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{{infobox erbium}}
'''Erbium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Er''' and [[atomic number]] 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a [[lanthanide]], a [[rare-earth element]], originally found in the [[gadolinite]] mine in [[Ytterby]], [[Sweden]], which is the source of the element's name.

Erbium's principal uses involve its pink-colored Er<sup>3+</sup> 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 Er<sup>3+</sup> ions are optically pumped at around 980 or {{val|1480|u=nm}} and then radiate light at {{val|1530|u=nm}} in stimulated emission. This process results in an unusually mechanically simple [[laser]] [[optical amplifier]] for signals transmitted by fiber optics. The {{val|1550|u=nm}} wavelength is especially important for [[optical communications]] because standard single mode [[optical 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's {{val|2940|u=nm}} emission (see [[Er: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 in [[laser surgery]], and for the efficient production of steam which produces enamel ablation by common types of [[dental laser]].

== Characteristics ==

===Physical properties===
[[Image:Erbium(III)chloride sunlight.jpg|thumb|left|Erbium(III) chloride in sunlight, showing some pink fluorescence of Er<sup>+3</sup> from natural ultraviolet.]]
A [[valence (chemistry)|trivalent]] element, pure erbium [[metal]] is malleable (or easily shaped), soft yet stable in air, and does not [[oxidation|oxidize]] as quickly as some other [[rare-earth metals]]. Its [[Salt (chemistry)|salts]] are rose-colored, and the element has characteristic sharp [[absorption spectra]] bands in [[visible light]], [[ultraviolet]], and near [[infrared]].<ref>{{Cite journal |last1=Humpidge |first1=J. S. |last2=Burney |first2=W. |date=1879-01-01 |title=XIV.—On erbium and yttrium |url=https://pubs.rsc.org/en/content/articlelanding/1879/ct/ct8793500111 |journal=Journal of the Chemical Society, Transactions |language=en |volume=35 |pages=111–117 |doi=10.1039/CT8793500111 |issn=0368-1645}}</ref> Otherwise it looks much like the other rare earths. Its [[sesquioxide]] is called [[erbia]]. 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 stimulate [[metabolism]].<ref name="emsley">{{cite book | title = Nature's Building Blocks: An A-Z Guide to the Elements | last = Emsley | first = John | publisher = Oxford University Press | date = 2001 | location = Oxford, England, UK | isbn = 978-0-19-850340-8 | chapter = Erbium | pages = [https://archive.org/details/naturesbuildingb0000emsl/page/136 136–139] | chapter-url = https://books.google.com/books?id=j-Xu07p3cKwC | url = https://archive.org/details/naturesbuildingb0000emsl/page/136 }}</ref>

Erbium is [[Ferromagnetism|ferromagnetic]] below 19&nbsp;K, [[Antiferromagnetism|antiferromagnetic]] between 19 and 80 K and [[Paramagnetism|paramagnetic]] above 80&nbsp;K.<ref>{{cite journal| author = Jackson, M.| title = Magnetism of Rare Earth| url = http://www.irm.umn.edu/quarterly/irmq10-3.pdf| journal = The IRM Quarterly| volume = 10| issue = 3| page = 1| date = 2000| access-date = 2009-05-03| archive-url = https://web.archive.org/web/20170712151422/http://www.irm.umn.edu/quarterly/irmq10-3.pdf| archive-date = 2017-07-12}}</ref>

Erbium can form propeller-shaped atomic clusters Er<sub>3</sub>N, where the distance between the erbium atoms is 0.35&nbsp;nm. Those clusters can be isolated by encapsulating them into [[fullerene]] molecules, as confirmed by [[transmission electron microscopy]].<ref>{{cite journal| title = Structures of ''D''<sub>5</sub>''<sub>d</sub>''-C<sub>80</sub> and ''I''<sub>h</sub>''-Er''<sub>3</sub>N@C<sub>80</sub> Fullerenes and Their Rotation Inside Carbon Nanotubes Demonstrated by Aberration-Corrected Electron Microscopy| date = 2007| journal = Nano Letters| volume = 7| page = 3704|bibcode = 2007NanoL...7.3704S| issue = 12 |doi =10.1021/nl0720152|last1 = Sato|first1 = Yuta| last2 = Suenaga| first2 = Kazu| last3 = Okubo| first3 = Shingo| last4 = Okazaki| first4 = Toshiya| last5 = Iijima| first5 = Sumio}}</ref>

