Luminescence quenching in polymer/filler nanocomposite films used in oxygen sensors

Luminescent oxygen sensors are devices in which the active element involves a luminescent dye in a polymer film. Oxygen partitions into the polymer from an adjacent gas or liquid phase and quenches the dye luminescence to an extent that depends on the amount of oxygen present in the film. When the dyes are dissolved in or attached to the molecules of a pure polymer film, the quenching kinetics can be described completely in terms of parameters that can be determined independently: the excited-state lifetime of the dye and the permeability (Po,) and diffusion coefficient (Do,) of oxygen in the polymer. In many sensors, nanometer-sized inorganic particles are often added to the active matrix. These particles are added either as carriers for the dye molecules or to reinforce the polymer film. The presence of these particles in the polymer complicates the quenching kinetics, because both the dyes and the oxygen molecules partition between the polymer matrix and the particle surfaces. The purpose of this article is to review the factors that operate to affect quenching kinetics in particle-filled polymer films. We provide a brief review of polymer composite systems used in sensors and a more detailed review of the factors that affect quenching kinetics in these systems. We end with a description of more sophisticated models that have been employed to analyze oxygen quenching of dyes adsorbed on the surface of inorganic particles in the hopes that similar models might be developed in the future to describe oxygen quenching in polymer composite films.