Saturday, May 23, 2009

Phosphorescence

Phosphorescence is the gradual re-emission of light at a lower energy (8).  Glow-in-the-dark objects use phosphorescence in order to work.  It differs from fluorescence because it can continue to emit light long after the source is taken away (5).  When a source of energy is applied, within the object the electrons become excited and start to move into a higher energy state.  They change their spin and get stuck in a metastable condition; the electron is not returning to ground state because it thinks it is stable.  In this way, glow-in-the-dark things are “charged up.”  They can be freed from this state by thermal energy.  This energy raises the electron to a higher level that makes it unstable and allows it to fall back to the ground state and release a photon.  This photon constitutes as the “glow” of the glow-in-the-dark object.  Because thermal energy is required to release the electron, phosphorescence is temperature dependent. The reason why the electrons are released so slowly is due to the changing spin of the electrons.  The decay of phosphorescence can vary from a fraction of a second to hours.  Phosphorescence saves the energy from its source and can continue to use it long after the source is removed (8).

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