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Name: David Ross
Status: student
Age: 20s
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Question:
I need to understand fluorescence. Specifcially I want to measure something that flureces. What is the waveleangth of fluoresced light (excited by UV)and what type of optical sensor can be used to measure it.



Replies:
Fluorescence involves the following:

1. Light is absorbed by a molecule (or atom). This excites the molecule (or atom) into an energetic electronic state. The exciting light must have at least enough energy to cause the excitation and must be at a wavelength that is absorbed by the molecule (or atom).

2. Often, though not always, the energy of the excited molecule is very rapidly redistributed to produce a lower energy state.

3. This lower energy state then emits a photon (fluoresces) to move to an even lower energy state (often the ground state -- usually the starting point for step 1).

Thus, the fluorescence wavelength depends on the particular molecule (or atom) that is excited but it is (almost) always at a longer wavelength (lower energy) than the excitation light. Typically, the wavelengths are in the visible.
Photomultiplier tubes are ideal sensors for these experiments.



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