Fluorolog-3 v. 2.2 (12 Jul 2002)
Glossary
16-3
Front-face detection
A mode of detection in which fluorescence is collected off the front
surface of the sample. Front-face detection usually is selected for
samples such as powders, thin films, pellets, cells on a cover-slip,
and solids.
Grating
Optical element in the spectrometer, consisting of finely scribed
grooves that disperse white light into a spectrum.
Intrinsic fluorescence
The natural fluorescent properties of molecules.
Laser
A monochromatic light source that provides high excitation inten-
sity.
Mercury lamp
Light source that emits discrete, narrow lines as opposed to a contin-
uum. A mercury lamp can be used to check the spectrometer calibra-
tion.
Mirror image rule
When the emission profile appears to be the mirror image of the ab-
sorption spectrum.
Modulated light
Light whose intensity varies in a sinusoidal manner, with a specified
frequency.
Optical density
A synonym of
Absorbance
. See
Absorbance
.
Optical-density effects
Fluorescence intensities are proportional to the concentration over a
limited range of optical densities. High optical densities can distort
the emission spectra as well as the apparent intensities.
Phase angle
The delayed relationship between the modulated emission relative to
the excitation.
Phase-modulation method
A technique for measuring fluorescence lifetimes, where a sample is
excited with light whose intensity is modulated sinusoidally. The
emission is a forced response to the excitation.
Phosphorescence
The emission of light or other electromagnetic radiation during the
transition of electrons from the triplet state to the ground state. Phos-
phorescence is generally red-shifted relative to fluorescence and oc-
curs within ~10
–6
s to several seconds. To enhance phosphorescence
detection, samples are often chilled to liquid-nitrogen temperature
(77 K).
Pockels cell
A light modulator that transmits ultraviolet and visible light, and can
be operated at variable frequencies. Highly collimated excitation
light is required.
Pulse-sampling method
A technique for measuring fluorescence lifetimes, in which an initial
population of fluorophores is excited by infinitely short pulses of
light. An advantage of this technique is the direct recording of time-
resolved emission spectra.
Raman scattering
Scattering caused by vibrational and rotational transitions. Raman
bands generally appear red-shifted relative to the incident electro-
magnetic radiation. The primary characteristic of Raman scatter is
that the difference in energy between the Raman peak and the inci-
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