Describe the mechanisms of Stokes direct line fluorescence and resonance fluorescence. In what way are the measurements based on direct line fluorescence better than that based on resonance fluorescence?
Atomic fluorescence spectrometry is u complementary technique lo atomic absorption in that it measures the light that is re-emitted after absorption. There are u number of different mechanisms by which electronic transitions in atoms can lead to fluorescence.
The fluorescence signal is normally measured at a 900 angle to the exciting line source to keep transmitted line source radiation out of the detector. An air/acetylene flame is the most common atom source, although Baird Corporation has marketed an instrument that employs an inductively-coupled plasma. The intensity ot’ the fluorescence is directly related to the intensity of the line source, so high intensity sources are sought and used. These include electrodeless discharge lamps. tuneable dye lasers, and pulsed hollow cathode lamps. For extremely intense sources, such as dye lasers, the fluorescence response becomes saturated. This is a desirable, in fact, ideal, condition since it renders the fluorescence insensitive to minor source
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