Editing Holmium

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{{infobox holmium}}
'''Holmium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Ho''' and [[atomic number]] 67. It is a [[rare-earth element]] and the eleventh member of the [[lanthanide series]]. It is a relatively soft, silvery, fairly [[corrosion]]-resistant and [[malleable]] metal. Like many other lanthanides, holmium is too reactive to be found in native form, as pure holmium slowly forms a yellowish [[oxide]] coating when exposed to air. When isolated, holmium is relatively stable in dry air at room temperature. However, it reacts with water and corrodes readily, and also burns in air when heated.

In nature, holmium occurs together with the other rare-earth metals (like [[thulium]]). It is a relatively rare lanthanide, making up 1.4 [[parts per million]] of the [[Earth's crust]], an abundance similar to [[tungsten]]. Holmium was discovered through isolation by Swedish chemist [[Per Theodor Cleve]]. It was also independently discovered by [[Jacques-Louis Soret]] and [[Marc Delafontaine]], who together observed it [[Spectroscopy|spectroscopically]] in 1878. Its oxide was first isolated from rare-earth ores by Cleve in 1878. The element's name comes from ''Holmia'', the Latin name for the city of [[Stockholm]].<ref name="Virginia" /><ref name="RSHolmium" /><ref name="Stwertka">{{cite book |last1=Stwertka |first1=Albert |title=A guide to the elements |date=1998 |page=161 |edition=2nd}}</ref>

Like many other [[lanthanides]], holmium is found in the minerals [[monazite]] and [[gadolinite]] and is usually commercially extracted from monazite using [[ion-exchange]] techniques. Its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho(III) [[ions]]. Trivalent holmium ions have [[fluorescent]] properties similar to many other rare-earth ions (while yielding their own set of unique [[Emission spectrum|emission light lines]]), and thus are used in the same way as some other rare earths in certain [[laser]] and glass-colorant applications.

Holmium has the highest [[magnetic permeability]] and [[Saturation (magnetic)|magnetic saturation]] of any element and is thus used for the [[pole piece]]s of the strongest static [[magnet]]s. Because holmium strongly absorbs [[neutrons]], it is also used as a [[burnable poison]] in [[nuclear reactors]].

==Properties==

Holmium is the eleventh member of the [[lanthanide]] series. In the periodic table, it appears in [[period 6]], between the lanthanides [[dysprosium]] to its left and [[erbium]] to its right, and above the [[actinide]] [[einsteinium]].

===Physical properties===

With a boiling point of {{convert|3000|K|C F|0}}, holmium is the sixth most [[Volatility (chemistry)|volatile]] lanthanide after [[ytterbium]], [[europium]], [[samarium]], [[thulium]] and [[dysprosium]]. At standard temperature and pressure, holmium, like many of the second half of the lanthanides, normally assumes a [[hexagonal crystal system|hexagonally close-packed (hcp)]] structure.<ref>{{Cite journal |last1=Strandburg |first1=D. L. |last2=Legvold |first2=S. |last3=Spedding |first3=F. H. |date=1962-09-15 |title=Electrical and Magnetic Properties of Holmium Single Crystals |url=https://link.aps.org/doi/10.1103/PhysRev.127.2046 |journal=Physical Review |volume=127 |issue=6 |pages=2046–2051 |doi=10.1103/PhysRev.127.2046|bibcode=1962PhRv..127.2046S |url-access=subscription}}</ref> Its 67 [[electron]]s are arranged in the configuration [Xe] 4f<sup>11</sup> 6s<sup>2</sup>, so that it has thirteen [[valence electron]]s filling the 4f and 6s subshells.<ref name=":0">{{Cite web |title=Holmium (Ho) - Periodic Table |url=https://www.periodictable.one/element/67 |access-date=2024-06-02 |website=www.periodictable.one |language=en}}</ref>

Holmium, like all of the lanthanides, is [[paramagnetic]] at standard temperature and pressure.<ref>{{cite book|last1=Cullity|first1=B. D.|last2=Graham|first2=C. D.|year=2005|page=172|title=Introduction to Magnetic Materials}}</ref> However, holmium is [[ferromagnetic]] at temperatures below {{convert|19|K|C F}}.<ref>{{cite book|title=Introduction to magnetism and magnetic materials|author=Jiles, David|page=228|date=1998}}</ref> It has the highest [[magnetic moment]] ({{val|10.6|u=[[Bohr magneton|''μ''<sub>B</sub>]]}}) of any naturally occurring element<ref name="emsley226" /> and possesses other unusual magnetic properties. When combined with [[yttrium]], it forms highly [[magnetism|magnetic]] compounds.<ref name="appl" />

===Chemical properties===

Holmium metal tarnishes slowly in air, forming a yellowish oxide layer that has an appearance similar to that of [[iron]] rust. It burns readily to form [[holmium(III) oxide]]:<ref>{{Cite journal |last=Wahyudi |first=Tatang |date=2015 |title=Reviewing the properties of rare earth element-bearing minerals, rare-earth elements and cerium oxide compound |url=https://jurnal.tekmira.esdm.go.id/index.php/imj/article/view/293 |journal=Indonesian Mining Journal |language=en |volume=18 |issue=2 |pages=92–108 |doi=10.30556/imj.Vol18.No2.2015.293 |doi-broken-date=1 November 2024 |issn=2527-8797}}</ref>

