The time-resolved
photoluminescence (PL) in the nanosecond time
scale of TiO2 materials undoped or codoped with nitrogen
and fluorine (N,F-doping) and modified by noble metals (NM, i.e. Au
or Pt) nanoparticles (NPs) photodeposition has been systematically
investigated in relation to their photocatalytic activity in hydrogen
production. The main aim of the study is to elucidate the origin of
the NM-dependent synergistic effects in photoactivity produced by
N,F-doping of TiO2 and NM NPs deposition on the oxide surface.
While TiO2 doping with fluorine and nitrogen introduces
new stabilized luminescent defective trap states below the conduction
band revealed by long-living PL components, the presence of NM NPs
on the TiO2 surface produces a PL intensity suppression,
which is more relevant for Au- rather than for Pt-NPs containing materials.
Time-resolved PL analysis indicates that the electron transfer occurring
at the TiO2/metal interface is affected by both the defective
structure of anatase N,F-doped TiO2 and the type of NM
(Au or Pt). In particular, Au rather than Pt NPs appear to strongly
interact with the charge carriers trapped at surface defect sites,
gold NPs being expected to preferentially grow on such sites during
photodeposition. Furthermore, plasmonic gold NPs excitation upon PL
light absorption is evidenced by the PL spectral shape variation observed
only in the case of Au/TiO2. Thus, the larger synergistic
effect on photocatalytic hydrogen production observed upon Au NPs
photodeposition on N,F-doped TiO2 results from the opening
of a new efficient electron transfer path from luminescent defective
trap states on doped TiO2 to Au NPs, where proton reduction
occurs.