Phosphor

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A phosphor is a substance that exhibits the optical phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons).

The chemical element phosphorus (Greek language. phosphoros, meaning "light bearer") was discovered by Germany alchemist Hennig Brand in 1669. Working in Hamburg, Brand attempted to distill some kind of "life essence" from his urine, and in the process produced a white material that glowed in the dark. Since that time, the term phosphorescence has been used to describe substances that shine in the dark without burning.

Phosphorus itself is not a phosphor; it is highly reactive and gives-off a faint chemoluminescence glow upon uniting with oxygen. The glow observed by Brand was actually caused by the very slow burning of the phosphorus, but as he saw no flame nor felt any heat he did not recognize it as burning.

Phosphors are transition metal compounds or rare earth element compounds of various types. The most common uses of phosphors are in cathode ray tube displays and fluorescent lights. CRT phosphors were standardized beginning around World War II and designated by the letter "P" followed by a number.

Materials Phosphors are usually made from a suitable host material, to which an activator is added. The best known type is a copper-activated zinc sulfide and the silver-activated zinc sulfide (zinc sulfide silver).

The host materials are typically oxides, sulfides, selenides, halides or silicates of zinc, cadmium, manganese, aluminum, silicon, or various Rare earth element metals. The activators prolong the emission time (afterglow). In turn, other materials (eg. nickel) can be used to quench the afterglow and shorten the decay part of the phosphor emission characteristics.

Glow-in-the-dark toys .

Calcium sulfide with strontium sulfide with bismuth as activator, (Ca,Sr)S:Bi, yields blue light with glow times up to 12 hours, red and orange are modifications of the zinc sulfide formula. Red color can be obtained from strontium sulfide.

Zinc sulfide with about 5 ppm of a copper activator is the most common phosphor for the glow-in-the-dark toys and items. It is also called GS phosphor.

Mix of zinc sulfide and cadmium sulfide emit color depending on their ratio; increasing of the CdS content shifts the output color towards longer wavelengths; its persistence ranges between 1-10 hours.

Strontium aluminate activated by europium, SrAl2O4:Eu:Dy, is a newer material with higher brightness and significantly longer glow persistence; it produces green and aqua hues, where green gives the highest brightness and aqua the longest glow time. SrAl2O4:Eu:Dy is about 10 times brighter, 10 times longer glowing, and 10 times more expensive than ZnS:Cu. The excitation wavelengths for strontium aluminate range from 200 to 450 nm. The wavelength for its green formulation is 520 nm, its blue-green version emits at 505 nm, and the blue one emits at 490 nm. Colors with longer wavelengths can be obtained from the strontium aluminate as well, though for the price of some loss of brightness.

In these applications, the phosphor is directly added to the plastic from which the toys are molded, or mixed with a binder for use as paints.

ZnS:Cu phosphor is used in glow-in-the-dark cosmetic creams frequently used for Halloween make-ups.

Generally, the persistence of the phosphor increases as the wavelength increases. .

See also lightstick for chemiluminescence-based glowing items.

Radioactive light sources Mixtures of zinc sulfide with radioactive materials, where the phosphor was excited by the alpha- and beta-decaying isotopes, were used to paint dials of watches and instruments. The formula used on watch dials between 1913 and 1950 was a mix of radium-228 and radium-226 with a scintillator made of zinc sulfide and silver (ZnS:Ag). However, zinc sulfide undergoes degradation of its crystal lattice structure, leading to gradual loss of brightness significantly faster than the depletion of radium.

The ZnS:Ag phosphor yields greenish glow. It is not suitable to be used in layers thicker than 25 mg/cm², as the self-absorption of the light then becomes a problem. ZnS:Ag coated screens were used by Ernest Rutherford in his experiments discovering atomic nucleus.

Copper-activated zinc sulfide (ZnS:Cu) is the most common phosphor used. It yields blue-green light.

Copper and magnesium activated zinc sulfide (ZnS:Cu,Mg) yields yellow-orange light.

Trasers are light producing devices composed of a sealed borosilicate glass tube with inner coat of a phosphor, filled with tritium. Betalights use tritium as energy source as well.

