materials are currently produced as by-products of refinement or extraction of more common materials and are bought from suppliers as waste products. Increased demand for these materials may surpass the amount extracted with current production methods, thus placing a risk on the scaling up of systems reliant on these elements. Elements that are known to pose joint-production risks are gallium, tellurium, and selenium. Gallium, an essential component of many high-efficiency thin-film and multi-junction photovoltaic cells, is obtained as a by-product of aluminum refining, and tellurium and selenium are most often obtained as by-products of copper refining. The locations of these common production metals will determine production of these ECEs and are shown in Figure 9.1. Cadmium is usually produced from zinc processing but is refined out because of its toxicity and thus is commercially available at relatively low and stable prices and not qualified as an ECE.5

The use of light-emitting diodes (LEDs) for lighting is another example of how optics is affecting energy conservation in several industrial nations. Several countries around the world have initiatives to phase out the use of incandescent lightbulbs by 2020. LEDs have been identified as the leading replacement technology for this mass market. One promising approach to obtain white light is to use gallium-nitride (GaN)-based blue LEDs in conjunction with fluorescent phosphors, which convert part of the blue light into yellow and red. Many of the efficient phosphors contain rare earth elements (REEs). The two key REEs that provide color LED lighting are europium and terbium. Currently, the majority of the REEs are produced in China, and the Chinese government has imposed export restrictions.6 The United States will have to develop a novel strategy either to develop new materials for LED applications or to encourage research toward cost-effective and environmentally friendly purification, mining, and production. Finally, the United States should consider reclamation from waste to extract rare materials inasmuch as U.S. waste management derives most of its profit from processing waste to remove precious and rare metals and other substances.

NOVEL STRUCTURES: SUB-WAVELENGTH OPTICS, METAMATERIALS, AND PHOTONIC CRYSTALS

In addition to new core materials, there is much promise in tailoring existing materials in novel ways to produce innovative results. These new materials, known as metamaterials or nanophotonic materials, are materials that can be developed

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5 APS and MRS. 2011. Energy Critical Elements.

6 Bradsher, K. 2010. “China Said to Widen Its Embargo of Minerals.” New York Times. October 19. Available at http://www.nytimes.com/2010/10/20/business/global/20rare.xhtml?pagewanted=all. Accessed August 29, 2011.



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