Editing Lanthanide (section)

==Physical properties==
[[File:Lanthanoide.jpg|thumb|450 px|center|Samples of lanthanide elements (excluding [[promethium]])]]
===Magnetic and spectroscopic===
All the trivalent lanthanide ions, except lanthanum and lutetium, have unpaired f electrons. (Ligand-to-metal charge transfer can nonetheless produce a nonzero f-occupancy even in La(III) compounds.)<ref name=LaF3>{{cite journal |last1=Xu |first1=Wei |last2=Ji |first2=Wen-Xin |first3=Yi-Xiang |last3=Qiu |first4=W. H. Eugen |last4=Schwarz |first5=Shu-Guang |last5=Wang |date=2013 |title=On structure and bonding of lanthanoid trifluorides LnF<sub>3</sub> (Ln = La to Lu) |journal=Physical Chemistry Chemical Physics |volume=2013 |issue=15 |pages=7839–47 |doi=10.1039/C3CP50717C|pmid=23598823 |bibcode=2013PCCP...15.7839X }}</ref> However, the magnetic moments [[magnetochemistry|deviate considerably from the spin-only values]] because of strong [[spin–orbit coupling]]. The maximum number of unpaired electrons is 7, in Gd<sup>3+</sup>, with a magnetic moment of 7.94 [[Bohr magneton|B.M.]], but the largest magnetic moments, at 10.4–10.7 B.M., are exhibited by Dy<sup>3+</sup> and Ho<sup>3+</sup>. However, in Gd<sup>3+</sup> all the electrons have parallel spin and this property is important for the use of gadolinium complexes as [[MRI contrast agent|contrast reagent]] in [[MRI]] scans.

[[File:HoOxideSolution.jpg|thumb|A solution of 4% [[Holmium(III) oxide|holmium oxide]] in 10% [[perchloric acid]], permanently fused into a quartz cuvette as a wavelength calibration standard]]
[[Crystal field splitting]] is rather small for the lanthanide ions and is less important than spin–orbit coupling in regard to energy levels.<ref name = "Greenwood&Earnshaw"/> Transitions of electrons between f orbitals are forbidden by the [[Laporte rule]]. Furthermore, because of the "buried" nature of the f orbitals, coupling with molecular vibrations is weak. Consequently, the spectra of lanthanide ions are rather weak and the absorption bands are similarly narrow. Glass containing [[Holmium(III) oxide|holmium oxide]] and holmium oxide solutions (usually in [[perchloric acid]]) have sharp optical absorption peaks in the spectral range 200–900&nbsp;nm and can be used as a [[wavelength]] calibration standard for [[Monochromator|optical spectrophotometers]],<ref>{{cite journal|url=http://www.clinchem.org/cgi/reprint/10/12/1117.pdf|journal=Clinical Chemistry|volume=10|year=1964|title=Uses for a Holmium Oxide Filter in Spectrophotometry|author=MacDonald, R. P.|pmid=14240747|issue=12|pages=1117–20|doi=10.1093/clinchem/10.12.1117|access-date=24 February 2010|archive-url=https://web.archive.org/web/20111205221417/http://www.clinchem.org/cgi/reprint/10/12/1117.pdf|archive-date=5 December 2011|url-status=dead}}</ref> and are available commercially.<ref>{{cite web| url=http://www.labshoponline.com/holmium-glass-filter-spectrophotometer-calibration-p-88.html| access-date=6 June 2009| title=Holmium Glass Filter for Spectrophotometer Calibration| url-status=usurped| archive-url=https://web.archive.org/web/20100314163906/http://www.labshoponline.com/holmium-glass-filter-spectrophotometer-calibration-p-88.html| archive-date=14 March 2010}}</ref>

As f-f transitions are Laporte-forbidden, once an electron has been excited, decay to the ground state will be slow. This makes them suitable for use in [[laser]]s as it makes the [[population inversion]] easy to achieve. The [[Nd:YAG laser]] is one that is widely used. Europium-doped yttrium vanadate was the first [[phosphor#Cathode-ray tubes|red phosphor]] to enable the development of color television screens.<ref>{{cite journal| doi = 10.1063/1.1723611| title = A new, highly efficient red-emitting cathodoluminescent phosphor (YVO4:Eu) for color television| year = 1964|author = Levine, Albert K.| journal = Applied Physics Letters| volume = 5|page = 118| first2 = Frank C.| last2 = Palilla| issue = 6| bibcode=1964ApPhL...5..118L}}</ref> Lanthanide ions have notable luminescent properties due to their unique 4f orbitals. Laporte forbidden f-f transitions can be activated by excitation of a bound "antenna" ligand. This leads to sharp emission bands throughout the visible, NIR, and IR and relatively long luminescence lifetimes.<ref>{{cite journal | last1 = Werts | first1 = M. H. V. | year = 2005 | title = Making Sense of Lanthanide Luminescence | journal = Science Progress | volume = 88 | issue = 2| pages = 101–131 | doi=10.3184/003685005783238435| pmid = 16749431 | pmc = 10361169 | s2cid = 2250959 | doi-access = free }}</ref>