50 results on '"Sebastian Bange"'
Search Results
2. Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe2
- Author
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Kai-Qiang Lin, Chin Shen Ong, Sebastian Bange, Paulo E. Faria Junior, Bo Peng, Jonas D. Ziegler, Jonas Zipfel, Christian Bäuml, Nicola Paradiso, Kenji Watanabe, Takashi Taniguchi, Christoph Strunk, Bartomeu Monserrat, Jaroslav Fabian, Alexey Chernikov, Diana Y. Qiu, Steven G. Louie, and John M. Lupton
- Subjects
Science - Abstract
Here, the authors report on evidence of an excitonic species formed by electrons in high-energy conduction band states with a negative effective mass, explaining previous observations of quantum interference phenomena in two-dimensional semiconductors.
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- 2021
- Full Text
- View/download PDF
3. Complete polarization of electronic spins in OLEDs
- Author
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Tobias Scharff, Wolfram Ratzke, Jonas Zipfel, Philippe Klemm, Sebastian Bange, and John M. Lupton
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Science - Abstract
Though literature reports magnetoelectroluminescence (MEL) affects in organic light‐emitting diodes (OLEDs), probing the organic layer’s effective spin polarization remains a challenge. Here, the authors utilize dual singlet‐triplet emitting OLEDs to reveal the spin polarization in the materials.
- Published
- 2021
- Full Text
- View/download PDF
4. Twist-angle engineering of excitonic quantum interference and optical nonlinearities in stacked 2D semiconductors
- Author
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Kai-Qiang Lin, Paulo E. Faria Junior, Jonas M. Bauer, Bo Peng, Bartomeu Monserrat, Martin Gmitra, Jaroslav Fabian, Sebastian Bange, and John M. Lupton
- Subjects
Science - Abstract
Here, the authors report on the large twist-angle susceptibility of excitons involving upper conduction bands in transition metal dichalcogenide bilayers. These high-lying excitons couple with band-edge excitons, and give rise to nonlinear quantum-optical processes that become tuneable by twisting.
- Published
- 2021
- Full Text
- View/download PDF
5. Picosecond time-resolved photon antibunching measures nanoscale exciton motion and the true number of chromophores
- Author
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Gordon J. Hedley, Tim Schröder, Florian Steiner, Theresa Eder, Felix J. Hofmann, Sebastian Bange, Dirk Laux, Sigurd Höger, Philip Tinnefeld, John M. Lupton, and Jan Vogelsang
- Subjects
Science - Abstract
Photon antibunching typically measures the time-averaged photophysics of multichromophoric nanoparticles. Here, the authors report on time-resolving photon antibunching, allowing the true number of chromophores and exciton diffusion to be measured in DNA origami and conjugated polymer aggregates.
- Published
- 2021
- Full Text
- View/download PDF
6. How Blinking Affects Photon Correlations in Multichromophoric Nanoparticles
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Jakob Schedlbauer, Jan Vogelsang, Tim Schröder, John M. Lupton, Sebastian Bange, Philip Tinnefeld, and Florian Steiner
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Quantum optics ,Physics ,Photons ,Photon ,Photon antibunching ,Quenching (fluorescence) ,Blinking ,ddc:530 ,General Engineering ,General Physics and Astronomy ,Nanoparticle ,Chromophore ,530 Physik ,Fluorescence ,Molecular physics ,single-molecule spectroscopy, photon statistics, DNA origami structures, photophysics, quantum optics ,Spectrometry, Fluorescence ,Energy Transfer ,Nanoparticles ,General Materials Science ,Excitation - Abstract
A single chromophore can only emit a maximum of one single photon per excitation cycle. This limitation results in a phenomenon commonly referred to as photon antibunching (pAB). When multiple chromophores contribute to the fluorescence measured, the degree of pAB has been used as a metric to "count" the number of chromophores. But the fact that chromophores can switch randomly between bright and dark states also impacts pAB and can lead to incorrect chromophore numbers being determined from pAB measurements. By both simulations and experiment, we demonstrate how pAB is affected by independent and collective chromophore blinking, enabling us to formulate universal guidelines for correct interpretation of pAB measurements. We use DNA-origami nanostructures to design multichromophoric model systems that exhibit either independent or collective chromophore blinking. Two approaches are presented that can distinguish experimentally between these two blinking mechanisms. The first one utilizes the different excitation intensity dependence on the blinking mechanisms. The second approach exploits the fact that collective blinking implies energy transfer to a quenching moiety, which is a time-dependent process. In pulsed-excitation experiments, the degree of collective blinking can therefore be altered by time gating the fluorescence photon stream, enabling us to extract the energy-transfer rate to a quencher. The ability to distinguish between different blinking mechanisms is valuable in materials science, such as for multichromophoric nanoparticles like conjugated-polymer chains as well as in biophysics, for example, for quantitative analysis of protein assemblies by counting chromophores.
- Published
- 2021
7. Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe2
- Author
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Steven G. Louie, John M. Lupton, Jaroslav Fabian, Alexey Chernikov, Nicola Paradiso, Bartomeu Monserrat, Bo Peng, Sebastian Bange, Jonas Zipfel, Jonas D. Ziegler, Kenji Watanabe, Kai-Qiang Lin, Christian Bäuml, Paulo E. Faria Junior, Christoph Strunk, Takashi Taniguchi, Diana Y. Qiu, Chin Shen Ong, Lin, Kai-Qiang [0000-0001-9609-749X], Ong, Chin Shen [0000-0001-8747-1849], Bange, Sebastian [0000-0002-5850-264X], Peng, Bo [0000-0001-6406-663X], Watanabe, Kenji [0000-0003-3701-8119], Taniguchi, Takashi [0000-0002-1467-3105], Monserrat, Bartomeu [0000-0002-4233-4071], Fabian, Jaroslav [0000-0002-3009-4525], Chernikov, Alexey [0000-0002-9213-2777], Louie, Steven G [0000-0003-0622-0170], Lupton, John M [0000-0002-7899-7598], and Apollo - University of Cambridge Repository
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Physics ,Multidisciplinary ,Annihilation ,Photoluminescence ,Phonon ,Exciton ,Science ,ddc:530 ,Ab initio ,General Physics and Astronomy ,General Chemistry ,Electron ,5104 Condensed Matter Physics ,530 Physik ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Molecular physics ,General Biochemistry, Genetics and Molecular Biology ,Condensed Matter::Materials Science ,Monolayer ,51 Physical Sciences ,Excitation - Abstract
Monolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe2 with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons.
- Published
- 2021
8. Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs
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Paul L. Burn, Sebastian Milster, Christoph Boehme, Hermann Kraus, John M. Lupton, Tobias Grünbaum, Sebastian Bange, Anna E. Leung, Dani M. Stoltzfus, Tamim A. Darwish, and Simon Kurrmann
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Materials science ,Electron ,010402 general chemistry ,01 natural sciences ,Magnetic Resonance | Very Important Paper ,Catalysis ,magnetic resonance ,symbols.namesake ,conjugated polymers ,Hyperfine structure ,isotopes ,Spin-½ ,deuteration ,Larmor precession ,Zeeman effect ,010405 organic chemistry ,Communication ,Resonance ,Magnetoreception ,General Medicine ,General Chemistry ,organic light-emitting diodes ,Communications ,0104 chemical sciences ,Magnetic field ,symbols ,Atomic physics - Abstract
The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (, Perdeuteration of a common OLED emitter allows the detection of paramagnetic resonances at field strengths comparable to Earth's. The competition between narrow resonance spectra and a quasistatic zero‐field feature resulting from reduced hyperfine coupling points at a low‐field limit for detecting paramagnetic resonances in radical‐pair‐based systems.
