We theoretically analyze the steady state emission spectrum and transient temporal dynamics in a coupled biexciton quantum dot(QD)–cavity system. For steady state, a phonon-assisted biexciton–exciton cascade model...We theoretically analyze the steady state emission spectrum and transient temporal dynamics in a coupled biexciton quantum dot(QD)–cavity system. For steady state, a phonon-assisted biexciton–exciton cascade model under continuous wave(CW) excitation is presented to explain the asymmetric QD–cavity emission spectrum intensities(intensities of cavity,exciton, and biexciton emission peak) in off-resonance condition. Results demonstrate that the electron–phonon process is crucial to the asymmetry of emission spectrum intensity. Moreover the transient characteristics of the biexciton–exciton cascade system under pulse excitation show abundant nonlinear temporal dynamic behaviors, including complicated oscillations which are caused by the four-level structure of QD model. We also reveal that under off-resonance condition the cavity outputs are slightly reduced due to the electron–phonon interaction.展开更多
The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton an...The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton and biexciton as well as an interchain exciton and biexciton through a double-photon excitation.It is found that a biexciton is energetically favourable to two single excitons even when there exists an interchain coupling.There is a turnover value t⊥c of the interchain coupling for the formation of a biexciton,beyond which two excitons are combined into one biexciton.The binding energy of a biexciton is calculated to decrease with the increase of interchain coupling,which indicates that a biexciton is relatively stable in polymers with a weak interchain coupling.The conclusion is consistent with the experimental observations.In addition,a suggestion about how to improve the yielding efficiency or the formation of biexcitons in actual applications is given.展开更多
A double cascade-type four-level multiple-quantum-well-based exciton-biexciton transitions are proposed. The study is carried out on a 4.8-rim ZnSe single-quantum well which is embedded into ZnMgSSe cladding layers an...A double cascade-type four-level multiple-quantum-well-based exciton-biexciton transitions are proposed. The study is carried out on a 4.8-rim ZnSe single-quantum well which is embedded into ZnMgSSe cladding layers and pseudomor- phically grown by molecular beam epitaxy on a (0 0 1) GaAs substrate. It is displayed that the exciton spin relaxation and relative phases between applied fields can influence the transient and steady-state behaviors of absorption, dispersion, and group velocity of two weak probe and signal fields. Also, transient behaviors of electron population of different levels are discussed. It is found that the probe or signal amplification occurs in the absence of population inversion.展开更多
We report the observed photon bunching statistics of biexciton cascade emission at zero time delay in single quantum dots by second-order correlation function g(2) (T) measurements under continuous wave excitation...We report the observed photon bunching statistics of biexciton cascade emission at zero time delay in single quantum dots by second-order correlation function g(2) (T) measurements under continuous wave excitation. It is found that the bunching phenomenon is independent of the biexciton binding energy when it varies from 0.59 meV to nearly zero. The photon bunching takes place when the exeiton photon is not spectrally distinguishable from the biexciton photon, and either of them can trigger the %tart' in a Hanbury-Brown and Twiss setup. However, if the exciton energy is spectrally distinguishable from the biexciton, the photon statistics will become asymmetric and a cross-bunching lineshape can be obtained. The theoretical calculations based on a model of three-level rate-equation analysis are consistent with the result of g(2)(τ) correlation function measurements.展开更多
Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals.Among them,two-dimensional nanoplatelets provide new adjustment freedom for...Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals.Among them,two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructures.Herein,we demonstrate that by fine-tuning the core size and the lateral quantum confinement,the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets.In addition,the transfer can be affected by a carrier blocking mechanism,i.e.,the filled carriers hinder further possible transfer.Furthermore,we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization,resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength.This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing,display,sensing,etc.展开更多
