Sensitivity to oxygen environments of mesoporous silica samples with different porosities

The emission properties of mesoporous silica with different pore diameters (3.2 and 18.2 nm) are investigated under different environmental conditions, namely after long air exposure (aging process) and oxygen purging. Beside the reduced optical transparency in the visible range, the emission properties of aged samples with larger pores show a larger contribution of the UV band peaked at about 320 nm with respect to the blue one peaked at about 400 nm and a larger sensitivity of the overall emission spectrum to the oxygen purging. The aging of the samples and the sensitivity to oxygen purging are discussed in terms of the distribution of silanol groups and the curvature of the silica surface in the two sets of samples.