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Europium

Europium — Material Page
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Europium (Eu, atomic number 63) is the most reactive and chemically anomalous of the lanthanides — a soft, silvery-white BCC metal with a melting point of only 826 °C, the lowest electrical resistivity-to-density ratio of any lanthanide, and uniquely among the rare earths, a stable divalent Eu²⁺ state that is directly exploited in phosphor technology, making Eu simultaneously the provider of both the red (Eu³⁺) and blue (Eu²⁺) primary color emissions in virtually all fluorescent lamp, CRT, and early flat-panel display phosphor systems. Eu has only two natural isotopes — ¹⁵¹Eu (47.81%) and ¹⁵³Eu (52.19%) — both NMR-active (I = 5/2), and ¹⁵¹Eu has the highest thermal neutron absorption cross-section of any lanthanide accessible in significant natural abundance (σ ≈ 9,200 barn). Eu's BCC crystal structure and low melting point reflect its divalent metallic bonding — Eu metal has a 4f⁷6s² configuration with the 4f electrons largely localized (analogous to Gd's 4f⁷), giving it an anomalously low density (5.264 g/cm³) and high electrical resistivity (920 nΩ·m) relative to its lanthanide neighbors. Eu is extracted from monazite and bastnäsite by solvent extraction; global production is ~400 tonnes/year, driven almost entirely by phosphor demand.

The pivotal role of Eu in 20th and early 21st century lighting and display technology cannot be overstated: Eu³⁺ in Y₂O₃:Eu³⁺ (red, 611 nm, ⁵D₀ → ⁷F₂ transition) and YVO₄:Eu³⁺ provided the bright red primary in every fluorescent lamp, CRT television and monitor, and tri-phosphor lamp manufactured from the 1960s through the 2010s — a market consuming hundreds of tonnes of Eu₂O₃ annually at peak. Eu²⁺ in BaMgAl₁₀O₁₇:Eu²⁺ (BAM, blue, ~450 nm) provided the blue primary in the same lamp phosphor blends; the combined Eu³⁺ red + Eu²⁺ blue + Tb³⁺ green triphosphor system was the standard for all tri-band fluorescent lamps and defined the color rendering of artificial lighting for 40 years. While LED lighting has displaced fluorescent lamps in most applications, Eu-doped phosphors remain critical in specialty display phosphors, fluorescent security inks, and Ce:YAG-free white LED phosphor research seeking broader spectral coverage.

The "Europium anomaly" is a fundamental diagnostic tool in igneous geochemistry — Eu²⁺ (ionic radius close to Ca²⁺ and Sr²⁺) is preferentially incorporated into plagioclase feldspar during magmatic crystallization, causing positive Eu anomalies in plagioclase cumulates and complementary negative Eu anomalies in residual melts, making the Eu/Eu* ratio a definitive fingerprint of plagioclase fractionation in chondrite-normalized REE patterns of igneous rocks, lunar samples, and meteorites. Eu is also critical for anti-counterfeiting: Eu-doped luminescent inks (emitting red under UV at 254/365 nm) are printed on euro banknotes, passports, and security documents worldwide — the sharp, characteristic Eu³⁺ emission lines (⁵D₀ → ⁷F₁, ⁷F₂ at 590/611 nm) are difficult to replicate without the correct Eu phosphor formulation. Eu-chelate time-resolved fluorescence (TRFIA, DELFIA) assays are standard immunoassay platforms for clinical diagnostics, exploiting Eu³⁺'s millisecond luminescence lifetime to eliminate autofluorescence background in complex biological matrices.

