Ultrafast and Multicolor Luminescence Switching in a Lanthanide-Based Hydrochromic Perovskite

Hydrochromic materials characterized by noticeable color change upon water exposure have attracted pervasive attention for their frontier applications in sensing and information technologies. However, existing hydrochromic materials typically suffer from a slow hydrochromic response as well as limited stability and color tunability. This work describes a novel hydrochromic perovskite crystal composed of zero-dimensional Cs₃TbF₆:Eu³⁺, which displays switchable luminescence due to the constituent Tb³⁺ and Eu³⁺ ions. Mechanistic investigation reveals that the hydrochromic property stems from a water-induced phase transformation into a one-dimensional structure through a CsF-stripping process. The phase transformation triggers energy coupling between Tb³⁺ and Eu³⁺ ions in adjacent lanthanide halide polyhedra, resulting in an emission color change from green to orange. Notably, the phase transformation is ultrafast (20 ms) and reversible, and the emission color in each phase can be fine-tuned by controlling the Eu³⁺ doping concentration along with Y³⁺ co-doping. The advances in these hydrochromic luminescent materials offer exciting opportunities for information security and data storage.