Full-spectrum hydrochromic upconversion switching via dimensional reconstruction for temporal optical multiplexing

Achieving dynamically switchable multicolor luminescence within a single material platform is crucial for next-generation applications in encryption, storage, anti-counterfeiting, and sensing. Hydrochromic materials, which change emission color upon exposure to water, hold particular promise for such applications. However, their development has been constrained by a predominant reliance on downshifting (Stokes) luminescence and narrow spectral tunability. Herein, we report a water-responsive phase-transition platform (0D Rb 3 LuF 6 -to-3D RbLu 2 F 7 ) that enables hydrochromic upconversion luminescence (UCL) with multicolor tunability across a broad spectral range (450–700 nm). Water-triggered dimensional reconstruction of the lanthanide sublattice universally amplifies energy-exchange interactions between Yb 3+ sensitizer and various activators (Tm 3+ , Ho 3+ , Er 3+ , Tb 3+ , Eu 3+ ), enabling distinct emission color switching. Furthermore, lattice fine-tuning on this platform can actively switch the underlying upconversion mechanism from the prevalent energy transfer upconversion (ETU) to the less common cooperative sensitization upconversion (CSU), thereby enabling controllable single-to-multicolor luminescence switching by generating distinct emission profiles within a single material. This work deepens the mechanistic understanding of upconversion modulation and establishes a versatile platform for advanced applications in multi-level encryption and multi-dimensional information storage.