Efficient radiation production in a weakly ionized, low-pressure, nonequilibrium gallium-iodide positive column discharge plasma

Present-day computational techniques provide a possibility of evaluating properties of macrosystems using ab initio quantum chemistry and theories of elementary processes. Physical and chemical phenomena on very different timescales have to be taken into account (excitation, emission, chemical reactions, diffusion) at different levels of refining. This refining covers a very wide region of parameters starting from the structure of species up to the macro chemical mechanism of their conversion. This multilevel approach is described in detail in the paper and includes interaction and data transfer between different levels of phenomena description. In the framework of the approach, unknown properties of molecules, ions and atoms (structure, potential energy curves, transition dipole moments) are calculated based on quantum-chemical methods. The calculation results are used to evaluate rate characteristics of physical and chemical processes. The developed kinetic state-to-state scheme is then used to calculate the macro properties of the system under investigation. As an example of the multilevel approach, the emission properties of the Ar–GaI3 positive column discharge plasma were calculated using the Chemical Work Bench computational environment. The calculations yield the electron energy balance and emission efficiency as functions of plasma parameters.

Section: Comparison With Experimentssupporting

confidence: 86%

Section: Calculations On Electronically Excited States Ab Initio Calc...mentioning

confidence: 99%

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Multiscale multiphysics nonempirical approach to calculation of light emission properties of chemically active nonequilibrium plasma: application to Ar–GaI₃system

Адамсон¹,

Astapenko²,

Chernysheva³

et al. 2007

“…Unfortunately due to a glass lens we were not able to detect emission from the UV lines at 287/294 nm (4d-4p) in this experimental study. A recent experimental study of a gallium-based RF excited lamp [14] showed that 287/294 nm and 403/417 nm emission constituted ∼20% and 50%, respectively, of the total spectral output of that light source. Currently our results suggest that Ga atoms in the downstream region are selectively excited into the 5s 2 S 1/2 levels by collisions with excited nitrogen species, most likely the long-lived N*( 2 P) metastables (see figure 6), via the slightly exothermic reaction:…”

Section: Downstreammentioning

confidence: 99%

Gas phase optical emission spectroscopy during remote plasma chemical vapour deposition of GaN and relation to the growth dynamics

Corr¹,

Boswell²,

Carman³

2011

A remote plasma chemical vapour deposition (RPCVD) system for the growth of gallium nitride (GaN) thin films is investigated using optical emission spectroscopy (OES). The intensities of the various excited species in pure nitrogen as well as nitrogen/hydrogen plasmas are correlated with GaN film growth characteristics. We show a correlation between the plasma source spectrum, the downstream spectrum where trimethylgallium is introduced and the GaN film quality. In particular, we investigate the addition of hydrogen, which greatly affects the gas phase species and the GaN film characteristics. OES is demonstrated to be a valuable monitoring tool in a RPCVD system for optimization of GaN growth.

“…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][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Nevertheless there still is no large-scale commercially applied discharge lamp type on the market whose radiation output is dominated by molecular emission.…”

mentioning

confidence: 99%

Novel molecular discharge light sources

Hilbig¹,

Koerber²,

Schwan³

et al. 2011

Abstract.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.PACS numbers: 42.72. Bj, 82.33.Xj 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 radiationare 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][2][3][4][5][6][7][8][9][10][11][12][13][14][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.