Spin-Flip of Polaron in Polymers with a Magnetic Impurity

Using a nonadiabatic evolution method, we investigate the spin-flip process of polaron in polymers with a magnetic impurity. Our results show that when the spin orientation of this impurity is fixed to be perpendicular to the spin of polaron （θ = π/2）, the magnetic impurity causes a spin-flip process. The probability of the spin-flip increases with the increase of exchange integral J up to about 0.35 eV and then decreases with the increase of J. In the case J is fixed while the spin orientation is adjustable, we find the probability of the spin-flip varies with the impurity orientation and reaches a maximum value at θ=π/2.     

Re-excited States in Conjugated Polymers

We investigate the re-exciting process of a soliton, a polaron and a bipolaron in conjugated polymers. For a soliton case, the processes S^0 ＋ hv→ S^± P↓± and S^± ＋ hv→S^0 ＋P± will take place, where S^0 ,S^± and p^± express a neutral soliton, charged solitons and charged polarons, respectively. For a polaron case, the processes P^± ＋ hv→ p^↓± ＋ Bp^±2 will occur, where BP^±2 expresses a charged bipolaron with two electronic units. For a bipolaron case, the processes BP^±2 ＋ hv→ P^± ＋ P^± and BP^±2 ＋ hv→ BP^＋2 ＋ E0 are obtained.     

Backward Charge Transfer in Conjugated Polymers

It has been known that the static polarizability of a polymer chain with a biexciton is negative. In order to understand this peculiar fact, this paper studies the dynamical process of the charge transfer in the polymer chain induced by an external electric field E during forming the biexciton. The time dependence of the charge distribution in the chain reveals that the charge transfer is backward: the positive charge shifts in the opposite direction of the external electric field. Such a backward charge transfer (BCT) produces an opposite dipole, which makes the polarization negative. The effect of electron interaction on the BCT is illustrated.     

Excitons and Optical Nonlinearities in Conjugated Polymers

Within the random phase approximation, single-exciton states in the 1D Peierlas-extended Hubbard model are investigated. Two low-lying bound-exciton states (lB_a and 2A_g) are found for a moderate interaction. The excitons are of an intermediate size. The electron correlation strongly affects energles of the bound-exciton states and leads to the change of the order between lB_a and 2A_g. The lB_a and 2A_g excitons are almost, degenerate for some interaction parameters. The calculated third-harmonic generation clearly shows a three-photon resonance at 0.6 eV and a two-photon resonance at 0.9 eV observed experimentally in polyacetylene.     

Impurities in Magnetic Insulators Studied by Low-Temperature Nuclear Orientation

Although the effects of impurities in metallic magnets have been extensively studied there have been far fewer experiments on impurities in insulating magnets, and, in an effort to understand this problem, we have investigated the effect of impurities in various systems. In MnCl₂⋅4H₂O samples doped with 1.6, 4.0 and 6.2% Co, the ⁵⁴Mn NMRON line is significantly broadened compared to the line in the pure crystal and shows structure on the low frequency side. The nuclear spin-lattice relaxation time is also lower by an order of magnitude. ⁵⁴Mn has also been doped into FeCl₂⋅4H₂O for which a 4-sublattice structure has been proposed and some details of this structure have been obtained. This revised version was published online in September 2006 with corrections to the Cover Date.     

共轭高聚物中的杂质分布：晶格形态及高浓度掺杂效应

基于扩展Su-Shrieffer-Heeger (SSH)模型,通过自洽计算的数值方法,研究了共轭高聚物链表现为孤子态和大极化子态两种不同晶格形态时链内的杂质分布情况,计算结果显示,分立的畴壁可导致高聚物链中形成多个稳定的势阱,有利于杂质在链中聚集分布。此外,还研究了在较高浓度的掺杂条件下,共轭高聚物链内的杂质分布规律。结果显示,杂质倾向于在中心区形成高浓度分布,而在链端区,杂质更倾向于离散分布。该研究表明,高浓度掺杂下杂质分布具有稳定的特征,晶格形态对杂质分布具有显著的影响,这些结论可为实验上操控杂质在共轭高聚物中的分布提供一定的帮助。     

Power-Law Behavior in Signal Scattering Process in Vertical Granular Chain with Light Impurities

We investigate the scattering process of impulse in vertical granular chain with light impurities. When the perturbation is weak, the quantities describing the reflection rate exhibit power-law behavior with the impurity depth. The exponent is nearly independent of vi. When the perturbation is very strong, the vertical chain shows similar behavior to that of the horizontal chain, so the exponent is nearly zero. Our numerical investigation begins from the weak perturbation region and extends to the nonlinear region and found a peak of the exponent. The difficulty in extending the numerical investigation to a stronger perturbation region is analyzed.     

