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Europium,63Eu
Europium
Pronunciation/jʊˈroʊpiəm/​(yuu-ROH-pee-əm)
Appearancesilvery white, with a pale yellow tint;[1]but rarely seen without oxide discoloration
Standard atomic weightAr°(Eu)
Europium in theperiodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
–
↑
Eu
↓
Am
samarium←europium→gadolinium
Atomic number(Z)63
Groupf-block groups(no number)
Periodperiod 6
Blockf-block
Electron configuration[Xe] 4f76s2
Electrons per shell2, 8, 18, 25, 8, 2
Physical properties
PhaseatSTPsolid
Melting point1099K​(826 °C, ​1519 °F)
Boiling point1802 K ​(1529 °C, ​2784 °F)
Density(at 20° C)5.246 g/cm3 [4]
when liquid (atm.p.)5.13 g/cm3
Heat of fusion9.21kJ/mol
Heat of vaporization176 kJ/mol
Molar heat capacity27.66 J/(mol·K)
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
atT(K) 863 957 1072 1234 1452 1796
Atomic properties
Oxidation states0,[5]+2,+3(a mildlybasicoxide)
ElectronegativityPauling scale: 1.2
Ionization energies
  • 1st: 547.1 kJ/mol
  • 2nd: 1085 kJ/mol
  • 3rd: 2404 kJ/mol
Atomic radiusempirical: 180pm
Covalent radius198±6 pm
Color lines in a spectral range
Spectral linesof europium
Other properties
Natural occurrenceprimordial
Crystal structure​body-centered cubic(bcc) (cI2)
Lattice constant
Body-centered cubic crystal structure for europium
a= 458.22 pm (at 20 °C)[4]
Thermal expansion26.3×10−6/K (at 20 °C)[4]
Thermal conductivityest. 13.9 W/(m⋅K)
Electrical resistivitypoly: 0.900 µΩ⋅m (atr.t.)
Magnetic orderingparamagnetic[6]
Molar magnetic susceptibility+34000.0×10−6cm3/mol[7]
Young's modulus18.2 GPa
Shear modulus7.9 GPa
Bulk modulus8.3 GPa
Poisson ratio0.152
Vickers hardness165–200 MPa
CAS Number7440-53-1
History
Namingafter Europe
Discoveryand first isolationEugène-Anatole Demarçay(1896, 1901)
Isotopes of europium
Main isotopes[8] Decay
abun­dance half-life(t1/2) mode pro­duct
150Eu synth 36.9 y β+ 150Sm
151Eu 47.8% 4.62×1018y α 147Pm
152Eu synth 13.54 y ε 152Sm
β− 152Gd
153Eu 52.2% stable
154Eu synth 8.59 y β− 154Gd
155Eu synth 4.76 y β− 155Gd
Category: Europium
|references

Europiumis achemical element;it hassymbolEuandatomic number63. Europium is a silvery-white metal of thelanthanideseries that reacts readily with air to form a dark oxide coating. It is the most chemically reactive, least dense, and softest of the lanthanide elements. It is soft enough to be cut with a knife. Europium was isolated in 1901 and named after the continent ofEurope.[9]Europium usually assumes theoxidation state+3, like other members of the lanthanide series, but compounds having oxidation state +2 are also common. All europium compounds with oxidation state +2 are slightlyreducing.Europium has no significant biological role and is relatively non-toxic compared to otherheavy metals.Most applications of europium exploit thephosphorescenceof europium compounds. Europium is one of the rarest of therare-earth elementson Earth.[10]

Etymology[edit]

Its discoverer,Eugène-Anatole Demarçaynamed the element after the continent ofEurope.[11]

Characteristics[edit]

Physical properties[edit]

About 300 g of dendritic sublimated 99.998% pure europium handled in a glove box
Oxidized europium, coated with yellow europium(II) carbonate

Europium is aductilemetal with a hardness similar to that oflead.It crystallizes in abody-centered cubiclattice.[12]Some properties of europium are strongly influenced by its half-filledelectron shell.Europium has the second lowest melting point and the lowest density of all lanthanides.[12]

Europium has been claimed to become asuperconductorwhen it is cooled below 1.8 K and compressed to above 80 GPa.[13]However the experimental evidence on which this claim is based has been challenged,[14]and the paper reporting superconductivity has been subsequently retracted.[15]If it becomes a superconductor this is believed to occur because europium isdivalentin the metallic state,[16]and is converted into the trivalent state by the applied pressure. In the divalent state, the strong localmagnetic moment(arising fromtotal electronic angular momentumJ=7/2) suppresses the superconductivity, which is induced by eliminating this local moment (J= 0 in Eu3+).

