Synthesis of ORMOSIL silica/rhodamine 6G: Powders and compacts

The sol-gel method was used to prepare a silica matrix with rhodamine 6G. This dye was chemically bonded to silica matrix by grafting reactions, obtaining ORMOSIL/R6G powder, at two different concentrations, 0.03 mmol of dye/g silica and 0.009 mmol of dye/g silica, called ORMOSIL1 and ORMOSIL2, respectively. Fluorescent compacts were also obtained, through the high-pressure processing of these powders, at 7.7 GPa and room temperature. The microstructure, chemical composition and thermal stability of the powders and compacts were comparatively studied, by N₂ adsorption/desorption isotherms, FTIR spectroscopy, thermogravimetric analyses (TGA) and elemental analyses for carbon, hydrogen, and nitrogen (CHN). The optical behavior was studied by fluorescence spectroscopy. The ORMOSIL1 compacts were completely opaque showing that the compaction was not effective, due to the high organic grade incorporated into the starting ORMOSIL1 powder. The ORMOSIL2 compacts were transparent showing an effective compaction, which are in agreement to the great surface area and porosity reduction. Additionally, it was observed in TGA results, the retention of the organics in these samples up to temperatures near 300 °C. The fluorescence emission showed that the dye was dispersed in molecular level in all samples.