Erbium's principal uses involve its pink-colored Er3+ ions, which have optical fluorescent properties particularly useful in certain laser applications. Erbium-doped glasses or crystals can be used as optical amplification media, where Er3+ ions are optically pumped at around 980 or1480 nm and then radiate light at1530 nm in stimulated emission. This process results in an unusually mechanically simplelaseroptical amplifier for signals transmitted by fiber optics. The1550 nm wavelength is especially important foroptical communications because standard single modeoptical fibers have minimal loss at this particular wavelength.
In addition to optical fiber amplifier-lasers, a large variety of medical applications (e.g. dermatology, dentistry) rely on the erbium ion's2940 nm emission (seeEr:YAG laser) when lit at another wavelength, which is highly absorbed in water in tissues, making its effect very superficial. Such shallow tissue deposition of laser energy is helpful inlaser surgery, and for the efficient production of steam which produces enamel ablation by common types ofdental laser.
Erbium(III) chloride in sunlight, showing some pink fluorescence of Er+3 from natural ultraviolet.
Atrivalent element, pure erbiummetal is malleable (or easily shaped), soft yet stable in air, and does notoxidize as quickly as some otherrare-earth metals. Itssalts are rose-colored, and the element has characteristic sharpabsorption spectra bands invisible light,ultraviolet, and nearinfrared.[9] Otherwise it looks much like the other rare earths. Itssesquioxide is callederbia. Erbium's properties are to a degree dictated by the kind and amount of impurities present. Erbium does not play any known biological role, but is thought to be able to stimulatemetabolism.[10]
Erbium can form propeller-shaped atomic clusters Er3N, where the distance between the erbium atoms is 0.35 nm. Those clusters can be isolated by encapsulating them intofullerene molecules, as confirmed bytransmission electron microscopy.[12]
Like mostrare-earth elements, erbium is usually found in the +3 oxidation state. However, it is possible for erbium to also be found in the 0, +1 and +2[13] oxidation states.
Erbium dissolves readily in dilutesulfuric acid to form solutions containing hydrated Er(III) ions, which exist as rose red [Er(OH2)9]3+ hydration complexes:[15]
2 Er (s) + 3 H2SO4 (aq) → 2 Er3+ (aq) + 3SO2− 4 (aq) + 3 H2 (g)
Naturally occurring erbium is composed of 6 stableisotopes,162Er,164Er,166Er,167Er,168Er, and170Er, with166Er being the most abundant (33.503%natural abundance). Of the artificialradioisotopes have been characterized, the most stable are169Er with ahalf-life of9.39 d,172Er with a half-life of49.3 h, and160Er with a half-life of28.58 h. All of the remainingradioactive isotopes have half-lives that are less than11 h, and the majority of these have half-lives that are less than 4 minutes. This element also has 26meta states, with the most stable being149m1Er with a half-life of8.9 s.[8]
The known isotopes of erbium range from143Er to180Er. The primarydecay mode before the most abundant stable isotope,166Er, iselectron capture, and the primary mode after isbeta decay. The primarydecay products before166Er are element 67 (holmium) isotopes, and the primary products after are element 69 (thulium) isotopes.[8]
165Er has been identified as useful for use inAuger therapy, as it decays via electron capture and emits nogamma radiation. It can also be used as aradioactive tracer to labelantibodies andpeptides, though it cannot be detected by any kind of imaging for the study of its biological distribution. The isotope can be produced via the bombardment of165Ho with beams of protons or deuterium, a reaction which is especially convenient because165Ho is amonoisotopic element and relatively inexpensive.[16]
Erbium(III) oxide (also known as erbia) is the only known oxide of erbium, first isolated byCarl Gustaf Mosander in 1843, and first obtained in pure form in 1905 byGeorges Urbain andCharles James.[17] It has acubic structure resembling thebixbyite motif. The Er3+ centers are octahedral.[18] The formation of erbium oxide is accomplished by burning erbium metal,[10] erbium oxalate or otheroxyacid salts of erbium.[19] Erbium oxide is insoluble in water and slightly soluble in heated mineral acids. The pink-colored compound is used as aphosphor activator and to produceinfrared-absorbing glass.[19]
