Optical spectroscopy methods

It is hard to And better monitoring tools than optical spectroscopy methods when high spatial and temporal resolution is required in addition to noninvasiveness. Traditionally, absorption, light scattering, chemiluminescence, and fluorescence measurements are used for this purpose (Janasek et al. 2006). Those are well-established techniques that establish a simple way of obtaining useful information. However, absorption and scattering measurements provide very little information about the chemical composition. Fluorescence spectroscopy provides more information but is... 

This approach was appUed to heterostructured seeded nanorods, both for CdSe-CdS (type I) and for ZnSe-CdS QD/QR core-shell nanocrystals. The former system was studied extensively, using a variety of optical spectroscopy methods the data acquired suggested a charge separation, where the hole is located in the QlSe core [positioned close to one end of the nanorod (NR)j and the electron extends over the CdS shell [84]. This picture is consistent with a small value of the conduction band offset, typically Ac<0.2eV, extracted from the bulk regime. However, a direct measurement of the band offsets and the consequent charge distribution in such nanocrystals is of major interest... 

N. Tkachenko, Optical Spectroscopy Methods and Instrumentations, Elsevier, Amsterdam, 2006. 

In the Varian series titled NMR at Work, one example cited in which optical spectroscopy is not satisfactory for the analysis is in the study of the conversion of 2-/-butyl-5-methyl cyclohexanone into its enol acetate [ ]. In this reaction an inseparable mixture is formed and it was shown that NMR spectroscopy can be used to obtain the percent of each isomer ptesent in the mixture. The uniqueness of NMR spectroscopy in solving this problem lies in the fact that the intensity of the signal observed by an NMR spectrometer is directly proportional to the number of nuclei contributing to that signal. Thus, if the total number of protons present in the sample are known, it is possible to calculate the number contributing to each signal observed in the spectrum. This technique cannot be utilized in the usual optical spectroscopy methods since an absorptivity constant is required to relate a peak intensity to concentration. 

Sol-gel-derived films, especially transparent sol-gel films and planar waveguides, can be studied by means of various optical spectroscopy techniques in order to characterize their structure and optical properties. Common optical spectroscopy methods include Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, UV-Vis-NIR, and fluorescence spectroscopies. These are well-known, powerful, nondestructive, and highly sensitive tools to investigate the structure and optical properties of the sol-gels. 

In this chapter, we review the characterization of sol-gel films by the more common optical spectroscopy methods, but also some more advanced techniques such as optical propagation loss and Z-scan measurements, for nonlinear optical (NLO) characterization, in connection with publkhed research works on inorganic, hybrid, and nanocomposite optical films and planar waveguides. 

Characterization ofSol-Gei Material by Optical Spectroscopy Methods... 

In this chapter, the characterization of sol-gel-derived films and planar waveguides by optical spectroscopy methods has been reviewed and discussed. FTIR, Raman, UV-Vis-NIR, and fluorescence spectroscopies were used to analyze the structures of sol-gel inorganic or hybrid optical films. NP sizes in films doped with noble metal NPs or quantum dots have also been reviewed. Optical loss and Z-scan measurements on sol-gel optical waveguides or NP-doped sol-gel films were also discussed. 

Nondispersive elements such as filters are also widely used in all of the optical spectroscopy methods, especially fluorescence measurements, and are based on either absorption or interference. Filters are conunerciaUy available for wavelengths above 200 nm and come in many forms, some of which are bandpass, cutoff, heat-absorbing, heat-reflecting, etc. The most common types are ... 

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