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- 2020
9. OLEDs as models for bird magnetoception: detecting electron spin resonance in geomagnetic fields
- Author
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Christoph Boehme, Sebastian Bange, Tobias Grünbaum, Viola Zeller, Sebastian Milster, Simon Kurrmann, John M. Lupton, Wolfram Ratzke, and Hermann Kraus
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Coherence time ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Molecular physics ,Fluorescence ,law.invention ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Physics - Biological Physics ,Singlet state ,Physical and Theoretical Chemistry ,010306 general physics ,Spin (physics) ,Electron paramagnetic resonance ,Hyperfine structure ,Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Electron Spin Resonance Spectroscopy ,530 Physik ,021001 nanoscience & nanotechnology ,Magnetic field ,Magnetic Fields ,Earth's magnetic field ,Models, Chemical ,Biological Physics (physics.bio-ph) ,Quantum Theory ,0210 nano-technology ,Phosphorescence - Abstract
Certain species of living creatures are known to orientate themselves in the geomagnetic field. Given the small magnitude of approximately 48 {\mu}T, the underlying quantum mechanical phenomena are expected to exhibit coherence times approaching the millisecond regime. In this contribution, we show sensitivity of organic light-emitting diodes (OLEDs) to magnetic fields far below Earth's magnetic field, suggesting that coherence times of the spins of charge-carrier pairs in these devices can be similarly long. By electron paramagnetic resonance (EPR) experiments, a lower bound for the coherence time can be assessed directly. Moreover, this technique offers the possibility to determine the distribution of hyperfine fields within the organic semiconductor layer. We extend this technique to a material system exhibiting both fluorescence and phosphorescence, demonstrating stable anticorrelation between optically detected magnetic resonance (ODMR) spectra in the singlet (fluorescence) and triplet (phosphorescence) channel. The experiments demonstrate the extreme sensitivity of OLEDs to both static as well as dynamic magnetic fields and suggest that coherent spin precession processes of Coulombically bound electron spin pairs may play a crucial role in the magnetoreceptive ability of living creatures., Comment: 25 pages, 11 figures, 1 table
- Published
- 2020
10. Excitonic resonances control the temporal dynamics of nonlinear optical wave mixing in monolayer semiconductors
- Author
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Jonas M. Bauer, Lijue Chen, Philipp Wilhelm, Kenji Watanabe, Takashi Taniguchi, Sebastian Bange, John M. Lupton, and Kai-Qiang Lin
- Subjects
ddc:530 ,530 Physik ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials - Abstract
Monolayer semiconductors are emerging platforms for strong nonlinear light-matter interaction, which is enhanced by the giant oscillator strength of tightly bound excitons. Little attention has been paid to the impact of excitonic resonances on the temporal dynamics of nonlinear light-matter interaction, since harmonic generation and optical-wave mixing are generally considered instantaneous processes. We find that a significant time difference, ranging from -40 fs to +120 fs, is necessary between two light pulses for optimal sum-frequency generation (SFG) and four-wave mixing (FWM) to occur from monolayer WSe2 when one of the pulses is in resonance with an excitonic transition. These resonances involve both band-edge A-excitons (AX) as well as high-lying excitons (HX) comprising electrons from conduction bands far above the gap. Numerical simulations of the density-matrix evolution reproduce and explain the distinct dynamics of SFG and FWM. The interpulse delays for maximal SFG and FWM are governed primarily by the lifetime of the one-photon and two-photon resonant states, respectively. The method therefore offers an unconventional probe of excitonic dynamics that are either one-photon or two-photon allowed. Remarkably, the longest delay times occur at the lowest excitation powers, indicating a strong nonlinearity that offers exploration potential for excitonic quantum nonlinear optics.
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- 2022
- Full Text
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11. Twist-angle engineering of excitonic quantum interference and optical nonlinearities in stacked 2D semiconductors
- Author
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Paulo E. Faria Junior, Jaroslav Fabian, Sebastian Bange, John M. Lupton, Bartomeu Monserrat, Bo Peng, Martin Gmitra, Jonas M. Bauer, Kai-Qiang Lin, Peng, Bo [0000-0001-6406-663X], Monserrat, Bartomeu [0000-0002-4233-4071], Bange, Sebastian [0000-0002-5850-264X], Lupton, John M [0000-0002-7899-7598], Apollo - University of Cambridge Repository, and Lupton, John M. [0000-0002-7899-7598]
- Subjects
639/766/119/1000/1018 ,Nonlinear optics ,Materials science ,Chalcogenide ,Electromagnetically induced transparency ,Exciton ,Science ,General Physics and Astronomy ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,Two-dimensional materials ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,5108 Quantum Physics ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,0103 physical sciences ,Dispersion (optics) ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,140/125 ,010306 general physics ,639/624/400/385 ,Condensed Matter - Materials Science ,Multidisciplinary ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,business.industry ,Condensed Matter::Other ,Bilayer ,ddc:530 ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,530 Physik ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,5104 Condensed Matter Physics ,Semiconductor ,chemistry ,0210 nano-technology ,business ,51 Physical Sciences ,Order of magnitude ,Physics - Optics ,Optics (physics.optics) - Abstract
Twist-engineering of the electronic structure in van-der-Waals layered materials relies predominantly on band hybridization between layers. Band-edge states in transition-metal-dichalcogenide semiconductors are localized around the metal atoms at the center of the three-atom layer and are therefore not particularly susceptible to twisting. Here, we report that high-lying excitons in bilayer WSe2 can be tuned over 235 meV by twisting, with a twist-angle susceptibility of 8.1 meV/°, an order of magnitude larger than that of the band-edge A-exciton. This tunability arises because the electronic states associated with upper conduction bands delocalize into the chalcogenide atoms. The effect gives control over excitonic quantum interference, revealed in selective activation and deactivation of electromagnetically induced transparency (EIT) in second-harmonic generation. Such a degree of freedom does not exist in conventional dilute atomic-gas systems, where EIT was originally established, and allows us to shape the frequency dependence, i.e., the dispersion, of the optical nonlinearity., Here, the authors report on the large twist-angle susceptibility of excitons involving upper conduction bands in transition metal dichalcogenide bilayers. These high-lying excitons couple with band-edge excitons, and give rise to nonlinear quantum-optical processes that become tuneable by twisting.
- Published
- 2021
12. Floquet spin states in OLEDs
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Shirin Jamali, Paul L. Burn, Anna E. Leung, Henna Popli, Christoph Boehme, Dani M. Stoltzfus, Hans Malissa, Tamim A. Darwish, Sebastian Milster, John M. Lupton, Adnan Nahlawi, V. V. Mkhitaryan, Sebastian Bange, and Tobias Grünbaum
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Floquet theory ,Electronic properties and materials ,Spin states ,Physics::Instrumentation and Detectors ,Science ,FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,Electron ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,High Energy Physics::Theory ,symbols.namesake ,Magnetic properties and materials ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Physics::Atomic Physics ,010306 general physics ,Hyperfine structure ,Spin-½ ,Physics ,Condensed Matter - Materials Science ,Multidisciplinary ,Zeeman effect ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Spins ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,530 Physik ,021001 nanoscience & nanotechnology ,symbols ,0210 nano-technology ,Hamiltonian (quantum mechanics) - Abstract
Weakly spin-orbit coupled electron and hole spins in organic light-emitting diodes (OLEDs) constitute near-perfect two-level systems to explore the interaction of light and matter in the ultrastrong-drive regime. Under such highly non-perturbative conditions, the frequency at which the spin oscillates between states, the Rabi frequency, becomes comparable to its natural resonance frequency, the Larmor frequency. For such conditions, we develop an intuitive understanding of the emergence of hybrid light-matter states, illustrating how dipole-forbidden multiple-quantum transitions at integer and fractional g-factors arise. A rigorous theoretical treatment of the phenomena comes from a Floquet-style solution to the time-dependent Hamiltonian of the electron-hole spin pair under resonant drive. To probe these phenomena experimentally requires both the development of a magnetic-resonance setup capable of supporting oscillating driving fields comparable in magnitude to the static field defining the Zeeman splitting; and an organic semiconductor which is characterized by minimal inhomogeneous broadening so as to allow the non-linear light-matter interactions to be resolved. The predicted exotic resonance features associated with the Floquet states are indeed found experimentally in measurements of spin-dependent steady-state OLED current under resonant drive, demonstrating that complex hybrid light-matter spin excitations can be formed and probed at room temperature. The spin-Dicke state arising under strong drive is insensitive to power broadening so that the Bloch-Siegert shift of the resonance becomes apparent, implying long coherence times of the dressed spin state with potential applicability for quantum sensing., Comment: Manuscript: 26 pages, 3 figures; supplementary information: 28 pages, 7 figures
- Published
- 2021
13. Picosecond time-resolved photon antibunching measures nanoscale exciton motion and the true number of chromophores
- Author
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Dirk Laux, Florian Steiner, Theresa Eder, Sigurd Höger, Sebastian Bange, John M. Lupton, Tim Schröder, Felix J. Hofmann, Jan Vogelsang, Gordon J. Hedley, and Philip Tinnefeld
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Science ,Exciton ,Physics::Optics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Molecular physics ,General Biochemistry, Genetics and Molecular Biology ,Article ,Diffusion (business) ,Single photons and quantum effects ,Quantum ,Physics ,Quantitative Biology::Biomolecules ,Mesoscopic physics ,Multidisciplinary ,Annihilation ,Photon antibunching ,Quantum Physics ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,530 Physik ,0104 chemical sciences ,Picosecond ,Nanoparticles ,0210 nano-technology ,Excitation - Abstract
The particle-like nature of light becomes evident in the photon statistics of fluorescence from single quantum systems as photon antibunching. In multichromophoric systems, exciton diffusion and subsequent annihilation occurs. These processes also yield photon antibunching but cannot be interpreted reliably. Here we develop picosecond time-resolved antibunching to identify and decode such processes. We use this method to measure the true number of chromophores on well-defined multichromophoric DNA-origami structures, and precisely determine the distance-dependent rates of annihilation between excitons. Further, this allows us to measure exciton diffusion in mesoscopic H- and J-type conjugated-polymer aggregates. We distinguish between one-dimensional intra-chain and three-dimensional inter-chain exciton diffusion at different times after excitation and determine the disorder-dependent diffusion lengths. Our method provides a powerful lens through which excitons can be studied at the single-particle level, enabling the rational design of improved excitonic probes such as ultra-bright fluorescent nanoparticles and materials for optoelectronic devices., Photon antibunching typically measures the time-averaged photophysics of multichromophoric nanoparticles. Here, the authors report on time-resolving photon antibunching, allowing the true number of chromophores and exciton diffusion to be measured in DNA origami and conjugated polymer aggregates.
