Yttrium aluminium garnet
Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP) in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y4Al2O9 (YAM).
| Yttrium aluminium garnet | |
|---|---|
| General | |
| Category | synthetic mineral |
| Formula (repeating unit) | Y3Al5O12 |
| Crystal system | Cubic |
| Identification | |
| Color | Usually colorless, but may be pink, red, orange, yellow, green, blue, purple |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Mohs scale hardness | 8.5 |
| Luster | Vitreous to subadamantine |
| Specific gravity | 4.5–4.6 |
| Polish luster | Vitreous to subadamantine |
| Optical properties | Single refractive |
| Refractive index | 1.833±0.010 |
| Birefringence | None |
| Pleochroism | None |
| Dispersion | 0.028 |
| Ultraviolet 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 |
| References | |
Due to its broad optical transparency, low internal stress, high hardness, chemical and heat resistance, YAG is used for a variety of optics. Its lack of birefringence (unlike sapphire) makes it an interesting material for high-energy/high-power laser systems. Laser damage levels of YAG ranged from 1.1 to 2.2 kJ/cm2 (1064 nm, 10 ns).
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 lasers. Rare earth elements such as neodymium and erbium can be doped into YAG as active laser ions, yielding Nd:YAG and Er:YAG lasers, respectively. Cerium-doped YAG (Ce:YAG) is used as a phosphor in cathode ray tubes and white light-emitting diodes, and as a scintillator.