What does excimer mean?
An excimer is a short-lived molecule formed when an atom or molecule in an electronically excited state binds temporarily to another atom or molecule of the same kind. Unlike ordinary molecules, an excimer cannot exist in its ground state: as soon as it loses its excitation energy, its components fly apart. This fleeting existence gives excimers a valuable property — when they decay, they release energy as light, often in the ultraviolet range. That behaviour underpins the excimer laser, a device that produces intense, finely controlled ultraviolet beams used to reshape corneas in LASIK eye surgery, etch microchips, and perform precision industrial work. The term derives from "excited dimer," reflecting the pair of identical units involved. Closely related is the "exciplex," an analogous complex formed from two different species. Though strictly scientific, the word has entered everyday awareness chiefly through its medical applications, where excimer lasers have enabled vision correction for millions of people worldwide.
nounA transient molecule formed by the association of an excited atom or molecule with another atom or molecule of the same kind, existing only in an energized state. Excimers are important because they dissociate upon losing their excitation, often emitting light in the process.
- A short-lived excited complex formed between two identical atoms or molecules that exists only while energized and dissociates on returning to the ground state.
- By extension, any similar excited complex involving unlike partners (more precisely called an exciplex), as used loosely in some technical contexts.
"An excimer laser uses a short-lived excited dimer of argon and fluorine to emit intense ultraviolet light."
"The ophthalmologist reshaped the cornea using pulses from an excimer laser."
"In solution, the aromatic hydrocarbons showed strong excimer emission at a longer wavelength than their normal fluorescence."
Regular English plural. The plural is common in scientific literature when discussing multiple such complexes or different types across various gas mixtures.
"Rare-gas halide excimers are the active media in most commercial excimer lasers."
The 'excimer' lasers that correct your vision at the eye doctor don't cut with heat — they break molecular bonds so precisely they remove less than a millionth of a millimetre of tissue per pulse.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of excimer
The word "excimer" originated in twentieth-century physical chemistry as a contraction of "excited dimer," describing a molecule composed of two identical units that exists only while one of them remains in an excited state. It belongs to a family of chemical terms built on the Greek-derived suffix "-mer" (from "meros," meaning "part") seen in "dimer," "monomer," "polymer," and "isomer." The term gained wider currency with the development of excimer lasers in the 1970s, which brought the word into medical and industrial vocabulary alongside its parent terms.
How excimer is actually used
"Excimer" is a technical term used almost exclusively in physics, chemistry, optics, and medicine (particularly ophthalmology). It is neutral in register but formal; it rarely appears outside scientific writing. Strictly speaking, a complex formed from two different species is an "exciplex," though "excimer" is sometimes applied loosely to both.
Easily confused with excimer
A dimer is a stable molecule of two identical subunits, whereas an excimer exists only in an excited state and falls apart when it returns to the ground state.