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.