Synthesis and properties of alloyed CdxZn1-xSe core and manganese-doped CdxZn1-xSe/ZnS core/shell nanocrystals

We have successfully synthesized ternary CdxZn1-xSe alloy quantum dots (QDs) and CdxZn1-xSe/ZnS core/shell nanocrystals. In order to be used as a fluorescent/paramagnetic bi-functional probe, the ZnS shell was doped with 0.1% and 5% of paramagnetic manganese ions. The compositions of Cd, Zn, and Se in the CdxZn1-xSe core QDs were identified by energy-dispersive X-ray spectroscopy (EDS), and the crystal structures of the alloy nanocrystals were identified by wide angle X-ray diffraction (WAXD). The particle size and distribution of nanocrystals were determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). By varying the ratio of Cd:Zn in the CdxZn1-xSe core, the band gaps of CdxZn1-xSe nanocrystals became adjustable and were in the range of 1.92 eV to 2.72 eV. Hence, the fluorescent color of nanocrystals varied from red to blue in the visible light region. The CdxZn1-xSe/ZnS core/shell nanocrystals exhibited superior photoluminescence (PL) quantum yield up to 50%. Compared with CdxZn1-xSe cores, the PL emission peaks of CdxZn1-xSe/ZnS core/shell QDs are red-shifted. Electron paramagnetic resonance (EPR) measurements for manganese-doped CdxZn1-xSe/ZnS nanocrystals showed paramagnetic properties at both low and high Mn2+ concentrations.