Notebook

Notebook, 1993-

RELATIONSHIPS

{From: Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.]

Phosphorescence
Fluorescence and phosphorescence are caused by light striking atoms. In the collision, energy is transferred from the light to the electrons of the atoms. This energy may be re-radiated as light or dissipated as heat. If the emitted light is of the same frequency as the incident light, the effect is a kind of scattering. In many cases, however, the emitted light is of a different (usually lower) frequency than the incident light, and is characteristic of the atom that emitted it. The immediate re-radiation of absorbed light energy as light of a different color is called fluorescence. [The color of the fluorescence depends on the nature of the mineral.]

Some materials continue to emit light for a time after the incident radiation has been cut off. This is phosphorescence, usually a property of crystals or of large organic molecules. Phosphorescence often depends on the presence of minute quantities of impurities or imperfections in the crystal that provide "traps" for excited electrons. These electrons have received extra energy from incident radiation. The electrons remain in the "traps" until shaken loose by the heat vibrations of the atoms in the crystal. Phosphorescent light is emitted as the electrons return to their normal positions. Solid substances that produce light in this way are called phosphors. [p. 52]

[Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.]









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