Two-dimensional lead-based perovskite halides have interesting optical properties, which could make them useful for optoelectronic devices. However, the toxicity of lead is a concern. Therefore, new lead-free 2D perovskite halides have garnered the attention of researchers.

Kanishka Biswas, Sarit S. Agasti, and colleagues, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India, have synthesized nanocrystals (NCs) and 2D nanosheets (NSs) of a layered mixed halide, Cs₃Bi₂I₆Cl₃, using a solution-based hot-injection method. BiI₃ and BiCl₃ were dissolved in 1-octadecene (ODE) along with oleic acid (OA) and oleylamine (OAm) under an inert atmosphere, followed by the hot-injection of cesium oleate. The morphology was controlled by varying the temperature during the synthesis. The formation of NCs was observed at a lower reaction temperature (120 °C), whereas a higher temperature (180 °C) led to the formation of 2D NSs.

The team analyzed the optical properties of the new materials using time-resolved photoluminescence (PL) measurements and fluorescence microscopy. PL emissions (pictured above) were observed for all samples. Both nanostructures showed dynamic fluctuations in their PL emission, i.e., a “blinking” or “flickering” effect. Single nanocrystals displayed time-dependent, intermittent blinking. The nanosheets showed a similar, localized blinking effect.

• Synthesis and Localized Photoluminescence Blinking of Lead‐free 2D Nanostructures of Cs₃Bi₂I₆Cl₃ Perovskite,
  Kaushik Kundu, Paribesh Acharyya, Krishnendu Maji, Ranjan Sasmal, Sarit S Agasti, Kanishka Biswas,
  Angew. Chem. Int. Ed. 2020.
  https://doi.org/10.1002/anie.202005966