Transient Charge Trapping in Eu3+-Doped Nanocomposites by Ultrafast Laser Excitation
来源期刊：JOURNAL OF RARE EARTHS2006年第6期
论文作者：Huimin Liu Jose Jimenez Sergie Lysenko Valentin Vikhnin
Key words：nanocomposite; europium; ultrafast; excitation; rare earths;
Abstract: Eu3+ was incorporated as probe ions into nanocomposite glasses, such as metal silver doped phosphate glass and crystalline nanocomposites Si-enriched SiO2 glass. Luminescence studies show that the doped europium ions are present as trivalent Eu3+, and are distributed in the matrix on the boundary surface of nanoparticles. The valence switching from Eu3+ to Eu2+ was observed in Si-SiO2 nanocomposites when ultrafast laser excitation was applied. In silver metal nanoparticles embedded aluminophosphate glass, a time-resolved ultrafast degenerate-four-wave-mixing (DFWM) experiment shows enhanced third-order nonlinearity at zero-delay time, followed by a bell-like signal buildup. It is attributed to the creation of electronic polaron and vibronic Wannier-Mott exciton (WME). In europium codoped sample, however, the bell-like signal is depressed. All the above observations are interpreted as the result of a strong Coulomb interaction between conduction electrons produced inside the nanoparticles by laser excitation and Eu3+ ions residing near the boundary surface. The trivalent europium ions play the role as positive charges attracting electrons. This results in temporary formation of Eu2+, and blocks the resonant tunneling transition in the silver-glass system to avoid creating large radius polaron.
Huimin Liu1，Jose Jimenez1，Sergie Lysenko1，Valentin Vikhnin1
(1.Department of Physics, University of Puerto Rico, Mayaguez, PR 00681, USA)
Abstract:Eu3+ was incorporated as probe ions into nanocomposite glasses, such as metal silver doped phosphate glass and crystalline nanocomposites Si-enriched SiO2 glass. Luminescence studies show that the doped europium ions are present as trivalent Eu3+, and are distributed in the matrix on the boundary surface of nanoparticles. The valence switching from Eu3+ to Eu2+ was observed in Si-SiO2 nanocomposites when ultrafast laser excitation was applied. In silver metal nanoparticles embedded aluminophosphate glass, a time-resolved ultrafast degenerate-four-wave-mixing (DFWM) experiment shows enhanced third-order nonlinearity at zero-delay time, followed by a bell-like signal buildup. It is attributed to the creation of electronic polaron and vibronic Wannier-Mott exciton (WME). In europium codoped sample, however, the bell-like signal is depressed. All the above observations are interpreted as the result of a strong Coulomb interaction between conduction electrons produced inside the nanoparticles by laser excitation and Eu3+ ions residing near the boundary surface. The trivalent europium ions play the role as positive charges attracting electrons. This results in temporary formation of Eu2+, and blocks the resonant tunneling transition in the silver-glass system to avoid creating large radius polaron.
Key words:nanocomposite; europium; ultrafast; excitation; rare earths;
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