Doped sol-gel materials as a matrix for fast-response photochromic devices and as a pororus cladding for fiber optic chemical sensors

Abstract

The effect of a porous sol-gel matrix on the optical limiting characteristics of chloroaluminum phthalocyanine (CAP) has been investigated. Excited state singlet-singlet absorption processes are found to be responsible for the fast response characteristics (ps to ns) for CAP doped xerogel glasses. Subsequent inter-system crossing and triplet-triplet absorption processes are responsible for the persistent absorbance (ns to ms) determined by the ISC rate and the phosphorescent lifetime of CAP. Inhomogeneous spectral broadening of CAP in the xerogel matrix relative to alcohol solutions was found to have a significant affect on the relative linear (i.e. ground state) versus non-linear (i.e. optically induced excited state) absorption processes. In addition, the faster absorption recovery observed for CAP in a silica xerogel relative to ethanol solution was attributed to an increased rate of electronic to vibrational internal conversion in the xerogel matrix. Porous xerogel glasses doped with sensor chromophores have also been in investigated as a novel cladding for fiber optic chemical sensor devices. The lower refractive index of the sol-gel film makes it a suitable cladding material while the porous channels allow analytes to diffuse into the evanescent field region where they are detected by changes in the photophysics of analyte sensitive chromophores.