General Properties

PropertyValueNotes
Atomic Number63Lanthanide, Period 6; 4f⁷6s² — the 4f shell is exactly half-filled (7 electrons, maximum spin S = 7/2), analogous to Gd ( 4f⁷5d¹6s²). The half-filled 4f shell stabilizes the divalent state: Eu²⁺ ( 4f⁷, ⁸S₇/₂ ground state) is unusually stable for a lanthanide and directly responsible for Eu²⁺ 4f→5d allowed-transition luminescence (broad, UV-visible emission tunable by crystal field) exploited in BAM and other Eu²⁺ blue phosphors. Eu³⁺ ( 4f⁶, ⁷F₀ ground state) emits sharp red lines from the non-degenerate ⁵D₀ → ⁷F₂ electric dipole transition at ~611 nm — the most intense lanthanide 4f emission line known.
Atomic Mass151.964 uOnly two natural isotopes: ¹⁵¹Eu (47.81%, I = 5/2, NMR-active, Stable*) and ¹⁵³Eu (52.19%, I = 5/2, NMR-active). Eu is one of only two lanthanides with just two stable isotopes (the other is Tm, monoisotopic). ¹⁵³Eu is the majority isotope and the primary isotope monitored in ICP-MS REE analysis of geological, environmental, and phosphor scrap samples.
Density (20 °C)5.264 g/cm³Anomalously low density for a lanthanide — significantly less than neighboring Sm (7.52) and Gd (7.90). This reflects Eu's divalent metallic bonding (Eu²⁺ metal, contributing only 2 conduction electrons vs. 3 for trivalent lanthanides), resulting in a larger atomic radius and lower cohesive energy. The low density is a useful identifier when processing Eu metal vs. other lanthanides.
Melting Point826 °C (1,099 K)Lowest melting point of any lanthanide after Ce (795 °C) — consistent with Eu's divalent metallic bonding and weak cohesive energy from the half-filled 4f shell. Eu metal ignites in air above ~150 °C and reacts vigorously with water; it must be stored under mineral oil or inert atmosphere. Processing uses Ar-atmosphere induction melting; Eu is reduced from EuF₃ or EuCl₃ by Ca metallothermy.
Boiling Point1,529 °CRelatively low boiling point for a lanthanide metal, consistent with weak cohesive energy. Eu has significant vapor pressure at its melting point, making vacuum arc melting difficult and requiring carefully controlled Ar overpressure. Eu evaporation losses during alloy melting and sputtering target fabrication must be accounted for in Eu-containing phosphor and thin-film composition control.
Thermal Conductivity13.9 W/m·KLow thermal conductivity consistent with divalent lanthanide metal bonding. Relevant to Eu₂O₃ ceramic thermal properties in phosphor applications and to EuO thin-film magnetic semiconductor research where thermal management of the Eu-containing layer in heterostructures is important.
Electrical Resistivity920 nΩ·m (20 °C)Exceptionally high resistivity — the highest of any lanthanide metal, ~11× that of Er (85 nΩ·m) and ~10× that of Cu (17 nΩ·m). This reflects Eu's BCC structure, localized 4f⁷ electrons, and Kondo-like scattering effects near the magnetic ordering temperature (~90 K). Eu metal is not used for its electrical properties; the high resistivity is a diagnostic physical property confirming Eu's divalent metallic state distinct from its trivalent lanthanide neighbors.
Crystal StructureBCC, a = 4.583 Å (room temperature)BCC structure — unusual among lanthanides, which are predominantly HCP or double-HCP. Eu adopts BCC (like Yb and Eu-analogue Ba) because it bonds as Eu²⁺ metal rather than Eu³⁺; this is the same reason for its anomalously low density and melting point. The BCC structure of Eu metal is used as a reference in DFT calculations of divalent vs. trivalent bonding transitions in lanthanide metals under pressure.