Chemical properties[edit]

Europium is the most reactive rare-earth element. It rapidly oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days.[17]Its reactivity with water is comparable to that ofcalcium,and the reaction is

2 Eu + 6 H2O → 2 Eu(OH)3+ 3 H2

Because of the high reactivity, samples of solid europium rarely have the shiny appearance of the fresh metal, even when coated with a protective layer of mineral oil. Europium ignites in air at 150 to 180 °C to formeuropium(III) oxide:[18][19]

4 Eu + 3 O2→ 2 Eu2O3

Europium dissolves readily in dilutesulfuric acidto form pale pink[20]solutions of [Eu(H2O)9]3+:

2 Eu + 3 H2SO4+ 18 H2O → 2 [Eu(H2O)9]3++ 3SO2−
4+ 3 H2

Eu(II) vs. Eu(III)[edit]

Although usually trivalent, europium readily forms divalent compounds. This behavior is unusual for most lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has anelectron configuration4f7because the half-filledf-shell provides more stability. In terms of size andcoordination number,europium(II) andbarium(II) are similar. The sulfates of both barium and europium(II) are also highly insoluble in water.[21]Divalent europium is a mild reducing agent, oxidizing in air to form Eu(III) compounds. In anaerobic, and particularly geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths. This ion-exchange process is the basis of the "negativeeuropium anomaly",the low europium content in many lanthanide minerals such asmonazite,relative to thechondriticabundance.Bastnäsitetends to show less of a negative europium anomaly than does monazite, and hence is the major source of europium today. The development of easy methods to separate divalent europium from the other (trivalent) lanthanides made europium accessible even when present in low concentration, as it usually is.[22]

Isotopes[edit]

Main article:Isotopes of europium

Naturally occurring europium is composed of twoisotopes,151Eu and153Eu, which occur in almost equal proportions;153Eu is slightly more abundant (52.2%natural abundance). While153Eu is stable,151Eu was found to be unstable toalpha decaywith ahalf-lifeof5+11
−3×1018yearsin 2007,[23]giving about one alpha decay per two minutes in every kilogram of natural europium. This value is in reasonable agreement with theoretical predictions. Besides the natural radioisotope151Eu, 35 artificial radioisotopes have been characterized, the most stable being150Eu with a half-life of 36.9 years,152Eu with a half-life of 13.516 years, and154Eu with a half-life of 8.593 years. All the remainingradioactiveisotopes have half-lives shorter than 4.7612 years, and the majority of these have half-lives shorter than 12.2 seconds; the known isotopes of europium range from130Eu to170Eu.[24][8]This element also has 17meta states,with the most stable being150mEu (t1/2=12.8 hours),152m1Eu (t1/2=9.3116 hours) and152m2Eu (t1/2=96 minutes).[8][25]

The primarydecay modefor isotopes lighter than153Eu iselectron capture,and the primary mode for heavier isotopes isbeta minus decay.The primarydecay productsbefore153Eu are isotopes ofsamarium(Sm) and the primary products after are isotopes ofgadolinium(Gd).[25]

Europium as a nuclear fission product[edit]

Medium-lived
fission products[further explanation needed]
t½
(year) 		Yield
(%) 		Q
(keV) 		βγ
155Eu  4.76 0.0803  252 βγ
85Kr 10.76 0.2180  687 βγ
113mCd 14.1  0.0008  316 β
90Sr 28.9  4.505   2826 β
137Cs 30.23 6.337   1176 βγ
121mSn 43.9  0.00005 390 βγ
151Sm 88.8  0.5314  77 β

Europium is produced by nuclear fission, but thefission product yieldsof europium isotopes are low near the top of the mass range forfission products.

