  The efforts in the optimization of the physical and chemical properties
related to the photocatalytic efficiency of TiO2 nanoparticles relies mainly on
defect engineering strategies, been the structural and the doping the most
common ones. The doping of the anatase TiO2 structure with lanthanides elements
potentially can turns the TiO2 optical absorption into the visible range
increasing drastically its photocatalytic efficiency. Here we show that the
processing of TiO2 nanoparticles in oxygen atmosphere and the La doping
stabilizes the anatase phase. The La incorporation takes place mainly in the
surface of the nanoparticles leading to small nanoparticles as compared to the
undoped TiO2. In spite of the effective La doping, the decrease of the energy
bandgap is compensated by a quantum confinement effect related to the decrease
in the nanoparticle size. However, the location of the La3+ ions on the surface
of the nanoparticles induces a local concentration of oxygen vacancies that can
increase the quantum efficiency of the system leading to higher photocatalytic
activity.
