Decay of trapped electrons by tunnelling to scavenger molecules in low-temperature glasses

“…The development of the concentration, ITL, and EPL integrals where there exists a zerotime distribution of charge pairs having decay rates dependent upon the pair separation and orientation is standard in the recent l~terature (4,17,20,21) and need not be repeated here. For our purposes a recapitulatioll of these integrals uslng the symbols of this work will ~u f f i c e .~ If R is the charge-pair separation and 0 the angle between the electron position vector (with origin at the cation) and the eventual field direction, then the number of pairs remaining at time t , N ( t ) , is given by where n,(R,8) is a linear density of charge pairs and k(R) is the zero-field tunnelling rate of [2].…”

Section: Theoretical Electron-tunnelling Ratesmentioning

confidence: 99%

“…Equatioils 6 and 7 have been integrated by various authors (4,17,20,21) using the squarebarrier approximation to k(R), i.e., k = v e-AR. Most often used for no, where one has correlated charge pairs.…”

Section: Theoretical Electron-tunnelling Ratesmentioning

confidence: 99%

“…For a constant distribution, one may take B = 0 in [8] or integrate [6] directly (17,20,21). in either case…”

Section: Theoretical Electron-tunnelling Ratesmentioning

confidence: 99%

“…In addition, the computergenerated ITL points are identical for isotropic and nonisotropic distributions when scaled for the R-distribution range, as long as other parameters remain unchanged. Finally, intermediate output can be compared with the analytic forms obtained in the square-barrier case, to see that local concentrations of electrons about cations are varying qualitatively as in the simpler cases (9,17,20). If charge pairs are generated by an energy pulse of duration s s then, at the end of the pulse, those pairs having lifetimes, r,, much shorter than r will have reached photostationary state concentrations, while the nunlber of those pairs with r, much longer than z will still be growing linearly with irradiation time.…”

Section: Appendixmentioning

confidence: 99%

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Electric field perturbed electron tunnelling in nonpolar organic glasses

Doheny¹,

Albrecht²

1977

Can. J. Chem.

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A. J. DOHENY and A. C. ALBRECHT. Can. J. Chem. 55,2065Chem. 55, (1977. Isothermoluminescence (ITL) and electrophotoluminescence (EPL) resulting from electroncation recombination are measured in a 2-methylpentane-methylcyclohexane glass. The ITL is more characteristic of quantum-mechanical tunnelling and the EPL signal is markedly stronger in this new glass than previous measurements in 3-methylpentane. Quantum-mechanical tunnelling theory is used to predict recombination rates of electrons in the potential field of a cation plus an applied field. Numerical integration of the nonhomogeneous kinetic equations resulting from a distribution of cation-electron separations leads to qualitative and quantitative predictions of the EPL signal that are observed experimentally. Fitting of the theory to experiment supports the conclusions that the angular distribution of the photoelectrons about the cations is close to isotropic, that the electrons active in ITL and EPL on the time scale of minutes are separated about 50 A from their parent cation, and that the trap ionization potential in this nonpolar hydrocarbon glass is in the range of 0.5 to 0.7 eV.A. 3. DOHEYY et A. C. ALBRECHT. Can. J. Chem. 55.2065Chem. 55. (1977. On a mesur6 l'isothermolun~inescence (ITL) et I'tlectrophotoluminescence (EPL) qui se produit a partir de recombinaisons electron-cation dans des verres de methyl-2 pentane et de mCthylcyclohexane. L'ITL est plus caractkristique d'un tunnel de n~ecanique quantique et le signal EPL est beaucoup plus fort dans ce nouveau verre que ceux mesurCs anterieurement dans le methyl-3 pentane. On utilise la theorie des tunnels de mecanique quantique pour predire les vitesses de recombinaison des electrons dans le champ potentiel d'un cation plus un champ appliqui. L'inlCgration numerique des equations cinetiques non-homogenes resultant des distributions des separations cation-electron conduit a des predictions qualitatives et quantitatives du signal EPL qui sont observees exptrimentalement. L'ajustement de la theorie avec les experiences supporte les conclusions voulant que la distribution angulaire des photoClectrons autours de cations est pres de l'isotropique, que les electrons actifs dans 1'ITL et 1'EPL sur une echelle de temps de minutes sont sCparts par environ 50 8, de leur cation parent et finalement que le potentiel d'ionisation de piege dans ce verre hydrocarbone non-polaire est d'environ 0.5 a 0.7 eV.[Traduit par le journal]~.

