Critical Metals: The Chemistry of Light

The 1880s were a time of rapid industrialization. Cities were growing. Factories were expanding. Inventors like Thomas Edison were racing to develop better ways to light up streets and buildings. The quest to find a long-lasting and affordable lamp drove research and experimentation with many unusual metals.

Auer realized that the incandescent properties of the rare earth metals might make them ideal for lighting. When heated properly, these metals glow rather than burn. Their incandescence can turn heat into light more efficiently than candles or gas fires.

Auer forms a company and goes into production. But the combination of magnesium, lanthanum, and yttrium gives off a sickly green light that consumers don’t like. Auer’s first company goes bankrupt in 1889. Auer tries a new formula in 1890. This thorium and cerium mix produces a warmer, whiter light, and Auer is soon back in business.

By 1910, more than 900 women worked at the Welsbach factory in Gloucester City, New Jersey. They sewed, trimmed, tested and packed lighting “mantles” for shipment across the United States. 

Thorium and cerium were extracted from ore that was shipped to New Jersey from North Carolina, Brazil, and India. The leftover sand was used as landfill at many places in Gloucester CIty and Camden, New Jersey. But thorium is a radioactive metal, and the Welsbach factory left behind a toxic legacy.

Today the former Welsbach factory is a Superfund site. The U.S. Environmental Protection Agency and the Army Corps of Engineers have spent more than $300 million removing radioactive soil and monitoring groundwater safety.

In an incandescent bulb, electrons are squeezed through a long, thin coil of metal. This filament gets hot and bright. An inert gas inside the glass globe keeps the filament from burning. But incandescent bulbs waste a lot of heat while making light.

Fluorescent light offers a cooler, more energy efficient alternative. A current of electrons creates ultraviolet radiation as it shoots through a tube filled with mercury vapor. This radiation hits the phosphors, metallic compounds that coat the tube’s inside. Each phosphor converts UV radiation into specific wavelengths of visible light.

Compact fluorescent lightbulbs use europium phosphors to generate light with 75% less electricity than a traditional tungsten incandescent bulb. The United States Congress enacted the first U.S. standards for lighting efficiency in 2007.

During the 2010s, as lightbulb makers shifted production and homeowners replaced burned out bulbs, residential electricity demand per household declined for the first time ever. 

In addition to incandescence and fluorescence, metals can make light through Light Amplification by Stimulated Emission of Radiation—the laser! 

Lasers are devices that use energy to stimulate molecules to emit light in specific wavelengths. The molecules of the lasing medium are often held in crystalline forms, like ruby or garnet.

One important application of laser light was the development of fiber optics. Thin, flexible fibers made of highly purified glass can channel laser light. When combined with signal processing technologies, fiber optics make it possible to carry a lot of digital information at the speed of light.

Researchers hope to develop alternatives to solvent extraction by better understanding chemical compounds. Neodymium and yttrium lasers provide pictures of how compounds vibrate and move, information that can be useful in finding metals separations that are more efficient and less toxic.