Name: David Ross
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: N/A
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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