- Published
- 2021
- Full Text
- View/download PDF
14. Measuring the Magnetic Field Amplitude of rf Radiation by the Quasistatic Magnetic Field Effect in Organic Light-Emitting Diodes
- Author
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John M. Lupton, Anna E. Leung, Paul L. Burn, Sebastian Bange, Tamim A. Darwish, Wei Jiang, and Tobias Grünbaum
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Zeeman effect ,Materials science ,Magnetoresistance ,Condensed matter physics ,General Physics and Astronomy ,Resonance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,530 Physik ,01 natural sciences ,law.invention ,Magnetic field ,Paramagnetism ,symbols.namesake ,law ,0103 physical sciences ,symbols ,Radio frequency ,010306 general physics ,0210 nano-technology ,Electron paramagnetic resonance ,Diode - Abstract
Electron paramagnetic resonance (EPR) is a versatile tool to probe spin physics in organic semiconductor materials. A common method used to detect the spin-�� paramagnetic resonance in organic light-emitting diodes (OLEDs) is to measure the device resistance under EPR conditions, i.e., to record electrically detected magnetic resonance (EDMR). Here, we present ultralow-frequency EDMR experiments on OLEDs that exhibit a qualitatively new line shape because of a quasistatic magnetic field effect: the modulation of the static ultrasmall field-effect magnetoresistance arising from the magnetic field amplitude B1 of the radio frequency (rf) radiation. The disappearance of spin-�� Zeeman resonances of individual charge carriers in the OLED, i.e., the resonances at magnetic fields where the Zeeman splitting matches the photon energy of the incident rf radiation, coincides with the emergence of the quasistatic effect. We discuss the origin of this quasistatic magnetic field effect, its characteristic line shape in terms of the magnetic field dependence, the influence of experimental parameters, and the application potential with regards to EDMR experiments. The EDMR line shape can be inferred numerically from the magnetoresistance measurements. This approach enables a unique means of determining the drive-field strength B1 in EDMR under driving conditions where alternative methods employing an analysis of the Zeeman resonance���such as power broadening and Rabi flopping���are not applicable.
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- 2021
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15. Complete polarization of electronic spins in OLEDs
- Author
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Jonas Zipfel, John M. Lupton, Sebastian Bange, Philippe Klemm, Tobias Scharff, and Wolfram Ratzke
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ddc:500 ,Physics::Instrumentation and Detectors ,Exciton ,Science ,General Physics and Astronomy ,FOS: Physical sciences ,02 engineering and technology ,Electron ,01 natural sciences ,Molecular physics ,Article ,General Biochemistry, Genetics and Molecular Biology ,High Energy Physics::Theory ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Electronic devices ,Singlet state ,010306 general physics ,Spin (physics) ,Physics ,Multidisciplinary ,Spins ,Spin polarization ,Condensed Matter - Mesoscale and Nanoscale Physics ,ddc:530 ,General Chemistry ,021001 nanoscience & nanotechnology ,530 Physik ,Semiconductors ,Charge carrier ,Condensed Matter::Strongly Correlated Electrons ,500 Naturwissenschaften ,0210 nano-technology ,Phosphorescence - Abstract
At low temperatures and high magnetic fields, electron and hole spins in an organic light-emitting diode become polarized so that recombination preferentially forms molecular triplet excited-state species. For low device currents, magnetoelectroluminescence perfectly follows Boltzmann activation, implying a virtually complete polarization outcome. As the current increases, the magnetoelectroluminescence effect is reduced because spin polarization is suppressed by the reduction in carrier residence time within the device. Under these conditions, an additional field-dependent process affecting the spin-dependent recombination emerges, possibly related to the build-up of triplet excitons and their interaction with free charge carriers. Suppression of the EL alone does not prove electronic spin polarization. We therefore probe changes in the spin statistics of recombination directly in a dual singlet-triplet emitting material, which shows a concomitant rise in phosphorescence intensity as fluorescence is suppressed. Finite spin-orbit coupling in these materials gives rise to a microscopic distribution in effective g-factors of electrons and holes, Δg, i.e., a distribution in Larmor frequencies. This Δg effect in the pair, which mixes singlet and triplet, further suppresses singlet-exciton formation at high fields in addition to thermal spin polarization of the individual carriers., Though literature reports magnetoelectroluminescence (MEL) affects in organic light‐emitting diodes (OLEDs), probing the organic layer’s effective spin polarization remains a challenge. Here, the authors utilize dual singlet‐triplet emitting OLEDs to reveal the spin polarization in the materials.
- Published
- 2020
16. Linearly Polarized Electroluminescence from MoS
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Robin P, Puchert, Felix J, Hofmann, Hermann S, Angerer, Jan, Vogelsang, Sebastian, Bange, and John M, Lupton
- Abstract
Break junctions in noble-metal films can exhibit electroluminescence (EL) through inelastic electron tunneling. The EL spectrum can be tuned by depositing a single-layer crystal of a transition-metal dichalcogenide (TMDC) on top. Whereas the emission from the gaps between silver or gold nanoparticles formed in the break junction is spectrally broad, the hybrid metal/TMDC structure shows distinct luminescence from the TMDC material. The EL from individual hotspots is found to be linearly polarized, with a polarization axis apparently oriented randomly. Surprisingly, the degree of polarization is retained in the EL from the TMDC monolayer at room temperature. In analogy to polarized photoluminescence experiments, such polarized EL can be interpreted as a signature of valley-selective transitions, suggesting that spin-flip transitions and dephasing for excitons in the K valleys are of limited importance. However, polarized EL may also originate from the metal nanoparticles formed under electromigration which constitute optical antenna structures. Such antennae can apparently change over time since jumps in the polarization are observed in bare silver-nanoparticle films. Remarkably, photon-correlation spectroscopy reveals that gold-nanoparticle films exhibit signatures of deterministic single-photon emission in the EL, suggesting a route to designing room-temperature polarized single-photon sources with tunable photon energy through the choice of TMDC overlayer.
- Published
- 2020
17. Ultrafast Single-Molecule Fluorescence Measured by Femtosecond Double-Pulse Excitation Photon Antibunching
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Jan Vogelsang, Sebastian Bange, Lennart Grabenhorst, Sigurd Höger, Philip Tinnefeld, Birka Lalkens, Philipp Wilhelm, Marie-Elisabeth Federl, Jakob Schedlbauer, John M. Lupton, Florian Hinderer, and Ullrich Scherf
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Photon ,Materials science ,Physics::Optics ,Metal Nanoparticles ,Bioengineering ,02 engineering and technology ,Photon energy ,Fluorescence ,law.invention ,law ,Nanotechnology ,General Materials Science ,Physics::Chemical Physics ,Fluorescent Dyes ,Photons ,Photon antibunching ,business.industry ,Mechanical Engineering ,Lasers ,Pulse duration ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Single-molecule experiment ,Laser ,Single Molecule Imaging ,Energy Transfer ,Femtosecond ,Optoelectronics ,Gold ,0210 nano-technology ,business ,Ultrashort pulse - Abstract
Most measurements of fluorescence lifetimes on the single-molecule level are carried out using avalanche photon diodes (APDs). These single-photon counters are inherently slow, and their response shows a strong dependence on photon energy, which can make reconvolution of the instrument response function (IRF) challenging. An ultrafast time resolution in single-molecule fluorescence is crucial, e.g., in determining donor lifetimes in donor-acceptor couples which undergo energy transfer, or in plasmonic antenna structures, where the radiative rate and non-radiative rates are enhanced. We introduce a femtosecond double-excitation (FeDEx) photon correlation technique, which measures the degree of photon antibunching as a function of time delay between two excitation pulses. In this boxcar integration, the time resolution of fluorescence transients is limited solely by the laser pulse length and is independent of the detector IRF. The versatility of the technique is demonstrated with a custom-made donor-acceptor complex with one donor and two acceptors and with single dye molecules positioned accurately between two gold nanoparticles using DNA origami. The latter structures show ∼75-fold radiative-rate enhancement and fluorescence lifetimes down to 19 ps, which is measured without the need for any reconvolution. With the potential of measuring subpicosecond fluorescence lifetimes, plasmonic antenna structures can now be optimized further.
- Published
- 2019
18. Polymer coatings tune electromagnetically induced transparency in two-dimensional semiconductors
- Author
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John M. Lupton, Kai-Qiang Lin, Sebastian Bange, and Robert Martin
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Materials science ,Electromagnetically induced transparency ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,010309 optics ,Condensed Matter::Materials Science ,0103 physical sciences ,Electrical and Electronic Engineering ,Quantum optics ,business.industry ,Solvatochromism ,ddc:530 ,Second-harmonic generation ,021001 nanoscience & nanotechnology ,530 Physik ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Semiconductor ,Atomic electron transition ,Quantum interference ,Polymer coating ,two-dimensional semiconductors, second-harmonic generation, electromagnetically induced transparency, solvatochromism, dielectric disorder, transparent polymers ,Optoelectronics ,0210 nano-technology ,business ,Biotechnology - Abstract
Electromagnetically induced transparency (EIT) arises because of quantum interference between electronic transitions. While the phenomenon is a “gold standard” in atomic quantum optics, it is hard to probe in bulk condensed matter and difficult to control in quantum-confined systems—prerequisites for exploitation in devices. EIT arises in excitonic transitions of single-layer transition-metal dichalcogenide crystals, which, in effect, constitute giant two-dimensional exfoliated molecules. We exploit the characteristic sensitivity of molecules to their immediate dielectric environment to demonstrate how chemical tuning of the exciton resonance over 5% of the exciton energy allows unprecedented control over quantum interference. EIT is probed in second-harmonic generation (SHG) of monolayer WSe2, where it gives rise to resonant suppression of SHG in response to the immediate surrounding. This solid-state solvatochromic effect arises primarily from changes in electronic band gap and exciton binding energy of monolayer WSe2. Surprisingly, the EIT resonance shifts linearly with exciton energy in response to the dielectric nonlocal manipulation. The approach demonstrates that concepts from atomic quantum optics can be ported directly to condensed-phase materials, stimulating synthetic challenges to develop materials to tune quantum-coherent phenomena.
