It is a cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP[2]) in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y4Al2O9 (YAM[3]).

[6] Its lack of birefringence (unlike sapphire) makes it an interesting material for high-energy/high-power laser systems.

However, after being doped with an appropriate ion, YAG is commonly used as a host material in various solid-state lasers.

Colored variants and their doping elements include:[1] green (chromium), blue (cobalt), red (manganese), yellow (titanium), blue/pink/purple (neodymium, depending on light source), pink, and orange.

[9] 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.

[1] Some demand exists as synthetic garnet, and for designs where the very high refractive index of cubic zirconia is not desirable.

[10] The thermal conductivity of Nd:YAG is higher and its fluorescence lifetime is about twice as long as that of Nd:YVO4 crystals, however it is not as efficient and is less stable, requiring more precisely controlled temperatures.

The dopant concentration in commonly used Nd:YAG crystals usually varies between 0.5 and 1.4 molar percent.

This is because energy is absorbed by the broad absorption bands of the Cr3+ dopant and then transferred to Nd3+ by dipole-dipole interactions.

[12] This material has been suggested for use in solar-pumped lasers, which could form part of a solar power satellite system.

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 material has a good resistance to damage caused by UV from the pump source, and low lasing threshold.

A dual-mode Tm:YAG laser emits two frequencies separated by 1 GHz.

It is replacing more traditional Q-switching materials like lithium fluoride and organic dyes.

[citation needed] Such a mirror provides compensation of both phase and polarization aberrations induced into the loop resonator.

Dy:YAG is sensitive in ranges of 300–1700 K.[20] The phosphor can be applied directly to the measured surface, or to an end of an optical fiber.

[citation needed] Ce:YAG is also used in some mercury-vapor lamps as one of the phosphors, often together with Eu:Y(P,V)O4 (yttrium phosphate-vanadate).