4f3

4f3 denotes the electron configuration 4f^3, indicating three electrons occupying the 4f subshell of an atom or ion. The 4f subshell contains seven orbitals and can hold up to 14 electrons; a 4f^3 occupancy occurs in several lanthanide ions, most notably trivalent neodymium, Nd3+, which has the ground-state configuration [Xe] 4f^3.

In 4f^3 configurations, the 4f electrons are relatively localized and shielded by the outer 5s and 5p electrons. This shielding makes the energy spacings between levels largely determined by intra-4f interactions and spin-orbit coupling, with less sensitivity to the surrounding lattice than outer-shell electrons. The resulting term structure comprises multiple microstates, and for Nd3+ the ground state is commonly described as 4I9/2, with a series of excited levels that give rise to distinct optical transitions.

Spectroscopy and materials science routinely exploit 4f^3 ions for their sharp, narrow lines arising from 4f-4f transitions. They are widely used in solid-state lasers and phosphors. The best-known example is neodymium-doped yttrium aluminum garnet, Nd:YAG, where the lasing transition originates from the 4F3/2 level to the 4I11/2 level, near 1064 nanometers. Beyond lasers, 4f^3 dopants appear in various host materials for luminescent applications, upconversion devices, and optical sensing.

See also: lanthanides, electron configuration, 4f block.