OPALS
Opals are amorphous form of silica. Opals are not hard mineral-like substances without regular geometrical crystallinity. However, they impress with their coloration since opals diffract light. This mysterious property of color change is called opalescence. Opalescence property occurs in natural and artificial structures. Now it is well-known that coloration comes from the periodic structures. Physicists call this opalescent structure "photonic crystals". (F. Marlow, et al., "Opals: Status and Prospectus," Angewandte Chemie, vol. 48 pp. 6212-6233, 2009).
Figure shows (a) natural opal, (b) SEM image of natural opal and (c) SEM image of artificial opal (adopted from "Opal Photonic Crystals: Structure, formation, and Optical Properties" Dissertation, Muldarisnur, F.Marlow, Andreas Dirk Wieck).
Figure shows periodic structures in nature (a) Morpho rhetenor butterfly, (b) detail of its scales, inset: lateral shematic of the scale (scale bar is 100 um), (c) the sea mouse, (d) one of the sea mouse`s spine and the corresponding TEM image of its cross section. The dark areas are chitin, the light areas are voids with radious of 0.51 um, (e) a Peacock, (f) an SEM image of barbules and (g) the cross section of the barbule. (adopted from "Opal Photonic Crystals: Structure, formation, and Optical Properties" Dissertation, Muldarisnur, F.Marlow, Andreas Dirk Wieck).
Opals are amorphous form of silica. Opals are not hard mineral-like substances without regular geometrical crystallinity. However, they impress with their coloration since opals diffract light. This mysterious property of color change is called opalescence. Opalescence property occurs in natural and artificial structures. Now it is well-known that coloration comes from the periodic structures. Physicists call this opalescent structure "photonic crystals". (F. Marlow, et al., "Opals: Status and Prospectus," Angewandte Chemie, vol. 48 pp. 6212-6233, 2009).
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