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 Cs 2 HfCl 6 perovskite NCs by a hot-injection method using hafnium acetylacetonate as metal precursors is reported. The passivation strategy of sub-bandgap trap states inside Cs 2 HfCl 6 NCs is proposed by doping Sb 3+ . 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 Hf 4+ cations and Cl – anions. Simultaneously, the introduction of Sb 3+ ions yields a bright orange emission. Employing lanthanide acetylacetonate compounds, four lanthanide ions including Pr 3+ , Eu 3+ , Tb 3+ , and Ho 3+ are doped into the Cs 2 HfCl 6 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.