Energy transfer nonradiative

Nonradiative energy transfer is induced by an interaction between the state of the system, in which the sensitizer is in the excited state and the activator in the ground state, and the state in which the activator is in the excited and the sensitizer in the ground state. In the presence of radiative decay, nonradiative decay, and energy transfer the emission of radiation from a single sensitizer ion decays exponentially with time, /. 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

Nemkovich NA, Gulis IM, TominV I (1982) Excitation-frequency dependence of the efficiency of directed nonradiative energy transfer in two-component solid solutions of organic compounds. Optic Spectros 53 140-143... 

Nonradiative energy transfer has a major role in the process of photosynthesis. Light is absorbed by large numbers of chlorophyll molecules in light-harvesting antennae and energy is transferred in a stepwise manner to photosynthetic reaction centres, at which photochemical reactions occur. This fundamental energy-transfer process will be considered in more detail in Chapter 12. 

Nonradiative energy transfer is very often used in practical applications, such as to enhance the efficiency of phosphors and lasers. A nice example is the commercial phosphor Cas(P04)3 (FCl), which is doubly activated by Sb + and Mn + ions. When the phosphor is singly activated by Mn + ions, it turns out to be very inefficient, due to the weak absorption bands of the divalent manganese ion. However, coactivation with Sb + ions produces a very intense emission from the Mn + ions, because the Sb + ions (the donor centers) efficiently absorb the ultraviolet emission (253.6 nm) of... 

F ure 5.17 Sequential steps for a nonradiative energy transfer process (see the text). 

FRET interactions are typically characterized by either steady-state or transient fluorescence emission signals from the donor or acceptor species. Efficient nonradiative energy transfer results in donor PL loss associated with acceptor gain in photoluminescence intensity (if the acceptor is an emitter). The rate of this energy transfer is related to the intrinsic lifetime of the isolated donor and depends strongly on the donor-acceptor separation distance ... 

Gandy and co-workers (134) have also observed energy transfer from cerium to neodymium in a silicate glass. The evidence is that this is again an example of nonradiative-energy transfer. Intensity measurements indicate... 

Axe and Weller (52) studied fluorescence and energy transfer of europium in yttrium oxide. In an experiment somewhat similar to that of Peterson and Bridenbaugh (54) on terbium, Axe and Weller were able to obtain experimental evidence for nonradiative-energy transfer between europium and other trivalent rare earth ions. Their study included both intensity and fluorescent-lifetime measurements. 

These three factors are included in the expression derived by Robinson and Frosch from time-dependent perturbation theory, for the nonradiative energy transfer or radiationless transition probability kNR per unit time,... 

The nonradiative energy transfer must be differentiated from radiative transfer which involves the trivial process of emission by the donor and subsequent absorption of the emitted photon by the acceptor ... 

In general, two different types of mechanisms are postulated for the nonradiative energy transfer phenomenon ... 

Basile (2) has shown that the nonradiating energy transfer occurring in the system PST-TPB can be described well by the theory of dipole-dipole interaction developed by Forster (7). His calculations show the possibility of a nonradiating energy transfer over distances of 20-25 A. 

At medium concentrations (10"2 mole %) the scintillation intensity is determined mainly by the product of the efficiency of the nonradiating energy transfer /NXy and the molecular quantum efficiency of Y q0Y (3). Because the decrease of the scintillation intensity is maximum at this concentration and (12) because the molecular quantum efficiency q0y does not depend strongly on temperature, the quantum efficiency of the nonradiating energy transfer must decrease. Therefore, the temperature-dependent behavior is determined mainly by the properties of the matrix material. 

The process of the nonradiating deactivation in the matrix competes with the nonradiating energy transfer process for the activation energy of an excited molecule in the matrix. With increasing temperature the decision is made for the nonradiating deactivation of the polystyrene molecules (9). 

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