Steady-state and time-resolved fluorescence study of some dyes in polymer microspheres showing morphology dependent resonances

Fluorescence emission spectra of N,N'-bis(2,5-di-tert-butylphenyl)-3,4:9,10- Perylenebis(dicarboximide) (DBPI), rhodamine 6G (R6G), and cresyl violet (CV) in spherical polymer beads of less than 20 mu m diameter show sharp ripple structures, The observed peak positions and the intervals of the structures are consistent with the calculations of the morphology dependent resonances (MDR). Observed intensities of the MDR in the fluorescence emission spectra are found to show excitation energy dependence. The fluorescence spectra have also been measured as a function of the refractive indexes of the medium and the bead. These MDR in the beads up to 4 mu m diameter do not appear to affect the fluorescence decay of the dyes, since the fluorescence lifetime remains constant irrespective of the size of the bead and the refractive index of a surrounding medium. Simulations based on the Lorentz-Mie theory for the microspheres of different refractive indexes have been used to quantify the observed effect on the basis of the available data on the homogeneous widths of the dye molecules, A fluorescence study of microcrystals of DBPI is also presented here from the point of view of comparison with fluorescence decay of dye impregnated beads. The microcrystals exhibit a size effect in the fluorescence decay which has been attributed mainly to the self-absorption effect. (C) 1996 American Institute of Physics.