Europium · element 63
The softest, most reactive rare earth, and the reason old colour televisions could show a proper red
Key facts
Europium is the odd one out among the lanthanides in almost every physical way. It is the softest of them, soft enough to mark with a fingernail. It is the least dense, nowhere near iron like its neighbours. And it is by far the most reactive, tarnishing within hours in air and fizzing with water much as calcium does.
All of this traces back to its electrons. Europium has exactly seven electrons in its 4f shell, which is half full, and it clings to that arrangement so strongly that it often gives up only two electrons rather than the usual three. That makes it behave in some ways more like barium than like a typical rare earth. The same quirk makes its compounds glow brilliantly, which has put europium into screens, lamps and banknotes.
Where it is found
Europium is one of the scarcer rare earths, present in monazite and bastnäsite ores at levels well below its neighbours samarium and gadolinium. Because of its tendency to form +2 ions, it also behaves differently in geology. Europium(II) is close in size to calcium, so it slips into calcium bearing minerals such as plagioclase feldspar. Geologists call the resulting excess or shortfall the europium anomaly and use it to work out how rocks formed. Rocks from the lunar highlands are famously rich in europium for exactly this reason.
Commercial europium comes from the same rare earth processing plants that supply the rest of the series, with China producing most of the world's output. Its unusual +2 chemistry actually helps here, because reducing europium to that state lets chemists separate it from the other lanthanides more easily.
How it was discovered
Europium hid for decades inside samples that chemists thought were pure samarium. The English chemist William Crookes noticed an unexplained spectral line in the 1880s, and Lecoq de Boisbaudran saw further hints in the 1890s. It was the French chemist Eugène-Anatole Demarçay, an expert in spectroscopy, who finally separated the new element in 1901 and named it after the continent of Europe.
Demarçay is also remembered for confirming that Marie and Pierre Curie's radium was a genuine new element by examining its spectrum.
What we use it for
The colour television owes its red to europium. In the 1960s, phosphors based on europium(III) in a yttrium compound gave a bright, pure red that earlier materials could not match, allowing screens to balance their colours properly. Europium(II) in a different host produces blue instead. Both are used in fluorescent tubes and in the white LEDs that light modern homes, where a mixture of phosphors converts blue light into a warm white.
Europium compounds fluoresce strongly under ultraviolet light, and this is used in security printing. Euro banknotes are widely reported to contain europium based inks that glow in distinct colours under a UV lamp.
In nuclear reactors europium is a useful neutron absorber for control rods. Combined with dysprosium in strontium aluminate, it also produces the long lasting green glow of modern glow-in-the-dark paints and toys.
Reading the numbers
Europium melts at about 826 °C and boils near 1529 °C, both far lower than gadolinium next door, which melts above 1300 °C. Its density of 5.26 grams per cubic centimetre is only about two thirds that of iron and the lowest of any lanthanide. These low values are all consequences of the metal contributing only two electrons to its metallic bonding instead of three, so the atoms are held together more loosely and sit further apart.
The configuration [Xe] 4f7 6s2 explains everything. A half filled 4f shell is unusually stable, so europium is reluctant to give up a third electron. Its electronegativity of 1.2 and first ionisation energy of about 547 kJ/mol mark it as a highly electropositive metal that readily hands over electrons, which is why it reacts so vigorously with air and water. The atomic mass of 151.96 reflects two natural isotopes in roughly equal amounts.
Safety and the environment
Europium metal must be stored under oil or inert gas because it oxidises quickly and can ignite in air when heated. It reacts with water to release hydrogen gas. Its compounds, on the other hand, are considered to have low toxicity, and no biological role is known.
Environmental concerns centre on mining and refining rare earths rather than on europium itself. Recycling fluorescent lamp phosphors to recover europium and terbium has been trialled in Europe, since the metals are both valuable and energy intensive to extract.
Did you know?
- Europium is soft enough to be dented with a fingernail and is the least dense of all the lanthanide metals.
- The bright red in early colour televisions came from a europium phosphor, and modern white LEDs still rely on europium to tune their colour.
- Rocks from the Moon's highlands contain unusually high levels of europium because europium(II) mimics calcium and slots into feldspar minerals.
- Europium is the most reactive rare earth, tarnishing in air within hours and reacting with cold water in a similar way to calcium.
- Europium-151, one of its two natural isotopes, was found to be very faintly radioactive, with a half-life of several quintillion years.
- Euro banknotes are widely reported to use europium based inks that glow in different colours under ultraviolet light as an anti-counterfeiting measure.
More in the lanthanides
The nearest neighbours of europium in the family, by atomic number.
See all 15 lanthanides on one page, or browse all 118 elements.
Frequently asked questions
Why is europium used in banknotes?
Europium compounds fluoresce very brightly under ultraviolet light, giving sharp red or blue glows that are hard to imitate with ordinary inks. Security printers use this to create hidden features that show up under a UV lamp, and euro notes are widely reported to use europium based inks.
Is europium dangerous?
The pure metal reacts vigorously with air and water and can catch fire when heated, so it is stored under oil or inert gas. Its compounds, as used in lamps and screens, are considered to have low toxicity and present no risk to the public.
Why is europium so different from other rare earths?
It has a half filled 4f shell of seven electrons, which is unusually stable, so it prefers to lose only two electrons instead of three. That makes the metal softer, lighter and more reactive than its neighbours and gives it chemistry closer to barium in some respects.
What is europium used for today?
Its main uses are as a red and blue phosphor in fluorescent lamps, LED lighting and displays, in security inks that glow under UV light, and as a neutron absorber in nuclear control rods. It is also a component of long lasting glow-in-the-dark materials.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Europium reference article. Spotted an error? Tell us.