Seite - 62 - in Advanced Chemical Kinetics

molecule occupying the excited state and the initially excitedmolecule in the electronic groundstate. ð4Þ Theenergytransfermechanismsinvolveanentitywhichpresents theexcessenergy,definedas donor (D) andan entity that can receive this excess energy, defined as acceptor (A). Theyare classifiedas radiativeoranon-radiativeprocess,dependingon theoccurrenceof the lumines- centemission fromthedonor. 3.1.Radiativeenergy transfer Thedonor in the electronic excited state relaxes to radiatively release its excess energy. Thus, fluorescence (orphosphorescence) needs to occur topromote the energy transfer through the absorptionof the fluorescenceof thedonorbytheacceptor [4]. It isknownasthetrivialenergy transfermechanismand it is enabledby the overlapbetween the absorption spectrumof the acceptor with the luminescence spectrum of the donor. It does not require that donor and acceptorbe in the sameenvironment and it is independentof the luminescence lifetimeof the donoranddependson theconcentrationof theacceptor ([A]), thequantumyieldof thedonor (φeD)andthemolarextinctioncoefficientof theacceptor (εA). ð5Þ Scheme inFigure3presents the trivialmechanismofenergy transfer. Figure3. Schemeof the trivialmechanismofenergy transfer. Advanced Chemical Kinetics62