page:  = 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 nonahydrate : 
   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 4f7 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 . Bastnäsite 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 150Eu 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 @.@ 7612 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 150mEu ( t1 / 2 = 12 @.@ 8 hours ) , 152m1Eu ( t1 / 2 = 9 @.@ 3116 hours ) and 152m2Eu ( 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 151Sm 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 154Sm 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 155Eu . 
   155Eu ( half @-@ life 4 @.@ 7612 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 nonabsorptive 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 ( Eu2 + ) in small amounts is the activator of the bright blue fluorescence of some samples of the mineral fluorite ( CaF2 ) . The reduction from Eu3 + to Eu2 + 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 LnPO 
   4 ( Ln denotes a mixture of all the lanthanides except promethium ) , and the third is a fluorocarbonate LnCO3F . 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 EuCl3 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 . Lipophilic europium complexes often feature acetylacetonate @-@ like ligands , e.g. , Eufod . 
   
   = = = Halides = = = 
   
   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 ) , yellow europium ( III ) chloride ( EuCl3 ) , gray europium ( III ) bromide ( EuBr3 ) , and colorless europium ( III ) iodide ( EuI3 ) . Europium also forms the corresponding dihalides : yellow @-@ green europium ( II ) fluoride ( EuF2 ) , colorless europium ( II ) chloride ( EuCl2 ) , colorless europium ( II ) bromide ( EuBr2 ) , and green europium ( II ) iodide ( EuI2 ) . 
   
   = = = 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 ( EuO ) , europium ( III ) oxide ( Eu2O3 ) , and the mixed @-@ valence oxide Eu3O4 , consisting of both Eu ( II ) and Eu ( III ) . Otherwise , the main chalcogenides are europium ( II ) sulfide ( EuS ) , europium ( II ) selenide ( EuSe ) and europium ( II ) telluride ( EuTe ) : all three of these are black solids . EuS is prepared by sulfiding 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 ( EuN ) . 
   
   = = 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 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 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 Molycorp 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 ( fod ) 3 , as shift reagents in NMR spectroscopy . Chiral shift reagents , such as Eu ( hfc ) 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 . 
   
   