Stimulus‐Responsive Photonic Crystals for Advanced Security

Abstract

Counterfeiting is a growing global issue causing severe negative impacts on the social economy and posing serious security threats to individuals and communities. However, the current anticounterfeiting technologies are relatively well known to fakers and lack sufficient security owing to the development and commercialization of high‐resolution equipment. Thus, designing new anticounterfeiting materials and systems is urgently needed. Photonic crystals (PCs) with vivid structural colors are promising materials for advanced security applications because of their unique optical characteristics. In particular, responsive PCs (RPCs), whose optical signals can be readily adjusted by external stimuli, are expected to provide improved security and may be used to determine the authenticity of banknotes, documents, and drugs. In this review, the strategies are summarized for designing RPCs, including filling responsive materials into the interstitial space of periodic photonic structures and using responsive materials as construction blocks of PCs. Subsequently, the latest progress in developing RPCs constructed for optical encryption and information security is discussed in detail. Finally, the challenges and outlook of using RPCs for optical encryption technologies are presented.

Preparation and Characterization of Degradable Cellulose−Based Paper with Superhydrophobic, Antibacterial, and Barrier Properties for Food Packaging

“…Solution II was sprayed on the coating paper to yield a superhydrophobic surface. During the spraying process, the synthesized superhydrophobic solution was uniformly coated on the surface of the paper samples using a spray gun with an air pressure of 30 psi from 30 cm [ 49 ]. The freshly coated surface was then dried at 60 °C for 5 min.…”

Fabrication of Pt cluster-loaded In2O3 inverse opal photonic crystals for fast and highly sensitive ethanol sensing

“…1 Because of their excellent ability to regulate the propagation of light, PCs have been widely studied in recent years. 2–4 Inverse opal photonic crystals (IOPCs), prepared by using precursor-filled opal PCs and template removal, show a three-dimensional ordered macroporous structure and extremely high porosity (as much as about 74% theoretically). 5 Due to the convenience, cost-effectiveness, and versatility of fabrication, a variety of IOPC materials have been synthesized in recent years, including metals, 6 metal oxides, 7 polymers, 8 hydrogels, 9 metal–organic frameworks (MOFs), 10 and carbon materials.…”

Bioinspired Dynamic Camouflage in Programmable Thermochromic‐Patterned Photonic Films for Sophisticated Anti‐Counterfeiting

“…[ 5 ] However, this single color change type can no longer meet the requirement as increasing attention to information security. [ 6 ] The photonic films were expected to carry encrypted information by changeable patterning. [ 7 ] On the one hand, the pattern should blend into the background, similar to the camouflage colors of many animals, such as zebras, stick insects, and so on.…”