SiO2-coated ZnS submicrospheres with enhanced thermal stability and photoluminescence

Uniform SiO2-coated ZnS submicrospheres were synthesized by a sol–gel method. The shell thickness was controlled from 50 to 320 nm by adjusting the concentration of tetraethyl orthosilicate (TEOS). The structure and morphology of the SiO2-coated ZnS spheres were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results indicate that the thermal stability of SiO2-coated ZnS spheres has been greatly improved comparing with the uncoated ZnS. The emission intensity of SiO2-coated ZnS submicrospheres increased greatly with increasing the SiO2-shell thickness, which can be ascribed to the improved thermal stability and reduced surface defects and electron–hole recombination of ZnS spheres.