Radiometric efficiency of low pressure barium discharges

Abstract

We have studied, both experimentally and numerically, the radiometric efficiency of low-pressure barium-argon positive column discharges. Using a 14 mm inner diameter alumina discharge tube to reduce chemical reactivity, we have operated discharges with Ba vapor pressures corresponding to a range of oven temperatures from 600 to 800°C, Ar buffer gas pressures of 0.5 and 5 Torr, and currents of 100-800 mA. The spectral power distribution has been determined by examining the visible radiation emitted perpendicular to the discharge axis from a small aperture in the side of the alumina discharge tube. Absolute emitted powers were determined by comparison to a calibrated tungsten-quartz-halogen lamp. The measured efficiencies for production of visible radiation from the positive column ranged from 2.5% to 52%. These efficiencies correspond to luminous efficacies ranging from 6 to 97 lm/W. Strong emission on Ba ion lines at 455.4, 493.4, 614.2, and 649.7 nm contributed significantly to the best efficiency, 52%, and yielded a white light. A numerical model, incorporating a substantial number of excited levels and atomic processes, has been used to examine the same conditions. The model reproduces most of the major experimental trends.

Feasibility study of a low pressure barium discharge lamp

“…The difference may be accounted for, at least in part, by the nonuniformity of the experimental discharges, leading to a higher ''local'' efficacy above the barium melt. This conclusion is consistent with experimental measurements by Peng et al 5 It must also be emphasized that the extra power required to maintain the discharge walls at 650-700°C would result in a considerable loss of efficacy, even if electrode losses ͑which are also considerable͒ could be eliminated by radio-frequency excitation.…”

“…Our latest theoretical efforts support this finding. Many of our conclusions are supported in an independent experimental activity by Peng et al 5 We begin the description of our work by noting that barium has some disadvantages as a potential light source. The strong reactivity of barium with a wide variety of standard lamp materials including glass, silica, and polycrystalline alumina ͑PCA͒ led to the selection of yttria (Y 2 O 3 ) as a viable arc tube material.…”

“…This is definitely true of arc tubes made of unprotected quartz, which exhibited a bright spot just above the barium. The higher efficacies reported by Peng et al 5 may be due to this effect. Axial variations are not included in the model, so it was not possible to investigate this effect numerically.…”

“…These lines represent most of those included in Peng et al. 5 All the spectral lines listed in Table III were treated as optically thick, since the lower states are highly populated and act as effective ground state levels. Electron impact excitation cross sections from the ground state to these levels were computed by Fursa and Bray.…”

Aktuelle Entwicklungen auf dem Gebiet der anorganischen Leuchtstoffe

“…Diese Eigenschaften führen zu vergleichsweise hohen Quantenausbeuten. [16,92] So hergestellte dotierte Nanopartikel La-PO 4 [94,95] Mo/Ar [96] oder Edelgasen mit Chlorbeimengungen wie Xe/Cl 2 [97] reagiert das Edelgasplasma kaum mit der Röhrenwand und dem Elektrodenmaterial. [98] Abbildung 4.…”