Scalable Design Principle of Anti-Counterfeiting System Based on Dynamic Structural Color Change and Phase Change of Upconversion Nanocrystals

In this presentation, we introduce novel optical anti-counterfeiting systems based on the structural color and upconversion nanocrystals (UCNs) using maskless lithography. To realize the optical signal changes that respond when exposed to the external environment perturbations (e.g., humidity, temperature), we utilized the three-dimensional refractive index change and crystal phase transition of UCNs. In the case of structural color-based system, various structural colors change and holographic patterns were expressed when introduced LCST and hygroscopic material through the volumetric change of hydrogel microstructures. We also introduce a 130-fold enhancement in the luminescence intensity change of UCNs when exposed to extreme thermal conditions above 900 oC. These approaches provide the design principle of scalable anti-counterfeiting systems that overcomes the limitations of conventional anti-counterfeiting systems