Reabsorption and Reemission

Fluorescence lifetime measurements can be severely impaired by reabsorption. Reabsorption becomes especially noticeable at high fluorophore concentrations. A fraction of the fluorophore molecules is excited by the fluorescence of other mole-eules. Reemission changes the shape of the measured decay curves and increases the measured lifetime. The size of the effect depends on the overlap of the absorption and the emission band of the fluorophore, on the coneentration, and on the optieal geometry [308]. The straightforward solution to reabsorption problems is to reduee the eoncentration. If this is not possible a thin sample cell should be used, and be illuminated from the front. 

Reabsorption and reemission ean be pitfalls, partieularly in poorly aligned optical systems. If the fluorescence is detected from outside the excited spot of the sample, the detected signal is almost exclusively excited by reabsorption. Therefore, the alignment of the detection system should be checked if odd fluorescence decays are detected. 

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Reabsorption and reemission. In scattering media the effect of reabsorption plays a very important role (see Section 6.3). The consecutive reemission will slow down the decay process (see Section 6.4). The effect is not very big, but it can be... 

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