Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer... more Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer multiple benefits to the light emitting and solar energy harvesting devices of modern photovoltaics. Recent advances in the fabrication technology of low dimensional perovskites has made the production of such supercrystals a reality and created a high demand for the modelling of excitonic phenomena inside them. Here we present a rigorous theory of Frenkel excitons in lead halide perovskite QD supercrystals with a square Bravais lattice. The theory shows that such supercrystals support three bright exciton modes whose dispersion and polarization properties are controlled by the symmetry of the perovskite lattice and the orientations of QDs. The effective masses of excitons are found to scale with the ratio of the superlattice period and the number of QDs along the supercrystal edge, allowing one to fine-tune the electro-optical response of the supercrystals as desired for applications. We also calculate the conductivity of perovskite QD supercrystals and analyze how it is affected by the optical generation of the three types of excitons. This paper provides a solid theoretical basis for the modelling of two- and three-dimensional supercrystals made of perovskite QDs and the engineering of photovoltaic devices with superior optoelectronic properties.
Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality a... more Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality arises from the nonuniformity of their thickness. We show that such gammadions distinguish between the two circular polarizations upon the absorption of light, unlike two-dimensional semiconductor nanostructures with planar chirality. Chiral semiconductor gammadions of inverse conical shape are found to exhibit the highest dissymmetry of optical response among the nanostructures of the same size. The results of our theoretical study can be used in future applications of semiconductor gammadions in biomedicine and optoelectronics.
Nanocrystals of AgInS$_2$ demonstrate giant Stokes shifts ~ 1 eV, the nature of which is still no... more Nanocrystals of AgInS$_2$ demonstrate giant Stokes shifts ~ 1 eV, the nature of which is still not clearly understood. We propose a theoretical model of this phenomenon bringing together several different mechanisms previously considered only separately. We take into account the contribution of electron-electron interaction with the hybrid density functional theory, as well as the renormalization of energy spectrum due to the electron-phonon coupling. Furthermore, we consider the presence of at least one point defect responsible for hole trapping and the formation of a localized polaron state. Our numerical simulations show that photoluminescence due to the recombination of a non-trapped electron and a trapped hole results in the giant Stokes shift in AgInS$_2$ nanocrystal, which is in close agreement with the recent experimental results.
We present here a simple quantum-mechanical model that describes interband optical activity of cu... more We present here a simple quantum-mechanical model that describes interband optical activity of cubical semiconductor nanocrystals with chiral shape irregularities. Using the developed model, we derive the analytical expression for the rotatory strengths of interband transitions and show that the circular dichroism spectra of the chiral-shape nanocrystal consists only of the electric dipole allowed transitions. Taking into account the splitting of the valence band, one can interpret experimental circular dichroism spectra using just a few fitting parameters. The results of our study may prove useful for various branches of nanophotonics, chiral chemistry, and biomedicine.
Abstract : The novel technique of coherent control of quantum states in semiconductor nanostructu... more Abstract : The novel technique of coherent control of quantum states in semiconductor nanostructures was applied to the inhomogeneously broadened ensemble of quantum dots. By taking an advantage of the interaction between electronic states in quantum dots and phonons in the host matrix the inhomogeneous broadening was effectively eliminated. The coherence decay rate was measured.
Covalently bonded complexes based on CdSe/ZnS quantum dots and chlorin e6 have been formed, and t... more Covalently bonded complexes based on CdSe/ZnS quantum dots and chlorin e6 have been formed, and their spectroluminescence properties have been investigated. It is established that the resulting complexes exhibit efficient (about 40%) energy transport from the quantum dots to the chlorin e6, with insignificant variation of its luminescence quantum yield.
Complexes of semiconductor CdSe/ZnS quantum dots and molecules of chlorin e6 in dimethyl sulfoxid... more Complexes of semiconductor CdSe/ZnS quantum dots and molecules of chlorin e6 in dimethyl sulfoxide have been formed. Conditions of formation and spectral and luminescent properties of the complexes have been studied. The quantum yield of luminescence of chlorin e6 in the complexes has been found to correspond to that of its monomer form. It has been shown that the complexes have energy transfer from the quantum dots to the molecules of chlorin e6 being observed, with its effectiveness being about 25%.
