Reversible Thermotropic Energy‐Transfer Dual‐Mode Luminescence in Perovskite Nanocrystals for Advanced Dynamic Anti‐Counterfeiting Applications

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The intrinsic instability of metal halide perovskites (MHPs) renders them highly susceptible to environmental factors, thereby posing significant challenges for their broad application. However, this sensitivity also imparts unique properties that are particularly advantageous for anti‐counterfeiting applications. Herein, blue and green dual‐mode luminescent CsPbBr₃ nanocrystals are devised by employing a confined growth strategy. By employing in situ growth within molecular sieves (MS), composite CsPbBr₃@MS@CsPbBr₃/Cs₄PbBr₆ nanocrystals are synthesized with a blue strongly‐confined core and a green shell structure. Leveraging the phonon disturbance effect, these nanocrystals exhibit a reversible thermotropic emission color transition between blue and green over a wide temperature range of −196–100 °C. This transition is attributed to the reversible variation in energy transfer (ET) efficiency between the dual‐mode nanocrystals. Notably, the thermal sensitivity of the fluorescence intensity ratio (FIR) at I₅₂₅nm/I₄₆₀nm reaches 0.19 K⁻¹ at 100 °C, which is significantly higher than that of traditional rare‐earth fluorescent thermosensitive materials. This remarkable thermal sensitivity highlights their high responsiveness to temperature changes. Nanocrystal labels are further fabricated that display reversible temperature‐driven spectral transitions, enabling dynamic anti‐counterfeiting functionality. This innovative approach offers a novel concept for the design of dual‐mode luminescent materials and dynamic anti‐counterfeiting devices.