Photoluminescence properties of silica-based mesoporous materials similar to those of nanoscale silicon

Photoluminescence (PL) from composites of 7- and 15-nm sized silica nanopar ticles (SNs) and mesoporous silicas (MSs) induced by 266- (4.66-) and 532-n m (2.33-eV) laser light has been studied at room temperature. The multiband PL from MSs in the range of 1.0-2.1 eV is evidenced to originate from isol ated bulk and surface non-bridging oxygens (NBOs) and from NBOs combined wi th variously placed 1-nm sized pore wall oxygen vacancies (OVs). The nature and diversity of NBO light-emitters are confirmed by ab initio calculation s. The PL from SNs exhibits only a short wavelength part of the bands (1.5- 2.1 eV) originated from isolated bulk and surface NBOs. This fact indicates that the highly OV-bearing structures occur only in extremely thin (simila r to 1 nm) silica layers. The similarity of spectroscopic properties of sil ica-based nanoscale materials to those of surface-oxidized silicon nanocrys tals and porous silicon, containing silica-passivating layers of the same w idth, is discussed.