Like most [[rare-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<ref>{{Cite journal |last1=MacDonald |first1=Matthew R. |last2=Bates |first2=Jefferson E. |last3=Fieser |first3=Megan E. |last4=Ziller |first4=Joseph W. |last5=Furche |first5=Filipp |last6=Evans |first6=William J. |date=2012-05-23 |title=Expanding Rare-Earth Oxidation State Chemistry to Molecular Complexes of Holmium(II) and Erbium(II) |url=https://pubs.acs.org/doi/10.1021/ja303357w |journal=Journal of the American Chemical Society |language=en |volume=134 |issue=20 |pages=8420–8423 |doi=10.1021/ja303357w |pmid=22583320 |bibcode=2012JAChS.134.8420M |issn=0002-7863|url-access=subscription }}</ref> oxidation states.

===Chemical properties===
Erbium metal retains its luster in dry air, however will tarnish slowly in moist air and burns readily to form [[erbium(III) oxide]]:<ref name="emsley" />
:4 Er + 3 O<sub>2</sub> → 2 Er<sub>2</sub>O<sub>3</sub>

Erbium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form [[erbium hydroxide]]:<ref>{{cite journal | url=https://iopscience.iop.org/article/10.1088/0957-4484/19/18/185606/meta | doi=10.1088/0957-4484/19/18/185606 | title=Synthesis of erbium hydroxide microflowers and nanostructures in subcritical water | year=2008 | last1=Assaaoudi | first1=H. | last2=Fang | first2=Z. | last3=Butler | first3=I. S. | last4=Kozinski | first4=J. A. | journal=Nanotechnology | volume=19 | issue=18 | article-number=185606 | pmid=21825694 | bibcode=2008Nanot..19r5606A | s2cid=24755693 | url-access=subscription }}</ref>
:2 Er (s) + 6 H<sub>2</sub>O (l) → 2 Er(OH)<sub>3</sub> (aq) + 3 H<sub>2</sub> (g)

Erbium metal reacts with all the halogens:<ref name="Webelements" />
:2 Er (s) + 3 F<sub>2</sub> (g) → 2 ErF<sub>3</sub> (s) [pink]
:2 Er (s) + 3 Cl<sub>2</sub> (g) → 2 ErCl<sub>3</sub> (s) [violet]
:2 Er (s) + 3 Br<sub>2</sub> (g) → 2 ErBr<sub>3</sub> (s) [violet]
:2 Er (s) + 3 I<sub>2</sub> (g) → 2 ErI<sub>3</sub> (s) [violet]

Erbium dissolves readily in dilute [[sulfuric acid]] to form solutions containing hydrated Er(III) ions, which exist as rose red [Er(OH<sub>2</sub>)<sub>9</sub>]<sup>3+</sup> hydration complexes:<ref name="Webelements">{{cite web| url =https://www.webelements.com/erbium/chemistry.html| title =Chemical reactions of Erbium| publisher=Webelements| access-date=2009-06-06}}</ref>

:2 Er (s) + 3 H<sub>2</sub>SO<sub>4</sub> (aq) → 2 Er<sup>3+</sup> (aq) + 3 {{chem|SO|4|2-}} (aq) + 3 H<sub>2</sub> (g)

=== Isotopes ===
{{main|Isotopes of erbium}}
Naturally occurring erbium is composed of 6 stable [[isotope]]s, {{Sup|162}}Er, {{Sup|164}}Er, {{Sup|166}}Er, {{Sup|167}}Er, {{Sup|168}}Er, and {{Sup|170}}Er, with {{Sup|166}}Er being the most abundant (33.503% [[natural abundance]]). Of the artificial [[radioisotope]]s have been characterized, the most stable are {{Sup|169}}Er with a [[half-life]] of {{val|9.39|u=days}}, {{Sup|172}}Er with a half-life of {{val|49.3|u=hours}}, and {{Sup|160}}Er with a half-life of {{val|28.58|u=hours}}. All of the remaining [[radioactive]] isotopes have half-lives that are less than {{val|11|u=hours}}, and the majority of these have half-lives that are less than 4 minutes. This element also has 26 [[meta state]]s, with the most stable being {{Sup|149m1}}Er with a half-life of {{val|8.9|u=seconds}}.{{NUBASE2020|ref}}

The known isotopes of erbium range from {{Sup|143}}Er to {{Sup|180}}Er. The primary [[decay mode]] before the most abundant stable isotope, {{Sup|166}}Er, is [[electron capture]], and the primary mode after is [[beta decay]]. The primary [[decay product]]s before {{Sup|166}}Er are element 67 ([[holmium]]) isotopes, and the primary products after are element 69 ([[thulium]]) isotopes.{{NUBASE2020|ref}}

