Metal Acetylacetonates are Suitable Metal Precursors to Make Cs2HfCl6 Nanocrystals

The high stability, low toxicity and exclusive optical properties of lead-free vacancy-ordered perovskite Cs₂M⁴⁺X₆ (X = Cl⁻, Br⁻, or I⁻) nanocrystals have gained considerable attention.

Metal acetates or metal halides are commonly used as metal precursors in the hot injection technique reported earlier for producing perovskite nanocrystals. But as far as several new perovskite nanocrystalline systems are concerned, the inability of these two kinds of metal salts to ionize in organic solvents is a significant cause for synthesis failure.

Under the guidance of Professor Keli Han and Professor Bin Yang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences, a group of researchers has recently found out that metal acetylacetonates are a highly appropriate type of metal precursors.

The researchers used hafnium acetylacetonate as a metal source and Hf-based vacancy-ordered perovskite as a model system to synthesize Cs₂HfCl₆ nanocrystals, for the first time, through the hot injection technique.

This study was reported in the journal Laser & Photonics Reviews on December 13^th, 2021.

The newly synthesized Cs₂HfCl₆ nanocrystal is different from those perovskite nanocrystals reported earlier and is a defect-intolerant semiconductor. The team suggested a passivation approach of Sb³⁺ doping to overcome the sub-bandgap defect states present within the Cs₂HfCl₆ nanocrystals. This approach had not been reported in perovskite studies performed earlier.

Furthermore, the team used rare earth acetylacetonates to dope four rare-earth ions, such as Tb³⁺, Pr³⁺, Ho³⁺, Eu³⁺, into the crystal lattice of the Cs₂HfCl₆ nanocrystal host, thus achieving tunable multicolor emissions.

In contrast to rare-earth ions-doped perovskite nanocrystals systems reported earlier, the use of rare earth acetylacetone compounds allowed rare earth element ions to be doped into the lattice of the nanocrystals under a comparatively milder temperature.

Our study not only provides an effective strategy for regulating the optical properties of vacancy ordered perovskite nanocrystals, but also enriches the hot-injection synthesis method, which may promote the development of new perovskite nanocrystal systems.

Keli Han, Professor, Dalian Institute of Chemical Physics, Chinese Academy of Sciences

Journal Reference:

Liu, S., et al. (2021) Colloidal Synthesis and Tunable Multicolor Emission of Vacancy-Ordered Cs₂HfCl₆ Perovskite Nanocrystals. Laser & Photonics Reviews. doi.org/10.1002/lpor.202100439.