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Nonclassical Light Sources Based on Selectively Positioned Deterministic Microlens Structures and (111) In(Ga)As Quantum Dots
摘要： The results of investigations of the optical characteristics of nonclassical light sources based on selectively positioned microlens structures and single (111) In(Ga)As quantum dots grown on a (111) BGaAs substrate are presented. The single-photon nature of the radiation is confirmed by measuring and analyzing second-order correlation functions g(2)(τ); g(2)(0) = 0.07. The fine structure of the exciton states of (111) In(Ga)As quantum dots is investigated. It is shown that, in the energy range of 1.320–1.345 eV, the splitting of exciton states is comparable to the natural width of the exciton lines, which is of interest for developing photon-pair emitters based on them.
关键词： quantum dots,single-photon sources,fine structure of exciton states,photon-pair sources
更新于2025-09-16 10:30:52
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Efficiency enhancement of small molecule organic solar cells using hexapropyltruxene as an interface layer
摘要： The quenching of excitons in organic solar cells can play a significant role in limiting their power conversion efficiency (PCE). In this article, we investigate the effect of a thin layer of hexapropyltruxene inserted at the interface between the electron donor boron subphthalocyanine chloride (SubPc) and its underlying hole contact in planar heterojunction solar cells. We find that a 3.8 nm hexapropyltruxene interlayer between the molybdenum oxide (MoOx) hole contact and SubPc is sufficient to improve PCE in SubPc/C60 fullerene solar cells from 2.6 % to 3.0 %, a ～20 % performance improvement. While the absorption stays roughly the same, the comparison of external and internal quantum efficiencies reveals a significant increase in SubPc’s contribution to the current for light with wavelengths between 520 and 600 nm. Microstructure and surface morphology assessed with in-situ Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) and Atomic Force Microscopy (AFM), are evaluated alongside in-situ spectroscopic ellipsometry, and photoluminescence measurements. The microstructural investigations demonstrate changes to the surface and bulk of SubPc grown atop a hexapropyltruxene interlayer indicating that the latter acts as a template layer in a similar way as MoOx. However, the improvement in PCE is found to be mainly via reduced exciton quenching at the MoOx contact with the insertion of the hexapropyltruxene layer.
关键词： hexapropyltruxene,power conversion efficiency,exciton quenching,organic solar cells,SubPc/C60
更新于2025-09-16 10:30:52
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Nonlinear optics at excited states of exciton polaritons in two-dimensional atomic crystals
摘要： Exciton polaritons (EP) are partial-light partial-matter quasiparticles in semiconductors demonstrating striking quantum phenomena such as Bose-Einstein condensation and single-photon nonlinearity. In these phenomena, the governing process is the EP relaxation into the ground states upon excitation, where various mechanisms are extensively investigated with thermodynamic limits. However, the relaxation process becomes drastically different and could significantly advance the understanding of EP dynamics for these quantum phenomena, when excited states of EP are involved. Here, for the first time, we observe nonlinear optical responses at the EP excited states in a monolayer tungsten disulphide (WS2) microcavity, including dark excited states and dynamically metastable upper polariton band. The nonlinear optics leads to unique emissions of ground states with prominent valley degree of freedom (DOF) via anomalous relaxation process, which is applicable to a wide range of semiconductors from monolayer transition metal dichalcogenides (TMDs) to emerging halide perovskites. This work promises possible approaches to challenging experiments such as valley polariton condensation. Moreover, it also constructs a valley-dependent solid state three-level system for terahertz photonics and stimulated Raman adiabatic passage.
关键词： excited states,exciton-polaritons,relaxation dynamics,Nonlinear optics,monolayer transition metal dichalcogenide
更新于2025-09-16 10:30:52
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Exciton polaritons based on planar dielectric Si asymmetric nanogratings coupled with J-aggregated dyes film
摘要： Optical cavity polaritons, originated from strong coupling between the excitons in materials and photons in the con?ned cavities ?eld, have recently emerged as their applications in the high-speed low-power polaritons devices, low-threshold lasing and so on. However, the traditional exciton polaritons based on metal plasmonic structures or Fabry-Perot cavities suffer from the disadvantages of large intrinsic losses or hard to integrate and nanofabricate. This greatly limits the applications of exciton poalritons. Thus, here we implement a compact low-loss dielectric photonic – organic nanostructure by placing a 2-nm-thick PVA doped with TDBC ?lm on top of a planar Si asymmetric nanogratings to reveal the exciton polaritons modes. We ?nd a distinct anti-crossing dispersion behavior appears with a 117.16 meV Rabi splitting when varying the period of Si nanogratings. Polaritons dispersion and mode anti-crossing behaviors are also observed when considering the independence of the height of Si, width of Si nanowire B, and distance between the two Si nanowires in one period. This work offers an opportunity to realize low-loss novel polaritons applications.