Mechanical Properties

PropertyValueNotes
Young's Modulus18.2 GPaExtremely low modulus — among the lowest of any metal, reflecting weak Eu²⁺ metallic bonding. Eu metal is among the softest and most compliant lanthanides, readily deformed at room temperature. Relevant to mechanical modeling of Eu-containing ceramic phosphor pellets under compressive loading and to EuO thin-film epitaxial strain calculations in magnetic semiconductor heterostructure design.
Hardness~17–20 HB (annealed)Among the softest lanthanide metals, reflecting Eu's divalent metallic bonding — comparable in hardness to lead. Eu can be cut with a knife and is handled primarily as Eu₂O₃ or salt precursors rather than bulk metal in most applications.
Poisson's Ratio0.15Unusually low Poisson's ratio for a metal — consistent with Eu's BCC structure and divalent bonding. Most metals have ν ≈ 0.25–0.35; Eu's low value reflects its anomalous elastic behavior. Used in stress modeling of Eu₂O₃ ceramic components and in theoretical studies of Eu metal compressibility under pressure (the Eu²⁺ → Eu³⁺ transition under pressure is a model system for valence change in lanthanide metals).

Chemical Properties

PropertyValue / BehaviorNotes
Oxidation States+2 (Eu²⁺: EuO, EuF₂, EuSO₄, BaMgAl₁₀O₁₇:Eu²⁺ phosphor); +3 (Eu³⁺: Eu₂O₃, EuCl₃, Y₂O₃:Eu³⁺ phosphor) — both stable and directly exploitedThe Eu²⁺/Eu³⁺ redox couple (E° ≈ −0.35 V in aqueous solution) makes Eu unique among lanthanides in having two technologically important valence states. Eu²⁺ (4f⁷, ⁸S₇/₂) has parity-allowed 4f→5d transitions giving broad-band blue/UV emission in phosphor hosts, while Eu³⁺ (4f⁶) has parity-forbidden but highly characteristic sharp ⁵D₀→⁷F₂ red emission at 611 nm. EuO (rock-salt structure) is a rare-earth semiconductor with T_C = 69 K and near-100% spin polarization — a model half-metal for spintronics research.
Corrosion ResistancePoor; oxidizes rapidly in moist air forming Eu₂O₃ surface layer; reacts vigorously with water releasing H₂; ignites as fine powder in airEu is among the most reactive lanthanides, comparable to Ca in air reactivity. Bulk Eu metal must be stored under mineral oil or sealed in an inert atmosphere; even brief exposure to moist air causes significant surface oxidation. Eu reacts with all dilute acids and dissolves readily in HCl and HNO₃ to form Eu³⁺ solutions. Eu powder is pyrophoric and must be handled with appropriate precautions.
Surface OxideEu₂O₃ (cubic C-type, pale yellow) and EuO (rock-salt, black) form depending on oxygen partial pressure and temperatureEu₂O₃ is the thermodynamically stable oxide in air — used as the primary precursor for phosphor synthesis (Y₂O₃:Eu³⁺ red phosphor by solid-state reaction of Y₂O₃ + Eu₂O₃ at 1,200 °C in air), for Eu-doped scintillator and OLED emitter fabrication, and for EuB₆ preparation. EuO (black, ferromagnetic below 69 K) is prepared by careful reduction of Eu₂O₃ under H₂ or by Eu metal oxidation in controlled O₂ — the most studied rare-earth magnetic semiconductor.
IdentifierValue
SymbolEu
Atomic Number63
CAS Number7440-53-1
UN NumberUN3089 (powder)
EINECS Number231-161-7
IsotopeTypeNotes
¹⁵¹Eu Stable* 47.81% natural abundance; I = 5/2, NMR-active; Stable* — alpha decay to ¹⁴⁷Pm has been experimentally bounded: t½ > 1.7 × 10¹⁸ yr. Thermal neutron absorption cross-section σ ≈ 9,200 barn — the highest of any lanthanide with substantial natural abundance, making natural Eu (effective σ ≈ 4,530 barn for natural element) the most neutron-absorbing of the light lanthanides. ¹⁵¹Eu NMR (I = 5/2, relatively narrow lines in high-symmetry environments; chemical shift range ~5,000 ppm) is used to characterize Eu²⁺ vs. Eu³⁺ environments in phosphor host lattices, glasses, and coordination compounds — the large chemical shift difference between Eu²⁺ and Eu³⁺ sites enables direct NMR-based valence state characterization. ¹⁵¹Eu(n,γ)¹⁵²Eu (σ = 9,200 barn) produces ¹⁵²Eu (t½ = 13.537 yr, β⁻+EC+γ), an important γ-ray calibration standard (121.8, 344.3, 1,408.0 keV) used to calibrate HPGe detectors and as a long-lived environmental contamination tracer from neutron activation in reactor materials.
¹⁵³Eu Stable 52.19% natural abundance — the majority Eu isotope; I = 5/2, NMR-active. Thermal neutron absorption cross-section σ ≈ 312 barn. ¹⁵³Eu NMR (I = 5/2; sharper lines than ¹⁵¹Eu in many environments due to slightly smaller quadrupole moment; ~5,000 ppm shift range) is the preferred isotope for solid-state ¹⁵³Eu NMR of Eu-doped phosphors and crystals, enabling direct characterization of Eu³⁺ site symmetry in Y₂O₃:Eu³⁺ and EuAlO₃ in relation to photoluminescence performance. ¹⁵³Eu(n,γ)¹⁵⁴Eu produces ¹⁵⁴Eu (t½ = 8.593 yr, β⁻+γ), a major fission product decay-heat contributor in spent nuclear fuel and a long-lived contamination isotope at reactor sites (Chernobyl, Fukushima soil contamination inventory). ¹⁵³Eu is the primary isotope used in ICP-MS quantification of Eu in geological samples (chondrite-normalized Eu/Eu* anomaly calculations in igneous petrology).

