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Optically active polyaniline film based on cellulose nanocrystals
摘要： Chiral transfer from cellulose nanocrystals (CNCs) chiral nematic liquid crystal to polyaniline (PANI) is successfully achieved through co-assembly method for the first time, affording the PANI film based on CNCs optical activity. Meanwhile, the CNCs/PANI composite film displays notable Cotton effect ascribed to the polaron band transitions of PANI in circular dichroism (CD) spectrum. Hydrogen bond and electrostatic attraction favor the combination of two molecular chains in the mixed aqueous suspension and will lead to the chiral assembly of the PANI in the host chiral nematic film. However, the CD signal disappears when cholesteric phase collapse by acid protonation, and which demonstrates the chiral nematic ordering of the CNCs is essential to the chiral transfer. With the assistance of CNCs, PANI chains form a helically stacked structure. Thus, the optical activity of PANI originates from its long range organization.
关键词： co-assembly,chiral transfer,polaron transition,optical activity,Cotton effect
更新于2025-09-23 15:23:52
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Concentration effects on the thermally-activated transport of polarons in conducting polymers
摘要： The impact of the polaron concentration on the temperature-mediated charge transport in one-dimensional organic materials is studied. Within the scope of a tight-binding description, our findings reveal that high-temperature diffusivity tends to increase as polaron concentration increases. Moreover, the activation energy for the polaron transport also increases with polaron concentration. Importantly, the polaron diffusivity follows an Arrhenius-like behavior with low activation energy.
关键词： Activation energy,Organic materials,Polaron concentration,Diffusivity
更新于2025-09-23 15:23:52
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Modified dielectric and ferroelectric properties in the composite of ferrimagnetic Co1.75Fe1.25O4 ferrite and ferroelectric BaTiO3 perovskite in comparison to Co1.75Fe1.25O4 ferrite
摘要： The ferrimagnetic Co1.75Fe1.25O4 ferrite with cubic spinel structure (space group Fd3m) was made into composite by mixing with ferroelectric BaTiO3 perovskite with tetragonal structure (space group P4mm) at the mass ratio 50:50. Disc shaped composite powder was finally heated at 1000 °C to study the structure, dielectric and ferroelectric properties. The electrical conductivity, dielectric response and ferroelectric properties of the composite samples are remarkably modified in comparison to their ferrite counterparts before making the composite. The composite system has shown improvement of dielectric constant with reduced dielectric loss factor and electrical conductivity in comparison to the ferrite samples. The mechanism of modified dielectric properties was understood by analyzing ac conductivity data using Jonscher's power law, complex impedance spectra in Cole-Cole plots using equivalent circuit model, and complex electrical modulus spectra using Kohlrausch, Williams and Watts (KWW) proposed model. Electrical conductivity in the composite material was determined by small polaron hoping (SPH) up to measurement temperature 400 K (close to ferroelectric transition of BaTiO3) and overlapping large polaron hopping conductivity at higher temperatures. In contrast, SPH dominates throughout the measurement temperature range for ferrite samples. The space charge polarization, which was largely effective at low frequencies and high measurement temperatures, is significantly reduced in composite samples. High capacitive response in composite samples and its extension up to high measurement temperature is confirmed from the temperature dependence of phase shift and well defined ferroelectric polarization loop and associated electrical parameters.
关键词： Composite dielectric,Polaron hopping,Ferroelectric polarization,Co rich spinel oxide
更新于2025-09-23 15:23:52
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-doped two-dimensional semiconductor quantum wells
摘要： We present a theoretical study of photoabsorption in n-doped two-dimensional (2D) and quasi-2D semiconductors that takes into account the interaction of the photocreated exciton with Fermi-sea (FS) electrons through (i) Pauli blocking, (ii) Coulomb screening, and (iii) excitation of FS electron-hole pairs—that we here restrict to one. The system we tackle is thus made of one exciton plus zero or one FS electron-hole pair. At low doping, the system ground state is predominantly made of a 'trion-hole'—a trion (two opposite-spin electrons plus a valence hole) weakly bound to a FS hole—with a small exciton component. As the trion is poorly coupled to photon, the intensity of the lowest absorption peak is weak; it increases with doping, thanks to the growing exciton component, due to a larger coupling between two-particle and four-particle states. Under a further doping increase, the trion-hole complex is less bound because of Pauli blocking by FS electrons, and its energy increases. The lower peak then becomes predominantly due to an exciton dressed by FS electron-hole pairs, that is, an exciton-polaron. As a result, the absorption spectra of n-doped semiconductor quantum wells show two prominent peaks, the nature of the lowest peak turning from trion-hole to exciton-polaron under a doping increase. Our work also nails down the physical mechanism behind the increase with doping of the energy separation between the trion-hole peak and the exciton-polaron peak, even before the anticrossing, as experimentally observed.
