1. Introduction
Excilamps (excimer and exciplex lamps) are sources of intense ultraviolet (UV) and vacuum ultraviolet (VUV) radiation based on spontaneous emission from excited rare-gas dimers (excimers) or rare-gas–halogen complexes (exciplexes). Unlike lasers, excilamps operate in an incoherent mode, offering high average power, relatively simple construction, long lifetime, and the ability to generate radiation at specific UV/VUV wavelengths without the use of mercury.
The development of excilamps has been actively pursued at the Laboratory of Optical Radiation of the High Current Electronics Institute (HCEI SB RAS, Tomsk, Russia). Their work demonstrates a wide range of lamp geometries, discharge modes, wavelengths, and practical applications.
2. Physical Principle of Excilamps
The operation of an excilamp is based on the formation of excited molecules such as Xe₂*, Kr₂*, Ar₂*, XeCl*, KrCl*, XeBr*, and others in an electrical discharge. These excited species are bound only in the excited state and dissociate after radiative decay, emitting photons at characteristic UV or VUV wavelengths (e.g., 172 nm for Xe₂*, 222 nm for KrCl*, 308 nm for XeCl*).
Dielectric barrier discharges (DBD), pulsed corona discharges, or capacitive discharges are typically used to excite the gas mixtures at pressures from tens to hundreds of Torr.
3. Types of Excilamps and Discharge Configurations
3.1 One- and Two-Barrier Dielectric Discharge Excilamps
In dielectric barrier discharge excilamps, one or both electrodes are covered by dielectric layers (commonly quartz). Two main configurations are used:
- One-barrier discharge lamps, where only one electrode is insulated.
- Two-barrier discharge lamps, where both electrodes are insulated.
These designs provide stable, uniform discharges and long gas mixture lifetimes. Xe₂* excilamps operating at 172 nm are a prominent example, achieving high radiation intensity and efficiency.
3.2 Cylindrical and Coaxial Designs
Typical designs include quartz cylindrical bulbs with internal and external electrodes. Often, the internal electrode also acts as a reflector to enhance radiation extraction. Such lamps can reach output powers of several watts to tens of watts, depending on geometry and excitation conditions.
3.3 Planar (Flat-Electrode) Excilamps
Planar excilamps use flat or slightly curved electrodes separated by a dielectric barrier. These lamps provide uniform irradiation over large areas and are especially suitable for surface treatment and photochemical applications. Radiation power densities up to tens of mW/cm² have been demonstrated for XeCl, XeBr, and KrCl excilamps.
3.4 Pulsed Corona and Windowless Excilamps
Dielectric barrier pulsed corona excilamps and windowless designs are used mainly for VUV radiation (Ar₂*, Kr₂*). By eliminating output windows and minimizing absorption losses, these lamps can efficiently deliver short-wavelength radiation (126–146 nm) directly into reactors or vacuum systems.
3.5 Capacitive Discharge Excilamps
Capacitive discharge excilamps are used primarily for rare-gas–halogen mixtures such as XeCl, XeBr, and KrCl. These lamps demonstrate good stability and long lifetimes, with output powers up to several watts and operational lifetimes exceeding thousands of hours.
4. Power Supply and Excitation
Efficient operation of excilamps requires specialized pulsed power supplies capable of delivering:
- High voltages (typically 2.5–5.5 kV),
- Frequencies from tens to hundreds of kHz,
- Short pulse durations (0.5–2 µs),
- Unipolar or bipolar excitation modes.
Such power supplies ensure uniform discharge formation, high excitation efficiency, and controlled power deposition into the gas.
5. Spectral Characteristics and Efficiency
Excilamps emit in narrow spectral bands characteristic of the excimer or exciplex molecule:
- Xe₂*: ~172 nm (VUV)
- Kr₂*: ~146 nm (VUV)
- Ar₂*: ~126 nm (VUV)
- KrCl*: ~222 nm (far-UV)
- XeBr*: ~282 nm (UV)
- XeCl*: ~308 nm (UV)
High efficiencies have been reported, reaching:
- Up to ~45% for Xe₂* emission,
- ~35% for Kr₂* emission,
- ~10% or more for XeCl*, XeBr*, and KrCl* excilamps.
