View source for Yttrium aluminium garnet

{{Short description|Synthetic crystalline material}}
{{Infobox mineral
| name        = Yttrium aluminium garnet
| category    = synthetic mineral
| boxwidth    =
| boxbgcolor  =
| image       = File:Yttrium-aluminum garnet (synthetic gemstone) 1.jpg
| imagesize   =
| caption     =
| formula     = Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>
| molweight   =
| color       = Usually colorless, but may be pink, red, orange, yellow, green, blue, purple
| habit       =
| system      = Cubic
| twinning    =
| cleavage    = None
| fracture    = Conchoidal to uneven
| mohs        = 8.5
| luster      = Vitreous to subadamantine
| polish      = Vitreous to subadamantine
| refractive  = 1.833±0.010
| opticalprop = Single refractive
| birefringence = None
| dispersion  = 0.028
| pleochroism = None
| fluorescence= ''Colorless'' stones - inert to moderate orange in long wave, inert to weak orange in short wave; ''blue'' and ''pink'' stones - inert; ''yellow-green'' stones - very strong yellow in long and short wave also phosphoresces; ''green'' stones - strong red in long wave, weak red in short wave
| absorption  =
| streak      =
| gravity     = 4.5–4.6
| density     =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  =
| diaphaneity =
| other       =
| references  = <ref name="GRG">[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, {{ISBN|0-87311-019-6}}</ref>
}}

'''Yttrium aluminium garnet''' ('''YAG''', [[Yttrium|Y]]<sub>3</sub>[[Aluminium|Al]]<sub>5</sub>[[Oxygen|O]]<sub>12</sub>) is a synthetic [[crystal]]line material of the [[garnet]] group. It is a [[Crystal system|cubic]] [[yttrium]] [[aluminium]] oxide phase, with other examples being YAlO<sub>3</sub> (YAP<ref>
{{cite web |url=https://materials.springer.com/isp/crystallographic/docs/sd_1924025 |title={{chem|Y|Al|O|3}}; YAP ({{chem|Y|Al|O|3}} ht) Crystal Structure |website=Springer Materials |access-date=2019-12-23}}.
</ref>) in a [[Crystal system|hexagonal]] or an orthorhombic, [[perovskite]]-like form, and the monoclinic Y<sub>4</sub>Al<sub>2</sub>O<sub>9</sub> (YAM<ref>
{{cite web |url=https://materials.springer.com/isp/crystallographic/docs/sd_1924026 |title={{chem|Y|4|Al|2|O|9}}; YAM ({{chem|Y|4|Al|2|O|9}} rt) Crystal Structure |website=Springer Materials |access-date=2020-01-28}}
</ref>).<ref name=Sim>{{cite journal |last1=Sim | first1=S.M. | last2=Keller | first2=K.A. | last3=Mah | first3=T.I. |year=2000 | title=Phase formation in yttrium aluminium garnet powders synthesized by chemical methods. | journal=Journal of Materials Science | volume=35 | issue=3 | pages=713–717 |bibcode = 2000JMatS..35..713S |doi = 10.1023/A:1004709401795 | s2cid=92455146 }}</ref>

Due to its broad optical transparency,<ref>{{Cite journal |last1=Franta |first1=Daniel |last2=Mureșan |first2=Mihai-George |date=2021-12-01 |title=Wide spectral range optical characterization of yttrium aluminum garnet (YAG) single crystal by the universal dispersion model |url=https://opg.optica.org/abstract.cfm?URI=ome-11-12-3930 |journal=Optical Materials Express |language=en |volume=11 |issue=12 |pages=3930 |doi=10.1364/OME.441088 |bibcode=2021OMExp..11.3930F |s2cid=239534251 |issn=2159-3930|doi-access=free }}</ref> low internal stress, high hardness, chemical and heat resistance, YAG is used for a variety of optics.<ref>{{Cite web |title=Custom YAG (Yttrium Aluminium Garnet, Yttrium Aluminium Oxide Y3Al5O12) optics |url=https://www.knightoptical.com/custom/infrared-optics/yag/ |access-date=2022-03-15 |website=Knight Optical |language=en}}</ref> Its lack of [[birefringence]] (unlike sapphire) makes it an interesting material for high-energy/high-power laser systems. [[Laser damage threshold|Laser damage]] levels of YAG ranged from 1.1 to 2.2&nbsp;kJ/cm<sup>2</sup> (1064&nbsp;nm, 10&nbsp;ns).<ref>{{Cite journal |last1=Do |first1=Binh T. |last2=Smith |first2=Arlee V. |date=2009-06-20 |title=Bulk optical damage thresholds for doped and undoped, crystalline and ceramic yttrium aluminum garnet |url=https://opg.optica.org/abstract.cfm?URI=ao-48-18-3509 |journal=Applied Optics |language=en |volume=48 |issue=18 |pages=3509–3514 |doi=10.1364/AO.48.003509 |pmid=19543361 |bibcode=2009ApOpt..48.3509D |issn=0003-6935|url-access=subscription }}</ref>

