Photonic glass for high contrast structural color

TL;DR

This paper demonstrates that combining specific particle geometries with short-range order in photonic glass can produce high-contrast, saturated structural colors by manipulating Fourier transforms of the particle arrangement.

Contribution

It introduces a novel approach using core-shell particles with tailored refractive index distributions to achieve sharp spectral features in photonic glass.

Findings

Core-shell particles enable sharp reflection spectra.

Shifting the Fourier transform zero enhances color saturation.

Theoretical predictions are confirmed by simulations.

Abstract

Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, also called photonic glass, show low color saturation due to gradual transition in reflectivity. No significant improvement is usually expected from particles optimization, as the Mie resonances are broad for small dielectric particles with moderate refractive index. Moreover, the short range order of a photonic glass alone is also insufficient to cause sharp spectral features. We show here, that the combination of a well-chosen particle geometry with the short range order of a photonic glass has strong synergetic effects. We demonstrate how core-shell particles can be used to obtain a sharp transition in the reflection spectrum of photonic glass which is essential to achieve a strong color saturation. The Fourier transform required for a highly saturated color can be achieved by shifting the first zero position of the motif Fourier transform to smaller wave numbers in respect to the peak of the lattice Fourier transform. We show that this can be obtained by choosing a non-monotonous refractive index distribution from the center of the particle through the shell and into the background material. The first-order theoretical predictions are confirmed by numerical simulations.