- Published
- 2019
19. Large‐Scale Mapping of Moiré Superlattices by Hyperspectral Raman Imaging (Adv. Mater. 34/2021)
- Author
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Tobias Korn, Philipp Parzefall, John M. Lupton, Sebastian Bange, Jonas M. Bauer, Johannes Holler, Kai-Qiang Lin, Marten Scheuck, Christian Schüller, and Bo Peng
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Materials science ,Scale (ratio) ,Mechanics of Materials ,Mechanical Engineering ,Superlattice ,Raman imaging ,Hyperspectral imaging ,General Materials Science ,Moiré pattern ,Remote sensing - Published
- 2021
20. Large‐Scale Mapping of Moiré Superlattices by Hyperspectral Raman Imaging
- Author
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John M. Lupton, Johannes Holler, Jonas M. Bauer, Tobias Korn, Kai-Qiang Lin, Christian Schüller, Marten Scheuck, Philipp Parzefall, Bo Peng, and Sebastian Bange
- Subjects
Materials science ,Phonon ,business.industry ,Mechanical Engineering ,Superlattice ,ddc:530 ,Resolution (electron density) ,Macroscopic quantum phenomena ,Hyperspectral imaging ,Moiré pattern ,530 Physik ,symbols.namesake ,Optics ,hyperspectral Raman imaging, interlayer breathing modes, low-frequency Raman scattering, moiré phonons, moiré superlattices ,Mechanics of Materials ,symbols ,General Materials Science ,van der Waals force ,business ,Raman scattering - Abstract
Moiré superlattices can induce correlated-electronic phases in twisted van der Waals materials: strongly correlated quantum phenomena emerge, such as superconductivity and the Mott-insulating state. However, moiré superlattices produced through artificial stacking can be quite inhomogeneous, which hampers the development of a clear correlation between the moiré period and the emerging electrical and optical properties. Here, it is demonstrated in twisted-bilayer transition-metal dichalcogenides that low-frequency Raman scattering can be utilized not only to detect atomic reconstruction, but also to map out the inhomogeneity of the moiré lattice over large areas. The method is established based on the finding that both the interlayer-breathing mode and moiré phonons are highly susceptible to the moiré period and provide characteristic fingerprints. Hyperspectral Raman imaging visualizes microscopic domains of a 5° twisted-bilayer sample with an effective twist-angle resolution of about 0.1°. This ambient methodology can be conveniently implemented to characterize and preselect high-quality areas of samples for subsequent device fabrication, and for transport and optical experiments.
- Published
- 2021
21. Perdeuteration of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (d-MEHPPV): control of microscopic charge-carrier spin-spin coupling and of magnetic-field effects in optoelectronic devices
- Author
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Shirin Jamali, Paul L. Burn, Tamim A. Darwish, Dani M. Stoltzfus, Henna Popli, Christoph Boehme, Sebastian Milster, Sabastian Atwood, Tobias Grünbaum, M. Y. Teferi, Hans Malissa, Sebastian Bange, Gajadhar Joshi, Marzieh Kavand, Anna E. Leung, Adnan Nahlawi, and John M. Lupton
- Subjects
Condensed Matter - Materials Science ,Materials science ,Spins ,Magnetoresistance ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,3. Good health ,Magnetic field ,Coupling (physics) ,Materials Chemistry ,Charge carrier ,0210 nano-technology ,Spectroscopy ,Spin (physics) ,Hyperfine structure - Abstract
Control of the effective local hyperfine fields in a conjugated polymer, poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV), by isotopic engineering is reported. These fields, evident as a frequency-independent line broadening mechanism in electrically detected magnetic resonance spectroscopy (EDMR), originate from the unresolved hyperfine coupling between the electronic spin of charge carrier pairs and the nuclear spins of surrounding hydrogen isotopes. The room temperature study of effects caused by complete deuteration of this polymer through magnetoresistance, magnetoelectroluminescence, coherent pulsed and multi-frequency EDMR, as well as inverse spin-Hall effect measurements, confirm the weak hyperfine broadening of charge carrier magnetic resonance lines. As a consequence, we can resolve coherent charge-carrier spin-beating, allowing for direct measurements of the magnitude of electronic spin-spin interactions. In addition, the weak hyperfine coupling allows us to resolve substantial spin-orbit coupling effects in EDMR spectra, even at low magnetic field strengths. These results illustrate the dramatic influence of hyperfine fields on the spin physics of organic light-emitting diode (OLED) materials at room temperature, and point to routes to reaching exotic ultra-strong resonant-drive regimes needed for the study of light-matter interactions., 22 pages (8 pages manuscript, 14 pages supplementary information)
- Published
- 2019
22. Interplay between J- and H-type coupling in aggregates of π-conjugated polymers: a single-molecule perspective
- Author
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Theresa Eder, Tristan J. Keller, Klaas Remmerssen, Daniela Schmitz, Jan Vogelsang, Sebastian Bange, Sigurd Höger, John M. Lupton, and Stefan-S. Jester
- Subjects
single-molecule spectroscopy ,ddc:540 ,Conjugated system ,010402 general chemistry ,01 natural sciences ,Catalysis ,Spectral line ,Superposition principle ,electronic coupling, macrocycles, organic electronics, single-molecule spectroscopy ,Molecule ,Organic Electronics ,Coupling ,Physics ,010405 organic chemistry ,Communication ,ddc:530 ,General Medicine ,General Chemistry ,electronic coupling ,Chromophore ,530 Physik ,Communications ,0104 chemical sciences ,Vibronic coupling ,macrocycles ,Chemical physics ,Atomic electron transition ,540 Chemie - Abstract
Strong dipole–dipole coupling within and between π‐conjugated segments shifts electronic transitions, and modifies vibronic coupling and excited‐state lifetimes. Since J‐type coupling between monomers along the conjugated‐polymer (CP) chain and H‐type coupling of chromophores between chains of a CP compete, a superposition of the spectral modifications arising from each type of coupling emerges, making the two couplings hard to discern in the ensemble. We introduce a single‐molecule H‐type aggregate of fixed spacing and variable length of up to 10 nm. HJ‐type aggregate formation is visualized intuitively in the scatter of single‐molecule spectra., Coupling therapy: In organic electronics, J‐type coupling between monomers along the chain and H‐type coupling of chromophores between chains compete, which makes the two types of coupling hard to discern in the ensemble. A single‐molecule H‐type aggregate of fixed spacing and variable length of up to 10 nm is introduced, and HJ‐type aggregate formation is visualized intuitively in the scatter of single‐molecule spectra.
- Published
- 2019
- Full Text
- View/download PDF
23. Linearly Polarized Electroluminescence from MoS 2 Monolayers Deposited on Metal Nanoparticles: Toward Tunable Room‐Temperature Single‐Photon Sources
- Author
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Sebastian Bange, Robin P. Puchert, Felix J. Hofmann, Hermann S. Angerer, John M. Lupton, and Jan Vogelsang
- Subjects
Photoluminescence ,Materials science ,Exciton ,Dephasing ,Physics::Optics ,General Chemistry ,Electroluminescence ,Polarization (waves) ,Molecular physics ,Overlayer ,Biomaterials ,Condensed Matter::Materials Science ,Degree of polarization ,General Materials Science ,Break junction ,Biotechnology - Abstract
Break junctions in noble-metal films can exhibit electroluminescence (EL) through inelastic electron tunneling. The EL spectrum can be tuned by depositing a single-layer crystal of a transition-metal dichalcogenide (TMDC) on top. Whereas the emission from the gaps between silver or gold nanoparticles formed in the break junction is spectrally broad, the hybrid metal/TMDC structure shows distinct luminescence from the TMDC material. The EL from individual hotspots is found to be linearly polarized, with a polarization axis apparently oriented randomly. Surprisingly, the degree of polarization is retained in the EL from the TMDC monolayer at room temperature. In analogy to polarized photoluminescence experiments, such polarized EL can be interpreted as a signature of valley-selective transitions, suggesting that spin-flip transitions and dephasing for excitons in the K valleys are of limited importance. However, polarized EL may also originate from the metal nanoparticles formed under electromigration which constitute optical antenna structures. Such antennae can apparently change over time since jumps in the polarization are observed in bare silver-nanoparticle films. Remarkably, photon-correlation spectroscopy reveals that gold-nanoparticle films exhibit signatures of deterministic single-photon emission in the EL, suggesting a route to designing room-temperature polarized single-photon sources with tunable photon energy through the choice of TMDC overlayer.