YAG, like garnet and [[sapphire]], has no uses as a laser medium when pure. However, after being doped with an appropriate ion, YAG is commonly used as a host material in various [[solid-state laser]]s.<ref name="kamisky97">{{cite book |last1=Kalisky |first1=Yehoshua |chapter=Hosts for Solid State Luminescent Systems |editor1-last=Rotman |editor1-first=Stanley R. |title=Wide-Gap Luminescent Materials: Theory and Applications: Theory and Applications |date=1997 |publisher=Springer Science & Business Media |isbn=9780792398370 |url=https://books.google.com/books?id=5C75sPGBUkkC}}</ref> Rare earth elements such as [[neodymium]] and [[erbium]] can be [[doping (semiconductors)|doped]] into YAG as active laser ions, yielding [[Nd:YAG laser|Nd:YAG]] and [[Er:YAG laser|Er:YAG]] lasers, respectively. [[Cerium]]-doped YAG (Ce:YAG) is used as a [[phosphor]] in [[cathode-ray tube]]s and white [[light-emitting diode]]s, and as a [[scintillator]].

==Gemstone YAG==
YAG for a period{{when|date=April 2022}} was used in [[jewelry]] as a [[diamond simulant|diamond]] and other [[gemstone]] simulant. Colored variants and their doping elements include:<ref name="GRG"/> green ([[chromium]]), blue ([[cobalt]]), red ([[manganese]]), yellow ([[titanium]]), blue/pink/purple ([[neodymium]], depending on light source), pink, and orange. As faceted gems they are valued (as synthetics) for their clarity, durability, high [[refractive index]] and [[Dispersion (optics)|dispersion]], and occasionally properties like simulating [[alexandrite]]'s color-changing property. The [[critical angle (optics)|critical angle]] of YAG is 33 degrees. YAG cuts like natural [[garnet]], with polishing being performed with [[alumina]] or [[diamond]] (50,000 or 100,000 grit) on common polishing laps. YAG has low heat sensitivity.<ref>{{cite web |title=How to Spot a Fake Diamond: What These 13 Tests Really Mean! |url=https://www.gemsociety.org/article/how-to-spot-a-fake-diamond/ |publisher=International Gem Society |first=Addison |last=Rice |access-date=2021-02-15}}</ref>

As a synthetic gemstone YAG has numerous varietal and trade names, as well as a number of misnomers. Synonymous names include: ''alexite'', ''amamite'', ''circolite'', ''dia-bud'', ''diamite'', ''diamogem'', ''diamonair'', ''diamone'', ''diamonique'', ''diamonite'', ''diamonte'', ''di'yag'', ''geminair'', ''gemonair'', ''kimberly'', ''Linde simulated diamond'', ''nier-gem'', ''regalair'', ''replique'', ''somerset'', ''triamond'', ''YAIG'', and ''yttrium garnet''. Production for the gem trade decreased after the introduction of synthetic [[cubic zirconia]]; {{as of|1995|lc=yes}} there was little production.<ref name="GRG"/> Some demand exists as synthetic garnet, and for designs where the very high refractive index of cubic zirconia is not desirable.{{Citation needed|date=February 2021}}

