Characterization and optimization of the fluorescence of nanoscale iron oxide/quantum dot complexes

In this paper, nanoscale iron oxide/quantum dot (QD) complexes were formed in an efficient and versatile reaction that relied on the nucleation of chalcogenides on preformed iron oxide nanocrystals. Iron oxide nanocrystals acted as seeds for the growth of CdSe quantum rods (QRs), CdSe QDs, and CdSe@ZnS QDs. A zinc sulfide shell was added to protect the CdSe core in the complex chemically and provide a reasonable fluorescence quantum yield (∼5%). High-resolution transmission electron microscopy revealed that QDs shared an interface with iron oxide, yielding structures that resemble pincushions with QDs or QRs studding the surface of the iron oxide. These complexes only formed under specific conditions of temperature, injection rate, and surfactant composition that minimized the formation of unbound QDs. As a superparamagnetic material, iron oxide provided a high purity (∼89%) of complexed materials without unbound QDs. The quantitative photoluminescence quantum yields of the purified complexes correlated with the number of QDs per iron oxide. These nanoscale complexes retained the size-dependent optical and magnetic properties of each component.