Editing Fluorescence (section)

==History==
{{See also|Physical crystallography before X-rays#Luminescence, fluorescence and phosphorescence}}
[[File:Lignum nephriticum - cup of Philippine lignum nephriticum, Pterocarpus indicus, and flask containing its fluorescent solution Hi.jpg|thumb|left|upright|A cup made from the wood of the narra tree (''[[Pterocarpus indicus]]'') beside a flask containing its fluorescent [[Solution (chemistry)|solution]] ''[[Lignum nephriticum]]''.]]
[[File:Matlaline structure.svg|thumb|right|Matlaline, the fluorescent substance in the wood of the tree ''Eysenhardtia polystachya'']]
Fluorescence was observed long before it was named and understood.<ref name=Valeur>
{{cite journal
 | last1 = Valeur          | first1 = B.
 | last2 = Berberan-Santos | first2 = M.R.N.
 | year  = 2011
 | title = A brief history of fluorescence and phosphorescence before the emergence of quantum theory
 | journal = Journal of Chemical Education
 | volume = 88  | issue = 6  | pages = 731–738
 | s2cid = 55366778  | doi = 10.1021/ed100182h
 | bibcode = 2011JChEd..88..731V
}}
</ref>
An early observation of fluorescence was known to the Aztecs<ref name=Valeur/>  and described in 1560 by [[Bernardino de Sahagún]] and in 1565 by [[Nicolás Monardes]] in the [[infusion]] known as ''[[lignum nephriticum]]'' ([[Latin]] for "kidney wood"). It was derived from the wood of two tree species, ''[[Pterocarpus indicus]]'' and ''[[Eysenhardtia polystachya]]''.<ref name="acuna">
{{cite journal
 |last1 = Acuña     |first1 = A. Ulises      |last2 = Amat-Guerri |first2 = Francisco
 |last3 = Morcillo  |first3 = Purificación   |last4 = Liras       |first4 = Marta
 |last5 = Rodríguez |first5 = Benjamín
 |year = 2009
 |title = Structure and formation of the fluorescent compound of ''lignum nephriticum''
 |journal = Organic Letters
 |volume = 11 |issue = 14 |pages = 3020–3023
 |doi = 10.1021/ol901022g |pmid = 19586062
 |url = http://202.127.145.151/siocl/siocl_0001/HHJdatabank/090707ol-6.pdf
 |url-status = live
 |archive-url = https://web.archive.org/web/20130728224629/http://202.127.145.151/siocl/siocl_0001/HHJdatabank/090707ol-6.pdf
 |archive-date = 28 July 2013
}}
</ref><ref name=saff>
{{cite book
 |author=Safford, W.E.  |author-link=William Edwin Safford
 |year=1916
 |chapter=''Lignum nephriticum''
 |title=Annual report of the Board of Regents of the Smithsonian Institution
 |location=Washington, DC
 |publisher=U.S. Government Printing Office
 |pages=271–298
 |chapter-url=https://archive.org/download/annualreportofbo1915smitfo/annualreportofbo1915smitfo.pdf |archive-url=https://web.archive.org/web/20130729063130/http://archive.org/download/annualreportofbo1915smitfo/annualreportofbo1915smitfo.pdf |archive-date=2013-07-29 |url-status=live
}}
</ref><ref>
{{cite journal
 | last1 = Muyskens | first1 = M.
 | last2 = Vitz     | first2 = Ed
 | year = 2006
 | title = The fluorescence of ''lignum nephriticum'': A flash back to the past and a simple demonstration of natural substance fluorescence
 | journal = Journal of Chemical Education
 | volume = 83  | issue = 5  | page = 765
 | doi = 10.1021/ed083p765
 | bibcode = 2006JChEd..83..765M
}}
</ref>
The chemical compound responsible for this fluorescence is matlaline, which is the oxidation product of one of the [[flavonoid]]s found in this wood.<ref name=acuna/>