Scientific & Research Applications

Use CaseForm Typically UsedDescription
Time-Resolved Fluorescence Immunoassay (TRFIA / DELFIA)Eu³⁺ chelate labels (Eu-DOTA, Eu-DTPA, Eu-TBP cryptate) conjugated to antibodies and nucleic acid probesEu³⁺ chelates have millisecond luminescence lifetimes (τ ~1 ms, vs. nanosecond for organic fluorophores) — time-gated detection after 980 nm excitation pulse eliminates all autofluorescence background, enabling sub-picomolar detection of analytes in complex serum matrices. DELFIA (Dissociation-Enhanced Lanthanide Fluorescence Immunoassay) and LANCE (Lanthanide Chelate Excitation) platforms using Eu³⁺ labels are standard in clinical diagnostics (thyroid hormones, cardiac troponin), drug discovery HTS (HTRF assays), and nucleic acid hybridization assays. The technology directly exploits Eu³⁺'s sharp ⁵D₀→⁷F₂ emission at 615 nm for background-free detection.
EuO Magnetic Semiconductor ResearchEuO thin films deposited by MBE from Eu metal + O₂ or by Eu₂O₃ reduction; EuO single crystalsEuO (rock-salt, T_C = 69 K) is a model rare-earth magnetic semiconductor — it undergoes a metal-insulator transition at T_C with near-100% spin polarization of conduction electrons (exchange splitting ~0.6 eV), making it a theoretical ideal spin injector. EuO thin films on Si and GaN are studied for spin-injection contacts in semiconductor spintronics and as a component in quantum computing architectures requiring spin-polarized electron injection.
Geochemistry (Eu Anomaly Analysis)Eu standard solutions for ICP-MS; ¹⁵³Eu as the analytical isotope; EuO or Eu(NO₃)₃ reference standardsChondrite-normalized Eu/Eu* (europium anomaly = Eu_N / √(Sm_N × Gd_N)) is a universal petrological diagnostic — positive Eu anomalies indicate plagioclase accumulation; negative anomalies indicate plagioclase fractionation from a melt. Applied to igneous rocks, lunar samples (Apollo basalts/highlands contrast is defined by Eu anomaly), achondrite meteorites, and seawater REE patterns. Eu anomaly analysis is routine in every igneous geochemistry ICP-MS dataset worldwide.
OLED Emissive Layer ResearchEu³⁺ β-diketonate complexes (Eu(TTA)₃phen, Eu(dbm)₃bath); thermally evaporated or solution-processed emittersEu³⁺ β-diketonate complexes are the most efficient red emitters in organic electroluminescence research — energy transfer from π→π* triplet of the diketonate antenna to Eu³⁺ ⁵D₀ level, followed by sharp ⁵D₀→⁷F₂ emission at 611 nm with near-unity intramolecular energy transfer efficiency and color purity (CIE x ~0.65, y ~0.34). External quantum efficiencies >10% in solution-processed OLEDs; studied as narrow-bandwidth red emitters for display applications requiring high color gamut.
Neutron Absorption & Control Rod ResearchEu₂O₃ pellets; Eu-containing ceramic composites; Eu-Al alloyNatural Eu's high effective neutron cross-section (~4,530 barn, dominated by ¹⁵¹Eu at 9,200 barn) makes Eu₂O₃ an effective burnable absorber and reactor control material. ¹⁵²Eu and ¹⁵⁴Eu produced by neutron activation of natural Eu are studied as long-lived fission product simulants in nuclear waste form leaching experiments, and ¹⁵²Eu (t½ = 13.5 yr) is the primary HPGe detector calibration source used in nuclear safeguards verification.

