Energy trap site

From the chemist s point of view, the keto defect sites can be formed during polymer synthesis as a consequence of incomplete monomer alkylation, as well as a result of photo-, electro-, or thermooxidative degradation processes occurring after polymer synthesis. Acting as low-energy trapping sites... 

For this complex cation the zero-phonon emission is peaked at 519.9 nm. The ODMR data showed that the emission is due to an excited triplet state localized on the thpy anion [65]. This anion is positioned at the same crystallographic site as the energy trapping site of Rh(TTB)+ [64,65]. The lifetimes and emissive properties of the triplet sublevels of the Rh(TPB)+ species are very similar to... 

Evidence for energy migration in synthetic aromatic polymers is often circumstantial, commonly being provided by observations of enhanced efficiency of emission from energy trap sites. Steady-state and. 

In PS I there are two j8,j8-dimers (indicated by arrows in Fig. 6) positioned symmetrically aroimd the special pair P700 absorbing around 700 nm. It has been speculated that these dimers form the so-called red Chls which act as energy-trapping sites in the antenna, about 1.8 nm away from P700 [16]. 

Figure 18 Schematic representation of the energy transfer to a trap site ( 0 ), formed during irradiation, depending on the molar fraction of CUA in LB films.

The trapping rate dPT/dt is given by the sum of energy-transfer rates from any site donor i to any trap site J. 

The proposal that holes are detrapped at lower temperatures than the excess electrons is based on the observations discussed above in Very Shallow Traps and Shallow Traps (Sec. 4.3.2). One expects that the activation energy needed to detrap the hole from Gua in duplex DNA is relatively small, an order of magnitude less than that needed to detrap the electron. This fits well with the observation that upon warming 4 K irradiated crystalline DNA to 77 K, 10-30% of the radicals anneal out, i.e., at least one of the trapping sites [fide infra Gua(N3-H) ] is very shallow. 

At lower temperatures (T < T,), a exhibits a temperature dependence characteristic of a small activation energy (= 0.03 eV) for excitation of charge carriers from stationary trap sites It is reasonable to suspect that small polarons tend to be trapped at impurity centers at low temperature. 

Because the escape probability of carriers from trapping sites is proportional to exp(-fi/ D, the location of a glow peak on the temperature scale provides encoded information on the value of thermal activation energy E. Hence, a glow curve represents a spectrum of energies that are required to free carriers from the various species of traps in the material. 

The absorption of energy by the grains produces conduction electrons and either free or trapped holes. The conduction electrons and the holes diffuse initially by a three-dimensional random walk. In chemically sensitized crystals, the holes are trapped by products of chemical sensitization which thus undergo photo-oxidation. Rapid recombination between a trapped hole and an electron is avoided by the delocalization as an interstitial Ag ion of the nonequilibrium excess positive charge created at the trapping site. Latent pre- and sub-image specks are formed by the successive combination of an interstitial Agi ion and a conduction electron at a shallow positive potential well. 

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