text: europium europium is a chemical element with symbol eu and atomic number 63 . it was isolated in 1901 and is named after the continent of europe . it is a moderately hard , silvery metal which readily oxidizes in air and water . being a typical member of the lanthanide series , europium usually assumes the oxidation state + 3 , but the oxidation state + 2 is also common : all europium compounds with oxidation state + 2 are slightly reducing . europium has no significant biological role and is relatively non - toxic compared to other heavy metals . most applications of europium exploit the phosphorescence of europium compounds . europium is one of the least abundant elements in the universe ; only about 5 × 10 − 8 % of all matter in the universe is europium . characteristics physical properties europium is a ductile metal with a hardness similar to that of lead . it crystallizes in a body - centered cubic lattice . some properties of europium are strongly influenced by its half - filled electron shell . europium has the second lowest melting point and the lowest density of all lanthanides . europium becomes a superconductor when it is cooled below 1 . 8 k and compressed to above 80 gpa . this is because europium is divalent in the metallic state , and is converted into the trivalent state by the applied pressure . in the divalent state , the strong local magnetic moment ( j 7 / 2 ) suppresses the superconductivity , which is induced by eliminating this local moment ( j 0 in eu3 + ) . chemical properties 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 . its reactivity with water is comparable to that of calcium , 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 form europium ( iii ) oxide : 4 eu + 3 o2 → 2 eu2o3 europium dissolves readily in dilute sulfuric acid to form pale pink solutions of the hydrated eu ( iii ) , which exist as a : 2 eu + 3 h2so4 + 18 h2o → 2 [ eu ( h2o ) 9 ] 3 + + 3 so2 − 4 + 3 h2 eu ( ii ) vs. eu ( iii ) although usually trivalent , europium readily forms divalent compounds . this behavior is unusual to most lanthanides , which almost exclusively form compounds with an oxidation state of + 3 . the + 2 state has an electron configuration because the half - filled f - shell gives more stability . the + 2 state is highly reducing . in terms of size and coordination number , europium ( ii ) and barium ( ii ) are similar . for example , the sulfates of both barium and europium ( ii ) are also highly insoluble in water . 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 " negative europium anomaly " , the low europium content in many lanthanide minerals such as monazite , relative to the chondritic abundance . tends 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 . isotopes naturally occurring europium is composed of 2 isotopes , 151eu and 153eu , with 153eu being the most abundant ( 52 . 2 % natural abundance ) . while 153eu is stable , 151eu was recently found to be unstable to alpha decay with half - life of 5 + 11 − 3 × 1018 years , giving about 1 alpha decay per two minutes in every kilogram of natural europium . this value is in reasonable agreement with theoretical predictions . besides the natural radioisotope 151eu , 35 artificial radioisotopes have been characterized , the most stable being with a half - life of 36 . 9 years , 152eu with a half - life of 13 . 516 years , and 154eu with a half - life of 8 . 593 years . all the remaining radioactive isotopes have half - lives shorter than 4 . years , and the majority of these have half - lives shorter than 12 . 2 seconds . this element also has 8 meta states , with the most stable being ( t1 / 2 12 . 8 hours ) , ( t1 / 2 9 . hours ) and ( t1 / 2 96 minutes ) . the primary decay mode for isotopes lighter than 153eu is electron capture , and the primary mode for heavier isotopes is beta minus decay . the primary decay products before 153eu are isotopes of samarium ( sm ) and the primary products after are isotopes of gadolinium ( gd ) . europium as a nuclear fission product europium is produced by nuclear fission , but the fission product yields of europium isotopes are low near the top of the mass range for fission products . like other lanthanides , many isotopes , especially isotopes with odd mass numbers and neutron - poor isotopes like 152eu , have high cross sections for neutron capture , often high enough to be neutron poisons . 151eu is the beta decay product of samarium - 151 , but since this has a long decay half - life and short mean time to neutron absorption , most instead ends up as 152sm . 152eu ( half - life 13 . 516 years ) and 154eu ( half - life 8 . 593 years ) cannot be beta decay products because 152sm and are non - radioactive , but 154eu is the only long - lived " shielded " nuclide , other than 134cs , to have a fission yield of more than 2 . 5 parts per million fissions . a larger amount of 154eu is produced by neutron activation of a significant portion of the non - radioactive 153eu ; however , much of this is further converted to . ( half - life 4 . years ) has a fission yield of 330 parts per million ( ppm ) for uranium - 235 and thermal neutrons ; most of it is transmuted to non - radioactive and gadolinium - 156 by the end of fuel burnup . overall , europium is overshadowed by caesium - 137 and strontium - 90 as a radiation hazard , and by samarium and others as a neutron poison . occurrence europium is not found in nature as a free element . many minerals contain europium , with the most important sources being bastnäsite , monazite , xenotime and loparite . depletion or enrichment of europium in minerals relative to other rare earth elements is known as the europium anomaly . europium is commonly included in trace element studies in geochemistry and petrology to understand the processes that form igneous rocks ( rocks that cooled from magma or lava ) . the nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks . divalent europium ( + ) in small amounts is the activator of the bright blue fluorescence of some samples of the mineral fluorite ( caf2 ) . the reduction from eu3 + to + is induced by irradiation with energetic particles . the most outstanding examples of this originated around weardale and 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 . production europium is associated with the