By Zhixun Luo and Jiannian Yao. By Paulo T. Freire, Felipe M. Lima, Francisco E. Barlow and Boyd M. By Antonio Aloi and Raffaele Tommasi. This is made possible by the EU reverse charge method. This was especially made possible by the setup of microRaman spectrometers.
Furthermore, the progress in microcomputer manufacturing together with the elabora- tion of rapid mathematical and statistical algorithms, could offer to Raman spectrosco- py the possibility of acting as a powerful imaging tool. A Raman image, collected from a complex biological system, i. This is the point where global information image can also carry local molecular information.
It was also natural to use Raman spectroscopy as a tool for diagnosis, for instance in analyzing metabolic effects in biological fluids, or alterations induced in tissues upon tumor for- mation, such as changes in DNA, protein and lipid conformations, or molecular degra- dation. Thanks to the continuing technical progress, portable miniature Raman spec- trometers can be used in the future as a non-invasive tool for medical diagnosis. Moreover, the contribution of water to Raman signal is rather low compared to infrared absorption.
The weakness of this technique arises from its low intensity: only one scattered photon out of one million incident ones, contributes to the Raman scattering process. As a consequence, the samples used for recording Raman spectra are generally much more concentrated than those needed for other optical spectroscopic methods such as fluorescence and circular dichroism.
To overcome this difficulty, two different approaches have been developed during the last years. The first one is the resonance Raman spectroscopy RRS , which is based on the excitation of a sample by means of a monochromatic light, of which the wavelength falls within its molecular absorption spectrum.
This phenomenon leads to a considera- ble enhancement of Raman intensity, and allows the sample concentration to be de- creased. However, the absorption of light by biological molecules corresponding to their absorption spectra, generally located in the ultra-violet range of electromagnetic radiation, can cause irreversible damages due to their degradation.
The second possibil- ity is to use the Raman signal enhancement effect by the so-called plasmon resonance, when the analyzed molecule is adsorbed on the surface of a noble metal, i. This method, known as surface enhanced Raman spec- troscopy SERS has found a large audience for analyzing the biological molecules. SERS signal was shown to be enhanced up to several orders of magnitude, depending on the molecular affinity for binding to the metal surface, as well as on the molecular group involved in the adsorption.
This technique is gradually becoming a routine tool in pharmacology and molecular biology for analyzing molecular samples at very low concentrations. Sheila E. Andrew T. Corals emerald and diamond treatments, and characterization of mounted gems [9]. Raman spectroscopy offers many advantages, such as Introduction short measurement times and the low amount of material required. For gemological purposes, it is particularly Gemology is a complex field where many disciplines appreciated, being a completely noninvasive, contactless converge: natural sciences geology, chemistry, physics, technique which does not require any sample preparation.
Economic aspects also play an important role in the of objects that cannot be moved, such as gems mounted on study of gems. The economic value of a gem depends not only on its D.
Usberti 7a, Parma, Italy general, on its agreeable aspect. This last characteristic e-mail: danilo. Lottici color, often due to impurities. A good example is beryl, e-mail: lottici fis. Bersani, P. Lottici ions, blue aquamarine due to the simultaneous presence of unreachable, being displayed in a glass case [18]. Defects can be responsible for the gem colora- useful.
Some of the most used fiber-optic probe heads, also tion, as in smoky quartz. Moreover, gemstones of the same used for applications in gemology, were described by Pitt et variety may show considerable variations in cost owing to al. As an example, the instrumentation. Usually faceted gemstones, most being subjected to some enhance- portable systems are affected by the fluorescence of the ment treatment to obtain a more agreeable aspect, in terms material surrounding the point analyzed, more than labora- of transparency and color.
So, most of the stones are not tory systems, owing to their lack of confocality. Some heat perform compositional studies. Cheap ultraportable systems treatments, not involving a phase transition, have been are also available on the market, but they have very low used for thousands of years [13] and are considered in some resolution and are often unable to work in the low- way traditional.
