Terbium is a silvery-white, malleable lanthanide metal used in green phosphors, solid-state devices, and magneto-optical materials. It is paramagnetic at room temperature.
The electron configuration of terbium is [Xe] 4f9 6s2. In compounds, terbium most often forms the +3 oxidation state, resulting in a 4f8 configuration for the Tb3+ ion.
The most common oxidation state of terbium is +3 (Tb3+). It can also exist in the +4 oxidation state in certain oxides such as TbO2. The +3 state dominates in aqueous chemistry and solid-state compounds.
Terbium ions (Tb3+) emit bright green fluorescence when excited by ultraviolet or electron radiation due to f–f transitions. This makes it ideal for color television screens, LED lights, and fluorescent lamps.
Terbium is used in:
Terfenol-D is an alloy of Terbium, Dysprosium, and Iron (Tb0.3Dy0.7Fe2). It exhibits large magnetostrictive effects — meaning it changes shape in a magnetic field. Terbium provides high magnetostrictive strain, making this alloy valuable in sonar systems, actuators, and sensors.
Terbium slowly oxidizes in air, forming an oxide layer of Tb2O3, and reacts with water to produce hydroxide and hydrogen gas:
\(\mathrm{4\,Tb(s) + 3\,O_2(g) \rightarrow 2\,Tb_2O_3(s)}\)
\(\mathrm{2\,Tb(s) + 6\,H_2O(l) \rightarrow 2\,Tb(OH)_3(s) + 3\,H_2(g)}\)
To prevent oxidation, terbium metal is stored under mineral oil or inert atmosphere.
Terbium is paramagnetic at room temperature but becomes ferromagnetic below 219 K and antiferromagnetic below 230 K. Its magnetic susceptibility is influenced by the 4f9 configuration and unpaired electrons. These properties are utilized in magneto-optical and magnetostrictive materials.
Terbium(III) compounds are typically light green to yellow-green. The green luminescence arises from 4f–4f electronic transitions within Tb3+. This property makes Tb compounds popular as dopants in phosphor materials.
Terbium is obtained from rare-earth minerals such as bastnäsite and monazite. It is extracted through chemical separation processes involving solvent extraction and ion-exchange chromatography, since terbium occurs mixed with other lanthanides in ores.
Terbium is considered to have low toxicity, but its dust and compounds should be handled carefully. Inhalation or ingestion may cause mild irritation to the respiratory tract. Terbium compounds should be handled with gloves and in ventilated areas.
When terbium is oxidized in air, the following reaction occurs:
\(\mathrm{4\,Tb(s) + 3\,O_2(g) \rightarrow 2\,Tb_2O_3(s)}\)
In aqueous solution, Tb3+ can be reduced electrochemically to metallic terbium:
\(\mathrm{Tb^{3+}(aq) + 3e^- \rightarrow Tb(s)}\)