Electron recombination rate

Table 6. Summary of the total ion-electron recombination rate constants, a, in ionised helium. 

Figure 4. Pressure dependence of the ion-electron recombination rate coefficient, (in cm s ) in pulse irradiated helium at 295 K. Bulk gas pressures are expressed as number gas densities (cm ).

Table 7. Comparison of experimental and theoretical values of the three-body ion-electron recombination rate constant, in helium at 295K.

Table 8. Experimental values of van Sonsbeek et al. [34] for the two- a ) and three-body (ttj) ion-electron recombination rate constants in irradiated helium over the temperature range 200-295K.

Kang et al. also prepared poly-31-33 [79]. The heterocycle units of poly-31 can form doubly hydrogen bonded homodimer, while the heterocycle units of poly-32 and poly-33 form triply hydrogen bonded heterodimer. In the solid state, these hydrogen bonding motifs would drive the ditopic molecules to form polymeric strucmres, both of which were utilized to increase the energy conversion efficiency of solid state DSSC up to 4.6 and 4.5 %, respectively, at 1 sun condition. Their better performance than the poly-30 electrolyte was attributed to the slower electron recombination rates and the faster ionic conductivity of the electrolytes formed from them. 

Nature of recombination The definition of the electron recombination rate is not known. In a dye-sensitized cell, unusually, two routes for electron... 

Recombination Because of the long range Coulomb interaction, the electronic recombination usually occurs much faster than the Langevin rate. The typical value of the recombination rate constant is v.lo-T cm /sec. We can find electron recombination rates in Ref. 34 and 35. So, for an electron density of vloA cm, we find the recombination rate to be on the order of 10 7sec. At the Royal Society Meeting in London (March, 198 ), David Smith surprised us by announcing that the... 

R, for electrons is the sum of the radiative and nonradiative recombination rates, and is given by equation 2 ... 

In LEDs, electrons are generally injected into a type active layer. The internal quantum efficiency, ie, the photons per injected electrons, is given by the radiative recombination rate divided by the total recombination rate ... 

Direct and Indirect Energy Gap. The radiative recombination rate is dramatically affected by the nature of the energy gap, E, of the semiconductor. The energy gap is defined as the difference in energy between the minimum of the conduction band and the maximum of the valence band in momentum, k, space. Eor almost all semiconductors, the maximum of the valence band occurs where holes have zero momentum, k = 0. Direct semiconductors possess a conduction band minimum at the same location, k = O T point, where electrons also have zero momentum as shown in Eigure la. Thus radiative transitions that occur in direct semiconductors satisfy the law of conservation of momentum. 

The equihbtium lever relation, np = can be regarded from a chemical kinetics perspective as the result of a balance between the generation and recombination of electrons and holes (21). In extrinsic semiconductors recombination is assisted by chemical defects, such as transition metals, which introduce new energy levels in the energy gap. The recombination rate in extrinsic semiconductors is limited by the lifetime of minority carriers which, according to the equihbtium lever relation, have much lower concentrations than majority carriers. Thus, for a -type semiconductor where electrons are the minority carrier, the recombination rate is /S n/z. An = n — is the increase of the electron concentration over its value in thermal equihbtium, and... 

Producing electron-hole pairs by light excitation in the small particles (d < dg ) electrons and holes can easily be transferred to an electron acceptor and donor, respectively, provided that the energetic requirements are fulfilled. The quantum efficiency of the reaction depends on the transfer rate at the interface, on the recombination rate within the particle and on the transit time, the latter being given by ... 

The donor-acceptor complexes [Ir(/r-dmpz)(CO)(PPh2 0(CH2)2R )]2 exhibit photo-induced electron-transfer rate constants of 1012s—1 and charge recombination rates slower than 2 x 10los-1 when R = pyridine and 4-phenylpyridine.534 Further studies on these complexes revealed that recombination reactions were temperature dependent and slower for the deuterated acceptors.535... 

Efficient operation of these cells requires, inter alia, that the M(III) species (obtained by electron injection) be reduced by 1 in solution preferentially to recombination with the electrons that were injected into the Ti02.To probe this competition, both recombination rates and iodide oxidation rates were determined. Recombination rates were investigated by monitoring the recovery of the characteristic ground-state M(II) MLCT bands in the visible region. These recovery rates were found to obey a rate law having two second-order terms, as in Eq. (22). 

The photoreactivity of the involved catalyst depends on many experimental factors such as the intensity of the absorbed light, electron-hole pair formation and recombination rates, charge transfer rate to chemical species, diffusion rate, adsorption and desorption rates of reagents and products, pH of the solution, photocatalyst and reactant concentrations, and partial pressure of oxygen [19,302,307], Most of these factors are strongly affected by the nature and structure of the catalyst, which is dependent on the preparation method. The presence of the impurities may also affect the photoreactivity. The presence of chloride was found to reduce the rate of oxidation by scavenging of oxidizing radicals [151,308] ... 

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