Europium (Eu)

The ground-state configuration of europium is [Xe] 4f⁷ 6s². This half-filled 4f⁷ subshell provides extra stability, similar to other elements with half-filled orbitals, and is responsible for its magnetic and chemical properties.

Europium mainly exhibits +3 and +2 oxidation states. The +3 state (Eu³⁺) is dominant in aqueous chemistry and most compounds, while the +2 state (Eu²⁺) is relatively stable due to the half-filled 4f⁷ configuration and is found in compounds like EuO, EuCl₂, and EuF₂.

Europium ions produce strong red and blue fluorescence depending on their oxidation state:

• Eu³⁺: emits red light (~610 nm), used in color television screens and LEDs.
• Eu²⁺: emits blue to green light depending on host material (e.g., BaMgAl₁₀O₁₇:Eu²⁺).

These properties make europium a key dopant in modern display and lighting technologies.

Europium is highly reactive and oxidizes rapidly in moist air to form Eu₂O₃. It also reacts slowly with water, forming hydroxide and hydrogen gas:

For storage, europium is usually kept under mineral oil or in an inert atmosphere.

Europium has several specialized uses:

• Phosphors: in red and blue components of fluorescent lamps, CRTs, and LEDs.
• Neutron absorbers: in nuclear control rods (especially Eu₂O₃).
• Anti-counterfeiting: as luminescent dopants in Euro banknotes.
• Magnetic alloys: in improving toughness and temperature resistance.

Eu²⁺ is stabilized by its half-filled 4f⁷ configuration, which gives it extra exchange energy and magnetic stability. This makes Eu(II) compounds like EuO and EuCl₂ thermodynamically more favorable compared to analogous Ln(II) ions in other lanthanides.

Europium metal and Eu²⁺ compounds are strongly paramagnetic due to seven unpaired 4f electrons. In solid state, certain europium compounds show antiferromagnetic ordering at very low temperatures.

Europium is extracted from rare-earth ores like bastnäsite and monazite. The ore is processed through acid leaching, followed by solvent extraction and ion exchange to separate Eu from other lanthanides. Eu³⁺ is then reduced to Eu²⁺ in hydrogen to yield the metal or its oxide.

Compounds of Eu³⁺ are typically colorless to pale pink, while Eu²⁺ compounds can be pale yellow or bluish. Under UV light, Eu³⁺ emits bright red luminescence, and Eu²⁺ shows blue to green fluorescence, depending on the host lattice.

Natural europium consists of stable isotopes (¹⁵¹Eu and ¹⁵³Eu). It has low toxicity, but fine powders can be mildly flammable and irritating. Some radioactive isotopes (like ¹⁵²Eu) are used as gamma-ray calibration sources in laboratories.

The interconversion between Eu²⁺ and Eu³⁺ is a classic redox equilibrium:

Eu(II) salts are powerful reducing agents, often used in the preparation of other lanthanide halides or to reduce organic substrates.