other rare earth elements and is , therefore , mined together with them . separation of the rare earth elements is a step in the later processing . rare earth elements are found in the minerals bastnäsite , loparite , xenotime , and monazite in mineable quantities . the first two are orthophosphate minerals 4 ( denotes a mixture of all the lanthanides except promethium ) , and the third is a . monazite also contains thorium and yttrium , 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 and subsequent 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 by solvent extractions or ion exchange chromatography yields 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 of alkaline earth metals and therefore it can be precipitated as carbonate or is co - precipitated with barium sulfate . europium metal is available through the electrolysis of a mixture of molten and nacl ( or cacl2 ) in a graphite cell , which serves as cathode , using graphite as anode . the other product is chlorine gas . a few large deposits produce or produced a significant amount of the world production . the bayan obo iron ore deposit contains significant amounts of bastnäsite and monazite and is , with an estimated 36 million tonnes of rare earth element oxides , the largest known deposit . 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 the mountain pass rare earth mine . 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 . compounds europium compounds tend to exist trivalent oxidation state under most conditions . commonly these compounds feature eu ( iii ) bound by 6 – 9 oxygenic ligands , typically water . these compounds , the chlorides , sulfates , nitrates , are soluble in water or polar organic solvent . europium complexes often feature acetylacetonate - like ligands , e.g. , . halides europium metal reacts with all the halogens : 2 eu + 3 x2 → 2 ( x f , cl , br , i ) this route gives white europium ( iii ) fluoride ( ) , yellow europium ( iii ) chloride ( ) , gray europium ( iii ) bromide ( ) , and colorless europium ( iii ) iodide ( ) . europium also forms the corresponding dihalides : yellow - green europium ( ii ) fluoride ( ) , colorless europium ( ii ) chloride ( ) , colorless europium ( ii ) bromide ( ) , and green europium ( ii ) iodide ( ) . chalcogenides and pnictides europium forms stable compounds with all of the chalcogens , but the heavier chalcogens ( s , se , and te ) stabilize the lower oxidation state . three oxides are known : europium ( ii ) oxide ( ) , europium ( iii ) oxide ( eu2o3 ) , and the mixed - valence oxide , consisting of both eu ( ii ) and eu ( iii ) . otherwise , the main chalcogenides are europium ( ii ) sulfide ( eus ) , europium ( ii ) selenide ( ) and europium ( ii ) telluride ( ) : all three of these are black solids . eus is prepared by the oxide at temperatures sufficiently high to decompose the eu2o3 : eu2o3 + 3 h2s → 2 eus + 3 h2o + s the main nitride is europium ( iii ) nitride ( ) . history of study 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 crookes observed the phosphorescent spectra of the rare elements and observed spectral lines later assigned to europium . europium was first found in 1890 by paul émile lecoq de boisbaudran , who obtained basic fractions from samarium - gadolinium concentrates which had spectral lines not accounted for by samarium or gadolinium . however , the discovery of europium is generally credited to french chemist eugène - anatole , 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 it europium . when the europium - doped yttrium orthovanadate red 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 , as the typical europium content in monazite is about 0 . 05 % . however , the bastnäsite deposit at the mountain 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 . 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 from bayan 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 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 be herbert newby mccoy who had developed a famous method of europium purification involving redox chemistry . applications relative to most other elements , commercial applications for europium are few and rather specialized . almost invariably , they exploit its phosphorescence , either in the + 2 or + 3 oxidation state . it is a dopant in some types of glass in lasers and other optoelectronic devices . europium oxide ( eu2o3 ) is widely used as a red phosphor in television sets and fluorescent lamps , and as an activator for yttrium - based phosphors . color tv screens contain between 0 . 5 and 1 g of europium oxide . whereas trivalent europium gives red phosphors , the luminescence of divalent europium depends on the host lattice , but tends to be on the blue side . the two classes of europium - based phosphor ( red and blue ) , combined with the yellow / green terbium phosphors 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 . europium is also used in the manufacture of fluorescent glass . one of the more common persistent after - glow phosphors besides copper - doped zinc sulfide is europium - doped strontium aluminate . europium fluorescence is used to interrogate biomolecular interactions in drug - discovery screens . it is also used in the anti - counterfeiting phosphors in euro banknotes . an application that has almost fallen out of use with the introduction of affordable superconducting magnets is the use of europium complexes , such as eu ( ) 3 , as shift reagents in nmr spectroscopy . chiral shift reagents , such as eu ( ) 3 , are still used to determine enantiomeric purity . a recent ( 2015 ) application of europium is in quantum memory chips which can reliably store information for days at a time ; these could allow sensitive quantum data to be stored to a hard disk - like device and shipped around the country . precautions there are no clear indications that europium is particularly toxic compared to other heavy metals . europium chloride , nitrate and oxide have been tested for toxicity : europium chloride shows an acute intraperitoneal ld50 toxicity of 550 mg / kg and the acute oral ld50 toxicity is 5000 mg / kg . europium nitrate shows a slightly higher intraperitoneal ld50 toxicity of 320 mg / kg , while the oral toxicity is above 5000 mg / kg . the metal dust presents a fire and explosion hazard .