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Oral presentation

Reduction of Eu$$^{3+}$$ by multiphoton excitation in alcohol solutions

Matsuda, Shohei; Nakashima, Nobuaki*; Yokoyama, Keiichi; Yatsuhashi, Tomoyuki*; Chosrowjan, H.*; Taniguchi, Seiji*; Somekawa, Toshihiro*

no journal, , 

The photoredox reactions of lanthanides as a photochemical separative technique proposed in the 1970s are expected to be applied for recovery and recycling of rare metals and nuclear fuel reprocessing. In this study, Eu$$^{3+}$$ ions in methanol and ethanol solutions were reduced to Eu$$^{2+}$$ ions upon irradiation with nanosecond laser pulses. Eu$$^{2+}$$ was observed when the laser wavelength was tuned to f-f transition bands at 394 and 465 nm. The formation rate of Eu$$^{2+}$$ was proportional to the square of the incident laser intensity, indicating that the photoreduction is induced by a two-photon process. The efficiency of the photoreduction in ethanol was higher than that in methanol.

Oral presentation

Fluence dependence of multiphoton reduction of Eu(III) via f-f transition

Matsuda, Shohei; Nakashima, Nobuaki*; Yokoyama, Keiichi; Yatsuhashi, Tomoyuki*; Chosrowjan, H.*; Taniguchi, Seiji*; Somekawa, Toshihiro*

no journal, , 

The photochemical reactions of lanthanide and actinide ions are expected to be utilized for recovery and recycling of rare earths, and nuclear fuel reprocessing. Heading towards research for implementation of photochemical purification, a unified evaluation of the efficiency of multiphoton processes is required. In this study, we have evaluated the fluence dependence of photoreduction of Eu(III) more precisely than before by measuring the beam profile of the excitation laser. The reduction rate of Eu(III)$$rightarrow$$Eu(II) is proportional to the square of the laser fluence, indicating that the photoreduction of Eu(III) is induced by a two-photon process.

Oral presentation

Photooxidation of trivalent americium in nitric acid

Matsuda, Shohei; Yokoyama, Keiichi; Yaita, Tsuyoshi; Kobayashi, Toru; Nakashima, Nobuaki*

no journal, , 

One of the spectroscopic properties for lanthanides and actinides is that they have f-f transitions in the visible region of their spectra. Those absorption appears at specific wavelength and has narrow line width even in the liquid phase owing to shielded f electrons. It has been reported that reduction reactions of Sm$$^{3+}$$, Eu$$^{3+}$$, and Yb$$^{3+}$$ are induced by multiphoton excitation through each f-f transition depending on conditions. This photochemical process may be applicable to mutual separation of f elements. In this study, we tried to optically control the oxidation state of americium. As a result, we found that trivalent americium (Am$$^{3+}$$) in nitric acid solution is oxidized to pentavalent one (AmO$$_{2}$$$$^{+}$$) during nanosecond pulsed-laser irradiation at 503 nm corresponding to the $$^{5}$$L$$_{6}$$ $$leftarrow$$ $$^{7}$$F$$_{0}$$ transition of Am$$^{3+}$$. Identification and quantification of the reactants and products were performed by absorption spectroscopy. Excitation wavelength dependence and fluence dependence of the oxidation suggest that it is initiated by a resonance-enhanced multiphoton process.

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