Ultraviolet absorption spectra of amphoteric SnO2 nanocrystallites

Aqueous sols having SnO2 nanocrystalline particles less than 2 nm in mean diameter were prepared by ultra-filtration from original acidic and alkaline sols with particle diameters extending over a wide range of 0.5–8 nm. Blue shifts were observed in ultraviolet absorption spectra of both the sols. The relationship between energy band gap and size distribution in the original and ultra-filtrated sols suggests that the blue shifts depend on not only the particle size but also the chemical state of nanoparticle surfaces in the acidic and alkaline sols.