- Terbium (Tb) is a silvery-gray, malleable, and ductile rare earth metal with atomic number 65, belonging to the lanthanide series of the periodic table.
- Its electron configuration is [Xe] 4f⁹ 6s², and it typically forms Tb³⁺ ions as its most stable oxidation state, although the +4 state occurs in some compounds such as terbium(IV) oxide (TbO₂). The atomic structure consists of sixty-five protons, generally ninety-three or ninety-four neutrons in its stable isotopes, and sixty-five electrons arranged in six shells.
- Naturally occurring terbium is composed of a single stable isotope, terbium-159 (¹⁵⁹Tb), making it monoisotopic.
- Terbium does not occur naturally in elemental form but is found in rare earth minerals such as monazite ((Ce,La,Nd,Th)PO₄), bastnäsite ((Ce,La)(CO₃)F), and xenotime (YPO₄). It is typically obtained through solvent extraction and ion-exchange processes used to separate it from other lanthanides. Major production sites are located in China, which is the dominant global supplier, with smaller sources in the USA, India, Brazil, and Australia.
- The element was discovered in 1843 by Swedish chemist Carl Gustaf Mosander, who separated it from yttrium oxide extracted from the mineral gadolinite. Terbium’s name comes from the Swedish village of Ytterby, the source of the mineral from which it was first identified—a site that also gave its name to several other elements, including yttrium, erbium, and ytterbium.
- Terbium is notable for its unique luminescent properties, especially in its trivalent state (Tb³⁺). Terbium-doped phosphors emit bright green light and are used in fluorescent lamps, LED lighting, and color television screens. In solid-state devices, terbium is employed in green phosphors such as terbium-doped gadolinium oxysulfide (Gd₂O₂S:Tb³⁺), which is used in X-ray imaging screens. Terbium is also used in magnetostrictive alloys such as Terfenol-D (an alloy of terbium, dysprosium, and iron), which changes shape in response to magnetic fields and is applied in precision actuators, sonar systems, and vibration control. Additionally, terbium compounds are used in laser crystals, optical devices, and as dopants in solid-state fuel cells.
- Chemically, terbium is moderately reactive. It oxidizes slowly in dry air but more rapidly in moist air, forming a protective oxide layer. Terbium reacts slowly with cold water, producing terbium hydroxide and hydrogen gas, and reacts more quickly with hot water or acids to form Tb³⁺ salts. Its +4 oxidation state is less common but chemically interesting, as terbium(IV) oxide acts as a strong oxidizing agent.
- Biologically, terbium has no known essential function in living organisms. Its compounds are considered to have low to moderate toxicity, but precautions should be taken to avoid inhalation of dust or ingestion of soluble salts.
- From an environmental standpoint, terbium in mineral form is stable and not inherently hazardous. However, mining and processing of rare earth elements, including terbium, can result in environmental challenges, such as the release of chemical waste and associated radioactive materials from thorium- and uranium-containing minerals.
