IN-SITU FLUORESCENCE PROBING OF THE CHEMICAL-CHANGES DURING SOL-GEL THIN-FILM FORMATION

Pyranine (8-hydroxy-1,3,6-trisulfonated pyrene) was used as an in situ fluorescence probe to monitor the chemical evolution during sol-gel thin film deposition of silica by the dip-coating process. The sensitivity of pyranine luminescence to protonation/deprotonation effects mas used to quantify changes in the mater/alcohol ratio in real time as the substrate was withdrawn from the sol reservoir. The spatially resolved spectral results showed that preferential evaporation of alcohol occurred, and that the solvent composition in the vicinity of the drying line reached values in excess of 80 vol% water Correlation of the luminescence results with the interference pattern of the depositing film allowed the solvent composition to be mapped as a function of film thickness.