Anisotropic accelerated emission of the chromophores in photonic crystals consisting of a polystyrene opal structure

Fluorescence behaviors of chromophores in photonic crystals were studied to investigate the effect of photonic band gaps on emission behaviors, leading to the control of the excited states of chromophores. A polystyrene opal structure was selected as a typical photonic crystal, and the fluorescence of rhodamine 6G adsorbed in that structure was observed. It was found that the fluorescence spectra were strongly modified by the opal structure. The intensity was attenuated at the wavelengths corresponding to the stop band of the opal structure, while it was enhanced accompanying strange sharp-pointed peaks at the edge of the stop band. Furthermore, the fluorescence lifetime was estimated by measuring time-resolved spectra for the investigation of the effect on excited states. By the comparison between the lifetime in the sample which influences emission behaviors and that in the reference sample which has no effect on them, it was surprisingly found that the lifetime of rhodamine 6G was shortened by the effect of photonic crystals, contrary to common prospects. This can be attributed to the increase of the radiative rate constant at the edge of the stop band.