Erbium(III) fluoride is a pinkish powder[20] that can be produced by reactingerbium(III) nitrate andammonium fluoride.[21] It can be used to make infrared light-transmitting materials[22] and up-converting luminescent materials,[23] and is an intermediate in the production of erbium metal prior to its reduction with calcium.[19]Erbium(III) chloride is a violet compounds that can be formed by first heating erbium(III) oxide andammonium chloride to produce theammonium salt of the pentachloride ([NH4]2ErCl5) then heating it in a vacuum at 350-400 °C.[24][25][26] It forms crystals of theAlCl3 type, withmonoclinic crystals and thepoint groupC2/m.[27] Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group ofP2/n (P2/c) -C42h. In this compound, erbium is octa-coordinated to form[Er(H2O)6Cl2]+ ions with the isolatedCl− completing the structure.[28]
Erbium(III) bromide is a violet solid. It is used, like other metal bromide compounds, in water treatment, chemical analysis and for certain crystal growth applications.[29]Erbium(III) iodide[30] is a slightly pink compound that is insoluble in water. It can be prepared by directly reacting erbium withiodine.[31]
Organoerbium compounds are very similar tothose of the other lanthanides, as they all share an inability to undergoπ backbonding. They are thus mostly restricted to the mostly ioniccyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.[32]
Carl Gustaf Mosander, the scientist who discovered erbium, lanthanum and terbium
Erbium (forYtterby, a village inSweden) wasdiscovered byCarl Gustaf Mosander in 1843.[33] Mosander was working with a sample of what was thought to be the single metal oxideyttria, derived from the mineralgadolinite. He discovered that the sample contained at least two metal oxides in addition to pure yttria, which he named "erbia" and "terbia" after the village of Ytterby where the gadolinite had been found. Mosander was not certain of the purity of the oxides and later tests confirmed his uncertainty. Not only did the "yttria" contain yttrium, erbium, and terbium; in the ensuing years, chemists, geologists and spectroscopists discovered five additional elements:ytterbium,scandium,thulium,holmium, andgadolinium.[34]: 701 [35][36][37][38][39]
Erbia and terbia, however, were confused at this time.Marc Delafontaine, a Swiss spectroscopist, mistakenly switched the names of the two elements in his work separating the oxides erbia and terbia. After 1860, terbia was renamed erbia and after 1877 what had been known as erbia was renamed terbia.[40] Fairly pure Er2O3 was independently isolated in 1905 byGeorges Urbain andCharles James. Reasonably pure erbium metal was not produced until 1934 whenWilhelm Klemm andHeinrich Bommer reduced theanhydrouschloride withpotassium vapor.[41][10]
The concentration of erbium in the Earth crust is about 2.8 mg/kg and in seawater 0.9 ng/L.[42] (Concentration of less abundant elements may vary with location by several orders of magnitude[43] making the relative abundance unreliable). Like other rare earths, this element is never found as a free element in nature but is found inmonazite andbastnäsite ores.[10] It has historically been very difficult and expensive to separate rare earths from each other in their ores bution-exchange chromatography methods[44] developed in the late 20th century have greatly reduced the cost of production of all rare-earth metals and theirchemical compounds.[45]
The principal commercial sources of erbium are from the mineralsxenotime andeuxenite, and most recently, the ion adsorption clays of southern China. Consequently, China has now become the principal global supplier of this element.[46] In the high-yttrium versions of these ore concentrates, yttrium is about two-thirds of the total by weight, and erbia is about 4–5%. When the concentrate is dissolved in acid, the erbia liberates enough erbium ion to impart a distinct and characteristic pink color to the solution. This color behavior is similar to what Mosander and the other early workers in the lanthanides saw in their extracts from the gadolinite minerals of Ytterby.[citation needed]
Crushed minerals are attacked by hydrochloric orsulfuric acid that transforms insoluble rare-earth oxides into soluble chlorides or sulfates. The acidic filtrates are partially neutralized with caustic soda (sodium hydroxide) to pH 3–4.Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated withammonium oxalate to convert rare earths into their insolubleoxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved innitric acid that excludes one of the main components,cerium, whose oxide is insoluble in HNO3. The solution is treated withmagnesium nitrate to produce a crystallized mixture ofdouble salts of rare-earth metals. The salts are separated byion exchange. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent.[42] Erbium metal is obtained from its oxide or salts by heating withcalcium at1450 °C under argon atmosphere.[42]
