Yttrium aluminium garnet
| 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 (+/- .010) |
| Birefringence | none |
| Pleochroism | none |
| Dispersion | .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 | |
Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is also one of three phases of the yttrium-aluminium composite, the other two being yttrium aluminium monoclinic (YAM, Y4Al2O9) and yttrium aluminium perovskite (YAP, YAlO3).
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.
YAG for a period was used in jewelry as a diamond and other gemstone simulant. Colored variants and their doping elements include: green (chromium), blue (cobalt), red (manganese), yellow (titanium), purple (neodymium), pink, and orange. As faceted gems they are valued (as synthetics) for their clarity, durability, high refractive index and dispersion. The critical angle of YAG is 33 degrees. YAG cuts similar to natural garnet, with polishing being performed with alumina or diamond (50,000 or 100,000) on common polishing laps. YAG has low heat sensitivity.
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