Measurements are made for variations of the effective secondary emission coefficient γ with reduced field E/p. Plane-parallel copper electrodes (5 cm diameter) are sustained with a dc voltage (0<V<1 kV) and can be separated by a variable distance (2 mm<d<1 cm). Current–voltage characteristics, Paschen curves, and γ(E/p) variations are shown for various rare gases (neon, argon, krypton, and xenon). γ(E/p) values are deduced from Paschen curves and published α/p(E/p) variations by using the self-sustain condition. Comparisons are made with various experimental or calculated results taken from the literature.
This experimental study concerns the secondary emission coefficient γ for two dielectrics (MgO and enamel) used in plasma display panels. Different pure rare gases were considered at pressures varying from 5 to 50 Torr. Here, we present the variations of coefficient γ as a function of the reduced field E/p. They were obtained by introducing the breakdown voltages measured experimentally on a sample of plasma panel, into the self-sustained equation. Concerning a 0.5 μm thick MgO layer, results are shown for five gases (helium, neon, argon, krypton, and xenon) whereas for a 25 μm thick enamel layer, they are presented for neon and xenon.
Borate phosphors, with formulations Y0.95Eu0.05BO3 (YBEu), Y0.95Tb0.05BO3 (YBTb), Y0.57Gd0.38Eu0.05BO3 (Y6G4BEu), and Y0.57Gd0.38Tb0.05BO3 (Y6G4BTb) have been synthesized by spray pyrolysis at the maximum temperature of 700 °C, and then annealed at 1200 °C. The yttrium oxide-doped phosphor Y0.95Eu0.05O1.5 (YOEu) was obtained by the same experimental conditions. The UV−VUV excitation spectra of the samples were recorded using synchrotron radiation. The emission intensities of these phosphors have also been investigated as a function of plasma gas pressure in a dedicated experimental setup. The intensities in the emission spectra were integrated, to compare the relative efficiencies of the phosphors. All phosphors were more efficient with increasing gas pressure in the plasma chamber. The emission intensity of YOEu was similar to that of YBEu or Y6G4BEu at low Ne−Xe pressure, but stronger at high pressure. For both lanthanide activators, the mixed borates Y6G4B and the pure YBO3 (YB) have about same luminescence efficiency at low pressure, but the Y6G4B are better matrices than YB at high Ne−Xe pressure. With the introduction of Gd3+ in the borates, the emission intensity is enhanced due to a better spectral overlap with the plasma emission at 173 nm, and also the occurrence of multiple energy transfers between Gd3+ ions before transfer to the emitter Eu3+ or Tb3+. A “color effect” with the variation of pressure in the plasma chamber is observed for the Eu3+-doped phosphors. The orange:red intensity ratio (i.e., 5D0 → 7F0,1 (560−600 nm)/5D0 → 7F2 (600−640 nm)) increases as the gas pressure is raised. This observation is related to the spectral changes occurring in the plasma, and it is corroborated by the observation of selective excitation in the VUV range of Eu3+ at C
i
versus C
1 crystallographic sites.
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