Colloidal Synthesis and Tunable Multicolor Emission of Vacancy‐Ordered Cs2HfCl6 Perovskite Nanocrystals.

Vacancy‐ordered perovskite nanocrystals (NCs) have recently attracted much interest owing to their unique structure and optical properties; however, regulating self‐trapped excitons (STEs) in vacancy‐ordered perovskite NCs to exhibit tunable multicolor emission is still challenging because of the highly localized charge distribution and strong carrier‐phonon coupling. Herein, the first colloidal synthesis of lead‐free vacancy‐ordered Cs2HfCl6 perovskite NCs by a hot‐injection method using hafnium acetylacetonate as metal precursors is reported. The passivation strategy of sub‐bandgap trap states inside Cs2HfCl6 NCs is proposed by doping Sb3+. X‐ray photoelectron spectroscopy (XPS) measurements verify that the passivation of sub‐bandgap trap states may be attributed to the enhanced chemical interaction between the Hf4+ cations and Cl– anions. Simultaneously, the introduction of Sb3+ ions yields a bright orange emission. Employing lanthanide acetylacetonate compounds, four lanthanide ions including Pr3+, Eu3+, Tb3+, and Ho3+ are doped into the Cs2HfCl6 NCs, which achieves tunable multicolor emissions (from blue to green to pink) through the energy transfer from STEs to lanthanide ions. This investigation not only develops a novel vacancy‐ordered perovskite NCs, but also provides effective strategies for tuning the optical properties of lead‐free vacancy‐ordered perovskite NCs. [ABSTRACT FROM AUTHOR]