Microwave-Driven Ultrafast Te4+ Doping in Cs2ZrCl6 Realizing Multiple Self-Trapped Excitons and TADF-Mediated Energy Transfer Toward Near-Unity PLQY

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.