As an example, most gem sellers accept as wavenumber part of the spectrum, in some cases being normal the heating of blue-green-shaded beryls to obtain useless. Stones with similar times. Almost all modern Raman laboratory equipment has aspect have a great difference in value according to the kind a micro-Raman configuration, being coupled with an of treatments; it is then very important to distinguish highly optical microscope to focus the laser beam on the sample valued untreated gems from low-priced gems which have and collect the scattered light.
This aspect will be discussed in the and solid inclusions in gemstones, minimizing the signal of following. In In the last 30—40 years, different papers have pointed out addition, different excitation wavelengths can usually be the main aspects of the applications of Raman spectroscopy chosen in laboratory systems: this is helpful to reduce the to gemology [9, 10, 15—18]; in this work we would like to disturbing fluorescence, when present, and to improve the give a quick overview of the main topics, with a closer look Raman signal when looking for resonance phenomena.
Even Fourier transform FT -based systems are effec- tively used in gemology. They allow the use of long-wavelength excitation, usually produced by a Nd:YAG laser, at The instrumentation for Raman spectroscopy may be 1, nm, requiring a Michelson interferometer coupled divided into two families: laboratory systems, usually with an IR detector, instead of a diffraction grating and a equipped with a microscope and multiple laser lines, and CCD as in standard dispersive systems.
Low-energy portable systems. In this case strong, sharp bands are mineral species which could be relevant in gemology have obtained, which can be confused with the Raman signal been published [1, 28—35], but they often appear in Ph. When fluorescence of rare earth elements is present, theses which are difficult to access [32, 33], or are related to FT-Raman spectroscopy cannot solve the problem either. It is obviously possible to extend the range of gives a better Raman signal [10]; however, in such a measurements, including some destructive techniques, to configuration some plasma lines secondary emissions of achieve a correct identification, but this may not be a the laser could be visible, disturbing the measurement in routine method with rare and highly valuable gems.
Thus, it the low-wavenumber part of the spectrum. As an example, Kiefert et al. It is musgravite. This scattered light. Raman polarizability is a nine-element orientational dependence is a powerful tool for crystallo- tensor relating, for each vibrational mode, the amplitudes graphic studies, but could cause mistakes when experimen- of the x, y, and z components of the electric field in the light tal results are compared with data in a database, as scattered by the Raman effect to the components of the discussed in the following.
Even in the case Raman spectroscopy can be fruitfully employed in of an ideal spectrometer, with a response independent of the teaching courses on gem identification owing to its ease of use [21]. Applications of Raman spectroscopy to gemology: identification The first question to answer when looking at a gem is simply: what is it?
The standard way to give an answer by means of Raman spectroscopy is by comparison of the spectral fingerprint of the gem with some spectra of standard minerals. Figure 1 shows the Raman spectra of some usual and unusual gems. Luckily, the availability of a large database of Raman spectra of mineral species is constantly increasing in time, so this question is often easy to answer using Raman spectroscopy.
In particular, some databases are free on the Web [22—27], and even more extended databases with automatic search engines are Fig.
In the traditional literature, the usual aquamarine and sapphire and unusual tanzanite, forsterite, and situation is now not so different from the one described by iolite, a variety of cordierite gems. Lottici polarization of the light, the intensity of each Raman peak nate between the most common gems starting from the would depend on the relative orientation between the laser main Raman peaks. In most cases the gems are Varieties of the same species are often present, even with obtained from single-crystal gemstones and the shape and different colors and aspects, but belonging to the same orientation of the cut gems depend on the crystalline species.
Emerald and aquamarine have different colors, and system, the symmetry, the crystal habit, and cleavage. The often different commercial value too, but both are beryl main edges of the gems are therefore often related in a Al2Be3Si6O Raman spectra responsible for the color [40—42]. Usually these small obtained in two perpendicular configurations in nonmono- variations cannot produce visible effects in the Raman metric species may be very different.
This could be spectra, but major variations in chemistry may be reflected misleading when the spectra are compared with spectra in in small intensity and frequency changes in the peaks. However, this fact is actually useful to distinguish emeralds of different provenance. Figure 2 spectra. Del Castillo et al. For gem danburite [CaB2 SiO4 2]. The changes in the relative multivariate analysis, the database should contain spectra intensities of the Raman features are clearly visible, from many samples of the same mineral measured in whereas their wavenumbers are almost the same.
