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 oxyg en vacancies into the SnO2 lattice or by doping the nanoparticles with anti mony. Autoclavation at temperatures above 250 degrees C is found to be nece ssary to achieve n-doping of the particles. Blue-colored oxygen-deficient n anoparticles are obtained in the absence of antimony by employing a reducin g atmosphere inside the autoclave..If these colloids are exposed to air, th eir blue color vanishes within 1 day, indicating back reaction of the vacan cies with oxygen. Antimony-doped tin dioxide nanoparticles have been prepar ed by using either (SbCl3)-Cl-III or (SbCl5)-Cl-V as the source of antimony . In contrast to the oxygen-deficient tin dioxide, the blue color of antimo ny-doped nanoparticles is stable in air. The blue color of the colloids cor responds 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 inte rpreted as a plasma excitation of free carriers in the n-doped nanoparticle s. High-resolution TEM images and X-ray powder diffraction patterns confirm the high crystallinity of the nanoparticles and the same rutile lattice st ructure as known from bulk SnO2.