Fluorescent compacts prepared by the entrapment of benzoxazole type dyes into a silica matrix at high pressure

We have produced silica-gel compacts doped with 2,5-Bis(benzoxazol-2′-yl)-4-methoxyphenol dye using high-pressure processing of powders synthesized by the sol–gel technique. The high-pressure compaction of powders with three different dye concentrations was done at 4.5 GPa and room temperature. We have measured optical and mechanical properties of the obtained compacts. They were very stable, transparent, crack free, hard (3.56 ± 0.07 GPa) and dense (1.95 ± 0.03 g/cm3), being resistant to polishing and leaching, which enables its use in optical applications. The Stokes shift observed was higher than 100 nm indicating that the intramolecular proton-transfer in the electronically excited state (ESIPT) of this dye is maintained, even in an OH rich environment like silica. A shift to higher wavelength in the fluorescence spectra of the compacts, attributed to the increasing in the conjugation of the π system, was observed.