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Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons
摘要： Hybrid inorganic-organic materials such as quantum dots (QDs) coupled with organic semiconductors have a wide range of optoelectronic applications, taking advantage of the respective materials strengths. A key area of investigation in such systems is the transfer of triplet exciton states to and from QDs, which has potential applications in the luminescent harvesting of triplet excitons generated by singlet fission, in photocatalysis and photochemical upconversion. While the transfer of energy from QDs to the triplet state of organic semiconductors has been intensely studied in recent years, the mechanism and materials parameters controlling the reverse process, triplet transfer to QDs have not been well investigated. Here, through a combination of steady state and time-resolved optical spectroscopy we study the mechanism and energetic dependence of triplet energy transfer from an organic ligand (TIPS-tetracene carboxylic acid) to PbS QDs. Over and energetic range spanning from exothermic (-0.3 eV) to endothermic (+0.1 eV) triplet energy transfer we find that the triplet energy transfer to the QD occurs through a single step process with a clear energy dependence that is consistent with an electron exchange mechanism as described by Marcus-Hush theory. In contrast, the reverse process, energy transfer from the QD to the triplet state of the ligand does not show any energy dependence in the studied energy range, interestingly a delayed formation of the triplet state occurs relative to the quantum dots decay. Based on the energetic dependence of triplet energy transfer we also suggest design criteria for future materials systems where triplet excitons from organic semiconductors are harvested via QDs, for instance in light emitting structures or the harvesting of triplet excitons generated via singlet fission.
关键词： singlet fission,quantum dots,solar energy,photon multiplication,triplet energy transfer
更新于2025-09-23 15:19:57
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European Microscopy Congress 2016: Proceedings || Characterizing Localized Surface Plasmons using Electron Energy-Loss Spectroscopy
摘要： Localized surface plasmon resonances (LSPRs) are the coherent and collective oscillations of conduction band electrons at the surface of metallic nanoparticles. LSPRs are known to localize far-field light to a sub-diffraction-limited length scale, yielding an intense electric field at the particle surface. This effect has been harnessed to dramatically enhance light-matter interactions, leading to a variety of applications such as surface-enhanced Raman spectroscopy (SERS), photothermal cancer therapy and solar energy harvesting. Though a variety of near- and far-field optical methods are used to probe LSPRs, the spatial resolution of these methods is on the order of tens of nanometers, limiting their effectiveness. In contrast, electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM) combines sub-nanometer resolving power with the capability to excite both optical-accessible and –inaccessible plasmon modes and therefore has emerged as one of the leading techniques (Figure 1). In this presentation, I will briefly introduce the STEM/EELS technique and demonstrate the power of STEM/EELS in the characterization of LSPRs. In addition to the traditional use of STEM/EELS for LSPR imaging, we have recently demonstrated that STEM/EELS can also be used to spatially map LSP-semiconductor energy transfer at the nanoscale. The future of STEM/EELS as a window into the nanoscopic world is especially promising, and we expect continued advances in the molecular, optical, materials, information, and energy sciences as a result.
关键词： Localized Surface Plasmon,Hot Electrons,Scanning Transmission Electron Microscopy,Energy Transfer,Electron Energy-Loss Spectroscopy
更新于2025-09-23 15:19:57
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Photophysical Impact of Diacetylenic Conjugation on Classical Donor-Acceptor Electronic Energy Pair
摘要： Organic fluorophores with extended π-conjugation are important for their wide-spread applications. The present work provides photophysical insights of a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its part molecular structures, naphthyl and pyrenyl acetylenes as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (~411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55–0.84) in non-aqueous media. In contrast to parent pyrene, the hybrid derivative shows strongly allowed S0→S1 transition. In mixed-aqueous media, the dye forms J-aggregates displaying a new red-shifted absorption (~425 nm) as well as emission (~510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited state photophysical properties of the dye is exploited to vapor sensing in solid state.
