Trapped electrons nature

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... 

Negative Ions and Trapped Electrons. At the present time we can only speculate on the nature of electron traps in irradiated polyethylene. Partridge (33) suggests that electrons are trapped between molecular chains because luminescence in irradiated polyethylene occurs in the temperature intervals where mechanical losses occur. For large doses, free radicals, R , are abundant enough to be significant in trapping electrons. The reaction ... 

A study on fulleroisoxazolines showed that these adducts undergo retro-cycloaddition by heating in the presence of copper(II) triflate as a catalyst and an excess of a dipolarophile to trap nitrile oxide. The electronic nature of the isoxazoline substituents strongly influences the reaction outcome <07JOC3840>. The fulleroisoxazolines 50 functionalized with electron-donor groups have been synthesized and their photophysical properties analyzed <07EJO2175>. 

The powder EPR signal is dominated by a hyperfine doublet due to the interaction between the trapped electron and a single proton ( H, I = 1/2). The H hyperfine couplings can be more precisely determined by ENDOR, with values of A] = 2.07G, A2 = 2.00G, A3 = 0.31 G [23]. These hyperfine parameters indicate that the local symmetry of the site is lower than axial for a purely axial system, the hyperfine parameters should take the form A] = A2 = Aj and A3 = Ay. Although the difference between A] and A2 is small, the slightly rhombic nature of the parameters is very important and extremely informative. The magnitude of these hyperfine couplings also indicates that the electron-proton interaction is weak. 

What is the nature of wb ( weakly bound ) electrons observed on the short time scale and in solids Does such a species exist in liquid water Are the wb electrons in alcohols partially solvated by their alkyl groups Are these solvent vacancy trapped electrons, as suggested for ice-Ih Are these the same species that are observed in low-temperature solids ... 

The absorbing sites have been discussed in terms of the cation-anion couples in low coordination on the surface, but no hypothesis has been made regarding the nature of the emitting sites. The emitting sites could be (i) extrinsic impurities on the surface, e.g., TMIS or organic materials (ii) point defects such as trapped electron or hole centers or (iii) sites identical or similar to the absorbing sites. These possibihties have been considered by Coluccia (13). 

The first two possibilities have been showm to be unlikely. Deliberate dopings and treatments known to increase the population of surface defects lead to the quenching of the photoluminescence (86). Moreover, surface defects are annealed at high temperatures, whereas sample treatment at high temperatures is required to observe the photoluminescence (87). Although it has been suggested that trapped electron centers (FJ) could play a role (88,89), it has been concluded by Coluccia (13) that the photolumines-cent sites are of the same nature as the absorbing sites and the emission process is as described by Eq. (12). 

The g-factors of electrons and holes reflect the nature of the conduction and valence bands in much the same way as the effective masses. Thus in AgF, AgCl, and AgBr, free electrons and shallowly trapped electrons whose wavefunctions are made up largely of conduction band functions are expected to be isotropic in nature. A free electron at the bottom of the band will have a single effective mass and g-factor. In contrast, free holes near the L-point and shallowly trapped holes whose wavefunctions are largely valence band functions are expected to show anisotropic behavior. A free hole will have parallel and perpendicular g-factors. The available data on electron and hole masses were given in Table 1 and the data on g-factors are given in Table 9. Thermalized electrons and holes in both modifications of Agl will be at the zone center. The anisotropic nature of the wurtzite crystal structure will be reflected in the effective masses and g-factors. 

---