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Long‐Lived Photoinduced Charge Separation in (Zinc, Lead) Phosphate Glass–C₆₀ Composites

Sahoo

Debnath²

2003

Advanced Materials

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Photoinduced charge separation and electron transfer are the fundamental phenomena involved [1±4] in the processes of light energy storage for photosynthesis in plants, xerography, photovoltaic (PV) energy conversion, etc. For the efficient photovoltaic harvesting of light energy, it is necessary, however, to have well-stabilized charge-transfer products. One impending problem in achieving a long-lived photoinduced charge transfer in an artificial system is its competing backtransfer reaction. The stability of the charge-separated state, on many occasions, is facilitated by carrier delocalization and by the spatial separation of electrons and holes, [1,3] and researchers often employ heterogeneous media [2,4] for this purpose. We report here the preparation of a group of (zinc, lead) phosphate glass±C 60 heterostructures that show a long-lived photoinduced electron transfer from the divalent lead center (Pb 2+ ) to the fullerene, upon 230±400 nm ultraviolet irradiation, which creates Pb 3+ -type hole centers and C 60 fullerene related anions in the system. Both the steady-state photoinduced absorption (PIA) and photoinduced electron spin resonance (PIESR) spectra of the irradiated system support the above view. An analysis of the carrier dynamics suggests that the electrons migrate from the hole sites to the fullerene sites in a tunneling mode. The charge-separated state thus formed in these systems has a lifetime ranging from a few hours to days, which is longer than those hitherto reported for various donor±acceptor systems. Figure 1 shows a photograph of one of the samples of the (Zn, Pb) phosphate glass±C 60 composites. Steady-state PIA spectra recorded at 300 K, in the region k = 250±1250 nm both before and after 90 min of UV-vis irradiation of the (Zn, Pb) phosphate glass±C 60 composite having a zinc oxide (ZnO) content of 40 mol-% and a fullerene (C 60 ) concentratioñ 5.0 10 ±5 M, are shown in Figure 2 (along with the absorption spectrum of a similarly irradiated base glass). Prior to irradiation, the composite exhibited a weak and broad absorption band at around 520 nm and another, less distinct, broad band around 830 nm.Considering the energy and weakness of the transition at 520 nm, one can easily recognize [5,6] it to be the highest-occupied molecular orbital to lowest-unoccupied molecular orbital (HOMO±LUMO) forbidden transition of the incorpo-COMMUNICATIONS Adv. Mater. 2003, 15, No. 3, February 5 Fig. 1. Photograph of a C 60 -doped (Zn, Pb)±phosphate glass sample.Fig. 2. Steady-state PIA spectra of a C 60 -doped (zinc, lead) phosphate glass (with ZnO = 40 mol-%; C 60 fullerene concentration = 5 10 ±5 M), along with the absorption spectrum of a similarly irradiated base glass (thickness, d = 0.2 cm, for both samples), recorded at 300 K, as a function of time. Inset: a plot of PIA intensity versus time.

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Decay of trapped electrons by tunnelling to scavenger molecules in low-temperature glasses

Cited by 141 publications

References 5 publications

Theory of tunneling recombination of defects stimulated by their motion I. General formalism

Theory of tunneling recombination of defects stimulated by their motion I. General formalism

Electric field perturbed electron tunnelling in nonpolar organic glasses

Long‐Lived Photoinduced Charge Separation in (Zinc, Lead) Phosphate Glass–C₆₀ Composites

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Decay of trapped electrons by tunnelling to scavenger molecules in low-temperature glasses

Cited by 141 publications

References 5 publications

Theory of tunneling recombination of defects stimulated by their motion I. General formalism

Theory of tunneling recombination of defects stimulated by their motion I. General formalism

Electric field perturbed electron tunnelling in nonpolar organic glasses

Long‐Lived Photoinduced Charge Separation in (Zinc, Lead) Phosphate Glass–C60 Composites

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Product

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Long‐Lived Photoinduced Charge Separation in (Zinc, Lead) Phosphate Glass–C₆₀ Composites