:4 Ho + 3 O<sub>2</sub> → 2 Ho<sub>2</sub>O<sub>3</sub>

It is a relatively soft and [[Ductility|malleable]] element that is fairly [[corrosion]]-resistant and chemically stable in dry air at [[standard temperature and pressure]]. In moist air and at higher temperatures, however, it quickly [[oxidation|oxidizes]], forming a yellowish oxide.<ref>{{Cite journal |last=Phillips |first=W. L. |date=1964-08-01 |title=Oxidation of several lanthanide elements |url=https://dx.doi.org/10.1016/0022-5088%2864%2990056-6 |journal=Journal of the Less Common Metals |language=en |volume=7 |issue=2 |pages=139–143 |doi=10.1016/0022-5088(64)90056-6 |issn=0022-5088 |url-access=subscription}}</ref> In pure form, holmium possesses a metallic, bright silvery luster.

Holmium is quite electropositive: on the Pauling [[electronegativity]] scale, it has an electronegativity of 1.23.<ref name="Win">{{cite web |last1=Winter |first1=Mark J. |title=Holmium - 67Ho: electronegativity |url=https://winter.group.shef.ac.uk/webelements/holmium/electronegativity.html#:~:text=Holmium%20%2D%2067Ho%3A%20electronegativity&text=The%20first%20scale%20of%20electronegativity,)%20to%203.98%20(fluorine). |website=WebElements |publisher=[[University of Sheffield]] |access-date=4 August 2023}}</ref> It is generally trivalent. It reacts slowly with cold water and quickly with hot water to form holmium(III) hydroxide:<ref>{{Cite journal |last1=An |first1=Tao |last2=Dou |first2=Chunyue |last3=Ju |first3=Jinning |last4=Wei |first4=Wenlong |last5=Ji |first5=Quanzeng |date=2019-06-01 |title=Microstructure, morphology, wettability and mechanical properties of Ho<sub>2</sub>O<sub>3</sub> films prepared by glancing angle deposition |url=https://www.sciencedirect.com/science/article/pii/S0042207X19302428 |journal=Vacuum |language=en |volume=164 |pages=405–410 |doi=10.1016/j.vacuum.2019.03.057 |bibcode=2019Vacuu.164..405A |s2cid=133466738 |issn=0042-207X |url-access=subscription}}</ref>
:2 Ho (s) + 6 H<sub>2</sub>O (l) → 2 Ho(OH)<sub>3</sub> (aq) + 3 H<sub>2</sub> (g)

Holmium metal reacts with all the stable [[halogen]]s:<ref name="Webelements" />
:2 Ho (s) + 3 F<sub>2</sub> (g) → 2 [[Holmium(III) fluoride|HoF<sub>3</sub>]] (s) [pink]

:2 Ho (s) + 3 Cl<sub>2</sub> (g) → 2 [[Holmium(III) chloride|HoCl<sub>3</sub>]] (s) [yellow]

:2 Ho (s) + 3 Br<sub>2</sub> (g) → 2 [[Holmium(III) bromide|HoBr<sub>3</sub>]] (s) [yellow]

:2 Ho (s) + 3 I<sub>2</sub> (g) → 2 [[Holmium(III) iodide|HoI<sub>3</sub>]] (s) [yellow]

Holmium dissolves readily in dilute [[sulfuric acid]] to form [[Solution (chemistry)|solution]]s containing the yellow Ho(III) ions, which exist as a [Ho(OH<sub>2</sub>)<sub>9</sub>]<sup>3+</sup> complexes:<ref name="Webelements">{{cite web| url =https://www.webelements.com/holmium/chemistry.html| title =Chemical reactions of Holmium| publisher=Webelements| access-date=2009-06-06}}</ref>

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

====Oxidation states====
As with many lanthanides, holmium is usually found in the +3 [[oxidation state]], forming compounds such as [[holmium(III) fluoride]] (HoF<sub>3</sub>) and [[holmium(III) chloride]] (HoCl<sub>3</sub>).  Holmium in solution is in the form of Ho<sup>3+</sup> surrounded by nine molecules of water. Holmium dissolves in [[acid]]s.<ref name="emsley226">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks|page=226|date=2011}}</ref> However, holmium is also found to exist in +2, +1 and 0 oxidation states.<ref>{{Cite web |title=Periodic Table of Elements: Los Alamos National Laboratory |url=https://periodic.lanl.gov/67.shtml |access-date=2024-06-02 |website=periodic.lanl.gov}}</ref><ref name=":0" />

===Isotopes===
{{further|Isotopes of holmium}}

The isotopes of holmium range from <sup>140</sup>Ho to <sup>175</sup>Ho. The primary [[decay mode]] before the most abundant [[stable isotope]], <sup>165</sup>Ho, is [[positron emission]], and the primary mode after is [[beta minus decay]]. The primary [[decay product]]s before <sup>165</sup>Ho are [[terbium]] and [[dysprosium]] isotopes, and the primary products after are [[erbium]] isotopes.<ref name="CRC" />

