Ionic Valence Change of Metal Ions in Solution by Femtosecond Laser Excitation Accompanied by White-Light Laser

Abstract

Three lanthanide ions (Ln^(3+)), Ln = Eu, Sm, and Yb, and two transition metals, Fe^(3+) and Ag^+, were found to be reduced to the corresponding Ln^(2+), Fe^(2+), and Agn in methanol or aqueous solution upon irradiation with intense femtosecond laser pulses. The major excitation wavelength was 800 nm and single-photon-non-resonant with the electronic transitions of metal ion solutions. Laser pulses with wavelengths of 970, 1190, and 1930 nm were used for particular cases. Whenever the white-light laser was generated, the reductions were observed. The reduction mechanisms would be explained in terms of self-focusing, solvated electron formation followed by trapping the electron. The electron ejection under focused beam conditions in solution has been known to be accompanied by white-light laser. In the exceptional case of Fe^(3+) at 800 nm, two-photon excitation of the charge transfer state followed by the reduction would be operative. Fe^(2+) was detected even with an intensity lower than the threshold of the white-light laser generation.