Multiband Optical Physical Unclonable Functions Based on Mixed‐Phase Multilevel Emissive Perovskites

Physical unclonable functions (PUFs) are hardware-based security primitives that exploit intrinsic physical randomness in materials or devices to prevent counterfeiting and enhance authentication across diverse applications. Among various sources of randomness, the optical signatures of luminescent materials represent a particularly robust and easily distinguishable feature. However, many optical PUF systems rely on environmentally hazardous materials or energy-intensive fabrication processes while remaining vulnerable to counterfeiting due to deterministic and spectrally fixed emission characteristics. Here, we demonstrate sustainable multiband optical PUFs by forming heterostructures between lead-free phase-mixed perovskites and cellulose fibers via a water-assisted drop-casting process. Cesium manganese bromide perovskites provide an environmentally benign composition while exhibiting excitation-dependent multilevel photophysical responses arising from mixed-phase interactions. By leveraging these excitation-dependent multilevel emission characteristics, we construct strong PUFs that significantly expand the challenge and response pairs from a single device through controlled optical feature extraction of the perovskites and the spatial randomness of cellulose fibers. Moreover, the multiband optical PUF platform is demonstrated for image encryption/decryption as well as currency authentication. These results establish an environmentally responsible optical PUF platform that combines sustainable materials and fabrication processes with distinctive photophysical characteristics for next-generation hardware security technologies.