Colloidal Synthesis of Giant Shell PbSe-Based Core/Shell Quantum Dots in Polar Solvent: Cation Exchange versus Epitaxial Growth

Shell thickness control of core/shell quantum dots (QDs) plays an important role in determining their optical properties as well as the corresponding device performance. PbSe-based core/shell QDs are attractive near-infrared (NIR) light emitters for photonic and optoelectronic applications. We herein report the colloidal synthesis of giant shell PbSe-based core/shell QDs through controllable reactions between preformed PbSe QDs and Cd2+ ions in polar solvents. The preformed PbSe QDs experienced cation-exchange reaction in N,N-dimethylformamide (DMF), while they underwent epitaxial growth of CdS shell in dimethyl sulfoxide (DMSO). The cation exchange of preformed PbSe QDs in DMF result in PbSe/CdSe core/shell QDs with similar size (ca. 6.3 nm) but tunable shell thickness from 0.5 to 2.9 nm. In comparison, the epitaxial growth of preformed PbSe QDs in DMSO produce PbSe/CdS core/shell QDs in DMSO with average core size of ∼5.7 nm but tunable shell thickness from 0.5 to 3.1 nm. These resulting PbSe-based core/shell QDs show tunable photoluminescence emission of 1393-1744 nm for PbSe/CdSe core/shell QDs and 1566-1719 nm for PbSe/CdS core/shell QDs. The cation exchange and epitaxial growth reactions of preformed PbSe QDs were further investigated by comparing the interactions between solvents and cation ions through nuclear magnetic resonance (NMR) measurements. The interactions between Cd2+ and DMSO are stronger than that of DMF, while the interactions between Pb2+ and DMSO are weaker than that of DMF. The difference accounts for the reaction transition from cation exchange to epitaxial growth, providing alternative route for fabricating shell controllable PbSe-based core/shell QDs.