Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Fluorescence
Name: David Ross
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: N/A

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.

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.

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory