4f electron

A 4f electron occupies one of the seven orbitals in the 4f subshell. In lanthanide atoms and ions, these electrons are relatively shielded by outer electrons and give rise to characteristic magnetic and spectroscopic properties.

Atomic orbital: A quantum state describing an electron’s spatial distribution and allowed energy in an atom. A 4f electron is defined by occupying a particular kind of atomic orbital.
Electron shielding: The reduction of an electron’s attraction to the nucleus by other electrons. Outer shells partly screen 4f electrons from changes in their chemical surroundings.
Lanthanide luminescence: Light emission from lanthanide ions, often produced by transitions between 4f electronic states. Shielded 4f transitions produce characteristic emission colors and narrow spectral lines.
3d electron: An electron occupying an orbital in the 3d subshell. 3d electrons are more exposed to bonding environments and often show stronger ligand-field effects.
Lanthanide series: The periodic-table series from lanthanum to lutetium, associated with progressive filling of the 4f subshell. The series displays how changing 4f occupancy alters atomic and ionic properties.
Azimuthal quantum number: The quantum number that specifies an electron subshell and its orbital angular momentum. Its value of three identifies the f subshell.
Spin–orbit interaction: The interaction between an electron’s spin and its orbital angular momentum. It splits and organizes the energy levels of lanthanide 4f configurations.
Neodymium-doped yttrium aluminum garnet: A solid-state laser material in which neodymium ions provide the active optical transitions. Its laser action relies on transitions involving the neodymium ion’s 4f electrons.
5f electron: An electron occupying an orbital in the 5f subshell, characteristic of actinide atoms and ions. 5f electrons are generally more spatially extended and chemically involved than 4f electrons.
Erbium: A lanthanide element whose trivalent ions have eleven 4f electrons. Er³⁺ provides well-known infrared transitions used in optical amplifiers.

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