Spectral and angular redistribution of photoluminescence near a photonic stop band

In this paper we present a detailed comparison of experimentally observed modifications of the emission behavior of dye molecules embedded in colloidal photonic crystals with corresponding theoretical calculations of the optical mode density. For this purpose, angle-resolved measurements of emission spectra and time-resolved measurements were performed with a high spatial resolution using a confocal microscopy setup. The spectra reveal a strongly modified radiation pattern, including a highly directional fourfold intensity enhancement at the high frequency edge of the photonic stop band, while the radiative lifetime is only slightly affected. For the first time these experimental results are quantitatively compared to theoretical predictions based on calculations of the angle-dependent local density of optical states. It is demonstrated that the observed modifications can be explained by a spectral and angular redistribution of the optical mode density inside the photonic crystal, suggesting an altered radiation probability of the dye molecules for certain frequencies and directions. Furthermore, our calculations reveal a strong dependence of these modifications on the exact location of the dye molecules within the photonic crystal.