Thermally Enhanced Self‐Trapped Exciton Emission Based on Thermochromic Ag+ doping 0D Zinc‐Based Halides

Abstract Thermochromic materials, known for their unique ability to change optical properties with temperature, have broad applications, including in thermochromic light‐emitting diodes (LEDs). However, the scarcity of efficient and stable thermochromic phosphors limits their development. In this study, the development of a novel thermochromic phosphor based on zero‐dimensional (0D) inorganic metal halides is reported. The 0D Cs 2 ZnBr 4 :Ag + phosphors show thermally enhanced self‐trapped exciton (STE) emission across a wide temperature range from 120 to 300 K with the emitted wavelength changing correspondingly. Temperature‐dependent photoluminescence (PL), time‐resolved PL, and density functional theory calculations confirm that the thermally enhanced STE emission originates from the passivated defect/traps in Cs 2 ZnBr 4 and the thermally assisted energy transfer from the host to STEs formed by [AgBr 4 ] 3– tetrahedron with matrix phonons complementing the energy mismatch. Furthermore, the reversible thermochromic LEDs based on Cs 2 ZnBr 4 :Ag + phosphors are successfully prepared. Overall, these findings provide a future design of high‐efficiency thermally enhanced luminescent materials and pave a new way for developing thermochromic materials for functional LED illumination.