Electroluminescence Electroluminescence can be exploited in light sources. Such sources typically emit from a large area, which makes them suitable for backlights of eg. LCD displays. The excitation of the phosphor is usually achieved by application of high-intensity electric field, usually with suitable frequency. Current electroluminescent light sources tend to degrade with use, resulting in their relatively short operation lifetimes.

ZnS:Cu was the first formulation successfully displaying electroluminescence, tested at 1936 by Georges Destriau in Madame Marie Curie laboratories in Paris.

Indium tin oxide (ITO, also known under trade name IndiGlo) composite is used in some Timex watches, though as the electrode material, not as a phosphor itself. "Californeon" is another trade name of an electroluminescent material, used in electroluminescent light strips.

See also a history of electroluminescent displays.

White LEDs White light-emitting diodes are usually blue InGaN LEDs with a coating of a suitable material. Cerium(III)-doped YAG (YAG:Ce3+, or Y3Al5O12:Ce3+) is often used; it absorbs the light from the blue LED and emits in a broad range from greenish to reddish, with most of output in yellow. The pale yellow emission of the Ce3+:YAG can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminium in the YAG with gallium. However, this process is not one of phosphorescence. The yellow light is produced by a process known as scintillation, the complete absence of an afterglow being one of the characteristics of the process.

White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminium doped zinc sulfide (ZnS:Cu,Al). This is a method analogous to the way fluorescent lamps work.

===Cathode ray tubes===The phosphors are usually poor electrical conductors. This may lead to deposition of residual charge on the screen, effectively decreasing the energy of the impacting electrons due to electrostatic repulsion (an effect known as "sticking"). To eliminate this, a thin layer of aluminium is deposited over the phosphors and connected to the conductive layer inside the tube. This layer also reflects the phosphor light to the desired direction, and protects the phosphor from ion bombardment resulting from an imperfect vacuum.

Combination of zinc sulfide with copper, the P31 phosphor or ZnS:Cu, provides green light peaking at 531 nm, with long glow.

Combination of zinc sulfide with few ppm of silver, the ZnS:Ag, when excited by electrons, provides strong blue glow with maximum at 450 nm, with short afterglow with 200 nanosecond duration. It is known as the P22B phosphor. This material, zinc sulfide silver, is still one of the most efficient phosphors in cathode ray tubes. It is used as a blue phosphor in color CRTs.

When mixed with cadmium sulfide, the resulting zinc cadmium sulfide (Zn,Cd)S:Ag, provides strong yellow light.

The mix of zinc cadmium sulfide and zinc sulfide silver, the ZnS:Ag+(Zn,Cd)S:Ag is the white P4 phosphor used in black and white television CRTs.

Yttrium oxide-sulfide activated with europium is used as red phosphor in color CRTs. The development of color TVs took a long time due to the long search for a red phosphor.

Zinc sulfide:Ag+(Zn,Cd)S:Ag (P4), white phosphor for black and white TV screens and display tubes
ZnS:Cu,Al (P22G), green phosphor for TV screens
ZnS:Ag+Co-on-Al2O3 (P22B), blue phosphor for television screens
ZnS:Ag,Cl or ZnS:Zn (P11, BE), blue (460 nm), 0.01-1 ms persistence, for display tubes and vacuum fluorescent displays
(Zn,Cd)S:Ag or (Zn,Cd)S:Cu (P20, KA), yellow-green, 1-100 ms persistence, for display tubes
(Zn,Cd)S:Cu,Cl (P28, KE), yellow, for display tubes
ZnS:Cu or ZnS:Cu,Ag (P31, GH), yellowish-green, 0.01-1 ms persistence, for oscilloscopes
ZnS:Ag+(Zn,Cd)S:Cu (P40, GA), white, for display tubes
ZnS:Ag,Al (P55, BM), blue (450 nm), for projection tubes
ZnS:Ag, blue (450 nm)
ZnS:Cu,Al or ZnS:Cu,Au,Al, green (530 nm)
(Zn,Cd)S:Cu,Cl+(Zn,Cd)S:Ag,Cl, white
ZnS:Ag+ZnS:Cu+yttrium oxysulfide:Eu, white, Cd-free replacement for P4, black and white CRT tubes, display tubes

