Short answers, pulled from the story.
Erbium-doped fiber amplifiers (EDFAs) use erbium ions to boost optical signals without converting them back to electricity. When pumped at around 980 or 1480 nanometers, Er3+ ions emit stimulated light at 1530 nanometers, very close to the 1550-nanometer wavelength at which standard single-mode optical fibers have minimal signal loss.
Carl Gustaf Mosander discovered erbium in 1843 while analyzing a sample of yttria derived from gadolinite mined at Ytterby, Sweden. He identified at least two additional metal oxides in the sample, which he named erbia and terbia after the village. Reasonably pure erbium metal was not produced until 1934, when Wilhelm Klemm and Heinrich Bommer reduced the anhydrous chloride with potassium vapor.
Swiss spectroscopist Marc Delafontaine mistakenly reversed the names erbia and terbia in his published work on separating the two oxides. The confusion persisted for decades: after 1860, terbia was renamed erbia, and after 1877, the original erbia was renamed terbia.
Er:YAG lasers, which use erbium's 2940-nanometer emission, are highly absorbed by water in tissue, depositing energy very shallowly. This makes them useful in laser surgery, dermatology, and dentistry, including ceramic cosmetic work and removal of orthodontic brackets, where they have been noted as more time-efficient than rotary dental instruments.
Erbium is found in minerals including monazite, bastnaesite, xenotime, and euxenite, and never as a free element in nature. The most commercially significant sources are the ion-adsorption clays of southern China, making China the principal global supplier of the element.
Erbium is slightly toxic if ingested, but erbium compounds are generally not toxic. Humans consume about 1 milligram of erbium per year on average, with the highest concentration accumulating in the bones. Erbium nitrates can increase triglyceride levels in the liver and cause leakage of hepatic enzymes into the blood, and metallic erbium dust presents a fire and explosion hazard.