关键词： Fermi sea,trion-hole complex,exciton-polaron,photoabsorption,Pauli blocking,n-doped semiconductors,Coulomb screening
更新于2025-09-23 15:23:52
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Light-induced EPR study of spin-assisted charge transport in PFOT:PC61BM composite
摘要： Magnetic resonance, relaxation and dynamic parameters of polaron spins and methanfullerene radical anions, initiated by the infrared-visible-ultraviolet photons in bulk heterojunctions of the composite formed by narrow-band poly[(9,9-dioctylfluorenyl-2.7-diyl)-co-(bithiophene)] (PFOT, F8T2) copolymer and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) globules were investigated by the direct Light-Induced Electron Paramagnetic Resonance (LEPR) spectroscopy. It was shown that some of the polarons are captured by spin traps formed in the copolymer matrix due to its disordering. The number, spatial distribution and energy depth of such traps depend on the structure and morphology of composite. It is shown that the main parameters of both charge carriers are determined by the exchange interaction of the spin ensembles, as well as the energy of the photons. The formation of spin traps in the copolymer matrix and the exchange interaction between different spin packets cause the extreme sensitivity of the composite's magnetic resonance and electronic parameters to the number and energy of the initiating photons. The predominant photoinitiation of localized polarons in the copolymer matrix was demonstrated. This process is substantially accelerated when the composite is illuminated by photons with the energy lying near 1.8 and 2.7 eV. The recombination of both charge carriers can be described in terms of a bimolecular process of the second order. It was found that the contributions of polarons and methanofullerene radical anions to the effective paramagnetic susceptibility increase substantially near the photon energy of 2.6 and 2.1 eV due to the exchange interaction of these charge carriers. It is shown that the mobility of polarons varies monotonically throughout all the photon energy range, whereas the librational spin dynamics of the methanofullerene globules is substantially accelerated near the photon energy of 2.0 and 2.7 eV.
关键词： Polymer nanocomposites,Spin recombination,Transport properties,Spin interaction,Polaron,Light-induced EPR
更新于2025-09-23 15:23:52
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Charged polariton luminescence from an organic semiconductor microcavity
摘要： Strong coupling light to polaron optical transitions in an organic semiconductor microcavity leads to an unusual class of polariton that possesses a net charge. This species may offer a range of technologically-useful optoelectronic properties but has thus far only been observed in passive reflectivity measurements. Here, we report room-temperature photoluminescence from both upper and lower branch polaron polariton states that originate from hole excitations in a p-doped 4,4’-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) microcavity. Our observations under non-resonant excitation are in good agreement with classical dipole emission modeling, which suggests that polariton states in this system are populated radiatively via fluorescence from the polaron excited state reservoir. These results constitute one of the first observations of polaron luminescence from an organic semiconductor thin film and are an important prerequisite for realizing a charged polariton condensate.
关键词： strong coupling,Polaron,fluorescence,cation
更新于2025-09-23 15:22:29
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High-efficiency blue phosphorescent organic light-emitting devices with low efficiency roll-off at ultrahigh luminance by reduced the triplet-polaron quenching
摘要： High performance phosphorescent organic light-emitting devices (PhOLEDs) at high luminance are still a remaining problem needing to be solved, especially blue PhOLEDs. Here, 5-(5-9H-carbazol-9-yl) pyridin-2-yl)-8-(9H-carbazol-9-yl) -5H-pyrido [3, 2-b] indole (p2PCB2CZ) with excellent characteristics as host is designed to realize a novel host-guest system without hole trapping effect in blue PhOLEDs. The device in which p2PCB2CZ and Bis (3, 5-difluoro-2-(2-pyridyl) phenyl-(2-carboxypyridyl)iridium(III) (FIrpic) is used as host and guest, respectively, is proposed to improve the performances of blue PhOLEDs at high luminance, especially ultrahigh luminance (>30000 cd/m2). The maximum external quantum efficiency (EQE) of this type blue PhOLEDs is 19.2%, while the maximum EQE of reference blue PhOLEDs is 18.7 %. Nevertheless, the p2PCB2CZ-based devices exhibit significant advantage at high luminance, because its EQE still attains to 10.8% even when the luminance increases to 30000 cd/m2, which is 1.67 times that of the reference device. From measurements based on steady-state and time-resolved spectroscopy, the reduction of triplet-polaron quenching in p2PCB2CZ-based devices is proved to the main reason for improving the performances of blue PhOLEDs at high luminance.
