Core-shell nanocrystals InAs-CdSe

The hot-soup method has also been applied to the production of semiconductor core/shell nanostructures, where a semiconductor nanocrystal is coated with a second semiconductor of wider bandgap. Shown in Figure 23 is a scheme for the synthesis of CdSe/CdS core/shell nanocrystals. These nanostructures were synthesized via a high-temperature route in a mixture of TOP and TOPO (223,224) and via a low-temperature route in pyridine (225). Among the semiconductor core/shell nanomaterials produced were CdSe/ZnS, CdSe/CdS, InAs/InP, InAs/CdSe, InAs/ZnSe, and InAs/ZnS (223,225-228). In these structures, the shell type and thickness allow further control of the optical, electronic, and other properties of semiconductor nanocrystals. For example, the shell may be used to passivate the imperfect surface of the core semiconductor, resulting in significantly improved luminescence efficiency. 

Figure 15.25 (a) Size- and material-dependent emission spectra of several snrfactant-coated semiconductor nanocrystals (quantnm dots) in a variety of sizes. The blue series (right) represents different sizes of CdSe nanocrystals with diameters of 2.1, 2.4, 3.1, 3.6 and 4.6 nm (from right to left). The green series (centre) is of InP nanocrystals with diameters of 3.0, 3.5 and 4.6 nm. The red series (left) is of InAs nanocrystals with diameters of 2.8, 3.6, 4.6, and 6.0 nm. (b) A true-colour image of the fluorescence of a series of silica-coated core (CdSe)-shell (ZnS or CdS) nanocrystals (reproduced from [39] with permission from AAAS). See plate section for colour version of this image. 

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