Preparation and characterization of ZnS:Fe/MX (M = Cd, Zn; X = S, Se) core-shell nanocrystals

ZnS:Fe/MX (M = Cd, Zn; X = S, Se) nanocrystals were synthesized by chemical precipitation method. Compared to ZnS:Fe nanocrystals, the diffraction peaks intensity of ZnS:Fe/ZnS nanocrystals reduced and the diffraction peaks of ZnS:Fe/ZnSe nanocrystals moved to lower angles. TEM photos show that ZnS:Fe and ZnS:Fe/ZnSe nanocrystals are spheroidal and the average particles size is about 2-4 nm. The selected-area electron diffraction pattern of ZnS:Fe/ZnSe nanocrystals shows the diffraction rings, indicating the ZnS:Fe/ZnSe nanocrystals have a polycrystalline structure. XPS shows that the divalent and trivalent of Fe ion are coexisted in ZnS:Fe nanocrystals. The emission peaks of ZnS:Fe nanocrystals were from S and Zn ions vacancy defects and surface defects for the range of 200-900 nm. The use of ZnS (CdS, ZnSe) as surface modifying reagent inhibited the luminescent intensity of ZnS:Fe nanocrystallines at 420 nm. The PL spectra of ZnS:Fe/CdS nanocrystals show a new peak at 554 nm.

► It was found that the surface state of nanocrystals is an important issue for the luminescent properties of nanocrystals. ► Several core/shell nanocrystals, such as CdSe/ZnS, and CdSe/CdTe/ZnSe have been shown to have much higher quantum efficiencies than that of the unpassivated ones. ► In this work, the ZnS:Fe/MX (M = Cd, Zn; X = S, Se) core-shell nanocrystals were prepared by chemical precipitation method, the structure and photoluminescence properties of ZnS:Fe/MX (M = Cd, Zn; X = S, Se) core/cell nanocrystals were studied.