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Temperature-dependent photo-response in multiferroic BiFeO 3 revealed by transmission measurements
摘要： We studied the light-induced effects in BiFeO3 single crystals as a function of temperature by means of optical spectroscopy. Here, we report the observation of several light-induced absorption features, which are discussed in terms of the photostriction effect and are interpreted in terms of excitons. The temperature dependence of their energy position suggests a possible coupling between the excitons and the lattice vibrations. Moreover, there are hints for anomalies in the temperature evolution of the excitonic features, which might be related to the temperature-induced magnetic phase transitions in BiFeO3. Our findings suggest a coupling between light-induced excitons and the lattice and spin degrees of freedom, which might be relevant for the observed ultrafast photostriction effect in multiferroic BiFeO3.
关键词： multiferroic,excitons,optical spectroscopy,BiFeO3,photostriction
更新于2025-11-25 10:30:42
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Lead Halide Post-Perovskite-Type Chains for High-Efficiency White-Light Emission
摘要： Hybrid metal halides containing perovskite layers have recently shown great potential for applications in solar cells and light-emitting diodes. Such compounds exhibit quantum confinement effects leading to tunable optical and electronic properties. Thus, broadband white-light emission has been observed from diverse metal halides and, owing to high color rendering index, high thermal stability, and low-temperature solution processability, these materials have attracted interest for application in solid-state lighting. However, the reported quantum yields for white photoluminescence (PLQY) remain low (i.e., in the range 0.5–9%) and no approach has shown to successfully increase the intensity of this emission. Here, it is demonstrated that the quantum efficiencies of hybrid metal halides can be greatly enhanced if they contain a polymorph of the [PbX4]2? perovskite-type layers: the [PbX4]2? post-perovskite-type chains showing a PLQY of 45%. Different piperazines lead to a hybrid lead halide with either perovskite layers or post-perovskite chains influencing strongly the presence of self-trapped states for excitons. It is anticipated that this family of hybrid lead halide materials could enhance all the properties requiring the stabilization of trapped excitons.
关键词： trapped excitons,solid-state lighting,post-perovskite,photoluminescence
更新于2025-11-14 15:16:37
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Efficient optical gain in CdSe/CdS Dot-in-Rod nanocrystals
摘要： Excitonic state-resolved pump/probe spectroscopy is performed on semiconductor dot-in-rod nanocrystals. Using excitonic state-resolved pumping we are able to resolve effects of the rod upon exciton dynamics of the core. The shell has the effect of lowering gain threshold, increasing absorption cross-section, and increasing the Auger lifetime, hence nanorods are shown to be an effective means of enhancing gain performance of nanomaterials.
关键词： nanocrystal,excitons,Auger processes,Quantum dot,optical gain,multiexcitons.
更新于2025-09-23 15:23:52
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Resonance Coupling in Heterostructures Composed of Silicon Nanosphere and Monolayer WS <sub/>2</sub> : A Magnetic-Dipole-Mediated Energy Transfer Process
摘要： Light?matter resonance coupling is a long-studied topic for both fundamental research and photonic and optoelectronic applications. Here we investigated the resonance coupling between the magnetic dipole mode of a dielectric nanosphere and 2D excitons in a monolayer semiconductor. By coating an individual silicon nanosphere with a monolayer of WS2, we theoretically demonstrated that, because of the strong energy transfer between the magnetic dipole mode of the nanosphere and the A-exciton in WS2, resonance coupling evidenced by anticrossing behavior in the scattering energy diagram was observed, with a mode splitting of 43 meV. In contrast to plexcitons, which involve plasmonic nanocavities, the resonance coupling in this all-dielectric heterostructure was insensitive to the spacing between the silicon nanosphere core and the WS2 shell. Additionally, the two split modes exhibited distinct light-scattering directionality. We further experimentally demonstrated the resonance coupling effect by depositing silicon nanospheres with different diameters onto a WS2 monolayer and collecting the scattering spectra of the resulting heterostructures under ambient conditions. We further demonstrated active control of the resonance coupling by temperature scanning. Our findings highlighted the potential of our all-dielectric heterostructure as a solid platform for studying strong light?matter interactions at the nanoscale.
关键词： magnetic dipole modes,two-dimensional materials,resonance coupling,two-dimension excitons,silicon nanospheres
更新于2025-09-23 15:23:52
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Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites
摘要： Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (?50 cm?1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.
