A highly reflective biogenic photonic material from core-shell birefringent nanoparticles
- 1 February 2020
- journal article
- research article
- Published by Springer Science and Business Media LLC in Nature Nanotechnology
- Vol. 15 (2), 138-+
- https://doi.org/10.1038/s41565-019-0609-5
Abstract
The birefringence of isoxanthopterin crystalline spherulites enhances the reflectivity of a biological photonic crystal. Spectacular natural optical phenomena are produced by highly reflective assemblies of organic crystals. Here we show how the tapetum reflector in a shrimp eye is constructed from arrays of spherical isoxanthopterin nanoparticles and relate the particle properties to their optical function. The nanoparticles are composed of single-crystal isoxanthopterin nanoplates arranged in concentric lamellae around a hollow core. The spherulitic birefringence of the nanoparticles, which originates from the radial alignment of the plates, results in a significant enhancement of the back-scattering. This enables the organism to maximize the reflectivity of the ultrathin tapetum, which functions to increase the eye's sensitivity and preserve visual acuity. The particle size, core/shell ratio and packing are also controlled to optimize the intensity and spectral properties of the tapetum back-scattering. This system offers inspiration for the design of photonic crystals constructed from spherically symmetric birefringent particles for use in ultrathin reflectors and as non-iridescent pigments.Funding Information
- Israel Science Foundation (354/18)
- Israeli centers of research excellence - “circle of light”
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