Cesium Alloying-Enhanced Stimuli-Responsive Photoluminescence in CsxRb2–xMnBr4(H2O)2 for Information Encryption

Metal halide perovskites (MHPs) with stimuli-responsive photoluminescence (PL) have attracted widespread attention for their application in optical encryption. However, existing metal halide perovskites typically exhibit a monochromatic PL emission and response to a single stimulus. As a result, they show limited encryption security. Therefore, it is crucial to develop a strategy to transition from single-stimulus responsive materials to multistimuli responsive ones. Herein, for the first time, we reported a strategy through cation alloying to form CsxRb2–xMnBr4(H2O)2 with multistimuli responsive PL. A continuous PL color change of CsxRb2–xMnBr4(H2O)2 was achieved from nonluminous, red and green light emissions with temperature, which is attributed to the chemical transformation from CsxRb2–xMnBr4(H2O)2 to Rb2MnBr4, RbMnBr3, Rb3MnBr5, and Cs3MnBr5. More importantly, Cs+ alloying can enable the chemical transformation from CsxRb2–xMnBr4(H2O)2 to RbMnBr3, Cs3MnBr5, and Rb3MnBr5 in isopropanol accompanied by PL change from red to green. Furthermore, such a chemical transformation of CsxRb2–xMnBr4(H2O)2 can also be triggered by water. These results highlight Cs alloying as a unique strategy to expand the multistimuli responsive PL modes of MHPs. Our findings present a straightforward approach for designing multistimuli responsive materials with potential applications in information storage, anticounterfeit labeling, and information security.