Nature
of Reduced States in Titanium Dioxide as Monitored
by Electron Paramagnetic Resonance. II: Rutile and Brookite Cases
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Abstract
We
have systematically used electron paramagnetic resonance (EPR)
to understand the nature of excess electron centers in titanium dioxide
and to classify their spectroscopic features. Excess electrons in
TiO<sub>2</sub> (probably the most important photoactive oxide) have
been generated either by photoinduced charge separation or by reductive
treatments and are stabilized in the solid by titanium ions which
reduce to paramagnetic Ti<sup>3+</sup>. These are monitored by EPR
and classified on the basis of their <b>g</b> tensor values
in order to amend a certain confusion present in the literature about
this subject. In the previous paper of this series (S. Livraghi et
al. <i>J. Phys. Chem. C</i> <b>2011</b>, <i>115</i>, 25413–25421), excess electron centers in anatase were investigated
while the present one is devoted to rutile and brookite, the two other
TiO<sub>2</sub> polymorphs, in the aim of providing a thorough and
consistent guideline to researchers working in the wide area of titanium
dioxide applications