Solution‐Processable Photonic Inks of Mie‐Resonant Hollow Carbon–Silica Nanospheres

Abstract

Whereas ordinary color comes from selective absorption by pigments or dyes, [1,2] structural color comes from coherent scattering from nanostructures. [3,4] However, ordered nanostructures lead to structural color that depends strongly on the viewing angle, which limits its practical applications. By contrast, materials with short-range order, such as colloidal glasses [5][6][7][8] or blue bird feathers, [9][10][11][12][13] show structural color that is independent of angle. While these materials could in principle be used in applications that require structural color that is indistinguishable from pigment, they also tend to diffuse or multiply scatter light, leading to colors that are not saturated. The multiple scattering can be suppressed by dyes such as carbon black.An alternative approach is to rely on the wavelengthdependent scattering of the particles themselves. Cho et al. [14] Hollow carbon-silica nanospheres that exhibit angle-independent structural color with high saturation and minimal absorption are made. Through scattering calculations, it is shown that the structural color arises from Mie resonances that are tuned precisely by varying the thickness of the shells. Since the color does not depend on the spatial arrangement of the particles, the coloration is angle independent and vibrant in powders and liquid suspensions. These properties make hollow carbon-silica nanospheres ideal for applications, and their potential in making flexible, angle-independent films and 3D printed films is explored. Photonic Inks

Colloidal Mie Resonators for All‐Dielectric Metaoptics

“…To achieve large area structural coloration by Mie resonators, Mie resonator color inks that are capable of being coated or inkjet printed on a substrate have been developed. Kim et al [ 93 ] presented hollow carbon–silica nanospheres that exhibit angle‐independent Mie scattering. The carbon inside the hollow silica increases the effective refractive index and the extinction coefficient.…”

Color Toning of Mie Resonant Silicon Nanoparticle Color Inks

“…In order to control multiple scattering, we propose a mixture system of a Si NP ink with light-absorbing materials. This approach, that is, adding carbon black (CB) ,, or melanin , to suppress multiple scattering, has been used in the colloidal solutions of low-index NPs. However, it has never been applied to a solution of high-index Mie resonators.…”

Colors from correlated disordered photonic systems -- can we outperform nature?

“…While combing different scattering approaches can help improving color purity and saturation in photonic glasses, they might be more challenging to realize in natural systems than simply combing different mechanisms, such as adding absorption. Once absorption is added, more pure and saturated colors can be achieved 10,28 . However in synthetic systems, especially in the case of metallic nanoparticles 29 , one might question the need of adding a structural component, as it plays a redundant role in the overall visual response.…”