Size-dependent optical properties of SnO2 nanoparticles prepared by soft chemical technique

SnO2 nanoparticles with uniform size and well crystallinity were prepared by using soft chemical technique. Surfactant was used to control the growth and agglomeration of the SnO2 nanoparticles. X-ray diffraction patterns and transmission electron microscopy were used to characterize the structures of SnO2 nanoparticles before and after thermal annealing. It is found that the size of SnO2 nanoparticles can be controlled by changing the preparation parameters and post-thermal annealing temperatures (400 degrees C-1000 degrees C). The optical band gap of SnO2 particles was enlarged compared to its bulk counterpart and the red-shift of the optical band gap with the particle size was observed which can be attributed to quantum size effect. A broad photoluminescence band in a range of 350-550 nm associating with the defect states on the SnO2 particle surface was detected and the intensity was significantly enhanced after the thermal annealing while the size-dependent luminescence excitation spectra were also observed.