Dual-mode photonic crystal films with enhanced fluorescent emission from slow photon effect for coding-decoding and anti-counterfeiting applications

The design and fabrication of photonic crystals with multiple optical states are significant and urgently desired. However, most conventional photonic crystals with scalable potential display only a single structural color mode, limiting their practical application. Herein, we successfully achieved a new type of dual-mode photonic crystal films through the co-assembly of polymer colloidal core@shell nanoparticles and InP@ZnS quantum dots at room temperature. The co-assembly process was completed with high efficiency by a powerful assembly technique called molecule-mediated shearing-induced assembly technique (MSAT). The obtained dual-mode photonic crystal films possessed two distinct optical states, including a structural color mode and a fluorescent color mode. The advantages of both photonic band gaps and fluorescence emission were synchronously integrated, exhibiting bright structural colors and vibrant fluorescent colors under sunlight irradiation and ultraviolet excitation, respectively. The switch of the two optical states was highly reversible and stable. Besides, we also found that the dual-mode photonic crystal films realized enhanced fluorescent emission from the slow photon effect, and the relationship between the fluorescence enhancement effect and order degrees of dual-mode PC films was studied. Finally, the dual-mode photonic crystal films were employed to design a visual coding-decoding system, and also as raw materials to produce anti-counterfeiting photonic paints. All the experiments provided a novel insight for achieving multiple optical states within a single system, creating opportunities for extending the application of photonic crystals in the realm of information storage, anti-counterfeiting, response materials, and pattern display.