Wavelength‐Multiplexed PUFs Through Single‐Host Multicolor Switching in Cs ₂ NaTbCl ₆ : Eu ³⁺ Double Perovskites

ABSTRACT Physical unclonable functions (PUFs) based on multi‐wavelength emission hold significant promise for advancing high‐capacity hardware security by harnessing intrinsic physical randomness. However, achieving spectrally isolated multi‐channel emission within a single matrix remains a daunting challenge. Herein, we demonstrate a single matrix platform using Cs 2 NaTbCl 6 : Eu 3+ double perovskite that enables excitation‐programmable multicolor switching through orthogonal optical activation of Tb 3+ and Eu 3+ centers. This monolithic system exhibits dominant green emission (Tb 3+ : 5 D 4 → 7 F 5, 6 ) under 275 nm excitation, while selective red emission (Eu 3+ : 5 D 0 → 7 F 1, 2 ) under 310 nm excitation, and distinct yellow emission under 275/310 nm co‐stimulation. This unique behavior arises from well‐separated excitation pathways, weak interionic interactions, and suppressed concentration quenching via the large Spacing of rare earth ions and low phonon energy. Leveraging this unique single‐host multiplexing capability, we develop a wavelength‐division multiplexing PUF (WDM‐PUF) featuring simplified information carriers, unprecedented encoding dimensions, and a near‐zero false negative rate through RGY/octal spectral‐channel encoding. Its flexible encoding method and operational simplicity enable its application in color image encryption and programmable information transmission, along with smartphone‐compatible authentication functionality. Our work establishes a new paradigm in optical encryption with wavelength‐multiplexed capacity in a single emissive platform, opening avenues for ultra‐secure anti‐counterfeiting technologies.