Metal fluorides passivate II-VI and III-V quantum dots

The interaction between II-VI and III-V quantum dots (QDs) and metal fluorides is investigated using optical absorption, photoluminescence, and nuclear magnetic resonance spectroscopies. QDs with metal fluoride passivated surfaces were prepared by ligand exchange with anhydrous oleylammonium fluoride. The photoluminescence quantum yield (PLQY) of II-VI QD cores and core-shell structures are dramatically enhanced following ligand exchange, near unity in some cases, but only after exposure to air. In the case of InP QDs, oleylammonium fluoride induces a gradual etching of the crystal, yielding oleylamine, PH3, and InF3 coproducts, resulting in a remarkable increase in PLQY (up to 83%). The frequency and breadth of ν(N–H) bands in the infrared spectrum supports the assignment of oleylamine ligand binding to InP. The fluoride content (1.6–9.2 nm-2) is compared with the coverage of oleylamine ligands (2.3–5.1 nm-2) and demonstrates the formation of surfaces densely covered by metal fluoride and amine ligands. The relationship between the electrophilicity and small steric profile of metal fluoride surface ligands and their surface passivating effects on QDs is discussed.