Interface engineering in atomically thin transition metal dichalcogenides(TMDs)is becoming an important and powerful technique to alter their properties,enabling new optoelectronic applications and quantum devices.Int...Interface engineering in atomically thin transition metal dichalcogenides(TMDs)is becoming an important and powerful technique to alter their properties,enabling new optoelectronic applications and quantum devices.Interface engineering in a monolayer WSe_(2)sample via introduction of high-density edges of standing structured graphene nanosheets(GNs)is realized.A strong photoluminescence(PL)emission peak from intravalley and intervalley trions at about 750 nm is observed at the room temperature,which indicated the heavily p-type doping of the monolayer WSe_(2)/thin graphene nanosheet-embedded carbon(TGNEC)film heterostructure.We also successfully triggered the emission of biexcitons(excited state biexciton)in a monolayer WSe_(2),via the electron trapping centers of edge quantum wells of a TGNEC film.The PL emission of a monolayer WSe_(2)/GNEC film is quenched by capturing the photoexcited electrons to reduce the electron-hole recombination rate.This study can be an important benchmark for the extensive understanding of light–matter interaction in TMDs,and their dynamics.展开更多
Auger recombination has been a long?standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical un...Auger recombination has been a long?standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical underpinnings and scaling laws for Auger recombination is essential to these applications. Previous studies of biexciton Auger recombination in various QDs established a universal scaling of biexciton lifetime (rxx) with QD volume (V):τxx =γV. However, recent measurements on perovskite nanocrystals (NCs), an emerging class of enablers for light harvest!ng and emitting applications, showed significant deviations from this universal scaling law, likely because the measured NCs are weakly-confined and also have relatively broad size-distributions. Here we study biexciton Auger recombination in mono-dispersed (size distributions within 1.7%—9.0%), quantunvconfined CsPbBr3 NCs (with confinement energy up to 410 meV) synthesized using a latest approach based on thermodynamic equilibrium control. Our measurements clearly reproduce the volume-scaling of τxx in confined CsPbBb QDs. However, the scaling factor γ(0.085 ± 0.001 ps/nm^3) is one order of magnitude lower than that reported for CdSe and PbSe QDs (1.00 ± 0.05 ps/nm^3), suggest!ng unique mechanisms enhancing Auger recombination rate in perovskite NCs.展开更多
在对In As单量子点施加流体静压的实验中,使用了带有压电陶瓷的连续加压装置,在低温连续施加流体静压的情况下,可以调节量子点单激子能量兰移约320 me V。在对不同流体静压下单激子发光的二阶关联函数测量之后,证明流体静压并不影响单...在对In As单量子点施加流体静压的实验中,使用了带有压电陶瓷的连续加压装置,在低温连续施加流体静压的情况下,可以调节量子点单激子能量兰移约320 me V。在对不同流体静压下单激子发光的二阶关联函数测量之后,证明流体静压并不影响单激子发光的单光子特性。同时通过流体静压,可以实现量子点双激子态由反束缚态到束缚态的转变,并且给出了这一过程的偏振分辨光谱图。最后观察到单量子点精细结构劈裂随流体静压的增加而增加,而且精细结构劈裂的增加量可以达到约150μe V。展开更多
The transition from the biexciton to the exciton can turn over the direction of the electric dipole of a polymericmolecule. This turning-over action combined with the photoinduced polarization reversion can be used as...The transition from the biexciton to the exciton can turn over the direction of the electric dipole of a polymericmolecule. This turning-over action combined with the photoinduced polarization reversion can be used as a switch. Theswitching speed is governed by the relaxation time of the turning-over process, which can be determined by a dynamicalsimulation.展开更多
It has been known that the static polarizability of a polymer chain with a biexciton is negative. In order to understand this peculiar fact, this paper studies the dynamical process of the charge transfer in the polym...It has been known that the static polarizability of a polymer chain with a biexciton is negative. In order to understand this peculiar fact, this paper studies the dynamical process of the charge transfer in the polymer chain induced by an external electric field E during forming the biexciton. The time dependence of the charge distribution in the chain reveals that the charge transfer is backward: the positive charge shifts in the opposite direction of the external electric field. Such a backward charge transfer (BCT) produces an opposite dipole, which makes the polarization negative. The effect of electron interaction on the BCT is illustrated.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61275201 and 61372037)the Beijing Municipal Excellent Ph.D. Thesis Guidance Foundation(Grant No.20131001301)the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications),China
