PbS quantum dots band gap tuning via Eu doping

We synthesize pristine and Eu-doped colloidal lead sulfide (PbS) quantum dots (QDs) by solvothermal process under mild conditions. The composition, structure, morphology, and optical properties of the products are characterized through x-ray diffraction, transmission electron microscopy, and UV–vis techniques. The obtained PbS QDs exhibit high crystallinity and uniformity and have sizes ranging from 4 to 10 nm, less than the excitonic Bohr radius of PbS. The initial Europium (Eu)/Pb molar ratio of the precursor is found to have a great effect on the optical properties and size of the synthesized particles. Larger proportions of Eu in the precursor result in a smaller particle size. A significant blue shift is observed in the UV–vis absorption spectrum due to the quantum confinement effect. The calculated optical band gaps of the PbS QDs are blue-shifted from 2.88 to 3.46 eV, which results from the larger concentration of Eu in the precursor.