Roles of alcohols and existing metal ions in surface chemistry and photoluminescence of InP cores

Surface oxidation and chemistry determine the optical properties of indium phosphide (InP) nanocrystals (NCs). In this study, existing metal ions from the reaction residuals and alcohols normally used in the washing process are investigated. It is found that existing metal ions and alcohols play key roles in the surface oxidation and potential surface reactions of aminophosphine-based InP NCs, which significantly affect their photoluminescence (PL), optical absorption and photo-stability. According to X-ray photoelectron spectroscopy (XPS) analysis, InP NCs after aging form InPOx oxide which could passivate the NC surface along with increased PL intensity and blue-shifted spectral peaks. Treating with the existing metal ions from reaction residuals and intentionally added alcohols (methanol or ethanol), InP NCs exhibit an enhanced PL quantum yield (QY) (similar to 25 times, from 0.1% to 2.5%), unexpected red-shifted spectral peaks and improved photo-stability (similar to 9 folds). The phenomenon is ascribed to the passivation effect of the ZnyIn1-yPOx layer formed from coupling of existing Zn2+ with the NC surface triggered by the alcohols. The alcohols are found to facilitate the surface modification of amine-capped NCs and may be utilized as agents in NC surface modifications.