Quantum dots, preparation

Figure 17.2 (A) Absorption and photoluminescence spectra of CdSe quantum dots prepared from CdO, CdC03, and Cd(AcO)2 in the presence of different ligands. (B) Increase in the optical density (at 400 nm) of a CdSe quantum dot reaction mixture with time under reaction at 75 "C. Color pictures in the inset of B represent CdSe (a,b) andCdSe-ZnS (c) quantum...

Mosadegh Sedghi S, Mortazavi Y, Khodadadi A (2009) Low temperature CO and CH4 dual selective gas sensor using Sn02 quantum dots prepared by sonochemical method. Sens Actu B (In Press)... 

Kim D, Miyamoto M, Nakayama M (2005) Photoluminescence properties of CdS and CdMnS quantum dots prepared by a reverse-micelle method. J Electron Microsc 54 131-134... 

TE0S/H20, NH, Cd (NO ,)2. (NH4)2S CdS core, shell, homogeneously dispersed, or surface bonded quantum dots prepared, depending on sequencing of CdS precipitation and TEOS hydrolysis presence of hexanol strengthened microemulsion against destabilization by ethanol reaction product (35-37)... 

A complete and satisfactory characterization of quantum dots prepared by any of these methods requires many of the same techniques listed for metal nanoparticles described already (see above). In addition to critical electronic properties, photoluminescence spectroscopy is an extremely valuable tool to obtain preliminary information on size and size distribution of quantum dots, which can in many cases (i.e., for larger sizes and quasi-spherical shapes) be estimated from 2max and the full width at half maximum (fwhm) of the absorption or emission peak using approximations such as Bras model or the hyperbolic band model [113]. 

Other approaches already realized include the development of a simple and rapid method for spironolactone determination based on the quenching of the fluorescence of CdSe quantum dots by the analyte52 or the determination of anthracene with a detection limit of 1.6 x 10-8 M based on the quenching effect of this polycyclic aromatic hydrocarbon on water-soluble CdSe/ZnS quantum dots, prepared via a simple sonochemical procedure using (3-cyclodextrin ((3-CD) as surface coating agent.53... 

Moussodia, R.-O. Balan, L. Schneider, R., Synthesis and Characterization of Water-Soluble ZnO Quantum Dots Prepared Through PEG-Siloxane Coating. NewJ. Chem. 2008, 32,1388-1393. 

Qian H, Dong C, Peng J, Qiu X, Xu Y, Ren J (2007) High-quality and walCT-soluble near-infrared photoluminescent CdHgTe/CdS quantum dots prepared by adjusting size and... 

Das P, Zhong W, Claverie J (2011) Copolymer nanosphere encapsulated CdS quantum dots prepared by RAFT copolymerization synthesis, characterization and mechanism of formation. Colloid Polym Sci 289 1519-1533... 

Z.H. Zhang, W.S. Chin, J.J. Vittal, Water-Soluble CdS Quantum Dots Prepared from a Refluxing Single Precursor in Aqueous Solution, J. Phys. Chem. B 108 (2004) 18569-18574. 

Mews A et al 1994 Preparation, oharaoterization and photophysios of the quantum dot quantum well system CdS/HgS/CdS J. Phys. Chem. 98 934... 

In the 1980s, CdSe quantum dots vere prepared by top-dovm techniques such as lithography ho vever, size variations, crystal defects, poor reproducibility, and poor optical properties of quantum dots made them inadequate for advanced applications. Introduction of bottom-up colloidal synthesis of CdSe quantum dots by Murray et al. [3] and its further advancements brought radical changes in the properties of quantum dots and their applications in devices and biology. The colloidal syntheses of CdSe quantum dots are broadly classified into organic-phase synthesis and aqueous-phase synthesis. 

Particle size and the method of nanoparticle preparation (including the capping agent used) determine the physical and electronic properties of the quantum dots produced. This gives chemists the unique ability to change the electronic and chemical properties of a semiconductor material by simply controlling particle size and preparative conditions employed. There are various methods for the preparation of nanoparticles however, not all methods work well for the preparation of compound semiconductor nanocrystallites. 

Table 15 Single-source precursors used in the preparation of quantum dots.

SILAR has been used for the synthesis of CdS/ZnS coatings for CdSe quantum dots. The precursor solutions were prepared by dissolving CdO, ZnO, and S in oleic acid and octadecane. The final coating consisted of three layers of CdS and three additional layers of ZnS. The photonic band structure of the photonic crystal had a modifying influence on the photoluminescence of the embedded quantum dots.90... 

As was demonstrated, a variety of polymeric materials are used for preparation of dye-doped beads. Dye-doped silica beads are also extremely popular due to their chemical robustness, biocompatibility and simplicity in preparation and further functionalization of the surface [55]. Thus, polymeric, silica and Ormosil beads (which occupy intermediate position) are widely used as nanosensors and labels. On the other hand, quantum dots possess much higher cytotoxicity which often limits their application in biological systems. 

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