Europium Eu

Discovery

Europium hid inside samarium. During the 1880s and 1890s several chemists noticed unexplained lines in the spectra of samarium samples. The French chemist Eugène-Anatole Demarçay suspected a new element around 1896 and, after a long series of fractional crystallisations of samarium magnesium nitrate, isolated it in 1901.

The metal itself was prepared much later because it reacts so readily with air and water. Even today pure europium metal is stored under mineral oil or an inert gas, and a freshly cut surface tarnishes within minutes.

Origin of the name

Demarçay named the element after the continent of Europe. It pairs neatly with americium (95), the actinide directly below it in the periodic table, which was later named after the Americas.

Main uses

• Red phosphors: trivalent europium in yttrium oxide or yttrium vanadate produced the red dots of colour cathode-ray-tube TVs and is still used in tri-phosphor fluorescent lamps and some LEDs.
• Blue and afterglow phosphors: divalent europium emits blue light and is the key activator in strontium aluminate glow-in-the-dark pigments used on safety signs.
• Anti-counterfeiting: europium compounds that fluoresce under UV are widely reported to be among the security features of euro banknotes.
• Nuclear: its strong neutron absorption has led to use and study in reactor control materials.

Isotopes

Natural europium is a mix of europium-151 (about 48%) and europium-153 (about 52%). Europium-153 is stable; europium-151 was long thought stable too, but experiments have reported an extraordinarily slow alpha decay. Reactors produce radioactive europium-152 and europium-154, which serve as gamma-ray calibration sources for detectors.

In everyday life

The bright reds of older colour TVs and fluorescent lighting, and the green glow of exit signs during a power cut, owe a lot to europium. Geologists also know the "europium anomaly": unlike most lanthanides, europium can form a 2+ ion that slips into feldspar crystals, so its relative abundance records how a magma cooled and crystallised. Europium compounds are generally considered to have low toxicity, though the fine metal can ignite.