文摘We theoretically analyze the steady state emission spectrum and transient temporal dynamics in a coupled biexciton quantum dot(QD)–cavity system. For steady state, a phonon-assisted biexciton–exciton cascade model under continuous wave(CW) excitation is presented to explain the asymmetric QD–cavity emission spectrum intensities(intensities of cavity,exciton, and biexciton emission peak) in off-resonance condition. Results demonstrate that the electron–phonon process is crucial to the asymmetry of emission spectrum intensity. Moreover the transient characteristics of the biexciton–exciton cascade system under pulse excitation show abundant nonlinear temporal dynamic behaviors, including complicated oscillations which are caused by the four-level structure of QD model. We also reveal that under off-resonance condition the cavity outputs are slightly reduced due to the electron–phonon interaction.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10804062 and 10874100)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant Nos 200804221005 and 20070422058)China Postdoctoral Science Foundation funded project (Grant No 20080431171)
文摘The effect of interchain coupling on the formation and the stability of a biexciton is studied in poly (p-phenylene vinylene) chains in the framework of the tight-binding approach. We obtain an intrachain exciton and biexciton as well as an interchain exciton and biexciton through a double-photon excitation.It is found that a biexciton is energetically favourable to two single excitons even when there exists an interchain coupling.There is a turnover value t⊥c of the interchain coupling for the formation of a biexciton,beyond which two excitons are combined into one biexciton.The binding energy of a biexciton is calculated to decrease with the increase of interchain coupling,which indicates that a biexciton is relatively stable in polymers with a weak interchain coupling.The conclusion is consistent with the experimental observations.In addition,a suggestion about how to improve the yielding efficiency or the formation of biexcitons in actual applications is given.
文摘A double cascade-type four-level multiple-quantum-well-based exciton-biexciton transitions are proposed. The study is carried out on a 4.8-rim ZnSe single-quantum well which is embedded into ZnMgSSe cladding layers and pseudomor- phically grown by molecular beam epitaxy on a (0 0 1) GaAs substrate. It is displayed that the exciton spin relaxation and relative phases between applied fields can influence the transient and steady-state behaviors of absorption, dispersion, and group velocity of two weak probe and signal fields. Also, transient behaviors of electron population of different levels are discussed. It is found that the probe or signal amplification occurs in the absence of population inversion.
基金Supported by the National Key Basic Research Program of China under Grant No 2013CB922304the National Natural Science Foundation of China under Grant Nos 11474275 and 11464034
文摘We report the observed photon bunching statistics of biexciton cascade emission at zero time delay in single quantum dots by second-order correlation function g(2) (T) measurements under continuous wave excitation. It is found that the bunching phenomenon is independent of the biexciton binding energy when it varies from 0.59 meV to nearly zero. The photon bunching takes place when the exeiton photon is not spectrally distinguishable from the biexciton photon, and either of them can trigger the %tart' in a Hanbury-Brown and Twiss setup. However, if the exciton energy is spectrally distinguishable from the biexciton, the photon statistics will become asymmetric and a cross-bunching lineshape can be obtained. The theoretical calculations based on a model of three-level rate-equation analysis are consistent with the result of g(2)(τ) correlation function measurements.
基金This work was supported by the National Natural Science Foundation of China(No.61875002)the National Key R&D Program of China(No.2018YFA0306302)+4 种基金the Beijing Natural Science Foundation(No.Z190005)the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices(No.KF202208)The author acknowledges the support of the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB36000000)the National Natural Science Foundation of China(Nos.11874130 and 22073022)the support from the DNL Cooperation Fund,CAS(No.DNL202016)of Dalian National Laboratory for Clean Energy。
文摘Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals.Among them,two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructures.Herein,we demonstrate that by fine-tuning the core size and the lateral quantum confinement,the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets.In addition,the transfer can be affected by a carrier blocking mechanism,i.e.,the filled carriers hinder further possible transfer.Furthermore,we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization,resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength.This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing,display,sensing,etc.
