Icosahedral colloidal clusters are a new class of spherical colloidal crystals. This cluster allows for potentially superior optical properties in comparison to conventional onion-like colloidal supraballs because of the quasi-crystal structure. However, the characterization of the cluster as an optical material has until now not been achieved. Here we successfully produce icosahedral clusters by assembling silica particles using bulk water-in-oil emulsion droplets and systematically characterize their optical properties. We exploit a water-saturated oil phase to control droplet drying, thereby preparing clusters at room temperature. In comparison to conventional onion-like supraballs with a similar size, the icosahedral clusters exhibit relatively strong structural colors with weak nonresonant scattering. Simulations prove that the crystalline array inside the icosahedral cluster strengthens the collective specular diffraction. To further improve color saturation, the silica particles constituting the cluster are coated with a thin-film carbon shell. The carbon shell acts as a broad-band absorber and reduces incoherent scattering with long optical paths, resulting in vibrant blue, green, and red colors comparable to inorganic chemical pigments.

中文翻译：

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二十面体胶体簇的受控组装用于结构着色

二十面体胶体簇是一类新型的球形胶体晶体。由于具有准晶体结构，因此与传统的洋葱状胶体超球相比，该簇具有潜在的优越光学性能。但是，迄今为止尚未实现将簇作为光学材料的表征。在这里，我们通过使用大量油包水型乳剂液滴组装二氧化硅颗粒，成功地制备了二十面体簇，并系统地表征了它们的光学性质。我们利用水饱和油相来控制液滴的干燥，从而在室温下制备团簇。与具有类似尺寸的常规洋葱状超球相比，二十面体簇表现出相对强的结构颜色，具有弱的非共振散射。仿真证明，二十面体簇内部的晶体阵列增强了集体镜面衍射。为了进一步提高色彩饱和度，构成簇的二氧化硅颗粒被薄膜碳壳覆盖。碳壳充当宽带吸收剂，并通过长光程减少不相干的散射，从而产生与无机化学颜料相当的鲜艳的蓝色，绿色和红色。