Erbium is a silvery lanthanide used in fiber-optic signal amplifiers (Er³⁺ dopants) and in pink colorants for glass and ceramics. It is malleable, relatively stable in air, and forms a protective oxide layer.
The ground-state electron configuration of erbium is [Xe] 4f12 6s2. In the common +3 oxidation state (Er3+), it loses the two 6s electrons and one 4f electron, resulting in a 4f11 configuration.
Erbium predominantly exhibits the +3 oxidation state in compounds such as Er2O3 and ErCl3. The +2 state is rare and unstable, typically found only in specialized intermetallic compounds or in reducing environments.
Erbium is used as a dopant in Erbium-Doped Fiber Amplifiers (EDFAs), which amplify optical signals in fiber-optic communication systems. The Er3+ ions emit light at around 1.55 µm wavelength — the optimal region for minimal loss in silica-based optical fibers.
In an EDFA, light from a laser pump (usually at 980 nm or 1480 nm) excites Er3+ ions in the fiber. These ions then emit photons through stimulated emission when signal light (at 1550 nm) passes through, amplifying the signal:
\(\mathrm{Er^{3+} + h\nu_{pump} \rightarrow Er^{3+*}}\)
\(\mathrm{Er^{3+*} + h\nu_{signal} \rightarrow 2h\nu_{signal} + Er^{3+}}\)
Common applications include:
Er3+ ions have distinct 4f–4f transitions that absorb light in the green region of the spectrum, transmitting pink to rose hues. This makes erbium a popular additive for artistic glass and eyewear lenses.
Erbium is a moderately reactive lanthanide. It forms a stable oxide layer in air and reacts slowly with water to form hydroxide and hydrogen gas:
\(\mathrm{2\,Er(s) + 6\,H_2O(l) \rightarrow 2\,Er(OH)_3(s) + 3\,H_2(g)}\)
With halogens, it forms typical trihalides such as ErCl3 and ErF3.
Erbium is paramagnetic at room temperature and becomes antiferromagnetic below ~19 K. Its magnetic behavior arises from the unpaired 4f electrons, which contribute to a strong magnetic moment.
Erbium and its compounds are considered to have low toxicity. However, fine powders may be irritating to skin, eyes, and lungs. Standard laboratory precautions (gloves, goggles, and ventilation) should be used when handling erbium compounds.
A typical oxidation reaction of erbium metal in air can be represented as:
\(\mathrm{4\,Er(s) + 3\,O_2(g) \rightarrow 2\,Er_2O_3(s)}\)
This oxide, Er2O3, is a pale pink solid used in ceramics, glass coloring, and as a precursor for erbium-doped materials.