Erbium

Erbium was discovered in 1843 by Carl Gustaf Mosander, who separated it, together with terbium, from the yttrium of the Ytterby ores. Its name is another fragment of Ytterby. Erbium is a soft, silvery rare-earth metal whose salts are a delicate rose-pink, used to colour glass and glazes and, most importantly, in the erbium-doped amplifiers that boost the light signals carrying data through the world's optical-fibre networks.

Beyond amplifying the light in those fibres, erbium colours glass and glazes a soft pink, filters glare in sunglasses and welders' goggles, and forms the doped crystals of surgical and dental lasers valued for cutting tissue with little heat. The erbium-doped fibre amplifier was developed in 1987 independently and almost simultaneously by David Payne's team at the University of Southampton and Emmanuel Desurvire's at Bell Labs, work the two later shared in the 2008 Millennium Technology Prize, and its ability to boost a light signal directly within the glass fibre itself, without ever converting it back to electricity, is often credited with making the modern high-capacity, transoceanic internet backbone economically practical, since a single erbium-doped stretch of cable can carry an amplified signal for tens of kilometres before needing a repeater. Before this breakthrough, long submarine cables needed frequent, costly electronic regeneration stations, a limitation erbium's rare-earth glow effectively removed.

Erbium is the third of the quartet, yttrium, terbium, erbium and ytterbium, whose names are all carved from Ytterby. Its early history was especially confused: for years the names erbium and terbium were applied to each other's substances, and only after repeated re-examination did chemists settle which element was which, a muddle typical of the rare earths and their maddening similarity. Erbium has no ancient or esoteric tradition, being a nineteenth-century discovery; its cultural identity is the Swedish quarry that named it, and its great modern significance is technological, for the faint pink element that once merely tinted glass now, doped into glass fibres, silently amplifies the pulses of light that carry the traffic of the internet across oceans.

Erbium-doped lasers are prized in dentistry and dermatology precisely because the wavelength they emit is very strongly absorbed by water, letting the beam vaporise a thin layer of tissue or tooth enamel with minimal heat spreading to the surrounding area, a property that has made erbium lasers a standard tool for skin resurfacing and for drilling cavities with markedly less discomfort than a mechanical dental drill. The rose-pink erbium salts that first caught nineteenth-century mineralogists' eyes are chemically the very same compounds still valued today for tinting glass and glaze a soft, consistent pink.