Daiyu Hayashi

Discharge efficiency in high-Xe-content plasma display panels

We study theoretically the overall output performance and the dominating reaction processes of the vacuum ultraviolet (UV) radiation production in high-Xe partial pressures in plasma display panels (PDPs) with Ne–Xe gas mixtures. A two-dimensional self-consistent fluid model is applied for the simulations of discharges and UV radiation in sustaining phases of PDPs. The UV intensity increases with the Xe partial pressure (PXe). The discharge efficiency also increases with PXe. The resonant radiation from Xe(3P1) dominates for 3.5%, while that from Xe2(3Σu+) becomes dominant over Xe(3P1) for 10%–30%. Remarkably for 30%, the intensity from Xe2(1Σu+) is even larger than that from Xe(3P1). It is found that for higher PXe, the UV radiation mainly consists of the excimer radiation from Xe2(1Σu+) and Xe2(3Σu+). Here, Xe(3P1) does not play a role itself as the UV radiator of the resonant radiation (147 nm), but as the precursor to Xe2(1Σu+), which results in the excimer radiation (173 nm).

Role of Reaction Products in F ¡ Production in Low-Pressure, High-Density CF4 Plasmas

In this paper we report on the role of reaction products in F- production in low-pressure, high-density CF4 plasmas. The spatial distributions and temporal variations of F- density (n-), and plasma parameters in the discharge phase and afterglow of helicon-wave CF4 plasmas which had an electron density (ne) of 1011–1013 cm-3 were measured by the laser-photodetachment technique combined with a heated Langmuir probe. The relationship between the n-/ne ratio and the degree of ionization was investigated in the discharge phase. The n-/ne ratios in the plasma column of highly ionized plasmas were much higher than those expected from dissociative electron attachment to CF4, and n-/ne ratios were larger by several orders of magnitude in the outer region. The efficient increase in n- was observed in the afterglow and n-/ne was enhanced by increasing the discharge duration. It is concluded that the attachment to the reaction products contributes greatly to F- production in low-pressure, high-density plasmas.

Diagnostics of Fluorine Negative Ions by Laser Photodetachment Combined with a Heated Probe in High-Density CF 4 Plasmas

This paper reports the absolute density and reaction kinetics of fluorine negative ions (F-) in a low-pressure, high-density CF4 plasma excited by helicon-wave discharge. Probe-assisted laser photodetachment has been adopted for the measurement of the F- density. To avoid the deposition of insulated fluorocarbon films on the probe surface, the probe tip was heated to approximately 1000 K. For a CF4 gas pressure of 2 mTorr, the ratio of the F- density to the electron density was n -/n e 0.06 in the active discharge plasma with a plasma density of 1.8 ×1012 cm-3. In the afterglow, the electron density decreased rapidly with a decay time constant of 10 µs, while the F- density had a peak at ~15 µs after the termination of the rf power. The ratio n -/n e increased up to ~5.7 in the afterglow. The production and loss processes of F- are discussed based on the experimental observations.

Low-pressure indium-halide discharges for fluorescent illumination applications

Low-pressure gas discharges of molecular radiators were studied for fluorescent lighting applications with a goal of reducing the energy loss due to the large Stokes shift in phosphors of conventional mercury-based fluorescent lamp technology. Indium halides (InCl, InBr, and InI) were chosen as the molecular radiators that generate ultraviolet to blue light emissions. The electrical characteristics and optical emission intensities were measured in discharges containing gaseous indium halides (InCl, InBr, and InI) as molecular radiators. The low-pressure discharges in indium halide vapor showed potential as a highly efficient gas discharge system for fluorescent lighting application.

Electronic Structures of CF3- for Studying Dissociative Electron Attachment to CF3 Radicals

To elucidate the process of dissociative electron attachment (DA) to CF3 radicals, the potential energy surfaces of CF3, CF3- and the electronic state CF3-* temporally produced in DA are calculated at the MP2/6-311++G** level by Gaussian 98. The electron affinities (EA) of the CF3, vibrational frequencies of CF3 and CF3- are also calculated. Our results are in good agreement with the experimental values (cf. EA=1.72 eV, experimental value = 1.7±0.2 eV). It is elucidated that the electron capture by CF3 under the adiabatic approximation occurs by the incident of a low-kinetic energy (~0.6 eV) electron. DA to CF3 is a slightly endothermic process with 0.2–0.4 eV. It is concluded that CF3 radicals produce F- ions via DA with low kinetic energies. This process is considered to be very important in the kinetics of low-energy electrons in fluorocarbon plasmas.

A broadband LED source in visible to short-wave-infrared wavelengths for spectral tumor diagnostics

Various tumor types exhibit the spectral fingerprints in the absorption and reflection spectra in visible and especially in near- to short-wave-infrared wavelength ranges. For the purpose of spectral tumor diagnostics by means of diffuse reflectance spectroscopy, we developed a broadband light emitting diode (LED) source consisting of a blue LED for optical excitation, Lu3Al5O12:Ce3+,Cr3+ luminescent garnet for visible to near infrared emissions, and Bismuth doped GeO2 luminescent glass for near-infrared to short-wave infrared emissions. It emits broad-band light emissions continuously in 470–1600 nm with a spectral gap at 900–1000 nm. In comparison to the currently available broadband light sources like halogen lamps, high-pressure discharge lamps and super continuum lasers, the light sources of this paper has significant advantages for spectral tissue diagnostics in high-spectral stability, improved light coupling to optical fibers, potential in low light source cost and enabling battery-drive.

Novel Molecular Discharge Light Sources

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 the most promising candidate combining highly attractive green and red emission band systems with very high dissociation energy (8.2 eV) which ensures that the molecule is stable even at 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 ZrX4 (X = Cl, Br, I) together with a stable, but volatile oxygen compound (like MoO2X2) and realized thus highly attractive, novel gas discharge light sources.