Natural holmium consists of one [[primordial isotope]], holmium-165;<ref name="emsley226" /> it is the only isotope of holmium that is thought to be stable, although it is predicted to undergo [[alpha decay]] to [[terbium-161]] with a very long half-life.<ref>{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140–1–140–7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref> Of the 35 [[synthetic element|synthetic]] radioactive isotopes that are known, the most stable one is holmium-163 (<sup>163</sup>Ho), with a half-life of 4570 years.<ref>{{Cite journal |last1=Naumann |first1=R. A. |last2=Michel |first2=M. C. |last3=Power |first3=J. L. |title=Preparation of long-lived holmium-163 |date=September 1960 |osti=4120223 |journal=Journal of Inorganic and Nuclear Chemistry |language=en |volume=15 |issue=1–2 |pages=195–196 |doi=10.1016/0022-1902(60)80035-8}}</ref> All other radioisotopes have ground-state half-lives not greater than 1.117 days, with the longest, holmium-166 (<sup>166</sup>Ho) having a half-life of 26.83 hours,<ref>{{Cite journal |last=Suzuki |first=Yuka S |year=1998 |title=Biodistribution and kinetics of holmium-166-chitosan complex (DW-166HC) in rats and mice. |url=https://jnm.snmjournals.org/content/jnumed/39/12/2161.full.pdf |journal=Journal of Nuclear Medicine |volume=39 |issue=12 |pages=2161–2166|pmid=9867162 }}</ref> and most have half-lives under 3 hours.

<sup>166m1</sup>Ho has a half-life of around 1200 years.<ref>{{Cite journal |last1=Klaassen |first1=Nienke J. M. |last2=Arntz |first2=Mark J. |last3=Gil Arranja |first3=Alexandra |last4=Roosen |first4=Joey |last5=Nijsen |first5=J. Frank W. |date=2019-08-05 |title=The various therapeutic applications of the medical isotope holmium-166: a narrative review |journal=EJNMMI Radiopharmacy and Chemistry |volume=4 |issue=1 |pages=19 |doi=10.1186/s41181-019-0066-3 |issn=2365-421X |pmid=31659560|pmc=6682843 |doi-access=free }}</ref> The high excitation energy, resulting in a particularly rich spectrum of decay [[gamma ray]]s produced when the metastable state de-excites, makes this isotope useful as a means for [[Calibration|calibrating]] [[gamma ray spectrometer]]s.<ref>{{Cite web |last=Oliveira |first=Bernardes, Estela Maria de |date=2001-01-01 |title=Holmium-166m: multi-gamma standard to determine the activity of radionuclides in semiconductor detectors |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:43130653 |language=Portuguese}}</ref>

== Compounds ==

=== Oxides and chalcogenides ===

[[Image:Holmium(III) oxide.jpg|thumb|right|[[holmium(III) oxide|Ho<sub>2</sub>O<sub>3</sub>]], left: natural light, right: under a [[cold-cathode]] fluorescent lamp]]

Holmium(III) oxide is the only oxide of holmium. It changes its color depending on the lighting conditions. In daylight, it has a yellowish color. Under [[trichromacy|trichromatic light]], it appears orange red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions.<ref>{{Cite book |last1=Ganjali |first1=Mohammad Reza |title=Lanthanides Series Determination by Various Analytical Methods |last2=Gupta |first2=Vinod Kumar |last3=Faridbod |first3=Farnoush |last4=Norouzi |first4=Parviz |date=2016-02-25 |page=27}}</ref> The color change is related to the sharp [[Spectral line|emission lines]] of trivalent holmium ions acting as red phosphors.<ref name="Su 2008">{{cite journal| doi=10.1246/cl.2008.762| title=Hydrothermal Synthesis of GdVO<sub>4</sub>:Ho<sup>3+</sup> Nanorods with a Novel White-light Emission| date=2008| last1=Su| first1=Yiguo| journal=Chemistry Letters| volume=37| pages=762–763| issue=7| last2=Li| first2=Guangshe| last3=Chen| first3=Xiaobo| last4=Liu| first4=Junjie| last5=Li| first5=Liping}}</ref> Holmium(III) oxide appears pink under a cold-cathode fluorescent lamp.

