Emission spectroscopy of ZnO inverse opal photonic crystals

Light emitted within a photonic crystal structure can be used to probe both the photonic density of states and the anisotropic propagation of light through the structure. Here we present results of angle- and polarization-resolved measurements of photoluminescence from three-dimensional ZnO photonic crystals. The ZnO inverse opals were fabricated by infiltration of polystyrene synthetic opal templates using atomic layer deposition. The resulting nanocrystalline ZnO structures exhibit strong UV emission as well as a broad defect emission peak, allowing us to observe the dispersion of the primary as well as higher-order PBGs over the entire visible spectrum. The spontaneous emission spectrum is strongly modified and anisotropic due to the effect of the photonic band structure. The observed features are correlated to transmission and reflection measurements as well as calculated (reduced) band structures in the F-L-K plane of the fee Brillouin zone. Apart from the suppression and redistribution of light near the primary and higher band gaps, we observe a strong enhancement in the PL peaks due to light propagation in higher (e.g. 5th and 6th) photonic bands at frequencies and angles where no PBG exists.