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Probing exciton/exciton interactions with entangled photons: Theory
摘要： Quantum entangled photons provide a sensitive probe of many-body interactions and offer a unique experimental portal for quantifying many-body correlations in a material system. In this paper, we present a theoretical demonstration of how photon–photon entanglement can be generated via interactions between coupled qubits. Here, we develop a model for the scattering of an entangled pair of photons from a molecular dimer. We develop a diagrammatic theory for the scattering matrix and show that one can correlate the von Neumann entropy of the outgoing bi-photon wave function with exciton exchange and repulsion interactions. We conclude by discussing possible experimental scenarios for realizing these ideas.
关键词： exciton exchange,repulsion interactions,quantum entangled photons,von Neumann entropy,many-body interactions
更新于2025-09-23 15:19:57
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Molecular vibrations reduce the maximum achievable photovoltage in organic solar cells
摘要： The low-energy edge of optical absorption spectra is critical for the performance of solar cells, but is not well understood in the case of organic solar cells (OSCs). We study the microscopic origin of exciton bands in molecular blends and investigate their role in OSCs. We simulate the temperature dependence of the excitonic density of states and low-energy absorption features, including low-frequency molecular vibrations and multi-exciton hybridisation. For model donor-acceptor blends featuring charge-transfer excitons, our simulations agree very well with temperature-dependent experimental absorption spectra. We unveil that the quantum effect of zero-point vibrations, mediated by electron-phonon interaction, causes a substantial exciton bandwidth and reduces the open-circuit voltage, which is predicted from electronic and vibronic molecular parameters. This effect is surprisingly strong at room temperature and can substantially limit the OSC’s efficiency. Strategies to reduce these vibration-induced voltage losses are discussed for a larger set of systems and different heterojunction geometries.
关键词： molecular vibrations,exciton bands,electron-phonon interaction,organic solar cells,photovoltage
更新于2025-09-23 15:19:57
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Excitonically Coupled Cyclic BF2 Arrays of Calix[8]a?? and Calix[16]phyrin as Neara??IRa?? Chromophores
摘要： A pair of giant calix[n]phyrin derivatives namely calix[8]- (4) and calix[16]phyrin (5), involving two and four BF2 units, respectively, were prepared via the condensation of bis-naphthobipyrrolylmethene-BF2 complex with pentafluorobenzaldehyde. Both systems and precursor 3 were fully characterized, including via single crystal X-ray diffraction analyses. Calix[n]phyrins 4 and 5 display extremely high extinction coefficients (3.67 and 4.82 105 M-1cm-1, respectively) in the near-IR region. This observation was taken as initial evidence for strong excitonic coupling within these cyclic multi-chromophoric systems. Detailed insights into the effect of excitonic coupling dynamics on the electronic structure and photophysical properties of the macrocycles came from fluorescence, time-correlated single-photon counting (TCSPC) and transient absorption (TA) measurements. Support for the experimental findings came from theoretical studies. Taken in concert this combination of theory and experiment served to confirm that the coupling between the excitons depends on the specifics of the calix[n]phyrin structure, not just its size.
关键词： Cyclic BODIPY,Boron,Exciton Coupling,Porphyrinoids,NIR Dye,Calix[n]phyrin
更新于2025-09-23 15:19:57
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Monitoring strong coupling in nonlocal plasmonics with electron spectroscopies
摘要： Plasmon-exciton polaritons provide exciting possibilities to control light-matter interactions at the nanoscale by enabling closer investigation of quantum optical effects and facilitating novel technologies based, for instance, on Bose-Einstein condensation and polaritonic lasing. Nevertheless, observing and visualizing polaritons is challenging, and traditional optical microscopy techniques often lead to ambiguities regarding the emergence and strength of the plasmon-exciton coupling. Electron microscopy offers a more robust means to study and verify the nature of plexcitons, but it is still hindered by instrument limitations and resolution. A simple theoretical description of electron beam-excited plexcitons is therefore vital to complement ongoing experimental efforts. Here we apply analytic solutions for the electron-loss and photon-emission probabilities to evaluate plasmon-exciton coupling studied either with the recently adopted technique of electron energy-loss spectroscopy, or with the so-far unexplored in this context cathodoluminescence spectroscopy. Foreseeing the necessity to account for quantum corrections in the plasmonic response, we extend these solutions within the framework of general nonlocal hydrodynamic descriptions. As a specific example, we study core-shell spherical plasmon-molecule hybrids, going beyond the standard local-response approximation through the hydrodynamic Drude model for screening and the generalized nonlocal optical response theory for nonlocal damping. We show that electron microscopies are extremely powerful in describing the interaction of emitters with the otherwise weakly excited by optical means higher-order plasmonic multipoles, a response that survives when quantum-informed models are considered. Our work provides, therefore, both a robust theoretical background and supporting argumentation to the open quest for improving and further utilizing electron microscopies in strong-coupling nanophotonics.
关键词： electron energy-loss spectroscopy,nonlocal hydrodynamic descriptions,cathodoluminescence spectroscopy,quantum plasmonics,Plasmon-exciton polaritons
更新于2025-09-23 15:19:57
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Multiscale Simulation of Photoluminescence Quenching in Phosphorescent OLED Materials
摘要： A multiscale simulation protocol to treat triplet–triplet annihilation (TTA) in phosphorescent organic light-emitting diodes (PhOLEDs), in which microscopic parameters are computed with ab initio electronic structure methods, is presented. Virtual photoluminescence experiments are performed on a prototypical PhOLED emission material consisting of 4,4?,4?-tris(N-carbazolyl)triphenylamine and fac-tris(2-phenylpyridine)iridium. The obtained TTA quenching rate is comparable to experimental results in the low-intensity limit.
