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Concept
Excimer lamp
Summary
An excimer lamp (or excilamp) is a source of ultraviolet light based on spontaneous emission of excimer (exciplex) molecules.
Excimer lamps are quasimonochromatic light sources operating over a wide range of wavelengths in the ultraviolet (UV) and vacuum ultraviolet (VUV) spectral regions. Operation of an excimer lamp is based on the formation of excited dimers (excimers), which spontaneously transiting from the excited state to the ground state result in the emission of UV-photons. The spectral maximum of excimer lamp radiation is specified by a working excimer molecule (see table below).
Excimers are diatomic molecules (dimers) or polyatomic molecules that have stable excited electronic states and an unbound or weakly bound (thermally unstable) ground state. Initially, only homonuclear diatomic molecules with a stable excited state but a repulsive ground state were called excimers (excited dimers). The term "excimer" was later extended to refer any polyatomic molecule with a repulsive or weakly bound ground state. One can also come across the term "exciplex", meaning an excited complex. It is also an excimer molecule but not a homonuclear dimer. For instance, Xe2*, Kr2*, Ar2* are excimer molecules, while XeCl*, KrCl*, XeBr*, ArCl*, Xe2Cl* are referred to exciplex molecules. Dimers of rare gases and rare gas-halogen dimers are the most spread and studied excimers. Rare gas-halide trimers, metal excimers, metal-rare gas excimers, metal-halide excimers, and rare gas-oxide excimers are also known, but they are rarely used.
An excimer molecule can exist in an excited electronic state for a limited time, as a rule from a few to a few tens of nanoseconds. After that, an excimer molecule transits to the ground electronic state, while releasing the energy of internal electronic excitation in the form of a photon. Owing to a specific electronic structure of an excimer molecule, the energy gap between the lowest bound excited electronic state and the ground state amounts from 3.
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