==Technical-use varieties==
{{More citations needed section|date=April 2013}}

===Nd:YAG===
{{Main article|Nd:YAG laser}}
[[File:Yag-rod.jpg|thumb|Nd:YAG laser rod 0.5 cm in diameter.]]
[[Neodymium]]-[[dopant|doped]] YAG ('''Nd:YAG''') was developed in the early 1960s, and the first working Nd:YAG laser was invented in 1964. Neodymium-YAG is the most widely used [[active laser medium]] in [[solid-state laser]]s, being used for everything from low-power continuous-wave lasers to high-power [[Q-switching|Q-switched]] (pulsed) lasers with power levels measured in the kilowatts.<ref>V. Lupei, A. Lupei "Nd:YAG at its 50th anniversary: Still to learn" Journal of Luminescence 2015, {{doi|10.1016/j.jlumin.2015.04.018}}</ref> The thermal conductivity of Nd:YAG is higher and its [[fluorescence]] lifetime is about twice as long as that of [[neodymium doped yttrium orthovanadate|Nd:YVO<sub>4</sub>]] crystals, however it is not as efficient and is less stable, requiring more precisely controlled temperatures.  The best absorption band of Nd:YAG for [[laser pumping|pumping the laser]] is centered at 807.5&nbsp;nm, and is 1&nbsp;nm wide.<ref>{{cite web |url=http://www.redoptronics.com/Nd-YAG-crystal.html |title=ND:YAG crystal (neodymium doped yttrium aluminium garnet) |work=Red Optronics}}</ref>

Most Nd:YAG lasers produce infrared light at a wavelength of 1064&nbsp;nm. Light at this wavelength is rather dangerous to vision, since it can be focused by the eye's [[lens (anatomy)|lens]] onto the [[retina]], but the light is invisible and does not trigger the [[blink reflex]]. Nd:YAG lasers can also be used with [[frequency doubling]] or frequency tripling [[crystal]]s, to produce green light with a wavelength of 532&nbsp;nm or ultraviolet light at 355&nbsp;nm, respectively.

The [[dopant]] concentration in commonly used Nd:YAG crystals usually varies between 0.5 and 1.4 molar percent. Higher dopant concentration is used for pulsed lasers; lower concentration is suitable for continuous-wave lasers. Nd:YAG is pinkish-purple, with lighter-doped rods being less intensely colored than heavier-doped ones. Since its absorption spectrum is narrow, the hue depends on the light under which it is observed.

===Nd:Cr:YAG===
YAG doped with [[neodymium]] and [[chromium]] ('''Nd:Cr:YAG''' or '''Nd/Cr:YAG''') has absorption characteristics which are superior to Nd:YAG.  This is because energy is absorbed by the broad absorption bands of the Cr<sup>3+</sup> dopant and then transferred to Nd<sup>3+</sup> by dipole-dipole interactions.<ref>{{cite journal | doi = 10.1109/PROC.1966.5112 | title = Crystalline solid lasers| author = Z. J. Kiss and R. J. Pressley| journal =Proceedings of the IEEE| volume =54 | issue =10 | year =1996| page =1236 }}</ref>  This material has been suggested for use in [[solar-pumped laser]]s, which could form part of a [[solar power satellite]] system.<ref>{{cite journal| doi =10.1016/j.optcom.2006.07.002| title =Disk-type Nd/Cr:YAG ceramic lasers pumped by arc-metal-halide-lamp| year =2006| author =Saiki, T| journal =Optics Communications| volume =268| issue =1| page =155| last2 =Imasaki| first2 =K| last3 =Motokoshi| first3 =S| last4 =Yamanaka| first4 =C| last5 =Fujita| first5 =H| last6 =Nakatsuka| first6 =M| last7 =Izawa| first7 =Y|bibcode = 2006OptCo.268..155S }}</ref>

