Wet-chemical synthesis of doped nanoparticles: Blue-colored colloids of n-doped SnO2:Sb

Nanocrystallites of antimony-doped tin dioxide have been prepared hydrothermally by treating colloids of tin antimony oxide in an autoclave. At a synthesis temperature of 270 $°$ C stable colloidal solutions of blue-colored ${\mathrm{SnO}}_2:\mathrm{Sb}$ nanocrystallites have been obtained. High resolution transmission electron microscopy (TEM) images show highly crystalline particles in the 4 to 9 nm size regime. X-ray powder diffraction patterns of the nanocrystals indicate the same rutile lattice structure as known from bulk ${\mathrm{SnO}}_2.$ Powders of the antimony-doped nanocrystals exhibit an up to ${10}^5$ fold increase in electrical conductivity as compared to the corresponding undoped systems. The blue color of the doped colloids corresponds to a broad absorption peak in the red and the IR region. The IR-absorption spectrum of doped nanoparticles deposited onto sapphire substrates has been fit to a model based on the Drude theory of a free electron gas in ${\mathrm{SnO}}_2:\mathrm{Sb}$ and an effective medium approximation. The model indicates that the IR absorption corresponds to a plasmon polariton excitation of weakly interacting n-doped nanoparticles.