Hybrid Exciton Research Articles

Control over Energy Transfer between Fluorescent BODIPY Dyes in a Strongly Coupled Microcavity

Hybridization of two fluorescent BODIPY dyes in a microcavity is achieved by coupling different exciton transitions to the same cavity mode. We characterize the luminescence of such a hybrid system following nonresonant laser excitation and show that the relative population along the different polariton branches can be controlled by changing cavity detuning. This effect is used to enhance exciton energy transfer to states along the lower polariton branch in negatively detuned cavities. We compare the efficiency of energy transfer via exciton hybridization with that achieved by dipole–dipole coupling.

Luminescence Properties of ZnO Twin Nanorod–Ag Heteronanocrystals and Interfacial Exciton–Surface Plasmon Coupling

The epitaxial semiconductor–metal interface has unique optical properties. However, people know little about the coupling modes at the semiconductor–metal interface of heteronanocrystals both experimentally and theoretically. The coupling between the semiconductor excitons and the metal surface plasmons in the ZnO twin nanorod–Ag heteronanocrystals is studied. These heteronanocrystals are synthesized through photoreduction of silver ions on the ZnO twin‐nanorods. The interfacial epitaxial relation of the perfect heteronanocrystals is found to be (0001)ZnO//(111)Ag. The hybrid exciton energy splitting of 97 meV is observed from the absorption spectrum. The photoluminescence of the hybrid excitons shifts to red significantly relative to that of the uncoupled excitons. The theoretical model concerning the exciton–surface plasmon coupling is proposed to account for the experimental phenomena.

Energy Transfer in a Cylindrical Nanostructure Consisting of a Metal Wire and a Coaxial Covering with Luminophore Molecules

Light absorption and nonradiative exchange of electronic excitation energy between a metal nanowire with a circular cross section and luminophore molecules surrounding it were studied theoretically. The energy-transfer rate from a single excited molecule to the nanowire and the decay kinetics of the luminophore excited state were calculated for molecules that did not interact with each other. The energy-transfer rate from a coaxial monolayer formed by molecules joined into J-aggregate complexes to the nanowire was also calculated. It was shown that a hybrid exciton–plasmon state could be generated. The geometric characteristics of the examined systems were found to influence considerably the electronic excitation energy transformation rate.

Temperature-Dependent Plasmon–Exciton Interactions in Hybrid Au/MoSe2 Nanostructures

Combining localized surface plasmons and confined excitons in hybrid metallic/semiconductor nanostructures is a promising route toward the manipulation of the light–matter interaction at the nanoscale and the generation of novel technological applications. In this context, we investigate the interference between plasmonic and excitonic resonances in hybrid MoSe2@Au nanostructures consisting of monolayer MoSe2 supported by Au nanodisks. The optical properties of the nanostructures are probed by means of spatially resolved optical transmission and photoluminescence spectroscopies and interpreted using an analytical model complemented by numerical simulations. A plasmonic–excitonic interaction energy of 42 ± 8 meV is obtained, clearly setting the coupling in the Fano-type regime. On the basis of numerical simulations of the electromagnetic near-field and on calculations of the excitonic transition dipole momentum, we show that the interaction energy is concentrated in the gap region between the disks. The te...

Plasmon–Exciton Coupling at Individual Porphyrin-Covered Silver Clusters

The feasibility to couple surface plasmons with molecular excitations is an intriguing feature of plasmonic–organic hybrid systems. To date, investigations of plasmonic–excitonic coupling have largely focused on ensembles of nanoparticles and on purely optical methods. Here we present a single-particle approach based on laser-spectroscopic photoemission electron microscopy. Localized surface plasmons give rise to photoemission resonances in laser excitation spectra of individual silver nanoclusters. As a most striking manifestation of plasmon–exciton coupling, upon deposition of a thin zinc tetraphenylporphyrin (ZnTPP) film, a second resonance near the ZnTPP Soret band appears in our spectra. In accordance with simulations, spectral repulsion of both resonances as well as intensity redistribution between both modes indicates their plasmonic–excitonic hybrid character.

