Clusters optical properties

This section will outline the simplest models for the spectra of both metal and semiconductor nanocrystals. The work described here has illustrated that, in order to achieve quantitative agreement between theory and experiment, a more detailed view of the molecular character of clusters must be incoriDorated. The nature and bonding of the surface, in particular, is often of crucial importance in modelling nanocrystal optical properties. Wlrile this section addresses the linear optical properties of nanocrystals, both nonlinear optical properties and the photophysics of these systems are also of great interest. The reader is referred to the many excellent review articles for more in-depth discussions of these and other aspects of nanocrystal optical properties [147, 148, 149, 150, 151, 152, 153 and 1541. 

In Section 4.5, we discuss the optical properties of clusters formed by sexi-thienyl molecules adopting the herringbone structure characteristic of their crystal structure [34]. The theoretical results arc compared to corresponding experimental measurements. 

U. Kreibig and M. Vollmer, Optical Properties of Metal Clusters, Springer Series Materials Science. Springer, New York, 1995. 

Wang Y (1991) Nonlinear optical properties of nanometer-sized semiconductor clusters. Acc Chem Res 24 133-139... 

Circular dichroism (CD) is another interesting example of an optical property of the small Au SR clusters. Since the first observation of Schaaff et al. [23,24], several reports have appeared regarding the CD activities of gold clusters protected by chiral thiols such as penicillamine [25] and A-isobutyryl-cysteine [26]. Figure 11 shows the CD spectra of 1-9, which is a good reproduction of the original report by Whetten s group [23,24]. 

There is great interest in the electrical and optical properties of materials confined within small particles known as nanoparticles. These are materials made up of clusters (of atoms or molecules) that are small enough to have material properties very different from the bulk. Most of the atoms or molecules are near the surface and have different environments from those in the interior—indeed, the properties vary with the nanoparticle s actual size. These are key players in what is hoped to be the nanoscience revolution. There is still very active work to learn how to make nanoscale particles of defined size and composition, to measure their properties, and to understand how their special properties depend on particle size. One vision of this revolution includes the possibility of making tiny machines that can imitate many of the processes we see in single-cell organisms, that possess much of the information content of biological systems, and that have the ability to form tiny computer components and enable the design of much faster computers. However, like truisms of the past, nanoparticles are such an unknown area of chemical materials that predictions of their possible uses will evolve and expand rapidly in the future. 

Abstract Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in common with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photostability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications. 

Zhu M, Aikens CM, Hollander FJ (2008) Correlating the crystal structure of a thiol-protected Au25 cluster and optical properties. J Am Chem Soc 130 5883-5885... 

Kreibig U, VoUmer M (1995) Optical properties of metal clusters. Springer, Berlin Heidelberg New York... 

We have overviewed some strategies for the surface-mediated fabrication of metal and alloy nanoscale wires and particles in mesoporous space, and their structural characterization and catalytic performances. Extension of the present approaches for metal/alloy nanowires may lead to the realization of the prospechve tailored design of super active, selective and stable catalysts applicable in industrial processes. The organometallic clusters and nanowires offer exciting and prospechve opportunities for the creahon of new catalysts for industry. Various metal/ alloy nanowires and nanoparhcles in the anisotropic arrangement in porous supports would help in understanding the unexpected electronic and optic properties due to the quantum effect, which are relevant to the rational design of advanced electronic and optic devices. 

Neiss, C., Hattig, C. Frequency-dependent nonlinear optical properties with explicitly correlated coupled-cluster response theory using the CCSD(R12) model. J. Chem. Phys. 2007, 126, 154101. 

In recent publications [120, 121, 122,123] it has been shown that both the ionization potentials and the optical properties of bare and uncharged mercury clusters in a molecular beam experiment demonstrate a gradual size dependent evolution of metallic properties, starting at about 13 atoms and already bulklike at about 70 atoms. It has been predicted theoretically [124] that plasmons should begin to develop for such mercury clusters at about Hgi5. We should keep this in mind in the discussion of the electronic properties of AU55. 

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