===Er:YAG===
{{Main article|Er:YAG laser}}
[[Erbium]]-doped YAG ('''Er:YAG''') is an active laser medium lasing at 2940&nbsp;nm. Its absorption bands suitable for pumping are wide and located between 600 and 800&nbsp;nm, allowing for efficient flashlamp pumping. The dopant concentration used is high: about 50% of the yttrium atoms are replaced. The Er:YAG laser wavelength couples well into water and body fluids, making this laser especially useful for medicine and dentistry uses; it is used for treatment of [[tooth enamel]] and in cosmetic surgery. Er:YAG is used for noninvasive monitoring of [[blood sugar]]. The mechanical properties of Er:YAG are essentially the same as Nd:YAG. Er:YAG operates at wavelengths where the threshold for eye damage is relatively high (since the light is absorbed before striking the [[retina]]), works well at room temperature, and has high [[slope efficiency]]. Er:YAG is pink.<ref>{{cite journal |last1=Lv |first1=Haodong |last2=Bao |first2=Jinxiao |last3=Chao |first3=Luomeng |last4=Song |first4=Xiwen |last5=An |first5=Shengli |last6=Zhou |first6=Fen |last7=Wang |first7=Qingchun |last8=Ruan |first8=Fei |last9=Zhang |first9=Wen |last10=Guo |first10=Wenrong |last11=Zhang |first11=Yonghe |title=Development mechanism of Ce-doped red zirconia ceramics prepared by a high-temperature reduction method |journal=Journal of Alloys and Compounds |date=2019 |volume=797 |pages=931–939 |doi=10.1016/j.jallcom.2019.05.216 |s2cid=182269171 |url=https://www.sciencedirect.com/science/article/abs/pii/S0925838819318985 |access-date=11 April 2022 |quote=Yttrium aluminum garnet (YAG) is an important optical ceramic material, especially when doped with Nd and Er, when it exhibits a specific color. For instance, Er:YAG is pink and Nd:YAG is a light reddish purple|url-access=subscription }}</ref>

===Yb:YAG===
[[Ytterbium]]-doped YAG ('''Yb:YAG''') is an active laser medium lasing at 1030&nbsp;nm, with a broad, 18&nbsp;nm wide absorption band at 940&nbsp;nm.<ref>{{Cite journal|last1=Grant-Jacob|first1=James A.|last2=Beecher|first2=Stephen J.|last3=Parsonage|first3=Tina L.|last4=Hua|first4=Ping|last5=Mackenzie|first5=Jacob I.|last6=Shepherd|first6=David P.|last7=Eason|first7=Robert W.|date=2016-01-01|title=An 115 W Yb:YAG planar waveguide laser fabricated via pulsed laser deposition|journal=Optical Materials Express|language=EN|volume=6|issue=1|pages=91|doi=10.1364/ome.6.000091|issn=2159-3930|bibcode=2016OMExp...6...91G|url=https://eprints.soton.ac.uk/384775/2/ome-6-1-91.pdf|doi-access=free}}</ref> It is one of the most useful media for high-power [[DPSS laser|diode-pumped solid state lasers]]. The dopant levels used range between 0.2% and 30% of replaced yttrium atoms. Yb:YAG has very low fractional heating, very high [[slope efficiency]],<ref>{{Cite book|last1=Beecher|first1=Stephen J.|last2=Grant-Jacob|first2=James A.|last3=Hua|first3=Ping|last4=Shepherd|first4=David|last5=Eason|first5=Robert W.|last6=Mackenzie|first6=Jacob I.|title=Lasers Congress 2016 (ASSL, LSC, LAC) |chapter=Laser Performance of Yb-doped-Garnet Thin Films Grown by Pulsed Laser Deposition |date=2016-10-30|chapter-url=https://www.osapublishing.org/abstract.cfm?URI=ASSL-2016-AM3A.3|pages=AM3A.3|language=EN|publisher=Optical Society of America|doi=10.1364/assl.2016.am3a.3|isbn=978-1-943580-20-0}}</ref> and no excited-state absorption or up-conversion, high mechanical strength and high thermal conductivity. Yb:YAG can be pumped by reliable [[InGaAs]] [[laser diode]]s at 940 or 970&nbsp;nm.

Yb:YAG is a good substitute for 1064&nbsp;nm Nd:YAG in high-power applications, and its frequency-doubled 515&nbsp;nm version can replace the 514&nbsp;nm [[argon laser]]s.

