Reproducible Pressure-Sensitive Fluorescence Switch for Anti-Counterfeiting and Information Encryption.

Abstract

Pressure-responsive smart materials with rapid response capabilities are promising candidates for sensing and information security. Here, a reversibly operable photoluminescence on-off switch activated by external pressure is first achieved in metal halide Cs3MnBr5 nanocrystals (NCs). The triggered pressure is as low as 0.43 GPa that can be easily accessible through manual squeeze. First-principles calculations reveal that the approaching [MnBr4] tetrahedral units with off-centering distortion facilitate cross-relaxation, energy migration and trap states activation, ultimately quenching the luminescence. Meanwhile, the all-inorganic and rigid framework of Cs3MnBr5 NCs contributes significantly to their stability after undergoing pressure cycles. Such reversible low-pressure-caused quenching (RLPCQ) enables the photoluminescence (PL) decay of butterfly patterns created with Cs3MnBr5 NCs to undergo darkening and recovery in response to manual pressing and release. Through the introduction of softer materials, a slight force applied at a specific point can induce a localized PL to monitor the pressure gradient within the film fabricated from Cs3MnBr5 NCs. Furthermore, Morse code information carried by Cs3MnBr5 NCs can remain concealed beneath a green luminescent substrate under normal pressure, but will become distinctly visible when subjected to artificial pressing. The work represents a significant breakthrough to intelligent materials design for applications in anti-counterfeiting, pressure alarm, and information encryption.