As with other lanthanides, many isotopes of europium, especially those that have odd mass numbers or are neutron-poor like152Eu, have highcross sectionsforneutron capture,often high enough to beneutron poisons.

Thermal neutron capture cross sections
Isotope 151Eu 152Eu 153Eu 154Eu 155Eu
Yield ~10 low 1580 >2.5 330
Barns 5900 12800 312 1340 3950

151Eu is thebeta decayproduct ofsamarium-151,but since this has a long decay half-life and short mean time to neutron absorption, most151Sm instead ends up as152Sm.

152Eu (half-life 13.516 years) and154Eu (half-life 8.593 years) cannot be beta decay products because152Sm and154Sm are non-radioactive, but154Eu is the only long-lived "shielded"nuclide,other than134Cs,to have a fission yield of more than 2.5parts per millionfissions.[26]A larger amount of154Eu is produced byneutron activationof a significant portion of the non-radioactive153Eu; however, much of this is further converted to155Eu.

155Eu(half-life 4.7612 years) has a fission yield of 330 parts per million (ppm) foruranium-235andthermal neutrons;most of it is transmuted to non-radioactive and nonabsorptive gadolinium-156 by the end of fuelburnup.

Overall, europium is overshadowed bycaesium-137andstrontium-90as a radiation hazard, and by samarium and others as a neutron poison.[27][28][29][30][31][32][33]

Occurrence[edit]

Monazite

Europium is not found in nature as a free element. Many minerals contain europium, with the most important sources beingbastnäsite,monazite,xenotimeandloparite-(Ce).[34]No europium-dominant minerals are known yet, despite a single find of a tiny possible Eu–O or Eu–O–C system phase in the Moon's regolith.[35]

Depletion or enrichment of europium in minerals relative to other rare-earth elements is known as theeuropium anomaly.[36]Europium is commonly included in trace element studies ingeochemistryandpetrologyto understand the processes that formigneous rocks(rocks that cooled frommagmaorlava). The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks. Themedian crustal abundanceof europium is 2 ppm; values of the less abundant elements may vary with location by several orders of magnitude.[37]

Divalent europium (Eu2+) in small amounts is the activator of the bright bluefluorescenceof some samples of the mineralfluorite(CaF2). The reduction from Eu3+to Eu2+is induced by irradiation with energetic particles.[38]The most outstanding examples of this originated aroundWeardaleand adjacent parts of northern England; it was the fluorite found here that fluorescence was named after in 1852, although it was not until much later that europium was determined to be the cause.[39][40][41][42][43]

Inastrophysics,the signature of europium in stellarspectracan be used toclassify starsand inform theories of how or where a particular star was born. For instance, astronomers in 2019 identified higher-than-expected levels of europium within the starJ1124+4535,hypothesizing that this star originated in adwarf galaxythat collided with the Milky Way billions of years ago.[44][45]

Production[edit]

Europium is associated with the other rare-earth elements and is, therefore, mined together with them. Separation of the rare-earth elements occurs during later processing. Rare-earth elements are found in the mineralsbastnäsite,loparite-(Ce),xenotime,andmonazitein mineable quantities. Bastnäsite is a group of related fluorocarbonates, Ln(CO3)(F,OH). Monazite is a group of related of orthophosphate mineralsLnPO
4(Ln denotes a mixture of all the lanthanides exceptpromethium), loparite-(Ce) is an oxide, and xenotime is an orthophosphate (Y,Yb,Er,...)PO4.Monazite also containsthoriumandyttrium,which complicates handling because thorium and its decay products are radioactive. For the extraction from the ore and the isolation of individual lanthanides, several methods have been developed. The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate. Roasting the ore, followed by acidic and basic leaching, is used mostly to produce a concentrate of lanthanides. If cerium is the dominant lanthanide, then it is converted from cerium(III) to cerium(IV) and then precipitated. Further separation bysolvent extractionsorion exchange chromatographyyields a fraction which is enriched in europium. This fraction is reduced with zinc, zinc/amalgam, electrolysis or other methods converting the europium(III) to europium(II). Europium(II) reacts in a way similar to that ofalkaline earth metalsand therefore it can be precipitated as a carbonate or co-precipitated with barium sulfate.[46]Europium metal is available through the electrolysis of a mixture of molten EuCl3and NaCl (or CaCl2) in a graphite cell, which serves as cathode, using graphite as anode. The other product ischlorinegas.[34][46][47][48][49]

