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In this paper, we compared the inactivation of Bacillus subtilis spores in water by means of a dielectric-barrier-discharge (DBD)-driven XeI* excilamp and a low-pressure mercury lamp. The main part ( ~ 76%) of the excilamp output was due to the B → X transition of XeI* exciplex at 253 nm. It is shown for the first time that a better sterilization action is achieved with the DBD-driven XeI* excilamp compared with the monochromatic mercury lamp at the same UV dose. The contribution of an atomic iodine emission in the range of 178-207 nm has been confirmed. Germ-reduction experiments with the XeI* excilamp have been carried out in a steady-state mode and in a water-flow reactor.

The near-UV and visible mercury emissions from low-pressure discharges were studied under a range of rare gas hosts and different modes of operation. The optimization of the emission line intensities is achieved under different buffer gases for different operating modes. It is hypothesized that energy transfer processes occur between the rare gas metastable states and mercury atoms leading to the observed spectra.

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes and of xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. In both cases, that is, inner electrode type and external electrode type, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the VUV radiation of xenon excimers. The emission of light from phosphor shows that xenon excimers are generated effectively by pulsed discharge of high pressure xenon, because they are generated by three-body collision at the low electron temperature Te during the non-discharge period.

Summary form only given. Conventional technology for disinfection by UV irradiation is based on mercury lamps. The development of a new mercury-free UV lamp is very important due to the environmentally unfriendly nature of mercury. In present study we compared the inactivation of Bacillus subtilis spores in water by means of a developed dielectric barrier discharge-driven Xel* excilamp and a conventional low- pressure mercury lamp. Experiments have been carried out with the air-cooled sealed off lamp, filled with a Xe/L = 13.3/0.04 kPa mixture, which has been determined as optimum from the viewpoint of maximal UV output. The main part (-76%) of the excilamp output was due to the BrarrX transition of Xel* exciplex at 253 nm. The excilamp was excited using a custom built power supply, providing bipolar pulses with peak-to-peak voltage U = 0-4.4 kV, rising and falling times of 0.9 and 0.6 mus, f= 21.5-115 kHz. A more detail description of the design and output characteristics of a developed Xel* excilamp has been presente. It has been shown for the first time that better sterilization action is achieved with the developed DBD-driven Xel* excilamp compared to a conventional monochromatic mercury lamp at the same UV fluence. A reduction by more than 6 orders of magnitude of B. subtilis spores concentration (CFU/ml) has been reached and the D-value was about 5-9.5 mJ/cm2. A reduction by four orders of magnitude (99.99% inactivated microorganisms) was achieved at 22-25 mJ/cm2 for the Xel* excilamp and at 40 mJ/cm2 for the mercury lamp. An additional effect of the I* radiation at 206 nm and in the VUV range (178-188 nm) has been confirmed. It has been tested that the DBD-driven Xel* excilamp can be used for the inactivation of the microorganisms in a steady state mode or in the movable systems (drinking water treatment or food package sterilization).

The fluorescent lamps are widely used for general lighting because of their high efficacy, long life and so forth. Mercury which is used in fluorescent lamps for general lighting has a possibility to cause environmental problems. The author's group has been developing fluorescent lamps which contain only rare gases without mercury. The wavelength of the xenon resonance line is the longest in the rare-gas resonance lines, so that the Stokes-loss becomes smaller than the other rare-gases' cases. Therefore the authors have investigated pulsed xenon fluorescent lamps. However luminous flux of xenon fluorescent lamps was not large enough. The authors have been making efforts to improve luminous flux of the xenon lamp by expanding positive column. By setting an auxiliary external electrode on the outside wall of the lamp, positive column expands and luminous flux increases. However luminous efficacy decreases because power consumption through the external electrode is too large. So by using resistor, the current flowing through the external electrode is suppressed and power consumption decreased. Consequently higher luminous efficacy up to 100 lm/W with high luminance 6894 cd/m2 is achieved.

