Novel molecular discharge light sources

R Hilbig (1) , A Koerber (1) , S Schwan (1) , D Hayashi (1)

1 Philips Research Europe

A systematic investigation into transition metal halides and ~oxides showed the high potential of transition metal oxides as visible radiators for highly efficient gas discharge light sources. Zirconium monoxide (ZrO) has been identified as most promising candidate combining highly attractive green and red emission band systems with very high dissociation energy (8.2eV) which assures that the molecule is stable even in the hot plasma centre. Thus far, however, it has been impossible to keep ZrO in the gas phase of a closed discharge vessel, because at wall temperature usually compounds are formed which have negligible vapour pressures. We succeeded in establishing a regenerative chemical cycle by filling ZrX 4 (X=Cl, Br, I) together with a stable, but volatile oxygen compound (like MoO 2 X 2) and realized thus highly attractive, novel gas discharge light sources. The aim of any lamp engineer is to develop a white light source with good colour rendering properties (Ra 8 > 80) and highest luminous efficacy . Current discharge lamps - emitting mainly atomic radiation - are reaching only about half of the theoretical efficacy limit of 200-230 lm/W. The possible efficacy rise by increasing atomic radiation is limited by self-absorption of the atomic lines (= radiation trapping). This limitation does not apply for molecular radiation, since the molecular emission is distributed over a huge number of molecular transitions which is several orders of magnitude higher than the corresponding number of atomic lines. As a matter of fact, various molecular radiators have been investigated in gas discharges for lighting applications in the course of the last century [ 1-15 ]. Nevertheless there still is no large-scale commercially applied discharge lamp type on the market whose radiation output is dominated by molecular emission. Molecular discharge light sources investigated in the past suffered from serious drawbacks: Severe chemical attack of the wall material, corrosion of the tungsten electrodes and - in most cases - poor plasma efficacy. Therefore, we strive for a breakthrough efficacy improvement by introducing novel molecular radiators for discharge lamps.

Mots clés: 42.72.Bj; 52.80.-s; 33.20.-t; 82.33.Xj

R Hilbig, A Koerber, S Schwan, D Hayashi. Novel molecular discharge light sources. Journal of Physics D: Applied Physics, 2011, 44 (22), pp.224009. ⟨10.1088/0022-3727/44/22/224009⟩. ⟨hal-00620594⟩