Excitons annihilation

Valkunas L, Trinkunas G and Liuolia V 1998 Exciton annihilation in molecular aggregates Resonance Energy Transfer ed D L Andrews and A A Demidov (New York Wiley) pp 244-307... 

Kolubayev T, Geacintov N E, Paillotin G and Breton J 1985 Domain sizes in chloroplasts and chlorophyll-protein complexes probed by fluorescence yield quenching induced by singlet-triplet exciton annihilation Biochimica Biophys. Acta 808 66-76... 

Nguyen TQ, Martini IB, Liu J, Schwartz BJ (2000) Controlling interchain interactions in conjugated polymers the effects of chain morphology on exciton-exciton annihilation and aggregation in MEH-PPV films. J Phys Chem B 104 237... 

Howard I A, Hodgkiss JM, Zhang XP, Kirov KR, Bronstein HA, Williams CK, Friend RH, Westenhoff S, Greenham NC (2010) Charge recombination and exciton annihilation reactions in conjugated polymer blends. J Am Chem Soc 132 328... 

The femtosecond fluorescence up-conversion setup has been described elsewhere [13,14]. Briefly, a second harmonic (SH) of a home-made chromium-forsterite femtosecond laser tunable from 610 to 660 nm was used to excite the sample (Fig.2) [14]. The pulse duration of the SH pulses was about 50 fs at the full width at half maximum (FWHM). We were successful in the cavity-dumping operation of this laser [14] and kept the repetition rate as low as 4 MHz. Reduction of the repetition rate was necessary to avoid multiple hits of the same location of the sample as small as possible. The excitation intensity, controlled by a neutral density filter before the sample cell, was (0.5-l)xl012 photons/cm2/pulse. Special care was taken to work at the lowest excitation light intensity so that the effect of the exciton-exciton annihilation process was negligible. 

Another example of simple bimolecular reaction is mobile exciton annihilation which is well studied in molecular crystals A + A —> 0 (zero means that usually we are not interested what is happening with reaction products) [10]. In this case the kinetic equation is obvious... 

A wide range of condensed matter properties including viscosity, ionic conductivity and mass transport belong to the class of thermally activated processes and are treated in terms of diffusion. Its theory seems to be quite well developed now [1-5] and was applied successfully to the study of radiation defects [6-8], dilute alloys and processes in highly defective solids [9-11]. Mobile particles or defects in solids inavoidably interact and thus participate in a series of diffusion-controlled reactions [12-18]. Three basic bimolecular reactions in solids and liquids are dissimilar particle (defect) recombination (annihilation), A + B —> 0 energy transfer from donors A to unsaturable sinks B, A + B —> B and exciton annihilation, A + A —> 0. 

The ES-mechanism of Frenkel-pair formation as a result of excitation of Rydberg atomic states was confirmed by recent molecular dynamics calculations [28,29]. After the bubble formation the surrounding ground state atoms appear to have moved to the second shell. It was found that the second-nearest neighboring vacancy-interstitial pairs could create the permanent defects, which remain in the lattice after exciton annihilation (Fig.Sb) [29],... 

The RYDMR spectrum of the TBPDA (C6o)2 crystals is interpreted by a model, which considers external-field modulation of a triplet-triplet exciton annihilation rate constant [6], The kinetic model of triplet-triplet exciton annihilation can be presented as follows ... 

In case of interaction between excitations, exciton-exciton annihilations (or fusion) are the most likely mechanisms to be employed for an energy density dependence of the transient decays. The dynamics is reflected in a Riccatti rate equation including simultaneous monomolecular and bimolecular processes,... 

Figure 7. Decays of photoinduced absorption in sexithienyl at pump intensities Io and Io/2 (picosecond range). Bi-molecular exciton-exciton annihilation is evidenced [21].

In Fig. 10, the transients exhibit quite different behavior from opal A to opal CT. In particular, a bi-exponential decay (Eq. 2) failed to reproduce the kinetics of opal CT. In this material, the emission is red-shifted towards 2.6 eV and the PL is strongly quenched at shorter time delays, with an unusual, non-linear kinetics in semi-log scale, indicating a complex decay channel either involving multi-exponential relaxation or exciton-exciton annihilations. Runge-Kutta integration of Eq. 5 seems to confirm the latter assumption with satisfactory reproduction of the observed decays. The lifetimes and annihilation rates are Tct = 9.3 ns, ta = 13.5 ns, 7ct o = 650 ps-1 and 7 0 = 241 ps-1, for opal CT and opal A, respectively. 

Singlet Exciton Annihilation by Paramagnetic (Doublet) Species... 

In addition to surface-enhanced exciton dissociation and geminate recombination, direct photoexcitation (Northrop and Simpson, 1956 Heilmeier et al., 1963 Harima et al., 1989) and exciton-exciton annihilation (Silver et al., 1963 Jortner et al., 1963 Braun, 1968 Johnston and Lyons, 1968 Foumy et al., 1968 Swenberg, 1969 Braun and Dobbs, 1970 Orlowski and Scher, 1983) arguments have been proposed. In direct photoexcitation, a free electron and free hole are created without the involvement of intermediate states. With the exception of the work of Harima et al. and Orlowski and Scher, there have been few references to direct or exciton-exciton photogeneration processes in the past one and a half decades. 

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