(Received 18 March 1977; accepted 15 April 1977)
Published Online: October
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Luminescence is defined as the emission from a sample of radiation that falls in the near ultraviolet, visible, or near infrared regions of the spectrum. Conventional luminescence (fluorescence and phosphorescence) is widely used and consists of excitation by electromagnetic radiation, usually of a wavelength greater than 200 nm, and the emission of radiation that has a longer wavelength than the excitation radiation. Other forms of luminescence differ from fluorescence and phosphorescence in that they derive the excitation energy from another source. Cathodoluminescence, for instance, uses a beam of low energy electrons as an excitation source. Chemiluminescence and bioluminescence derive their excitation from chemical reactions, bioluminescence being a special case where the chemical reaction occurs in a biological specimen. Thermoluminescence derives its excitation energy from ultraviolet or ionizing radiation, but the excitation is “trapped” in the material, only to be released when the material is heated.
Graduate demonstrator, Royal Military College of Science, Shrivenham, Swindon, Wiltshire
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