Low-Angle-Dependent Anticounterfeiting Label Decoded by Alcohol Tissue Wiping Based on a Multilayer Photonic Crystal Structure

The application of photonic crystals (PCs) as anticounterfeiting materials has been widely investigated because of their tunable photonic stop band and corresponding changeable structural colors. In this work, we designed a composite PC structure including an information CdS PC layer at the bottom and a polymer-based layer composed of an inverse opal PC (IOPC) layer and a disordered porous layer on the top, which can be decoded by an alcohol tissue. The high refractive index of the bottom patterned CdS PC layer provides the structure with a vivid low-angle-dependent structural color in the decoded mode, which ensures the stability of the information conveyed by this label. When the incident angle changed from 5 to 45°, the structural color of the patterned CdS layer changed slightly. In the hidden mode, the low transmittance shields the structural color of the CdS layer. When the structure was wiped with the alcohol tissue, the transmittance of the upper IOPC layer could be increased quickly due to the similar refractive indexes of the used polymer and alcohol, and the pattern of the CdS layer was decoded. Thus, the designed composite PC can act as an anticounterfeiting label, in which the encrypted pattern can be decoded by alcohol tissue wiping and shows a vivid low-angle-dependent structural color. To enhance the anticounterfeiting ability of the designed structure, a double-sided label with different encryption patterns on both sides was designed. Based on the simple reversible encryption and decryption process as well as the color stability, the label shows great application potential in the daily anticounterfeiting field.