Synthesis and photophysics of colloidal ZnS/PbS/ZnS nanocomposites—An analysis of dynamics of charge carriers

The deposition of Q-ZnS layer as shell at the interface of Q-ZnS/PbS produces ZnS/PbS/ZnS nanocomposite. The electronic properties of the nanocomposite have been examined as a function of thickness of ZnS shell and in the presence of excess [Zn2+]. The monolayer of ZnS shell red shifts the onset of absorption of precursor ZnS/PbS accompanied with an increase in absorption coefficient in the wavelength range of 200–600 nm having an excitonic absorption at 280 nm. These particles display relatively intense blue-shifted 505 nm (2.45 eV) emission associated with a tremendous enhancement of fluorescence lifetime to 150 ns from 5.5 ns, observed for precursor ZnS/PbS. The addition of Zn2+ further improves the charge separation in this system. These electronic changes are understood by the distribution of traps of varied energy (160–365 meV) at the interface and confinement of e−–h+ on the entire heterostructure.