基金The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China(Nos.62104155,52275565,52005343,and 62204117)of Chinathe Natural Science Foundation of Guangdong Province(No.2022A1515011667)+1 种基金the financial support from Jiangsu Province Science Foundation for Youths(No.BK20210275)Guangdong Kangyi Special Fund(No.2020KZDZX1173).
文摘Interface engineering in atomically thin transition metal dichalcogenides(TMDs)is becoming an important and powerful technique to alter their properties,enabling new optoelectronic applications and quantum devices.Interface engineering in a monolayer WSe_(2)sample via introduction of high-density edges of standing structured graphene nanosheets(GNs)is realized.A strong photoluminescence(PL)emission peak from intravalley and intervalley trions at about 750 nm is observed at the room temperature,which indicated the heavily p-type doping of the monolayer WSe_(2)/thin graphene nanosheet-embedded carbon(TGNEC)film heterostructure.We also successfully triggered the emission of biexcitons(excited state biexciton)in a monolayer WSe_(2),via the electron trapping centers of edge quantum wells of a TGNEC film.The PL emission of a monolayer WSe_(2)/GNEC film is quenched by capturing the photoexcited electrons to reduce the electron-hole recombination rate.This study can be an important benchmark for the extensive understanding of light–matter interaction in TMDs,and their dynamics.
基金We gratefully acknowledge financial supports from the MinistryScience and Technology of China (No. 2018YFA028703)the National Natural Science Foundation of China (No. 21773239).
文摘Auger recombination has been a long?standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical underpinnings and scaling laws for Auger recombination is essential to these applications. Previous studies of biexciton Auger recombination in various QDs established a universal scaling of biexciton lifetime (rxx) with QD volume (V):τxx =γV. However, recent measurements on perovskite nanocrystals (NCs), an emerging class of enablers for light harvest!ng and emitting applications, showed significant deviations from this universal scaling law, likely because the measured NCs are weakly-confined and also have relatively broad size-distributions. Here we study biexciton Auger recombination in mono-dispersed (size distributions within 1.7%—9.0%), quantunvconfined CsPbBr3 NCs (with confinement energy up to 410 meV) synthesized using a latest approach based on thermodynamic equilibrium control. Our measurements clearly reproduce the volume-scaling of τxx in confined CsPbBb QDs. However, the scaling factor γ(0.085 ± 0.001 ps/nm^3) is one order of magnitude lower than that reported for CdSe and PbSe QDs (1.00 ± 0.05 ps/nm^3), suggest!ng unique mechanisms enhancing Auger recombination rate in perovskite NCs.
文摘在对In As单量子点施加流体静压的实验中,使用了带有压电陶瓷的连续加压装置,在低温连续施加流体静压的情况下,可以调节量子点单激子能量兰移约320 me V。在对不同流体静压下单激子发光的二阶关联函数测量之后,证明流体静压并不影响单激子发光的单光子特性。同时通过流体静压,可以实现量子点双激子态由反束缚态到束缚态的转变,并且给出了这一过程的偏振分辨光谱图。最后观察到单量子点精细结构劈裂随流体静压的增加而增加,而且精细结构劈裂的增加量可以达到约150μe V。
基金This work was supported by the National Natural Science Foundation of China (Grants 19874014 and 20074007), Doctoral Fund for Universities and "863" Projects.
文摘The transition from the biexciton to the exciton can turn over the direction of the electric dipole of a polymericmolecule. This turning-over action combined with the photoinduced polarization reversion can be used as a switch. Theswitching speed is governed by the relaxation time of the turning-over process, which can be determined by a dynamicalsimulation.
文摘It has been known that the static polarizability of a polymer chain with a biexciton is negative. In order to understand this peculiar fact, this paper studies the dynamical process of the charge transfer in the polymer chain induced by an external electric field E during forming the biexciton. The time dependence of the charge distribution in the chain reveals that the charge transfer is backward: the positive charge shifts in the opposite direction of the external electric field. Such a backward charge transfer (BCT) produces an opposite dipole, which makes the polarization negative. The effect of electron interaction on the BCT is illustrated.