Phosphor

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

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

Note: phosphorus, the chemical element, can emit light under certain conditions, but this is due to chemiluminescence, not phosphorescence.^[1]

Contents 1 Principles 2 Materials 2.1 Phosphor Thermometry 2.2 Glow-in-the-dark toys 2.3 Radioactive light sources 2.4 Electroluminescence 2.5 White LEDs 2.6 Cathode ray tubes 3 Standard phosphor types 3.1 Various 4 References 5 See also 6 External links

[edit] Principles

A material can emit light either by thermal emission, where all atoms radiate, or by luminescence, where only a small fraction of atoms, called emission centers or luminescence centers, emit light. In inorganic phosphors, these nonhomogenities in the crystal structure are created usually by addition of a trace amount of impurities, called activators. (In rare cases dislocations or other crystal defects can play the role of the impurity.) The wavelength emitted by the emission center is dependent on the atom itself, and on the surrounding crystal structure.

[edit] 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, nitrides and oxynitrides^[2], sulfides, selenides, halides or silicates of zinc, cadmium, manganese, aluminum, silicon, or various rare earth 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.

Many phosphor powders are produced in low-temperature processes, such as sol-gel and usually require post-annealing at temperatures of ~1000 °C, which is undesirable for many applications. However, proper optimization of the growth process allows to avoid the annealing.^[3]

The commonly quoted parameters for phosphors are the wavelength of emission maximum (in nanometers, or alternatively color temperature in kelvins for white blends), the peak width (in nanometers at 50% of intensity), and decay time (in seconds).

[edit] Phosphor Thermometry

Phosphor thermometry is a temperature measurement approach that utilizes the temperature dependence of certain phosphors for this purpose. For this, a phosphor coating is applied to a surface of interest and, usually, the decay time is the emission parameter that indicates temperature. Because the illumination and detection optics can be situated remotely, the method may be used for moving surfaces such as high speed motor surfaces. Also, phosphor may be applied to the end of an optical fiber as an optical analog of a thermocouple.

[edit] 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(II):Dy(III), 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.

[edit] 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 spinthariscope 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.

[edit] 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.

[edit] 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.

[edit] Cathode ray tubes

Cathode ray tubes produce signal-generated light patterns in a (typically) round or rectangular format. Bulky CRTs were used in the black-and-white household television ("TV") sets that became popular in the 1950s, as well as first-generation, tube-based color TVs, and most earlier computer monitors. CRTs have also been widely used in scientific and engineering instrumentation, such as oscilloscopes, usually with a single phosphor color, typically green.

White (in black-and-white): 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.

Red: Yttrium oxide-sulfide activated with europium is used as the red phosphor in color CRTs. The development of color TVs took a long time due to the long search for a red phosphor. The first red emitting rare earth phosphor, YVO4,Eu3, was introduced by Levine and Palilla as a primary color in television in 1964.^[4] In single crystal form, it was used as an excellent polarizer and laser material.^[5]

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

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

Blue: 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.

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.

[edit] Standard phosphor types

Standard phosphor types^[6]

