Raman spectroscopy: Analytical perspectives in mineralogical research
Lutz Nasdala, David C. Smith, Reinhard Kaindl, Martin A. Ziemann, 2004. "Raman spectroscopy: Analytical perspectives in mineralogical research", Spectroscopic methods in mineralogy, Anton Beran, Eugen Libowitzky
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It is said that during a voyage to Europe in the summer of 1921, the Indian physicist Chandrasekhara Venkata Raman (1888–1970) looked at the wonderful blue opalescence of the Mediterranean Sea and questioned where the sea's blue colour came from and why it should be different from the sky's blue. Raman started a series of experiments to address these questions, and he found the blue colour of the sea was not merely due to simple reflection of the sky in water, as most people imagined, but was additionally affected by molecular scattering of light. This led to the discovery of a new inelastic scattering process that is the optical analogue of the “Compton effect”; it is nowadays known as the “Raman effect”. It describes a change in the wavelength of light that occurs when a light beam interacts with molecular vibrations. The possibility for such interaction between matter and light had already been predicted theoretically by Smekal (1923). The first verification was obtained by Raman and Krishnan (1928) in light scattering experiments on liquids. Only two years later, Sir C.V. Raman (who was knighted in 1929) was the Nobel laureate in physics, honoured for his work on the scattering of light and the discovery of the effect named after him. In his Nobel lecture, given on 11th December 1930, Sir C.V. Raman said “The frequency differences determined from the spectra, the width and character of the lines appearing in them, and the intensity and state of polarization of the scattered radiations enable us to obtain an insight into the ultimate structure of the scattering substance. […] It follows that the new field of spectroscopy has practically unrestricted scope in the study of problems related to the structure of matter” In 1948, he founded the Raman Research Institute in Bangalore, India, with funds from private sources.
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Spectroscopic methods provide information about the local structure of minerals. The methods do not depend on long-range periodicity or crystallinity. The geometric arrangement of atoms in a mineral phase is only one aspect of its constitution. Its vibrational characteristic, electronic structure and magnetic properties are of greatest importance when we consider the behaviour of minerals in dynamic processes. The characterisation of the structural and physico-chemical properties of a mineral requires the application of several complementary spectroscopic techniques. However, it is one of the main aims of this School to demonstrate that different spectroscopic methods work on the same basic principles. Spectroscopic techniques represent an extremely rapidly evolving area of mineralogy and many recent research efforts are similar to those in materials science, solid state physics and chemistry. Applications to different materials of geoscientific relevance have expanded by the development of microspectroscopic techniques and by in situ measurements at low- to high-temperature and high-pressure conditions.