In the context of @[email protected], the integral, \(J=\int _{0}^{\infty }f_{\text{D}}^{'}\left(\sigma \right)\ ɛ_{\text{A}}\left(\sigma \right) \ \mathrm{d}\sigma \), which measures the overlap of the @[email protected] of the excited donor, D, and the @[email protected] of the @[email protected] acceptor, A; \(f_{\text{D}}^{'}\) is the measured normalized emission of D, \(f_{\text{D}}^{'}=\frac{f_{\text{D}}\left(\sigma \right)}{\int _{0}^{\infty }f_{\text{D}}\left(\sigma \right) \ \mathrm{d}\sigma }\), \(f_{\text{D}}(\sigma)\) is the @[email protected] of the donor at wavenumber \(\sigma \), and \(ɛ_{\text{A}}(\sigma)\) is the decadic @[email protected] of A at wavenumber \(\sigma \). In the context of @[email protected], \(J\) is given by: \[J=\int _{0}^{\infty }\frac{f_{\text{D}}^{'}\left(\sigma \right)\ ɛ_{\text{A}}\left(\sigma \right)}{\sigma ^{4}} \ \mathrm{d}\sigma \] In the context of @[email protected], \(J\) is given by: \[J=\int _{0}^{\infty }f_{\text{D}}\left(\sigma \right)\ ɛ_{\text{A}}\left(\sigma \right) \ \mathrm{d}\sigma \] In this case \(f_{\text{D}}\) and \(ɛ_{\text{A}}\), the @[email protected] of donor and @[email protected] of acceptor, respectively, are both normalized to unity, so that the @[email protected] for energy transfer, \(k_{\text{ET}}\), is independent of the @[email protected] of both transitions (contrast to Förster mechanism).