Optical properties, spectroscopy visible

SnC>2 nanoparticles have been successfully synthesized by chemical co-precipitation method using ethanol, acetone, tetrahydrofuran (THF) and ether as solvents. X-ray Diffraction (XRD), Field Emission Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) have been used to study the crystallographic and morphological properties of synthesized SnC>2 nanoparticles, while their optical properties have been studied by UV-Visible absorption spectroscopy. UV-Vis absorption spectra shows a weak quantum confinement in all the synthesized SnCL samples. The photo-catalytic activity of as-synthesized SnC>2 nanoparticles under UV irradiation has been evaluated using Methylene Blue (MB) dye as a test contaminant in water. The results showed that solvents played a key role to control the morphology and photo-catalytic activity of SnCE nanoparticles. 

Magnetic properties Electrical properties Optical properties Scanning probe technologies Scanning probe technologies UV-visible Spectroscopy... 

It is not surprising therefore that the optical properties of small metal particles have received a considerable interest worldwide. Their large range of applications goes from surface sensitive spectroscopic analysis to catalysis and even photonics with microwave polarizers [9-15]. These developments have sparked a renewed interest in the optical characterization of metallic particle suspensions, often routinely carried out by transmission electron microscopy (TEM) and UV-visible photo-absorption spectroscopy. The recent observation of large SP enhancements of the non linear optical response from these particles, initially for third order processes and more recently for second order processes has also initiated a particular attention for non linear optical phenomena [16-18]. Furthermore, the paradox that second order processes should vanish at first order for perfectly spherical particles whereas experimentally large intensities were collected for supposedly near-spherical particle suspensions had to be resolved. It is the purpose of tire present review to describe the current picture on the problem. 

The definitions given above for An and Ca are in terms of the anisotropies in the optical properties over the wavelength range of visible light. Similar anisotropies can also exist or can be induced in other wavelength ranges. For example, infrared dichroism (the absorption of different amounts of polarized infrared radiation in the directions parallel and perpendicular to the direction of orientation) is useful in characterizing polymers by vibrational spectroscopy. 

Modem methods for study of metal-activated enzymes include NMR and ESR spectroscopy, water relaxation rates by pulsed NMR (PRR), atomic absorption, Mbssbauer, X-ray and neutron diffraction, high-resolution electron microscopy, UV/visible/IR spectroscopy, laser lanthanide pertubation methods, fluorescence, and equilibrium and kinetic binding techniques. Studies with Mg(II)-activated enzymes have been hampered by the lack of paramagnetic or optical properties that can be used to probe its environment, and the relative lack of sensitivity of other available methods initial velocity kinetics, changes in ORD/CD, fluorescence, or UV properties of the protein, atomic absorption assays for equilibrium binding, or competition with bound Mn(II) °. Recent developments in Mg and 0-NMR methodology have shown some promise to provide new insights . ... 

Spectroscopies such as UV-visible absorption and phosphorescence and fluorescence detection are routinely used to probe electronic transitions in bulk materials, but they are seldom used to look at the properties of surfaces [72]. As with other optical techniques, one of the main problems here is the lack of surface discrimination, a problem that has sometime been b q)assed by either using thin films of the materials of interest [73, 74], or by using a reflection detection scheme. Modulation of a parameter, such as electric or magnetic fields, stress, or temperature, which affects the optical properties of the sample and detection of the AC component of the signal induced by such periodic changes, can also be used to achieve good surface sensitivity [75]. This latter approach is the basis for techniques such as surface reflectance spectroscopy, reflectance difference spectroscopy/reflectance anisotropy spectroscopy, surface photoadsorption... 

UV-VISIBLE reflectance spectroscopy is used to investigate the optical properties of metal surfaces and its change with electrode potential, to detect surface states at the metal-electrolyte interface. Differential reflectance spectroscopy gives information on surface reactions or adsorbate formation. 

The selection rules help to predict the probability of a transition but are not always strictly followed. If the transition obeys the rules it is allowed, otherwise it is forbidden. A molecule can become excited in a variety of ways, corresponding to absorption in different regions of the spectrum. Thus certain properties of the radiation that emerges from the sample are measured. The fraction of the incident radiation absorbed or dissipated by the sample is measured in optical (ultraviolet and visible) absorption spectroscopy and some modes of nuclear magnetic resonance spectrometry (NMR). Because the relative positions of the energy levels depend characteristically on the molecular structure, absorption spectra provide subtle tools for structural investigation. 

Optical properties of the films have also been studied by UV-visible absorption spectroscopy before and after SHI irradiation to stndy the variation of band gap. Figure 6.5a and b shows the UV-visible spectra for pure and Co-implanted ZnO films before SHI irradiation. As no systematic variation in band gap with Co implantation has been observed in Figure 6.5a, one can say that Co... 

Both molecular and transition dipole moment orientation can be probed within the solid state samples, especially upon combining structural information with polarized absorption measurements. Small-area electron diffraction experiments are also effective since they allow the orientation of crystalline regions within polymer nanofibers to be probed. Most of these techniques are already well established from the study of polymer alignment in thin-films. Improved analysis methods, which make use of combined polarized Raman spectroscopy and UV-visible absorption data, are especially worthwhile to be mentioned as valuable tools to investigate the orientational properties of light-emitting polymer systems. We will come back in depth to optical properties of polymer nanofibers in Chapter 5. 

In ordinary infrared measurements, the requirements for the optical properties of cell windows and other materials (flatness, transparency, etc.) are not as severe as needed for ultraviolet and visible spectroscopy. Sometimes it is even necessary to make the window surface slightly coarse or to make its surfaces slightly deviated from parallel to avoid interference effects. However, such measures should never be taken in VCD measurements in order to ensure that circularly polarized radiation may be generated without fail. In VCD measurements, cell windows must be flat and parallel. A mirror cannot be used for any purpose. Samples should be transparent. VCD will not be observed in samples such as colloids because of scattering. 

A third type of measurement is aimed at characterizing the optical properties of the nanomaterials, and for this both conventional optical microscopy and transmission UV-visible spectroscopy are applicable. Another method-circular dichroism-can be used to study the heUcity of silica nanomaterials, while Raman spectroscopy has also been used for their characterization. 

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