Size-Dependent Critical Transition In The Origin Of Light Emission From Core-Shell Si-Sio2 Nanoparticles

The origin of the light emission from nanosilicon systems, such as crystalline silicon nanoparticles (Si-NPs), has been an intensively debated issue, with seemingly contradicting literature results pointing to different mechanisms. Here, the origin of the photoluminescence (PL) from application-grade Si-SiO(2)core-shell nanoparticles with different sizes and synthesized with the industrially scalable high-yield nonthermal silane plasma method has been elucidated. It is found that the commonly observed PL from these Si-NPs originates, in general, from two processes: recombination within the nanoparticle silicon core and recombination within the oxide shell. The photon energies of both emissions increase with decreasing nanoparticle size. Importantly, a nanoparticle size dependence of the relative contribution of the two processes to the overall PL is established. For large (small) Si-NPs, the luminescence is dominated by the core (oxide-shell) emission. Interestingly, the transition between these two regime limits occurs within an extremely narrow nanoparticle size range (similar to 0.5 nm). This critical transition, in combination with the close photon energies of the two emission components, is responsible for the common observation of only a single unstructured PL band for Si-NPs and for the seemingly conflicting assignments of the origin of this luminescence found in the literature for apparently similar Si-NPs.