in iridophores play a vital role in the dynamic camouflage of chameleons, including the bright skin color and color tuning sensitivity to external stimulus. Here, the nonclose-packed photonic crystals consisting of ZnS nanospheres and polymers, which have similar refractive indices with guanine nanocrystals and cytosols, respectively, are constructed by a two-step filling strategy. ZnS@SiO₂ nanospheres are self-assembled to build intermediate close-packed photonic crystals followed by filling polymers in their interstices. The nonclose-packed photonic crystal is successfully achieved when the silica portion is etched by HF solution and refilled by polymers. Excitingly, the stimulus response of the designed photonic crystal is as sensitive as the skin of chameleons due to the similar contrast of refractive indices and nonclose-packed structure. The reflection peak of the structure can blue-shift more than 200 nm as the temperature increases from 30 to 55 °C or under 20% compressional strain. This work not only builds the nonclose-packed photonic crystals by introducing a two-step filling strategy but also proves that high refractive contrast in photonic crystals is an effective strategy to achieve ultrasensitivity, which is highly desirable for various applications.

Internal nanocavity based high-resolution and stable structural colours fabricated by laser printing

Bioinspired structural colors are attracting increasing attention in photonics, display, labeling and so forth. High-resolution and stable coloration is significant but is challenging to be fabricated in a facile and low-cost way. Herein, multilayer architecture containing an internal nanocavity as the structural color unit is obtained conveniently by direct nanosecond laser printing in atmosphere condition. Arbitrary colorful patterns with submicron accuracy can be realized only by a single step. And such structural colors induced by inner structures in the interlayer are antipollutive, antioxidative and easy to clean.