High‐Temperature Afterglow Color Tuning via Förster Resonance Energy Transfer

Persistent luminescence materials (LPMs) are attractive for sensing, anti-counterfeiting, and bioimaging owing to their long afterglow. However, their performance suffers from thermal quenching at high temperatures. While inorganic matrices like boric acid provide rigidity to suppress molecular vibrations, their high-temperature processing hinders organic dopant incorporation and color control. Here, we report a strategy combining a low-temperature processed boric acid matrix with triplet-to-singlet Förster resonance energy transfer (FRET) to achieve high-temperature LPMs with tunable colors. Doping triphenylboronic acid (TPBA) into boric acid and heating at 120°C for 4 h forms a crystalline metaborate network that confines TPBA, giving a phosphorescence lifetime up to 2.56 s at 460 K. This framework suppresses vibrational loss and enables stable triplet exciton capture/release even at elevated temperatures. Adding Rhodamine 6G as an acceptor establishes efficient FRET from blue-green phosphorescence to red fluorescence. The afterglow color can be precisely tuned by varying acceptor concentration or temperature, leveraging their distinct quenching rates. This mild synthesis avoids dopant decomposition, expands organic-inorganic hybrid FRET systems, and provides a simple route to thermally stable, multicolor LPMs.