Transient Charge Trapping in Eu^(3+)-Doped Nanocomposites by Ultrafast Laser Excitation

作     者：Sergie Lysenko Jose Jimenez Valentin Vikhnin 

作者机构：Department of Physics University of Puerto Rico Mayaguez PR 00681USA 

出 版 物：《Journal of Rare Earths》 (稀土学报（英文版）)

年 卷 期：2006年第24卷第6期

页      面：663-667页

核心收录：

学科分类：0709[理学-地质学] 0819[工学-矿业工程] 081704[工学-应用化学] 07[理学] 08[工学] 0817[工学-化学工程与技术] 0708[理学-地球物理学] 0703[理学-化学] 070301[理学-无机化学] 

基　　金：Foundation ite m:Project was supported by NASAand NSF-EPSCoRand US-DOD 

主　　题：nanocomposite europium ultrafast excitation rare earths 

摘      要：Eu^3＋ 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 Eu^3＋ , and are distributed in the matrix on the boundary surface of nanoparticles. The valence switching from Eu^3＋ to Eu^2＋ was observed in Si-SiO2 nanocomposites when ultrafast laser excitation was applied. In silver metal nan-oparticles 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 Eu^3＋ ions residing near the surface. The trivalent europium ions play the role as positive boundary charges attracting electrons. This results in temporary formation of Eu^2＋ , and blocks the resonant tunneling transition in the silver-glass system to avoid creating large radius polaron.