Editing Cathode-ray tube (section)

===Phosphors===
[[Phosphor]]s in CRTs emit secondary electrons due to them being inside the vacuum of the CRT. The secondary electrons are collected by the anode of the CRT.<ref name="auto82"/> Secondary electrons generated by phosphors need to be collected to prevent charges from developing in the screen, which would lead to reduced image brightness<ref name="auto68"/> since the charge would repel the electron beam.

The phosphors used in CRTs often contain rare earth metals,<ref name="auto23">{{cite journal |last1=Yin |first1=Xiaofei |last2=Wu |first2=Yufeng |last3=Tian |first3=Xiangmiao |last4=Yu |first4=Jiamei |last5=Zhang |first5=Yi-Nan |last6=Zuo |first6=Tieyong |title=Green Recovery of Rare Earths from Waste Cathode Ray Tube Phosphors: Oxidative Leaching and Kinetic Aspects |journal=ACS Sustainable Chemistry & Engineering |date=5 December 2016 |volume=4 |issue=12 |pages=7080–7089 |doi=10.1021/acssuschemeng.6b01965 }}</ref><ref name="auto8">{{cite web |url=https://www.fh-muenster.de/ciw/downloads/personal/juestel/juestel/CRT-Phosphors.pdf |archive-url=https://web.archive.org/web/20201117063744/https://www.fh-muenster.de/ciw/downloads/personal/juestel/juestel/CRT-Phosphors.pdf |archive-date=2020-11-17 |url-status=live |title=Phosphors for Cathode-Ray Tubes |website=www.fh-muenster.de |access-date=2020-12-11}}</ref><ref name="auto33"/> replacing earlier dimmer phosphors. Early red and green phosphors contained Cadmium,<ref>{{Cite patent |country=US |number=4925593A |url=https://patents.google.com/patent/US4925593A/en |title=US4925593A - Method for producing cadmium free green emitting CRT phosphor}}</ref> and some black and white CRT phosphors also contained beryllium in the form of Zinc beryllium silicate,<ref name="auto93"/> although white phosphors containing cadmium, zinc and magnesium with silver, copper or manganese as dopants were also used.<ref name="auto68"/> The rare earth phosphors used in CRTs are more efficient (produce more light) than earlier phosphors.<ref>{{Cite patent |country=US |number=4035524A |url=https://patents.google.com/patent/US4035524A/en |title=Process for coating a phosphor slurry on the inner surface of a color cathode ray tube faceplate}}</ref> The phosphors adhere to the screen because of Van der Waals and electrostatic forces. Phosphors composed of smaller particles adhere more strongly to the screen. The phosphors together with the carbon used to prevent light bleeding (in color CRTs) can be easily removed by scratching.<ref name="Lee & Hsi 2002"/><ref>{{Cite book|url=https://books.google.com/books?id=Il7LBQAAQBAJ&q=phosphor+adhesion&pg=PA415|title = Phosphor Handbook|isbn = 9781420005233|last1 = Shionoya|first1 = Shigeo|last2 = Yen|first2 = William M.|last3 = Yamamoto|first3 = Hajime|date = 3 October 2018| publisher=CRC Press }}</ref>

Several dozen types of phosphors were available for CRTs.<ref>{{cite web |url=http://www.bunkerofdoom.com/tubes/crt/crt_phosphor_research.pdf |archive-url=https://web.archive.org/web/20130119132302/http://www.bunkerofdoom.com/tubes/crt/crt_phosphor_research.pdf |archive-date=2013-01-19 |url-status=live |title=Cathode Ray Tube Phosphor|website=www.bunkerofdoom.com|access-date=2020-12-11}}</ref> Phosphors were classified according to color, persistence, luminance rise and fall curves, color depending on anode voltage (for phosphors used in penetration CRTs), Intended use, chemical composition, safety, sensitivity to burn-in, and secondary emission properties.<ref name="auto64">{{Cite book|url=https://books.google.com/books?id=QazTBwAAQBAJ&q=crt+aluminized+screen&pg=PA240|title = Color in Electronic Displays|isbn = 9781475797541|last1 = Widdel|first1 = Heino|last2 = Post|first2 = David L.|date = 29 June 2013| publisher=Springer }}</ref> Examples of rare earth phosphors are [[yttrium]] oxide for red<ref>{{Cite web|url=https://patents.google.com/patent/US4151442A/en|title=Color television cathode ray tube}}</ref> and yttrium silicide for blue in beam index tubes,<ref>{{cite web
|url=https://www.labguysworld.com/crt_phosphor_research.pdf|title=Cathode Ray Tube Phosphors|website=labguysworld.com|access-date=27 March 2024}}</ref> while examples of earlier phosphors are copper cadmium sulfide for red,