A few large deposits produce or produced a significant amount of the world production. TheBayan Oboiron ore deposit inInner Mongoliacontains significant amounts of bastnäsite and monazite and is, with an estimated 36 million tonnes of rare-earth element oxides, the largest known deposit.[50][51][52]The mining operations at the Bayan Obo deposit made China the largest supplier of rare-earth elements in the 1990s. Only 0.2% of the rare-earth element content is europium. The second large source for rare-earth elements between 1965 and its closure in the late 1990s was theMountain Pass rare earth minein California. The bastnäsite mined there is especially rich in the light rare-earth elements (La-Gd, Sc, and Y) and contains only 0.1% of europium. Another large source for rare-earth elements is the loparite found on the Kola peninsula. It contains besides niobium, tantalum and titanium up to 30% rare-earth elements and is the largest source for these elements in Russia.[34][53]

Compounds[edit]

Main article:Europium compounds
Europium(III) sulfate, Eu2(SO4)3
Europium(III) sulfate fluorescing red under ultraviolet light

Europium compounds tend to exist in a trivalent oxidation state under most conditions. Commonly these compounds feature Eu(III) bound by 6–9 oxygenic ligands. The Eu(III) sulfates, nitrates and chlorides are soluble in water or polar organic solvents. Lipophilic europium complexes often featureacetylacetonate-like ligands, such asEuFOD.

Halides[edit]

Europium metal reacts with all the halogens:

2 Eu + 3 X2→ 2 EuX3(X = F, Cl, Br, I)

This route gives white europium(III) fluoride (EuF3), yelloweuropium(III) chloride(EuCl3), gray[54]europium(III) bromide(EuBr3), and colorless europium(III) iodide (EuI3). Europium also forms the corresponding dihalides: yellow-green europium(II) fluoride (EuF2), colorlesseuropium(II) chloride(EuCl2) (although it has a bright blue fluorescence under UV light),[55]colorlesseuropium(II) bromide(EuBr2), and green europium(II) iodide (EuI2).[12]

Chalcogenides and pnictides[edit]

Europium forms stable compounds with all of the chalcogens, but the heavier chalcogens (S, Se, and Te) stabilize the lower oxidation state. Threeoxidesare known: europium(II) oxide (EuO),europium(III) oxide(Eu2O3), and themixed-valenceoxide Eu3O4,consisting of both Eu(II) and Eu(III). Otherwise, the main chalcogenides areeuropium(II) sulfide(EuS), europium(II) selenide (EuSe) and europium(II) telluride (EuTe): all three of these are black solids. Europium(II) sulfide is prepared by sulfiding the oxide at temperatures sufficiently high to decompose the Eu2O3:[56]

Eu2O3+ 3 H2S → 2 EuS + 3 H2O + S

The mainnitrideof europium is europium(III) nitride (EuN).

History[edit]

Although europium is present in most of the minerals containing the other rare elements, due to the difficulties in separating the elements it was not until the late 1800s that the element was isolated.William Crookesobserved the phosphorescent spectra of the rare elements including those eventually assigned to europium.[57]

Europium was first found in 1892 byPaul Émile Lecoq de Boisbaudran,who obtained basic fractions from samarium-gadolinium concentrates which had spectral lines not accounted for by samarium orgadolinium.However, the discovery of europium is generally credited toFrenchchemistEugène-Anatole Demarçay,who suspected samples of the recently discovered element samarium were contaminated with an unknown element in 1896 and who was able to isolate it in 1901; he then named iteuropium.[58][59][60][61][62]

