When you look at the bright green color on your smartphone screen, thank terbium. This rare earth metal produces the brightest green phosphor in the world. Tb³⁺ ions emit green light with over 90% efficiency. The human eye is most sensitive to exactly this wavelength — 543 nm.
Terbium also made metal "move" with magnets. The Terfenol-D alloy based on terbium changes shape in a magnetic field. A 10 cm rod stretches by 2 mm! This is used in submarine sonars and precision sensors. Terbium is one of the rarest and most expensive rare earth elements.
Terbium is a silvery soft metal from the lanthanide group. It is quite rare: only 1.2 mg/kg in Earth's crust. That is less than gold in some deposits. 80% of world production comes from clays in southern China. Swedish chemist Carl Gustaf Mosander discovered terbium in 1843, isolating it from the mineral yttria. The element was named after the Swedish village of Ytterby — the same village that gave names to yttrium, erbium, and ytterbium.
Bulk terbium is stable in air. However, terbium powder is pyrophoric — it can ignite spontaneously when heated to 200 °C or from a spark. Terbium compounds have low toxicity, but Tb₂O₃ dust irritates eyes and the respiratory tract. Handle powder in a fume hood, wearing gloves and safety goggles. Store in sealed containers under argon.
Terbium produces the brightest green phosphor in the world. Tb³⁺ ions emit green light at 543 nm with over 90% efficiency. This is the exact wavelength that the human eye is most sensitive to.
The Terfenol-D alloy (terbium + dysprosium + iron) holds the record for magnetostriction. In a magnetic field, it changes length by 0.2%. A 10 cm rod stretches by a full 2 mm! This powers submarine sonars.
The village of Ytterby in Sweden gave its name to four elements: yttrium, terbium, erbium, and ytterbium. Scientists isolated four new elements from one rock — the mineral gadolinite. That has never happened anywhere else!
Terbium fluorescence fades extraordinarily slowly — over 1 to 2 milliseconds. That is a thousand times longer than ordinary dyes. So terbium is used as a marker in medical tests, where its signal is easy to distinguish from background noise.
Terbium is one of the most expensive rare earth elements. A kilogram of its oxide costs $600 to $1,500. The reason is scarcity: only 1.2 mg of terbium per kilogram of rock in Earth's crust.
Below 219 K (−54 °C), terbium becomes ferromagnetic — a magnet attracts it just like iron. This is one of the highest Curie temperatures among lanthanides. That is why terbium is studied for magnetic refrigeration.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
159Tb | 158.925347 | 100.00% | stable | — |
Separation from yttria