===Nd:Ce:YAG===
[[Neodymium]]-[[cerium]] double-doped YAG ('''Nd:Ce:YAG''', or '''Nd,Ce:YAG''') is an active laser medium material very similar to Nd:YAG. The added cerium atoms strongly absorb in the [[ultraviolet]] region and transfer their energy to the neodymium atoms, increasing the pumping efficiency; the result is lower thermal distortion and higher power output than Nd:YAG at the same pumping level. The lasing wavelength, 1064&nbsp;nm, is the same as for Nd:YAG. The material has a good resistance to damage caused by UV from the pump source, and low [[lasing threshold]]. Usually 1.1–1.4% of Y atoms are replaced with Nd, and 0.05–0.1% with Ce.

===Ho:Cr:Tm:YAG===
[[Holmium]]-[[chromium]]-[[thulium]] triple-doped YAG ('''Ho:Cr:Tm:YAG''', or '''Ho,Cr,Tm:YAG''') is an active laser medium material with high efficiency. It lases at 2080&nbsp;nm and can be pumped by a flashlamp or a laser diode.<ref name="Koechner">{{cite book| page=49|url = https://books.google.com/books?id=8yM4yF_B72QC&pg=PA49| title =Solid-state laser engineering| author =Koechner, Walter | publisher= Springer| date = 2006| isbn = 978-0-387-29094-2}}</ref> It is widely used in military, medicine, and meteorology. It works well at room temperature, has high [[slope efficiency]], and operates at a wavelength where the threshold for eye damage is relatively high. When pumped by a diode, the 785&nbsp;nm band for Tm<sup>3+</sup> ion can be used.<ref name="Koechner"/> Other major pump bands are located between 400 and 800&nbsp;nm. The dopant levels used are 0.35 atom.% Ho, 5.8 atom.% Tm, and 1.5 at.% Cr. The rods have green color, imparted by chromium(III).

===Tm:YAG===
[[Thulium]]-doped YAG ('''Tm:YAG''') is an active laser medium that operates between 1930 and 2040&nbsp;nm. It is suitable for diode pumping. A dual-mode Tm:YAG laser emits two frequencies separated by 1&nbsp;GHz.

===Cr<sup>4+</sup>:YAG===
[[Chromium]] (IV)-doped YAG ('''Cr:YAG''') provides a large absorption cross section in the 0.9-1.2 micrometer spectral region, which makes it an attractive choice as a passive [[Q-switch]] for Nd-doped lasers. The resulting devices are solid-state, compact and low-cost. Cr:YAG has high damage threshold, good thermal conductivity, good chemical stability, resists [[ultraviolet]] radiation, and is easily machinable. It is replacing more traditional Q-switching materials like [[lithium fluoride]] and organic [[dye]]s. The dopant levels used range between 0.5 and 3 percent (molar). Cr:YAG can be used for passive Q-switching of lasers that operate at wavelengths between 1000 and 1200&nbsp;nm, such as those based on Nd:YAG, [[Neodymium doped yttrium lithium fluoride|Nd:YLF]], [[Neodymium doped yttrium orthovanadate|Nd:YVO<sub>4</sub>]], and Yb:YAG.

Cr:YAG can be also used as a laser gain medium itself, producing [[tunable laser]]s with outputs adjustable between 1350 and 1550&nbsp;nm. The Cr:YAG laser can generate [[ultrashort pulse]]s (in the femtoseconds range) when it is pumped at 1064&nbsp;nm by a Nd:YAG laser.<ref>{{cite encyclopedia  |title=Chromium-doped gain media |url=https://www.rp-photonics.com/chromium_doped_gain_media.html |encyclopedia=Encyclopedia of Laser Physics and Technology |publisher=RP Photonics |first=Rüdiger |last=Paschotta |access-date=April 2, 2011}}</ref>

Cr:YAG has been demonstrated in an application of [[non-linear optics]] as a self-pumped [[phase-conjugate mirror]] in a Nd:YAG "loop resonator".{{Citation needed|date=April 2011}} Such a mirror provides compensation of both phase and polarization aberrations induced into the loop resonator.

