 = 7 / 2 ) <unk> the <unk> , which is induced by eliminating this local moment ( J = 
 0 in <unk> + ) . 
 
 = = = 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 <unk> appearance of the fresh metal , even when coated with a protective layer of mineral oil . Europium <unk> in air at 150 to 180 ° C to form europium ( III ) oxide : 
 4 Eu + 3 O2 → 2 Eu2O3 
 Europium dissolves readily in <unk> sulfuric acid to form pale pink solutions of the hydrated Eu ( III ) , which exist as a <unk> : 
 2 Eu + 3 <unk> + 18 H2O → 2 [ Eu ( H2O ) 9 ] 3 + + 3 <unk> − 
 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 <unk> 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 <unk> of both barium and europium ( II ) are also highly <unk> in water . <unk> europium is a mild reducing agent , oxidizing in air to form Eu ( III ) compounds . In <unk> , and particularly <unk> conditions , the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline <unk> . 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 <unk> abundance . <unk> 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 × <unk> 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 <unk> 151Eu , 35 artificial <unk> have been characterized , the most stable being <unk> 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 @.@ <unk> 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 <unk> ( t1 / 2 = 12 @.@ 8 hours ) , <unk> ( t1 / 2 = 9 @.@ <unk> hours ) and <unk> ( 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 ( <unk> ) and the primary products after are isotopes of gadolinium ( <unk> ) . 
 
 = = = = 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 <unk> instead ends up as <unk> . 
 152Eu ( half @-@ life 13 @.@ 516 years ) and 154Eu ( half @-@ life 8 @.@ 593 years ) cannot be beta decay products because <unk> and <unk> are non @-@ radioactive , but 154Eu is the only long @-@ lived " shielded " <unk> , other than <unk> , to have a fission yield of more than 2 @.@ 5 parts per million <unk> . 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 <unk> . 
 <unk> ( half @-@ life 4 @.@ <unk> 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 <unk> gadolinium @-@ 156 by the end of fuel <unk> . 
 Overall , europium is overshadowed by caesium @-@ 137 and <unk> @-@ 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 , <unk> and loparite . 
 <unk> or <unk> 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 <unk> and <unk> to understand the processes that form igneous rocks ( rocks that cooled from <unk> or <unk> ) . The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks . 
 <unk> europium ( <unk> + ) in small amounts is the <unk> of the bright blue fluorescence of some samples of the mineral <unk> ( <unk> ) . The reduction from <unk> + to <unk> + is induced by irradiation with energetic particles . The most outstanding examples of this originated around <unk> and adjacent parts of northern England ; it was the <unk> 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 . <unk> of the rare earth elements is a step in the later processing . Rare earth elements are found in the minerals bastnäsite , loparite , <unk> , and monazite in <unk> quantities . The first two are <unk> minerals <unk> 
 4 ( <unk> denotes a mixture of all the lanthanides except <unk> ) , and the third is a <unk> <unk> . <unk> also contains thorium and yttrium , which <unk> 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 . <unk> the ore and subsequent acidic and basic <unk> 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 <unk> or ion exchange chromatography yields a fraction which is enriched in europium . This fraction is reduced with zinc , zinc / <unk> , 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 <unk> and <unk> ( or <unk> ) in a graphite cell , which serves as <unk> , using graphite as <unk> . 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 @-@ <unk> , <unk> , and Y ) and contains only 0 @.@ 1 % of europium . Another large source for rare earth elements is the loparite found on the <unk> peninsula . It contains besides niobium , tantalum and <unk> 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 <unk> <unk> , typically water . These compounds , the <unk> , <unk> , <unk> , are soluble in water or polar organic solvent . <unk> europium complexes often feature <unk> @-@ like <unk> , e.g. , <unk> . 
 
 = = = Halides = = = 
 
 Europium metal reacts with all the <unk> : 
 2 Eu + 3 <unk> → 2 <unk> ( X = F , Cl , <unk> , I ) 
 This route gives white europium ( III ) fluoride ( <unk> ) , yellow europium ( III ) chloride ( <unk> ) , gray europium ( III ) bromide ( <unk> ) , and colorless europium ( III ) iodide ( <unk> ) . Europium also forms the corresponding <unk> : yellow @-@ green europium ( II ) fluoride ( <unk> ) , colorless europium ( II ) chloride ( <unk> ) , colorless europium ( II ) bromide ( <unk> ) , and green europium ( II ) iodide ( <unk> ) . 
 
 = = = <unk> and <unk> = = = 
 
 Europium forms stable compounds with all of the <unk> , but the heavier <unk> ( S , Se , and Te ) stabilize the lower oxidation state . Three oxides are known : europium ( II ) oxide ( <unk> ) , europium ( III ) oxide ( Eu2O3 ) , and the mixed @-@ valence oxide <unk> , consisting of both Eu ( II ) and Eu ( III ) . Otherwise , the main <unk> are europium ( II ) sulfide ( EuS ) , europium ( II ) selenide ( <unk> ) and europium ( II ) telluride ( <unk> ) : all three of these are black solids . EuS is prepared by <unk> the oxide at temperatures sufficiently high to <unk> the Eu2O3 : 
 Eu2O3 + 3 <unk> → 2 EuS + 3 H2O + S 
 The main <unk> is europium ( III ) <unk> ( <unk> ) . 
 
 = = 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 <unk> observed the <unk> spectra of the rare elements and observed spectral lines later assigned to europium . 
 Europium was first found in 1890 by Paul Émile <unk> de <unk> , 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 @-@ <unk> <unk> , 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 <unk> 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 <unk> 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 <unk> 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 " <unk> " europium content of 0 @.@ 2 % . 
 Frank <unk> , 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 <unk> 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 <unk> 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 <unk> McCoy who had developed a famous method of europium purification involving <unk> chemistry . 
 
 = = Applications = = 
 
 Relative to most other elements , commercial applications for europium are few and rather specialized . Almost invariably , they exploit its <unk> , either in the + 2 or + 3 oxidation state . 
 It is a <unk> in some types of glass in lasers and other <unk> devices . Europium oxide ( Eu2O3 ) is widely used as a red phosphor in television sets and fluorescent lamps , and as an <unk> 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 <unk> 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 . <unk> the same three classes is one way to make <unk> 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 <unk> <unk> . Europium fluorescence is used to <unk> <unk> interactions in drug @-@ discovery screens . It is also used in the anti @-@ counterfeiting phosphors in euro <unk> . 
 An application that has almost fallen out of use with the introduction of affordable <unk> magnets is the use of europium complexes , such as Eu ( <unk> ) 3 , as shift reagents in NMR spectroscopy . <unk> shift reagents , such as Eu ( <unk> ) 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 <unk> LD50 toxicity of 550 mg / kg and the acute oral LD50 toxicity is 5000 mg / kg . Europium nitrate shows a slightly higher <unk> LD50 toxicity of 320 mg / kg , while the oral toxicity is above 5000 mg / kg . The metal dust presents a fire and explosion hazard . 
 
 