When the europium-dopedyttrium orthovanadatered phosphor was discovered in the early 1960s, and understood to be about to cause a revolution in the color television industry, there was a scramble for the limited supply of europium on hand among the monazite processors,[63]as the typical europium content in monazite is about 0.05%. However, the Molycorpbastnäsitedeposit at theMountain Pass rare earth mine,California,whose lanthanides had an unusually high europium content of 0.1%, was about to come on-line and provide sufficient europium to sustain the industry. Prior to europium, the color-TV red phosphor was very weak, and the other phosphor colors had to be muted, to maintain color balance. With the brilliant red europium phosphor, it was no longer necessary to mute the other colors, and a much brighter color TV picture was the result.[63]Europium has continued to be in use in the TV industry ever since as well as in computer monitors. Californian bastnäsite now faces stiff competition fromBayan Obo,China, with an even "richer" europium content of 0.2%.

Frank Spedding,celebrated for his development of the ion-exchange technology that revolutionized the rare-earth industry in the mid-1950s, once related the story of how[64]he was lecturing on the rare earths in the 1930s, when an elderly gentleman approached him with an offer of a gift of several pounds of europium oxide. This was an unheard-of quantity at the time, and Spedding did not take the man seriously. However, a package duly arrived in the mail, containing several pounds of genuine europium oxide. The elderly gentleman had turned out to beHerbert Newby McCoy,who had developed a famous method of europium purification involving redox chemistry.[48][65]

Applications[edit]

Europium is one of the elements involved in emitting red light in CRT televisions.

Relative to most other elements, commercial applications for europium are few and rather specialized. Almost invariably, its phosphorescence is exploited, either in the +2 or +3 oxidation state.

It is adopantin some types ofglassinlasersand other optoelectronic devices. Europium oxide (Eu2O3) is widely used as a redphosphorintelevision setsandfluorescent lamps,and as an activator foryttrium-based phosphors.[66][67]Color TV screens contain between 0.5 and 1 g of europium oxide.[68]Whereas trivalent europium gives red phosphors,[69]the luminescence of divalent europium depends strongly on the composition of the host structure. UV to deep red luminescence can be achieved.[70][71]The two classes of europium-based phosphor (red and blue), combined with the yellow/greenterbiumphosphors give "white" light, the color temperature of which can be varied by altering the proportion or specific composition of the individual phosphors. This phosphor system is typically encountered in helical fluorescent light bulbs. Combining the same three classes is one way to make trichromatic systems in TV and computer screens,[66]but as an additive, it can be particularly effective in improving the intensity of red phosphor.[10]Europium is also used in the manufacture of fluorescent glass, increasing the general efficiency of fluorescent lamps.[10]One of the more common persistent after-glow phosphors besides copper-doped zinc sulfide is europium-dopedstrontium aluminate.[72]Europium fluorescence is used to interrogate biomolecular interactions in drug-discovery screens. It is also used in the anti-counterfeiting phosphors ineurobanknotes.[73][74]

An application that has almost fallen out of use with the introduction of affordable superconducting magnets is the use of europium complexes, such asEu(fod)3,as shift reagents inNMRspectroscopy.Chiralshift reagents, such as Eu(hfc)3,are still used to determineenantiomericpurity.[75]

Europium compounds are used to labelantibodiesfor sensitive detection ofantigensin body fluids, a form ofImmunoassay.When these europium-labeled antibodies bind to specific antigens, the resulting complex can be detected with laser excited florescence.[76]Europium compounds also find applications in molecular biology and environmental monitoring due to their reliable luminescent properties.[77]

Precautions[edit]

Europium
Hazards
GHSlabelling:
GHS02: Flammable
Danger
H250
P222,P231,P422[78]
NFPA 704(fire diamond)
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
0
3
1
W

There are no clear indications that europium is particularly toxic compared to otherheavy metals.Europium chloride, nitrate and oxide have been tested for toxicity: europium chloride shows an acute intraperitoneal LD50toxicity of 550 mg/kg and the acute oral LD50toxicity is 5000 mg/kg. Europium nitrate shows a slightly higher intraperitoneal LD50toxicity of 320 mg/kg, while the oral toxicity is above 5000 mg/kg.[79][80]The metal dust presents a fire and explosion hazard.[81]

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