Europium, Terbium and Yttrium
Rare earth elements
Atomic numbers: 63; 65; 39
Used in: energy-efficient lighting
Criticality ratings: critical; critical; critical
Europium and terbium have long been an entertaining double act: their phosphorescent properties – terbium in yellow-green and europium in blue and red – help to produce the images on most television screens. Their rare earth cousin yttrium plays a quiet but crucial supporting role, hosting the red-releasing europium ions.
These colourful qualities have recently secured the europium-terbium duo another gig in energy-saving compact fluorescent light bulbs. These bulbs work by exciting mercury vapour to emit ultraviolet light, which is then absorbed by phosphorescent materials coating their insides to produce visible frequencies of light. One complaint made about early versions was that they did not produce the same warm light as the incandescent tungsten bulbs they replaced – a problem resolved by switching the coating to the right blend of terbium and europium.
The next generation of energy-efficient lighting, based on LEDs, might see europium strike out alone: adding europium ions to a blue LED turns some of its light yellow, giving a white output overall. That could free up terbium to pursue its own projects, such as perhaps replacing dysprosium in the manufacture of high temperature permanent magnets.
All that depends on securing additional supplies, however. According to the DoE, europium could be in short supply as early as 2015 – and terbium even sooner. For yttrium we have already reached crunch time: demand outstripped supply in 2010.
Lymphoma sufferers will recognize 90 Yttrium as the isotope that is used in Zevelin used as a treatment