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Mapping of the Photoinduced Electron Traps in TiO 2 by Picosecond X‐ray Absorption Spectroscopy
Author(s) -
RittmannFrank M. Hannelore,
Milne Chris J.,
Rittmann Jochen,
Reinhard Marco,
Penfold Thomas J.,
Chergui Majed
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201310522
Subject(s) - anatase , picosecond , materials science , photoexcitation , amorphous solid , absorption edge , nanosecond , spectroscopy , photocatalysis , electron , absorption (acoustics) , ultrafast laser spectroscopy , photochemistry , absorption spectroscopy , titanium dioxide , chemistry , optoelectronics , optics , atomic physics , band gap , excited state , crystallography , physics , laser , biochemistry , quantum mechanics , composite material , catalysis , metallurgy
Titanium dioxide (TiO 2 ) is the most popular material for applications in solar‐energy conversion and photocatalysis, both of which rely on the creation, transport, and trapping of charges (holes and electrons). The nature and lifetime of electron traps at room temperature have so far not been elucidated. Herein, we use picosecond X‐ray absorption spectroscopy at the Ti K‐edge and the Ru L 3 ‐edge to address this issue for photoexcited bare and N719‐dye‐sensitized anatase and amorphous TiO 2 nanoparticles. Our results show that 100 ps after photoexcitation, the electrons are trapped deep in the defect‐rich surface shell in the case of anatase TiO 2 , whereas they are inside the bulk in the case of amorphous TiO 2 . In the case of dye‐sensitized anatase or amorphous TiO 2 , the electrons are trapped at the outer surface. Only two traps were identified in all cases, with lifetimes in the range of nanoseconds to tens of nanoseconds.