Recombination dynamics

We interpret this finding as follows. After excitation at 3.4 eV, the photogenerated excitons thermalize and initially occupy extended states in the QW. These free excitons then rapidly relax toward lower-lying localized states, which is the reason for the rapid spectral diffusion as well as for the rapid initial decay of the PL transient. Once they reach the localized states, the excitons are subject to a much slower redistribution within the band of the localized states, described by a stretched exponential [89]. Mathematically, we thus deal with the following situation  

500 ps and (b) temporal variation of the photon energy at the PL spectral peak. Note the different slopes for short and long times. The lines are fits according to the equation AE = —kTac In(vt). 

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Papanikolas J M, Gord J R, Levinger N E, Ray D, Versa V and Lineberger W C 1991 Photodissociation and geminate recombination dynamics of t in mass-seiected, (Cfjj j ciuster ions J. Phys. Chem. 90 8028-40... 

Ben]amin I, Barbara P F, Gertner B J and Hynes J T 1995 Nonequilibrium free energy functions, recombination dynamics, and vibrational relaxation of tjin acetonitrile molecular dynamics of charge flow in the electronically adiabatic limit J. Phys. Chem. 99 7557-67... 

To examine the soUd as it approaches equUibrium (atom energies of 0.025 eV) requires molecular dynamic simulations. Molecular dynamic (MD) simulations foUow the spatial and temporal evolution of atoms in a cascade as the atoms regain thermal equiUbrium in about 10 ps. By use of MD, one can foUow the physical and chemical effects that induence the final cascade state. Molecular dynamics have been used to study a variety of cascade phenomena. These include defect evolution, recombination dynamics, Hquid-like core effects, and final defect states. MD programs have also been used to model sputtering processes. 

For lock-in amplification the pump is modulated at a reference frequency w (see Fig. 7-1), which means that AT is not constant over time. Rather, its magnitude (and its phase) depends on the modulation frequency [8. In order to find the frequency-dependent A7 (cu), let us assume that the recombination dynamics are monomolecular with a single lifetime r. Then we can write for the number density of excitations N at time / ... 

The first reaction filmed by X-rays was the recombination of photodisso-ciated iodine in a CCI4 solution [18, 19, 49]. As this reaction is considered a prototype chemical reaction, a considerable effort was made to study it. Experimental techniques such as linear [50-52] and nonlinear [53-55] spectroscopy were used, as well as theoretical methods such as quantum chemistry [56] and molecular dynamics simulation [57]. A fair understanding of the dissociation and recombination dynamics resulted. However, a fascinating challenge remained to film atomic motions during the reaction. This was done in the following way. 

The I2 system has been investigated experimentally, theoretically, and computationally by several groups, as a prototype for the study of dissociation and recombination dynamics influenced by the interactions with a surrounding solvent or cluster of solvent molecules[9],[36]-[41]. The system can be effectively modelled by two VB states[9],[41], which allows a focus on several key aspects of the implementation of the theory, without being hindered by the complexity of a multistate calculation. The implementation steps are conveniently collected in the flow chart in Table 1, to which the reader is referred to for a comprehensive overview of our strategy. All the details of the calculation are reported in BH-II. The effective wave function for the I2 reaction system can be written as... 

E. Palomares, J.N. Clifford, S.A. Haque, T. Lutz, J.R. Durrant, Control of charge recombination dynamics in dye sensitized solar cells by the use of conformally deposited metal oxide blocking layers,... 

Choi W, Termin A, Hoffmann MR (1994) The role of metal ion dopants in quantum-sized Ti02 Correlation between photoreactivity and charge carrier recombination dynamics. J Phys Chem 98 13669-13679... 

A transient optical absorption study of charge recombination dynamics was recently reported on CD CdS with a crystal size of 5 nm (no details of the deposition were provided) [35]. Three different time constants for the decay of the transient absorption bleaching were measured (0.8 psec, 17 psec, and 800 psec) and were attributed to three groups of nanocrystals with specific defects. Tri-octylphosphine oxide (TOPO), a well-known passivating agent for CdSe nanocrystals that acts by binding to Cd, was found to increase the relative contribution of the 800-psec recombination, which was therefore attributed to volume recombination, since the TOPO is expected to reduce the relative contribution of surface recombination (represented by the two shorter time constants). 

