Absence of Red Structural Color in Photonic Glasses, Bird Feathers and Certain Beetles

TL;DR

This paper explains why natural and synthetic disordered photonic structures lack angle-independent red colors, attributing it to particle backscattering resonances that hinder red light formation.

Contribution

The study introduces a scattering theory model that explains the absence of red structural color in disordered photonic materials and provides design rules for achieving red colors.

Findings

Backscattering resonances in particles prevent red color formation.

Disordered structures produce angle-independent colors due to isotropic microstructures.

Design guidelines for creating red structural colors in colloidal glasses.

Abstract

Colloidal glasses, bird feathers, and beetle scales can all show structural colors arising from short-ranged spatial correlations between scattering centers. Unlike the structural colors arising from Bragg diffraction in ordered materials like opals, the colors of these photonic glasses are independent of orientation, owing to their disordered, isotropic microstructures. However, there are few examples of photonic glasses with angle-independent red colors in nature, and colloidal glasses with particle sizes chosen to yield structural colors in the red show weak color saturation. Using scattering theory, we show that the absence of angle-independent red color can be explained by the tendency of individual particles to backscatter light more strongly in the blue. We discuss how the backscattering resonances of individual particles arise from cavity-like modes, and how they interact with the structural resonances to prevent red. Finally, we use the model to develop design rules for colloidal glasses with red, angle-independent structural colors.