Synthesis of water-soluble blue photoluminescent silicon nanocrystals with oxide surface passivation

A facile method to synthesize colloidal silicon nanocrystals with oxide surface passivation, showing good dispersibility in water and exhibiting strong and stable blue photoluminescence, was reported. The high-resolution TEM (HRTEM) image show that the silicon nanocrystals have high crystallinity and the lattice spacings of 0.32 nm are related to the (111) plane of the diamond structured silicon. In addition to binding energy at 99.5 eV for Si, the distinct Si 2p signal at 103.3 eV due to Si in SiO₂ is also observed. It is also seen that a large band gap of 4.8 eV is usually observed for only 1-2 nm silicon nanocrystals. The monotonic shift of emission wavelength with the excitation wavelength could be attributed to the excitation of different sizes of silicon nanocrystals. The results also show that the quantum yield for the silicon nanocrystals sample immersion in water for 6 months is about 12% at the peak wavelength of 480 nm.