Phase transition and energy transfer of lead-free Cs₂SnCl₆ perovskite nanocrystals by controlling the precursors and doping manganese ions

Perovskite quantum dots (QDs), such as all-inorganic CsPbX₃ (X = Cl, Br, and I), are novel fluorescent semiconductor nanocrystals (NCs) that have attracted tremendous attention due to their excellent optical properties and great applications (e.g. display backlights, light-emitting diodes, and photodetectors). The instability and toxicity of lead-based perovskite QDs, however, are intrinsic defects that obstruct their application and commercialization. Poison is released from the lead of the unstable CsPbX₃ NCs, which are generally ascribed to the labile surface, ionic character, and metastable structure. In this work, lead-free Cs₂SnCl₆ perovskite NCs are successfully synthesized via hot injection. Particularly, by controlling the different precursor ratios, phase transition (CsCl to Cs₂SnCl₆) was clearly observed from X-ray diffraction (XRD) measurements. The Cs₂SnCl₆ NCs exhibited a highly efficient deep-blue emission at 425 nm, with a 55 nm Stokes shift and an 84 nm full width at half maximum (FWHM). After doping Mn ions, the preferred formation of CsSnCl₃:Mn²⁺ with double-wavelength emission was demonstrated based on the XRD and photoluminescence spectra. The study showed that doping synthesis should be widely used in lead-free perovskite NCs as an important strategy for next-generation solid-state lighting.