Effect of excitation wavelength on the charge recombination dynamics of excited donor acceptor complexes... 

Charge injection and charge recombination dynamics have also been examined for [(dcb)20s(CN)2] and [(dcb)Os(SCN)2]. Injection occurs with rate constants > 108 s 1 (probably much greater), but recombination rate constants are on the microsecond timescale. Detailed analysis of the combined... 

Finally, relating the charge-separation and charge-recombination dynamics with the distance between electron donor and acceptor (i.e. center-to-center distance Rcc), allows the evaluation of the attenuation factor / . The corresponding relationships in THF are represented in Fig. 9.8. Both reveal linear dependencies and the derived attenuation factors are in perfect agreement with each other ... 

Additionally, in order to examine the charge-recombination dynamics we turned to complementary nanosecond transient absorption measurements. Once more, the spectral fingerprints of the radical ion pair state emerged immediately after the laser pulse and their decays yielded charge-recombination lifetimes in the order of 4.0 ps (Fig. 9.38). 

Table 9.5 Charge-separation and charge-recombination dynamics as determined by femtosecond and nanosecond time-resolved spectroscopic measurements for 18a and 18b in THF...

Rothenberger G, Moser J, Graetzel M, Serpone N, Sharma DK. Charge carrier trapping and recombination dynamics in small semiconductor particles. J Am Chem Soc 1985 107 8054. 

The correlation of the landscape measures the fitness similarity between a sequence and its d-mutant neighbors, where d is the number of mutations. As a sequence accumulates mutations, the fitness is increasingly altered. On smooth landscapes, the rate of fitness change is slow and therefore the landscape is correlated. Conversely, on rugged landscapes, the rate is more rapid and the landscape is uncorrelated. Studies of the relationship between fitness and distance have been used to quantitate the correlation among population ensembles on the RNA landscape (Fontana and Shuster, 1987), recombination dynamics (Born-holdt, 1998), and the success of genetic algorithms (Manderick et al., 1991 Jones and Forrest, 1995). 

Since GaN materials contain a high density of extended defects (10 - 1010 cm 2), it is expected that the carrier and exciton recombination dynamics vary from sample to sample. Studies have revealed that the exciton lifetime is correlated with the yellow emission line at about 2.2 eV the stronger the yellow... 

This review will proceed as follows. After a description of the primary processes common to all colloidal semiconductor applications, the thermodynamic requirements of those processes will be discussed, with special emphasis on those relevant to photocatalysis. This will be followed by a short section on how the colloidal state affects the semiconductor band structure and photogenerated charge carrier recombination dynamics, leading into a longer section on the dynamics of interfacial charge transfer... 

The first picosecond laser spectroscopic study to examine charge carrier trapping and recombination dynamics was reported by Gratzel, Serpone and co-workers [15]. The mean lifetime of a single electron/hole pair was determined to be 30 15 ns at low occupancy of electron/hole pairs in the titanium dioxide particles. At high occupancies, where recombination followed second-order kinetics, the bulk rate coefficient for recombination was (3.2 1.4) x 10-11 cm3 s 1. 

Ogrodnik, A., Keupp, W., Volk, M., Auermeier, G., and Michel-Beyerle, M. E., 1994, Inhomogeneity of radical pair energies in photosynthetic reaction centers revelaed by differences in recombination dynamics of P when detected in delayed emission and in absorption. J. Phys. Chem., 98 343293439. 

Volk, M., Ogro(hiik, A., and Michel-Beyerle, M. E., 1995, The recombination dynamics of die radical pair P H- in external magnetic and electric fields. In Anoxygenic Photosynthetic Bacteria, (R. E. Blankenship, M. T. Madigan, and C. E. Bauer, eds.) pp. 595n626, Kluwer Academic Publishers, Dordrecht, The Nedierlands. 

Time-Resolved Resonance Raman Study of the Recombination Dynamics Photodissociated Carbon Monoxide to Sperm Whale Myoglobin and Its Mutants... 

The photodissodation/recombination dynamics of I2 in an Ar matrix Wave packet propagation... 

U. Schmitt, J. Brickmann, The photodissociation/recombination dynamics of I2 in an Ar matrix Wave packet dynamics in a mixed quantum classical picture, J. Mol. Model., 2 (1996) 300.,... 

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