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Polariton-enhanced exciton transport
摘要： The transport distance of excitons in exciton-polariton systems has previously been assumed to be very small ((cid:2)1 μm). The sharp spatial pro?les observed when generating polaritons by nonresonant optical excitation show that this assumption is generally true. In this paper, however, we show that the transport distances of excitons in two-dimensional planar cavity structures with even a slightly polaritonic character are much longer than expected (≈20 μm). Although this population of slightly polaritonic excitons is normally small compared to the total population of excitons, they can substantially outnumber the population of the polaritons at lower energies, leading to important implications for the tailoring of potential landscapes and the measurement of interactions between polaritons.
关键词： interactions,exciton-polariton,transport distance,potential landscapes,nonresonant optical excitation
更新于2025-09-04 15:30:14
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monolayers on the hBN-layer thickness
摘要： The optical properties of two-dimensional transition-metal dichalcogenide monolayers, such as MoS2 or WSe2 are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due to the presence of hexagonal-boron nitride (hBN) surrounding layers have been investigated by solving the Bethe-Salpeter equation on top of GW wave functions in density functional theory calculations. We have calculated the dependence of both the quasiparticle gap and the binding energy of the neutral exciton ground-state Eb as a function of the hBN-layer thickness. This paper demonstrates that the effects of screening at this level of theory are more short ranged than is widely believed. The encapsulation of a WSe2 monolayer by three sheets of hBN (～1 nm) already yields a 20% decrease in Eb, whereas the maximal reduction is 27% for thick hBN. We have performed similar calculations in the case of a WSe2 monolayer deposited on stacked hBN layers. These results are compared to the recently proposed quantum electrostatic heterostructure approach.
关键词： GW wave functions,density functional theory,hexagonal-boron nitride,two-dimensional transition-metal dichalcogenide,Bethe-Salpeter equation,exciton
更新于2025-09-04 15:30:14
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Theoretical Study of Auger Recombination of Excitons in Monolayer Transition-metal Dichalcogenides
摘要： Excitons are the most prominent features of the optical properties of monolayer transition-metal dichalcogenides(TMDC). In view of optoelectronics it is very important to understand the decay mechanisms of the excitons of these materials. Auger recombination of excitons are regarded as one of the dominant decay processes. In this paper the Auger constant of recombination is computed based on the approach proposed by Kavoulakis and Baym. We obtain both temperature dependent (from type A, A’ processes) and temperature independent (from type B, B’ processes) contributions, and a numerical estimate of theoretical result yields the value of constant in the order of 10?2 cm2s?1, being consistent with existing experimental data. This implies that Auger decay processes severely limit the photoluminescence yield of TMDC-based optoelectronic devices.
关键词： Auger recombination,Transition-metal dichalcogenides,Exciton
更新于2025-09-04 15:30:14
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Chiroptical Protocol for the Absolute Configurational Assignment of Alkyl-Substituted Epoxides Using Bis(zinc porphyrin) as a CD-Sensitive Bidentate Host
摘要： The absolute configurations of simple alkyl-substituted chiral epoxides not bearing other ligating groups are readily determined via the exciton-coupled circular dichroism (ECCD) protocol using a bidentate bis(zinc porphyrin) host system BP1 as a CD-sensitive chirality probe. In this situation, chiral epoxides can successfully be incorporated into the cleft of the V-shaped host BP1 by double coordination of both oxygen lone pairs of the guest to the two central zinc ions of the host. We also propose a working model based on an MM2 optimized structure of the substrates that enables nonempirical prediction of the chirality of the bound epoxide.
关键词： chirality probe,alkyl-substituted epoxides,bis(zinc porphyrin),absolute configurations,exciton-coupled circular dichroism
更新于2025-09-04 15:30:14
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Charge transfer across monolayer/bilayer MoS<sub>2</sub> lateral interface and its influence on exciton and trion characteristics
摘要： The charge transfer phenomenon is identified to be a major factor determining exciton and trion characteristics of atomically thin MoS2 layers in various stacking configurations. We report photoluminescence (PL) from CVD-grown layered MoS2 in the presence of a skewed or a deformed triangular-shaped monolayer/bilayer (1L/2L) lateral interface. Integrated PL mapping images over the 1L and 2L MoS2 regions revealed that the neutral exciton emission was significantly enhanced and exhibited an oscillatory behavior in its intensity in the 1L region near the 1L/2L boundary, whereas the negative trion emission remained unchanged. The interplays among the number of MoS2 layers, a substrate, and a geometric boundary structure of the 1L/2L lateral interface turned out to be important in charge transfer due to a modulation in work functions. As a result, PL intensity profiles showed rich features such as a stacking dependent decomposition of excitons and trions, a sharp spectroscopic contrast along the 1L/2L boundary, and a charge transfer relevant to the work function difference at the lateral interface. Our results demonstrate that understanding the MoS2 PL is useful in characterizing the electronic properties in two-dimensional layered nanostructures and sheds light on possible new device applications.
关键词： density functional theory,work function,charge transfer,MoS2,exciton
更新于2025-09-04 15:30:14
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Is Vibrational Coherence a Byproduct of Singlet Exciton Fission?
摘要： A phenomenological wavefunction-based model of vibrationally coherent absorption modulation is proposed and applied to reproduce the triplet-triplet absorption spectra of bis-triisopropylsilylethynyl (TIPS)-pentacene, with the objective of testing whether the singlet fission process in that system spontaneously generates coherent vibrational packets, as recently suggested for TIPS-tetracene. The model is parametrized by a complete set of Franck-Condon parameters obtained from methodologically consistent DFT calculations for all relevant normal modes in all relevant electronic states. The results strongly depend on inhomogeneous broadening of absorption bands, which is explicitly included. They very well agree with the recently published experimental coherence spectra of the pertinent system, validating our underlying principal assumption that the singlet fission process, which generates the observed triplet states, is neutral with respect to vibrational coherences. Experimental confirmation of this interpretational posit demonstrates that in the pentacene derivative, apparently in contrast to the case of its tetracene analogue, fission is not a source of vibrational coherence. Our finding suggests that although the singlet fission process may possibly in individual cases induce vibrational coherence, this feature is not a constitutive characteristic of the fission phenomenon.
关键词： DFT calculations,singlet exciton fission,Franck-Condon parameters,TIPS-pentacene,vibrational coherence
更新于2025-09-04 15:30:14