Ex situ synthesis and optical properties of ZnO–PbS nanocomposites

Zinc oxide (ZnO) and lead sulphide (PbS) nanoparticles separately synthesized by a precipitation method were combined by an ex situ route to prepare ZnO–PbS nanocomposites with different molar ratios of ZnO and PbS. The structure and morphology of the ZnO, PbS and ZnO–PbS samples were analyzed with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A UV–vis spectrophotometer was used to collect the absorption and 325 nm He–Cd and 488 nm Ar lasers were used to collect the photoluminescence data from the samples. ZnO nanoparticles showed a broad and stable emission peak at ∼570 nm, while a strongly quantum confined emission from PbS nanoparticles was detected at ∼1344–1486 nm. The ZnO–PbS nanocomposites exhibited dual emission in the visible and near-infrared (NIR) regions that is associated with defects and recombination of excitonic centres in the ZnO and PbS nanoparticles, respectively. The PL intensity of the visible emission from the ZnO–PbS nanocomposite was shown to increase when the ZnO to PbS molar ratio was 5:1 and the emission was almost quenched at molar ratios of 1:1 and 1:5. For different molar ratios of ZnO to PbS, the PL intensity of the NIR emission from the ZnO–PbS nanocomposites was more intense than that of PbS nanoparticles.