- Published
- 2021
24. Towards Room-Temperature Single-Photon LEDs by FRET from Metal Nanoparticles to Exfoliated 2D Crystal Overlayers
- Author
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Florian Steiner, Tobias Korn, Felix J. Hofmann, John M. Lupton, Philipp Nagler, Robin P. Puchert, Alexey Chernikov, Gerd Plechinger, Sebastian Bange, Christian Schüller, and Jan Vogelsang
- Subjects
Materials science ,Photon ,business.industry ,Physics::Optics ,Resonance ,Nanoparticle ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,010309 optics ,Crystal ,Dipole ,Förster resonance energy transfer ,law ,0103 physical sciences ,Monolayer ,Optoelectronics ,0210 nano-technology ,business ,Light-emitting diode - Abstract
Localized surface-plasmon resonances enable efficient coupling to proximal resonant dipole transitions. By exploiting energy transfer from metal nanoparticles to monolayers of 2D crystals we point a way to generate single photons at room temperature.
- Published
- 2018
25. Direct Detection of Singlet-Triplet Interconversion in OLED Magnetoelectroluminescence with a Metal-Free Fluorescence-Phosphorescence Dual Emitter
- Author
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John M. Lupton, Sebastian Bange, and Wolfram Ratzke
- Subjects
Materials science ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,530 Physik ,01 natural sciences ,Fluorescence ,Molecular physics ,Excited state ,0103 physical sciences ,OLED ,Singlet state ,010306 general physics ,0210 nano-technology ,Phosphorescence ,Luminescence ,Spin (physics) ,Common emitter - Abstract
We demonstrate that a simple phenazine derivative can serve as a dual emitter for organic light-emitting diodes, showing simultaneous luminescence from the singlet and triplet excited states at room temperature without the need of heavy-atom substituents. Although devices made with this emitter achieve only low quantum efficiencies of < 0.2%, changes in fluorescence and phosphorescence intensity on the subpercent scale caused by an external magnetic field of up to 30 mT are clearly resolved with an ultra-low-noise optical imaging technique. The results demonstrate the concept of using simple reporter molecules, available commercially, to optically detect the spin of excited states formed in an organic light-emitting diode and thereby probe the underlying spin statistics of recombining electron-hole pairs. A clear anticorrelation of the magnetic-field dependence of singlet and triplet emission shows that it is the spin interconversion between singlet and triplet which dominates the magnetoluminescence response: the phosphorescence intensity decreases by the same amount as the fluorescence intensity increases. The concurrent detection of singlet and triplet emission as well as device resistance at cryogenic and room temperature constitute a useful tool to disentangle the effects of spin-dependent recombination from spin- dependent transport mechanisms.
- Published
- 2018
- Full Text
- View/download PDF
26. Exciton Localization in Extended π-Electron Systems: Comparison of Linear and Cyclic Structures
- Author
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Jan Vogelsang, Alexander Thiessen, A. Vikas Aggarwal, Dominik Würsch, John M. Lupton, Stefan-S. Jester, Sigurd Höger, Alissa Idelson, and Sebastian Bange
- Subjects
Photoexcitation ,Dipole ,Materials science ,Exciton ,Monte Carlo method ,Materials Chemistry ,Electron ,Physical and Theoretical Chemistry ,Polarization (waves) ,Anisotropy ,Molecular physics ,Excitation ,Surfaces, Coatings and Films - Abstract
We employ five π-conjugated model materials of different molecular shape-oligomers and cyclic structures-to investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red shift within ∼100 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while, in the macrocycle, the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the π-conjugated system in terms of disorder parameters.
- Published
- 2015
27. Visualizing the radical-pair mechanism of molecular magnetic field effects by magnetic resonance induced electrofluorescence to electrophosphorescence interconversion
- Author
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Christoph Boehme, Ullrich Scherf, Hermann Kraus, Sebastian Bange, John M. Lupton, and Felix Frunder
- Subjects
Materials science ,Spin states ,Field (physics) ,Magnetoresistance ,ddc:530 ,02 engineering and technology ,530 Physik ,021001 nanoscience & nanotechnology ,01 natural sciences ,Fluorescence ,Molecular physics ,Magnetic field ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,LIGHT-EMITTING-DIODES ,SINGLET-TRIPLET GAP ,CONJUGATED POLYMER ,ROOM-TEMPERATURE ,PHOSPHORESCENCE ,DEVICES ,ELECTROLUMINESCENCE ,MAGNETORESISTANCE ,RECOMBINATION ,EMISSION ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Phosphorescence ,Hyperfine structure - Abstract
We probe the interconversion of spin permutation symmetry of weakly bound electron-hole carrier pairs in an organic light-emitting diode by monitoring the changes in yield of recombinant species-singlet and triplet excitons-through fluorescence and phosphorescence, respectively. Spin mixing occurs by spin precession in local hyperfine fields and is suppressed by an external magnetic field, leading to an anticorrelation of fluorescence and phosphorescence yield, which follows the same functionality as magnetoresistance. A resonant radio-frequency field reverses this effect, enhancing spin mixing to raise the phosphorescence and lower the fluorescence. The experiment offers a direct simultaneous optical probe of the two interconverting spin states in the radical-pair mechanism, which features prominently in models of biological magnetoception.
- Published
- 2017
28. Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing
- Author
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Michael Foerster, Riccardo Frisenda, David Perez de Lara, Sebastian Bange, Miguel Angel Niño, Emilio M. Pérez, Jose L. Lado, John M. Lupton, Joaquín Fernández-Rossier, Tobias Korn, Patricia Gant, Philipp Nagler, Lucia Aballe, Emerson Giovanelli, Andres Castellanos-Gomez, Christian Schüller, Joshua O. Island, Aday J. Molina-Mendoza, European Commission, European Research Council, Ministerio de Economía y Competitividad (España), Comunidad de Madrid, Netherlands Organization for Scientific Research, German Research Foundation, Universidad de Alicante. Departamento de Física Aplicada, and Grupo de Nanofísica
- Subjects
Materials science ,Photoluminescence ,Física de la Materia Condensada ,optoelectronics ,FOS: Physical sciences ,Transition metal halides ,lead iodide ,Bioengineering ,02 engineering and technology ,Two-dimensional materials ,010402 general chemistry ,01 natural sciences ,symbols.namesake ,PbI2 ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,Optoelectronics ,transition metal halides ,two-dimensional materials ,Electrical and Electronic Engineering ,Electronic band structure ,Spectroscopy ,Lead iodide ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Precipitation (chemistry) ,ab initio calculations ,Mechanical Engineering ,direct bandgap ,PbI ,2 ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Characterization (materials science) ,Direct bandgap ,Mechanics of Materials ,symbols ,Direct and indirect band gaps ,Ab initio calculations ,0210 nano-technology ,business ,Raman spectroscopy ,Visible spectrum - Abstract
Two-dimensional semiconducting materials are particularly appealing for many applications. Although theory predicts a large number of two-dimensional materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectros-copy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties., main text 20 pages + 10 figures, supporting information 16 pages + 17 figures
- Published
- 2017
29. Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs
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Tobias Korn, Philipp Nagler, Gerd Plechinger, John M. Lupton, Johanna Kirschner, I. Caspers, Alexey Chernikov, Florian Steiner, Jan Vogelsang, Felix J. Hofmann, Sebastian Bange, Christian Schüller, and Robin P. Puchert
- Subjects
Biomedical Engineering ,Physics::Optics ,FOS: Physical sciences ,Bioengineering ,02 engineering and technology ,Electroluminescence ,01 natural sciences ,Silver nanoparticle ,law.invention ,Overlayer ,Condensed Matter::Materials Science ,law ,Physics - Chemical Physics ,0103 physical sciences ,General Materials Science ,Electrical and Electronic Engineering ,010306 general physics ,Nanoscopic scale ,Plasmon ,Quantum tunnelling ,Chemical Physics (physics.chem-ph) ,Condensed Matter - Materials Science ,business.industry ,ddc:530 ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,530 Physik ,Atomic and Molecular Physics, and Optics ,Dipole ,Optoelectronics ,0210 nano-technology ,business ,Physics - Optics ,Light-emitting diode ,Optics (physics.optics) - Abstract
The demonstration of energy transfer from hotspots of electroluminescent silver nanoparticles to a two-dimensional crystal overlayer of a transition-metal dichalcogenide provides a tunable, sub-diffraction, electrically driven light source. Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit ‘cold’ electroluminescence in percolation films1,2, tunnel diodes3, electromigrated nanoparticle aggregates4,5, optical antennas6 or scanning tunnelling microscopy7,8,9. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET–light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides10. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes11 in on-chip optical interconnects.
