Bio‐Derived Nanophotonic Hybrids Enabling Reconfigurable Upconversion for Multilevel Optical Encryption

ABSTRACT

Upconversion nanoparticle (UCNP)‐based optical encryption has emerged as a promising strategy for advanced cryptography owing to its covert near‐infrared (NIR) activation and tunable multicolor emission. However, most existing UCNP encryption systems rely on deterministic, synthesis‐defined spectral signatures, fundamentally limiting cryptographic complexity and post‐fabrication reconfigurability. Here, we present a reconfigurable and scalable optical encryption platform enabled by the synergistic integration of lanthanide‐doped UCNPs with a stimuli‐responsive nanophotonic platform. The nanophotonic multilayer, composed of alternating high‐refractive‐index zirconia and silk fibroin regenerated from Bombyx mori cocoons, exhibits a reversible photonic stopband shift of up to ∼115 nm upon hydration and drying. This dynamic modulation enables selective resonant coupling with multispectral anti‐Stokes emission bands of UCNPs, resulting in visually discernible emission color modulation under identical NIR excitation. As a proof of concept, spatially and spectrally patterned UCNP–nanophotonic hybrids configured as a 5‐bit barcode demonstrate scalable, multilevel optical encryption. Orthogonal activation by NIR excitation and ambient humidity generates decoy and authentic optical states that remain indistinguishable without the correct stimulus combination. This materials‐integrated nanophotonic strategy is fully compatible with established dopant‐based spectral engineering and spatial patterning techniques, offering a versatile and scalable route toward next‐generation UCNP‐based optical encryption and anticounterfeiting systems.