{{Sup|165}}Er has been identified as useful for use in [[Auger therapy]], as it decays via electron capture and emits no [[Gamma ray|gamma radiation]]. It can also be used as a [[radioactive tracer]] to label [[Antibody|antibodies]] and [[Peptide|peptides]], 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 of {{Sup|165}}[[Holmium|Ho]] with beams of protons or deuterium, a reaction which is especially convenient because {{Sup|165}}Ho is a [[monoisotopic element]] and relatively inexpensive.<ref>{{Cite book |last=IAEA |title=Alternative Radionuclide Production with a Cyclotron |date=2021 |isbn=978-92-0-103221-8 |chapter=4.11. Erbium-165 |publisher=International Atomic Energy Agency |oclc=1317842424}}</ref>

==Compounds==

{{Main article|Erbium compounds}}

===Oxides===

[[File:ErOPulver.jpg|thumb|right|Erbium(III) oxide powder]]

{{Main article|Erbium(III) oxide}}

[[Erbium(III) oxide]] (also known as erbia) is the only known oxide of erbium, first isolated by [[Carl Gustaf Mosander]] in 1843, and first obtained in pure form in 1905 by [[Georges Urbain]] and [[Charles James (chemist)|Charles James]].<ref>{{cite book| pages =378–379| url =https://books.google.com/books?id=34KwmkU4LG0C&pg=PA377| title = The development of modern chemistry| author = Aaron John Ihde| publisher = Courier Dover Publications| year = 1984| isbn = 978-0-486-64235-2}}</ref> It has a [[cubic crystal system|cubic]] structure resembling the [[bixbyite]] motif. The Er<sup>3+</sup> centers are octahedral.<ref name=CR>{{cite journal |doi=10.1021/cr940055h|title=The Binary Rare Earth Oxides |year=1998 |last1=Adachi |first1=Gin-ya |last2=Imanaka |first2=Nobuhito |journal=Chemical Reviews |volume=98 |issue=4 |pages=1479–1514 |pmid=11848940 }}</ref> The formation of erbium oxide is accomplished by burning erbium metal,<ref name="emsley" /> erbium oxalate or other [[oxyacid]] salts of erbium.<ref name=":0">{{Cite book |last1=Larrañaga |first1=Michael D. |url=https://onlinelibrary.wiley.com/doi/book/10.1002/9781119312468 |title=Hawley's Condensed Chemical Dictionary, Sixteenth Edition |last2=Lewis |first2=Richard J. |last3=Lewis |first3=Robert A. |date=September 2016 |publisher=Wiley |isbn=978-1-118-13515-0 |edition=16th |page=564 |language=en |doi=10.1002/9781119312468}}</ref> Erbium oxide is insoluble in water and slightly soluble in heated mineral acids. The pink-colored compound is used as a [[phosphor]] activator and to produce [[infrared]]-absorbing glass.<ref name=":0" />

