Lifetime investigation of excimer UV sources

The principle underlying the operation of excimer lamps relies on the radiative decomposition of excimer states created by a dielectric barrier discharge in a rare gas or a mixture of rare gas±halogen. In excimer lamp technology, no electrodes are in direct contact with the discharge gases, thus avoiding any reaction between the discharge and the electrodes or contamination of the gas with evaporated electrode material, as well as electrode corrosion which can occur in conventional lamps leading to short operational lifetimes. Therefore, an investigation of the lifetime of these lamps is of vital importance before any industrial application can be seriously considered. In this paper, the detailed lifetime of 172, 222, and 308 nm excimer lamps as well as overall ef®ciency, stability, and any output ¯uctuations, have been investigated. It was found that ef®ciency increased as input power decreased. It was noted however that colour centres were formed within the ®rst 60 h of operation for 172 nm excimer lamps which reduced their output intensity during their time. By contrast, 100% of the original UV intensity output by the 222 and 308 nm lamps was still maintained after up to 4000 h operating time. These results are compared with the lifetime of conventional mercury lamps. # 2000 Elsevier Science B.V. All rights reserved