Multiphoton reduction of Eu3+ to Eu2+ in methanol using intense, short pulses from a Ti : Sapphire laser

Multiphoton reduction of Eu3+ to Eu2+ in methanol was induced by irradiatio n with the second harmonic (394 nm, 2 ps) of a Ti:sapphire laser. The conve rsion efficiencies were increased to 0.3 for short pulse excitation, as com pared to on the order of 10(-5) for a nanosecond dye laser pulse. It appear s that a three-photon process pumps a deep charge-transfer state from which Eu3+ efficiently dissociates to Eu2+. On the basis of the excitation spect ra, the first intermediate state is the L-5(6) state, which is one of the f -electronic excited states. The Eu2+ concentration increased shot by shot a nd approached a plateau. The saturation behavior will be explained in terms of the back photooxidation of Eu2+ to Eu3+.