Air-stable luminescent silicon nanoparticles with effective surface protection are reported as a quantum dot material with high emission quantum yield. The silicon nanoparticles are prepared by a novel reaction of SiO2 with phenol resins and characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle size of the silicon nanoparticles is controlled by an acid-etching process with hydrofluoric and nitric acids in methanol. The particle size estimated from emission spectra was less than 5 nm. The surfaces of the silicon nanoparticles are protected using a photoassisted reaction with styrene molecules after the acid-etching process. The surface-protected silicon nanoparticles exhibit luminescence at around 650 nm, and their emission quantum yield is estimated to be 55%.

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Luminescent silicon nanoparticles have attracted considerable attention for their potential uses in various applications. Many approaches have been reported to protect the surface of silicon nanoparticles and prevent their easy oxidation. Various air-stable luminescent silicon nanoparticles have been successfully prepared. However, the effect of interactions of the π-electron system with the silicon surface on the excited state properties of silicon nanoparticles is unclear. In this study, we have successfully prepared silicon nanoparticles protected with three organic compounds (styrene, 1-decene, and 1-vinyl naphthalene) and have examined their photophysical properties. The ligand π-electron systems on the silicon surface promoted the light harvesting ability for the luminescence through a charge transfer transition between the protective molecules and silicon nanoparticles and also enhanced the radiative rate of the silicon nanoparticles.

Active surface of luminescent silicon nanoparticles was terminated by the photochemical reaction of chiral molecules, (S)-or (R)-5-allyl-2-oxabicyclo[3,3,0]oct-8-ene ((S) -or (R) -AOBE) under UV light. The particle size and shapes were characterized using Transmission Electron Microscope (TEM). The average particle size was found to be 5.7 nm. Circular dichroism (CD) signals with large dissymmetry factors from silicon nanoparticles terminated with (S) -and (R) -AOBE were observed at around 300 nm and 500 nm, which were much larger than those of (S)-and (R)-AOBE molecules. The silicon nanoparticles covered with (S)-or (R)-AOBE provided red luminescence based on the indirect electronic transition. Effective circular polarized luminescence (CPL) was not observed from indirect transition band.