Zinc silicate:Mn (P1, GJ), yellowish-green (525 nm), 1-100 ms persistence, for display tubes
Zn2SiO4:Mn,As (P39, GR), green (525 nm), for display tubes
Yttrium silicate:Ce (P47, BH), blue (400 nm), for beam index tubes
Y2SiO5:Tb, green (545 nm), for projection tubes

Zinc oxide:Zn (P24, GE), green (505 nm), 1-10 µs persistence, for vacuum fluorescent displays

Gadolinium oxysulfide:Tb (P43, GY), yellow-green (545 nm), for display tubes
Yttrium oxysulfide:Eu+Fe2O3 (P22R), red phosphor for TV screens
Y2O2S:Tb (P45, WB), white (545 nm), for viewfinders
Y2O2S:Tb, green (545 nm), for display tubes
Yttrium aluminate:Ce (P46, KG), green (530 nm), for beam index tubes
Y3(Al,Ga)5O12:Ce, green (520 nm), for beam index tubes
Y3Al5O12:Tb (P53, KJ), yellow-green (544 nm), for projection tubes
Y3(Al,Ga)5O12:Tb, yellow-green (544 nm), for projection tubes

Magnesium fluoride:Mn (P33, LD), orange (590 nm), over 1 second persistence, for radar screens
(KF,MgF2):Mn (P19, LF), yellow (590 nm), for radar screens
(KF,MgF2):Mn (P26, LC), orange (595 nm), over 1 second persistence, for radar screens
(Zn,Mg)F2:Mn (P38, LK), orange (590 nm), for radar screens

Indium borate:Tb, yellow-green (550 nm)
InBO3:Eu, yellow (588 nm)
InBO3:Tb+InBO3:Eu, amber
InBO3:Tb+InBO3:Eu+ZnS:Ag, white

Fluorescent lamps

(Ba,Eu)Mg2Al16O27, blue phosphor for trichromatic fluorescent lamps
(Ce,Tb)MgAl11O19, green phosphor for trichromatic fluorescent lamps
Ce0.67Tb0.33MgAl11O19:Ce,Tb, green (543 nm), for trichromatic lamps
BaMgAl10O17:Eu,Mn, blue-green (456/514 nm)
BaMgAl10O17:Eu,Mn, blue (450 nm), for trichromatic lamps
BaMg2Al16O27:Eu(II), blue (452 nm)
BaMg2Al16O27:Eu(II),Mn(II), blue (450+515 nm)
(Ce,Tb)MgAl11O19, green

zinc silicate:Mn, green (528 nm)
Zn2SiO4:Mn,Sb2O3, green (528 nm)
calcium silicate:Pb,Mn, orange-pink (615 nm)

magnesium tungstate, pale blue (473 nm), wide bandwidth, deluxe blend component
calcium tungstate (Scheelite), blue (417 nm)
CaWO4:Pb, blue (433 nm), wide bandwidth

(Sr,Eu,Ba,Ca)5(PO4)3Cl, blue phosphor for trichromatic fluorescent lamps
(La,Ce,Tb)PO4, green phosphor for trichromatic fluorescent lamps
(La,Ce,Tb)PO4:Ce,Tb, green (546 nm), for trichromatic lamps
(Ba,Ti)2P2O7:Ti, blue-green (494 nm), wide bandwidth, deluxe blend component
strontium phosphate:Sn, blue (460 nm), wide bandwidth, deluxe blend component
Ca5F(PO4)3:Sb, blue (482 nm), wide bandwidth
Sr5F(PO4)3:Sb,Mn, blue-green (509 nm), wide bandwidth
lanthanum phosphate:Ce,Tb, green phosphor (544 nm), for trichromatic blends
(Sr,Ca,Ba)10(PO4)6Cl2:Eu, blue phosphor (453 nm) for trichromatic blends
(Ca,Zn,Mg)3(PO4)2:Sn, orange-pink (610 nm), wide bandwidth, blend component
(Sr,Mg)3(PO4)2:Sn, orange-pinkish white (626 nm), wide bandwidth, deluxe blend component
Ca5F(PO4)3:Sb,Mn, yellow, for Lite-white blend
Ca5(F,Cl)(PO4)3:Sb,Mn, warm white to cool white or blue or daylight
(Ca,Sr,Ba)3(PO4)2Cl2:Eu, blue (452 nm)
3 strontium phosphate.strontium fluoride:Sb,Mn, blue (502 nm)
(Zn,Sr)3(PO4)2:Mn, orange-red (625 nm)
(Sr,Mg)3(PO4)2:Sn(II), orange-red (630 nm)

