Visible and infrared dual-band anti-counterfeiting with self-assembled photonic heterostructures

Self-assembled photonic structures have greatly expanded the paradigm of optical materials due to their ease of access, the richness of results offered and the strong interaction with light. Among them, photonic heterostructure shows unprecedent advances in exploring novel optical responses that only can be realized by interfaces or multiple components. In this work, we realize visible and infrared dual-band anti-counterfeiting using metamaterial (MM) - photonic crystal (PhC) heterostructures for the first time. Sedimentation of TiO₂ nanoparticles in horizontal mode and polystyrene (PS) microspheres in vertical mode self-assembles a van der Waals interface, connecting TiO₂ MM to PS PhC. Difference of characteristic length scales between two components support photonic bandgap engineering in the visible band, and creates a concrete interface at mid-infrared to prevent interference. Consequently, the encoded TiO₂ MM is hidden by structurally colored PS PhC and visualized either by adding refractive index matching liquid or by thermal imaging. The well-defined compatibility of optical modes and facility in interface treatments further paves the way for multifunctional photonic heterostructures.