Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO₂ nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.