Se4+-Doped Indium-Based Perovskites via NaCl-Driven Structural Transformation for Dynamic Luminescence Modulation in Multimodal Anti-counterfeiting and Encryption

The growing risks of counterfeiting and information security breaches have spurred the demand for high-security stimuli-responsive optical materials. However, many reported materials exhibit discontinuous luminescence switching or require harsh external stimuli. Herein, we report a facile luminescence modulation strategy for indium-based perovskites by employing Se4+ as an efficient luminescent modulator, which enables continuous color evolution via a mild NaCl-triggered 0D-to-3D phase transition. During this phase transition, the Se4+-doped Cs2InCl5·H2O converts to the Cs2NaInCl6 phase, accompanied by emission color evolution from orange-red to green. This optical evolution stems from the altered local coordination environment of Se4+ dopants, which modulates the formation and emission energy of self-trapped excitons (STEs). For practical applications, the as-prepared functional ink is fabricated into patterned films via screen printing to realize dynamic anti-counterfeiting with tunable emission colors and response kinetics by adjusting NaCl concentration and temperature. Furthermore, a multi-level optical encryption design enables three-stage information readout through sequential stimuli. This work establishes a mild, phase-transition-driven luminescence evolution approach for indium-based perovskites, providing a versatile platform with continuous dynamic color evolution for advanced anti-counterfeiting and information encryption.