===Halides===

[[Erbium(III) fluoride]] is a pinkish powder<ref>{{Cite web|url=https://www.americanelements.com/erbium-fluoride-13760-83-3|title = Erbium Fluoride}}</ref> that can be produced by reacting [[erbium(III) nitrate]] and [[ammonium fluoride]].<ref>{{cite journal|journal=Journal of Materials Chemistry C|volume=2|issue=15|language=en|issn=2050-7526|date=2014|page=2765|doi=10.1039/c3tc32540g|url=http://xlink.rsc.org/?DOI=c3tc32540g|title=Facile synthesis and enhancement upconversion luminescence of ErF3 nano/microstructures via Li+ doping|access-date=2019-03-26|author=Linna Guo, Yuhua Wang, Zehua Zou, Bing Wang, Xiaoxia Guo, Lili Han, Wei Zeng|url-access=subscription}}</ref> It can be used to make infrared light-transmitting materials<ref>{{Cite journal |last1=Su |first1=W. T. |last2=Li |first2=B. |last3=Yin |first3=L. |last4=Yang |first4=L. |last5=Liu |first5=D. Q. |last6=Zhang |first6=F. S. |date=2007-05-15 |title=Crystallization and surface morphology evolution of erbium fluoride films on different substrates |url=https://linkinghub.elsevier.com/retrieve/pii/S0169433207001523 |journal=Applied Surface Science |volume=253 |issue=14 |pages=6259–6263 |doi=10.1016/j.apsusc.2007.01.087 |bibcode=2007ApSS..253.6259S |issn=0169-4332|url-access=subscription }}</ref> and up-converting luminescent materials,<ref>{{cite journal|journal=RSC Advances|volume=8|issue=22|language=en|issn=2046-2069|date=2018|pages=12165–12172|doi=10.1039/C8RA01245H|title=Understanding differences in Er 3+ –Yb 3+ codoped glass and glass ceramic based on upconversion luminescence for optical thermometry|author=Yingxin Hao, Shichao Lv, Zhijun Ma, Jianrong Qiu|pmid=35539388|pmc=9079277|bibcode=2018RSCAd...812165H|doi-access=free}}</ref> and is an intermediate in the production of erbium metal prior to its reduction with calcium.<ref name=":0" /> [[Erbium(III) chloride]] is a violet compounds that can be formed by first heating erbium(III) oxide and [[ammonium chloride]] to produce the [[ammonium]] salt of the pentachloride ([NH<sub>4</sub>]<sub>2</sub>ErCl<sub>5</sub>) then heating it in a vacuum at 350-400&nbsp;°C.<ref name=Brauer>{{cite book|title=Handbook of Preparative Inorganic Chemistry|edition=2nd|editor=Brauer, G. |publisher=Academic Press|year=1963|place=New York}}</ref><ref name=IS>{{cite book | last =Meyer | first =G. | title =The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides-The Example of YCl<sub>3</sub> | chapter =The Ammonium Chloride Route to Anhydrous Rare Earth Chlorides—The Example of Ycl <sub>3</sub> | series =Inorganic Syntheses | volume =25 | year =1989 | pages =146–150 | doi =10.1002/9780470132562.ch35 | isbn =978-0-470-13256-2}}
</ref><ref name="EdelmannPoremba1997">{{cite book |title=Synthetic Methods of Organometallic and Inorganic Chemistry |volume=VI |last=Edelmann |first=F. T. |author2=Poremba, P. |editor=Herrmann, W. A. |year=1997 |publisher=Georg Thieme Verlag |location=Stuttgart |isbn=978-3-13-103021-4 }}</ref> It forms crystals of the [[aluminium chloride|{{chem2|AlCl3}}]] type, with [[monoclinic]] crystals and the [[point group]] ''C''2/m.<ref name="Tempelton">{{cite journal |vauthors=Tempelton DH, Carter GF | title= The Crystal Structure of Yttrium Trichloride and Similar Compounds | journal=J Phys Chem | year=1954 | pages=940–943 | doi= 10.1021/j150521a002 | volume= 58 | issue=11 | bibcode= 1954JPhCh..58..940T }}</ref> Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of ''P''2/''n'' (''P''2/''c'') - ''C''<sup>4</sup><sub>2h</sub>. In this compound, erbium is octa-coordinated to form {{chem2|[Er(H2O)6Cl2]+}} ions with the isolated {{chem2|Cl−}} completing the structure.<ref>{{cite journal |vauthors=Graebner EJ, Conrad GH, Duliere SF | title=Crystallographic data for solvated rare earth chlorides| journal=[[Acta Crystallographica]] | year=1966 | pages=1012–1013 | volume=21 | issue=6| doi=10.1107/S0365110X66004420 | bibcode=1966AcCry..21.1012G}}</ref>

[[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.<ref>{{Cite web|last=Elements|first=American|title=Erbium Bromide|url=https://www.americanelements.com/erbr.html|access-date=2020-11-16|website=American Elements|language=en}}</ref> [[Erbium(III) iodide]]<ref name="Taylor & Francis - Handbook of Inorganic Compounds, 2011 - p 163">{{cite book|last=Perry|first=Dale L|title=Handbook of Inorganic Compounds|publisher=[[Taylor & Francis]]|date=2011|edition=2|page=163|isbn=978-1-4398-1462-8|url=https://books.google.com/books?id=SFD30BvPBhoC&q=%22Erbium+Boride%22&pg=PA163|access-date=14 December 2013}}</ref> is a slightly pink compound that is insoluble in water. It can be prepared by directly reacting erbium with [[iodine]].<ref>{{Cite web|last=Elements|first=American|title=Erbium Iodide|url=https://www.americanelements.com/erbium-iodide-13813-42-8|access-date=2020-11-16|website=American Elements|language=en}}</ref>

