Near-Infrared Light Trapping in Disordered Inverse Opals

We show that the optical properties of CdSe inverse opal films prepared from electrodeposition within the pore space of self-assembled polystyrene bead colloidal crystal templates are highly dependent upon both the pore size (300, 400, or 500 rim) and the degree of disorder within the film. These features cause a significant amount of infrared light (from 800-1300 rim) to undergo multiple scattering events and become trapped within the film. The disordered 500 nm pore size inverse opal is shown to effect the greatest near-infrared light scattering, which increases the path length of light by a factor of similar to 10, approaching the theoretical limit. Light trapping over a wide portion of the near-infrared region, driven by both the randomly disordered pore structure and the high refractive index contrast present in the CdSe inverse opal architecture, was demonstrated for the first time and can potentially be used to manipulate the absorption and emission properties in a range of optoelectronic materials.