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

Abstract

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.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

“…[ 86 ] The reaction was carried out on dried CsPbCl 3 NCs, giving direct contact between ligands and the solid Mn 2+ precursor (i.e., MnCl 2 ·4H 2 O, Figure A). [ 86 ] Mn 2+ dopant amounts could be controlled through the alteration of ligand composition, which could be monitored using 1 H NMR (Figure 10B–E) in the initial colloidal solution before NC drying. [ 86 ] Increased OAm amount allows for a higher Mn 2+ doping concentration as a result of the interplay among ligands, the Mn 2+ precursor identity, and the NC surface all together in a confined space (Figure 10F).…”

“…[ 86 ] Mn 2+ dopant amounts could be controlled through the alteration of ligand composition, which could be monitored using 1 H NMR (Figure 10B–E) in the initial colloidal solution before NC drying. [ 86 ] Increased OAm amount allows for a higher Mn 2+ doping concentration as a result of the interplay among ligands, the Mn 2+ precursor identity, and the NC surface all together in a confined space (Figure 10F). [ 86 ] In another example, manganese oleate complexes were reported in cation exchange reactions to achieve Mn 2+ doping, and were proven to aid in enhancing the ability of Mn 2+ to replace Pb 2+ in a halide‐driven cation exchange environment.…”

Ligand‐Mediated Synthesis of Mixed‐Phase Mn2+‐Doped Cesium Lead Chloride Nanocrystals

“…Such interaction facilitates shape and phase tuning by varying amine species and/or concentration [32,55] . When Mn 2+ is also present, it will compete with the Pb 2+ to bind with the amines, both as precursors and on the Mn−CPC surfaces [56] . Similar to the bromide system, excess amines in the chloride perovskite will facilitate the phase transformation to the low dimension structure, Cs 4 PbCl 6 .…”

Stereoselective C−C Oxidative Coupling Reactions Photocatalyzed by Zwitterionic Ligand Capped CsPbBr3 Perovskite Quantum Dots

“…Given the Pb-rich surface nature of the CsPbBr 3 perovskite QDs (Supporting Information, Figure S17), the reactants and resultant free radical intermediates can dynamically attach to surface Pb 2+ ions through donating alone pair of electrons of the oxygen atom in the carbonyl group,acting as aL-type ligand, which was supported by the broadening and shifting of the CH and COCH 3 peaks of the substrate in the NMR spectra (Supporting Information, Figure S18). [18,27] Consequently,d imer products can be formed by the C À Cb ond formation between two neighboring radicals.D epending on the relative configuration of the two radicals on the QD surfaces,e ither dl-o rmeso-isomers can be obtained (Figure 5). However,l ess steric hinderance between the aryl groups of the radicals in the trans-arrangement makes the dlisomer akinetically favored reaction product ( Figure 5).…”