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Unformatted text preview: Chapter 12- Luminescent, Electrical and Thermal Properties of Gemstones Luminescence (Fluorescence and Phosphorescence) When certain materials acquire energy in one form or another, below the level which would cause incandescence or burning, they convert this energy into a cold radiation whose wavelength usually lies in the visible section of the spectrum The mechanism producing this cold radiation, or luminescence, is associated with the excitation of atoms within the material The surplus energy acquired by luminescing substances is used up in moving electrons out of their normal orbital shells into orbits of a higher energy level When these electrons eventually return to their more stable orbits, they give up the surplus energy in the form of electromagnetic radiation The light emitted is either due to some intrinsic property of the material, or the presence of luminescent impurities called activators Luminescence Due to Impurities In the case of luminescence due to crystal defects, the exciting energy is sufficient to cause an...
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- Fall '08