Editing Phosphorescence (section)

==Materials==
{{main|Phosphor}}
Common pigments used in phosphorescent materials include [[zinc sulfide]] and [[strontium aluminate]]. Use of zinc sulfide for safety related products dates back to the 1930s.

The development of strontium aluminate pigments in 1993 was spurred on by the need to find a substitute for glow-in-the-dark materials with high luminance and long phosphorescence, especially those that used [[promethium]].<ref>{{Citation|title=Glow in the Dark Pigments - Japan's Top Inventions - TV {{!}} NHK WORLD-JAPAN Live & Programs|url=https://www3.nhk.or.jp/nhkworld/en/tv/topinventions/20200130/2072028/|language=en|access-date=2021-03-25}}</ref><ref>{{cite news|last=Kanji|first=Takamasu|date=May–June 2006|title=Shining in the Niche Market withLuminous Pigment and IPRs Strategy|work=Japan Spotlight|url=https://www.jef.or.jp/journal/pdf/BP%20Nemoto_0605.pdf}}</ref> This led to the discovery by Yasumitsu Aoki (Nemoto & Co.) of materials with luminance approximately 10 times greater than zinc sulfide and phosphorescence approximately 10 times longer.<ref>{{Cite journal|last1=Matsuzawa|first1=T.|last2=Aoki|first2=Y.|last3=Takeuchi|first3=N.|last4=Murayama|first4=Y.|date=1996-08-01|title=A New Long Phosphorescent Phosphor with High Brightness, SrAl<sub>2</sub>O<sub>4</sub>: Eu<sup>2+</sup>, Dy<sup>3+</sup>|url=https://iopscience.iop.org/article/10.1149/1.1837067|journal=Journal of the Electrochemical Society|language=en|volume=143|issue=8|pages=2670–2673|doi=10.1149/1.1837067|bibcode=1996JElS..143.2670M |issn=0013-4651|url-access=subscription}}</ref><ref>{{Cite patent|number=US5424006A|title=Phosphorescent phosphor|gdate=1994-02-25|url=https://patents.google.com/patent/US5424006A/en}}</ref> This has relegated most zinc sulfide based products to the novelty category. Strontium aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage.<ref>Zitoun, D.; Bernaud, L.; Manteghetti, A. Microwave Synthesis of a Long-Lasting Phosphor.  J. Chem. Educ. 2009, 86, 72-75.{{doi|10.1021/ed086p72}}</ref>

<gallery>
File:Phosphorescent pigments, in light, in dark, after 4 min - zinc sulfide and strontium aluminate.jpg|Zinc sulfide (left) and strontium aluminate (right), in visible light, in darkness, and after 4 minutes in the dark.
File:Phosphorescent pigment calcium sulfide and silicate, emitting red and blue.jpg|Calcium sulfide (left) and metal-earth silicate (right) phosphoresce in red and blue respectively.
</gallery>
Since both phosphorescence (transition from T<sub>1</sub> to S<sub>0</sub>) and the generation of T<sub>1</sub> from an excited singlet state (e.g., S<sub>1</sub>) via intersystem crossing (ISC) are spin-forbidden processes, most organic materials exhibit insignificant phosphorescence as they mostly fail to populate the excited triplet state, and, even if T<sub>1</sub> is formed, phosphorescence is most frequently outcompeted by non-radiative pathways. One strategy to enhance the ISC and phosphorescence is the incorporation of heavy atoms, which increase spin-orbit coupling (SOC).<ref>{{Cite journal|last1=Wang|first1=J.|last2=Gu|first2=X.|last3=Ma|first3=H.|last4=Peng|first4=Q.|last5=Huang|first5=X.|last6=Zheng|first6=X.|last7=Sung|first7=S. H. P.|last8=Shan|first8=G.|last9=Lam|first9=J. W. Y.|last10=Shuai|first10=Z.|last11=Tang|first11=B. Z.|title=A facile strategy for realizing room temperature phosphorescence and single molecule white light emission|journal=Nature Communications|date=2018|volume=9|issue=1 |pages= 2963|doi=10.1038/s41467-018-05298-y|pmid=30054473 |pmc=6063922 |bibcode=2018NatCo...9.2963W |s2cid=50788897 }} </ref> Additionally, the SOC (and therefore the ISC) can be promoted by coupling n-π* and π-π* transitions with different angular momenta, also known as [[Mostafa El-Sayed]]'s rule. Such transitions are typically exhibited by carbonyl or triazine derivatives, and most organic room-temperature phosphorescent (ORTP) materials incorporate such moieties. <ref>{{Cite journal|last1=An|first1=Z.|last2=Zheng|first2=C.|last3=Tao|first3=Y.|last4=Chen|first4=R.|last5=Shi|first5=H.|last6=Chen|first6=T.|last7=Wang|first7=Z.|last8=Li|first8=H.|last9=Deng|first9=R.|last10=Liu|first10=X.|last11=Huang|first11=W.|title=Stabilizing triplet excited states for ultralong organic phosphorescence|journal=Nature Materials|date=2015|volume=14|issue=7 |pages=685–690|doi=10.1038/nmat4259|pmid=25849370 |bibcode=2015NatMa..14..685A }}</ref><ref>{{Cite journal|last1=Hamzehpoor|first1=E.|last2=Perepichka|first2=D. F.|title=Crystal Engineering of Room Temperature Phosphorescence in Organic Solids|journal= Angewandte Chemie International Edition|date=2020|volume=59|issue=25 |pages=9977–9981|doi=10.1002/anie.201913393|pmid=31725174 |s2cid=208019093 }}</ref>  In turn, to inhibit competitive non-radiative deactivation pathways, including vibrational relaxation and oxygen quenching and triplet-triplet annihilations, organic phosphors have to be embedded in rigid matrices such as polymers, and molecular solids (crystals,<ref>{{Cite journal|last1=Yuan|first=W. Z.|last2=Shen|first2=X. Y.|last3=Zhao|first3=H.|last4=Lam|first4=J. W. Y.|last5=Tang|first5=L.|last6=Lu|first6=P. |last7=Wang|first7=C. L.|last8=Liu|first8=Y.|last9=Wang|first9=Z. M.|last10=Zheng|first10=Q.|last11=Sun|first11=J. Z.|last12=Ma|first12=Y. G.|last13=Tang|first13=B. Z.|title=Crystallization-Induced Phosphorescence of Pure Organic Luminogens at Room Temperature|journal=J. Phys. Chem. C|date=2010|volume=114|issue=13 |pages=6090–6099|doi=10.1021/jp909388y}}</ref> covalent organic frameworks,<ref>{{Cite journal|last1=Hamzehpoor|first1=E|last2=Ruchlin|first2=C.|last3=Tao|first3=Y.|last4=Liu|first4=C. H.|last5=Titi|first5=H. M.|last6=Perepichka|first6=D. F.|title=Efficient room-temperature phosphorescence of covalent organic frameworks through covalent halogen doping|journal=Nature Chemistry|date=2022|volume=15|issue=1|pages=83–90|doi=10.1038/s41557-022-01070-4|pmid=36302870|s2cid=253183290}}</ref> and others).