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research paper - Joseph Leonard Green H Research Paper Glow...

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Joseph Leonard Green H Research Paper 12/19/08
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Glow in the Dark The glowing stars on the roof of a child’s room in the night, the flickering of a firefly in the black of night, and the light emitted by a glow stick on Halloween are all made possible by luminescence, or cold light. Luminescence is the emission of light that does not result in the production of heat, such as phosphorescence or chemiluminescence. There are a variety of circumstances that could cause an item to glow in the dark, all of which involve some form of luminescence. What makes most toys glow in the dark is phosphorescence, which uses chemicals known as phosphors to in order to produce light. Phosphorescence is a form of fluorescence that occurs when an object is removed from a previously existing form of radiation and then emits radiation at a different wavelength for some prolonged amount of time. A phosphor is a substance that radiates light after being energized. Phosphors are used in a variety places including toys, television screens, and fluorescent lights. Phosphors must first be exposed to some form of radiation in order for them to glow in the dark. During this period, the electrons in the atoms of the phosphor get excited and move to higher energy levels. When electrons in an atom move to higher energy levels, energy is absorbed by the atom. When the source of radiation that is charging the phosphor is removed, the electrons begin to move back down to lower energy levels. When this happens, the energy that was absorbed by the atoms is emitted in the form of radiation. There are countless different varieties of phosphors, many of which are created in laboratories, but each phosphor has different characteristics. Each phosphor is energized by a different form of radiation, and each phosphor emits a different form of radiation. In the glow in the dark items that we see in everyday life, the type of radiation that is needed to charge the phosphors needs to be white light, and the radiation that it emits must be some form of visible light. The phosphors also must have a high persistence, which is the amount of time it glows for after the source of radiation is removed. For this reason, zinc sulfide and strontium aluminate are the most commonly used phosphors in manufacturing. Some glow-in-the-dark products are made so that they don’t need to be charged by visible light before they can glow in the dark. Instead the phosphors are charged by a small amount of a radioactive element such as radium. The radium is not in large enough quantity to be harmful, but it is able to charge the
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phosphors much like exposure to light would. Some examples of naturally occurring phosphorescence can be found in some minerals. After these minerals are exposed to
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This note was uploaded on 12/09/2009 for the course CHEM 204 taught by Professor Donnegan during the Spring '08 term at Alabama.

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research paper - Joseph Leonard Green H Research Paper Glow...

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