关键词： exciton polaritons,dielectric Si asymmetric,TDBC J-aggregated dyes ?lm,nanogratings
更新于2025-09-16 10:30:52
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Spectroscopic monitoring of the evolution of size and structural defects in kinetic growth of CdSe quantum dots
摘要： We report here on the exciton-phonon coupling and role of trap states formed at the interface of structural dislocations in CdSe quantum dots (QDs) synthesized by kinetic growth method. Even though non-luminescing, our studies recognize their signatures in the temperature dependent photoluminescence characteristics of lowest QD excitonic state and have some useful implications for structural quality of thus synthesized QDs. We have explained the observed temperature dependence of PL intensity in terms of a simple model taking account of different radiative and nonradiative recombination processes as well as carrier trapping/detrapping and determined the depth of potential well formed due to such long range defects. Our studies indicate the presence of such defect states only in QD samples size sorted by aliquoting at intermediate intervals during the reaction and do not appear when the reaction proceeds uninterrupted.
关键词： Temperature dependent photoluminescence,Exciton-phonon coupling,Thermal escape,CdSe Quantum Dots
更新于2025-09-16 10:30:52
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Manipulating Light–Matter Interactions in Plasmonic Nanoparticle Lattices
摘要： Rationally assembled nanostructures exhibit distinct physical and chemical properties beyond their individual units. Developments in nanofabrication techniques have enabled the patterning of a wide range of nanomaterial designs over macroscale (>in.2) areas. Periodic metal nanostructures show long-range diffractive interactions when the lattice spacing is close to the wavelength of the incident light. The collective coupling between metal nanoparticles in a lattice introduces sharp and intense plasmonic surface lattice resonances, in contrast to the broad localized resonances from single nanoparticles. Plasmonic nanoparticle lattices exhibit strongly enhanced optical fields within the subwavelength vicinity of the nanoparticle unit cells that are 2 orders of magnitude higher than that of individual units. These intense electromagnetic fields can manipulate nanoscale processes such as photocatalysis, optical spectroscopy, nonlinear optics, and light harvesting. This Account focuses on advances in exciton?plasmon coupling and light?matter interactions with plasmonic nanoparticle lattices. First, we introduce the fundamentals of ultrasharp surface lattice resonances; these resonances arise from the coupling of the localized surface plasmons of a nanoparticle to the diffraction mode from the lattice. Second, we discuss how integrating dye molecules with plasmonic nanoparticle lattices can result in an architecture for nanoscale lasing at room temperature. The lasing emission wavelength can be tuned in real time by adjusting the refractive index environment or varying the lattice spacing. Third, we describe how manipulating either the shape of the unit cell or the lattice geometry can control the lasing emission properties. Low-symmetry plasmonic nanoparticle lasing responses, and multiscale plasmonic superlattices—finite patches of lattices can show polarization-dependent nanoparticles grouped into microscale arrays—can support multiple plasmon resonances for controlled multimodal nanolasing. Fourth, we discuss how the assembly of photoactive emitters on the nanocavity arrays behaves as a hybrid materials system with enhanced exciton?plasmon coupling. Positioning metal?organic framework materials around nanoparticles produces mixed photon modes with strongly enhanced photoluminescence at wavelengths determined by the lattice. Deterministic coupling of quantum emitters in two-dimensional materials to plasmonic lattices leads to preserved single-photon emission and reduced decay lifetimes. Finally, we highlight emerging applications of nanoparticle lattices from compact, fully reconfigurable imaging devices to solid-state emitter structures. Plasmonic nanoparticle lattices are a versatile, scalable platform for tunable flat optics, nontrivial topological photonics, and modified chemical reactivities.
关键词： nanoscale lasing,surface lattice resonances,exciton?plasmon coupling,light?matter interactions,plasmonic nanoparticle lattices
更新于2025-09-16 10:30:52
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Temperature Dependence of Raman and Photoluminescence Spectra of Ternary Alloyed CdSe0.3Te0.7 Quantum Dots
摘要： The Raman and photoluminescence spectra of ternary alloyed CdSe0.3Te0.7 quantum dots (QDs) have been studied at temperatures between 84 K and 293 K. The average diameter of QDs is about 5.1 nm. The temperature dependence of the longitudinal optical (LO) phonon frequencies and the phonon band width was analyzed and the anharmonic constants relating to various high-order phonon processes was determined. While the three-phonon processes plays a dominant role in the temperature-dependent shift of the LO-phonon frequencies, the four-phonon processes contribute to the increase of the phonon linewidth with increasing temperature. The photoluminescence (PL) spectra were used to study the temperature dependence of the bandgap, the linewidth and the integrated PL intensity. At low temperatures below about 120 K, the PL linewidth decreases and the PL intensity increases as temperature increases. This temperature behavior can be ascribed to the exciton ?ne structure.
