On the origin of photoluminescence enhancement of Si nanocrystals on silica glass template and Si/SiO2 superlattice

Photoluminescence (PL) properties of Si nanocrystals on silica glass template and Si/SiO2 superlattice measured under different gas environments, laser excitation times, and powers were reported. Both Si nanostructures show broad PL bands in the visible region. The emission intensity dramatically increases under a continuous 325 nm He-Cd laser illumination; however, it quenches when air is introduced. The PL enhancement is possibly due to the photocatalytic activity of Si nanocrystals. It is related to the splitting of surface-absorbed water molecules into OH and H radicals which passivate the dangling bands left at the Si nanocrystals, leading to the suppression of nonradiative processes. The decrease of the PL intensity in the air is caused by the oxidation of the Si-H bonds and the formation of dangling bonds, which again act as nonradiative centers. The PL intensity enhancement and the photocatalytic activities under UV illumination make these Si nanostructures potential candidates for op-toelectronics and photocatalysis applications.