Cesium Alloying-Enhanced Stimuli-Responsive Photoluminescence in Cs_xRb_2–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 Cs x Rb 2– x MnBr 4 (H 2 O) 2 with multistimuli responsive PL. A continuous PL color change of Cs x Rb 2– x MnBr 4 (H 2 O) 2 was achieved from nonluminous, red and green light emissions with temperature, which is attributed to the chemical transformation from Cs x Rb 2– x MnBr 4 (H 2 O) 2 to Rb 2 MnBr 4, RbMnBr 3, Rb 3 MnBr 5, and Cs 3 MnBr 5 . More importantly, Cs + alloying can enable the chemical transformation from Cs x Rb 2– x MnBr 4 (H 2 O) 2 to RbMnBr 3, Cs 3 MnBr 5, and Rb 3 MnBr 5 in isopropanol accompanied by PL change from red to green. Furthermore, such a chemical transformation of Cs x Rb 2– x MnBr 4 (H 2 O) 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.