Study of pulsed neon–xenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization

Abstract

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.PACS:

Efficiency of an Exciplex DBD Lamp Excited Under Different Methods

“…Finally, it is interesting to point out that this paper, devoted to exciplex molecules radiation, complements previous investigations reporting significant enhancement of the lamp performance with pulsed mode supplies, for lamps where radiation is mainly obtained from excimer molecules (both for DBD [28] and non-DBD reactors [29]); as formation of excimer and exciplex molecules are based on different mechanisms and evidence of an impact of the supply method over the exciplex molecules formations was found in this research, further studies about this impact are recommended.…”

Comparison of surface vacuum ultraviolet emissions with resonance level number densities. II. Rare-gas plasmas and Ar-molecular gas mixtures

“…15,16 Rare gas plasmas at higher pressure are also used in lighting (including VUV light sources) and plasma display panels. 17,18 We have previously reported VUV fluxes in pure argon ICP discharges, determined from the concentrations of Ar (3p 5 4s) resonance atoms that produce the VUV emissions, measured using noninvasive optical emission spectroscopy (OES) in the visible/near-infrared wavelength range. 19 A model for VUV emissions that couples radiation trapping and the measured rare-gas resonance level densities compared favorably with measurements along an axial line of sight made with a calibrated VUV photodiode sensitive below 120 nm.…”

Positive columns sustained jointly by microwaves and DC voltages for lighting applications: experimental results in pure argon

“…Among the recent proposals for the elimination of mercury in UV discharges sources, the use of xenon (Xe) and krypton (Kr) based mixtures has been favorably envisaged [2][3][4] since, with rare-gas discharges, there is no problem of chemical reactivity with electrodes, especially when heated at high temperatures. Unfortunately, the lighting efficiency of xenon fluorescent discharges [3] and of pulsed neon-xenon discharges [4] reaches only 50% of the lighting efficiency obtained with mercury-based mixtures, a too low value for envisaging lighting applications.…”