Induced absorption of C-60 and a water-soluble C-60-derivative in SiO2 sol-gel matrices

Porous sol-gel glasses, either impregnated with pure C-60 or doped with a m ethanofullerene derivative, have been studied and induced absorption or "re verse saturable absorption" (RSA) has been observed in both types of solid materials. The samples impregnated by pure C-60 mainly contain well-dispers ed fullerene molecules. Unlike crystalline films of C-60, their absorption dynamics can be well described by a 5-level model, developed for non-intera cting C-60-molecules in solutions. Methanofullerene samples, on the other h and, show signs of micellar aggregation and therefore RSA dynamics that are influenced by solid state effects. We observe an important decrease of tra nsmission at high fluences for both kinds of samples, a shortened singlet-s tate lifetime to that observed in solution, but nonetheless, a triplet yiel d, that cannot be considered as negligible. In the case of pure C-60 in a s ol-gel matrix, we can explain the faster de-excitation dynamics, relative t o behavior in solution, mainly by the absence of stabilizing aromatic solve nts and also by the interaction of the amorphous environment with the molec ules. Concerning the methanofullerene samples, the acceleration of the de-e xcitation dynamics can be principally attributed to solid-state effects due to the micellar aggregation.