Radiation power densities above 100 mW/cm² and average output powers up to ~100 W have been demonstrated for some barrier-discharge excilamps.
6. Lifetime and Reliability
A major advantage of excilamps is their long operational lifetime. Experimental studies show:
- Gas mixture lifetimes exceeding 1,000 hours for most excilamps,
- Lifetimes over 12,000 hours for XeCl barrier discharge excilamps,
- Stable radiant output during long-term continuous operation.
These characteristics make excilamps suitable for industrial and continuous-use applications.
7. Reactors and System Integration
Excilamps are often integrated into photoreactors for chemical and environmental processes. Reactor configurations include:
- Single-emitter reactors for laboratory-scale experiments,
- Multi-emitter systems with several Xe₂* excilamps for higher throughput,
- Modular reactor designs for industrial-scale applications.
Such systems enable efficient irradiation of gases, liquids, or surfaces with VUV/UV light.
8. Applications of Excilamps
8.1 Water and Air Purification
UV and far-UV excilamps (especially KrCl at 222 nm and Xe₂ at 172 nm) are effective for disinfection, decomposition of organic pollutants, and advanced oxidation processes. They are used for contact-free water purification and air treatment.
8.2 Surface Treatment and Material Processing
Excilamps are widely applied for:
- Surface activation of polymers,
- Cleaning and modification of materials,
- Improving adhesion and wettability.
Short-wavelength UV radiation enables efficient photochemical reactions without excessive heating.
8.3 Photochemistry and Photocatalysis
VUV excilamps initiate photochemical reactions that are difficult to achieve with longer-wavelength UV sources. Applications include ozone generation, VOC decomposition, and photocatalytic processes.
8.4 Biomedical and Sterilization Applications
Far-UV excilamps (around 222 nm) are of particular interest for sterilization and disinfection, as they can inactivate microorganisms while reducing damage to human tissue compared to conventional 254 nm sources.
8.5 Scientific and Industrial Research
Due to their spectral selectivity and high intensity, excilamps are valuable tools in spectroscopy, plasma physics, and experimental photonics research.
9. Conclusion
Excilamps represent a versatile and efficient class of UV and VUV radiation sources. Research and development at HCEI SB RAS have demonstrated a wide range of lamp designs, high efficiencies, long lifetimes, and scalable output powers. With applications spanning environmental protection, materials science, photochemistry, and healthcare, excilamps are an important alternative to traditional mercury-based UV lamps and continue to gain significance in modern technology.
References
S. M. Avdeev, M. I. Erofeev, and V. F. Tarasenko, “Photoreactors with Xe2* excilamps for environmental and industrial applications,” High Energy Chemistry, vol. 44, no. 6, pp. 433–440, 2010.
V. F. Tarasenko, M. I. Lomaev, E. A. Sosnin, V. S. Skakun, D. V. Shitz, M. I. Erofeev, and S. M. Avdeev, VUV and UV excilamps, High Current Electronics Institute, Siberian Branch of the Russian Academy of Sciences (HCEI SB RAS), Tomsk, Russia, December 2009.
V. F. Tarasenko, E. A. Sosnin, M. I. Lomaev, and D. V. Shitz, “Barrier discharge excilamps: Physics, technology and applications,” Plasma Sources Science and Technology, vol. 15, no. 2, pp. 161–175, 2006.
E. A. Sosnin, M. I. Lomaev, and V. F. Tarasenko, “Excimer lamps and their applications,” Journal of Physics D: Applied Physics, vol. 39, no. 16, pp. R333–R366, 2006.
V. F. Tarasenko (Ed.), Excilamps: Efficient Sources of Ultraviolet Radiation, Nova Science Publishers, New York, 2008.
M. I. Lomaev, E. A. Sosnin, V. S. Skakun, and V. F. Tarasenko, “High-power dielectric barrier discharge excilamps and their applications,” IEEE Transactions on Plasma Science, vol. 38, no. 4, pp. 948–956, 2010.
D. V. Shitz, V. F. Tarasenko, and E. A. Sosnin, “VUV excilamps based on rare-gas dimers,” Quantum Electronics, vol. 40, no. 4, pp. 335–343, 2010.
