Microwave‐Driven Ultrafast Te 4+ Doping in Cs 2 ZrCl 6 Realizing Multiple Self‐Trapped Excitons and TADF‐Mediated Energy Transfer Toward Near‐Unity PLQY

Abstract This work employs an ultrafast microwave‐assisted synthesis to achieve efficient and uniform Te 4+ doping in Cs 2 ZrCl 6 within 30 min at 60 °C, addressing key challenges of slow kinetics and inhomogeneous distribution prevalent in conventional methods. Structural and optical analyses confirm that temperature and concentration critically govern dopant incorporation and luminescent properties. Temperature‐dependent spectroscopy reveals undoped Cs 2 ZrCl 6 hosts dual self‐trapped excitons (Zr‐STE1 and Zr‐STE2) exhibiting excitation‐dependent thermally activated delayed fluorescence (TADF) with a minimal singlet‐triplet gap (0.060 eV). Te 4+ doping introduces efficient [TeCl 6 ] 2− emitters and modifies energy transfer pathways. Lifetime analysis demonstrates that host TADF, especially synergistic dual‐channel activation under 254 nm excitation, enables highly efficient (>83.1%) resonance energy transfer to [TeCl 6 ] 2− centers. Microwave optimization, achieving homogeneous shallow doping, yields an exceptional photoluminescence quantum yield (PLQY) of 95.43% for Cs 2 ZrCl 6 :Te, significantly outperforming conventional syntheses. The material exhibits outstanding stability under thermal, UV, humidity, cycling, and ambient conditions, with prototype LEDs demonstrating superior reliability. These findings establish a synergistic design strategy combining controlled doping and TADF‐mediated energy transfer for high‐performance luminescence.