Study of pulsed neonxenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization

E Robert (1) , S Point (1) , S Dozias (1) , R Viladrosa (1) , J M Pouvesle (1)

1 GREMI - Groupe de recherches sur l'énergétique des milieux ionisés

This work deals with the study and optimization of mercury free fluorescent discharge tubes for publicity lightning applications. The experimental set up allows for the time resolved spectroscopy from 110 nm up to 900 nm, the photometric characterization in a large volume integrating sphere, and the current and voltage measurement of microsecond duration signals delivered by lab-developed pulsed drivers. The glow and afterglow radiative process analysis indicates that the best performance measured with the pulsed excitation of rare gas plasma, in comparison with the conventional AC excitation, essentially originates from the efficient plasma relaxation during the afterglow at the benefit of the VUV resonance line radiated at 146.9 nm for xenon. The fit of the VUV time resolved experimental measurements with the results issued from a simplified kinetic model of neon xenon plasmas, evidence the crucial role of molecular ions production during the glow phase and of their radiative recombination during the afterglow. The pulse duration and the gas mixture pressure appear as two experimental parameters which influence, studied over an extended range, has been demonstrated to allow a significant sign performance enhancement. There exists an optimum pulse duration range, which results in the appearance of limited stepwise excitation and ionization processes, favourable for an intense afterglow VUV production. The pressure dependence study shows that the best performance for pulsed excitation are obtained in Ne/Xe (100/1) mixtures around 50 mbar, at the difference of AC driven Ne/Xe plasma for which the best conditions were reported to be of a few mbar. This pressure increase results both in the VUV and sign light output enhancement and the successful continuous operation of pulsed mercury free signs for time as long as 4000 hours with neither electrode erosion, nor glass or phosphor degradation nor chromatic coordinate variation. For the green phosphor covered, 65 cm long and 13 mm inside diameter signs, the efficiency of pulsed neon xenon discharge likely to be operated for a few thousand hours reaches 50 % of that of the same tube filled with mercury based mixtures.

Mots clés: Physical Sciences

E Robert, S Point, S Dozias, R Viladrosa, J M Pouvesle. Study of pulsed neonxenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization. Journal of Physics D: Applied Physics, 2010, 43 (13), pp.135202. ⟨10.1088/0022-3727/43/13/135202⟩. ⟨hal-00569567⟩