===Dy:YAG===
[[Dysprosium]]-doped YAG ('''Dy:YAG''') is a temperature-sensitive [[phosphor]] used in temperature measurements.<ref>{{cite journal |last1=Sevic |first1=Dragutin |title=Temperature sensing using YAG:Dy single-crystal phosphor |journal=The European Physical Journal D |date=2021 |volume=75 |issue=2 |page=56 |doi=10.1140/epjd/s10053-021-00068-w |bibcode=2021EPJD...75...56S |s2cid=234033077 |url=https://link.springer.com/article/10.1140/epjd/s10053-021-00068-w |access-date=20 April 2023|url-access=subscription }}</ref> The phosphor is excited by a laser pulse and its temperature-dependent fluorescence is observed. Dy:YAG is sensitive in ranges of 300–1700 [[kelvin|K]].<ref>{{cite journal| title=Surface thermometry by laser-induced fluorescence| last=Goss| first=L.P.|author2=Smith, A.A. |author3=Post, M.E. | journal=Review of Scientific Instruments| volume=60| issue=12| pages=3702–3706| year=1989| doi=10.1063/1.1140478|bibcode = 1989RScI...60.3702G }}</ref> The phosphor can be applied directly to the measured surface, or to an end of an [[optical fiber]]. It has also been studied as a single-phase white emitting phosphor in phosphor-converted white light-emitting diodes.<ref>{{cite journal|last1=Carreira|first1=J. F. C.|title=YAG:Dy – Based single white light emitting phosphor produced by solution combustion synthesis|journal=Journal of Luminescence|date=2017|volume=183|pages=251–258|doi=10.1016/j.jlumin.2016.11.017|bibcode=2017JLum..183..251C}}</ref>

===Sm:YAG===
[[Samarium]]-doped YAG ('''Sm:YAG''') is a temperature-sensitive phosphor similar to Dy:YAG.

===Tb:YAG===
[[Terbium]]-doped YAG ('''Tb:YAG''') is a phosphor used in [[cathode-ray tube]]s. It emits at yellow-green color, at 544&nbsp;nm.

===Ce:YAG===
[[Cerium]](III)-doped YAG ('''Ce:YAG''' or '''YAG:Ce''') is a phosphor, or a [[scintillator]] when in pure [[single-crystal]] form, with a wide range of uses. It emits yellow light when subjected to blue or ultraviolet light or to x-rays.<ref>[[George Blasse|G. Blasse]] and A. Bril, "A new phosphor for flying-spot cathode-ray tubes for color televisions", Appl. Phys. Lett., 11, 1967, 53-54 {{doi|10.1063/1.1755025}}</ref> It is used in white [[light-emitting diode]]s as a coating on a high-brightness blue InGaN diode, converting part of the blue light into yellow, which together then appear as white. Such an arrangement gives less than ideal [[color rendering]]. The output brightness decreases with increasing temperature, further altering device color output.{{Citation needed|date=August 2009}}

Ce:YAG is also used in some [[mercury-vapor lamp]]s as one of the phosphors, often together with Eu:Y(P,V)O<sub>4</sub> (yttrium phosphate-vanadate). It is also used as a phosphor in cathode-ray tubes, where it emits green (530&nbsp;nm) to yellow-green (550&nbsp;nm) light. When excited by electrons, it has virtually no afterglow (70 ns decay time). It is suitable for use in [[photomultiplier]]s.

Ce:YAG is used in [[Positron emission tomography|PET scanner]]s, high-energy [[gamma radiation]] and [[charged particle]] detectors, and high-resolution imaging screens for gamma, [[x-ray]]s, [[beta radiation]] and [[ultraviolet radiation]].

Ce:YAG can be further doped with [[gadolinium]].

==See also==
* [[Er:YAG laser]]
* [[Micro-pulling-down]]
* [[Nd:YAG laser]]
* [[Yttrium iron garnet]]

==References==
{{reflist}}
{{yttrium compounds}}
{{aluminium compounds}}

{{DEFAULTSORT:Yttrium Aluminium Garnet}}
[[Category:Yttrium compounds]]
[[Category:Aluminium compounds]]
[[Category:Synthetic minerals]]
[[Category:Optical materials]]
[[Category:Laser gain media]]
[[Category:Phosphors and scintillators]]
[[Category:Diamond simulants]]
[[Category:Aluminates]]