This letter presents a method for the synthesis of copper-doped TiO2 nanoparticles. The semiconductors synthesized were characterized in order to know the composition, crystalline structure, the band gap energy, etc. The nanoparticles obtained have a very low band gap (1.6 eV for 7.5% Cu-doping) compared with the values reported in the literature. The results obtained revealed that internal doping of the TiO2 structure is produced, and that the predominant crystalline phase is anatase. The semiconductors synthesized would be of great use in photocatalytic and photovoltaic applications due to the high specific surface and the low band gap energy values. (C) 2013 Elsevier B.V. All rights reserved.