A new mechanism of Raman enhancement and its application.
Strong electronic Raman bands corresponding to the transition between 4I9/2 and 4I11/2 manifolds of Nd3+, caused by a Raman-enhancement effect, are observed in the FT-Raman spectrum of Nd2O3. Neither resonance enhancement (RR) nor surface enhancement (SERS) accounts for the Raman enhancement observed here. We propose a new mechanism of Raman enhancement called the "feed-back" mechanism. A YAG laser excites the final state of the Raman transition (4I11/2 of Nd3+) to the 4F3/2 state and causes a significant decrease in the population of Nd3+ at the 4I11/2 state. This causes the population ratio of Nd3+ at 4I9/2 and 4I11/2 to deviate from the value required by Boltzmann's law. To restore equilibrium, Raman scattering is enhanced so that more Nd3+ ions are brought from the 4I9/2 state to the 4I11/2 state. This hypothesis gets support from the temperature-variable FT-Raman spectroscopic results. Additionally, obvious differences between the Stokes and anti-Stokes Raman spectrum of Nd3+ provide further evidence to support the feed-back mechanism. The Raman-enhancement effect confers on the electronic Raman bands a special ability to reflect the variation of coordinated structure around metal ions. The structural variations in polymer-metal ion composites and biomineralization systems have been investigated by using the electronic Raman bands.
Xu
Yizhuang
Y
Department of Chemistry, Peking University, State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, P. R. China. xyz@pku.edu.cn.wjg@chem.pku.edu.cn
Wu
Jinguang
J
Sun
Wenxiu
W
Tao
Dongliang
D
Yang
Limin
L
Song
Zengfu
Z
Weng
Shifu
S
Xu
Zhenhua
Z
Soloway
Roger D
RD
Xu
Duanfu
D
Xu
Guangxian
G