- Published
- 2017
- Full Text
- View/download PDF
30. Nanotesla magnetoresistance in π-conjugated polymer devices
- Author
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Agnes Pöllmann, John M. Lupton, Philippe Klemm, Christoph Boehme, and Sebastian Bange
- Subjects
Conductive polymer ,Materials science ,Condensed matter physics ,Field (physics) ,Magnetoresistance ,ddc:530 ,Field strength ,02 engineering and technology ,021001 nanoscience & nanotechnology ,530 Physik ,01 natural sciences ,Magnetic field ,PEDOT:PSS ,0103 physical sciences ,OLED ,ORGANIC SEMICONDUCTORS ,MAGNETIC COMPASS ,MODEL ,MAGNETORECEPTION ,HYPERFINE ,010306 general physics ,0210 nano-technology ,Diode - Abstract
We demonstrate submicrotesla sensitivity of organic magnetoresistance in thin-film diodes made of the conducting polymer poly(styrene sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS). The magnetoresistance sensitivity is shown to be better than 20 parts per billion (ppb). As for other conjugated polymers, magnetoresistance can be separated into two regimes of field strength: the nonmonotonic ultrasmall magnetic field effect on magnetic field scales below 2 mT, and the monotonic intermediate magnetic field effect on scales over several tens of mT. The former gives the PEDOT:PSS magnetoresistance curve a characteristic W-shaped functionality, with inverted turning points compared to those found in conventional organic light-emitting diode (OLED) devices. We succeed in resolving the ultrasmall magnetic field effect of the PEDOT: PSS layer incorporated within an OLED structure, which is responsible for an additional magnetoresistive feature on the ppm scale. Such a device shows unprecedented complexity in magnetoresistance with a total of four extrema within a field range of +/- 1 mT. We propose that these unique characteristics arise from spin-spin interactions in the weakly bound carrier pairs responsible for the spin-dependent recombination probed in magnetoresistance.
- Published
- 2017
31. Metal-Free OLED Triplet Emitters by Side-Stepping Kasha’s Rule
- Author
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Debangshu Chaudhuri, Eva Sigmund, Annemarie Meyer, Lisa Röck, Philippe Klemm, Sebastian Lautenschlager, Agnes Schmid, Shane R. Yost, Troy Van Voorhis, Sebastian Bange, Sigurd Höger, and John M. Lupton
- Subjects
General Medicine - Published
- 2013
32. Metal-Free OLED Triplet Emitters by Side-Stepping Kasha’s Rule
- Author
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Agnes Schmid, Philippe Klemm, Sebastian Bange, Shane R. Yost, Troy Van Voorhis, Annemarie Meyer, Sebastian Lautenschlager, Debangshu Chaudhuri, Lisa M. Röck, John M. Lupton, Eva Sigmund, and Sigurd Höger
- Subjects
Kasha's rule ,Metal free ,Chemistry ,OLED ,General Chemistry ,Atomic physics ,Photochemistry ,Catalysis - Published
- 2013
33. Imaging of cellular oxygen via two-photon excitation of fluorescent sensor nanoparticles
- Author
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Xu-dong Wang, Daniela E. Achatz, Christina Hupf, Joachim Wegener, Michaela Sperber, Otto S. Wolfbeis, John M. Lupton, and Sebastian Bange
- Subjects
Chemistry ,Metals and Alloys ,Analytical chemistry ,Nanoparticle ,chemistry.chemical_element ,Condensed Matter Physics ,Fluorescence ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ruthenium ,Two-photon excitation microscopy ,Materials Chemistry ,Electrical and Electronic Engineering ,Absorption (electromagnetic radiation) ,Luminescence ,Instrumentation ,Oxygen sensor ,Excitation - Abstract
Polystyrene nanoparticles (PSNPs) with an average size of 85 nm and loaded with an oxygen-quenchable luminescent ruthenium complex were used to sense and image oxygen inside cells following 2-photon excitation (2-PE). The ruthenium probe possesses a large two-photon absorption cross-section, and 2-PE is achieved by irradiation in the near infrared with commercially available fs-pulsed laser systems. The luminescence of the dye-loaded PSNPs is strongly quenched by oxygen, and Stern–Volmer plots are linear for both conventional single-photon excitation (1-PE) and for 2-PE. The particles do not show any significant cytotoxicity below a threshold concentration of 5 μg/mL and are readily taken up by mammalian cells (MCF-7), presumably via membrane mediated pathways. Thus, the PSNPs promise to be well suited to image the oxygen distribution in living cells and tissues. The 2-PE is considered to be advantageous over conventional imaging techniques because it works in the near-infrared where background absorption and luminescence of biomatter is much weaker than at excitation wavelengths below 600 nm.
- Published
- 2013
34. Effect of Conjugation Pathway in Metal-Free Room-Temperature Dual Singlet-Triplet Emitters for Organic Light-Emitting Diodes
- Author
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Olav Schiemann, Christoph Bannwarth, Stefan Grimme, Wolfram Ratzke, John M. Lupton, Sebastian Bange, Hideto Matsuoka, Marius Retegan, Philippe Klemm, Frank Neese, Lisa Schmitt, and Sigurd Höger
- Subjects
Phenazine ,Relaxation (NMR) ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Fluorescence ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Excited state ,OLED ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Singlet state ,Physical and Theoretical Chemistry ,Triplet state ,0210 nano-technology ,Phosphorescence - Abstract
Metal-free dual singlet–triplet organic light-emitting diode (OLED) emitters can provide direct insight into spin statistics, spin correlations and spin relaxation phenomena, through a comparison of fluorescence to phosphorescence intensity. Remarkably, such materials can also function at room temperature, exhibiting phosphorescence lifetimes of several milliseconds. Using electroluminescence, quantum chemistry, and electron paramagnetic resonance spectroscopy, we investigate the effect of the conjugation pathway on radiative and nonradiative relaxation of the triplet state in phenazine-based compounds and demonstrate that the contribution of the phenazine nπ* excited state is crucial to enabling phosphorescence.
- Published
- 2016
35. Two-Photon Excitation Temperature Nanosensors Based on a Conjugated Fluorescent Polymer Doped with a Europium Probe
- Author
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Michaela Sperber, Vladimir Ondrus, Joachim Wegener, Uwe Beifuss, Ulrich Henne, Robert J. Meier, John M. Lupton, Sebastian Bange, Otto S. Wolfbeis, Christian Klein, Michael Schäferling, and Xu-dong Wang
- Subjects
Materials science ,fluorescence resonance energy transfer ,Nanoparticle ,chemistry.chemical_element ,02 engineering and technology ,Excitation temperature ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Polyfluorene ,chemistry.chemical_compound ,two-photon excitation ,temperature ,Fluorescent polymer ,021001 nanoscience & nanotechnology ,Fluorescence ,Acceptor ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Förster resonance energy transfer ,chemistry ,nanosensor ,0210 nano-technology ,Luminescence ,Europium - Abstract
A strongly fluorescent organic semiconducting polymer doped with a highly temperature dependent fluorescent europium(III) complex is converted into a nanosized material that is capable of optically sensing temperature (T) in the range from 0 to 50 °C via two-photon excitation at 720 nm. The nanosensors are prepared from a blue-fluorescent polyfluorene that acts as both a lightharvesting antenna (to capture two-photon energy) and an energy donor in a fluorescence resonance energy transfer (FRET) system. The photonic energy absorbed by the polymer is transferred to the T-sensitive red-luminescent europium complex contained in the nanoparticles. The close spatial proximity of the donor and the acceptor warrants efficient FRET. A poly(ethylene glycol)-co-poly(propylene oxide) block copolymer is also added to render the particles biocompatible. It is shown that T can be calculated from a) the intensity of the luminescence of the europium complex, b) the ratio of the intensities of the red and blue luminescence, or c) the T-dependent luminescence lifetime of the Eu(III) complex.
- Published
- 2016
36. Absence of Singlet Fission and Carrier Multiplication in a Model Conjugated Polymer: Tracking the Triplet Population through Phosphorescence
- Author
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John M. Lupton, Ullrich Scherf, and Sebastian Bange
- Subjects
Models, Molecular ,education.field_of_study ,Molecular Structure ,Polymers ,Chemistry ,Fission ,Population ,General Chemistry ,Biochemistry ,Fluorescence ,Catalysis ,Multiple exciton generation ,Colloid and Surface Chemistry ,Intersystem crossing ,Luminescent Measurements ,Singlet fission ,Photoluminescence excitation ,Triplet state ,Atomic physics ,Phosphorescence ,education - Abstract
Singlet fission, or multiple exciton generation, has been purported to occur in a variety of material systems. Given the current interest in exploiting this process in photovoltaics, we search for the direct signature of singlet fission, phosphorescence from the triplet state, in a model polymeric organic semiconductor for which photoinduced absorption experiments have implied a tripling of the intersystem crossing yield at the onset of fission. Fluorescence and phosphorescence are clearly discriminated using a picosecond gated photoluminescence excitation technique, at variable temperature. At low excitation densities, in a quasi-steady-state experiment, we detect no change of the relative triplet yield to within 4% for photon energies of almost three times the triplet energy of 2.1 eV. Identical results are obtained under nonlinear two-photon excitation. We conclude that assignments of singlet fission based on induced absorptions alone should be treated with caution and may substantially overestimate excited-state intersystem crossing yields, raising questions with regards to the applicability of the process in devices.
