Controlled organic/inorganic interface leading to the size-tunable luminescence from Si nanoparticles

Abstract

Highly luminescent Si nanoparticles (NPs) terminated with alkoxy monolayers have been synthesized via sodium biphenylide reduction of SiCl₄ encapsulated with inverse micelles of dimethyldioctylammonium bromide in a mixture of toluene and glyme, and subsequent alkoxylation of surface Si–Cl bonds. The optical absorption and emission spectra are blueshifted with reduction in size of the Si NPs (d ≤ 5 nm), relatively. Interestingly, it is found that the monolayers, which serve as a shell to protect the Si core from surface oxidation, play an important role in the appearance of the quantum size effect which generates a size-tunable photoluminescence (PL) property with a high PL QY. Decrease in molecular coverage of an alkoxy shell causes the partial surface oxidation of a Si NP, leading to the appearance of the interfacial-related PL feature. Time-resolved study of the fluorescence in Si NPs with and without oxide is performed to understand the essential difference of the electron–hole recombination process between each NP systems. The synthesis of highly luminescent NPs with tailored PL properties in the ultraviolet–visible region required full control of the NP size distribution and the chemical property at the heterogeneous interface between the Si cores and the organic shells.