关键词： vapor sensing,Organic fluorophores,donor-acceptor electronic energy pair,diacetylene bridged,naphthalene-pyrene,locally excited emission,J-aggregates,electronic energy transfer,π-conjugation,fluorescence quantum yields
更新于2025-09-23 15:19:57
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High External Quantum Efficiency in Fluorescent OLED by Cascade Singlet Harvesting Mechanism
摘要： The cascade singlet harvesting (CSH) organic light-emitting diodes (OLEDs) are devised to resolve the low quantum efficiency issue of fluorescent OLEDs by efficient singlet exciton harvesting of the fluorescent emitters. The CSH mechanism is realized by doping a fluorescent emitter in the singlet exciton harvesting matrix consisted of high energy exciplex and low energy exciplex. The high energy exciplex serves as the main component of the emitting layer and the low energy exciplex is a medium harvesting the singlet excitons of the fluorescent emitter. Both exciplexes are thermally activated delayed fluorescence type exciplexes to effectively harvest singlet excitons by reverse intersystem crossing process. The singlet excitons of the low energy exciplex are harvested by the high energy exciplex through F?rster energy transfer and then the singlet excitons of the fluorescent emitter are harvested by the low energy exciplex through the second F?rster energy transfer process. The CSH mechanism maximizes the singlet exciton formation in the fluorescent emitter, which significantly enhances the external quantum efficiency (EQE) of the fluorescent OLEDs. The optimization of the emitting layer structure provides high EQE of 19.9% in the fluorescent OLEDs compared with 10.4% of a conventional singlet harvesting fluorescent OLED.
关键词： energy transfer,external quantum efficiency,fluorescent OLEDs,thermally activated delayed fluorescence,cascade singlet harvesting,exciplex
更新于2025-09-23 15:19:57
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Measurement and Theoretical Interpretation of Exciton Diffusion as a Function of Intermolecular Separation for Squaraines Targeted for Bulk Heterojunction Solar Cells
摘要： The efficiency of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices depends significantly upon absorption of photons and the migration of the photogenerated excited state to the heterojunction interface between the electron donor and electron acceptor. Within anilino-squaraine, molecules known for their successful use in the active layer of OPV devices, electronic aggregation strongly influences the absorption spectrum, energy transfer (EnT), and exciton migration to this heterojunction interface. Therefore, the long-range transition dipole coupling and the relative populations of the associated excited states dictate the general effectiveness of these materials in optoelectronic devices. This work presents subpicosecond transient absorption (TA) data that probe the excited-state photophysics of samples with a continuum of intermolecular separation, from monomers in solution to high-concentration solid solution thin films analogous to OPV active layers. EnT times are calculated for each squaraine concentration, and pump-power dependence provides evidence for significant EnT despite a high preponderance of H-aggregation. Theoretical modeling of essential states supports the interpretation from TA spectra that excited states relax into more tightly packed H-aggregates. This work prompts further questions regarding a far-reaching mechanistic EnT bottleneck for molecular and polymeric BHJ devices.
关键词： H-aggregation,squaraine,organic photovoltaic,bulk heterojunction,exciton diffusion,energy transfer
更新于2025-09-23 15:19:57
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Highly efficient Mn doped CsPb(Cl/Br)3 quantum dots for white light-emitting diodes
摘要： White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted great attention, which rely on mixing several colors of perovskites. However, this inevitably leads to a non-uniform light distribution and serious light loss. Here, a novel strategy was demonstrated to obtain white emission by combining the orange and blue emission from CsPb/Mn(Cl/Br)3 QDs. Notably, highly efficient white emission with photoluminescence quantum yield (PLQY) of 94% was achieved by an anion exchange surface engineering (AESE) strategy. After the AESE treatment, the surface traps can be eliminated, resulting in improved exciton and Mn2+ emission. A prototype WLED device is fabricated, which exhibits excellent optical stability, demonstrating great potential for the perovskite QDs in the field of optoelectronics.
关键词： quantum dots,perovskite,WLEDs,Mn doping,energy transfer
更新于2025-09-23 15:19:57
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Effect of fast electrons on the gain of a direct-drive laser fusion target
摘要： The results of numerical and theoretical studies of the gain of a direct-drive inertial con?nement fusion target, which includes a kinetic description of energy transfer by laser-accelerated fast electrons, are presented. The range of the initial temperature of the fast electrons and the fraction of laser energy contained in these particles were chosen based on the results of recent experiments at the National Ignition Facility. The effect of ‘wandering’ of fast electrons is taken into account which is due to the remoteness of the region of fast electron generation from the ablation surface of the imploded target. As a result a signi?cant fraction of particles do not fall into the compressed part of target. The ‘wandering’ effect leads to a decrease in the negative effect of fast electron generation on the gain of the target.
