The effect of the incomplete photonic bandgap (PBG) provided by the opal template upon the emission properties of the laser dyes (Coumarin 6 and perylene derivative) dissolved in the solidified polymer has been studied. The bandgap of dye-polymer-opal composite is highly anisotropic because of the insufficient refractive index contrast (RIC), moreover, the extent of anisotropy depends on the volume fraction of the polymer. The anisotropic bandgap enforces the corresponding directionality of the emission, but the emission anisotropy is restricted, as compared with the bandgap anisotropy, within the energy range of the Stocks shift between emission and absorption spectra of the dye. The bands of amplified spontaneous emission, which show the same anisotropy as the bandgap, have been observed. Besides, the isotropic amplified spontaneous emission band has been detected at the high intensity excitation, which band was tentatively understood as the result of the weak localization of photons in the gain medium with embedded scatterers.
S. G. Romanov, T. Maka, C. M. Sotomayor Torres, M. ller, and R. Zentel, "Emission Properties of Dye-Polymer-Opal Photonic Crystals," J. Lightwave Technol. 17, 2121- (1999)