A large variety of medical applications (i.e., dermatology, dentistry) utilize erbium ion's2940 nm emission (seeEr:YAG laser), which is highly absorbed in water (absorption coefficient about12000/cm). Such shallow tissue deposition of laser energy is necessary for laser surgery, and the efficient production of steam for laser enamel ablation in dentistry.[47] Common applications of erbium lasers in dentistry include ceramiccosmetic dentistry and removal of brackets inorthodontic braces; such laser applications have been noted as more time-efficient than performing the same procedures with rotarydental instruments.[48]
Erbium-dopedoptical silica-glass fibers are the active element inerbium-doped fiber amplifiers (EDFAs), which are widely used inoptical communications.[49] The same fibers can be used to create fiberlasers. In order to work efficiently, erbium-doped fiber is usually co-doped with glass modifiers/homogenizers, often aluminium or phosphorus. These dopants help prevent clustering of Er ions and transfer the energy more efficiently between excitation light (also known as optical pump) and the signal. Co-doping of optical fiber with Er and Yb is used in high-power Er/Yb fiber lasers. Erbium can also be used inerbium-doped waveguide amplifiers.[10]
When added tovanadium as analloy, erbium lowers hardness and improves workability.[50] An erbium-nickel alloy Er3Ni has an unusually high specific heat capacity at liquid-helium temperatures and is used incryocoolers; a mixture of 65% Er3Co and 35% Er0.9Yb0.1Ni by volume improves the specific heat capacity even more.[51][52]
Erbium does not have a biological role, but erbium salts can stimulatemetabolism. Humans consume 1 milligram of erbium a year on average. The highest concentration of erbium in humans is in thebones, but there is also erbium in the humankidneys andliver.[10]
Erbium is slightly toxic if ingested, but erbium compounds are generally not toxic.[10] Ionic erbium behaves similar to ionic calcium, and can potentially bind to proteins such ascalmodulin. When introduced into the body, nitrates of erbium, similar to other rare earth nitrates, increasetriglyceride levels in theliver and cause leakage of hepatic (liver-related)enzymes to the blood, though they uniquely (along with gadolinium and dysprosium nitrates) increaseRNA polymerase II activity.[56] Ingestion[57] and inhalation[58] are the main routes of exposure to erbium and other rare earths, as they do not diffuse through unbroken skin.[56]
Metallic erbium in dust form presents a fire and explosion hazard.[59][60][61]
^abArblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Yttrium and all lanthanides except Ce and Pm have been observed in the oxidation state 0 in bis(1,3,5-tri-t-butylbenzene) complexes, seeCloke, F. Geoffrey N. (1993). "Zero Oxidation State Compounds of Scandium, Yttrium, and the Lanthanides".Chem. Soc. Rev.22:17–24.doi:10.1039/CS9932200017. andArnold, Polly L.; Petrukhina, Marina A.; Bochenkov, Vladimir E.; Shabatina, Tatyana I.; Zagorskii, Vyacheslav V.; Cloke (2003-12-15). "Arene complexation of Sm, Eu, Tm and Yb atoms: a variable temperature spectroscopic investigation".Journal of Organometallic Chemistry.688 (1–2):49–55.doi:10.1016/j.jorganchem.2003.08.028.
^All thelanthanides, except Pm, in the +2 oxidation state have been observed in organometallic molecular complexes, seeLanthanides Topple Assumptions andMeyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2".Angewandte Chemie International Edition.53 (14):3550–51.doi:10.1002/anie.201311325.PMID24616202.. Additionally, all thelanthanides (La–Lu) form dihydrides (LnH2), dicarbides (LnC2), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln3+ ions with electrons delocalized into conduction bands, e. g. Ln3+(H−)2(e−).
^IAEA (2021). "4.11. Erbium-165".Alternative Radionuclide Production with a Cyclotron. International Atomic Energy Agency.ISBN978-92-0-103221-8.OCLC1317842424.
^Brauer, G., ed. (1963).Handbook of Preparative Inorganic Chemistry (2nd ed.). New York: Academic Press.
^Meyer, G. (1989). "The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides—The Example of Ycl3".The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides-The Example of YCl3. Inorganic Syntheses. Vol. 25. pp. 146–150.doi:10.1002/9780470132562.ch35.ISBN978-0-470-13256-2.
^Edelmann, F. T.; Poremba, P. (1997). Herrmann, W. A. (ed.).Synthetic Methods of Organometallic and Inorganic Chemistry. Vol. VI. Stuttgart: Georg Thieme Verlag.ISBN978-3-13-103021-4.
^Abundance of elements in the earth's crust and in the sea,CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17
^Early paper on the use of displacement ion-exchange chromatography to separate rare earths:Spedding, F. H.; Powell, J. E. (1954). "A practical separation of yttrium group rare earths from gadolinite by ion-exchange".Chemical Engineering Progress.50:7–15.
^Asad, F. M. M. (2010).Optical Properties of Dye Sensitized Zinc Oxide Thin Film Deposited by Sol-gel Method (Doctoral dissertation, Universiti Teknologi Malaysia).
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