https://doi.org/10.1351/goldbook.R05063
Transfer of excitation energy by radiative deactivation of a donor molecular entity and reabsorption of the emitted radiation by an acceptor molecular entity.
Notes:
- Radiative transfer results in a decrease of the donor fluorescence intensity in the region of spectral overlap. Such a distortion of the fluorescence spectrum is called inner-filter effect.
- Radiative energy transfer depends on the shape and size of the vessel utilized and on the configuration of the latter with respect to excitation and observation.
- The fraction \(a\) of photons emitted by D and absorbed by A is given by \[a = \frac{1}{\mathit{\Phi}_{\rm{D}}^{0}}\int _{_{\lambda }}I_{\lambda}^{\rm{D}}(\lambda)\left [ 1 - 10^{-\varepsilon_{\rm{A}}(\lambda)c_{\rm{A}}\, l} \right ]\rm{d}\lambda\] where \(c_{\rm{A}}\) is the molar concentration of acceptor, \(\mathit{\Phi} _{\rm{D}}^{0}\) is the fluorescence quantum yield in the absence of acceptor, \(l\) is the thickness of the sample, \(I_{\lambda}^{\rm{D}}(\lambda)\) and \(\varepsilon_{\rm{A}}(\lambda )\) are the spectral distribution of the spectral radiant intensity of the donor fluorescence and the molar decadic absorption coefficient of the acceptor, respectively, with the normalization condition \(\mathit{\Phi} _{\rm{D}}^{0} = \int_{\lambda}I_{\lambda}^{\rm{D}}(\lambda)\, \rm{d}\lambda\).
For relatively low absorbance, \(a\) can be approximated by \[a = \frac{2.3}{\mathit{\Phi}_{\rm{D}}^{0}}c_{\rm{A}}\, l\int _{\lambda}I_{\lambda}^{\rm{D}}(\lambda)\varepsilon_{\rm{A}}(\lambda)\rm{d}\lambda\] where the integral represents the overlap between the donor fluorescence spectrum and the acceptor absorption spectrum.