Other [[chalcogenide]]s are known for holmium. [[Holmium(III) sulfide]] has orange-yellow [[crystal]]s in the [[monoclinic crystal system]],<ref name="CRC" /> with the [[space group]]  ''P''2<sub>1</sub>/''m'' (No. 11).<ref>{{Cite book |chapter-url=https://link.springer.com/chapter/10.1007%2F10681735_623 |chapter=Ho<sub>2</sub>S<sub>3</sub>: crystal structure, physical properties |access-date=2021-06-22 |archive-date=2018-09-01 |archive-url=https://web.archive.org/web/20180901182621/https://link.springer.com/chapter/10.1007/10681735_623 |url-status=live|doi=10.1007/10681735_623|title=Non-Tetrahedrally Bonded Binary Compounds II |series=Landolt-Börnstein - Group III Condensed Matter |year=2000 |volume=41D |pages=1–3 |publisher=Springer |isbn=3-540-64966-2 }}</ref> Under high pressure, holmium(III) sulfide can form in the [[cubic crystal system|cubic]] and [[orthorhombic crystal system|orthorhombic]] [[crystal system]]s.<ref name="E. Yu Tonkov">{{cite book|first1=E. Yu |last1=Tonkov|title=Compounds and Alloys Under High Pressure A Handbook|year=1998|page=272}}</ref> It can be obtained by the reaction of holmium(III) oxide and [[hydrogen sulfide]] at {{convert|1598|K|C F}}.<ref name="Meyer">{{cite book|editor1=G. Meyer|editor2= Lester R. Morss|title=Synthesis of Lanthanide and Actinide Compounds|year=1991|page=329}}</ref> Holmium(III) selenide is also known. It is antiferromagnetic below 6&nbsp;K.<ref>{{Cite journal |last1=Bespyatov |first1=M. A. |last2=Musikhin |first2=A. E. |last3=Naumov |first3=V. N. |last4=Zelenina |first4=L. N. |last5=Chusova |first5=T. P. |last6=Nikolaev |first6=R. E. |last7=Naumov |first7=N. G. |date=2018-03-01 |title=Low-temperature thermodynamic properties of holmium selenide (2:3) |url=https://www.sciencedirect.com/science/article/pii/S0021961417303804 |journal=The Journal of Chemical Thermodynamics |language=en |volume=118 |pages=21–25 |doi=10.1016/j.jct.2017.10.013 |bibcode=2018JChTh.118...21B |issn=0021-9614 |url-access=subscription}}</ref>

=== Halides ===

All four trihalides of holmium are known. Holmium(III) fluoride is a yellowish powder that can be produced by reacting holmium(III) oxide and [[ammonium fluoride]], then crystallising it from the ammonium [[salt (chemistry)|salt]] formed in solution.<ref>{{Cite book |title=Riedel, moderne anorganische Chemie |date=2012 |publisher=De Gruyter |others=Erwin Riedel, Christoph Janiak, Hans-Jürgen Meyer}}</ref> Holmium(III) chloride can be prepared in a similar way, with [[ammonium chloride]] instead of ammonium fluoride.<ref>{{Cite web |title=Holmium chloride {{!}} 10138-62-2 |url=https://www.chemicalbook.com/ChemicalProductProperty_EN_CB0255341.htm |access-date=2023-08-09 |website=ChemicalBook |language=en}}</ref> It has the [[yttrium(III) chloride|YCl<sub>3</sub>]] layer structure in the solid state.<ref>{{Cite book |last=Wells |first=A. F. |title=Structural inorganic chemistry |page=421}}</ref> These compounds, as well as holmium(III) bromide and holmium(III) iodide, can be obtained by the direct reaction of the elements:<ref name="Webelements" />

:2 Ho + 3 X<sub>2</sub> → 2 HoX<sub>3</sub>

In addition, holmium(III) iodide can be obtained by the direct reaction of holmium and [[mercury(II) iodide]], then removing the [[mercury (element)|mercury]] by [[distillation]].<ref>{{cite journal| doi = 10.1021/ic50018a015| title = Preparation and crystal data for lanthanide and actinide triiodides| year = 1964| last1 = Asprey| first1 = L. B.| last2 = Keenan| first2 = T. K.| last3 = Kruse| first3 = F. H.| journal = Inorganic Chemistry| volume = 3| issue = 8| pages = 1137–1141| url = https://digital.library.unt.edu/ark:/67531/metadc867868/ |url-access=subscription}}</ref>

===Organoholmium compounds===
{{See also|Organolanthanide chemistry}}
Organoholmium compounds are very similar to [[organolanthanide chemistry|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 [[alkyl]]s and [[aryl]]s, some of which may be [[polymeric]].<ref name="Greenwood1248">Greenwood and Earnshaw, pp. 1248{{ndash}}1249</ref>

==History==

Holmium ({{lang|la|Holmia}}, [[Latin]] name for [[Stockholm]]) was [[discovery of the chemical elements|discovered]] by the Swiss chemists [[Jacques-Louis Soret]] and [[Marc Delafontaine]] in 1878 who noticed the aberrant [[Spectrophotometry|spectrographic]] [[emission spectrum]] of the then-unknown element (they called it "Element X").<ref>{{cite journal|title = Sur les spectres d'absorption ultra-violets des terres de la gadolinite|author = Jacques-Louis Soret|journal = Comptes rendus de l'Académie des sciences|volume = 87|pages = 1062|date = 1878|url = http://gallica.bnf.fr/ark:/12148/bpt6k3043m/f1124.table}}
</ref><ref>{{cite journal|title = Sur le spectre des terres faisant partie du groupe de l'yttria
|author = Jacques-Louis Soret|journal = Comptes rendus de l'Académie des sciences
|volume = 89|pages = 521|date = 1879|url = https://gallica.bnf.fr/ark:/12148/bpt6k3046j/f550.table}}
</ref>