Industrial & Commercial Applications

SectorForm / Grade UsedDescription
Fluorescent Lamp & Display Phosphors (Red)Y₂O₃:Eu³⁺ (YOE) powder (0.5–6 mol% Eu³⁺ in Y₂O₃; 99.95%+ Eu₂O₃ precursor); YVO₄:Eu³⁺Y₂O₃:Eu³⁺ (YOE) is the standard red phosphor for all tri-band fluorescent lamps (T5, T8, CFL), CRT television tubes, and early LCD backlights — Eu³⁺ ⁵D₀→⁷F₂ emission at 611 nm provides high color rendering red primary with near-100% quantum yield under UV excitation. While LED lighting is displacing fluorescent lamps, YOE and YVO₄:Eu³⁺ remain in production for specialty lamp applications and for legacy display maintenance. This application historically consumed the majority of global Eu₂O₃ production.
Fluorescent Lamp Phosphors (Blue) & White LED ResearchBaMgAl₁₀O₁₇:Eu²⁺ (BAM) powder (1–10 mol% Eu²⁺; 99.9%+ EuF₂ or Eu metal precursor reduced in H₂)BAM (BaMgAl₁₀O₁₇:Eu²⁺) provides blue primary emission at ~450 nm (Eu²⁺ 4f→5d, broad band) in tri-band fluorescent lamp phosphor blends, complementing the YOE red and LAP (Ce,Tb):LaPO₄ green. BAM + YOE + LAP defined the color rendering of all tri-phosphor fluorescent lighting from the 1970s–2010s. Eu²⁺-doped nitrido-silicate and aluminate phosphors (e.g., Sr₂Si₅N₈:Eu²⁺, red; Ba₃Si₆O₁₂N₂:Eu²⁺, green) are key components in high-CRI LED phosphor blends seeking to supplement or replace Ce:YAG for broader spectral coverage in warm-white LEDs.
Anti-Counterfeiting Security InksEu³⁺-doped luminescent pigments (Y₂O₃:Eu³⁺, EuDBC, EuTTA complexes) in security printing inksEu³⁺ sharp-line emission (590/611 nm, ⁵D₀→⁷F₁/⁷F₂) under 254 nm UV is printed on euro banknotes, passports, postage stamps, and pharmaceutical packaging as an overt or covert security feature. The characteristic emission wavelengths are specific enough that simple UV lamp + spectrometer verification distinguishes genuine Eu-labeled documents from counterfeits using non-Eu fluorescent inks. EU currency production (European Central Bank) uses Eu-based fluorescent security threads and inks in all euro denominations.
Scintillator Crystals (EuI₂, Eu:SrI₂, Eu:CsBr)Eu²⁺-doped scintillator single crystals: SrI₂:Eu²⁺ (0.5–5 mol% Eu²⁺), EuI₂, CsBr:Eu²⁺SrI₂:Eu²⁺ is a high-energy-resolution scintillator (~2.6% energy resolution at 662 keV, vs. ~6–7% for NaI:Tl) with high light yield (~80,000 photons/MeV, the highest of any known inorganic scintillator) — developed for portable γ-ray isotope identification (nuclear security, treaty verification, border monitoring). Eu²⁺ 5d→4f emission at ~435 nm is well-matched to SiPM and PMT spectral response; SrI₂:Eu²⁺ is commercially produced for handheld gamma-ray spectrometers (e.g., Mirion RADEYE G).
PurityCommon UsesNotes
99.9% (3N)Phosphors, general electronics, lab-scale researchSuitable for most academic and low-impurity applications.
99.95% (3N5)Display-grade phosphors, high-purity targetsPreferred where enhanced luminescence or purity is critical.
Synonym / Alternative NameContext
