Luminescence techniques in Earth Sciences1
Lutz Nasdala, Jens Götze, John M. Hanchar, Michael Gaft, Matthias R. Krbetschek, 2004. "Luminescence techniques in Earth Sciences", Spectroscopic methods in mineralogy, Anton Beran, Eugen Libowitzky
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The term luminescence (originally “luminescence glow”) is derived from lumen (Latin for light). It describes the ability of minerals to emit light after being excited with various kinds of energy (optical, electric, mechanical, chemical etc.). Luminescence is often described as the “cold glow” of minerals and other matter and, thus, it is not identical to the (temperature-induced) “black-body” light emission of red-hot minerals or melts. Another characteristic feature of luminescence is that the excitation process that finally causes luminescence is reversible and does not cause permanent changes or damage to a mineral sample. Luminescence emission is a remarkably widespread phenomenon; it is known from more than two-thirds of all insulator minerals (McKeever, 1985). We will discuss below that luminescence is based on energetic transitions (on the order of several electron volts) in the electronic shells of atoms in materials. Therefore, this phenomenon is sensitively controlled by the short-range order of minerals.
Luminescence has been a well-established technique in materials science research for decades. Up to the 1980's, there was already a wealth of luminescence studies on natural minerals (see Pagel et al., 2000). Unfortunately, these problems with the interpretation seem to have made the whole luminescence field of geoscientific investigation appear an uncertain and speculative technique.
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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.