Impurity center

Ndi g5Ceo.i5Cu04 Localization-delocalization of copper pairs on Zn impurity centers in the copper sublattice of the HTc superconductor Ndj g5Ceo.i5Cu04 was observed by Zn Mossbauer emission spectroscopy... 

Ga( Zn) and Cu( Zn) Mossbauer emission spectroscopy on bulk GaP, GaAs and GaSb semiconductors point at isolated zinc metal centers at Ga sites. The observed center shift to higher positive velocities at the transition from p- to n-type samples corresponds to the recharging of zinc impurity centers... 

Most of the other metal-related deep levels in Si are also passivated by reaction with hydrogen (Pearton, 1985). Silver, for example, gives rise in general to a donor level at Ee + 0.54 eV and an acceptor level at Ec - 0.54 e V (Chen and Milnes, 1980 Milnes, 1973). These levels are very similar to those shown by Au, Co and Rh and raise the question of whether Au might actually be introduced into all of the reported samples or a contaminant, or whether as discussed by several authors there is a similar core to these impurity centers giving rise to similar electronic properties (Mesli et al., 1987 Lang et al., 1980). This problem has not been adequately decided at this time. It has been... 

Steady-state luminescence of feldspars is well studied. The following impurity centers have been found Tl, Pb, Pb, TR + (Ce, Dy, Sm, Tb, Nd), Eu +, Mn +, Fe, Cr (Tarashchan 1978 Walker 1985 Bakhtin and Moroshkin 1986 White et al. 1986 Kuznetsov and Tarashchan 1988 Waychunas 1989 Gotse 2000 Correcher and Garcia-Guinea 2001 Gorobets and Rogojine 2001 Krbetschek et al. 2002). 

The mineral matrix is formed chiefly by La " or Ce ". The last one is widely regarded as the luminescence impurity center, but in rare-earth bearing minerals it is subjected to concentration quenching because of strong exchange... 

At lower temperatures (T < T,), a exhibits a temperature dependence characteristic of a small activation energy (= 0.03 eV) for excitation of charge carriers from stationary trap sites It is reasonable to suspect that small polarons tend to be trapped at impurity centers at low temperature. 

When lithium oxide is dissolved in nickel oxide, monovalent lithium ions replace nickel ions. We obtain, therefore, an increase of the electron—hole concentration with increasing concentration of Li.O, The prime represents the negative charge of this impurity center Li> (Ni). 

We mentioned the main models for generation, transfer, and recombination of the charge carriers in polymers. Very often, these models are interwoven. For example, the photogeneration can be considered in the frame of the exciton model and transport in the frame of the hopping one. The concrete nature of the impurity centers, deep and shallow traps, intermediate neutral and charged states are specific for different types of polymers. We will try to take into account these perculiarities for different classes of the macro-molecules materials in the next sections. 

An alternative possibility cannot be excluded. Since the time scale for proton mobility and infrared vibration are greatly different, infrared is not the pertinent technique for studying proton mobility. Therefore, the exchange with D2 can occur with only a small fraction of the hydroxyls, at impurity centers, or at a limited number of defects. The isotopes should mix then by a rapid diffusion. This possibility has been envisaged by Cant and Hall (13) for the exchange reaction of surface hydroxyls of... 

Although these reactions may contribute to the effect of oxygen, the decrease in sensitivity also could be explained by a direct reaction of the photoelectron with oxygen to form the superoxide ion O2 (83). An oxygen molecule diffuses to a site where an electron is trapped temporarily by a crystal defect, dye, or impurity center, or an electron from the conduction band is captured by a physically adsorbed oxygen molecule... 

Stone writes this reaction as occurring with Ni2+ ions, but it is more likely that if it takes place, the small number of Ni3+, which are almost certainly present, are involved.) This extraction reaction would become rate-determining at higher temperatures, say, > 160°. Under the conditions used by Schwab, the irreversible formation of (COl /n7)(er/D7) by direct reaction of gaseous CO would be rate-determining and would be influenced in the way observed by him if the complex were stabilized by neighboring impurity centers. This explanation of the discrepancy is not impossible but... 

The temperature dependence of the homogeneous width of zero-phonon lines (ZPLs) in the optical spectra of the impurity centers in crystals is determined by... 

To describe the effect of the change of the elastic springs on the optical spectrum of an impurity center, we use the adiabatic approximation. In this approximation, phonons are described by different phonon Hamiltonians in different electronic states. The optical spectrum, which corresponds to a transition between different electronic states is determined by the expression /( >) = const X oj1 1 I(oj) [28], where the — sign corresponds to the absorption spectrum and the + sign stands for the emission spectrum,... 

V. Hizhnyakov and I. Tehver, in Physics of Impurity Centers of Crystals (ed. G. Zavt), Academy of Sciences of the Estonian SSR, Institute of Physics and Astronomy, Tallinn, 1972, p. 607. 

Impurity Centers in Quartz Glass Carbon in the Silica Structure. 314... 

A. F. Lubchenko, Quantum Transitions in Impurity Centers of Solids, Naukova Dumka, Kiev, 1978. 

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