Controllable synthesis and optical properties of SnO2 core-shell microspheres

SnO₂ core-shell microspheres were synthesised via a hydrothermal method with hexamethylenetetramine as a surfactant. The structure and the morphology of the products were characterised by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that the overall dimension of the core-shell microspheres and the diameter of the spherical nuclei could be adjusted by changing the concentration of NaOH and hexamethylenetetramine or the reaction time. Based on the time dependent reactions, a possible growth mechanism is proposed. It is believed that the Kirkendall effect plays an important role in the formation of the core-shell structure. The optical properties of the core-shell structure microspheres were also studied through the photoluminescence and the Raman spectra.