Efficient Thermally Activated Delayed Fluorescence from All‐Inorganic Cesium Zirconium Halide Perovskite Nanocrystals

Thermally activated delayed fluorescence (TADF) is generally observed in solid‐state organic molecules or metal‐organic complexes. However, TADF in all‐inorganic colloidal nanocrystals (NCs) is rare. Herein, we report the first colloidal synthesis of an air‐stable all‐inorganic lead‐free Cs2ZrCl6 perovskite NCs. The Cs2ZrCl6 NCs exhibit long‐lived triplet excited state (138.2 μs), and feature high photoluminescence (PL) quantum efficiency (QY=60.37 %) due to TADF mechanism. The emission color can be easily tuned from blue to green by synthesizing the mixed‐halide Cs2ZrBrxCl6−x (0≤x≤1.5) NCs. Femtosecond transient absorption and temperature dependent PL measurements are performed to clarify the emission mechanism. In addition, Bi3+ ions are successfully doped into Cs2ZrCl6 NCs, which further extends the PL properties. This work not only develops a new lead‐free halide perovskite NCs for potential optoelectronic applications, but also offers unique strategies for developing new inorganic phosphors. Lead‐free perovskite Cs2ZrCl6 NCs with a PLQY up to 60.37 % is synthesized. The emission color can be easily tuned from blue to green by synthesizing the mixed‐halide Cs2ZrBrxCl6−x (0≤x≤1.5) NCs. The efficient PL originates from thermally activated delayed fluorescence.