Evidence of Hybrid Excitons in Weakly Interacting Nanopeapods (original) (raw)
Related papers
Nature Materials, 2006
Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals details of their collective excited states, characterized by atoms or molecules working together to capture and redistribute excitation. What is special about excitons in nanometre-sized materials? Here we present a cross-disciplinary review of the essential characteristics of excitons in nanoscience. Topics covered include confinement effects, localization versus delocalization, exciton binding energy, exchange interactions and exciton fine structure, exciton-vibration coupling and dynamics of excitons. Important examples are presented in a commentary that overviews the present understanding of excitons in quantum dots, conjugated polymers, carbon nanotubes and photosynthetic light-harvesting antenna complexes.
Exciton−Plasmon Interaction and Hybrid Excitons in Semiconductor−Metal Nanoparticle Assemblies
Nano Letters, 2006
We describe the physical properties of excitons in hybrid complexes composed of semiconductor and metal nanoparticles. The interaction between individual nanoparticles is revealed as an enhancement or suppression of emission. Enhanced emission comes from electric field amplified by the plasmon resonance, whereas emission suppression is a result of energy transfer from semiconductor to metal nanoparticles. The emission intensity and energy transfer rate depend strongly on the geometrical parameters of the superstructure and the physical and material properties of the nanoparticles. In particular, the emission enhancement effect appears for nanoparticles with relatively small quantum yield, and silver nanoparticles have stronger enhancement compared to gold ones. Using realistic models, we review and analyze available experimental data on energy transfer between nanoparticles. In hybrid superstructures conjugated with polymer linkers, optical emission is sensitive to environmental parameters such as, for example, temperature. This sensitivity comes from expansion or contraction of a linker. With increasing temperature, emission of polymer-conjugated complexes can decrease or increase depending on the organization of a superstructure. The structures described here have potential as sensors and actuators.
Physical Review B, 2012
We provide a simple scheme for predicting the electronic structure of van der Waals bound systems, based on the mere knowledge of the electronic structure of the subunits. We demonstrate this with the example of nanopeapods, consisting of polythiophene encapsulated in single-wall carbon nanotubes. Using density functional theory we disentangle the contributions to the level alignment. The main contribution is shown to be given by the ionization potential of the polymer inside the host, which in turn is determined by the curvature of the tube. Only a small correction arises from charge redistributions within the domains of the constituents. Polarization effects turn out to be minor due to the cylindrical geometry of the peapods and their dielectric characteristics. Our findings open the possibility of designing optoelectronic properties of such complex materials.
Photonics meets excitonics: natural and artificial molecular aggregates
Nanophotonics, 2013
Organic molecules store the energy of absorbed light in the form of charge-neutral molecular excitations -Frenkel excitons. Usually, in amorphous organic materials, excitons are viewed as quasiparticles, localized on single molecules, which diffuse randomly through the structure. However, the picture of incoherent hopping is not applicable to some classes of molecular aggregatesassemblies of molecules that have strong near field interaction between electronic excitations in the individual subunits. Molecular aggregates can be found in nature, in photosynthetic complexes of plants and bacteria, and they can also be produced artificially in various forms including quasi-one dimensional chains, two-dimensional films, tubes, etc. In these structures light is absorbed collectively by many molecules and the following dynamics of molecular excitation possesses coherent properties. This energy transfer mechanism, mediated by the coherent exciton dynamics, resembles the propagation of electromagnetic waves through a structured medium on the nanometer scale. The absorbed energy can be transferred resonantly over distances of hundreds of nanometers before exciton relaxation occurs. Furthermore, the spatial and energetic landscape of molecular aggregates can enable the funneling of the exciton energy to a small number of molecules either within or outside the aggregate. In this review we establish a bridge between the fields of photonics and excitonics by describing the present understanding of exciton dynamics in molecular aggregates. * Electronic address: saykin@fas.harvard.edu † Electronic address: eisfeld@mpipks-dresden.mpg.de ‡ Electronic address: aspuru@chemistry.harvard.edu 1 E. Yablonovitch; Inhibited Spontaneous Emission in
Excitons: from excitations at surfaces to confinement in nanostructures
Surface Science Reports, 2005
We present a review of optical properties of excitonic semiconductors. We consider the interaction of light with surfaces, thin films, multilayered systems, small particles and rough surfaces accounting for excitonic transitions. The first part of the paper is devoted to studies done using classical electrodynamics within the nonlocal dielectric response theory. For the dielectric function we take the Hopfield and Thomas coupled harmonic oscillator model, which yields excitonic modes beyond the usual optical waves. Therefore, studies of the coupling of light to exciton-polaritons in the presence of surfaces require additional boundary conditions (ABC's) to determine the reflected and transmitted electromagnetic field amplitudes within models of abruptly terminated semiconductors. An alternative consisting in solving Maxwell's equations for the electromagnetic field together with an equation for the excitonic polarization derived from the quantum mechanical dynamics of electrons and holes, including a surface potential that accounts for the interaction of excitons with the surface is explored in the latter part of the paper. The surface potential may be modeled by an infinite barrier, or by smooth repulsive exponential potentials and Morse-type potential wells. Surface potential wells may produce entrapped excitonic states, which are explored at surfaces, films and superlattices. Scattering of light from non-ideal rough surfaces is also discussed. Comparison between theory and experiment is emphasized all along the paper. The final section is devoted to a microscopic theory which is ABC independent and explains the experimental measurements of transmission in thin films.
arXiv: Optics, 2017
The optical response of an artificial hybrid molecule system composed of two metallic nanoparticles (MNPs) and a semiconductor quantum dot (SQD) is investigated theoretically due to the plasmon-exciton-plasmon coupling effects on the absorption properties of the hybrid nanosystem, which depends on the interaction between the induced dipole moments in the SQD and the MNPs, respectively. We show that the strong coupling of exciton and localized surface plasmons in such a hybrid molecules leads to appealing, tunable optical properties by adjusting the symmetry of the hybrid molecule nanosystem with controllable interparticle distances. We also address here the influence of the size of the MNPs and dielectric constant of the background medium on the optical absorption of the MNPs and SQD, respectively, which results in the interparticle Foster resonance energy transfer (FRET). Our results will open an avenue to deal with the surface-enhanced spectroscopies and potential application of t...