Photogenerated electron- and hole-trap distributions in Al-doped anatase TiO2 crystals measured by cryogenic EPR imaging

Abstract

Electron paramagnetic resonance (EPR) imaging was performed on aluminium-doped anatase titanium dioxide (TiO2) crystals to demonstrate the distributions of photogenerated trapped electrons and holes at cryogenic temperatures. Complementary distributions of trapped electrons and holes were observed at 25 K; trapped electrons were predominant on the {101} planes, whereas trapped holes were predominant on the (001) and {110} planes in the tetragonal crystal structure. These separate distributions are consistent with the reported facet-dependent photocatalytic efficiency of photoreduction and photooxidation in anatase crystals, resulting from crystal plane-dependent carrier transfer. By this extrinsic trap system, the carrier transport properties were derivatively extracted through electron and hole traps. This report provides insight into the fundamental physics governing the facet dependence of photocatalytic effects.