The Swedish chemist [[Per Teodor Cleve]] also independently discovered the element while he was working on [[erbia]] earth ([[erbium oxide]]). He was the first to isolate impure oxide of the new element.<ref name="RSHolmium">{{cite web |title=Holmium |url=https://www.rsc.org/periodic-table/element/67/holmium |website=Royal Society of Chemistry|date= 2020 |access-date=4 January 2020}}</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 name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date=1956 |publisher=Journal of Chemical Education |page=710}}</ref> Using the method developed by the Swedish chemist [[Carl Gustaf Mosander]], Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance ''holmia'' (after the Latin name for Cleve's home town, Stockholm) and the green one ''thulia''. ''Holmia'' was later found to be the [[holmium oxide]], and ''thulia'' was [[thulium oxide]].<ref name="emsley225" /> The pure oxide was only isolated in 1911 and the metal in 1939 by Heinrich Bommer.<ref name="Sicius-2024">{{Cite book |last=Sicius |first=Hermann |url=https://link.springer.com/10.1007/978-3-662-68921-9 |title=Handbook of the Chemical Elements |date=2024 |publisher=Springer Berlin Heidelberg |isbn=978-3-662-68920-2 |location=Berlin, Heidelberg |language=en |doi=10.1007/978-3-662-68921-9}}</ref>{{rp|959}}<ref>{{Cite journal|last=Bommer |first=Heinrich |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/zaac.19392420307 |journal=Zeitschrift für anorganische und allgemeine Chemie|volume=242|issue=3|title=Kristallstruktur und magnetisches Verhalten des metallischen Holmiums |date=1939 |pages=277–280 |language=de |doi=10.1002/zaac.19392420307}}</ref>

In the English physicist [[Henry Moseley]]'s classic paper on [[atomic number]]s, holmium was assigned the value 66. The holmium preparation he had been given to investigate had been impure, dominated by neighboring dysprosium. He would have seen [[X-ray emission spectroscopy|x-ray emission lines]] for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity.<ref>{{cite journal|last1=Egdell|first1=Russell G.|last2=Bruton|first2=Elizabeth|date=2020|title=Henry Moseley, X-ray spectroscopy and the periodic table|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=378|issue=2180|doi=10.1002/chem.202004775|pmid=32811359|doi-access=free}}</ref>

==Occurrence and production==
[[File:Gadolinitas.jpg|thumb|A specimen of [[gadolinite]] - holmium is the black part of it. ]]
Like all the other [[rare-earth element]]s, holmium is not naturally found as a [[free element]]. It occurs combined with other elements in gadolinite, [[monazite]] and other rare-earth minerals. No holmium-dominant mineral has yet been found. The main mining areas are China, United States, Brazil, India, Sri Lanka, and Australia with reserves of holmium estimated as 400,000 tonnes.<ref name="emsley225" /> The annual production of holmium metal is of about 10 tonnes per year.<ref>{{Cite web |title=Ho - Holmium |url=https://mmta.co.uk/metals/ho/ |access-date=5 December 2022 |publisher=MMTA |language=}}</ref>

Holmium makes up 1.3 parts per million of the [[Abundance of elements in Earth's crust|Earth's crust]] by mass.<ref name=CRCAbundanceTable>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> Holmium makes up 1 part per million of the [[soil]]s, 400 parts per [[Names of large numbers#Standard dictionary numbers|quadrillion]] of seawater, and almost none of [[Earth's atmosphere]], which is very rare for a lanthanide.<ref name="emsley225">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks|page=225|date=2011}}</ref> It makes up 500 parts per trillion of the universe by mass.<ref>{{cite web|url=http://www.webelements.com/periodicity/abundance_universe/.|title=WebElements Periodic Table » Periodicity » Abundance in the universe » periodicity|first=Mark Winter, University of Sheffield and WebElements|last=Ltd|website=www.webelements.com|access-date=27 March 2018|archive-url=https://web.archive.org/web/20170929183039/https://www.webelements.com/periodicity/abundance_universe/|archive-date=2017-09-29}}</ref>

Holmium is commercially extracted by [[ion exchange]] from monazite sand (0.05% holmium), but is still difficult to separate from other rare earths. The element has been isolated through the [[redox|reduction]] of its [[anhydrous]] [[chloride]] or [[fluoride]] with metallic [[calcium]].<ref name="CRC" /> Its estimated abundance in the Earth's crust is 1.3&nbsp;mg/kg. Holmium obeys the [[Oddo–Harkins rule]]: as an odd-numbered element, it is less abundant than both dysprosium and erbium. However, it is the most abundant of the odd-numbered heavy [[lanthanides]]. Of the lanthanides, only [[promethium]], [[thulium]], lutetium and terbium are less abundant on Earth. The principal current source are some of the ion-adsorption clays of southern China. Some of these have a rare-earth composition similar to that found in [[xenotime]] or gadolinite. Yttrium makes up about two-thirds of the total by mass; holmium is around 1.5%.<ref name="patnaik">{{cite book|last =Patnaik|first =Pradyot|date = 2003|title =Handbook of Inorganic Chemical Compounds|publisher = McGraw-Hill|pages = 338–339| isbn =0-07-049439-8|url= https://books.google.com/books?id=Xqj-TTzkvTEC&pg=PA338|access-date = 2009-06-06|archive-url=https://archive.org/details/handbookofinorga0000patn/page/n3/mode/2up|archive-date=2023-06-14}}</ref> Holmium is relatively inexpensive for a rare-earth metal with the price about 1000&nbsp;[[USD]]/kg.<ref>{{cite news| publisher = USGS| title =Rare-Earth Metals| author = James B. Hedrick| access-date = 2009-06-06| url =http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/740798.pdf}}</ref>