===Organoerbium compounds===
{{See also|Organolanthanide chemistry}}
Organoerbium compounds are very similar to [[organolanthanide compound|those of the other lanthanides]], as they all share an inability to undergo [[pi backbonding|π backbonding]]. They are thus mostly restricted to the mostly ionic [[cyclopentadienide]]s (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.<ref name="Greenwood1248">Greenwood and Earnshaw, pp. 1248–9</ref>

== History ==
[[File:Mosander Carl Gustav bw.jpg|thumb|right|[[Carl Gustaf Mosander]], the scientist who discovered erbium, lanthanum and terbium]]
Erbium (for [[Ytterby]], a village in [[Sweden]]) was [[discovery of the chemical elements|discovered]] by [[Carl Gustaf Mosander]] in 1843.<ref>{{cite journal|author=Mosander, C. G. |date=1843|url=https://books.google.com/books?id=CJEOAAAAIAAJ&pg=PA241|title=On the new metals, Lanthanium and Didymium, which are associated with Cerium; and on Erbium and Terbium, new metals associated with Yttria|journal=Philosophical Magazine|volume= 23|issue=152| pages =241–254|doi=10.1080/14786444308644728|url-access=subscription}} Note: The first part of this article, which does NOT concern erbium, is a translation of: C. G. Mosander (1842) [https://books.google.com/books?id=XK4tAAAAcAAJ&pg=387 "Något om Cer och Lanthan"] [Some (news) about cerium and lanthanum], ''[[Scandinavian Scientist Conference|Förhandlingar vid de Skandinaviske naturforskarnes tredje möte (Stockholm)]]'' [Transactions of the Third Scandinavian Scientist Conference (Stockholm)], vol. 3, pp. 387–398.</ref> Mosander was working with a sample of what was thought to be the single metal oxide [[yttria]], derived from the mineral [[gadolinite]]. 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]], and [[gadolinium]].<ref name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date=1956 |publisher=Journal of Chemical Education |location=Easton, PA |url=https://archive.org/details/discoveryoftheel002045mbp |edition=6th }}</ref>{{rp|701}}<ref name="XVI">{{cite journal | author = Weeks, Mary Elvira |author-link=Mary Elvira Weeks| title = The discovery of the elements: XVI. The rare earth elements | journal = Journal of Chemical Education | year = 1932 | volume = 9 | issue = 10 | pages = 1751&ndash;1773 | doi = 10.1021/ed009p1751 | bibcode=1932JChEd...9.1751W}}</ref><ref name="Beginnings">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Beginnings |journal=The Hexagon |date=2015 |pages=41–45 |url=http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/Hexagon%20Articles/rare%20earths%20I.pdf |access-date=30 December 2019}}</ref><ref name="Virginia">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Confusing Years |journal=The Hexagon |date=2015 |pages=72–77 |url=http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/Hexagon%20Articles/rare%20earths%20II.pdf |access-date=30 December 2019}}</ref><ref>{{Cite journal|last=Piguet|first=Claude|year=2014|title=Extricating erbium|journal=Nature Chemistry|volume=6|issue=4|page=370|doi=10.1038/nchem.1908|pmid=24651207|bibcode=2014NatCh...6..370P|doi-access=free}}</ref><ref name="RSErbium">{{cite web |title=Erbium |url=https://www.rsc.org/periodic-table/element/68/erbium |website=Royal Society of Chemistry|date= 2020 |access-date=4 January 2020}}</ref>

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.<ref>{{Cite book |last=Voncken |first=J.H.L. |title=The Rare Earth Elements: An Introduction |publisher=Cham : Springer International Publishing |year=2016 |isbn=978-3-319-26809-5 |edition=1st |series=SpringerBriefs in Earth Sciences |pages=10–11 |language=en |doi=10.1007/978-3-319-26809-5}}</ref> Fairly pure Er<sub>2</sub>[[oxygen|O]]<sub>3</sub> was independently isolated in 1905 by [[Georges Urbain]] and [[Charles James (chemist)|Charles James]]. Reasonably pure erbium metal was not produced until 1934 when [[Wilhelm Klemm]] and [[Heinrich Bommer]] reduced the [[anhydrous]] [[chloride]] with [[potassium]] vapor.<ref>{{cite web |title=Facts About Erbium |url=https://www.livescience.com/38389-erbium.html |website=Live Science |access-date=22 October 2018|date=July 23, 2013}}</ref><ref name="emsley" />

