Photoluminescence (PL) from mesoporous silica is evidenced to originate from non-bridging oxygens (NBOs) located inside similar to1 nm pore walls and on the pore internal surfaces. Based on density functional calculations, we showed that the PL band diversity in the range of 1.0-2.1 eV results from both isolated bulk and surface NBOs and those combined with variously placed pore wall oxygen vacancies. The spectroscopic features are found to be similar to those of surface-oxidized silicon nanocrystals and porous silicon. The results obtained are expected to be useful to clarify the nature of light-emitters in silicon nanoscale materials. (C) 2002 Elsevier Science B.V. All rights reserved.