Photonic Crystals for Energy Transfer Experiments Michael D. Julian, Ryan Desousa, G. K. Surya Prakash, and Aaron W. Harper 1 Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, University Park 837 Bloom Walk, Los Angeles, California 90089-1661 ABSTRACT Incorporation of two dyes into polystyrene beads was achieved through a core – shell emulsion free polymerization. The beads consisted of a central core, a dye containing emissive layer, and an overcoat layer. The overcoat layer thickness determined the final size of the nanospheres. The nanospheres were monodisperse and spherical. The nanospheres were used to assemble two photonic crystals. One in which the stop band overlapped with the dye emission of the donor dye, and one which had no overlap. The crystals formed were characterized by photoluminescence and reflectance studies. The crystal’s emission was suppressed where the stop band overlapped the emission. This suppression shows the expected angular dependence and contributes to changes in the efficiency of energy transfer from Coumarin 334 to Nile Red. Suppression of emission and energy transfer impart an angular dependence of the color of emission to the crystal. This results in a material that is tunable with angle of both its reflectivity and its emission. Keywords: photonic crystal, suppression, spontaneous emission, energy transfer, nanospheres 1. INTRODUCTION Much research has gone into studying the effects of Photonic Crystals on the spontaneous emission of materials inside the crystal. While a three-dimensional omnidirectional Photonic Crystal has not been produced to fully realize the suppression of spontaneous emission, several groups have reported mixed results of incomplete Photonic Band Gap (PBG) materials. Mischa Megens and coworkers have very eloquently used a core –shell approach in placing a dye inside silica spheres. 1 This protected the dye from the outside environment and isolated the emissive layers inside each bead. While they did not necessarily show the desired enhancement of lifetimes inside a Photonic Crystal, they showed very clear suppression of emission of the dye inside the crystal. Romanov and coworkers incorporated dye molecules into poly(methylmethacrylate) beads and used them to study the effects of the Photonic Crystals on the spontaneous emission. 2 Their work focused on the changes in the effects of the crystals on spontaneous emission with various excitation intensities. The predicted effects of a Photonic Crystal on emissive materials include suppression of emission inside the stop band, increased lifetimes of the material, Amplified Spontaneous Emission at the low energy band gap edge, and other potentially very useful effects. Incorporation of these effects in an energy transfer system could create enhancements in energy transfer efficiency. While the incorporation of dyes inside efficient Photonic Crystals remains difficult; several of these effects could contribute to sizeable changes in energy transfer efficiencies despite their minor individual effects on spontaneous emission. 1 Correspondence via E-mail awharper@usc.edu ; phone: 1 213 740-6716; fax: 1 213 740-2701 Proceedings of SPIE Vol. 5224 Nanomaterials and Their Optical Applications, edited by Guozhong Cao, Younan Xia, Paul V. Braun (SPIE, Bellingham, WA, 2003) · 0277-786X/03/$15.00 121