Sensitization energy transfer

Sensitizer singlet formed Intersystem crossing of sensitizer Energy transfer to reactant molecule... 

This unusual concentration dependence was caused by two mechanisms of sensitization, energy transfer and hydrogen transfer, occurring in the same reaction, as shown by the following scheme ... 

Bond distortion, spin crossover Sensitization, energy transfer Photoinduced electron transfer Hydrogen atom abstraction Photooxidation, photoreduction Photoaddition, photosubstitution Photodissociation, photo-cleavage Photoisomerizations Photodimerization, photo-pol3nnerization... 

In this section we review the important theoretical developments relevant to host-sensitized energy transfer. The basic interaction between two isolated ions or molecules is discussed first, then the effects of having an ensemble of sensitizer and activator ions is presented. The mathematical description of energy transfer by multi-step migration among sensitizer ions is developed and the effects of trapping at activator sites is discussed. The importance of phonons in both single-step and multi-step transfer processes is also described. 

From the preceding section it is clear that certain important questions must be answered in characterizing host sensitized energy transfer in a specific material. The first question is whether the transfer is a single-step or multistep process. If it is a single-step process, the type of interaction mechanism must be identified and the strength of the interaction determined. The latter is usually characterized by the critical interaction distance Rq. Finally, it is important to determine whether the energy transfer is a resonant or phonon-assisted process. If the transfer is a multistep process, two distinct sets of parameters must be determined ... 

In this section we will review experimental results which have contributed to our knowledge of host-sensitized energy transfer. A large part of these results is of a qualitative nature only. Nevertheless this is instructive and often of large value in predicting energy transfer phenomena in new materials. On the other hand the number of reliable, quantitative results is increasing, especially after the introduction of laser spectroscopy in this field of research. 

If we consider the material presented above, we conclude that host-sensitized energy transfer in systems like vanadates, niobates and tungstates can be described satisfactprily by a qualitative model. The actual situation differs from compound to compound due to a difference in the temperature dependence of the exciton diffusion rate. A low value of the quenching temperature of the emission of the intrinsic... 

Laser action has been obtained in 1203 Ho + by pumping through host-sensitized energy transfer ). The Er —Ho + energy transfer was demonstrated through the excitation spectrum but mechaiusm and characteristics of the transfer process were not identified. 

Luminescence kinetics studies of host-sensitized energy transfer in Eu -doped Cap2 crystals have also been reported and both radiative transfer and exciton diffusion have been found to contribute to the results. The diffusion distance is found to be about 25 A at low temperatures and increases by about an order of magnitude at high temperatures. Single-step electric dipole-dipole interaction also contributes to the energy transfer with the critical interaction distance calculated to be about 16 A. 

Energy Transfer Sensitization. Energy transfer is a process where an excited state donor molecule is returned to the ground state, with simultaneous promotion of an acceptor molecule to its... 

SCHEME 12.6 Photolysis of diaryliodonium salts—sensitized energy transfer. 

Once the excited state of the reactant has been formed, either by direct or sensitized energy transfer, the stage is set for a photochemical reaction. There are still, however, competitive processes that can occur and result in the return of... 

To proceed with our discussion about the host-sensitized energy transfer in the system of pentacene in p-terphenyl, we review the simplest of energy transfers. This is the transfer in a system that consists of a molecule or ion S (sensitizer) and a molecule (ion) A (activator). If any possible interaction (i.e., exchange interaction) between S and A is disregarded, the system may be represented by the product of the wavefunction of S and the wavefunction of A. In particular, two states of the system are of interest ... 

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