Transparent Encryption of Nanostructured Photonic Patterns by Erasing the Structural Colors of Visible Patterns: Implications for Anti-Counterfeiting and Information Encryption Applications

Simple but efficient encryption of photonic crystals (PCs) with tunable optical properties is highly desired for information encryption and anti-counterfeiting. Here, a transparent encryption strategy was developed by fabricating nanostructured PC patterns with encrypted colors based on combining ordered and disordered porous photonic crystals (OPPCs and DPPCs). The OPPCs with collapsed long-range orders and DPPCs with collapsed disorders were prepared by similar self-assembly and etching processes except for the different volume fractions of colloids (silica). Under the dry state, PC patterns are highly transparent and encrypted due to the lack of ordered nanostructures of both OPPCs and DPPCs. In contrast, once soaked in solvents, the PC patterns with tunable colors will appear due to the selective recovery of the structural color from OPPCs. In addition, the structural color and color saturation can be adjusted by solvents and alcohol, respectively. This work provides a simple, efficient, and convenient way to encrypt PC with transparent and invisible characteristics and will facilitate their applications in camouflage, information encryption, and anti-counterfeiting.