FLUORESCENCE-SPECTRA OF 1-NAPHTHOL DURING THE SOL-GEL PROCESS OF A MIXED ALUMINUM-SILICON ALKOXIDE (SI-AL=94/6)

The fluorescence and fluorescence-excitation spectra of 1-naphthol during sol to gel to xerogel transitions of a mixed solution comprising silicon and aluminum alkoxides (Si:Al = 94:6) catalyzed by a small amount of NaOH aqueous solution have been observed as a function of time. During the reaction of the system, the spectrum shifted to the red in the first stage and shifted to the blue in the next stage. This behavior reflects the changes of polarity and microviscosity of the matrix surrounding the doped 1-naphthol molecules during the sol to gel to xerogel transitions of the mixed metal alkoxide. The gelation occurred at 10 d. On the other hand, the most remarkable red-shift in the fluorescence spectrum was observed at 9 d. Comparing the fluorescence and fluorescence-excitation spectra of 1-naphthol in typical solvents with those of the sol-gel process, it has become apparent that a part of the doped 1-naphthol molecules in the ground state form a contact ion pair on the surface in cages of the prepared gel.