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 Cs(2)ZrCl(6)perovskite NCs. The Cs2ZrCl6NCs exhibit long-lived triplet excited state (138.2 mu s), 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, Bi(3+)ions are successfully doped into Cs2ZrCl6NCs, 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.