Enhancement of surface plasmon resonances on the nonlinear optical properties in a GaAs quantum dot

In this paper, the nonlinear optical properties of a metallic nanoparticle (MNP)-semiconductor quantum dot (SQD) hybrid nanosystem with the hybrid exciton effect have been studied. Considering the influence of quantum-size effect to the dielectric function of MNP, the quantum corrected dielectric function was applied to our calculation. By using the compact-density-matrix method, the interaction between MNP and SQD has been studied theoretically. The results show that the surface plasmon resonances (SPRs) of MNP enhance indeed the nonlinear optical properties of SQD. Further more, the enhancement depends on two factors: (a) the center-to-center 7distance between MNP and SQD; (b) the radius ratio between MNP and SQD.

Plasmon–Exciton Coupling between Metallic Nanoparticles and Dye Monomers

We investigate electromagnetic coupling between localized surface plasmons and excitons in a Ag nanoparticle (NP) and monomer dye conjugate. Strong coupling is observed as Rabi splitting in the optical scattering response of the conjugate. We measure the strength of coupling as a function of NP–dye separation distance using bifunctional molecules that link the dye and NP with nanoscale control. Coupling strength follows a single-exponential decay with a decay length of 13.7 ± 5 nm, indicating that the conjugates can be used as a plasmon ruler. In addition, we find that at separation distances below 2 nm the coupling strength is strongly decreased by quantum effects such as electron tunneling which interfere with plasmon–exciton hybridization. Using single NP spectroscopy to investigate conjugate coupling energy, we are able to tune separation distance to achieve coupling energies as high as 600 meV, among the highest energies reported for Ag NPs.

Ultrafast Charge Transfer and Hybrid Exciton Formation in 2D/0D Heterostructures.

Photoinduced interfacial charge transfer is at the heart of many applications, including photovoltaics, photocatalysis, and photodetection. With the emergence of a new class of semiconductors, i.e., monolayer two-dimensional transition metal dichalcogenides (2D-TMDs), charge transfer at the 2D/2D heterojunctions has attracted several efforts due to the remarkable optical and electrical properties of 2D-TMDs. Unfortunately, in 2D/2D heterojunctions, for a given combination of two materials, the relative energy band alignment and the charge-transfer efficiency are locked. Due to their large variety and broad size tunability, semiconductor quantum dots (0D-QDs) interfaced with 2D-TMDs may become an attractive heterostructure for optoelectronic applications. Here, we incorporate femtosecond pump-probe spectroscopy to reveal the sub-45 fs charge transfer at a 2D/0D heterostructure composed of tungsten disulfide monolayers (2D-WS2) and a single layer of cadmium selenide/zinc sulfide core/shell 0D-QDs. Furthermore, ultrafast dynamics and steady-state measurements suggested that, following electron transfer from the 2D to the 0D, hybrid excitons, wherein the electron resides in the 0D and the hole resides in the 2D-TMD monolayer, are formed with a binding energy on the order of ∼140 meV, which is several times lower than that of tightly bound excitons in 2D-TMDs.

Transport properties of a single plasmon interacting with a hybrid exciton of a metal nanoparticle–semiconductor quantum dot system coupled to a plasmonic waveguide

The transport properties of a single plasmon interacting with a hybrid system composed of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP) coupled to a one-dimensional surface plasmonic waveguide are investigated theoretically via the real-space approach. We considered that the MNP–SQD interaction leads to the formation of a hybrid exciton and the transmission and reflection of a single incident plasmon could be controlled by adjusting the frequency of the classical control field applied to the MNP–SQD hybrid nanosystem, the kinds of MNPs and the background media. The transport properties of a single plasmon interacting with such a hybrid nanosystem discussed here could find applications in the design of next-generation quantum devices, such as single-photon switching and nanomirrors, and in quantum information processing.