In 1819, [[Edward Daniel Clarke|E.D. Clarke]]<ref>
{{cite journal
 |author=Clarke, E.D.  |author-link=Edward Daniel Clarke
 |year=1819
 |title=Account of a newly discovered variety of green fluor spar, of very uncommon beauty, and with remarkable properties of colour and phosphorescence
 |journal=The Annals of Philosophy
 |volume=14 |pages=34–36
 |quote=The finer crystals are perfectly transparent. Their colour by transmitted light is an intense ''emerald green''; but by reflected light, the colour is a deep ''sapphire blue''.
 |url=https://books.google.com/books?id=KWc7AQAAIAAJ&pg=PA34
 |url-status=live
 |archive-url=https://web.archive.org/web/20170117092607/https://books.google.com/books?id=KWc7AQAAIAAJ&pg=PA34
 |archive-date=17 January 2017
}}
</ref>
and in 1822 [[René Just Haüy]]
<ref name=Haüy-1822>
{{cite book
 |author=Haüy, R.J. |author-link=René Just Haüy
 |title=Traité de Minéralogie |language=fr
 |trans-title=Treatise on Mineralogy
 |edition=2nd
 |place=Paris, France
 |publisher=Bachelier and Huzard
 |year=1822
 |volume=1 |page=[https://books.google.com/books?id=MvcTAAAAQAAJ&pg=PA512 512]
 |url=https://books.google.com/books?id=MvcTAAAAQAAJ  |via=Google Books
 |archive-url=https://web.archive.org/web/20170117122039/https://books.google.com/books?id=MvcTAAAAQAAJ&pg=PA512
 |archive-date=17 January 2017
}}
</ref>
described some varieties of [[fluorite]]s that had a different color depending on whether the light was reflected or (apparently) transmitted.  Haüy incorrectly viewed the effect as light scattering similar to [[opalescence]].<ref name=Valeur/>{{rp|loc=Fig.5|q=The green color is due to Sm2+ absorption (in the blue and in the red) (14), whereas the deep blue color is due to Eu2+ fluorescence...}} In 1833 [[Sir David Brewster]] described a similar effect in [[chlorophyll]] which he also considered a form of opalescence.<ref>
{{cite journal
 |author=Brewster, D. |author-link=Sir David Brewster
 |year=1834
 |title=On the colours of natural bodies
 |journal=Transactions of the Royal Society of Edinburgh
 |volume=12  |issue=2  |pages=538–545, esp.&nbsp;542
 |doi=10.1017/s0080456800031203
 |s2cid=101650922
 |url=https://books.google.com/books?id=I_UQAAAAIAAJ&pg=PA538
 |url-status=live
 |archive-url=https://web.archive.org/web/20170117120622/https://books.google.com/books?id=I_UQAAAAIAAJ&pg=PA538
 |archive-date=17 January 2017
}}
On page&nbsp;542, Brewster mentions that when white light passes through an alcohol solution of chlorophyll, red light is reflected from it.
</ref>
[[Sir John Herschel]] studied [[quinine]] in 1845<ref>
{{cite journal
 |author=Herschel, J. |author-link=Sir John Herschel
 |year=1845
 |title=On a case of superficial colour presented by a homogeneous liquid internally colourless
 |journal=Philosophical Transactions of the Royal Society of London
 |volume=135 |pages=143–145
 |doi=10.1098/rstl.1845.0004
 |doi-access=free
 |url=https://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA143
 |url-status=live
 |archive-url=https://web.archive.org/web/20161224220539/https://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA143
 |archive-date=24 December 2016
}}
</ref><ref>
{{cite journal
 |author=Herschel, J. |author-link=Sir John Herschel
 |year=1845
 |title=On the epipŏlic dispersion of light, being a supplement to a paper entitled, "On a case of superficial colour presented by a homogeneous liquid internally colourless"
 |journal=Philosophical Transactions of the Royal Society of London
 |volume=135 |pages=147–153
 |doi=10.1098/rstl.1845.0005
 |doi-access=free
 |url=https://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA147
 |url-status=live
 |archive-url=https://web.archive.org/web/20170117093409/https://books.google.com/books?id=GmwOAAAAIAAJ&pg=PA147
 |archive-date=17 January 2017
}}
</ref> and came to a different incorrect conclusion.<ref name=Valeur/>

