Compound · Y3Al5O12

Yttrium aluminium garnet

A synthetic garnet that holds rare earth ions in a rigid lattice — the host crystal of most solid-state lasers, and the yellow in a white LED.

Optical medium

YAG is a synthetic crystal with the garnet structure, and almost none of its usefulness is about YAG itself. It is a host: a rigid, transparent, thermally conductive lattice with sites that a rare earth ion will sit in, and the ion is what does the work.

Which ion decides what the crystal is for. Neodymium gives the workhorse infrared laser used for cutting and marking; erbium gives a wavelength water absorbs strongly, which is what makes it a surgical and dental tool; holmium gives the wavelength used to break kidney stones; ytterbium gives the efficiency that fibre lasers exploit. Cerium turns blue light yellow, which is how a white LED is made.

Processing

Laser-grade YAG is grown by the Czochralski method, pulled from a melt at close to 2,000 °C over days, and the dopant is added to the charge so it enters the lattice as the crystal forms. Optical quality is unforgiving: a boule with a strain field or a scattering inclusion is not a slightly worse laser rod, it is not a laser rod.

For lighting the crystal quality does not matter, and cerium-doped YAG is used as a powder — a phosphor coating over a blue LED die, absorbing some of the blue and re-emitting yellow so the mixture reads as white. Almost every white LED in the world works this way.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

contains

Yttrium — element · the cation the dopant substitutes for — a rare earth ion of similar size slots into the yttrium site, which is what makes YAG a host at all
Aluminium — element · the other cation, and the rigid part of the lattice
Oxygen — element · the framework the two cations sit in
Neodymium — element · the commonest dopant, giving the infrared laser used for cutting, welding and marking
Erbium — element · doped in for a wavelength water absorbs strongly, which is what makes it a surgical and dental instrument
Holmium — element · for the wavelength used to break kidney stones, and effectively the only reason holmium is produced
Thulium — element · for a wavelength close to holmium's, in surgical and lidar use
Ytterbium — element · the efficient one — a small quantum defect means less waste heat, which is what fibre and disc lasers exploit
Lutetium — element · as lutetium aluminium garnet, the same structure with lutetium in the yttrium site, used where higher density is wanted
Cerium — element · the dopant that turns blue light yellow, which is how almost every white LED in the world is made

is produced by

Czochralski process — process · pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms

is used as

Lighting — application · as cerium-doped powder over a blue LED die, absorbing some of the blue and re-emitting yellow so the mixture reads as white

Sources

Material World
Our own writing
Wikidata
Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Yttrium aluminium garnet back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is sourced from (reduced with carbon in an electric arc furnace) → Quartz
Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (reduced with carbon to metallic tin) → Cassiterite
Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (reduced with coke in a blast furnace) → Hematite
Yttrium aluminium garnet → is produced by (pulled from a melt at close to 2,000 °C over days, with the dopant added to the charge so it enters the lattice as the crystal forms) → Czochralski process → takes as input (charged to the crucible already refined; the process changes its arrangement and its purity, not its identity) → Silicon → is produced by (carbothermic reduction of silica with coke in a submerged arc furnace, which is smelting in the strict sense even though no ore is involved) → Smelting → takes as input (the phosphate rock charged to the electric furnace, with coke to reduce it and silica to take up the calcium) → Apatite

These are the most distinct paths back. Yttrium aluminium garnet can be traced through others besides.

Downstream — what it becomes

Yttrium aluminium garnet → is used as (as cerium-doped powder over a blue LED die, absorbing some of the blue and re-emitting yellow so the mixture reads as white) → Lighting