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 the reflectivity spectrum. No significant improvement is usually expected from particles optimization, as 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. Using a first-order approximation and an Ewald sphere construction the reflectivity of such structures can be related to the Fourier transform of the permittivity distribution. The Fourier transform required for a highly saturated color can be achieved by tailoring the substructure of the motif. We show that this can be obtained by choosing core-shell particles with 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.
Highlights
Structural color is a color based on selective light scattering and reflection from nanostructures[1,2,3]
We show that sharp transitions in the FT of the photonic glass (PhG) structure can be obtained by tailoring the sub-structure of the motif which leads to a shift of the first zero position of the motif Fourier transform to smaller wave numbers
If we further increase the wave number, the light will be backscattered into a cone of light with its opening angle spreading as the wavelength is further reduced
Summary
Guoliang Shang[1], Lukas Maiwald[1], Hagen Renner[1], Dirk Jalas[1], Maksym Dosta[2], Stefan Heinrich[2], Alexander Petrov 1,3 & Manfred Eich[1,4]. Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, called photonic glass, show low color saturation due to gradual transition in the reflectivity spectrum. The Fourier transform required for a highly saturated color can be achieved by tailoring the substructure of the motif We show that this can be obtained by choosing core-shell particles with a non-monotonous refractive index distribution from the center of the particle through the shell and into the background material. To the best of our knowledge, for the first time, we are providing a comprehensive theoretical and simulation treatment of structural colors employing photonic glasses based on first-order Born approximation It helps to explain the main mechanisms of color generation and supplies clear design and synthesis rules to achieve high color saturation. Numerical simulations confirm the appearance of sharp transitions in the reflection spectra for the optimized structures
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