Effect of synthesis conditions on porous structure, luminescence and absorption properties of dye-loaded silica xerogels

Silica xerogels were prepared at different pH values in the range −0.8 to 1.2 and loaded with Rhodamin6G (Rh6G) dyes using the sol–gel technique and by variation of the HCl/TEOS and H2O/TEOS ratios. The luminescence properties such as the spectral range of emission and the photostability of the laser dyes remain unchanged as a function of pH value at which the xerogels are prepared, although the porous structure of the xerogels is significantly changed. Inclusion of the dyes after gelation results in similar luminescence spectra as during-synthesis admixture of the dye. A detailed structural study using small angle X-ray scattering and nitrogen adsorption reveals that the dyes embedded by the postloading procedure occupy mainly micropores, while the dyes added during the sol–gel process are located mainly in mesopores. This is reflected in the position of the absorption maximum of the Rh6G dye, which is found at 506–516 nm for dyes in micropores and at 530–540 nm for dyes in mesopores.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Combine SAXS and N2-adsorption to located dye molecules in micro- or mesopores. ► pH-value of starting composition does not alter luminescence properties. ► Absorption properties of dyes depend on pore size.