Relationship between the emission spectrum and excitation wavelength

3 Relationship between the emission spectrum and excitation wavelength 

Emission occurs from the excited state Si, and so is in principle independent from the excitation wavelength. 

Since not all the molecules present at the excited states will participate in the fluorescence process, a quantum yield exists  

Equation (7.14) describes the relationship that exists between fluorescence intensity at a precise emission wavelength and intensity of incident light (Iq), fluorophore quantum yield, and its optical density at the excitation wavelength. 

Io is the intensity of the incident beam that will excite the sample. Thus, excitation with a laser will allow yield a better fluorescence intensity than if a lamp were used for excitation. The fluorescence intensity is proportional to the quantum yield, i.e., a high quantum yield leads automatically to a high fluorescence intensity. 

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