The Trivial or Radiative Mechanism of Energy Transfer

Trivial mechanism Coulombic mechanism E ectron exchange 

This process involves the emission of a quantum of light by an excited donor, followed by the absorption of the emitted photon by the acceptor. 

this mechanism requires that A must be capable of absorbing the photon emitted by D that is, the acceptor absorption spectrum must overlap with the donor emission spectrum. Radiative energy transfer can operate over very large distances because a photon can travel a long way and A simply intercepts the photon emitted by D.  

Since the photon emitted by D is absorbed by A, the same rules will apply to radiative energy transfer as to the intensity of absorption. Because singlet-triplet transitions are spin-forbidden and singlet-triplet absorption coefficients are usually extremely small, it is not possible to build up a triplet state population by radiative energy transfer. For this 

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