This article was taken from the July 2012 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
Each month Wired's chemist Dr John Emsley deconstructs an everyday product. He is the author of 110 research papers and ten books, including his most recent: Nature's Building Blocks, 2nd edition (OUP).
Ingredients
Arsenic
Gallium
Indium
Yttrium
Lanthanoids
Selenium
Gallium
Gallium arsenide (GaAs) was the basis of the original red LEDs, joined by gallium phosphide (GaP), which glows yellow-green.
It was gallium nitride (GaN) that revolutionised LEDs because it emits blue-violet light, completing the full spectrum of colours.
Indium
As indium gallium nitride (InGaN), this provides green LED light. Indium has a much wider role as indium tin oxide (ITO), which acts as an electrode in solar panels and flatscreen displays.
Indium nitride, phosphide and antimonide are used in microchips.
Yttrium
Yttrium aluminium garnet (YAG) is used to coat blue-emitting LEDs, where it turns some of their light to other colours of the spectrum. Yttrium, as mixed yttrium, barium, copper oxide (YBa2Cu3O7), is part of the superconductor magnets used in MRI equipment.
Lanthanoids
These are added to YAG to boost the white light. Cerium absorbs UV and re-emits it as visible light; gadolinium and terbium soften the light produced by YAG. Cerium oxide is found in catalytic convertors and gadolinium is used in regulating nuclear reactors.
Selenium
In LEDs, zinc selenide glows with a bluish light. When light falls on metallic selenium, its electrical conductivity increases 1,000-fold, and it used to be found in light meters, solar cells and photoelectric cells. Selenium compounds are still used in anti-dandruff shampoos.
Arsenic
Employed as gallium arsenide phosphide (GaAsP), this glows red-orange in an LED. Arsenic (in tiny amounts) is also vital to semiconductor production. In the past, arsenic could be found in weedkillers, rat poisons, cosmetics and medicines. Some medicines still use it.
This article was originally published by WIRED UK
