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.