الفهرس 
الملخص العربى
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Abstract
When a substance absorbs energy in some form or other, a fraction of the absorbed energy may be re-emitted in the form of electromagnetic radiation in the visible or near visible region of the spectrum. This phenomena is called luminescence. Luminescence is a process which involves at least two steps : the excitation of the electronic system of the phosphor and the Subsequent emission of photons, These steps mayor may not be separated by intermediate processes. Excitation may be achieved by bombardment with photons (photoluminescence) , with electrons (cathodoluminescence), or with other particles. Luminescence can also be induced as the result of a chemical reaction (chemiluminescence) or by the application of electric field (electroluminescence).