Colloids optical properties

Wilcoxon J P, Williamson R L and Baughman R 1993 Optical properties of gold colloids formed in inverse micelles J. Chem. Phys. 98 9933... 

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. 

As expected from the visual observations and as suggested by optical properties, the Cg- digestively ripened colloid shows only ordered 3D superlattices (Figure 22A)... 

Colloidal crysfals can be viewed as the mesoscopic counterpart of atomic or molecular crystals. They have been used to explore diverse phenomena such as crystal growth [52-54] and glass transition [55,56], and have many interesting applications for sensors [57], in catalysis [58,59], advanced coatings [60], and for optical/electro-optical devices for information processing and storage [61,62]. In particular, their unusual optical properties, namely the diffraction of visible light and the existence of a photonic stop band, make them ideal candidates for the development of photonic materials [61,63-66]. They may lead to the fabrication... 

Penners, N.H.G. Koopal, L.K. (1986) Preparation and optical properties of homodisperse hematite hydrosols. Colloids Surfaces 19 337-349... 

Bright RM, Walter DG, Musick MD, Jackson MA, Allison KJ, Natan MJ (1996) Chemical and electrochemical Ag deposition onto preformed Au colloid monolayers Approaches to uniformly-sized surface features with Ag-like optical properties. Langmuir 12 810-817... 

Wilcoxon JP, Williamson RL, Baughman R (1993) Optical-Properties of Gold Colloids Formed in Inverse Micelles. J Chem Phys 98 9933-9950... 

Van der Zande BMI, Bohmer MR, Fokkink LGJ, SchOnenberger C (2000) Colloidal Dispersions of Gold Rods Synthesis and Optical Properties. Langmuir 16 451-458... 

Quantum size effects in semiconductor nanocrystals became an important field of research in the 1980s, when a number of groups, notably those of Brus at Bell Labs and Henglein at the Hahn Meitner Institute, published seminal papers on the effects of the size of semiconductor colloids on their optical properties and correlated crystal size with changes in electronic band structure. 

Table 6. Summary of the measured physical and optical properties of unfractionated and fractionated colloids [591]...

Particles in the nanometer-size regime necessarily have large surface-to-volume ratios approximately one-third of the atoms are located on the surfaces of 40 A CdS particles, for example. Furthermore, colloid chemical preparations typically result in the development of surface imperfections and in the incorporation of adventitious or deliberately added dopants. Such surface defects act as electron and/or hole traps and, thus, substantially modify the optical and electro-optical properties of nanosized semiconductor particles. Altered photostabilities [595], fluorescence [579, 594, 596, 597], and non-linear optical properties [11, 598-600] are manifestations of the surface effects in colloidal semiconductors. 

An intense femtosecond laser spectroscopy-based research focusing on the fast relaxation processes of excited electrons in nanoparticles has started in the past decade. The electron dynamics and non-linear optical properties of nanoparticles in colloidal solutions [1], thin films [2] and glasses [3] have been studied in the femto- and picosecond time scales. Most work has been done with noble metal nanoparticles Au, Ag and Cu, providing information about the electron-electron and electron-phonon coupling [4] or coherent phenomenon [5], A large surface-to-volume ratio of the particle gives a possibility to investigate the surface/interface processes. 

Preparation of Motallic Tantalum—Colloidal Tantalum—Physical Properties of the Metal, Optical Properties, Are and Spark Spectra—Chemical Properties—Electromotive Behaviour—Atomic Weight—Alloys. 

The more recent expts involving UV and X-ray irradiations were performed by Wiegand (Ref 226) who determined the changes in the optical properties of Pb and thallous azides. The same type of extinction due to colloidal metal was caused by both types of radiation and is increased in magnitude with decreasing wavelength to the band edge... 

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