Light sources emitting in the UV spectral region are widely used in techniques involving photo-chemical processes, e.g., curing of inks, adhesives, varnishes and coatings, photolithography, UV induced growth of dielectrics, UV induced surface modification, and cleaning or material deposition. Incoherent sources of UV radiation have some advantages over laser sources because of their lower cost, a huge area of irradiation, and ease of use, especially when large-scale industrial processes are envisaged.
Mercury lamps (λ = 253.7 nm) are widely spread UV sources, but their production, use, and disposal of old lamps pose a threat to human health and environmental pollution. Comparing with commonly used mercury lamps, excimer lamps have a number of advantages. A specific feature of an excimer molecule is the absence of a strong bond in the ground electronic state. Thanks to this, high-intensity UV radiation can be extracted from a plasma without significant self-absorption. This makes possible to convert efficiently energy deposited to the active medium into UV radiation.
Excimer lamps are referred to cold sources of UV radiation since the radiating surface of excimer lamps remains at relatively low temperatures in contrast with traditional UV lamps like a mercury one. Because the medium does not need to be heated, excimer lamps reach their peak output almost immediately after they are turned on.
Rare gas and rare gas-halide excimer lamps generally radiate in the ultraviolet (UV) and vacuum-ultraviolet (VUV) spectral regions (see table). 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.
Light sources emitting photons in the energy range of 3.5–10 eV find applications in many fields due to the ability of high-energy photons to cleave most chemical bonds and kill microbes destroying nucleic acids and disrupting their DNA. Examples of excimer lamp applications include purification and disinfection of drinking water, pool water, air, sewage purification, decontamination of industrial waste, photochemical synthesis and degradation of organic compounds in flue gases and water, photopolymerization of organic coatings and paints, and photo-enhanced chemical vapor deposition. In all cases UV photons excite species or cleave chemical bonds, resulting in the formation of radicals or other chemical reagents, which initiate a required reaction.
An excimer lamp has selective action. UV radiation of a given wavelength can selectively excite species or generate required radicals. Such lamps can be useful for photophysical and photochemical processing such as UV curing of paints, varnishes, and adhesives, cleansing and modifying surface properties, polymerization of lacquers and paints, and photo-degradation of a variety of pollutants. Photo-etching of polymers is possible using different wavelengths: 172 nm by xenon excimer, 222 nm by krypton chloride, and 308 nm by xenon chloride. Excimer UV sources can be used for microstructuring large-area polymer surfaces. XeCl-excimer lamps (308 nm) are especially suitable to get tan.
Fluorescence spectroscopy is one of the most common methods for detecting biomolecules. 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. Detecting this re-emitted light, one can judge the density of labeled molecules. Lanthanide complexes are commonly used as fluoroprobes. Due to their long lifetime, they play an important role in Förster resonance energy transfer (FRET) analysis.
At present, excimer lamps are coming into use in ecology, photochemistry, photobiology, medicine, criminalistics, petrochemistry, physics, microelectronics, different engineering tasks, wide-ranging technologies, science, various branches of industry including the food industry, and many others.