Dynamics of Photogenerated Charge Carriers on Ni- and Ta-Doped SrTiO3 Photocatalysts Studied by Time-Resolved Absorption and Emission Spectroscopy

The behavior of photogenerated charge carriers on SrTiO3 photocatalysts doped with transition metals (such as Ni and Ta) was examined by time-resolved visible to mid-IR absorption and emission spectroscopy. When SrTiO3 was co-doped with Ni and Ta, the catalyst absorbed visible light and exhibited photocatalytic activity under visible light irradiation. However, activity under UV light was decreased significantly compared to that before doping. The results of time-resolved measurements showed that monodoping of Ni or Ta accelerated the recombination but co-doping Ni with Ta increased the lifetime of charge carriers compared to those without doping. Furthermore, electrons excited by a visible laser pulse had longer lifetimes compared to those excited by a UV laser pulse. Time-resolved photoluminescence measurements suggested that doped Ni cations act as recombination centers, giving a luminescence peak at ∼8000 cm–1 due to the downward d–d transition at Ni2+. However, the lifetime of the emission was much s...