Many minerals emit radiation, referred to as luminescence, when bombarded by an energy source. Emissions are commonly in the visible range; however, ultraviolet (UV) and infrared (IR) emissions may also occur (Marshall, 1988, p. 1). Luminescence is given different names depending upon the energy source: e.g., bombardment by high-energy UV photons generates photoluminescence; a beam of energetic ions produces ionoluminescence; X-rays generate radioluminescence; and bombardment by high-energy electrons produces cathodoluminescence (Pagel et al., 2000a). Cathodoluminescence refers to emission of characteristic visible (and UV) luminescence by a substance that is under bombardment by electrons, where the cathode is the source of the electrons. Note: the word cathodoluminescence is often abbreviated to CL.

The phenomenon of luminescence was recognized as early as the seventeenth century (Leverenz, 1968); however, systematic observations and discussion of cathodoluminescence did not take place until around 1965 (e.g., Smith and Stenstrom, 1965). Early cathodoluminescence studies were carried out with a cathodoluminescence microscope, which is fundamentally a petrographic microscope to which some kind of cathode gun is attached. Subsequently, the electron-probe microanalyzer and, especially, the scanning electron microscope have been utilized to generate high-resolution, high-magnification cathodoluminescence images (Chapter 3).

Early applications of cathodoluminescence to geological materials included observations of the CL characteristics of both carbonate and silicate minerals, particularly quartz and feldspars. Many investigators noted, for example, that some carbonate minerals display zoning in CL images, which was not visible in other kinds of images.