Relaxation of excitations in porous silica gels

The relaxation of an initially excited donor molecule due to the presence of acceptor molecules embedded in porous solids has been studied. The time evolution of the relaxation process has been related to the geometrical restrictions imposed on the participatingmolecules by the porous structures. We have focused on two limits: (a) donor and acceptors adsorbed on the solid interfaces, (b) gas phase acceptors diffusing within the pore interior towards the donor. In both cases a homologous series of silica gels has been investigated. When corroborated with structural studies, the results lead to classical pore models for the embedding systems. The mean pore size, R_p, appears to be a relevant scaling parameter for both dynamical and structural observables.