Electrical and optoelectronic properties of [6,6]-phenyl C61-butyric acid methyl ester: Black phosphorus/p-type Si devices

The [6,6]-phenyl C61-butyric acid methyl ester (PCBM):black phosphorus (BP)/p-type Si devices are fabricated and the electrical and optoelectronic properties of PCBM:BP devices are determined. Correlation effects are evaluated using the well-known expressions for the thermionic emission. Rectification behavior is affected by the bulk effects of the PCBM layer. The dark forward-bias current is proportional to BP content. The incorporation of BP into PCBM leads to an increase in the absorptivity of the PCBM layer, the occurrence of the hybrid excitons at the PCBM/BP interface, efficient hole transport and modification of the interface of PCBM/p-type Si, which results in an improvement in the electrical and optoelectronic performance of PCBM/p-type Si devices.

Optical characterization of ZnSe/CdSe nanocrystals with π-conjugated organic ligands

Organic–inorganic hybrid systems having the excitation resonance state are predicted to exhibit unique optical properties owing to a new type of excitons, i.e., hybrid excitons. The formation of the hybrid excitons requires the resonance between the excited states in organic and inorganic parts and the strong interactions with each other. In this study, we synthesized an organic–inorganic hybrid system (ZnSe/CdSe–2-aminoanthracene (AAn)) in order to realize the excitation resonance state. For the ZnSe/CdSe–AAn system in which PL wavelengths of the organic and inorganic parts are almost the same, the PL peak shifts by ∼20 nm toward longer wavelength and the decay time constant decrease with the addition of AAn. These changes in the hybrid cannot be explained simply in terms of self-absorption or excitation energy transfer. These results strongly suggest that a new excited states or new decay route was formed by the resonance of the excited states.

External pumping of hybrid nanostructures in microcavity with Frenkel and Wannier–Мott excitons

Abstract The exciton–exciton interaction in hybrid nanostructures with resonating Frenkel and Wannier–Mott excitons was investigated in many publications. In microcavity the hybrid nanostructures can be exposed to different types of optical pumping, the most common one being pumping through one of the microcavity side. However, not investigated and thus never been discussed the hybrid excitons generation by pumping of confined quantum wells from the side of empty microcavity without nanostructures in a wave guided configuration. Here, we consider the hybrid excitations in cavity with organic and inorganic quantum wells and with different types of pumping from external source. The frequency dependence for intensity of excitations in hybrid structure is also investigated. The results may be used for search of most effective fluorescence and relaxation processes. The same approach may be used when both quantum wells are organic or inorganic.

Coherent Controllable Transport of a Surface Plasmon Coupled to a Plasmonic Waveguide with a Metal Nanoparticle-Semiconductor Quantum Dot Hybrid System

By using the real-space method, the switching of a single plasmon interacting with a hybrid nanosystem composed of a semiconductor quantum dot (SQD) and a metallic nanoparticle (MNP) coupled to a 1D surface plasmonic waveguide is investigated theoretically. We discussed that the dipole coupling between an exciton and a localized surface plasmon results in the formation of a hybrid exciton and the transmission and reflection of the propagating single plasmon could be controlled by changing the interparticle distance between the SQD and the MNP and the size of the nanoparticles. The controllable transport of the propagating single surface plasmon by such a nanosystem discussed here could find significant potential in the design of next-generation quantum devices such as plasmonic switches, single photon transistors, and nanolasers, and quantum information.

Coulomb Mediated Hybridization of Excitons in Coupled Quantum Dots.

We report Coulomb mediated hybridization of excitonic states in optically active InGaAs quantum dot molecules. By probing the optical response of an individual quantum dot molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single-particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole single-particle orbitals. Comparisons of experimental observations with microscopic eight-band k·p calculations taking into account a realistic quantum dot geometry show good agreement and reveal that the Coulomb resonances arise from broken symmetry in the artificial semiconductor molecule.

