Structural and optical properties of upconversion CuInS/ZnS quantum dots

A facile one-pot method to synthesis CuInS/ZnS (CIS/ZnS) QDs was developed. The prepared CIS/ZnS QDs exhibited a high bright emission. Moreover, the upconversion photoluminescence (PL) of the CIS/ZnS QDs was explored. Interestingly, extraordinary excitation-independent emission for both up and down conversion fluorescence of the CIS/ZnS QDs were observed. Analysis of X-ray diffraction (XRD) of CIS/ZnS QDs showed chalcopyrite crystal structure. The high-resolution transmission electron Microscopy (HRTEM) images demonstrated crystalline CIS/ZnS QDs with spherical shape and average diameter sizes of 2.5 nm and 3.6 nm for CIS core and CIS/ZnS QDs core shell, respectively. The selected area electron diffraction (SAED) suggested that the prepared CIS/ZnS QDs are polycrystalline with about 0.32 nm lattice distance. The PL peaks position was almost fixed and exhibited a strong peak at about 640 nm for both up and down conversion emission with a linear relationship between the intensity of the PL emission peaks and excitation wavelengths.