Highly Luminescent Water-Soluble InP/ZnS Nanocrystals Prepared via Reactive Phase Transfer and Photochemical Processing

摘要

Highly luminescent water-soluble InP/ZnS core-shell nanocrystals were prepared using a newly developed method that incorporates reactive phase transfer and photochemical processing.Poor-emitting InP nanocrystals(NCs,2-4 nm)prepared solvothermally using toluene were transferred into alkaline aqueous solution containing thiol and zinc ions.When these NCs in aqueous solution were subsequently irradiated by ultraviolet(UV)light,they showed intense size-dependent photoluminescence(PL)from green to red due to the formation of a thick(more than 1 nm)ZnS shell on the NCs.The surface dissolution of the NCs,under conditions in which bulk InP does not dissolve due to its covalent bond nature,was observed at two steps:phase transfer and shell formation.This dissolution competed with the formation of the ZnS layer at the start of UV irradiation.Since the UV irradiation enables creation of a thick shell by optimizing the synthesizing conditions,high PL efficiency(30-68%)was obtained in water with sufficient stability.This was quantitatively explained by quantum mechanical calculations.The PL decay behavior of these water-soluble InP/ZnS NCs did not show obvious size-dependence,unlike HF-treated ones.This is attributed to the well-passivated surface states of the NCs due to their thick ZnS shell.The NCs showed a significantly higher In/P ratio than those previously reported.This indicates that In ions were preferentially located on the surface of the InP core in the NCs.