Core-shell NCs

For core-shell NCs, this CdSe core is coated by a shell of one or more epitaxial layers of ZnS. 

We use four types of CdSe/ZnS core-shell NCs with crystal diameters of 1.9 nm, 2.4 nm, 3.2 nm, and 5.2 nm, and size distributions of 5 %. Their emission colors are cyan, green, yellow and red, with corresponding photoluminescence peaks at 500 nm, 540 nm, 580 nm and 620 nm, respectively. We use n-UV LEDs with their electroluminescence peak wavelength at 383 nm. 

Schematic illustration of the influence and related mechanism of Ln " doping on the size of BaF2 Srp2 core-shell NCs.

In order to basically interpret the aforementioned seed-promoted core-shell NC growth mechanism, Tsuji et al. examined the two-step synthesis of Au-Ag core-shell nanostructures [207, 253]. Based on the fact that Au and Ag show the same fee crystal structure with similar lattice constants, nanostructures exhibiting comparable shapes and sizes are expected to evolve. Furthermore Au-Ag core-shell S5 ems are ideal candidates to be investigated at TEM structural analyses as they own different mass contrast therefore easily distinguishable in TEM images [33,253]. 

Harpeness et al. reported the synthesis of roughly spherical Au-Pd core-shell NCs by the MW-polyol-assisted simultaneous reduction of gold and palladium salts. In this case the largely different Au + or Au+ and PdJ redox potentials firstly ensured gold reduction and the formation of metal seeds which in turn promoted heterogeneous nucleation of Pd [255] (Fig. 10.11a). In a similar fashion Pd-Pt core-shell NCs consisting of cubic Pd NC evenly decorated by Pt pellets was very recently described [256] (Fig. 10.11b). 

Hybrid synthesis approaches based on first convective and second dielectric heating allowed to fabricate core-shell NCs composed of 50 nm Ag cores and 5 nm of polydiacetylene (PADA) shell. Ag is initially reduced in aqueous sodium citrate solution then in a second step uniform and concentric PADA precipitation on metal seed is MW-promoted (Fig. 10.11c). 

DPE measurements were performed on CdTe/CdSe core/shell NCs using the experimental setup described in Section 6.3. The collected data were processed according to the procedure described in Section 6.3.2 to produce 2D spectra at different population times. For comparison, a sample of CdSe and type-I CdSe/CdS/ZnS was also measured. 

Figure 7.5 HAADF image (top) and EDS line scan (bottom) across a single NaYF4/NaCdF4 core/shell NC showing Y in the core of the particle and Gd located in the shell. Reproduced with permission from [31]. Copyright 2011, American Chemical Society.

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