SMPTE-C phosphors have properties defined by the SMPTE-C standard, which defines a color space of the same name. The standard prioritizes accurate color reproduction, which was made difficult by the different phosphors and color spaces used in the NTSC and PAL color systems. PAL TV sets have subjectively better color reproduction due to the use of saturated green phosphors, which have relatively long decay times that are tolerated in PAL since there is more time in PAL for phosphors to decay, due to its lower framerate. SMPTE-C phosphors were used in professional video monitors.<ref>{{cite web |url=https://www.cinemaquestinc.com/pdf/whitepaper.pdf |archive-url=https://web.archive.org/web/20160614153708/http://cinemaquestinc.com/pdf/whitepaper.pdf |archive-date=2016-06-14 |url-status=live |title= Implementing Display Standards in Modern Video Display Technologies |website=www.cinemaquestinc.com |access-date=2020-12-11}}</ref><ref>{{cite web |url=https://www.broadcaststore.com/pdf/model/20624/sonymonitorguide.pdf |archive-url=https://web.archive.org/web/20201214192909/https://www.broadcaststore.com/pdf/model/20624/sonymonitorguide.pdf |archive-date=2020-12-14 |url-status=live |title=Sony monitor guide |website= www.broadcaststore.com|access-date=2020-12-11}}</ref>

The phosphor coating on monochrome and color CRTs may have an aluminum coating on its rear side used to reflect light forward, provide protection against ions to prevent ion burn by negative ions on the phosphor, manage heat generated by electrons colliding against the phosphor,<ref name="auto28">{{Cite web|url=http://www.tuopeek.com/CRTs.html|title=Tuopeek: CRT Electron Guns|website=www.tuopeek.com}}</ref> prevent static build up that could repel electrons from the screen, form part of the anode and collect the secondary electrons generated by the phosphors in the screen after being hit by the electron beam, providing the electrons with a return path.<ref>{{cite web |url=https://www.circuitstoday.com/crt-cathode-ray-tube |title=CRT|website=www.circuitstoday.com|date=25 September 2009|access-date=2020-12-11}}
{{Cite patent |country=US |number=3893877A |url=https://patents.google.com/patent/US3893877A/en |title=Method and structure for metalizing a cathode ray tube screen}}</ref><ref name="auto63"/><ref>{{Cite web|url=https://www.thevalvepage.com/teletech/crt_manu/crt_manu.htm|title=Manufacture of C.R.T.'s|website=www.thevalvepage.com}}
{{cite web |url= https://frank.pocnet.net/sheets/201/1/12AGP7.pdf |archive-url=https://web.archive.org/web/20160909040652/http://frank.pocnet.net/sheets/201/1/12AGP7.pdf |archive-date=2016-09-09 |url-status=live|title=Rauland |website=frank.pocnet.net |access-date=2020-12-11}}</ref><ref name="auto28"/><ref name="auto68"/> The electron beam passes through the aluminum coating before hitting the phosphors on the screen; the aluminum attenuates the electron beam voltage by about 1&nbsp;kV.<ref name="auto31">{{Cite patent |country=US |number=4720655A |url=https://patents.google.com/patent/US4720655A/en |title=Flat color cathode-ray tube with phosphor index stripes}}</ref><ref name="auto68"/><ref name="auto64"/> A film or lacquer may be applied to the phosphors to reduce the surface roughness of the surface formed by the phosphors to allow the aluminum coating to have a uniform surface and prevent it from touching the glass of the screen.<ref>{{Cite patent |country=US |number=5800234 |url=https://patents.justia.com/patent/5800234|title=Method for manufacturing a metallized luminescent screen for a cathode-ray tube Patent |pubdate=1998-09-01}}</ref><ref name="auto80">{{Cite patent |country=US |number=5178906A |url=https://patents.google.com/patent/US5178906A/en |title=Method of manufacturing a phosphor screen for a CRT using an adhesion-promoting, blister-preventing solution}}</ref> This is known as filming.<ref name="auto52">{{cite web |url=http://www.one-electron.com/Archives/GE/GE_Cathode%20Ray%20Tube%20Dept%201958%20Syracuse%20Factory%20Brochure.pdf |archive-url=https://web.archive.org/web/20190828164614/http://www.one-electron.com/Archives/GE/GE_Cathode%20Ray%20Tube%20Dept%201958%20Syracuse%20Factory%20Brochure.pdf |archive-date=2019-08-28 |url-status=live |title=Cathode ray tube department |website=www.one-electron.com |access-date=2020-12-11}}</ref> The lacquer contains solvents that are later evaporated; the lacquer may be chemically roughened to cause an aluminum coating with holes to be created to allow the solvents to escape.<ref name="auto80"/>

====Phosphor persistence====
Various phosphors are available depending upon the needs of the measurement or display application. The brightness, color, and persistence of the illumination depends upon the type of phosphor used on the CRT screen. Phosphors are available with persistences ranging from less than one [[microsecond]] to several seconds.<ref>{{cite book |last= Doebelin |first= Ernest |title= Measurement Systems |publisher= McGraw Hill Professional |year= 2003 |page= 972 |url= https://books.google.com/books?id=q1mOopLHnTEC&pg=PA972 |isbn=978-0-07-292201-1}}</ref> For visual observation of brief transient events, a long persistence phosphor may be desirable. For events which are fast and repetitive, or high frequency, a short-persistence phosphor is generally preferable.<ref>{{cite book |last= Shionoya |first= Shigeo |title= Phosphor handbook |publisher= CRC Press |year= 1999 |page= 499 |url= https://books.google.com/books?id=lWlcJEDukRIC&pg=PA499 |isbn=978-0-8493-7560-6}}</ref> The phosphor persistence must be low enough to avoid smearing or ghosting artifacts at high refresh rates.<ref name="auto4"/>