Ligand Engineering for Mn²⁺ Doping Control in CsPbCl₃ Perovskite Nanocrystals via a Quasi-Solid–Solid Cation Exchange Reaction

Manganese-doped cesium lead chloride (CsPbCl₃) perovskite nanocrystals (NCs) have recently garnered attention because of their unique magneto-optical properties, giving them potential in a variety of optoelectronic applications. One common method to dope Mn²⁺ into host CsPbCl₃ NCs is through a postsynthetic ion exchange reaction. However, most ion exchange strategies utilize a Mn²⁺-containing precursor solution, which adds limitations to the reaction due to compatibility and stability issues. Here, we report a new method of cation exchange in CsPbCl₃ NCs where Pb²⁺ cations are partially replaced by Mn²⁺ cations using a solid Mn²⁺–precursor source, resulting in a quasi-solid-solid cation exchange at ambient conditions. The ability to perform the cation exchange without the addition of any external solvents allowed for a systematic study on the NC doping. The reaction takes place at the interface between the Mn²⁺-containing solid precursor and the NC surface. Electron paramagnetic resonance and optical characterizations including a shortened Mn²⁺ photoluminescence lifetime immediately following the exchange indicated initial heterogeneous doping with the Mn²⁺ dopants localized on the NC surface. Spatial distribution of dopants within the NCs is observed by inward diffusion over time. Additionally, dopant concentration can be controlled through engineering starting ligand compositions, which not only changes the ligands present at the Mn²⁺–precursor–NC interface but also leads to varying degrees of precursor activation. This study not only provides a clean and facile doping method without the need for additional solvents but also a cation exchange strategy which can be closely studied to improve the understanding of doping processes at the molecular level in perovskite NC systems.