关键词： resonant impulsive stimulated Raman spectroscopy,polaronic character,two-dimensional perovskites,density functional theory,excitons,phonon coherences
更新于2025-09-23 15:23:52
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Monolayer transition metal dichalcogenides in strong magnetic fields: Validating the Wannier model using a microscopic calculation
摘要： Using an equation of motion (EOM) approach, we calculate excitonic properties of monolayer transition metal dichalcogenides perturbed by an external magnetic field. We compare our findings to the widely used Wannier model for excitons in two-dimensional materials and to recent experimental results. We find good agreement between the calculated excitonic transition energies and the experimental results. In addition, we find that the exciton energies calculated using the EOM approach are slightly lower than the ones calculated using the Wannier model. Finally, we also show that the effect of the dielectric environment on the magnetoexciton transition energy is minimal due to counteracting changes in the exciton energy and the exchange self-energy correction.
关键词： monolayer transition metal dichalcogenides,magnetic field,Wannier model,excitons,magnetoexcitons,equation of motion
更新于2025-09-23 15:23:52
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Effects of Spatial Dispersion in Symmetric and Asymmetric Semiconductor Quantum Wells
摘要： Effects of spatial dispersion in quantum wells are discovered and investigated in detail in reflection experiments. We studied oblique incidence of pure s and p polarized light which has been reflected elliptically polarized. The polarization degree of the reflected light is governed by the in-plane photon momentum which is the distinctive feature of the spatial dispersion effects. The effects of spatial dispersion are allowed by symmetry in inversion-asymmetric systems only. Therefore we investigated bulk-inversion asymmetric ZnSe/ZnMgSSe and structure-asymmetric GaAs/AlGaAs and CdZnTe/CdTe/CdMgTe quantum wells. We studied the reflected light polarization state in the vicinity of the heavy- and light-exciton resonances where the spatial dispersion effects are resonantly enhanced.
关键词： semiconductor quantum wells,light polarization conversion,excitons,spatial dispersion
更新于2025-09-23 15:22:29
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Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2
摘要： Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS2, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.
关键词： photoluminescence,monolayer semiconductor,phonons,energy gain,room temperature,WS2,excitons,trions,upconversion
更新于2025-09-23 15:22:29
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Probing exciton species in atomically thin WS<sub>2</sub>–graphene heterostructures
摘要： We report on a detailed study of temperature-dependent photoluminescence spectroscopy of monolayer WS2 grown on epitaxial graphene. The study reveals for the first time the intrinsic excitonic effects of WS2 supported on one- and two-layer graphene from room temperature to 83K, with both excitons and trions evidenced in the entire temperature range and temperature-independent trion dissociation. All emission peaks exhibit a shift towards higher energy with decreasing temperature due to band gap renormalisation induced by electron-phonon interaction. A highly linear dependence of the photoluminescence with the excitation power is found for both WS2 on one- and two-layer graphene, confirming the excitonic nature of associated transitions and the high crystal quality of the WS2-graphene heterostructure.
关键词： trions,2D heterostructures,excitons
更新于2025-09-23 15:22:29
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Direct observation of cross-polarized excitons in aligned single-chirality single-wall carbon nanotubes
摘要： Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been studied extensively, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, by using a macroscopic film of highly aligned single-chirality (6,5) SWCNTs, we performed a systematic polarization-dependent optical absorption spectroscopy study. In addition to the commonly observed angular-momentum-conserving interband absorption of parallel-polarized light, which generates E11 and E22 excitons, we observed a small but unambiguous absorption peak whose intensity is maximum for perpendicular-polarized light. We attribute this feature to the lowest-energy cross-polarized interband absorption processes that change the angular momentum along the nanotube axis by ±1, generating E12 and E21 excitons. Unlike previous observations of cross-polarized excitons in polarization-dependent photoluminescence and circular dichroism spectroscopy experiments, our direct observation using absorption spectroscopy allowed us to quantitatively analyze this resonance. Specifically, we determined the energy and oscillator strength of this resonance to be 1.54 and 0.05, respectively, compared with the values for the E11 exciton peak. These values, in combination with a comparison with theoretical calculations, in turn led to an assessment of the environmental effect on the strength of Coulomb interactions in this aligned single-chirality SWCNT film.
关键词： polarization-dependent,single-wall carbon nanotubes,cross-polarized excitons,aligned film,optical absorption spectroscopy,Coulomb interactions
更新于2025-09-23 15:22:29