Ternary non-close-packed photonic crystals with tunable optical properties through varying shell thickness of hollow silica

Fabrication of photonic crystals with tunable optical properties is an important issue. Herein, we have prepared a series of hollow silica (h-SiO 2 ) with different sizes and shell thicknesses and use them to construct ternary non-close-packed photonic crystals (TNCPPCs) in liquid and gel states (air, SiO 2 , propylene carbonate/resin). Meanwhile, with the shell thickness of the h-SiO 2 from 15   nm to 40   nm, the color purity of the photonic crystal structural color can be tuned from 53% to 82%, and the transparency of the photonic crystal film can be tuned from 96% to 91%. Due to the existence of cavities and the index matching of the resin and SiO 2 , h-SiO 2 photonic crystal films have no structural color unless wetted by water. Furthermore, a patterned film is obtained using an electric field and the patterned information is invisible until wetted by water, which has achieved the process of information encryption and decryption. Overall, this work will provide new guidance for fabricating photonic crystals with tunable optical properties (structural color, color purity, and transparency) and will broaden the application of h-SiO 2 photonic crystals in sensing and information anti-counterfeiting.