关键词： Ultrahigh luminance,Efficiency roll-off,Blue PhOLED,Hole trapping,Triplet-polaron quenching.
更新于2025-09-23 15:22:29
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Can one introduce long range ferromagnetism by doping transition metal in wide band gap semiconducting ZnO?
摘要： In this report, we present a systematic study of magnetic behavior of transition metal (TM = Fe or Cu) doped ZnO and co-doped (Cu, Fe) ZnO nanoparticles. All the samples show antiferromagnetic (AFM) like inverse susceptibility at low temperatures. In all the samples AFM Curie-Weiss temperature TAF M increases with increase in TM ion concentration indicating enhanced antiferromagnetic correlation upon TM doping. We observe a crossover from antiferromagnetic correlation state to ferromagnetic correlation around temperature (T) 100 - 150K. We shall try to explain all the experimental observations by invoking the role of oxygen vacancies, valency of transition metal ions, formation and interaction between bound magnetic polaron (BMP) and their melting in ZnO matrix. Even though we observe ferromagnetic correlation around room temperature in all these samples from the inverse magnetic susceptibility data, but no true long range ferromagnetic transition was observed in magnetization down to lowest measured temperature of 5K. Our study indicates the di?culties in achieving long range ferromagnetism arising due to the formation of BMPs upon lowering the temperature where these BMPs get antiferromagnetically correlated due to superexchange interaction occurring in transition metal doped wide band gap semiconducting ZnO matrix.
关键词： Dilute magnetic semiconductor,Bound magnetic polaron,Antiferromagnetism,Transition metal doping,ZnO,Ferromagnetism
更新于2025-09-23 15:21:21
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Understanding degradation of organic light-emitting diodes from magnetic field effects
摘要： The impact of magnetic field effects on the electroluminescence of organic light-emitting diodes is commonly used to characterize exciton dynamics such as generation, annihilation, and performance degradation. However, interpreting these effects is challenging. Here, we show that magnetic field effects in organic light-emitting diodes can be understood in terms of the magnetic response of device characteristics derived from polaron-pair and triplet exciton quenching processes, such as triplet-polaron interactions and triplet-triplet annihilation. Device degradation shows a clear relationship with the amplitude of the magnetic field effects, enabling non-destructive measurement of the degradation. The results and proposed mechanism provide a better understanding of magnetic field effects on organic light-emitting diodes and device degradation phenomena.
关键词： magnetic field effects,device degradation,organic light-emitting diodes,triplet-polaron interactions,triplet-triplet annihilation,exciton dynamics
更新于2025-09-23 15:21:01
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Design of hole transport type host for stable operation in blue organic light-emitting diodes
摘要： Molecular design of the hole transport type host for mixed host was investigated to improve the lifetime of the phosphorescent organic light-emitting diodes. A negative polaron stabilizing hole transport type host design was employed and the effect of the negative polaron stabilizing unit was investigated. Dibenzofuran or benzonitrile was introduced as the negative polaron stabilizing unit in the bicarbazole backbone structure of the hole transport type host. Two host materials were synthesized and the comparison of them proposed that the negative polaron stabilizing unit is a key to the lifetime of the phosphorescent organic light-emitting diodes. The dibenzofuran and benzonitrile embedded bicarbazole hosts performed better than the mCBP host. The dibenzofuran and benzonitrile modified bicarbazole hosts demonstrated high external quantum efficiency of 18.6 and 19.1%, respectively and lifetime extension by 30% compared with the conventional host without the negative polaron stabilizing unit.
关键词： Negative polaron,Lifetime,Mixed host,Hole type host
更新于2025-09-23 15:21:01