==Applications==

[[File:HoOxideSolution.jpg|thumb|A solution of 4% holmium oxide in 10% perchloric acid, permanently fused into a quartz [[cuvette]] as an optical calibration standard]]
Glass containing holmium oxide and holmium oxide solutions (usually in [[perchloric acid]]) have sharp optical [[Absorption (electromagnetic radiation)|absorption]] peaks in the spectral range 200 to 900&nbsp;nm. They are therefore used as a calibration standard for [[Monochromator|optical spectrophotometers]].<ref name="Allen 2007">{{cite journal | last=Allen | first=David W. | title=Holmium oxide glass wavelength standards | journal=Journal of Research of the National Institute of Standards and Technology | volume=112 | issue=6 | year=2007 | pages=303–306 | issn=1044-677X | doi=10.6028/jres.112.024 | pmid=27110474 | pmc=4655923 }}</ref><ref name="Travis 2002">{{cite journal | last1=Travis | first1=John C. | last2=Zwinkels | first2=Joanne C. | last3=Mercader | first3=Flora | display-authors=etal | title=An International Evaluation of Holmium Oxide Solution Reference Materials for Wavelength Calibration in Molecular Absorption Spectrophotometry | journal=Analytical Chemistry | volume=74 | issue=14 | date=2002-06-05 | issn=0003-2700 | doi=10.1021/ac0255680 | pages=3408–3415| pmid=12139047 }}</ref><ref>{{cite journal|url=http://www.clinchem.org/cgi/reprint/10/12/1117.pdf| journal =Clinical Chemistry| volume = 10| date =1964|title =Uses for a Holmium Oxide Filter in Spectrophotometry| author = R. P. MacDonald| pmid=14240747| issue=12|pages=1117–20| doi =10.1093/clinchem/10.12.1117 |url-access=subscription}}</ref> The radioactive but long-lived <sup>166m1</sup>Ho is used in calibration of [[gamma-ray spectrometer]]s.<ref>{{cite journal|title = The absolute counting of <sup>166m</sup>Ho, <sup>58</sup>Co and <sup>88</sup>Y|author = Ming-Chen Yuan|author2 = Jeng-Hung Lee|author3 = Wen-Song Hwang|name-list-style = amp|doi = 10.1016/S0969-8043(01)00226-3 |pmid = 11839051|journal = Applied Radiation and Isotopes
|volume = 56|issue = 1–2|pages = 429–434|date = 2002| bibcode=2002AppRI..56..429Y }}</ref>

Holmium is used to create the strongest artificially generated [[magnetic field]]s, when placed within high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator).<ref>{{cite journal| journal =IEEE Transactions on Magnetics| volume = 21| date =1985| display-authors = 6| author = R. W. Hoard| title =Field enhancement of a 12.5-T magnet using holmium poles| author2 = S. C. Mance| author3 = R. L. Leber| author4 = E. N. Dalder| author5 = M. R. Chaplin| author6 = K. Blair| author7 = D. H. Nelson| author8 = D. A. Van Dyke| issue=2|pages=448–450| doi=10.1109/tmag.1985.1063692|bibcode = 1985ITM....21..448H | s2cid = 121828376| url = https://digital.library.unt.edu/ark:/67531/metadc1200738/}}</ref> Holmium is also used in the manufacture of some [[permanent magnet]]s.

Holmium can act as a sensitizer in sodium yttrium fluoride which takes advantage of its absorption in the [[Near-infrared spectroscopy|NIR-II]] window. Holmium allows for lanthanide nanomaterials to have tunable emission and excitation in the NIR-II. Under 1143 nm excitation the interfacial energy transfer to other lanthanides allows a redshift in emission for biological applications.<ref>{{Cite journal |last=Wang |first=Xusheng |last2=Wu |first2=Wenxiao |last3=Yun |first3=Baofeng |last4=Huang |first4=Liwen |last5=Chen |first5=Zi-Han |last6=Ming |first6=Jiang |last7=Zhai |first7=Fuheng |last8=Zhang |first8=Hongxin |last9=Zhang |first9=Fan |date=2025-01-15 |title=An Emerging Toolkit of Ho3+ Sensitized Lanthanide Nanocrystals with NIR-II Excitation and Emission for in Vivo Bioimaging |url=https://pubs.acs.org/doi/10.1021/jacs.4c16451 |journal=Journal of the American Chemical Society |volume=147 |issue=2 |pages=2182–2192 |doi=10.1021/jacs.4c16451 |issn=0002-7863}}</ref> This allows deeper penetration than typically used 980 nm and 808 nm lasers.

