Energy-trapping phenomena

Such extremely fast energy-migration and energy-trapping phenomena cannot be explained by NRET theory based on the dipole-dipole mechanisms [62]. If chromophores are arrayed, photoexcitation energy can be delocalized over an array as an exciton [63]. This may be true, at least locally, for the 1-Np cluster in the microdomain of poly(A/l-Np/Py) [26]. 

As will be seen further, modifications of the free carriers concentration will probably involve new catalytic properties. But one has to stress that other states of electronic excitation should be taken into account, for instance, excitons. Furthermore, under irradiation, the distribution of the electrons among all the characteristic energy levels of the solid do not correspond to the thermal distribution given by the Fermi-Dirac statistics. Let us also indicate that the electronic imperfections, transient by nature, may sometimes possess a quasi-permanent character with regard to the trapping phenomenon. 

Hillman AR, Efimov I, Ryder KS (2005) Timescale-and temperature-dependent properties of viscoelastic PEDOT films. J Am Chem Soc 127 16611 Mohamoud MA, Hillman AR, Efimov I (2008) Film mechanical resonance phenomenon during electrochemical deposition of polyaniline. Electrochim Acta 53(21) 6235-6243 Hillman AR, Dong Q, Mohamoud MA, Efimov I (2010) Characterization of viscoelastic properties of composite films involving polyaniline and carbon nanotubes. Electrochim Acta 55(27) 8142-8153 Efimov I, Hillman AR, Schultze JW (2006) Sensitivity variation of the electrochemical quartz crystal microbalance in response to energy trapping. Electrochim Acta... 

The trapped electron provides a classic example of an electron in a box . A series of energy levels are available for the electron, and the energy required to transfer from one level to another falls in the visible part of the electromagnetic spectrum, hence the colour of the F-centre. There is an interesting natural example of this phenomenon The mineral... 

Despite limitations, the most common sorption medium is activated charcoal — a form of carbon treated in such a way as to open a large number of pores. The surface energy of the material and the pores combine to produce a material that can first attract and then trap small organic molecules. The attraction is via adsorption rather than absorption. Adsorption applies to attachment to the surface absorption is a bulk effect. Extraction is a bulk phenomenon. Simply put, adsorption is a function of surface area while absorption is a mass effect. 

It appears at this time that one of the most important mechanisms involved in the luminescence of rare earth ions is energy exchange between them. One may clearly differentiate between two distinct mechanisms (a) radiative exchange and (b) nonradiative exchange. In the radiative mechanism, a photon emitted by ion A is captured by ion B. Since the photon has left the A system, the capture of it by B cannot decrease the lifetime of A. However, f the photon is shuttled back and forth between similar or dissimilar ions, the fluorescent lifetime could well be increased by radiation trapping. This is an interesting phenomenon and warrants further discussion. 

Concerning ices, it has been discussed that they must be amorphous (Smoluchowski 1983) in the interstellar medium and not crystalline. This implies that the adsorbed H atoms are localized in deep traps so that their wavefunctions have a limited spatial extent. This fact reduces significantly their mobility and hence the interaction with another H atom absorbed on another site is slow as compared to the residence time unless the two atoms happens to be localized near each other. This phenomenon reduces the rate of H2 formation by several orders of magnitude when compared to the situation on crystalline surfaces. Computational simulations on soft and hard ice model surfaces have shown that for a cross-section of 4,000 nm2 the reaction probability is 1 (Takahashi et al. 1999). Furthermore, the H2 formed, due to the high amount of energy liberated is rapidly desorbed in an excited state from the ice mantle in timescales of 500 fs (Takahashi et al. 1999). 

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