Multi‐Component Lanthanide Halides for Multidimensional Optical Dynamic Anti‐Counterfeiting and Encryption Based on Stimulus‐Responsive Luminescence Regulation

ABSTRACT The luminescent multi‐component rare earth halides have great potential in optoelectronic applications. However, due to the complex structure and unclear structure‐property relationship, it is difficult to achieve precise luminescence regulation. Therefore, it remains challenging to ensure that the performance meets the on‐demand applications in complex scenarios. This study describes a new Tb‐Eu energy transfer systems, Cs 2 Tb 1‐x Eu x Cl 5 ·6H 2 O (X = 0–1), in which the chemical structure and luminescent color transitions are regulated via external stimuli of Lewis bases with varying strengths. Mechanistic investigation reveals that the addition or removal of CsCl units within the structural backbone modulates the donor–acceptor interionic distance, thereby tuning the energy transfer efficiency and enabling reversible switching between the characteristic green luminescence of Tb 3+ (547 nm) and red luminescence of Eu 3+ (592 / 613 nm). Finally, the Cs 2 Tb 1‐x Eu x Cl 5 ·6H 2 O (X = 0–1) was successfully applied to multilevel anti‐counterfeiting, information storage, and data encryption. These findings provide a promising strategy for the design of advanced luminescent materials with programmable optoelectronic properties.