EuChemical symbol; named for Europe by Eugène-Anatole Demarçay, who isolated Eu in 1901. Used as the primary identifier in ICP-MS REE analysis (¹⁵³Eu monitored for Eu quantification and Eu/Eu* anomaly calculations in igneous geochemistry), phosphor specification documents (Y₂O₃:Eu³⁺ and BAM:Eu²⁺ phosphor datasheets), and TRFIA assay kits (Eu-chelate label concentration specified in µg Eu/mL).
Eu metalAbbreviated commercial designation for elemental Eu in ingot, rod, or powder form; used in phosphor precursor procurement specifications (Eu metal reduction to prepare EuF₂ for BAM synthesis), sputtering target datasheets, and EuO thin-film research publications specifying Eu metal evaporation source purity and outgassing requirements.
Eu elementScientific designation distinguishing elemental Eu from Eu compounds; used in condensed matter physics literature on EuO magnetic semiconductor properties, Eu metal pressure-induced valence transitions (Eu²⁺→Eu³⁺ under ~10 GPa), and spectroscopy papers analyzing Eu³⁺ vs. Eu²⁺ valence states in phosphor hosts by X-ray absorption spectroscopy (XANES).
Europium metalFull commercial designation used in REACH/RoHS compliance documentation, ASTM standards for REE metals, industrial procurement specifications for Eu metal additions to phosphor synthesis processes, and in anti-counterfeiting ink formulation documents requiring Eu metal or Eu₂O₃ precursor purity certification.
Europium elementScientific designation used in academic databases and educational resources; used in luminescence textbooks specifying Eu³⁺ and Eu²⁺ photophysics, in geochemistry literature discussing Eu anomaly as a petrological indicator, and in nuclear engineering texts specifying Eu's neutron absorption cross-section for burnable absorber design.
Europium rare earth metalTrade and regulatory designation classifying Eu among the 17 rare-earth elements in critical materials lists; Eu is classified as moderately critical (higher supply risk than Ce/La but less critical than Dy/Tb) due to its specialized role in phosphor and security ink applications and its near-exclusive sourcing from Chinese bastnäsite and ion-adsorption clay deposits.
Europium rare earth elementGeochemical and mineralogical designation used in REE deposit assessments, Eu anomaly interpretation in igneous petrology and cosmochemistry (lunar highlands Eu enrichment, chondrite REE patterns), and in IUPAC nomenclature for Eu-bearing mineral phases (europite, Eu-bearing monazite) and Eu coordination compounds.
Element 63Periodic table designation used in XRF/ICP-MS analytical software, nuclear data libraries (ENDF/B-VIII for ¹⁵¹Eu neutron cross-section at 9,200 barn), reactor physics codes (MCNP, ORIGEN) tracking ¹⁵²Eu and ¹⁵⁴Eu as activation products and decay-heat contributors in spent fuel, and in nuclear safeguards databases where ¹⁵²Eu gamma lines (344.3, 1,408 keV) are used for HPGe detector calibration.
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