Optical adsorption

Fig. 8 Kubelka-Munk optical absorption spectra of as-prepared mesostructured (black) and mesoporous NU-Ge-1 (red) semiconductors and NU-Ge-1 incorporating into the pores TCNE (blue) and TTF (green line) organic molecules. The recovered optical adsorption spectra of NU-Ge-1 by encapsulation of TCNE-TTF complexes are also given (dashed lines). Inset optical absorption spectrum of NU-Ge-1 encapsulating anthracene...

Namely, when electron-transfer adsorbates such as the electron-acceptor tetra-cyanoethylene (TCNE) and electron-donor tetrathiafulvalene (TTF) molecules interact with the inorganic framework, the energy gap of the mesoporous NU-Ge-1 (1.87 eV) is red-shifted to 1.71 and 1.64 eV, respectively. Indeed, this change in electronic structure is reversible and the optical adsorption onsets going to 1.83 eV upon formation of the inactive TTF-TCNE complex inside the pores. Incorporation of molecules without electron-acceptor or electron-donor properties such as anthracene did not affect the electronic structure of NU-Ge-1. 

An AMl/ZINDO-CI approach was used to predict the optical adsorption spectra for a series of polybenzobisox-azoles such as 5. The calculations indicated that the adsorption peaks should become blue-shifted as the torsion angle increases <2004PLM8871>. 

The resemblance of the photocurrent to the optical adsorption spectrum has suggested the involvement of molecular excited states in the creation of charge carriers. While this resemblance is by no means universally observed, the concept of carrier creation via exciton interactions at or very near the illuminated electrode has become increasingly favored. Many of the data leading to these conclusions have been obtained by the use of pulsed light techniques (6, 7,3). These methods are virtually independent of electrode effects and the subsequent analysis of the transient current has led to considerable advances in the theory of charge transfer in molecular crystals. 

A number of analytical methods were developed for determination of elemental mercury. The methods are reviewed in Refs. [1-4]. They include traditional analytical techniques, such as atomic adsorption spectroscopy (AAS), atomic fluorescence spectroscopy (AFS), and atomic emission spectroscopy (AES). The AAS is based on measurements of optical adsorption at 253.7 or 184.9 nm. Typical value of the detection limit without pre-concentration step is over 1 pg/l. The AEF is much more sensitive and allows one to detect less than 0.1ng/l of mercury... 

Another plasmon resonance approach for detection of mercury vapour is based on localized plasmon resonance in gold nanoparticles deposited on transparent support (Fig. 12.4, right). Changes of the refractive index of gold nanoparticles due to adsorption of mercury should lead to modification of the gold plasmon band of optical adsorption spectra. This approach has been applied successfully for investigation of interaction of biomolecules however, to our knowledge there is still no report on its applications for detection of mercury vapour. 

Shifting the edge of optical adsorption to the ultraviolet region at loading an excess electron on the nanoparticles is a well known manifestation of the quantum size effect in the nanoparticle optical characteristics. This results in shift of the absorption spectrum near the edge of absorption. When the excess electron emerges at the colloidal particle due to its illumination, the effect is called photobleaching. There are several explanations of this effect in literature. 

In figs. 2-(a), (b) and (c), the diffuse reflection spectra of every solid solution are illustrated. All the optical adsorption edges are successively shifted with the amount of dopants. The corresponding peaks to the 3d-3d transition were observed in the ZnGa204... 

Khlebtsov NG, Fomina VI, Sirota AI. Effect of polymer additives on electro-optical, adsorptional and aggregational properties of water cellulose suspensions. In Jennings BR, Stoylov SP, eds. Colloid and Molecular Electro-Optics. Bristol, Philadelphia IOP, 1992 177-180. 

When the materials become solid solutions in the process of doping, some new luminescence phenomena can occur. In a sohd solution, the dopants enter the crystal lattice without bringing variation to the whole crystal structure and symmetry, whereas the lattice size and composition change. The photoluminescence from each component can present in the solid solution. For instance, the photoluminescence band at 2.5 eV for nano-sized ZnW04 originates from radiative-electron transitions within the WOg anions, and this PL band becomes modulated by the optical adsorption spectra of Ni ions in the ZnxNii xW04 solid solution [65]. 

Optical phenomena based on electron transition Optical adsorption (electrochromism, photochromism) Luminescence (fluorescence, electroluminescence) EC display Chromatic glasses Optical switch Phosphors for CRT, lump, etc. Solid state laser EL display... 

The adsorption of proteins from solution onto polymeric surfaces depends on protein water, protein surface and surface-water interactions [51,52]. Our optical adsorption study indicates that hydrophobic surfaces preferentially adsorb denatured proteins from a mixed solution. This finding underhnes the amphiphilic nature of proteins and the important role of... 

Functional characterization is related to the final use of the material and includes such properties as adhesion, electrical resistivity, hardness, optical adsorptance, color, etc. Subsequent processing, storage, and service may alter the functional properties and these possibilities must be evaluated. 

Extinction coefficient (optical) The optical adsorption per unit path length in a material. Also called Optical adsorptivity. 

Optical adsorption spectroscopy (process control) The characterization of a gaseous medium hy measuring the adsorption of a spectrum of radiation as it passes through the gas or vapor. Characteristic wavelengths are adsorbed by the gas and the amount of adsorption depends on the number density of atoms along the path length. Can be used as a vaporization rate monitor. 

Thickness, property (film characterization) The thickness measured by some property of the film, such as optical adsorption. 

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