Resonance occurs when either the excitation or the scattered light has energy equal to or very close to a real Applications of Raman spectroscopy to gemology: electronic transition of the material analyzed. This leads to composition a large increase in the whole Raman signal and is often accompanied by a change in the relative intensities of the In many cases, gems belong to a mineral group which different peaks.
The latter aspect could add some difficulty constitutes an isomorphic series whose chemical composi- when the spectrum acquired on a gem is compared with tion changes continuously within a specified range. The spectra reported in a database obtained with a different laser extreme terms of the compositional range are the so-called line because the overall aspect of the spectrum could be end members of the series and, in general, every member of different, even if the wavenumbers of the peaks are the the group can be considered a solid-state solution of the end same.
However, the enhancement due to resonance can members. PDF Principles of Raman Spectroscopy - [email protected] The enhancement factor can be as much as 10 10 to 10 11, which means the technique may detect single molecules. Spectroscopy IR, Raman Vibrational spectroscopy Vibrational spectroscopy is an energy sensitive method.
Dkp22 - Molecular Spectroscopy Raman Spectroscopy is based on Raman scattering Raman scattering Raman effect was first observed in and was used to investigate the vibrational states of many molecules in the s. Raman spectroscopy is an analytical technique that provides detailed information about the chemical structure, polymorphism, crystallinity, and molecular interactions within a compound. Raman spectroscopy. Infrared and Raman Spectroscopy: Principles and Spectral However, Raman scattering is a rare phenomenon with an exceptionally low probability.
Raman spectroscopy is one of the most essential laser spectroscopic methods. PDF CORE - Aggregating the world's open access research papers PDF Raman Spectroscopy Exciting developments in the optical, quantum mechanical, and spectroscopic fields during the past few decades have provided new insights into research on nanomaterials.
PDF Raman spectroscopy: Basic principles and applications This observation can be explained on the basis of quantum mechanics.
PDF Raman Spectroscopy: Introductory Tutorial This work covers principles of Raman theory, analysis, instrumentation, and measurement, specifying up-to-the-minute benefits of Raman spectroscopy in a variety of industrial and academic fields, and how to cultivate growth in new disciplines.
Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. This presents deep understanding of new techniques from basic introduction to the advance level for scientists and. Raman spectroscopy works on the principle of Raman scattering. Raman spectroscopy is a powerful technique in chemical information characterization. The sample is irradiated by a monochromatic light and a spectrometer examines the scattered light. Raman Spectroscopy Raman is a vibrational spectroscopy technique where a single wavelength laser is focused on a sample.
A Raman spectrometer was deployed on the Viking landers in and in other missions. Principles of Diffuse Reflectance Method K is the absorption coefficient, and S is the scattering coefficient.
Infrared spectroscopy. Spectroscopy is the study of the interaction of electromagnetic radiation with matter. This book illustrates necessary insight and guidance in the field of Raman spectroscopy with detailed figures and explanations. ISBN: hardback 1. The technique involves shining a monochromatic light source i. Furthermore, it summarized and forecast the research progress of Raman.
This means that it analyzes a sample chemically, by using light to create excite molecular vibration, and interpreting this interaction afterwards. What are the Basic Principles of Raman Spectroscopy. Plasmon-enhanced Raman spectroscopy PERS is a highly sensitive technique that can provide molecular fingerprint information.
It is the shift in wavelength of the inelastically scattered radiation that provides the chemical and structural information. It is a simple, non-invasive system and requires no elaborate sample preparation. Raman spectroscopy is a non-destructive chemical analysis technique which offers detailed information regarding chemical structure, phase and polymorphic crystallinity, and molecular interactions.
However, this spectral method is subject to two obstacles in nano-material detection. Raman Spectroscopy is based on Raman scattering Raman scattering Raman effect was first observed in and was used to investigate the vibrational states of many molecules in the s. Abstract This contribution reports on the theoretical foundations of Raman spectroscopy.
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