Fig. 4. Enhanced PS photonic crystals with various GQDs concentrations. (a) Photographs of polystyrene PCs films at various GQDs concentration. The concentration from left to right, was 0 wt%, 0.1 wt%, 0.5 wt%, 1 wt%. The scale bar is 2.5 mm. (b) Reflectance spectra of PS/GQDs photonic crystal films. (c) Corresponding normalized reflection peak intensity of PS/GQDs photonic crystal films. (The size of PS nanoparticles was 214 nm. GQDs underwent hydrothermal reaction for 7 hours.).