Influence of surface heterogeneity on the luminescence decay of probe molecules in heterogeneous systems Ru(bpy) 2+3 on clays

Abstract

The decay of a luminescent probe [Ru(bpy)²⁺₃] adsorbed on solids (clays) containing quenching impurities (Fe³⁺) has been examined. The time law is a multi-exponential function which stems from (i) the quasi-total translational immobility of the probe on the microsecond scale, and (ii) the heterogeneous nature of the surface, which is influenced by the local concentration of iron in the clay lattice. An elementary model has been proposed based on a randomly decorated 2-dimensional lattice for the probe and a second underlying and randomly decorated 2-dimensional lattice for the quencher ions. Assuming that the quenching probability for an excited probe is linearly related to the number of neighbouring quenchers, a decay function has been derived which, for very low quencher concentrations, reduces to the Infelta–Grätzel–Thomas equation for quenching in micellar solutions. The parameters of the decay function have been correlated to the chemical composition of the clays and to their swelling properties.