Erbium

Erbium is a silvery lanthanide with the configuration [Xe]4f12 6s2, and it forms the Er3+ ion, whose salts and oxide are rose pink. Its value comes from one particular electronic transition: excited Er3+ ions emit light at about 1.55 micrometres. That happens to be the wavelength at which silica optical fibre loses the least light, a coincidence that underpins modern long-distance telecommunications.

In an erbium-doped fibre amplifier, a short length of fibre containing a trace of erbium is pumped by a laser at 980 or 1480 nanometres. Incoming weak signals then stimulate the excited erbium ions to emit identical photons, boosting the signal directly without converting it to electricity. These amplifiers made transoceanic fibre cables practical in the 1990s. Erbium is also used in Er:YAG lasers, whose 2.94-micrometre light is absorbed almost entirely by water, and as a pink colourant in glass and porcelain glazes.

Discovery

Carl Gustaf Mosander discovered erbium in 1843, separating the earth yttria from Ytterby, Sweden, into fractions he named yttria, erbia and terbia. The names erbia and terbia were later swapped, so today's erbium corresponds to Mosander's 'terbia'. Erbium oxide was itself later shown to contain ytterbium, scandium, holmium and thulium. Reasonably pure erbium metal was first produced in 1934 by Wilhelm Klemm and Heinrich Bommer by reducing anhydrous erbium chloride with potassium vapour.