Fig. 1. Structural color films based on nanoparticles. TEM images of SiO₂ nanospheres with four particle sizes, particle sizes are (a1) (210±10) nm, (a2) (240±8) nm, (a3) (270±13) nm, (a4) (300±11) nm, respectively; (b) SEM image of opal structure formed by self-assembly of 240 nm SiO₂ particles; (c) digital photos of structured color films at different shooting angles obtained by using glass slides as substrates; (d) reflection spectra of opal structure formed by arrangement of nanoparticles with different particle sizes (0°); (e) reflection spectra of opal structure filled with carbon black doped epoxy resin (0°); (f) digital photos of opal structure filled with transparent epoxy resin; (g) digital photos of etched epoxy resin IO structure film and its angle dependence

Fig. 2. Structural color films with long afterglow anti-counterfeiting function. (a) Structured color films with long afterglow anti-counterfeiting layer excited by ultraviolet light; (b) long afterglow anti-counterfeiting films with words "YSU" and flower and leaf patterns

Fig. 3. Performance characterization of anti-counterfeiting film. (a) 20 rewriting tests and reflection spectra of films before and after test; (b) luminescence spectra of two long afterglow materials and reflection spectra of corresponding IO structure films; (c) display and hiding of anti-counterfeiting marks realized by ethanol wetting and scraping; (d) film without matching photonic band gap

Fig. 4. Robustness test of films. (a) Bending test results; (b) digital photos of corrosion test and spectral comparison before and after immersion