TY - JOUR A1 - Amthor, Matthias A1 - Weißenseel, Sebastian A1 - Fischer, Julian A1 - Kamp, Martin A1 - Schneider, Christian A1 - Höfling, Sven T1 - Electro-optical switching between polariton and cavity lasing in an InGaAs quantum well microcavity N2 - We report on the condensation of microcavity exciton polaritons under optical excitation in a microcavity with four embedded InGaAs quantum wells. The polariton laser is characterized by a distinct nonlinearity in the input-output-characteristics, which is accompanied by a drop of the emission linewidth indicating temporal coherence and a characteristic persisting emission blueshift with increased particle density. The temporal coherence of the device at threshold is underlined by a characteristic drop of the second order coherence function to a value close to 1. Furthermore an external electric field is used to switch between polariton regime, polariton condensate and photon lasing. KW - Quantum-well, -wire and -dot devices KW - Scattering KW - stimulated KW - Resonators KW - Microcavity devices Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-111130 ER - TY - JOUR A1 - Weissenseel, Sebastian A1 - Gottscholl, Andreas A1 - Bönnighausen, Rebecca A1 - Dyakonov, Vladimir A1 - Sperlich, Andreas T1 - Long-lived spin-polarized intermolecular exciplex states in thermally activated delayed fluorescence-based organic light-emitting diodes JF - Science Advances N2 - Spin-spin interactions in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) are pivotal because radiative recombination is largely determined by triplet-to-singlet conversion, also called reverse intersystem crossing (RISC). To explore the underlying process, we apply a spin-resonance spectral hole-burning technique to probe electroluminescence. We find that the triplet exciplex states in OLEDs are highly spin-polarized and show that these states can be decoupled from the heterogeneous nuclear environment as a source of spin dephasing and can even be coherently manipulated on a spin-spin relaxation time scale T-2* of 30 ns. Crucially, we obtain the characteristic triplet exciplex spin-lattice relaxation time T-1 in the range of 50 mu s, which far exceeds the RISC time. We conclude that slow spin relaxation rather than RISC is an efficiency-limiting step for intermolecular donor:acceptor systems. Finding TADF emitters with faster spin relaxation will benefit this type of TADF OLEDs. KW - detected magnetic-resonance KW - population oscillations KW - polaron delocalization KW - charge separation KW - hole KW - phosphorescence KW - singlet KW - absorption KW - tryptophan KW - emission Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-265508 VL - 7 IS - 47 ER - TY - THES A1 - Weißenseel, Sebastian Günter T1 - Spin-Spin Interactions and their Impact on Organic Light-Emitting Devices T1 - Spin-Spin-Wechselwirkungen und ihre Einflüsse auf organische Leuchtdioden N2 - This work investigates the correlations between spin states and the light emission properties of organic light-emitting diodes (OLEDs), which are based on the principle of thermally activated delayed fluorescence. The spin-spin interactions responsible for this mechanism are investigated in this work using methods based on spin-sensitive electron paramagnetic resonance (EPR). In particular, this method has been applied to electrically driven OLEDs. The magnetic resonance has been detected by electroluminescence, giving this method its name: electroluminescence detected magnetic resonance (ELDMR). Initial investigations on a novel deep blue TADF emitter were performed. Furthermore, the ELDMR method was used in this work to directly detect the spin states in the OLED. These measurements were further underlined by time-resolved experiments such as transient electro- and photoluminescence. N2 - Diese Arbeit untersucht die Zusammenhänge zwischen Spinzuständen und den Lichtemissions Eigenschaften von Organischen Leuchtdioden (OLEDs), welche auf dem Prinzip der thermisch aktivierten verzögerten Fluoreszenz basieren. Die für diesen Mechanismus verantwortlichen Spin-Spin-Wechselwirkungen werden im Rahmen der Arbeit mit Methoden untersucht, die auf der spinsensitiven Elektron Paramagnetische Resonanz (EPR) basieren. Insbesondere wurde diese Methode auf elektrisch betriebene OLEDs angewendet und die magnetische Resonanz durch Elektrolumineszenz nachgewiesen, was dieser Methode ihren Namen verleiht: Elektrolumineszenz detektierte magnetische Resonanz (ELDMR). Erste Untersuchungen an einem neuartigen tiefblauen TADF-Emitters wurden durchgeführt. Ebenfalls konnte in dieser Arbeit mit Hilfe der ELDMR-Methode direkt die Spinzustände in der OLED detektiert werden. Unterstützt wurden diese Messungen von Zeit-aufgelösten Experimenten wie transiente Elektro- und Photolumineszenz. KW - Elektronenspinresonanz KW - Technische Optik KW - Nanometerbereich KW - Organische Leuchtdioden KW - OLED Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257458 ER - TY - JOUR A1 - Bunzmann, Nikolai A1 - Krugmann, Benjamin A1 - Weissenseel, Sebastian A1 - Kudriashova, Liudmila A1 - Ivaniuk, Khrystyna A1 - Stakhira, Pavlo A1 - Cherpak, Vladyslav A1 - Chapran, Marian A1 - Grybauskaite‐Kaminskiene, Gintare A1 - Grazulevicius, Juozas Vidas A1 - Dyakonov, Vladimir A1 - Sperlich, Andreas T1 - Spin‐ and Voltage‐Dependent Emission from Intra‐ and Intermolecular TADF OLEDs JF - Advanced Electronic Materials N2 - Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) utilize molecular systems with a small energy splitting between singlet and triplet states. This can either be realized in intramolecular charge transfer states of molecules with near‐orthogonal donor and acceptor moieties or in intermolecular exciplex states formed between a suitable combination of individual donor and acceptor materials. Here, 4,4′‐(9H,9′H‐[3,3′‐bicarbazole]‐9,9′‐diyl)bis(3‐(trifluoromethyl) benzonitrile) (pCNBCzoCF\(_{3}\)) is investigated, which shows intramolecular TADF but can also form exciplex states in combination with 4,4′,4′′‐tris[phenyl(m‐tolyl)amino]triphenylamine (m‐MTDATA). Orange emitting exciplex‐based OLEDs additionally generate a sky‐blue emission from the intramolecular emitter with an intensity that can be voltage‐controlled. Electroluminescence detected magnetic resonance (ELDMR) is applied to study the thermally activated spin‐dependent triplet to singlet up‐conversion in operating devices. Thereby, intermediate excited states involved in OLED operation can be investigated and the corresponding activation energy for both, intra‐ and intermolecular based TADF can be derived. Furthermore, a lower estimate is given for the extent of the triplet wavefunction to be ≥ 1.2 nm. Photoluminescence detected magnetic resonance (PLDMR) reveals the population of molecular triplets in optically excited thin films. Overall, the findings allow to draw a comprehensive picture of the spin‐dependent emission from intra‐ and intermolecular TADF OLEDs. KW - color tuning KW - exciplexes KW - organic light emitting diodes KW - spin KW - triplets Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224434 VL - 7 IS - 3 ER -