- Published
- 2012
37. Temperature and current dependence of the magnetoresistive behavior of poly(styrene-sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS)
- Author
-
Philippe Klemm, Christoph Boehme, Sebastian Bange, John M. Lupton, and Hans Malissa
- Subjects
Conductive polymer ,Materials science ,Condensed matter physics ,Magnetoresistance ,Renewable Energy, Sustainability and the Environment ,Magnetism ,02 engineering and technology ,530 Physik ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Magnetic field ,Organic semiconductor ,chemistry.chemical_compound ,chemistry ,PEDOT:PSS ,0103 physical sciences ,organic semiconductors ,conducting polymers ,magnetoresistance ,magnetic field effects ,poly(styrene-sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) ,Thin film ,010306 general physics ,0210 nano-technology ,Poly(3,4-ethylenedioxythiophene) - Abstract
We investigate the magnetic field effects in thin-film diodes made of the conducting polymer poly(styrene-sulfonate)-doped poly(3,4-ethylenedioxythiophene) as a function of temperature and electrical current. Magnetoresistance of these devices can be measured to high precision on two distinct magnetic field scales
- Published
- 2018
38. Charge transport and recombination in bulk heterojunction solar cells containing a dicyanoimidazole-based molecular acceptor
- Author
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Sebastian Bange, Dieter Neher, Marcel Schubert, Robert Steyrleuthner, and Alan Sellinger
- Subjects
Electron mobility ,Chemistry ,Analytical chemistry ,Charge (physics) ,Surfaces and Interfaces ,Condensed Matter Physics ,Acceptor ,Space charge ,Polymer solar cell ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Photoexcitation ,Chemical physics ,Materials Chemistry ,Charge carrier ,Electrical and Electronic Engineering ,Recombination - Abstract
Carrier transport and recombination have been studied in single component layers and blends of the soluble PPV- derivative poly[2,5-dimethoxy-1,4-phenylenevinylene-2-methoxy-5-(2-ethyl-hexyloxy)- 1,4-phenylenevinylene] (M3EH-PPV) and the small molecule acceptor 4,7-bis(2-(1-hexyl-4,5-dicyanoimidazole-2-yl)vinyl) benzo[c][1,2,5]-thiadiazole (HV-BT). Measurements on single carrier devices show significantly smaller electron mobility in the blend compared to the pure HV- BT layer, which is suggestive of the formation of isolated clusters of the acceptor in a continuous polymer matrix. The significant change in fill factor (FF) with increasing illumination intensity is consistently explained by a model taking into account bimolecular recombination and space charge effects. The decay of the carrier density after photoexcitation has been studied by performing photo-CELIV measurements on pure and blend layers. It is found that the decay at long delay times follows a power-law dependence, which is, however, not consistent with a Langevin-type bimolecular recombination of free charges. A good description of the data is obtained by assuming trimolecular recombination to govern the charge carrier dynamics in these systems.
- Published
- 2009
39. Spontaneous fluctuations of transition dipole moment orientation in OLED triplet emitters
- Author
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Jan Vogelsang, Sebastian Bange, John M. Lupton, and Florian Steiner
- Subjects
Physics ,Chemical Physics (physics.chem-ph) ,Linear polarization ,Spontaneous symmetry breaking ,Transition dipole moment ,FOS: Physical sciences ,Polarization (waves) ,Molecular physics ,Dipole ,Polarization scrambling ,Excited state ,Physics - Chemical Physics ,General Materials Science ,Physical and Theoretical Chemistry ,Phosphorescence ,Optics (physics.optics) ,Physics - Optics - Abstract
The efficiency of an organic light-emitting diode (OLED) depends on the microscopic orientation of transition dipole moments of the molecular emitters. The most effective materials used for light generation have threefold symmetry, which prohibit a priori determination of dipole orientation due to the degeneracy of the fundamental transition. Single-molecule spectroscopy reveals that the model triplet emitter tris(2-phenylisoquinoline)iridium(III) (Ir(piq)3) does not behave as a linear dipole, radiating with lower polarization anisotropy than expected. Spontaneous symmetry breaking occurs in the excited state, leading to a random selection of one of the three ligands to form a charge transfer state with the metal. This non-deterministic localization is revealed in switching of the degree of linear polarization of phosphorescence. Polarization scrambling likely raises out-coupling efficiency and should be taken into account when deriving molecular orientation of the guest emitter within the OLED host from ensemble angular emission profiles.
- Published
- 2015
40. Hot-electron intraband luminescence from single hot spots in noble-metal nanoparticle films
- Author
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Philippe Klemm, Sebastian Bange, John M. Lupton, and Tobias Haug
- Subjects
Physics ,Incandescent light bulb ,ddc:530 ,General Physics and Astronomy ,Nanoparticle ,Physics::Optics ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,530 Physik ,01 natural sciences ,Molecular physics ,law.invention ,law ,0103 physical sciences ,Femtosecond ,Light emission ,Emission spectrum ,010306 general physics ,0210 nano-technology ,Luminescence ,Plasmon ,Excitation ,Astrophysics::Galaxy Astrophysics - Abstract
Disordered noble-metal nanoparticle films exhibit highly localized and stable non-linear light emission from sub-diffraction regions upon illumination by near-infrared femtosecond pulses. Such hot spot emission spans a continuum in the visible and near-infrared spectral range. Strong plasmonic enhancement of light-matter interaction and the resulting complexity of experimental observations have prevented the development of a universal understanding of the origin of light emission. Here, we study the dependence of emission spectra on excitation irradiance and provide the most direct evidence yet that the continuum emission observed from both silver and gold nanoparticle aggregate surfaces is caused by recombination of hot electrons within the conduction band. The electron gas in the emiting particles, which is effectively decoupled from the lattice temperature for the duration of emission, reaches effective temperatures of several thousand Kelvin and acts as a sub-diffraction incandescent light source on sub-picosecond time scales.
- Published
- 2015
41. Time-Domain Interferometry of Surface Plasmons at Nonlinear Continuum Hot Spots in Films of Silver Nanoparticles
- Author
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Sebastian Bange, Philippe Klemm, Tobias Haug, and John M. Lupton
- Subjects
Materials science ,Scattering ,business.industry ,ddc:530 ,Surface plasmon ,General Physics and Astronomy ,Nanoparticle ,Physics::Optics ,530 Physik ,Molecular physics ,Silver nanoparticle ,Interferometry ,Optics ,Excited state ,Quasiparticle ,business ,Plasmon - Abstract
Nonlinear continuum generation from diffraction-limited hot spots in rough silver films exhibits striking narrow-band intensity resonances in excitation wavelength. Time-domain Fourier spectroscopy uncovers how these resonances arise due to the formation of a "plasmon staircase", a discreteness in the fundamental oscillation of the plasmon excitations responsible for generating the white-light continuum. Whereas multiple scattering from discrete antennas can be invoked to explain hot spot formation in random assemblies of isolated particles, hot spots in films of fused nanoparticles are excited by interfering propagating surface plasmons, launched by scattering from individual nanoparticle antennas. For closed films, discrete propagating plasmons interact coherently over distances of tens of microns to pump the hot spot.
- Published
- 2014
- Full Text
- View/download PDF
42. Temporal switching of homo-FRET pathways in single-chromophore dimer models of π-conjugated polymers
- Author
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Daniela Schmitz, Sigurd Höger, Sebastian Bange, Jan Vogelsang, Thomas Stangl, John M. Lupton, and Dominik Würsch
- Subjects
Models, Molecular ,Quantitative Biology::Biomolecules ,Quenching (fluorescence) ,Chemistry ,Polymers ,Analytical chemistry ,Quantum yield ,Fluorescence correlation spectroscopy ,General Chemistry ,Conjugated system ,Chromophore ,Linear dichroism ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Förster resonance energy transfer ,Chemical physics ,Fluorescence Resonance Energy Transfer ,Spectroscopy ,Dimerization - Abstract
A set of π-conjugated oligomer dimers templated in molecular scaffolds is presented as a model system for studying the interactions between chromophores in conjugated polymers (CPs). Single-molecule spectroscopy was used to reveal energy transfer dynamics between two oligomers in either a parallel or oblique-angle geometry. In particular, the conformation of single molecules embedded in a host matrix was investigated via polarized excitation and emission fluorescence microscopy in combination with fluorescence correlation spectroscopy. While the intramolecular interchromophore conformation was found to have no impact on the fluorescence quantum yield, lifetime, or photon statistics (antibunching), the long-term nonequilibrium dynamics of energy transfer within these bichromophoric systems was accessible by studying the linear dichroism in emission at the single-molecule level, which revealed reversible switching of the emission between the two oligomers. In bulk polymer films, interchromophore coupling promotes the migration of excitation energy to quenching sites. Realizing the presence and dynamics of such interactions is crucial for understanding limitations on the quantum efficiency of larger CP materials.
