Electric field perturbed electron tunnelling in nonpolar organic glasses

Abstract

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]~.

Positive-charge scavenging by amines in pulse-irradiated sec-butyl chloride glasses at 77 K. Dependence of rate on the ionization potential of amines

“…Theoretical calculation where the distribution was taken into account was successful in the explanation of the data of electrophotoluminescence resulting from charge recombination in the presence of external electric field, though comparison between the Coulombic and square-barrier models was not made. 31 The present results provide poor materials for the discussion of the Franck-Condon factor. The theories predict that the Franck-Condon factor increases first with the free-energy difference -AG to a maximum, -AGm, and then decreases, and that -AGm is governed by vibrational properties of a super molecule consisting of donor, acceptor, and solvent molecules.13 '15 The values of -AG for electron transfer to matrix holes from propylamine and triethylamine are estimated crudely at 1.8 and 3.1 eV, respectively.…”

The Recombination Luminescence of Tryptophan in Aqueous Glasses, I. Quenching Effect of Electron Scavengers

“…9.5 M LiCl glasses. Doheny and Albrecht [15], and Tachiya and Mozumder [16] discussed the relation between the m value and the distribution of trapped electrons using the tunneling kinetics. However, it seems to be unreasonable to analyze the m value by the pure tunneling mechanism because of the involvement of the redistribution of trapped electrons between deep-and shallow-traps in the RP decay process.…”

Trapped and solvated electrons produced in ethanol glass in the presence of an applied electric field

“…Three main processes which are perturbed by the applied electric field are probably as follows: (1) the recombination process in which the recombination time, consequently the escape probability, depends upon the strength of the electric field and the angle between the direction joining the electron to the positive ion and that of the field; (2) the nonradiative transition process for electrons from a delocalized state to a localized state where the transition is a consequence of an electron-phonon coupling interaction; and (3) a transfer or detrapping process from a localized state to a delocalized state or another localized state by hopping or tunneling. 11 Kato et al 8 showed that the increase in the yield of e80f, e.g., ODe/ODq 1.06 for E = 50 kV cm-1, can be theoretically predicted by assuming that the electric field mainly perturbs process 1. They also comment that whatever the forms of the initial distribution function of thermalized electrons are, the calculated yield of eaof is always larger in the presence of an electric field than in ©…”

“…Reagent grade ethanol was filled between the mylar films. Uncracked ethanol glass was made at 77 K. A Spellman dc power supply was used to apply a high voltage of 11 kV between the electrodes during y irradiation. The electric field strength inside the sample was estimated to be 50 kV cm"1.10 7 irradiation was carried out at 77 and 4 K at a 0022-3654/79/2083-0822S01.00/0 dose rate of 0.48 Mrd h"1 to a dose of 0.16 Mrd.…”