Energy non-radiative

The use of either pairs of differently fluorescent-labeled receptors or fluorescent-labeled receptors and fluorescent-labeled peptides allows fluorescence resonance energy transfer (FRET) studies. The prerequisite is that the used chromophores form a FRET pair. This means, when in close proximity, that fhe so-called donor, excited at a certain wavelength, transfers its radiation energy non-radiatively to the closely located acceptor chromophore. Emission at the acceptor s emission wave-... 

Fig. 5.7 Principle of FRET. A donor fluorophore is excited at a certain wavelength and transfers its radiation energy non-radiatively to a closely located acceptor fluorophore. Emission at the acceptor s wavelength can therefore be measured to determine whether the two chromophores are co-localized or not.

Energy, non-radiative transfer (NRET) 137,186, 908 Engineering polymer, definition 2, 3,12, 62,1349... 

Figure Bl.1.3. State energy diagram for a typical organic molecule. Solid arrows show radiative transitions A absorption, F fluorescence, P phosphorescence. Dotted arrows non-radiative transitions.

There are many ways of increasing tlie equilibrium carrier population of a semiconductor. Most often tliis is done by generating electron-hole pairs as, for instance, in tlie process of absorjition of a photon witli h E. Under reasonable levels of illumination and doping, tlie generation of electron-hole pairs affects primarily the minority carrier density. However, tlie excess population of minority carriers is not stable it gradually disappears tlirough a variety of recombination processes in which an electron in tlie CB fills a hole in a VB. The excess energy E is released as a photon or phonons. The foniier case corresponds to a radiative recombination process, tlie latter to a non-radiative one. The radiative processes only rarely involve direct recombination across tlie gap. Usually, tliis type of process is assisted by shallow defects (impurities). Non-radiative recombination involves a defect-related deep level at which a carrier is trapped first, and a second transition is needed to complete tlie process. 

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