Preparation and near-infrared absorption of nano-SnO2/SiO2 assemblies with doping and without doping

The assemblies of nano-SnO2/SiO2 and Sb- or Pd-doped nano-SnO2/SiO2, in which the nano-SnO2 particles are located in the pores of mesoporous SiO2 dry gels, were synthesized. Only for the Sb-doped nano-SnO2/SiO2 assemblies, a broad near-infrared absorption step occurs in the optical absorption spectrum of the wavelength range from 300 to 1500 nm. The near-infrared absorption phenomenon is attributed to electronic transitions from the ground states to the excitation states of the impurity energy levels, which are formed by Sb doping in SnO2. With increasing the weight ratio of SnO2:SiO2 or the annealing temperature, the near-infrared absorption step slope side exhibits “red shift”, which is caused by the quantum confinement effect weakening due to the increased SnO2 crystalline diameter.