- Introduction
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- This on-line tutorial introduces some physics related to
fluorescence and the emission of light by solids. As part of
the interactive nature of this tutorial you should record answers
to the questions posed and observations completed. We recommend
that you paste each question into your word processor and type
your answer. For sketches you may capture our images and add
to them with a drawing program.
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- In solids the energy bands are separated by an energy gap
that results from the interactions of numerous closely spaced
atoms. These energy bands and gap play a very important role
in the light emission process of luminescent materials and devices
because most of these materials and devices consist of solids.
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- If electrons in the valence band are supplied enough energy
— mechanical, chemical, electrical, or light — they
change to energy levels in the conduction band. These electrons
can lose this recently acquired energy in the form of light by
changing from energy levels in the conduction band to energy
levels in the valence band. In some cases the energy supplied
to these valence electrons equals the energy of the light emitted
by the luminescent solid; in others only a fraction of the incoming
energy goes out as light.
Fluorescence, for example, involves a luminescent solid absorbing
ultraviolet (UV) light and emitting visible light. Because UV
light has higher energy than the visible light, the simple energy
band and one gap model cannot explain this process. Thus, the
simple energy band model needs to be modified to explain fluorescent
materials.
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