Size effects on structural and optical properties of tin oxide quantum dots with enhanced quantum confinement

Abstract

Size-controllable tin oxide (SnO2) quantum dots (QDs) in aqueous solution were prepared by using stannous chloride and thiourea as source materials and the hydrothermal treatment was employed for size control during the self-assembly of SnO2 QDs. The size effects on structural and optical properties of QDs were discussed. The prepared QDs were confirmed to be of rutile structure with (202), (211) and (330) facets observed. The crystal lattice constants changed their dimensions during grain growth and secondary grain boundaries appeared if grain size was over 7nm. The composition and valence states were found independent with grain size. A negative correlation was observed between size and band gap, which exhibited much greater values than the calculation results from the theory of effective mass approximation and illustrated a strong quantum confinement in the present SnO2 QDs. The size effect of photoluminescence property illustrated a fluorescence inhibition, which could be ascribed to the additional energy levels provided by the lattice distortions at secondary grain boundaries. The depletion region in QDs was extended by these defects, which strengthened the quantum confinement effect.