In this study, the spectroscopic characteristics of radiations from xenon pulsed plasma are measured experimentally as a study on a mercury-free fluorescent lamp. Each radiation waveform has two peaks and they vary according to the inner diameter of lamp and the pressure of xenon as follows: (a) As the inner diameter of lamps increases, the afterglow radiation, that is the second peak, decays faster. (b) As the xenon pressure increases the first peak of radiation just after the start of discharge decreases and the afterglow increases. The characteristics of afterglow are explained by the rate equation of metastable xenon atoms Xem, and its coefficients are determined through the experimental results. This equation shows that in order to obtain intense phosphor afterglow, i.e. strong radiation of xenon excimer, high pressure of xenon and large lamp diameter are desirable. Moreover, high pressure of xenon brings fast decay of afterglow. Then the afterglow radiation has no overlap on the first peak of next discharge at a high frequency. Consequently, higher pressure of xenon and large lamp diameter are desirable for high intensity and high efficacy for xenon fluorescent lamps.

A phosphor, SrAl12O19 doped with Pr (SA : Pr), is investigated in this research in order to improve the luminous efficacy of a mercury-free Xe discharge fluorescent lamp (FL). The obtained sample works as a quantum cutting phosphor which converts an absorbed photon of Xe emission at 172 nm into two visible photons, one at 401.8 nm and the other at 486.3, 526.3, 623.7 or 644.6 nm. The concentration of Pr is optimized and the visible emission of the phosphor becomes maximum at 5 mol%. The photoluminescence measurements show that the relative quantum efficiency of SA : Pr (Pr: 5 mol%) is 38.4% of BaMgAl10O17 : Eu2+ (BAM : Eu). The luminance of a Xe dielectric-barrier-discharge (DBD) FL coated with SA : Pr (Pr: 5 mol%) achieves 28.8% of the same lamp with BAM : Eu. The CIE colour coordinate of the SA : Pr (Pr: 5 mol%) excited by the Xe-DBD lamp is x = 0.307 and y = 0.292. The SA : Pr phosphor has an excitation band peaking at 468 nm corresponding to the 1I6 state and a low intensity excitation band lying from 250 to 420 nm. The latter is attributed to the self-trapped exciton (STE) band. This STE band causes an energy path due to non-radiative transition from 1S0 to 3P0 in the excitation at 172 nm. The former excitation band around 468 nm coincides with an ordinary blue LED's emission. When the phosphor is excited at this wavelength, the emission spectra are observed at 486.3, 526.3, 623.7 and 644.6 nm. Therefore, the SA : Pr may alternatively be useful for white LEDs excited by blue light.

The characteristics of electrodeless xenon discharge fluorescent lamps using dielectric barrier discharge are described in this paper. All lamps were operated with pulsed discharge. The luminance of phosphor increases as the pressure of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, in order to obtain high luminance, xenon should be filled at high pressure. In the case of the lamp operated by inner electrodes, if only xenon is contained in the lamp, the cathode is bombarded and is damaged by the large mass of a xenon ion. On the other hand, the external electrode type is never damaged by the ions or electrons. Moreover, the efficacy of the external electrode type is as great as the inner electrode type, and it can be improved by increasing the distance between electrodes.

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes are described in this paper. All lamps were operated by pulsed discharge. When the partial pressure of neon is high, the ignition voltage and operation voltage are low because of the Penning effect. Thus, a higher mixing ratio of neon is desirable for lower ignition and operation voltages. However, the luminance of phosphor increases as the mixing ratio of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission in afterglow increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, though there is the problem of ion bombardment of the cathode under a high operation voltage, the pulsed discharge of the xenon-neon mixture at a high xenon mixing ratio is desirable in mercuryless fluorescent lamps because a strong radiation of xenon excimer is obtained.

It is qualitatively verified by the energy conservation equation that high electron temperature is attained by the pulsed discharge with rapid current rise. In the glow discharge of the tube filled with mercury vapor and neon gas, luminous color of the positive column varies from the color close to red emitted by neon to blue of mercury by the square-wave pulsed discharge. Brightness of blue light is hundreds nits but that of red light is 100 nts at most. In the arc discharge, red light with strong brightness is easily obtained by square-wave pulses. On the other hand, blue light may be obtained at high frequency but the discharge becomes unstable at that frequency. Therefore, the current waveform alteration method is effective for luminous color control of the arc discharge.

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes, and xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. If only xenon is filled in the lamp of inner electrode type, the cathode is bombed and damaged by the large mass xenon ions. Consequently, the most suitable mixing ratio of xenon and neon or some buffer gas should be found experimentally for inner electrode type. On the other hand, when the lamp filled only with xenon is operated by external electrodes, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the UV light of xenon excimers. However, the starting voltage becomes high at high xenon pressure. So, the optimization of some conditions such as electrodes, pulse frequency, etc. is required for external electrode type.