Angular redistribution of near-infrared emission from quantum dots in 3D photonic crystals

We study the angle-resolved spontaneous emission of near-infrared light sources in 3D photonic crystals over a wavelength range from 1200 to 1550 nm. To this end PbSe quantum dots are used as light sources inside titania inverse opal photonic crystals. Strong deviations from the Lambertian emission profile are observed. An attenuation of 60% is observed in the angle dependent radiant flux emitted due to photonic stop bands. At angles that correspond to the edges of the stop band the emitted flux is increased by up to 34%. This increase is explained by the redistribution of Bragg-diffracted light over the available escape angles. The results are quantitatively explained by an expanded escape-function model. This model is based on diffusion theory and adapted to photonic crystals using band structure calculations. We identify the need to separately consider the transport mean free path of both the emitted light and the light used for excitation. Here, the model is applied to describe emission in the regime where samples are optically thick for the excitation light, yet relatively thin for the photoluminesence light.