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

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 Cs₂NaTbCl₆: Eu³⁺ double perovskite that enables excitation-programmable multicolor switching through orthogonal optical activation of Tb³⁺ and Eu³⁺ centers. This monolithic system exhibits dominant green emission (Tb³⁺: ⁵D₄→⁷F_{5, 6}) under 275 nm excitation, while selective red emission (Eu³⁺: ⁵D₀→⁷F_{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.