in your element glows green Geng Deng relates how terbium, a garden-variety , has found its way into our daily lives owing to its green phosphorescence.

t may be one of the rarer rare-earth model allowed a wide range of colours elements in the Earth’s crust, but terbium to be produced. Between the 1950s and Iis actually quite common around us. 1990s, those monitors delivered terbium Despite their name, the rare-earth elements compounds to millions of households (which consist of the as well as around the globe. Although the advent of and ) aren’t all that scarce; flat-panel technologies in the late 2000s element 65 for example is more abundant has curbed that application, terbium- than mercury, and as numerous and containing compounds have also found use monitors of modern life have made use of as probes in the biomedical field, such as in green terbium-based , it has seeped fluoroimmunoassays4 and supramolecular into our homes and working environments. luminescent sensors5. The story of terbium discovery started in LIBRARY PHOTO SCIENCE A perhaps more exotic use of element , a prolific small village in Sweden that 65 is in an called terfenol-D, which has no fewer than four rare-earth elements ground electronic-state transitions1, with one consists of terbium, iron and : it named directly after it — yttrium, terbium, transition contributing the main emission is a magnetostrictive material that contracts and — and from whose peak at 545 nm. Many of its rare-earth and expands in a magnetic field. Because it earths (as were then called) several cousins also luminesce brightly in different is able to withstand high strains, terfenol-D other elements were also isolated (scandium, colours; for example, (iii) is a red has been used in actuators and underwater , , and lutetium). emitter while its reduced form europium(ii) transducers. It also serves in the portable It took decades to identify the composition is a blue one. But although those emissions system ‘SoundBug’, which can be attached of a black found in Ytterby by Carl were well-known, it wasn’t until the second to any resonant flat surface (such as, wood, Axel Arrhenius in 1787, first referred to as part of the twentieth century that they were or ) to turn it into a speaker: the ytterbite. It was later renamed after taken advantage of for practical applications magnetostrictive material converts electrical Johan Gadolin, who realized it contained an in lighting. input into vibrations by changing the applied unknown earth; that is, the of a new The incandescent lamp, invented by magnetic field, which are then amplified by element, which he called yttria. Thomas Edison in 1879, had been widely the resonant surface. In 1843 Swedish chemist Carl Gustaf used for over a century. But it is inherently Located in the middle of the Mosander separated an yttria sample into energy-inefficient: heating a wire with an lanthanides — a part of the three components: yttria (mostly consisting electric current to the point that it will that has remained relatively unexplored of yttrium oxide), as well as erbia and terbia, glow means that most of the energy used — terbium has shone through owing to its each of which, he believed, contained a is dissipated in the form of heat and only a distinctive green phosphorescence and found new element. He was right — but a mix- small fraction is converted into . In the exciting uses. ❐ up of Mosander’s samples during their 1960s, rare-earth salts came into focus2,3 as spectroscopic analysis means that terbium they waste little energy during the emission GENG DENG is a graduate student in was isolated from his original erbia, while process. Furthermore, the green-emitting the Department of Chemistry, Tsinghua erbium was found in his terbia. This was terbium compounds could be combined with University, Beijing 100084, China. He is also just too confusing, so the later the red- and blue-emitting europium ones to one of the authors of the textbook: Physical also swapped names to match those of their make white-light fluorescent lamps. The first Organic Chemistry: Structure and Principle. principal components. commercial such rare-earth-based energy- e-mail: [email protected]. Like the other lanthanides, terbium’s efficient lamp was made in 1974, and this most common is +iii. The type of lighting soon spread across the world. References 1. Andres, J. & Chauvin A.-S. in The Rare Earth Elements (ed. Atwood, green (or light-lime) phosphorescence under Meanwhile, traditional colour television D. A.) 135−152 (John Wiley & Sons, 2012) light of its trivalent salts, such as sets and monitors were also being developed 2. Ropp, R. C. J. Electrochem. Soc. 111, 311−317 (1964). Tb2(SO4)3 (pictured), has long been known that used cathode ray tubes, in which 3. Wanmaker, W. L. & Bril, A. Philips Res. Repts. 19, 479−497 (1964). — it is so intense that it can be seen with the electron beams are sent to the screen to 4. Moore, E. G. Samuel, A. P. S. & Raymond K. N. Acc. Chem. Res. 42, 542−552 (2009). naked eye. It arises from several excited-to- excite phosphors and in turn generate 5. dos Santos, C. M. G. Harte, A. J. Quinn, S. J. & Gunnlaugsson T. images. Here as well the combination of Coord. Chem. Rev. 252, 2512−2527 (2008). terbium and europium compounds in the red–green–blue (RGB) additive colour Corrected after print: 31 January 2018 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb 110 NATURE CHEMISTRY | VOL 10 | JANUARY 2018 | www.nature.com/naturechemistry ©2018 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.

Correction In the In Your Element ‘Terbium glows green’ (Nat. Chem. 10, 110; 2018), phosphorescence was mistakenly described as in three instances: the standfirst, the fourth paragraph, and the final paragraph. Furthermore, the line from the fourth paragraph “Many of its rare-earth cousins also fluoresce” was changed to “Many of its rare-earth cousins also luminesce”. This has been corrected after print 31 January 2018.

©2018 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.