Ripple structures in the fluorescence spectra of N,N'-bis(2,5-di-tert-butylphenyl)3,4:9,10-perylenebis(dicarboximide) (DBPI) in spherical micrometer-sized polystyrene beads

Emission spectra of DBPI in polystyrene spherical 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 calculations of the morphology dependent resonances (MDR). These MDRs in beads up to 4 mu m diameter do not appear to affect the fluorescence decay of DBPI since the fluorescence lifetime of DBPI remains constant at 3.7 +/- 0.1 ns irrespective of the size of the bead and the refractive index of a surrounding medium.