Material · Engineered

Phosphor

A material that absorbs energy and gives it back as visible light — and the reason europium and terbium are mined.

A phosphor absorbs energy — ultraviolet light, an electron beam, an X-ray — and re-emits it as visible light. Nothing about that requires a rare earth, and phosphors were made from zinc sulfide and other cheap compounds for decades. What rare earths brought was colour purity.

A rare earth ion emits at sharply defined wavelengths, because the electrons involved are shielded from the crystal around them. That makes a red that is genuinely red rather than a broad orange smear, and it is why colour television and the fluorescent lamp both changed abruptly when europium became available.

Despite the name, phosphors need contain no phosphorus. The word is older than the element's chemistry and means light-bearing.

Economic significance

Phosphors are why europium and terbium have a market. Europium gives red and blue, terbium green, and the trichromatic fluorescent lamp needed all three — which made a handful of rare earths strategically interesting decades before magnets did.

That market has since shrunk, and instructively. LED lighting uses far less phosphor than a fluorescent tube and a different one, and the collapse in europium demand after the lighting transition is one of the clearer examples of a critical-material shortage being solved by the application disappearing rather than by new supply.

X-ray intensifying screens and scintillators are the other significant use, and the one gadolinium and lutetium are bought for.

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

Europium — element · red and blue, and the reason a colour television picture and a fluorescent lamp both changed abruptly when it became available
Terbium — element · green, and the third of the trichromatic set
Yttrium — element · the host lattice of the red phosphor rather than the emitter — yttrium oxysulfide and vanadate carry the europium
Gadolinium — element · in X-ray intensifying screens, which is the use gadolinium is actually bought for
Cerium — element · in the scintillators and in the yellow LED phosphor

is used as

Lighting — application · every fluorescent lamp and every white LED — the diode makes blue and the phosphor makes the rest
Medical imaging — application · as the intensifying screen that turns X-rays into light a detector can read, which is what keeps the dose down

is produced by

Firing — process · the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it

succeeded

Incandescent lamp — object · by way of fluorescent and then LED lighting, where the light comes from a phosphor converting shorter wavelengths rather than from anything being hot

is used in

Smartphone — object · in the display, where rare earth emitters convert the backlight or drive the pixel directly

Sources

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

Questions this page answers

Where it comes from, and what it becomes

Follow Phosphor 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

Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (to 1200–1300 °C, which is the vitrification that separates it from earthenware — and it is a temperature rather than a recipe) → Stoneware → is sourced from (a clay that survives 1200 °C and above, which an earthenware clay does not) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (to 1000–1150 °C, below vitrification, which is why it stays porous and why it was achievable before anybody could build a hotter kiln) → Earthenware → is sourced from (almost any clay, which is why it is the ceramic every early culture reached first) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (shaped and dried, then heated past the point where its minerals break down irreversibly) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Refractory brick → is composed of (as silica brick, which is what made the Siemens-Martin open hearth possible and is destroyed by a basic slag) → Quartz
Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (present in most clay bodies, and the reason firing schedules slow through 573 degrees in both directions) → Quartz
Phosphor → is produced by (the host lattice and the activator ion are fired together at high temperature, so the rare earth is built into the crystal rather than mixed with it) → Firing → takes as input (shaped and dried, then heated past the point where its minerals break down irreversibly) → Clay → is sourced from (plagioclase weathers to clay as readily as potassium feldspar does) → Plagioclase

These are the most distinct paths back. Phosphor can be traced through others besides.

Downstream — what it becomes

Phosphor → is used in (in the display, where rare earth emitters convert the backlight or drive the pixel directly) → Smartphone → is used in (and it is where four separate raw-material arguments meet — the 3TG conflict minerals, cobalt, the rare earths, and everything too dispersed to recover) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
Phosphor → is used as (every fluorescent lamp and every white LED — the diode makes blue and the phosphor makes the rest) → Lighting
Phosphor → is used as (as the intensifying screen that turns X-rays into light a detector can read, which is what keeps the dose down) → Medical imaging
Phosphor → is used in (in the display, where rare earth emitters convert the backlight or drive the pixel directly) → Smartphone → is associated with (the object the whole period arrives at, and the one that put roughly sixty elements into a pocket) → The semiconductor era complete chain
Phosphor → is used in (in the display, where rare earth emitters convert the backlight or drive the pixel directly) → Smartphone → is used as (and the radio front end alone reaches gallium arsenide, gallium nitride and a dozen filters made of piezoelectric ceramic) → Telecommunications