Blueshifts in the ultraviolet absorption spectra of amphoteric SnO2-x nanocrystalline particles

Blueshifts in the ultraviolet absorption spectra of amphoteric SnO2-x nanocrystalline particles differ greatly in acidic and alkaline sols. X-ray diffraction measurements show that the average lattice strain of the nanocrystalline particles in aqueous ammonia sols is about twice as large as that in oxalic acid sols. The size dependence of the blueshift without lattice strain is proposed to be about three times as large as that in an alkaline sol with large strain. X-ray photoelectron spectroscopic measurements reveal that the valence of Sn in acidic and alkaline sols is not 4 but less than 3. It is strongly suggested that the blueshift depends not only on the crystalline size but also most importantly on the lattice strain and second on the valence state of the Sn ions. (C) 2002 American Institute of Physics.