关键词： light-emitting diodes,anharmonicity,exciton ?ne structure,photoluminescence,Raman scattering,phonon
更新于2025-09-16 10:30:52
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Performance Enhancement of All-Inorganic Quantum Dot Light-Emitting Diodes via Surface Modification of Nickel Oxide Nanoparticles Hole Transport Layer
摘要： All-inorganic quantum dot light-emitting diodes (QLEDs) show promise for advanced lighting and display due to their superior advantage in stability. However, all-inorganic QLEDs suffer from the low efficiency because of the exciton quenching and inefficient hole transport from inorganic hole transport layer (HTL) to QDs. Herein, we demonstrate an efficient all-inorganic QLED with NiO nanoparticals (NPs) HTL modified by 11-mercaptoundecanoic acid (MUA). The MUA can passivate the defects of NiO and suppress the exciton quenching. Moreover, the declined valance band level of modified NiO could facilitate the hole transport, promoting the charge balance. In addition, the surface engineering improves the quality of NiO film, leading to the decrease of current leakage. As a result, the maximum current efficiency and external quantum efficiency (EQE) of our QLEDs achieve 5.50 cd/A and 1.28%, respectively, exhibiting the enhancement of 4.5 and 1.72 folds, respectively. Meanwhile, the stability of the device is drastically improved by more than 20 folds after modifying the NiO with MUA. The strategy offers a pathway to enhance the efficiency and the operation lifetime of all-inorganic QLEDs.
关键词： exciton quenching,nickel oxide nanoparticles,performance enhancement,surface modification,all-inorganic quantum dot light-emitting diodes
更新于2025-09-16 10:30:52
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revealed by time-resolved photoluminescence spectroscopy
摘要： We systematically investigate the recombination mechanism of photogenerated charge carriers in bulk CsPbBr3 by means of time-resolved photoluminescence (TR-PL) spectroscopy at low temperature and various laser excitation powers. A dynamic recombination model is proposed to describe the TR-PL that predicts the time-dependent exciton and free-charge populations. It provides a clear representation of competing mono- and bimolecular recombination processes. A decrease in carrier lifetime with increasing laser intensity was observed that was attributed to exciton-exciton scattering. A bimolecular recombination coef?cient of ～10?7 cm3/s was obtained for exciton recombination. As the concentration of photoexcited carriers increases, stronger exciton-exciton annihilation occurs. The exciton-exciton annihilation rate for CsPbBr3 is 3.63 × 10?7 cm3 s?1 at 10-mW laser power. Notably, the exciton-exciton annihilation rate in bulk material is comparable to that obtained for photoexcited CsPbBr3 nanoscale quantum dots.
关键词： carrier recombination,bimolecular recombination,exciton-exciton annihilation,time-resolved photoluminescence,CsPbBr3
更新于2025-09-12 10:27:22
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Ultrafast coherent exciton dynamics in size-controlled perylene bisimide aggregates
摘要： For H-aggregates of perylene bisimide (PBI), it has been reported that upon photoexcitation, an initially delocalized Frenkel exciton is localized by excimer formation. However, in recent studies, the beforehand exciton dynamics preceding the excimer formation was suggested in larger aggregates consisting of at least more than 10-PBI subunits, which was not observed in small aggregates comprising less than four-PBI subunits. This feature implies that the size of molecular aggregates plays a crucial role in the initial exciton dynamics. In this regard, we have tried to unveil the initial exciton dynamics in PBI H-aggregates by tracking down the transient reorientations of electronic transition dipoles formed by interactions between the PBI subunits in systematically size-controlled PBI H-aggregates. The ultrafast coherent exciton dynamics depending on the molecular aggregate sizes can be distinguished using polarization-dependent femtosecond-transient absorption anisotropy spectroscopic measurements with a time resolution of ~40 fs. The ultrafast decay profiles of the anisotropy values are unaffected by vibrational relaxation and rotational diffusion processes; hence, the coherent exciton dynamics of the PBI H-aggregates prior to the excimer formation can be directly revealed as the energy migration processes along the PBI H-aggregates.
关键词： exciton dynamics,femtosecond-transient absorption anisotropy,perylene bisimide,coherent exciton dynamics,H-aggregates
更新于2025-09-12 10:27:22