Efficient excitation energy transfer among multiple dyes in polystyrene microspheres

Our comparison of fluorescence excitation and absorption spectra from 40 nm polystyrene spheres containing six different dyes illustrates efficient excitation energy transfer among the dyes. The six-dye spheres collective absorption covers the entire visible region. The five dyes with the highest first excited state energy levels transfer their excitations to the sixth dye of the lowest energy level. The average excitation transfer efficiency to the sixth dye is 95% over most of the visible spectrum. As a result of this transfer, the spheres have a fluorescence maximum at 718 nm, the peak of emission from the lowest energy level dye. Each sphere functions as an artificial light-harvesting network. They have practical applications as fluorescent labels for biological systems and act as an efficient, broadly absorbing wavelength converter.