== Occurrence ==
[[File:MonaziteUSGOV.jpg|thumb|left|Monazite sand]]
The concentration of erbium in the Earth crust is about 2.8&nbsp;mg/kg and in seawater 0.9&nbsp;ng/L.<ref name="patnaik">{{cite book | last =Patnaik | first =Pradyot | date = 2003 | title =Handbook of Inorganic Chemical Compounds | publisher = McGraw-Hill | pages = 293–295| isbn =978-0-07-049439-8 | url= https://books.google.com/books?id=Xqj-TTzkvTEC&pg=PA293 | access-date = 2009-06-06}}</ref>  (Concentration of less abundant elements may vary with location by several orders of magnitude<ref name=CRC>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</ref> making the relative abundance unreliable). Like other rare earths, this element is never found as a free element in nature but is found in [[monazite]] and [[bastnäsite]] ores.<ref name="emsley" /> It has historically been very difficult and expensive to separate rare earths from each other in their ores but [[ion-exchange]] chromatography methods<ref>Early paper on the use of displacement ion-exchange chromatography to separate rare earths: {{cite journal | last1 = Spedding | first1 = F. H. | last2 = Powell | first2 = J. E. | date = 1954 | title = A practical separation of yttrium group rare earths from gadolinite by ion-exchange | journal = Chemical Engineering Progress | volume = 50 | pages = 7–15 }}</ref> developed in the late 20th century have greatly reduced the cost of production of all rare-earth metals and their [[chemical compound]]s.<ref>{{Cite journal |last1=El Ouardi |first1=Youssef |last2=Virolainen |first2=Sami |last3=Massima Mouele |first3=Emile Salomon |last4=Laatikainen |first4=Markku |last5=Repo |first5=Eveliina |last6=Laatikainen |first6=Katri |date=2023-04-01 |title=The recent progress of ion exchange for the separation of rare earths from secondary resources – A review |journal=Hydrometallurgy |volume=218 |article-number=106047 |doi=10.1016/j.hydromet.2023.106047 |bibcode=2023HydMe.21806047E |issn=0304-386X|doi-access=free }}</ref>

The principal commercial sources of erbium are from the minerals [[xenotime]] and [[euxenite]], and most recently, the ion adsorption clays of southern China. Consequently, China has now become the principal global supplier of this element.<ref>Asad, F. M. M. (2010). ''Optical Properties of Dye Sensitized Zinc Oxide Thin Film Deposited by Sol-gel Method'' (Doctoral dissertation, Universiti Teknologi Malaysia).</ref> 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|date=September 2024}}

==Production==
Crushed minerals are attacked by hydrochloric or [[sulfuric 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 with [[ammonium oxalate]] to convert rare earths into their insoluble [[oxalate]]s. The oxalates are converted to oxides by annealing. The oxides are dissolved in [[nitric acid]] that excludes one of the main components, [[cerium]], whose oxide is insoluble in HNO<sub>3</sub>. The solution is treated with [[magnesium nitrate]] to produce a crystallized mixture of [[double salt]]s of rare-earth metals. The salts are separated by [[ion 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.<ref name="patnaik" /> Erbium metal is obtained from its oxide or salts by heating with [[calcium]] at {{val|1450|u=°C}} under argon atmosphere.<ref name="patnaik" />

== Applications ==
[[File:Erbium-glass.jpg|thumb|Erbium-colored glass]]

===Lasers and optics===
A large variety of medical applications (i.e., dermatology, dentistry) utilize erbium ion's {{val|2940|u=nm}} emission (see [[Er:YAG laser]]), which is highly absorbed in water ([[Attenuation coefficient|absorption coefficient]] about {{val|12000|up=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.<ref>{{Citation |last1=Šulc |first1=J. |title=5 - Solid-state lasers for medical applications |date=2013-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780857092373500059 |work=Lasers for Medical Applications |pages=127–176 |editor-last=Jelínková |editor-first=Helena |series=Woodhead Publishing Series in Electronic and Optical Materials |publisher=Woodhead Publishing |language=en |doi=10.1533/9780857097545.2.127 |isbn=978-0-85709-237-3 |access-date=2022-04-28 |last2=Jelínková |first2=H.|url-access=subscription }}</ref> Common applications of erbium lasers in dentistry include ceramic [[cosmetic dentistry]] and removal of brackets in [[orthodontic braces]]; such laser applications have been noted as more time-efficient than performing the same procedures with rotary [[Dental instrument|dental instruments]].<ref>{{Cite journal |last1=Deeb |first1=Janina Golob |last2=Grzech-Leśniak |first2=Kinga |last3=Brody |first3=Erica R. |last4=Matys |first4=Jacek |last5=Bencharit |first5=Sompop |date=December 2022 |title=Erbium laser-assisted ceramic debonding: a scoping review |journal=Journal of Prosthodontics |language=en |volume=31 |issue=9 |pages=e100–e124 |doi=10.1111/jopr.13613 |issn=1059-941X |pmc=10099628 |pmid=36269672}}</ref>

