Lead-free lanthanide-based Cs3LnCl6 metal halides

Abstract

All-inorganic lead-free luminescent metal halides have attracted considerable interest for their special optical properties in various optoelectronic applications. Among them, lanthanide-based Cs₃LnCl₆ metal halides, with low phonon energies and suitable crystallographic features, have been in the spotlight due to their appealing optical properties. However, it remains challenging for us to know how to simply and efficiently synthesize lanthanide-based Cs₃LnCl₆ metal halides, and how to optimize their low absorption and emission efficiencies owing to the parity-forbidden f–f transitions. In this minireview, we summarized several synthesis approaches towards both Cs₃LnCl₆ polycrystals and nanocrystals. The association of the crystal/electronic structure, optical properties and applications is discussed in three sections: self-trapped emission, down-conversion luminescence, and upconversion luminescence. We provide not only the synthesis strategies and recent progress in the luminescence properties of Cs₃LnCl₆, but also their promising future as alternatives to their toxic and poorly stable lead-based counterparts.