- Published
- 2012
43. Charge mobility determination by current extraction under linear increasing voltages : case of nonequilibrium charges and field-dependent mobilities
- Author
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Dieter Neher, Marcel Schubert, and Sebastian Bange
- Subjects
Work (thermodynamics) ,Condensed Matter - Materials Science ,Materials science ,Field (physics) ,Condensed matter physics ,Relaxation (NMR) ,Field dependence ,Non-equilibrium thermodynamics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Institut für Physik und Astronomie ,Charge (physics) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Current (fluid) ,Voltage - Abstract
The method of current extraction under linear increasing voltages (CELIV) allows for the simultaneous determination of charge mobilities and charge densities directly in thin films as used in organic photovoltaic cells (OPV). In the past, it has been specifically applied to investigate the interrelation of microstructure and charge transport properties in such systems. Numerical and analytical calculations presented in this work show that the evaluation of CELIV transients with the commonly used analysis scheme is error prone once charge recombination and, possibly, field dependent charge mobilities are taken into account. The most important effects are an apparent time-dependence of charge mobilities and errors in the determined field dependencies. Our results implicate that reports on time-dependent mobility relaxation in OPV materials obtained by the CELIV technique should be carefully revisited and confirmed by other measurement methods., 15 pages, 9 figures
- Published
- 2010
44. Tuning of the excited-state properties and photovoltaic performance in PPV-based polymer blends
- Author
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Michael U. Kumke, Dieter Neher, Marcel Schubert, Hans-Heinrich Hörhold, Burkhard Stiller, Mauro Castellani, Sebastian Bange, and Chunhong Yin
- Subjects
chemistry.chemical_classification ,Chloroform ,Materials science ,Photoluminescence ,Morphology (linguistics) ,Exciton ,Analytical chemistry ,Polymer ,Photochemistry ,Excimer ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,General Energy ,chemistry ,Excited state ,Institut für Chemie ,Polymer blend ,Physical and Theoretical Chemistry - Abstract
The authors use solvents with different boiling points and a mixture of these solvents to tune the morphology of blends formed from poly[2,5-dimethoxy-1,4-phenylenevinylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (M3EH-PPV) and poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethylene-1,4-phenylene] (CN-ether-PPV). In photoluminescence (PL), the emission of as-prepared films spin-coated from chloroform (CF) is entirely dominated by an exciplex, with no evidence for the radiative decay of either the M3EH-PPV or the CN-ether-PPV exciton. Evidently these intrachain excited species dissociate rapidly by intermolecular charge transfer, pointing to a highly intermixed blend morphology. On the other hand, the PL of films deposited from 1,2,4-trichlorobenzene (TCB) exhibits predominant emission from the M3EH-PPV exciton, indicating the presence of rather pure M3EH-PPV domains in the phase-separated polymers layers. The blend morphology is shown to have a large ...
- Published
- 2008
45. Reliable electron-only devices and electron transport in n-type polymers
- Author
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Dieter Neher, Sebastian Bange, and Robert Steyrleuthner
- Subjects
Electron mobility ,Materials science ,business.industry ,Oxide ,Institut für Physik und Astronomie ,General Physics and Astronomy ,Electron ,Electron transport chain ,Organic semiconductor ,chemistry.chemical_compound ,chemistry ,Electrode ,Optoelectronics ,Charge carrier ,business ,Leakage (electronics) - Abstract
Current-voltage analysis of single-carrier transport is a popular method for the determination of charge carrier mobilities in organic semiconductors. Although in widespread use for the analysis of hole transport, only a few reports can be found where the method was applied to electron transport. Here, we summarize the experimental difficulties related to the metal electrode leakage currents and nonlinear differential resistance (NDR) effects and explain their origin. We present a modified preparation technique for the metal electrodes and show that it significantly increases the reliability of such measurements. It allows to produce test devices with low leakage currents and without NDR even for thin organic layers. Metal oxides were often discussed as a possible cause of NDR. Our measurements on forcibly oxidized metal electrodes demonstrate that oxide layers are not exclusively responsible for NDR effects. We present electron transport data for two electron-conducting polymers often applied in all-polymer solar cells for a large variety of layer thicknesses and temperatures. The results can be explained by established exponential trapping models.
- Published
- 2009
46. Exciton Localization in Extended π-ElectronSystems: Comparison of Linear and Cyclic Structures.
- Author
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Alexander Thiessen, Dominik Würsch, Stefan-S. Jester, A. Vikas Aggarwal, Alissa Idelson, Sebastian Bange, Jan Vogelsang, Sigurd Höger, and John M. Lupton
- Published
- 2015
- Full Text
- View/download PDF
47. The role of poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) as a hole injection layer in a blue-emitting polymer light-emitting diode
- Author
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Aurélie Ludemann, Dieter Neher, Susanne Heun, Sebastian Bange, Andriy Kuksov, Norbert Koch, and Antje Vollmer
- Subjects
Conductive polymer ,Photocurrent ,Materials science ,business.industry ,Photoconductivity ,General Physics and Astronomy ,Electroluminescence ,chemistry.chemical_compound ,PEDOT:PSS ,chemistry ,OLED ,Optoelectronics ,business ,Ohmic contact ,Poly(3,4-ethylenedioxythiophene) - Abstract
The authors study the role of the conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulphonate) (PEDOT:PSS) in determining the transient and steady-state operation of a blue-emitting polymer light-emitting diode. Combining the results from photoemission spectroscopy, time-of-flight photocurrent measurements, and studies on hole-only devices reveals a significant barrier for the injection of holes into the polymer. Simulations with a numerical drift-diffusion model, however, show that the injection currents determined from single-carrier devices cannot account for the rapid transient luminance onset and the efficient steady-state luminance output of the corresponding bipolar light-emitting devices. It is shown that the transient electroluminescence traces measured at different external bias can be well reproduced when assuming the presence of a weak barrier for electron extraction at this interface, which is attributed to electron accumulation at a thin phase-segregated PSS-rich layer at the surface of PEDOT:PSS. In addition, interface conditioning, presumably due to electron trapping near PEDOT:PSS, renders the anode-polymer interface nearly Ohmic. This conditioning, however, occurs on intermediate time scales normally not addressed by either transient or steady-state measurements.
- Published
- 2008
48. Sensing electron transport in a blue-emitting copolymer by transient electroluminescence
- Author
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Andriy Kuksov, Sebastian Bange, and Dieter Neher
- Subjects
chemistry.chemical_classification ,Electron mobility ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Polymer ,Electron ,Electroluminescence ,Electron transport chain ,Anode ,chemistry ,Copolymer ,Optoelectronics ,business ,Diode - Abstract
A variation of the transient electroluminescence technique is introduced which allows us to selectively study the electron transport in a thin polymer layer. It relies on the formation of an insoluble interlayer from a formerly solvable polymer and enables probing of unipolar electron transport despite of injection barriers. It opens up possibilities to gain insight into the operation of light-emitting diodes. Applicability to a blue-emitting spirobifluorene-based copolymer is shown by comparison to time-of-flight results for electron and hole transport and evidence supplied for an intermixing of electron and hole dynamics through blocking of electrons at the polymer/anode interface.
- Published
- 2007
49. Electrical detection of ferromagnetic resonances with an organic light-emitting diode.
- Author
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Tobias Grünbaum, Sebastian Bange, Matthias Kronseder, Christian H Back, and John M Lupton
- Subjects
- *
YTTRIUM iron garnet , *PARAMAGNETIC resonance , *MAGNETIC structure , *MAGNETIC films , *ORGANIC semiconductors , *ORGANIC light emitting diodes , *OPTICAL resonance - Abstract
Organic semiconductors show strong magnetic-field effects in transport and luminescence because of inherently spin-dependent recombination. We explore whether paramagnetic resonance features can be enhanced in a hybrid structure comprising a thin yttrium iron garnet (YIG) film, undergoing ferromagnetic resonance (FMR) and an organic light-emitting diode (OLED). We investigate the effect of radio-frequency (RF) driving of this hybrid structure in a magnetic field. Under these conditions, an indirect bolometric effect enables the detection of FMR driven in the YIG film in the DC resistance of the OLED. The increased RF power absorption of the YIG film under resonance gives rise to a heating of the magnetic film. Subsequent heat transfer to the OLED causes a change in transport characteristics of the device. Good agreement of this electrically detected signal is found with a direct measurement of the RF power absorption. Using temperature dependent measurements, the thermal nature of the resistance signal is confirmed. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
50. Characterization of highly crystalline lead iodide nanosheets prepared by room-temperature solution processing.
- Author
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Riccardo Frisenda, Joshua O Island, Jose L Lado, Emerson Giovanelli, Patricia Gant, Philipp Nagler, Sebastian Bange, John M Lupton, Christian Schüller, Aday J Molina-Mendoza, Lucia Aballe, Michael Foerster, Tobias Korn, Miguel Angel Niño, David Perez de Lara, Emilio M Pérez, Joaquín Fernandéz-Rossier, and Andres Castellanos-Gomez
- Subjects
SEMICONDUCTORS ,LEAD iodide ,RAMAN spectroscopy - Abstract
Two-dimensional (2D) semiconducting materials are particularly appealing for many applications. Although theory predicts a large number of 2D materials, experimentally only a few of these materials have been identified and characterized comprehensively in the ultrathin limit. Lead iodide, which belongs to the transition metal halides family and has a direct bandgap in the visible spectrum, has been known for a long time and has been well characterized in its bulk form. Nevertheless, studies of this material in the nanometer thickness regime are rather scarce. In this article we demonstrate an easy way to synthesize ultrathin, highly crystalline flakes of PbI
2 by precipitation from a solution in water. We thoroughly characterize the produced thin flakes with different techniques ranging from optical and Raman spectroscopy to temperature-dependent photoluminescence and electron microscopy. We compare the results to ab initio calculations of the band structure of the material. Finally, we fabricate photodetectors based on PbI2 and study their optoelectronic properties. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
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