Effects of Protic and Aprotic Solvents in Mesoporous Silica: Tuning the UV-Vis Emission Properties by Means of Surface Activation

The emission properties of mesoporous silica in the visible and ultraviolet range are affected by the reaction of the surface centers with different nonpolar and protic/aprotic polar solvents, that is, oxidized water, acetone, chloroform, and methanol. The samples were analyzed under wet conditions and after annealing above 60 degrees C, showing that the quantum efficiency of the emission is strongly reduced by the presence of residual solvent engulfed within the pores of the samples. The relative weight of the two main emission bands recorded at about 320 and 400 nm depends on the solvent, the contribution of the UV band being larger in the case of methanol treatment. The recorded changes in the emission spectrum are compared with the ones detected in samples with different pore diameters treated with oxidized water and annealed at 90 degrees C. The reported data are interpreted within the scenario of the emitting surface centers, and their models are discussed in view of the effects of the reaction with different solvents and the porosity of the samples: the reaction to oxygen pressure of methanol-treated samples is discussed in terms of adsorption and desorption from the emitting centers.