Holmium-doped [[yttrium iron garnet]] (YIG) and [[yttrium lithium fluoride]] have applications in [[solid-state laser]]s, and Ho-YIG has applications in [[optical isolator]]s and in [[microwave]] equipment (e.g., [[YIG sphere]]s). Holmium lasers emit at 2.1 micrometres.<ref>{{cite journal| title=The holmium laser in urology| journal=Journal of Clinical Laser Medicine & Surgery | pmid=9728125 | volume=16 | issue=1 | date=Feb 1998| pages=13–20| last1=Wollin | first1=T. A. | last2=Denstedt | first2=J. D. | doi=10.1089/clm.1998.16.13 }}</ref> They are used in medical, dental, and [[optical fiber|fiber-optical]] applications.<ref name="appl">{{cite book| page = 30| url = https://books.google.com/books?id=F0Bte_XhzoAC&pg=PA32| title = Extractive metallurgy of rare earths| author = C. K. Gupta| author2 = Nagaiyar Krishnamurthy| publisher =CRC Press| date = 2004| isbn =0-415-33340-7}}</ref> It is also being considered for usage in the [[enucleation (surgery)|enucleation]] of the [[prostate]].<ref>{{Cite journal |last1=Gilling |first1=Peter J. |last2=Aho |first2=Tevita F. |last3=Frampton |first3=Christopher M. |last4=King |first4=Colleen J. |last5=Fraundorfer |first5=Mark R. |date=2008-04-01 |title=Holmium Laser Enucleation of the Prostate: Results at 6 Years |url=https://www.sciencedirect.com/science/article/pii/S0302283807005933 |journal=European Urology |language=en |volume=53 |issue=4 |pages=744–749 |doi=10.1016/j.eururo.2007.04.052 |pmid=17475395 |issn=0302-2838 |url-access=subscription}}</ref>

Since holmium can absorb [[nuclear fission]]-bred neutrons, it is used as a [[burnable poison]] to regulate nuclear reactors.<ref name="emsley225" /> It is used as a [[Colourant|colorant]] for [[cubic zirconia]], providing pink coloring,<ref>{{Cite journal|last=Nassau|first=Kurt|date=Spring 1981|title=Cubic zirconia: An Update.|journal=Gems & Gemology|volume=1|issue=1 |pages=9–19|doi=10.5741/GEMS.17.1.9|bibcode=1981GemG...17....9N |url=https://www.gia.edu/doc/Cubic-Zirconia.pdf}}</ref> and for [[glass]], providing yellow-orange coloring.<ref>{{Cite journal |last1=El-Batal |first1=Hatem A. |last2=Azooz |first2=Moenis A. |last3=Ezz-El-Din |first3=Fathy M. |last4=El-Alaily |first4=Nagia A. |date=2004-12-20 |title=Interaction of Gamma Rays with Calcium Aluminoborate Glasses Containing Holmium or Erbium |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1151-2916.2001.tb00959.x |journal=Journal of the American Ceramic Society |language=en |volume=84 |issue=9 |pages=2065–2072 |doi=10.1111/j.1151-2916.2001.tb00959.x |url-access=subscription}}</ref> In March 2017, [[IBM]] announced that they had developed a technique to store one [[bit]] of data on a single holmium atom set on a bed of [[magnesium oxide]].<ref>{{cite web|url=https://techcrunch.com/2017/03/08/storing-data-in-a-single-atom-proved-possible-by-ibm-researchers/|access-date=2017-03-10|title=Storing data in a single atom proved possible by IBM researchers|website=[[TechCrunch]]|last1=Coldeway|first1=Devin|date=March 9, 2017}}</ref> With sufficient quantum and classical control techniques, holmium may be a good candidate to make [[quantum computers]].<ref>{{Cite journal|last1=Forrester|first1=Patrick Robert|last2=Patthey|first2=François|last3=Fernandes|first3=Edgar|last4=Sblendorio|first4=Dante Phillipe|last5=Brune|first5=Harald|last6=Natterer|first6=Fabian Donat|date=2019-11-19|title=Quantum state manipulation of single atom magnets using the hyperfine interaction|journal=Physical Review B|language=en|volume=100|issue=18|pages=180405|doi=10.1103/PhysRevB.100.180405| arxiv=1903.00242 |issn=2469-9950|bibcode=2019PhRvB.100r0405F|doi-access=free}}</ref>

Holmium is used in the medical field, particularly in [[laser surgery]] for procedures such as kidney stone removal and prostate treatment, due to its precision and minimal tissue damage.<ref>{{cite web |url=https://www.stanfordmaterials.com/blog/holmium-properties-and-applications.html |title=Holmium: Properties and Applications |last=Loewen |first=Eric |website=Stanford Advanced Materials |access-date=Oct 23, 2024}}</ref><ref>{{cite journal |last1=Younis |first1=Zaid |last2=Ayyed |first2=Atheer |title=Influence of stone location on rate of stone clearance and complication for holmium laser lithotripsy |journal=International Journal of Urology Research |volume=6 |issue=1 |year=2024 |pages=84–90 |doi=10.33545/26646617.2024.v6.i1b.38}}</ref> Its [[isotope]], holmium-166, is applied in targeted cancer therapies, especially for liver cancer,<ref>{{cite journal |last1=Kuhnel |first1=Christian |last2=Kohler |first2=Alexander |year=2024 |title=Clinical Results of Holmium-166 Radioembolization with Personalized Dosimetry for the Treatment of Hepatocellular Carcinoma |journal=J. Pers. Med. |volume=14 |issue=7 |page=747 |doi=10.3390/jpm14070747|doi-access=free |pmid=39064001 |pmc=11278198 }}</ref> and it also enhances [[MRI]] imaging as a contrast agent.<ref>{{cite journal |last1=Maat |first1=Gerrit |last2=Seevinck |first2=Peter |year=2013 |title=MRI-based biodistribution assessment of holmium-166 poly(L-lactic acid) microspheres after radioembolisation |journal=European Radiology |volume=23 |issue=3 |pages=827–835 |doi=10.1007/s00330-012-2648-2 |doi-access=free|pmid=23014797 |pmc=3563959 }}</ref>