共轭高聚物中的杂质分布:晶格形态及高浓度掺杂效应

基于扩展Su-Shrieffer-Heeger(SSH)模型,通过自洽计算的数值方法,研究了共轭高聚物链表现为孤子态和大极化子态两种不同晶格形态时链内的杂质分布情况,计算结果显示,分立的畴壁可导致高聚物链中形成多个稳定的势阱,有利于杂质在链中聚集分布.此外,还研究了在较高浓度的掺杂条件下,共轭高聚物链内的杂质分布规律.结果显示,杂质倾向于在中心区形成高浓度分布,而在链端区,杂质更倾向于离散分布.该研究表明,高浓度掺杂下杂质分布具有稳定的特征,晶格形态对杂质分布具有显著的影响,这些结论可为实验上操控杂质在共轭高聚物中的分布提供一定的帮助.     

Magnetic Resonance of Impurities, Intrinsic Defects and Dopants in ZnO

In the last years an increasing technological interest in the wide band gap semiconductor ZnO has widely stimulated research on this material. The electrical and optical properties of ZnO are strongly affected by the presence of defects and dopant. For instance, to obtain p-type conductivity it requires not only to find a suitable doping element but also to suppress counteracting intrinsic defects. Magnetic resonance experiments can contribute considerable knowledge to this subject. We review the current knowledge on impurities, intrinsic defects and doping elements in ZnO as obtained by magnetic resonance experiments in this paper.     

Power-Law Behavior in Signal Scattering Process in Vertical Granular Chain with Light Impurities

We investigate the scattering process of impulse in vertical granular chain with light impurities. When the perturbation is weak, the quantities describing the reflection rate exhibit power-law behavior with the impurity depth. The exponent is nearly independent of vi. When the perturbation is very strong, the vertical chain shows similar behavior to that of the horizontal chain, so the exponent is nearly zero. Our numerical investigation begins from the weak perturbation region and extends to the nonlinear region and found a peak of the exponent. The difficulty in extending the numerical investigation to a stronger perturbation region is analyzed.PACS numbers: 45.70.-n, 43.25. y, 46.40.Cd     

单光子和双光子激发的超歧化聚合物的光谱学特性研究

研究了二种新型超歧化聚合物在氯仿和二甲基甲酰胺溶剂中的飞秒激光单光子和双光子激发的光谱学特性．这二种聚合物是以苯为核、以对二甲氧基苯为连接单元，分别以二甲基苯胺为端基或以特丁基苯为端基的超歧化共轭聚合物．结果表明这种超歧化聚合物具有较大的溶剂极性相关的飞秒双光子吸收截面，不同的端基不仅影响分子内的电荷转移，而且导致超歧化分子共轭程度的变化．作为一种潜在的光学非线性材料，利用这种大的双光子吸收截面的超歧化聚合物可实现了飞秒双光子直写的三维高密度数据存储．     

Polarons in linear chains of fullerenes

Polaron states in linear chains of fullerenes are studied with the use of the generalized model of Su-Shrieffer-Heeger (SSH) for the intermolecular and intramolecular degrees of freedom. Electron charge distributions over the molecular surface and Jahn-Teller distortions of carbon atoms in C₆₀ are calculated self-consistently for linear C₆₀ polymer and C ₆₀ ⁻ polyanion chains. A polaron band narrowing is examined. It is shown that the polymerization of C₆₀ molecules in phase transitions may be caused by the cooperative Jahn-Teller effect. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 521–525 (25 October 1996) Published in English in the original Russian Journal. Edited by Steve Torstveit.     

Spin-Flip and Elastic Processes in Slow Collisions of Mesic Atoms

The reduced adiabatic hyperspherical (RAHS) basis suggested previously is used for the calculation of elastic and spin-flip cross sections in the processes (aμ) _F + a → (aμ) _F′ + a, a = (p, d, t), for collision energies 10⁻³ ≤ ε ≤ 10² eV. The rapid convergence of the method is demonstrated. A comparison of the obtained results with previous ones is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation and Characterization of Stable Fluorescent Complexes Between Neutral Conjugated Polymers and Cyclodextrins

Solubilisation and stabilization of conjugated polymers, CPs, in aqueous media remains a challenge for many researches trying to extend the biological and environmental applications of this kind of polymers. A number of different alternatives have been considered to address this problem, which are mostly based on the enhancement of the macromolecule polarity, by appending hydrophilic side chains on the polymer backbone. In this work we have investigated a new strategy in which water solubilization is reached by external addition of classical cyclodextrins (α-, β- and γ-CDs) to a solution of non-polar CPs. This strategy allows working with such polymers eliminating the need to synthesize new water-soluble species. The polymer selected for the study was poly-[9,9-bis(6′-bromohexyl-2,7-fluoren-dyil)-co-alt-(benzene-1,4-diy)], PFPBr₂, a polyfluorene previously synthesized in our laboratory. Results show that PFPBr₂ forms fluorescent complexes in aqueous media with β-CD and γ-CD, and much less efficiently with α-CD, probably due to the small size of its cavity. The new PFPBr₂/CD complexes are stable in time and in a large range of pH, however, at high concentration and temperature, they tend to aggregate and precipitate. In order to increase stabilization and minimize polymer aggregation, complexes were encapsulated inside the pores of silica glasses fabricated using the sol-gel process, obtaining transparent and fluorescent hybrid matrices which were stable in time and temperature. In addition, immobilization of the complexes allows an easy manipulation of the material, thus offering promising applications in the development of biological and chemical sensors.