Fig. 1.

Natural PCs: a) mine stone b) peacock feathers c) butterfly wing d) chameleon skin and artificial: e) PCs opal films f) IOs. Schematic representation of PCs structures g) 1D h) 2D i) 3D (the red and blue colors representing periodicity in 1D, 2D, and 3D PCs) with related SEM images. Copyright 2019, Royal Society of Chemistry. Reproduced from Ref. [40]. Copyright 2008, International Society for Optics and Photonics. Reproduced from Ref. [41]. (PCs: photonic crystals, IOs: inverse opals, 1D: One-dimensional, 2D: Two-dimensional, 3D: Three-dimensional, SEM: Scanning electron microscopy). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)