Assertion: opal | /r/HasProperty | photonic crystals
Facets:
value: for visible light
type: PURPOSE
Source sentences:
text: The notion that opals are photonic crystals for visible light was expressed in 1995 by Vasily Astratov's group.
text: The notion that opals are photonic crystals for visible light was expressed in 1995 by Vasily Astratov's group.