Fluorolog-3 v. 2.2 (11 Jul 2002)
Applications
10-5
Emission (solid line) and synchronous (broken line) scans of a mixture of
polynuclear aromatic hydrocarbons.
The solid line in the figure above is the emission spectrum acquired on a Fluorolog
®
system (single-grating monochromators) with constant wavelength excitation. As
shown by the broken line, when the sample is scanned synchronously, five individual
components are resolved into unique, sharp peaks indicative of the individual com-
pounds.
Operating in the IR region
The Fluorolog
®
-3 series of spectrofluorometers can be equipped to operate in the infra-
red region of the spectrum, thereby opening up totally new areas of applications for
fluorescence spectroscopy. Typically, an IR spectrofluorometer requires components
significantly different from those found in conventional instruments. Because the most
widely used photomultiplier detector is insensitive above 860 nm, an IR spectrofluoro-
meter must be equipped with a red-sensitive photomultiplier, or a solid-state detector
whose response is effective far into the IR region. With a photomultiplier sensitive to 1
µm, only minimal system modification is necessary. A phase-sensitive lock-in amplifier
and a light chopper are required.
Phosphorescence for time-resolved data
Both fluorescence and phosphorescence spectra are photon emissions that occur when
molecules return from an excited electronic state to the ground state. The nature of the
excited state distinguishes the two: fluorescence is associated with relaxation from a
singlet excited state, while phosphorescence is associated with relaxation from a triplet
excited state. Fluorescence usually occurs within a few nanoseconds after excitation.
300 400 500
Wavelength (nm)
1.0
7.5
5
2.5
0
Intens
ity (×
10
6
count
s s
–1
)
Perylene
436 nm
Acenaphthene
323 nm
Fluorene
303 nm
2,3-Benzofluorene
342 nm
Anthracene
382 nm
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