Erbium-doped [[optical fibers|optical silica-glass fibers]] are the active element in [[erbium-doped fiber amplifier]]s (EDFAs), which are widely used in [[optical communications]].<ref>{{cite book | isbn = 978-0-12-084590-3 | url = https://books.google.com/books?id=uAOq75yt5CcC | last1 = Becker|first1= P. C. | last2 = Olsson|first2= N. A. | last3 = Simpson| first3 = J. R. | date = 1999 | publisher = Academic Press | location = San Diego | title = Erbium-doped fiber amplifiers fundamentals and technology}}</ref> The same fibers can be used to create fiber [[lasers]]. 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 in [[erbium-doped waveguide amplifier]]s.<ref name="emsley" />

===Other applications===
When added to [[vanadium]] as an [[alloy]], erbium lowers hardness and improves workability.<ref name="CRC2000">{{cite book| last= Hammond |first= C. R. |title = The Elements, in Handbook of Chemistry and Physics |edition = 81st| publisher =CRC press| date = 2000| isbn = 978-0-8493-0481-1}}</ref> An erbium-[[nickel]] alloy Er<sub>3</sub>Ni has an unusually high specific heat capacity at liquid-helium temperatures and is used in [[cryocoolers]]; a mixture of 65% Er<sub>3</sub>[[cobalt|Co]] and 35% Er<sub>0.9</sub>[[Ytterbium|Yb]]<sub>0.1</sub>Ni by volume improves the specific heat capacity even more.<ref>{{cite book | title= Advances in Cryogenic Engineering | volume= 39a | editor=Kittel, Peter }}</ref><ref>{{cite book | title= Cryogenic Regenerative Heat Exchangers | first = Robert A. | last = Ackermann | publisher = Springer | date = 1997 | isbn = 978-0-306-45449-3 | page = 58 | url = https://books.google.com/books?id=nIzviZ_-_NsC}}</ref>

[[Erbium oxide]] has a pink color, and is sometimes used as a colorant for [[glass]], [[cubic zirconia]] and [[porcelain]]. The glass is then often used in [[sunglasses]] and [[jewellery]],<ref name="emsley" /><ref name="CRC2000" /><ref name="Stwertka">Stwertka, Albert. ''A Guide to the Elements'', Oxford University Press, 1996, p. 162. {{ISBN|0-19-508083-1}}</ref> or where infrared absorption is needed.<ref name=":0" />

Erbium is used in [[Nuclear power|nuclear]] technology in neutron-absorbing [[control rod]]s.<ref name="emsley" /><ref>{{cite book | isbn = 978-0-7923-5593-9 | chapter = Use of UraniumErbium and PlutoniumErbium Fuel in RBMK Reactors | pages = 121–125 | editor= Parish, Theodore A. | editor2= Khromov, Vyacheslav V. | editor3= Carron, Igor | date = 1999 | publisher = Kluwer | location = CBoston | title = Safety issues associated with Plutonium involvement in the nuclear fuel cycle | chapter-url = https://books.google.com/books?id=aamn7uifb3gC}}</ref> or as a [[Neutron poison|burnable poison]] in nuclear fuel design.<ref>{{Cite web|last=Grossbeck, Renier, and Bigelow|date=September 2003|title=Development of improved burnable poisons for commercial nuclear power reactors
|url=https://digital.library.unt.edu/ark:/67531/metadc739371/m2/1/high_res_d/820689.pdf|website=University of North Texas (UNT) digital library}}</ref>

==Biological role and precautions==
Erbium does not have a biological role, but erbium salts can stimulate [[metabolism]]. Humans consume 1 milligram of erbium a year on average. The highest concentration of erbium in humans is in the [[bone]]s, but there is also erbium in the human [[kidneys]] and [[liver]].<ref name="emsley" />

