Generation of plasmas in liquid media and its application to light emitting devices

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We have investigated characteristics of the electrical discharge and optical emission of the plasmas in/on/with liquid media such as pure water, several aqueous solution and hydrocarbons. In order to perform these investigations, we have constructed following electrical discharge devices ; dielectric barrier discharge systems with liquid electrodes, mangrove-type barrier discharge systems, single-bubble discharge systems, water-electrolysis-bubble discharge systems and porous-dielectric-covered metal electrode systems. On the basis of the characteristics obtained, we have discussed possibility of these plasmas as light emitting devices. In electrical discharge on the water surface, sufficient visible luminescence has been obtained when we employ argon or helium for discharge gases in addition to the air. We have also found that the intense discharge on the water can decompose organic compounds in the water, and that OH radicals seem to be responsible for the decomposition. In case of t … More he discharge in the single bubble floating in a water-filled tube, we have obtained electrical discharge in the bubble only when we employ the water which includes metal particles. Ignition of discharge in the bubble has become easier when the bubbles are on metal surface. We have employed an electrolysis technique for generating and fixing the bubbles on metal surface without feeding gases into the water, and have successfully obtained discharge in hydrogen or oxygen bubbles on the electrolysis electrode although its optical emission is not high enough at present. In order to obtain gas bubbles without feeding gases into a liquid medium, we have also utilized a metal electrode covered with a porous dielectric film on which high voltage is applied in the ethanol. The bubbles in the ethanol have been generated by Joule heating in this case. Although we cannot observe any optical emission from the bubbles floating in the ethanol, we have obtained discharge and its optical emission in the bubbles between the dielectric film and the metal electrode. In summary, we have demonstrated several possible types of electrical discharge with, on or in liquid media, although, at this moment, intensity of the optical emission obtained in this work is not high enough to apply this technique to light emitting devices. Less