关键词： implosion,energy transfer,fast electrons,direct-drive targets,inertial con?nement fusion
更新于2025-09-23 15:19:57
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High-power operation of double-pass pumped Nd:YVO <sub/>4</sub> thin disk laser
摘要： A simple, compact, double-pass pumped Nd:YVO4 thin disk laser is demonstrated. Its continuous-wave performance with different Nd doping concentrations and thicknesses is investigated experimentally. The maximum output power of 17.7 W is achieved by employing a 0.5 at.% doped sample, corresponding to an optical-to-optical ef?ciency of 46% with respect to the absorbed pump power. In addition, a numerical analysis and an experimental study of the temperature distribution, and thermal lens effect of the Nd:YVO4 thin disk, are presented considering the in?uence of the energy transfer upconversion effect and the temperature dependence of the thermal conductivity tensor. The simulated results are in good agreement with the experimental results.
关键词： energy transfer upconversion effect,Nd:YVO4,thin disk laser,thermal lens effect
更新于2025-09-23 15:19:57
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Microwave assisted synthesis of boron and nitrogen rich graphitic quantum dots to enhance fluorescence of photosynthetic pigments
摘要： Energy transfer between quantum dots and biomolecules is of interest due to high absorption capacity and high quantum efficiency of quantum dots. Amongst all types of quantum dots, graphene and graphitic quantum dots have great potential for energy transfer studies due to their high biocompatibility and low toxicity. In this study, a simple route to synthesize boron and nitrogen rich graphitic quantum dots (C-BN) and boron carbon nitride (BCN) quantum dots is demonstrated. Quantum dots were synthesized in a domestic microwave oven. Composition of quantum dots was controlled by tuning initial mole ratio of boron and nitrogen precursors. As molar ratio of boron precursor was increased, formation of C-BN quantum dots was favoured. C-BN quantum dots were mainly composed of boron and nitrogen (with around 10 % carbon) in their main composition, and sized around 2 nm with bright photoluminescence. To the best of our knowledge, this is the first study which proposes a bottom-up synthesis method to synthesize C-BN quantum dots based on domestic microwaves. Also, treating photosynthetic pigments with quantum dots resulted in 20 % enhancement of fluorescence of photosynthetic pigments at 670 nm, which demonstrates that C-BN and BCN quantum dots can be important constituents of artificial antenna systems for photosynthetic organisms.
关键词： Photosynthetic pigments,Boron nitride,Energy transfer,Graphitic quantum dots
更新于2025-09-23 15:19:57
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Deepa??Blue Thiophenea??Based Steric Oligomers as a Lowa??Threshold Laser Gain and Host Material
摘要： Thiophene-based (Th-based) derivatives have received wide attentions in organic optoelectronics due to their excellent and tuneable optoelectrical properties as well as chemical modification. However, the low photoluminescence quantum yield in solid state limits their application in solution-processed light-emitting optoelectronic devices, especially in organic lasers. Herein, a novel blue-emitting steric Th-based fluorophore (MC8-Th) with excellent optical gain behavior for organic laser is reported. Interestingly, MC8-Th neat film exhibits efficient exceptional deep-blue amplified spontaneous emission (ASE) behavior with a remarkably low threshold of 6.0 μJ cm?2 and full-width-at-half-maximum value of 2.6 nm. Furthermore, random laser signals are also obtained with the lowest threshold of 4.1 μJ cm?2 when incorporating the compound into an inert polystyrene (PS) matrix. In addition, low threshold (16 μJ cm?2, fivefold lower than those of F8BT neat films) yellow–green ASE emission (560 nm) is achieved through F?rster resonance energy transfer. Meanwhile, ultrafast transient absorption spectroscopy is deployed here to observe the single-molecular excitonic behavior in solution and PS-blend, intermolecular excited state in neat film, and efficient energy transfer in MC8-Th:F8BT-blend films. As far as known, MC8-Th shows lower threshold ASE/lasing behavior for the Th-based conjugated materials.
关键词： transient absorption spectroscopy,optical gain behavior,organic laser,thiophene-based derivatives,F?rster resonance energy transfer
更新于2025-09-23 15:19:57