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.