关键词： multiscale modeling,organic light-emitting diodes,exciton quenching,triplet–triplet annihilation
更新于2025-09-23 15:19:57
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Temperature dependence of an amorphous organic thin film polariton laser
摘要： Since its first observation, the polariton lasing threshold in organic films has been anomalously high, given that Bosonic condensation should occur at vanishingly small pumping powers. Here, we investigate the temperature dependence of a polariton laser employing an amorphous organic thin film, 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene, in a vertical optical microcavity. An increase in laser threshold is observed at temperatures < 45 K, while the threshold remains unchanged as the temperature increases up to room temperature. In contrast, the energy dispersion characteristic of cavity polaritons is independent of temperature. At low temperature, an energy relaxation bottleneck along the polariton dispersion takes place below threshold. The bottleneck is found to be responsible for the anomalous increase in threshold with decreasing temperature. As the pumping power increases, amplified spontaneous emission (ASE) is observed prior to the onset of lasing. We also study the photoluminescence of the neat organic film versus temperature to explain the origin of the bottleneck in the exciton polariton dispersion.
关键词： exciton,polariton lasing,light-matter interaction,cavity,Strong-coupling
更新于2025-09-23 15:19:57
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Size- and Composition-Dependent Exciton Spin Relaxation in Lead Halide Perovskite Quantum Dots
摘要： The strong spin-orbital coupling in lead halide perovskites allows for facile spin injection for spintronics applications, but on the other hand also limits the lifetime of the injected spins. Full-dimensional confinement of the carriers using quantum dots (QDs) has been envisioned as an effective means to prolong the spin relaxation lifetime and has been explored for II-VI and III-V group QDs. Here we applied this idea to colloidal lead halide perovskite QDs and measured the exciton spin dynamics of QDs of varying sizes and compositions using circularly polarized transient absorption spectroscopy at room temperature. Interestingly, the spin lifetimes of CsPbI3 and CsPbBr3 QDs were prolonged and shortened, respectively, as compared to their bulk counterparts. Both CsPbI3 and CsPbBr3 QDs showed decreasing spin lifetime with decreasing QD size. Possible spin relaxation mechanisms, including those that are unique to these quantum-confined systems, were proposed, with important ramifications for the use of these perovskite QDs in spin-related applications.
关键词： lead halide perovskites,spin-orbital coupling,exciton spin dynamics,circularly polarized transient absorption spectroscopy,quantum dots
更新于2025-09-23 15:19:57
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Excitonically Coupled Cyclic BF2 Arrays of Calix[8]a?? and Calix[16]phyrin as Neara??IRa?? Chromophores
摘要： A pair of giant calix[n]phyrin derivatives namely calix[8]- (4) and calix[16]phyrin (5), involving two and four BF2 units, respectively, were prepared via the condensation of the bis-naphthobipyrrolylmethene-BF2 complex with pentafluorobenzaldehyde. Both systems and precursor 3 were fully characterized, including via single crystal X-ray diffraction analyses. Calix[n]phyrins 4 and 5 display extremely high extinction coefficients (3.67 and 4.82 105 M-1cm-1, respectively) in the near-IR region. This observation was taken as initial evidence for strong excitonic coupling within these cyclic multi-chromophoric systems. Detailed insights into the effect of excitonic coupling dynamics on the electronic structure and photophysical properties of the macrocycles came from theoretical studies. Taken in concert this combination of theory and experiment served to confirm that the coupling between the excitons depends on the specifics of the calix[n]phyrin structure, not just its size.
关键词： Cyclic BODIPY,Boron,Exciton Coupling,Porphyrinoids,NIR Dye,Calix[n]phyrin
更新于2025-09-23 15:19:57
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A method to detect triplet exciton transfer from singlet fission materials into silicon solar cells: Comparing different surface treatments
摘要： Singlet fission is one of the most promising routes to overcome the single-junction efficiency limit for solar cells. Singlet fission-enhanced silicon solar cells are the most desirable implementation, but transfer of triplet excitons, the product of singlet fission, into silicon solar cells has proved to be very challenging. Here, we report on an all optical measurement technique for the detection of triplet exciton quenching at semiconductor interfaces, a necessary requirement for triplet exciton or charge transfer. The method relies on the growth of individual, single-crystal islands of the singlet fission material on the silicon surface. The islands have different heights, and we correlate these heights to the quenching efficiency of triplet excitons. The quenching efficiency is measured by spatially resolved delayed fluorescence and compared to a diffusion–quenching model. Using silicon capped with a blocking thermal oxide and aromatic monolayers, we demonstrate that this technique can quickly screen different silicon surface treatments for triplet exciton quenching.
关键词： singlet fission,delayed fluorescence,surface treatments,triplet exciton transfer,silicon solar cells
更新于2025-09-23 15:19:57
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Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study
摘要： Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.
关键词： coherent electronic dynamics,pump-probe transient absorption spectroscopy,CdSe quantum dots dimers,exciton dynamics,size dispersion effects
更新于2025-09-23 15:19:57