Erbium is slightly toxic if ingested, but erbium compounds are generally not toxic.<ref name="emsley" /> Ionic erbium behaves similar to ionic calcium, and can potentially bind to proteins such as [[calmodulin]]. When introduced into the body, nitrates of erbium, similar to other rare earth nitrates, increase [[triglyceride]] levels in the [[liver]] and cause leakage of hepatic (liver-related) [[Enzyme|enzymes]] to the blood, though they uniquely (along with gadolinium and dysprosium nitrates) increase [[RNA polymerase II]] activity.<ref name=":1">{{Cite journal |last1=Hirano |first1=S. |last2=Suzuki |first2=K. T. |date=March 1996 |title=Exposure, metabolism, and toxicity of rare earths and related compounds |journal=Environmental Health Perspectives |volume=104 Suppl 1 |issue=Suppl 1 |pages=85–95 |doi=10.1289/ehp.96104s185 |issn=0091-6765 |pmc=1469566 |pmid=8722113|bibcode=1996EnvHP.104S..85H }}</ref> Ingestion<ref>{{Cite journal |last1=Yang |first1=Daoyuan |last2=Sui |first2=Haixia |last3=Mao |first3=Weifeng |last4=Wang |first4=Yibaina |last5=Yang |first5=Dajin |last6=Zhang |first6=Lei |last7=Liu |first7=Zhaoping |last8=Yong |first8=Ling |last9=Song |first9=Yan |date=2022-11-24 |title=Dietary Exposure Assessment of Rare Earth Elements in the Chinese Population |journal=International Journal of Environmental Research and Public Health |volume=19 |issue=23 |article-number=15583 |doi=10.3390/ijerph192315583 |doi-access=free |issn=1660-4601 |pmc=9738814 |pmid=36497658}}</ref> and inhalation<ref>{{Cite journal |last1=Pagano |first1=Giovanni |last2=Thomas |first2=Philippe J. |last3=Di Nunzio |first3=Aldo |last4=Trifuoggi |first4=Marco |date=2019-04-01 |title=Human exposures to rare earth elements: Present knowledge and research prospects |url=https://linkinghub.elsevier.com/retrieve/pii/S0013935119300775 |journal=Environmental Research |volume=171 |pages=493–500 |doi=10.1016/j.envres.2019.02.004 |pmid=30743241 |bibcode=2019ER....171..493P |issn=0013-9351|url-access=subscription }}</ref> are the main routes of exposure to erbium and other rare earths, as they do not diffuse through unbroken skin.<ref name=":1" />

Metallic erbium in dust form presents a fire and explosion hazard.<ref>{{cite journal|last1=Haley|first1= T. J.|last2=Koste|first2= L.|last3= Komesu|first3= N.|last4= Efros|first4= M.|last5= Upham|first5= H. C. |year=1966 |title=Pharmacology and toxicology of dysprosium, holmium, and erbium chlorides |journal=Toxicology and Applied Pharmacology |volume=8 |issue=1 |pages=37–43 |doi=10.1016/0041-008x(66)90098-6 |pmid=5921895 |bibcode= 1966ToxAP...8...37H}}</ref><ref>{{cite journal |author=Haley, T. J. |year=1965 |title=Pharmacology and toxicology of the rare earth elements |journal=Journal of Pharmaceutical Sciences |volume=54 |issue=5 |pages=663–70 |doi=10.1002/jps.2600540502 |pmid=5321124 |bibcode=1965JPhmS..54..663H }}</ref><ref>{{cite journal |last1=Bruce|first1= D. W.|last2= Hietbrink|first2= B. E.|last3= Dubois|first3= K. P. |year=1963 |title=The acute mammalian toxicity of rare earth nitrates and oxides |journal=Toxicology and Applied Pharmacology |volume=5 |issue=6 |pages= 750–9|doi=10.1016/0041-008X(63)90067-X|pmid= 14082480|bibcode= 1963ToxAP...5..750B}}</ref>

== References ==
{{reflist|30em}}

==Further reading==
* ''Guide to the Elements – Revised Edition'', Albert Stwertka (Oxford University Press; 1998), {{ISBN|0-19-508083-1}}.

== External links ==
{{Commons}}
{{wiktionary|erbium}}
* [http://education.jlab.org/itselemental/ele068.html It's Elemental – Erbium]
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{{Erbium compounds}}

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[[Category:Erbium| ]]
[[Category:Chemical elements]]
[[Category:Chemical elements with hexagonal close-packed structure]]
[[Category:Ferromagnetic materials]]
[[Category:Lanthanides]]
[[Category:Reducing agents]]