Photonic pigments
Creating colored effects from disordered nanostructured materials
Kevin Vynck
Institut Lumière Matière (iLM), Villeurbanne (Lyon), France
Email: kevin.vynck@univ-lyon1.fr
Web: https://ilm-perso.univ-lyon1.fr/~kvynck/

Kingfisher(martin-pêcheur)© Bodo Wilts (U. Salzburg)

Stavenga et al.,J. Exp. Biol. 214, 3960 (2011)

Visual appearance of disordered materials
Opacity, mattness, whitenessColors created by absorption

David (Michelangelo)

2Colored effects due to nanostructures in nature
Parrot (bird)

H. Yin et al., PNAS 109, 10798 (2012)

Opal (gemstone)

Pollia condensata (plant)

2 µm

H. Miguez et al., Appl. Phys. Lett. 71, 1148 (1997)

Vignolini et al., PNAS 109, 15712 (2012)3

Man-made nanostructured materials for coloring applications
Thin-film interference & disorderInterference pigments

Cellulose-based
photonic pigments

Parker et al., Nat. Commun. 13, 3378 (2022)

Resonant scattering & correlated disorder
Photonic glasses
Nanostructured
surfaces

Schertel et al.,Adv. Opt. Mater. 7, 1900442 (2019)

Vynck et al., Nat. Mater. 21, 1035 (2022)
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Light transport in 3D disordered media (volume scattering)

Differential scatteringcross-section (µm2 . sr −1 )

𝜌 : number density of scattering events (μm−3 )Scattering mean free path (µm)

Transport mean free path (µm)

5Link between microscopic properties and light transport

Scattering by an assembly ofparticles – Far-field interference
depending on 𝑎/𝜆 and 𝜃

Differential scattering crossStructure factor
section of an individual particle (correlation between
particle pairs)
𝜌 : particle number density (μm−3 )Fraden & Maret, Phys. Rev. Lett. 65, 512 (1990) ; Saulnier et al., Phys. Rev. B 42, 2621(R) (1990)

Review on light in correlated disordered media
Vynck et al., Rev. Mod. Phys., to appear (2023)
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Single particle scattering: optical resonances

Spherical particle of radius 𝑟 madeof some material (Ag, Si, SiO2, ...)

Colours predicted from the spectra
Particle resonances constitutea first degree of freedom tocreate structural colors.
But high refractive index
materials are required7

Coherent scattering by particle pairs: structural correlations
Structure factor 𝑆Scattering angle θ𝑎𝜃4𝜋 sin𝜆2

Enhanced backscattering(structural color)
Reduction ofscattering efficiency(transparency)

Reduced frequency 4πa/λ

Structural correlations
constitute a 2nd degree offreedom to create structuralcolors.

8Microspheres of core-shell particles
Park et al., Angew. Chem. Int. Ed. 53, 2899 (2014)9

Microspheres of core-shell particles
Park et al., Angew. Chem. Int. Ed. 53, 2899 (2014)

Solution of photonic pigments

Vivid structural colors thanks to anengineering of short-range correlations

10Structural colors of 3D photonic glasses
Schertel et al., Adv. Opt. Mater. 7, 1900442 (2019)

Polystyrene spheres in air
1 µm

Integrating sphere measurements

11Palette of structural colors from 3D photonic glasses
From light transport (Monte-Carlo) simulations
Hwang et al., PNAS 118, e201551118 (2021)

Volume multiple scattering generally leads to faint (whitish) colors
12Light scattering by nanostructured surfaces (surface scattering)

𝐄b𝐄s
Scattering surface

DiffuseScattering surface

I. Simonsen, Eur. Phys. J. Special Topics 181, 1-103 (2010)

Approximate reflectance model to predict the visual appearance of nanostructured objects

Vynck et al., Nat. Mater. 21, 1035 (2022)

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Noniridescent diffuse colors with particle resonances

Random (uncorrelated) assembly ofsilicon particles on a glass substrate

Noniridescent diffuse colors,nearly independent on theparticle density

Specular iridescence thatstrongly depends on theparticle density

14

Importance of both diffuse and specular components

15

Engineering of structural correlations• Suppression of the diffuse intensity near
the specular direction• Sharp high-intensity lobes at larger angles

16« Diffuse halo »Silver, r=90 nm, on glass, ρ=5 µm-2

17

A quite unusual visual appearance

Predictive rendering by Romain Pacanowski (INRIA Bordeaux Sud-Ouest)
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Take-home messages• Many approaches to structural colors exist: thin-film interference,particle resonances, structural correlations
Photonic microspheres

Nanostructured
surfaces

Park et al., Angew. Chem. Int. Ed. 53, 2899 (2014)

Vynck et al., Nat. Mater. 21, 1035 (2022)• Diffuse colors are produced by disordered nanostructures• Single scattering leads to more vivid colors : microspheres / surfaces• Correlated disorder (ubiquitous in nature) allows creating coloredeffects with low-index materials

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Acknowledgments

Glenna Drisko
Philippe Lalanne

Mona Tréguer
Delapierre

Adrian Hereu

Adrian Agreda

Xavier Granier
Romain Pacanowski

Pascal Barla

Silvia Vignolini

Mélanie Bay20