Energy migration, phonon-assisted

Energy Migration Resonant and Phonon-Assisted Processes. 83... 

Fig. 2 a Energy migration, that is multi-step energy transfer between chemically identical chromophores. b Within the inhomogeneous distribution it can proceed via an resonant process (straight arrow) or via a phonon-assisted process whereby the energy mismatch between the donor and the acceptor is made up by lattice phonons (curly arrows)... 

At 4.2 K the spectrum does not show any narrowed features, that is at 4.2 K, energy migration is dominated by the phonon-assisted process in accordance with previous observations on chromium(III) containing systems [14]. As the temperature is lowered to 1.8 K, sharp features appear in the FLN spectrum. Such sharp features are indicative of energy selective and thus of resonant processes. However, the spectrum observed at 1.8 Kwith its... 

For nc-Si/SiO2 structures of type 1 the PL band maximum shifts from 1.3 to 1.7 eV when d decreases from 4.5 to 1.5 nm the intrinsic PL of nc-Si is commonly explained by the radiative recombination of excitons confined in nc-Si, while the size dependent spectral shift is attributed to the quantum confinement effect [21]. A considerable width of the PL band can be explained by nc-Si size distribution [21] as well as by phonon-assisted electron-hole recombination [22]. The external quantum yield of the exciton PL was found to reach -1 % for the samples with d = 3 - 4 nm at room temperature [18]. The lower quantum yield of the nc-Si/SiO2 structure in comparison with that observed for single Si quantum dots [22] and for III-V and II-VI compounds [22] can be explained by lower probability of the optical transitions, which are still indirect in nc-Si [21], as well as by the exciton energy migration in the assembly of closely packed nc-Si [18]. 

Energy transfer between two inorganic ions can occur either by multipolar interaction or an exchange mechanism in dilute systems (Reisfeld and Jorgensen, 1977 Reisfeld, 1973, 1975, 1976a), or by multi-step migration in concentrated systems (Powell and Blasse, 1980). In addition to resonant transfer, phonon-assisted transfer is a quite common phenomenon (Reisfeld, 1976a, 1986). 

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