Preparation and use of photonic band gap structures to manipulate the optical properties of photoactive materials

A systematic study of the stop band properties of face centered cubic photonic crystals was performed. These properties and the factors that determine them were examined by a series of experiments beginning with the formation of silica nanospheres and their controlled assembly into photonic crystals with incomplete band gaps. The effects of the crystal growth were studied and were found to be in good agreement with those reported in the literature. Two methods of crystal growth were chosen to be studied more extensively, vertical deposition and the use of packing cells. Vertical deposition methods provided high quality photonic crystals from silica spheres. These crystals exhibited unusual optical clarity. When further analyzed, these crystals demonstrated multiple, symmetric reflections caused by the crystal's stop bands. These reflections were assigned to the (111) and (1, -1, 1) Bragg planes.; Photonic crystals were made from dye doped monodisperse polystyrene nanospheres. These nanospheres were synthesized in a core - shell approach to avoid changes in the chemical environment of the dyes from one bead to another. The stop band of these crystals was found to strongly suppress the spontaneous emission of the dyes when the emission peaks overlapped the stop band position predicted by Bragg's law. The crystals' photoluminescence and reflection was fully characterized with respect to observation angle. Three dimensional plots of these scans allowed accurate visualization of the effects the stop band of the crystal had upon the fluorescence of the dyes. Polystyrene nanospheres were then made with a shell containing Coumarin 334 and Nile Red. These dyes have sufficient overlap between the Coumarin's emission and the Nile Red absorption to facilitate energy transfer from the Coumarin to the Nile Red. The efficiency of energy transfer in the beads was significantly lower than bulk dye doped polystyrene with the same composition. However, when the stop band of the assembled crystals overlapped with the Coumarin 334 emission, slightly increased energy transfer to the Nile Red occurred. Effects from multiple Bragg planes were observed in the polystyrene crystals both in the reflectance and photoluminescence experiments. This material has potential applications in security, defense, and display devices.