A series of upconversion luminescent erbium-doped SrTiO3 (ABO3-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er3+ ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO6 octahedra promoted energy transfer from the high-energy excited states of Er3+ with B-site occupancy to the host SrTiO3 and thus enhanced the band-to-band transition of the host SrTiO3. Consequently, the erbium-doped SrTiO3 species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H2 or O2 evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H2 and O2 evolution and that the site occupancy of doped elements in ABO3-type perovskite oxides greatly determines the photocatalytic activity.
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