The quantum efficiency of photoelectrochemical etching (eta(PE)) in aqueous H2SO4, photocurrent-potential curves. and the photoluminescence intensity (I-PL) were measured for photoetched (mostly the (1 0 0)-face exposed) and non-photoetched (various faces exposed) n-TiO2 (rutile) electrodes as a function of the illumination intensity (1). The photocurrent onset for the photoetched electrode under low I showed a negative shift relative to the non-photoetched electrode. indicating that the (1 0 0) face has high activity for the water photooxidation under low I. This conclusion was supported by low eta(PL) for the photoetched electrode under low I compared with the non-photoetched electrode, Such crystal-face dependences became negligible under middle and high I. The IPL showed a strong saturation with increasing I. A possible mechanism for surface reactions is proposed to explain the above results as well as the formation of rectangular nano-holes or grooves with the (1 0 0) face by photoetching. The mechanism has led to a detailed assignment of the PL to a transition from conduction-band electrons to surface-trapped holes at the atomic grooves in the (1 0 0) face. The results indicate the importance of atomic-scale regulation of the TiO2 surface for improvement of the photoelectrochemical and photocatalytic activity. (C) 2003 Elsevier Science B.V. All rights reserved.