Fluorescence spectra basic principles

Morawetz et al. [105,106] were the first to use non-radiative energy transfer (NRET) fluorospectroscopy for exploring polymer-polymer miscibility. The basic principle is as follows. In a system containing two kinds of fluorescence chromophore, if the emission spectrum of one (donor D) overlaps the absorption spectrum of the other (acceptor A), a non-radiative energy transfer from the former to the latter may occur when the system is excited by irradiation that the former selectively absorbs. The efflciency of energy transfer (E) inversely proportional to Icj/Ia> where Id and la denote the emission intensities of D and A, respectively, depends on the average distance r between D and A according to the relationship ... 

Raman scatter, and excitation emission fluorescence spectroscopy (EEFS). They use interaction with radiation from different regions of the electromagnetic spectrum to identify the chemical nature of molecules. For example, absorption of UV and VIS radiation causes valence electron transitions in molecules which can be used to measure species down to parts per million concentrations for fluorophores (i.e., EEFS) determination can even go down to parts per billion levels. Whereas UV, VIS, and EEFS are limited to a smaller, select group of molecules, the NIR, IR, and Raman scatter spectroscopy techniques are probing molecular vibrations present in almost any species their quantification limits are somewhat higher but can still be impressive. The reader is referred to textbooks for further details on basic principles of these spectroscopic techniques [3]. 

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