Excimer lamp
The term "excimer" was later extended to refer any polyatomic molecule with a repulsive or weakly bound ground state.
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.
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 3.5 to 10 eV, depending on a kind of an excimer molecule and provides light emission in the UV and VUV spectral region.
A typical spectral characteristic of excimer lamp radiation consists mainly of one intense narrow emission band.
The full width at half maximum of the emission band depends on a kind of an excimer molecule and excitation conditions and ranges within 2 to 15 nm.
The first way is due to a reaction of ion-ion recombination, i.e., recombination of a positive rare gas ion and a negative halogen ion: where RgX* is an exciplex molecule, and M is a collisional third partner, which is usually an atom or molecule of a gaseous mixture or buffer gas.
The pressure of a gaseous mixture is of great importance for efficient production of exciplex molecules due to the reaction of ion-ion recombination.
In this case, a halogen molecule or halogen-containing compound captures a weakly bound electron of an excited rare gas atom, and an exciplex molecule in an excited electronic state is formed: Since the harpoon reaction is a process of a two-body collision, it can proceed productively at a pressure significantly lower than that required for a three-body reaction.
Thus, the harpoon reaction makes possible the efficient operation of an excimer lamp at low pressures of a gaseous mixture.
Due to this, a low-pressure excimer lamp ensures the maximum efficiency in converting the pumping energy to UV radiation.
A feature of alkali halides is a similarity of their chemical bond with that of exciplex molecules in excited electronic states.
An advantage of using alkali halides is that both the substitution reactions can simultaneously proceed at low pressures with comparable productivity.
[10] Moreover, both excited atoms and ions of rare gas are effectively used in the production of exciplex molecules in contrast to excimer lamps using other halogen-carriers.
[11][12] A benefit of the DBD excimer lamps is that the electrodes are not in direct contact with the active medium (plasma).
Moreover, a dielectric barrier discharge ensures effective excitation of a gas mixture in a wide range of working pressures from a few torrs to more than one atmosphere.
Excimer lamps can be made in any desired shape of the radiating surface, satisfying requirements of a specific task.
Because the medium does not need to be heated, excimer lamps reach their peak output almost immediately after they are turned on.
Their unique narrow-band emission characteristics, high quantum efficiency, and high-energy photons make them suitable for applications such as absorption spectroscopy, UV curing, UV coating, disinfection, ozone generation, destruction of gaseous organic waste, photo-etching and photo-deposition and more other applications.
Biomolecules can be labeled with fluoroprobe, which then is excited by a short pulse of UV light, leading to re-emission in the visible spectral region.
Due to their long lifetime, they play an important role in Förster resonance energy transfer (FRET) analysis.
