Europium

Europium was isolated in 1901 by the French chemist Eugene-Anatole Demarcay, after Lecoq de Boisbaudran and William Crookes had suspected its presence in samarium samples. He named it after the continent of Europe. Europium is a soft, silvery rare-earth metal, the most reactive of the lanthanides, and prized above all for its brilliant red and blue fluorescence, long used in colour television screens and in the anti-counterfeiting marks of euro banknotes. So reactive that it must be stored away from air and water, europium is one of the rarest and costliest of the lanthanides, and its readiness to absorb neutrons also finds use in the control materials of nuclear reactors.

Europium's reactivity is extreme even among the lanthanides, a fresh surface tarnishing within seconds of exposure to air, which is part of why Demarcay needed the newly refined technique of spark spectroscopy, examining the light emitted from an electric spark passed through a sample, to confirm its presence before it could be chemically isolated and purified in any quantity. The red fluorescence used to authenticate euro notes appears only under ultraviolet light invisible to the naked eye, a deliberately hidden security feature most people who handle the currency daily have never consciously noticed.

Europium's name, taken from the continent, carries a deeper mythological echo, for Europe itself is named after Europa, the Phoenician princess of Greek legend whom Zeus, disguised as a gentle white bull, carried across the sea to Crete. The element's naming is a plain geographical tribute, matching the later americium, named for the Americas and placed directly below it in the periodic table by deliberate analogy. Europium has no alchemical or ancient tradition of its own, being a twentieth-century isolation, but its glowing red phosphors gave the world the vivid reds of the cathode-ray television and now help to authenticate its namesake continent's currency, a quiet modern role for an element named, at the last remove, after a woman borne away by a god. Europium sits oddly beside its neighbours in the naming record.

Cerium took its name from the asteroid Ceres in 1803, part of a genuine early nineteenth century fashion for borrowing freshly minted astronomical names as fast as they were coined. Europium was named in 1901, a full century later, and for a continent rather than anything in the sky, so it belongs to neither that fashion nor that category. Europium's continental namesake and cerium's asteroid namesake both belong to that brief window, a reminder that the periodic table absorbed the excitement of contemporary astronomy directly into its own vocabulary at a moment when both sciences were expanding rapidly and often crossing paths in the same journals and academies.