==Biological role and precautions==

Holmium plays no [[composition of the human body|biological role in humans]], but its salts are able to stimulate [[metabolism]].<ref name="CRC">{{cite book| author = C. R. Hammond |title = The Elements, in Handbook of Chemistry and Physics |edition = 81st| publisher =CRC press| date = 2000| isbn = 0-8493-0481-4}}</ref> Humans typically consume about a milligram of holmium a year. Plants do not readily take up holmium from the soil. Some vegetables have had their holmium content measured, and it amounted to 100 parts per trillion.<ref name="emsley224">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks|page=224|date=2011}}</ref> Holmium and its soluble salts are slightly toxic if ingested, but insoluble holmium salts are [[nontoxic]]. Metallic holmium 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}}</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> Large amounts of holmium salts can cause severe damage if [[inhaled]], consumed [[mouth|orally]], or [[injection (medicine)|injected]]. The biological effects of holmium over a long period of time are not known. Holmium has a low level of [[acute toxicity]].<ref>{{Cite web |date=2011-04-15 |title=Holmium: Biological Action |url=http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e06740.html |access-date=2023-03-05 |archive-url=https://web.archive.org/web/20110415162101/http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e06740.html |archive-date=2011-04-15 }}</ref>

==See also==
*[[:Category:Holmium compounds]]
* [[Period 6 element]]

==References==
{{Reflist|30em}}

==Bibliography==
*{{cite book|author=Emsley, John|author-link=John Emsley|title=Nature's Building Blocks: An A-Z Guide to the Elements|date=2011|publisher=[[Oxford University Press]]|isbn=978-0-19-960563-7|ref=none}}
* {{cite book |last1=Greenwood |first1=Norman N. |last2=Earnshaw |first2=Alan |title=Chemistry of the Elements |date=1997 |publisher=Butterworth-Heinemann |isbn=978-0-08-037941-8 |edition=2nd |ref=none}}
*{{cite book |last1=Stwertka |first1=Albert |title=A guide to the elements |date=1998 |publisher=Oxford University Press |isbn=0-19-508083-1 |edition=2nd |ref=none}}
*{{cite book|last1=Cullity|first1=B. D.|last2=Graham|first2=C. D.|year=2005|title=Introduction to Magnetic Materials|publisher=[[John Wiley & Sons]]|isbn=978-1-118-21149-6 |ref=none}}
*{{cite book|title=Introduction to magnetism and magnetic materials|author=Jiles, David|url=https://books.google.com/books?id=axyWXjsdorMC|publisher=CRC Press|date=1998|isbn=0-412-79860-3 |ref=none}}
*{{Cite book |last1=Ganjali |first1=Mohammad Reza |url=https://books.google.com/books?id=WtecBAAAQBAJ&dq=holmium+oxide+under+trichromatic+light&pg=PP1 |title=Lanthanides Series Determination by Various Analytical Methods |last2=Gupta |first2=Vinod Kumar |last3=Faridbod |first3=Farnoush |last4=Norouzi |first4=Parviz |date=2016-02-25 |publisher=Elsevier |isbn=978-0-12-420095-1 |language=en |ref=none}}
*{{cite book|first1=E. Yu |last1=Tonkov|title=Compounds and Alloys Under High Pressure A Handbook|publisher=CRC Press|year=1998|isbn=978-90-5699-047-3|url=https://books.google.com/books?id=q2u4kUX8HsIC&pg=PA272
|ref=none}}
*{{cite book|editor1=G. Meyer|editor2= Lester R. Morss|title=Synthesis of Lanthanide and Actinide Compounds|publisher=Kluwer Academic Publishers|year=1991|isbn=0792310187|url=https://books.google.com/books?id=bnS5elHL2w8C&pg=PA329|ref=none }}
*{{Cite book |title=Riedel, moderne anorganische Chemie |date=2012 |publisher=De Gruyter |others=Erwin Riedel, Christoph Janiak, Hans-Jürgen Meyer |isbn=978-3-11-024900-2 |edition=4. Aufl |location=Berlin |oclc=781540844 |language=de|ref=none}}
*{{Cite book |last=Wells |first=A. F. |title=Structural inorganic chemistry |date=1984 |publisher=Clarendon Press |isbn=9780198553700 |edition=5th |location=Oxford [Oxfordshire] |oclc=8866491|ref=none}}
*{{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=none }}

== Further reading ==
* R. J. Callow, ''The Industrial Chemistry of the Lanthanons, Yttrium, Thorium, and Uranium'', Pergamon Press, 1967.

==External links==
{{Commons}}
* [http://www.periodicvideos.com/videos/067.htm Holmium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
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{{Periodic table (navbox)}}
{{Holmium compounds}}

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