How The Detector Operates - Agilent Technologies 1100 Series Reference Manual

How the Detector Operates

Luminescence Detection
Luminescence, the emission of light, occurs when molecules change from an excited
state to their ground state. Molecules can be excited by different forms of energy, each
with its own excitation process. For example, when the excitation energy is light, the
process is called photoluminescence.
In basic cases, the emission of light is the reverse of absorption, see
sodium vapor, for example, the absorption and emission spectra are a single line at the
same wavelength. The absorption and emission spectra of organic molecules in
solution produce bands instead of lines.
Figure 70
When a more complex molecule transforms from its ground energy state into an
excited state, the absorbed energy is distributed into various vibrational and rotational
sub-levels. When this, same molecule returns to the ground state, this vibrational and
rotational energy is first lost by relaxation without any radiation. Then the molecule
transforms from this energy level to one of the vibrational and rotational sub-levels of
its ground state, emitting light, see
for a substance is its λ
1100 Series FD Reference Manual 239
Absorption of Light Versus Emission of Light
Figure
, and for emission its λ
EX
Introduction to the Fluorescence Detector 7
71. The characteristic maxima of absorption
.
EM
Figure 70. With