Au Exchange or Au Deposition: Dual Reaction Pathways in Au-CsPbBr₃ Heterostructure Nanoparticles

We have designed a facile synthetic strategy for the selective deposition of Au metal on all-inorganic CsPbBr₃ perovskite nanocrystals that includes the addition of PbBr₂ salt along with AuBr₃ salt. PbBr₂ is necessary because the addition of Au³⁺ to solutions of CsPbBr₃ nanocrystals otherwise results in the exchange of Au³⁺ ions from solution with Pb²⁺ cations within the nanocrystal lattice to produce Cs₂Au^IAu^IIIBr₆ nanocrystals with a tetragonal crystal structure and a band gap of about 1.6 eV, in addition to Au metal deposition. Including excess Pb²⁺ ions in solution prevents the exchange reaction. Au metal deposits on the surface of the nanocrystals to produce the Au-CsPbBr₃ heterostructure nanoparticles with an Au particle diameter determined by the Au³⁺ ion concentration. Fluorescence quenching caused by Au deposition monotonically increases with deposition size, but the fluorescence quantum yield (QY) is significantly greater than if any cation exchange has occurred. An optimized synthesis can produce Au-CsPbBr₃ nanoparticles with 70% QY and no evidence of cation exchange.