Phosphor	Composition	Color	Wavelength	Peak width	Persistence	Usage	Notes
P1, GJ	Zn2SiO4:Mn (Willemite)	Green	528 nm	40 nm[7]	1-100ms	CRT, Lamp	Oscilloscopes
P4	ZnS:Ag+(Zn,Cd)S:Ag	White	-	-	Short	CRT	Black and white TV CRTs and display tubes.
P4 (Cd-free)	ZnS:Ag+ZnS:Cu+Y2O2S:Eu	White	-	-	Short	CRT	Black and white TV CRTs and display tubes, Cd free.
P4, GE	ZnO:Zn	Green	505nm	-	1-10µs	VFD	VFDs
P7	?	Yellow	-	-	Long	CRT	Radar PPI
P11, BE	ZnS:Ag,Cl or ZnS:Zn	Blue	460nm	-	0.01-1 ms	CRT, VFD	Display tubes and VFDs
P19, LF	(KF,MgF2):Mn	Orange-Yellow	590nm	-	Long	CRT	Radar screens
P20, KA	(Zn,Cd)S:Ag or (Zn,Cd)S:Cu	Yellow-green	-	-	1-100 ms	CRT	Display tubes
P22R	Y2O2S:Eu+Fe2O3	Red	-	-	Short	CRT	Red phosphor for TV screens
P22G	ZnS:Cu,Al	Green	-	-	Short	CRT	Green phosphor for TV screens
P22B	ZnS:Ag+Co-on-Al2O3	Blue	-	-	Short	CRT	Blue phosphor for TV screens
P26, LC	(KF,MgF2):Mn	Orange	595nm	-	Long	CRT	Radar screens
P28, KE	(Zn,Cd)S:Cu,Cl	Yellow	-	-	-	CRT	Display tubes
P31, GH	ZnS:Cu or ZnS:Cu,Ag	Yellowish-green	-	-	0.01-1 ms	CRT	Oscilloscopes
P33, LD	MgF2:Mn	Orange	590nm	-	> 1sec	CRT	Radar screens
P38, LK	(Zn,Mg)F2:Mn	Orange-Yellow	590nm	-	Long	CRT	Radar screens
P39, GR	Zn2SiO4:Mn,As	Green	525nm	-	-	CRT	Display tubes
P40, GA	ZnS:Ag+(Zn,Cd)S:Cu	White	-	-	-	CRT	Display tubes
P43, GY	Gd2O2S:Tb	Yellow-green	545nm	-	-	CRT	Display tubes
P45, WB	Y2O2S:Tb	White	545nm	-	Short	CRT	Viewfinders
P46, KG	Y3Al5O12:Ce	Green	530nm	-	-	CRT	Beam-index tube
P47, BH	Y2SiO5:Ce	Blue	400nm	-	-	CRT	Beam-index tube
P53, KJ	Y3Al5O12:Tb	Yellow-green	544nm	-	Short	CRT	Projection tubes
P55, BM	ZnS:Ag,Al	Blue	450nm	-	Short	CRT	Projection tubes
?	ZnS:Ag	Blue	450nm	-	-	CRT	-
?	ZnS:Cu,Al or ZnS:Cu,Au,Al	Green	530nm	-	-	CRT	-
?	(Zn,Cd)S:Cu,Cl+(Zn,Cd)S:Ag,Cl	White	-	-	-	CRT	-
?	Y2SiO5:Tb	Green	545nm	-	-	CRT	Projection tubes
?	Y2OS:Tb	Green	545nm	-	-	CRT	Display tubes
?	Y3(Al,Ga)5O12:Ce	Green	520nm	-	Short	CRT	Beam-index tube
?	Y3(Al,Ga)5O12:Tb	Yellow-green	544nm	-	Short	CRT	Projection tubes
?	InBO3:Tb	Yellow-green	550nm	-	-	CRT	-
?	InBO3:Eu	Yellow	588nm	-	-	CRT	-
?	InBO3:Tb+InBO3:Eu	Amber	-	-	-	CRT	Computer displays
?	InBO3:Tb+InBO3:Eu+ZnS:Ag	White	-	-	-	CRT	-
?	(Ba,Eu)Mg2Al16O27	Blue	-	-	-	Lamp	Trichromatic fluorescent lamps
?	(Ce,Tb)MgAl11O19	Green	546nm	9nm	-	Lamp	Trichromatic fluorescent lamps[7]
?	BaMgAl10O17:Eu,Mn	Blue	450nm	-	-	Lamp	Trichromatic fluorescent lamps
?	BaMg2Al16O27:Eu(II)	Blue	450nm	52nm	-	Lamp	Trichromatic fluorescent lamps[7]
?	BaMgAl10O17:Eu,Mn	Blue-Green	456nm,514nm	-	-	Lamp	-
?	BaMg2Al16O27:Eu(II),Mn(II)	Blue-Green	456nm, 514nm	50nm 50%[7]	-	Lamp
?	Ce0.67Tb0.33MgAl11O19:Ce,Tb	Green	543 nm	-	-	Lamp	Trichromatic fluorescent lamps
?	Zn2SiO4:Mn,Sb2O3	Green	528 nm	-	-	Lamp	-
?	CaSiO3:Pb,Mn	Orange-Pink	615 nm	83 nm[7]	-	Lamp
?	CaWO4 (Scheelite)	Blue	417 nm	-	-	Lamp	-
?	CaWO4:Pb	Blue	433 nm/466 nm	111 nm	-	Lamp	Wide bandwidth[7]
?	MgWO4	Blue pale	473 nm	118 nm	-	Lamp	Wide bandwidth, deluxe blend component [7]
?	(Sr,Eu,Ba,Ca)5(PO4)3Cl	Blue	-	-	-	Lamp	Trichromatic fluorescent lamps
?	Sr5Cl(PO4)3:Eu(II)	Blue	447 nm	32 nm[7]	-	Lamp	-
?	(Ca,Sr,Ba)3(PO4)2Cl2:Eu	Blue	452 nm	-	-	Lamp	-
?	(Sr,Ca,Ba)10(PO4)6Cl2:Eu	Blue	453 nm	-	-	Lamp	Trichromatic fluorescent lamps
?	Sr2P2O7:Sn(II)	Blue	460 nm	98 nm	-	Lamp	Wide bandwidth, deluxe blend component[7]
?	Sr6P5BO20:Eu	Blue-Green	480 nm	82 nm[7]	-	Lamp	-
?	Ca5F(PO4)3:Sb	Blue	482 nm	117 nm	-	Lamp	Wide bandwidth[7]
?	(Ba,Ti)2P2O7:Ti	Blue-Green	494 nm	143 nm	-	Lamp	Wide bandwidth, deluxe blend component [7]
?	3Sr3(PO4)2.SrF2:Sb,Mn	Blue	502 nm	-	-	Lamp	-
?	Sr5F(PO4)3:Sb,Mn	Blue-Green	509 nm	127 nm	-	Lamp	Wide bandwidth[7]
?	Sr5F(PO4)3:Sb,Mn	Blue-Green	509 nm	127 nm	-	Lamp	Wide bandwidth[7]
?	LaPO4:Ce,Tb	Green	544 nm	-	-	Lamp	Trichromatic fluorescent lamps
?	(La,Ce,Tb)PO4	Green	-	-	-	Lamp	Trichromatic fluorescent lamps
?	(La,Ce,Tb)PO4:Ce,Tb	Green	546 nm	6 nm	-	Lamp	Trichromatic fluorescent lamps[7]
?	Ca3(PO4)2.CaF2:Ce,Mn	Yellow	568 nm	-	-	Lamp	-
?	(Ca,Zn,Mg)3(PO4)2:Sn	Orange-Pink	610 nm	146 nm	-	Lamp	Wide bandwidth, blend component[7]
?	(Zn,Sr)3(PO4)2:Mn	Orange-Red	625 nm	-	-	Lamp	-
?	(Sr,Mg)3(PO4)2:Sn	Orange-Pinkish White	626 nm	120 nm	-	Lamp	Wide bandwidth, deluxe blend component[7]
?	(Sr,Mg)3(PO4)2:Sn(II)	Orange-Red	630 nm	-	-	Lamp	-
?	Ca5F(PO4)3:Sb,Mn	3800K	-	-	-	Lamp	Lite-white blend[7]
?	Ca5(F,Cl)(PO4)3:Sb,Mn	White-Cold/Warm	-	-	-	Lamp	2600K to 9900K, for very high output lamps[7]
?	(Y,Eu)2O3	Red	-	-	-	Lamp	Trichromatic fluorescent lamps
?	Y2O3:Eu(III)	Red	611 nm	4 nm	-	Lamp	Trichromatic fluorescent lamps[7]
?	Mg4(F)GeO6:Mn	Red	658 nm	17 nm	-	Lamp	[7]
?	Mg4(F)(Ge,Sn)O6:Mn	Red	658 nm	-	-	Lamp	-
?	Y(P,V)O4:Eu	Orange-Red	619 nm	-	-	Lamp	-
?	Y2O2S:Eu	Red	626 nm	-	-	Lamp	-
?	3.5 MgO . 0.5 MgF2 . GeO2 :Mn	Red	655 nm	-	-	Lamp	3.5 MgO . 0.5 MgF2 . GeO2 :Mn
?	Mg5As2O11:Mn	Red	660 nm	-	-	Lamp	-
?	SrAl2O7:Pb	Ultraviolet	313 nm	-	-	Lamp	Ultraviolet
?	BaSi2O5:Pb	Ultraviolet	355 nm	-	-	Lamp	Ultraviolet
?	SrFB2O3:Eu(II)	Ultraviolet	366 nm	-	-	Lamp	Ultraviolet
?	SrB4O7:Eu	Ultraviolet	368 nm	-	-	Lamp	Ultraviolet
?	MgGa2O4:Mn(II)	Blue-Green	-	-	-	Lamp	Black light displays

