Tristate Photonic Crystal Film with Structural, Fluorescent, and Up-Conversion Luminescent Color for Multilevel Anticounterfeiting.

Counterfeit items are growing worldwide, affecting the global economy and human health. Anticounterfeiting tags based on a physical microstructure or chemical materials have enjoyed long-term commercial success due to their visualization and inexpensive production. However, conventional anticounterfeiting tags can be readily imitated. Herein, we have overcome this limitation by assembling colloidal nanospheres and two luminescent micromaterials into a composited photonic crystal (PhC) and achieved massive scale-up fabrication of multilevel anticounterfeiting PhC films in just several minutes of thermal rolling. The fabricated PhC film exhibits three optical states, including angle-dependent structural color (reflectivity = 66%) under white light, emits green light under 980 nm light, and emits red light under ultraviolet light. Multilevel anticounterfeiting colorful images were obtained by further use of masking templates, which integrate colors from both physically colored microstructures and chemical luminescent materials. Besides, the thermal-rolling process also shows excellent feasibility for assembling microunits with different sizes into high-quality functional PhC films.

A Directional Chitosan Sound Sensor Based on Piezoelectric-Triboelectric Sensing.

Herein, we have constructed a directional sound sensor based on an anisotropic chitosan aerogel. Because of the lamellar porous structure, this chitosan aerogel exhibits a distinct anisotropic behavior, featuring the compressive stress along the direction of the parallel laminate structure, being approximately 2.6 times that in the orthogonal direction. Simultaneously, the chitosan aerogel is used as a directional sound-sensing material, which exhibits excellent acoustic-electric conversion performance with a marked difference in the direction perpendicular to the laminate structure than in the parallel direction. The CSANG has an optimum electrical output of 66 V and 9.2 µA under a sound stimulation of 150 Hz and 120 dB in the orthogonal direction of the laminate structure. Therefore, this directional chitosan sound sensor with excellent biocompatibility and sound sensitivity demonstrates promising application potential in the field of intelligent sensing and artificial cochlea.