Fluorescence-lifetime measurements in monodispersed suspensions of polystyrene particles

The fluorescence lifetime of the dye Kiton Red S in monodispersed polystyrene colloids was measured by using the single-photon-counting technique. The measured lifetime changed from 1.6 ns when the dye was in water to 3–4 ns when it was in colloidal suspensions of various monodispersed polystyrene microspheres. Interaction of electrons of the dye molecule with electrons of the medium accounts for a major fraction of the change in the measured lifetime. Variation of the lifetime with the diameter of the polystyrene microspheres may be, in part, a result of the quantum-electrodynamics effect caused by the local photon-field interaction with the dye molecules.