Er3

Er3+ refers to the trivalent oxidation state of erbium, the lanthanide element with atomic number 68. In most inorganic compounds, erbium exists as Er3+. Its electron configuration is [Xe] 4f11, and the 4f electrons are largely shielded by outer shells, producing sharp, relatively environment-insensitive optical transitions.

In solid-state lasers and optical amplifiers, Er3+ ions show important transitions within the 4f manifold, most notably the 4I13/2 to 4I15/2 transition around 1530–1565 nm, which yields emission near 1550 nm—a standard band for telecommunications. Population is typically created by pumping Er3+ at about 980 nm to the 4I11/2 level (followed by nonradiative relaxation to 4I13/2) or directly at around 1480 nm to the 4I13/2 level (in-band pumping).

Er3+-doped materials include silica-based glasses and fibers, phosphate glasses, tellurites, and crystalline hosts such as Er:YAG (erbium-doped yttrium aluminum garnet). The Er:YAG laser emits around 2.94 μm, arising from transitions involving the Er3+ energy levels in the solid-state crystal. Er3+-doped fiber technology forms the backbone of many long-haul optical communication systems, providing low-noise amplification in the 1550 nm window and enabling compact solid-state and fiber lasers.

Historically, erbium was discovered in 1842 by Carl Gustaf Mosander in minerals from Ytterby, Sweden, with the element named after the same locality. The Er3+ ion remains a central subject of study for photonics due to its favorable energy levels, long lifetimes, and compatibility with diverse host materials.