Overview

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.