spectral overlap

https://doi.org/10.1351/goldbook.S05818
In the context of @R05063@, 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 @E02060@ of the excited donor, D, and the @A00043@ of the @G02704@ 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 @P04631@ of the donor at wavenumber $$\sigma$$, and $$ɛ_{\text{A}}(\sigma)$$ is the decadic @M03972@ of A at wavenumber $$\sigma$$. In the context of @F02488@, $$J$$ 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 @D01654@, $$J$$ 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 @E02060@ of donor and @A00043@ of acceptor, respectively, are both normalized to unity, so that the @O04322@ for energy transfer, $$k_{\text{ET}}$$, is independent of the @O04339@ of both transitions (contrast to Förster mechanism).
See:
energy transfer (in photochemistry)
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2275 [Terms] [Paper]