The properties of a series of negatively-charged phosphorus (P)-doped titanium(IV) oxide (TiO2) particles were investigated for their dependence on P concentration. XRD peak broadening demonstrated that the crystallite sizes of the P-doped TiO2 particles decreased with increasing P concentration, suggesting that P atom dopants inhibit crystalline growth. The P-doped TiO2 nanoparticles exhibited a pale yellow color. The UV-vis diffuse reflection spectra of the P-doped TiO2 nanoparticles demonstrated a continuous and tailing absorption in the visible region. The broad absorption band in the range of 500-600 nm increased with increasing P content, presumably due to an increase in the density of oxygen vacancies. However, the increase in the density of the oxygen vacancies did not correspond to the change of phenol degradation rate under visible-light irradiation. The results suggest that the oxygen vacancies in P-doped TiO2 are inactive to visible light. (C) 2013 Elsevier B.V. All rights reserved.