(Y,Eu)2O3, red phosphor for trichromatic fluorescent lamps
yttrium oxide:Eu, red phosphor (611 nm), for trichromatic blends
Y2O3:Eu(III), red (611 nm), for trichromatic lamps

Mg4(F)GeO6:Mn, red (658 nm)
Mg4(F)(Ge,Sn)O6:Mn, red (658 nm)
Sr5Cl(PO4)3:Eu(II), blue (447 nm)
Sr6P5BO20:Eu, blue-green (480 nm)

Y(P,V)O4:Eu, orange-red (619 nm)
Y2O2S:Eu, red (626 nm)
3.5 magnesium oxide . 0.5 magnesium fluoride . germanium dioxide :Mn, red (655 nm)
Mg5As2O11:Mn, red (660 nm)
calcium phosphate.calcium fluoride:Ce,Mn, yellow (568 nm)

SrAl2O7:Pb, ultraviolet (313 nm)
BaSi2O5:Pb, ultraviolet (355 nm)
SrFB2O3:Eu(II), ultraviolet (366 nm)
SrB4O7:Eu, ultraviolet (368 nm)

MgGa2O4:Mn(II), blue-green, used in black light displays

Detergents Optical brighteners act as UV-sensitive phosphors with close-to-zero afterglow. Usually they are organic compounds.

Various Some other phosphors commercially available, for use as X-ray screens, neutron detectors, alpha-particle scintillators, etc, are:

Gd2O2S:Tb (P43), green (peak at 545 nm), 1.5 ms decay to 10%, low afterglow, high X-ray absorption, for X-ray, neutrons and gamma
Gd2O2S:Eu, red (627 nm), 850 µs decay, afterglow, high X-ray absorption, for X-ray, neutrons and gamma
Gd2O2S:Pr, green (513 nm), 7 µs decay, no afterglow, high X-ray absorption, for X-ray, neutrons and gamma
Gd2O2S:Pr,Ce,F, green (513 nm), 4 µs decay, no afterglow, high X-ray absorption, for X-ray, neutrons and gamma

Y2O2S:Tb (P45), white (545 nm), 1.5 ms decay, low afterglow, for low-energy X-ray
Y2O2S:Tb (P22R), red (627 nm), 850 µs decay, afterglow, for low-energy X-ray
Y2O2S:Tb, white (513 nm), 7 µs decay, no afterglow, for low-energy X-ray

Zn(0.5)Cd(0.4)S:Ag (HS), green (560 nm), 80 µs decay, afterglow, efficient but low-res X-ray
Zn(0.4)Cd(0.6)S:Ag (HSr), red (630 nm), 80 µs decay, afterglow, efficient but low-res X-ray

CdWO4, blue (475 nm), 28 µs decay, no afterglow, intensifying phosphor for X-ray and gamma
CaWO4, blue (410 nm), 20 µs decay, no afterglow, intensifying phosphor for X-ray
MgWO4, white (500 nm), 80 µs decay, no afterglow, intensifying phosphor

Y2SiO5:Ce (P47), blue (400 nm), 120 ns decay, no afterglow, for electrons, suitable for photomultipliers
YAlO3:Ce (YAP), blue (370 nm), 25 ns decay, no afterglow, for electrons, suitable for photomultipliers
Y3Al5O12:Ce (YAG), green (550 nm), 70 ns decay, no afterglow, for electrons, suitable for photomultipliers
Y3(Al,Ga)5O12:Ce (YGG), green (530 nm), 250 ns decay, low afterglow, for electrons, suitable for photomultipliers

CdS:In, green (525 nm),

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A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to oxygen or energized particles such as electrons).

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