Physics of Optically Active Technology
If a single photon approaches an atom which is receptive to it, the photon can be absorbed by the atom in a manner very similar to a radio wave being picked up by an aerial. At the moment of absorption the photon ceases to exist and the total energy contained within the atom increases. This increase in energy is usually described symbolically by saying that one of the outermost electrons "jumps" to a "higher orbit". This new atomic configuration is unstable and the tendency is for the electron to fall back to its lower orbit or energy level, emitting a new photon as it goes. The entire process may take no more than 1 x 10−9 seconds. The result is much the same as with reflective colour, but because of the process of absorption and emission, the substance emits a glow. According to Planck, the energy of each photon is given by multiplying its frequency in cycles per second by a constant (Planck’s constant, 6.626 x 10−27 erg seconds). It follows that the wavelength of a photon emitted from a luminescent system is directly related to the difference between the energy of the two atomic levels involved.
In terms of wavelength, this relationship is an inverse one so that if an emitted photon is to be of short wavelength (high energy), the gap to be jumped by the electron must be a large one. The numerical relationship between these two aspects is the inverse of Planck's constant. Chemical engineers are able to devise molecules with these energy levels in mind, so as to adjust the wavelength of the emitted photons to produce a specific colour.
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