Bright Visible Luminescence in Silica Nanoparticles

We demonstrate that a porous film of silicananoparticles emits a bright visible luminescence associatedwith defects stabilized by oxygen chemisorption at oxygendeficientcenter sites. Time-resolved spectra excited by atunable laser allow us to distinguish the luminescence at 1.99 eV,characteristic of the nonbridging oxygen hole center (NBOHC)(tSi O)3Si O•, and a fast and a slow emission: the first(lifetime τ ≈ 25 ns) is peaked at 2.27 eV with an excitationspectrum centered at 5.5 eV; the second (τ ≈ 7.5 μs) is peakedat 2.41 eV and is excited around 3.2 and 5.2 eV. Reaction in anair atmosphere leads to the disappearance of the NBOHCluminescence and of the fast band, whereas the slow one remains stable. On the basis of the comparison with previous experimentaland computational works, we discuss the role of the silanone SidO and of the dioxasilyrane Si(O2) as the emitting defects.