Thermal Modulation of Exciton Recombination for High‐Temperature Ultra‐Long Afterglow

Developing smart materials with tunable high‐temperature afterglow (HTA) luminescence remains a formidable challenge. This study presents a metal‐free doping system using boric acid as matrix and polycyclic aromatic hydrocarbons as dopants. This composition achieves dynamically tunable afterglow combining a bright blue HTA lasting for over ten seconds even at 150°C and an ultra‐long yellow room‐temperature phosphorescence below 110°C. The observed HTA is attributed to the thermally released exciton recombination within the dopant molecules, which shows excellent temperature tolerance compared to traditional triplet related phosphorescence and thermally activated delayed fluorescence. The planarity of dopants is extensively investigated playing a pivotal role in modulating Dexter electron transfer (ET) for capturing released electrons and thereby affecting the overall performance of tunable HTA. This work provides an efficient and universal doping strategy to engineer tunable HTA through the synergistic action of thermally releasing electrons, Dexter ET and exciton recombination.