Calculation of photo-nuclear reaction cross sections for16O

Because of the high thermal expansion coefficient of uranium, the fuel used in nuclear power plants is usually in the form of UO2 which has ceramic structure and small thermal expansion coefficient. UO2 include one uranium atom and two oxygen atoms. After fission progress, total energy values of emitted gamma are about 14 MeV. This gamma energy may cause transmutation of 16 O isotopes. Transmutation of 16 O isotopes changes physical properties of nuclear fuel. Due to above explanations, it is very important to calculate photo-nuclear reaction cross sections of 16 O. In this study; for (γ,p), (γ,np), (γ,n) and (γ,2n) reactions of 16 O, photo-nuclear reaction cross-sections were calculated using different models for pre-equilibrium and equilibrium effects. Taking incident gamma energy values up to 40 MeV, Hybrid and Cascade Exciton Models were used for pre-equilibrium calculations and Weisskopf-Ewing (Equilibrium) Model was used for equilibrium model calculations. Calculation results were compared with experimental and theoretical data. While experimental results were obtained from EXFOR, TENDL-2013, JENDL/PD-2004 and ENDF/B VII.1 data base were used to get theoretical results.

Optical properties of excitons in metal-insulator-semiconductor nanowires

The theoretical model for the metal-insulator-semiconductor nanowires is established and the optical properties are investigated. The linear absorption of the hybrid excitons, formed due to the exciton-plasmon interaction, shows obvious red shift on the magnitude of several meVs. The mechanism of the red shift is found to be the joint action of the increased excitonic binding energy attributed to the indirect Coulomb interaction and the decreased effective bandgap caused by the additional self-energy potential. The conclusion is also supported by the evolution of the absorption spectra with the adjustable structural parameters.

Evidence of Hybrid Excitons in Weakly Interacting Nanopeapods

Nanopeapods, consisting of optically active π-conjugated molecules encapsulated inside of the cavity of carbon nanotubes, exhibit efficient photon emission in the visible spectral range. Combining optical experiments with ab initio theory, we show that the puzzling features observed in photoluminescence spectra are of excitonic nature. The subunits though being van der Waals bound are demonstrated to interact in the excited state, giving rise to the formation of hybrid excitons. We rationalize why this many-body effect makes such nanohybrids useful for optoelectronic devices.

Equilibrium and pre-equilibrium calculations of cross-sections of (p, xn) reactions on 89 Y, 90 Zr and 94 Mo targets used for the production of 89 Zr, 90 Nb and 94 Tc positron-emitting radionuclides

In this study, the pre-equilibrium and equilibrium calculations of cross-sections of 89Y(p, xn), 90Zr(p, xn) and 94Mo(p, xn) reactions, which were used for the production of 89Zr, 90Nb and 94Tc positron-emitting radioisotopes, have been investigated. Pre-equilibrium calculations have been performed at different proton incident energies by using the hybrid, geometry-dependent-hybrid and full exciton models. The Weisskopf–Ewing model is used for calculating the equilibrium effects at the same incident energies. The calculated results have been discussed and compared with the experimental results.

Long-Range, Photon-Mediated Exciton Hybridization in an All-Organic, One-Dimensional Photonic Crystal

We demonstrate an all-organic, one-dimensional photonic crystal tuned to the regime of strong exciton-photon coupling. The structure consists of a high index of refraction light-absorbing active layer periodically distributed in a low index of refraction nonabsorbing background medium. The strongly coupled state in this structure is shared between multiple active layers separated by distances longer than the wavelength of light in the structure. In order to investigate the potential for long-range energy transfer, photon-mediated exciton hybridization is demonstrated between multiple absorbing species spatially separated in the photonic crystal.

Nonradiative resonance energy transfer directed from colloidal CdSe/ZnS quantum dots to epitaxial InGaN/GaN quantum wells for solar cells

AbstractWe report on Förster‐type nonradiative resonance energy transfer (NRET) directed from colloidal quantum dots (QDs) to epitaxial quantum wells (QWs) with an efficiency of 69.6% at a rate of 1.527 ns–1 for potential application in III‐nitride based photovoltaics. This hybrid exciton generation–collection system consists of chemically‐synthesized cyan CdSe/ZnS core/shell QDs (λPL = 490 nm) intimately integrated on epitaxially‐grown green InGaN/GaN QWs (λPL = 512 nm). To demonstrate directional NRET from donor QDs to acceptor QWs, we simultaneously show the decreased photoluminescence decay lifetime of dots and increased lifetime of wells in the hybrid dipole–dipole coupled system. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)