Omnidirectional brightness and UV-shielding bifunctional pigments via CeO2 photonic crystal microbeads

Abstract

Photonic crystal microbeads with symmetrical structures exhibit non-iridescent colors, making them valuable as stable and vibrant colorants. However, their brightness is limited by small refractive index (RI) contrast. Enhancing this contrast is key to achieving more vivid structural colors. Herein, CeO₂@SiO₂ photonic crystal microbeads (10–30 µm) with a high RI were successfully fabricated by the microfluidic method. By tuning the diameter of CeO₂@SiO₂ colloidal particles from 160 nm to 265 nm, blue, green, and orange-red microbead pigments were successfully fabricated, exhibiting vivid structural colors across a wide viewing angle range of 0° to 75°. Interestingly, films composed of these microbead pigments and polymers showed bright, angle-independent colors and strong UV absorption. These CeO₂@SiO₂ microbeads can not only be used as pigments for bright, omnidirectional structural colors but also have potential applications in various fields that require UV-shielding, such as color lenses, decorative coatings, and cosmetics.