[edit] 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:Eu (P22R), red (627 nm), 850 µs decay, afterglow, for low-energy X-ray
• Y₂O₂S:Pr, 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), <1 ns decay, no afterglow, ultrafast, for electrons
• ZnO:Ga, blue (390 nm), <5 ns decay, no afterglow, ultrafast, for electrons
• ZnO:Zn (P15), blue (495 nm), 8 µs decay, no afterglow, for low-energy electrons

• (Zn,Cd)S:Cu,Al (P22G), green (565 nm), 35 µs decay, low afterglow, for electrons
• ZnS:Cu,Al,Au (P22G), green (540 nm), 35 µs decay, low afterglow, for electrons
• ZnCdS:Ag,Cu (P20), green (530 nm), 80 µs decay, low afterglow, for electrons

• ZnS:Ag (P11), blue (455 nm), 80 µs decay, low afterglow, for alpha particles and electrons
• anthracene, blue (447 nm), 32 ns decay, no afterglow, for alpha particles and electrons
• plastic (EJ-212), blue (400 nm), 2.4 ns decay, no afterglow, for alpha particles and electrons

• Zn₂SiO₄:Mn (P1), green (530 nm), 11 ms decay, low afterglow, for electrons

• ZnS:Cu (GS), green (520 nm), decay in minutes, long afterglow, for X-rays

• NaI:Tl, for X-ray, alpha, and electrons
• CsI:Tl, green (545 nm), 5 µs decay, afterglow, for X-ray, alpha, and electrons

• ⁶LiF/ZnS:Ag (ND), blue (455 nm), 80 µs decay, for thermal neutrons
• ⁶LiF/ZnS:Cu,Al,Au (NDg), green (565 nm), 35 µs decay, for neutrons

[edit] References

[edit] See also

• photoluminescence
• cathodoluminescence
• laser

[edit] External links

Look up phosphor in Wiktionary, the free dictionary.

• a history of electroluminescent displays.
• Fluorescence, Phosphorescence
• CRT Phosphor Characteristics (P numbers)
• Composition of CRT phosphors
• Safe Phosphors
• Silicon-based oxynitride and nitride phosphors for white LEDs—A review
• [1] & [2] - RCA Manual, Fluorescent screens (P1 to P24)