Effect of disorder on the optical properties of colloidal crystals

Colloidal crystals offer a promising route for the formation of three-dimensional photonic crystals. The primary constraint in working with these materials is the disorder present in these self-assembled materials. Sphere vacancies, line dislocations, and random position errors all lead to a degradation in the optical properties. It is important to characterize these effects so as to guide further developments in colloidal crystal optics. Here, we report a systematic and quantitative study of disorder in colloidal crystals with visible diffractive properties. Using optical spectroscopy and digital imaging we have correlated several measures of structural disorder with variations in the transmissive and reflective optical properties. We observe a critical size distribution above which rapid deterioration of the lowest stop band is observed. Below this critical size distribution, we observe excellent optical quality, nearly independent of the size distribution. Single sphere vacancies also increase in crystals formed from more polydisperse spheres. The primary effect of this type of defect is to increase the broadband diffuse scattering.