Nanocrystal synthesis strategies

There are many ingenious and sueeessful routes now developed for nanociystalline synthesis some rely on gas phase reactions followed by produet dispersal into solvents [7, 9, 13, 14 and 15]. Others are adaptations of classic colloidal syntheses [16,17,18 and 19]. Electrochemical and related template methods can also be used to form nanostructures, especially those with anisotropic shapes [20, 21,22 and 21]. Rather than outline all of the available methods, this section will focus on two different techniques of nanocrystal synthesis which together demonstrate the general strategies. 

Li Y, Peng Q, Wang X, Zhuang J. 2005. A general strategy for nanocrystal synthesis. Nature 437 121- 2A. 

Apart from Eu + and Tb +, few studies have been reported on optical properties of lanthanide ions doped in ZnS nanocrystals. Bol et al. (2002) attempted to incorporate Er + in ZnS nanocrystal by ion implantation. They annealed the sample at a temperature up to 800 °C to restore the crystal structure around Er +, but no Er + luminescence was observed. Schmidt et al. (1998) employed a new synthesis strategy to incorporate up to 20 at% Er + into ZnS (1.5-2 nm) cluster solutions which were stabilized by (aminopropyl)triethoxysilane (AMEO). Ethanolic AMEO-stabilized Er ZnS clusters in solutions fluoresce 200 times stronger at 1540 nm than that of ethanolic AMEO-Er complexes. This is explained by the very low phonon energies in ZnS QDs, and indicates that Er + ions are trapped inside chalcogenide clusters. However the exact position of Er + in ZnS clusters remains unknown. Further spectroscopic and structural analyses are required in order to obtain more detailed information. 

Recently, DHBCs have been used as a good stabilizer for the in-situ formation of various metal nanocolloids and semiconductor nanocrystals such as Pd, Pt [328-330], Au [280,328-330], Ag [331], CdS [332], and lanthanum hydroxide [333]. PAA-fe-PAM and PAA-fc-PHEA were used as stabihzer for the formation of hairy needle-Uke colloidal lanthanum hydroxide through the complexation of lanthanum ions in water and subsequent micelhzation and reaction [333]. The polyacrylate blocks induced the formation of starshaped micelles stabilized by the PAM or PHEA blocks. The size of the sterically stabilized colloids was controlled by simply adjusting the polymer-to-metal ratio, a very easy and versatile synthesis strategy for stable colloids in aqueous environment [333]. The concept of induced micelhzation of anionic DHBCs by cations was also apphed in a systematic study of the direct synthesis of highly stable metal hydrous oxide colloids of AP+, La +, Ni +, Zn ", Ca ", or Cu " via hydrolysis and inorganic polycondensation in the micelle core [334,335]. The AP+ colloids were characterized in detail by TEM [336], and the intermediate species in the hydrolysis process by SANS, DLS, and cryo-TEM [337]. 

Gautam, U. K. Ghosh, M. Rao, C. N. R, A Strategy for the Synthesis of Nanocrystal Films of Metal Chalcogenides and Oxides by Employing the Liquid-Liquid Interface. Chem. Phys. Lett. 2003, 381,1-6. 

This section first provides a general discussion of the synthetic strategy employed for group III-V semiconductor nanocrystals, followed by a description of the synthesis of InAs nanocrystals as a prototypical example. The characterization of the particles produced, using a variety of methods, is briefly reviewed, after which details are provided of the synthesis of core-shell nanocrystals with III-V semiconductor cores, focusing particularly on InAs cores. 

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