Phosphor Substance
A phosphor is a solid material that emits visible light when activated (excited) by an external energy source such as an electron beam, heavy charged particles, or ultraviolet light. A characteristic feature of such emission is the persistence of the emitted light after the excitation is removed. Many phosphors have been developed having emission in various parts of the visible spectrum and persistence times ranging from a few billionths of a second to many hundreds of seconds. Major applications include coating of flourescent light bulbs, cathode ray tubes, radar screens, television picture tubes, and luminous intrument dials. If phosphor contain in mixed with other substances called as phosphorus.
Phosphorescence of Phosphor Substance
Phosphorescence is a form of light emission caused by the excitation of atoms by an outside source. Phosphorescence differ from fluorescence only by long persistence of the emitted light after the excitation is turned off. The initial excitation can arise by electron beam bormbardiment, impact by charged particles from radioactive decay, chemical reactions, and absorption of ultraviolet light. The process involve the excitation of electrons to intermediate metastable energy levels, or "electron traps," from which the electrons rarely decay directly to the original ground state. Instead excitation usually transfer the excitation energy to other levels that then rapidly decay by emitting light.
Practical applications of phosphorescent emission are based on the long term energy storage aspect, the efficiency of the energy conversion process, and the averaging effect provided by the long term persistence. The latter is especially important in television picture tubes and oscilloscopes.