In 1842, [[A. E. Becquerel|A.E.&nbsp;Becquerel]] observed that [[calcium sulfide]] emits light after being exposed to solar [[ultraviolet]], making him the first to state that the emitted light is of longer wavelength than the incident light. While his observation of [[photoluminescence]] was similar to that described 10 years later by Stokes, who observed a fluorescence of a solution of [[quinine]], the phenomenon that Becquerel described with calcium sulfide is now called [[phosphorescence]].<ref name=Valeur/>

In his 1852 paper on the "Refrangibility" ([[wavelength]] change) of light, [[George Gabriel Stokes]] described the ability of [[fluorite|fluorspar]], [[uranium glass]] and many other substances to change invisible light beyond the violet end of the visible spectrum into visible light. He named this phenomenon ''fluorescence''<ref name=Valeur/>
: "I am almost inclined to coin a word, and call the appearance ''fluorescence'', from fluor-spar [i.e., fluorite], as the analogous term ''opalescence'' is derived from the name of a mineral."<ref name=Stokes-1852>
{{cite journal
 |author  = Stokes, G.G. |author-link=George Gabriel Stokes
 |year    = 1852
 |title   = On the change of refrangibility of light
 |journal = Philosophical Transactions of the Royal Society of London
 |volume  = 142   |pages = 463–562, esp.&nbsp; 479
 |doi     = 10.1098/rstl.1852.0022  |doi-access= free
 |url     = https://books.google.com/books?id=CE9FAAAAcAAJ&pg=PA463
 |url-status = live
 |archive-url = https://web.archive.org/web/20170117061614/https://books.google.com/books?id=CE9FAAAAcAAJ&pg=PA463
 |archive-date = 17 January 2017
}}
</ref>{{rp|style=ama|p= 479, footnote}}

Neither Becquerel nor Stokes understood one key aspect of photoluminescence: the critical difference from [[incandescence]], the emission of light by heated material. To distinguish it from incandescence, in the late 1800s, [[Gustav Wiedemann]] proposed the term [[luminescence]] to designate any emission of light more intense than expected from the source's temperature.<ref name=Valeur/>

Advances in [[spectroscopy]] and [[quantum electronics]] between the 1950s and 1970s provided a way to distinguish between the three different mechanisms that produce the light, as well as narrowing down the typical timescales those mechanisms take to decay after absorption. In modern science, this distinction became important because some items, such as lasers, required the fastest decay times, which typically occur in the nanosecond (billionth of a second) range. In physics, this first mechanism was termed "fluorescence" or "singlet emission", and is common in many laser mediums such as ruby. Other fluorescent materials were discovered to have much longer decay times, because some of the atoms would change their [[Spin (physics)|spin]] to a [[triplet state]], thus would glow brightly with fluorescence under excitation but produce a dimmer afterglow for a short time after the excitation was removed, which became labeled "phosphorescence" or "triplet phosphorescence". The typical decay times ranged from a few microseconds to one second, which are still fast enough by human-eye standards to be colloquially referred to as fluorescent. Common examples include fluorescent lamps, organic dyes, and even fluorspar. Longer emitters, commonly referred to as glow-in-the-dark substances, ranged from one second to many hours, and this mechanism was called persistent phosphorescence or [[persistent luminescence]], to distinguish it from the other two mechanisms.<ref>{{Cite book |last1=Qiu |first1=Jianrong |title=Persistent phosphors: from fundamentals to applications |last2=Li |first2=Yang |last3=Jia |first3=Yongchao |date=2021 |publisher=Woodhead Publishing, an imprint of Elsevier |isbn=978-0-12-818772-2 |series=Woodhead publishing series in electronic and optical materials |location=Duxford Cambridge, MA Kidlington}}</ref>{{rp|1–25}}

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