Wet-Chemical Synthesis of Doped Nanoparticles:  Optical Properties of Oxygen-Deficient and Antimony-Doped Colloidal SnO₂

Blue-colored aqueous colloids of n-doped tin dioxide nanoparticles in the 4−9-nm size regime have been prepared hydrothermally either by inducing oxygen vacancies into the SnO 2 lattice or by doping the nanoparticles with antimony. Autoclavation at temperatures above 250 °C is found to be necessary to achieve n-doping of the particles. Blue-colored oxygen-deficient nanoparticles are obtained in the absence of antimony by employing a reducing atmosphere inside the autoclave. If these colloids are exposed to air, their blue color vanishes within 1 day, indicating back reaction of the vacancies with oxygen. Antimony-doped tin dioxide nanoparticles have been prepared by using either Sb III Cl 3 or Sb V Cl 5 as the source of antimony. In contrast to the oxygen-deficient tin dioxide, the blue color of antimony-doped nanoparticles is stable in air. The blue color of the colloids corresponds to a broad absorption peak in the red and IR regions, independent of the method of n-doping. As for bulk material, this IR absorption is interpreted as a plasma excitation of free carriers in the n-doped nanoparticles. High-resolution TEM images and X-ray powder diffraction patterns confirm the high crystallinity of the nanoparticles and the same rutile lattice structure as known from bulk SnO 2 .