Lead chalcogenide nanocrystals (NCs) are an emerging class of photoactive materials that have bec... more Lead chalcogenide nanocrystals (NCs) are an emerging class of photoactive materials that have become a versatile tool for fabricating new generation photonics devices operating in the near-IR spectral range. NCs are presented in a wide variety of forms and sizes, each of which has its own unique features. Here, we discuss colloidal lead chalcogenide NCs in which one dimension is much smaller than the others, i.e., two-dimensional (2D) NCs. The purpose of this review is to present a complete picture of today’s progress on such materials. The topic is quite complicated, as a variety of synthetic approaches result in NCs with different thicknesses and lateral sizes, which dramatically change the NCs photophysical properties. The recent advances highlighted in this review demonstrate lead chalcogenide 2D NCs as promising materials for breakthrough developments. We summarized and organized the known data, including theoretical works, to highlight the most important 2D NC features and giv...
In this Letter, we analyze circular dichroism (CD) enhancement of a helical semiconductor nanorib... more In this Letter, we analyze circular dichroism (CD) enhancement of a helical semiconductor nanoribbon exposed to a weak homogenous electric field. By creating a periodic superlattice for the confined electrons, the electric field splits the electronic sub-bands into minibands and gives rise to critical points in the electronic density of states. We show that the modification of the electronic energy spectrum results in the appearance of new optically active transitions in the CD and absorption spectra, and that the CD signal of the nanoribbon is significantly enhanced at the critical points. The ability to dynamically control the chiroptical response of semiconductor nanoribbons by an external electric field makes them promising for the next-generation nanophotonic devices.
Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer... more Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer multiple benefits to the light emitting and solar energy harvesting devices of modern photovoltaics. Recent advances in the fabrication technology of low dimensional perovskites has made the production of such supercrystals a reality and created a high demand for the modelling of excitonic phenomena inside them. Here we present a rigorous theory of Frenkel excitons in lead halide perovskite QD supercrystals with a square Bravais lattice. The theory shows that such supercrystals support three bright exciton modes whose dispersion and polarization properties are controlled by the symmetry of the perovskite lattice and the orientations of QDs. The effective masses of excitons are found to scale with the ratio of the superlattice period and the number of QDs along the supercrystal edge, allowing one to fine-tune the electro-optical response of the supercrystals as desired for applications. We also calculate the conductivity of perovskite QD supercrystals and analyze how it is affected by the optical generation of the three types of excitons. This paper provides a solid theoretical basis for the modelling of two- and three-dimensional supercrystals made of perovskite QDs and the engineering of photovoltaic devices with superior optoelectronic properties.
Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality a... more Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality arises from the nonuniformity of their thickness. We show that such gammadions distinguish between the two circular polarizations upon the absorption of light, unlike two-dimensional semiconductor nanostructures with planar chirality. Chiral semiconductor gammadions of inverse conical shape are found to exhibit the highest dissymmetry of optical response among the nanostructures of the same size. The results of our theoretical study can be used in future applications of semiconductor gammadions in biomedicine and optoelectronics.
Nanocrystals of AgInS$_2$ demonstrate giant Stokes shifts ~ 1 eV, the nature of which is still no... more Nanocrystals of AgInS$_2$ demonstrate giant Stokes shifts ~ 1 eV, the nature of which is still not clearly understood. We propose a theoretical model of this phenomenon bringing together several different mechanisms previously considered only separately. We take into account the contribution of electron-electron interaction with the hybrid density functional theory, as well as the renormalization of energy spectrum due to the electron-phonon coupling. Furthermore, we consider the presence of at least one point defect responsible for hole trapping and the formation of a localized polaron state. Our numerical simulations show that photoluminescence due to the recombination of a non-trapped electron and a trapped hole results in the giant Stokes shift in AgInS$_2$ nanocrystal, which is in close agreement with the recent experimental results.
We present here a simple quantum-mechanical model that describes interband optical activity of cu... more We present here a simple quantum-mechanical model that describes interband optical activity of cubical semiconductor nanocrystals with chiral shape irregularities. Using the developed model, we derive the analytical expression for the rotatory strengths of interband transitions and show that the circular dichroism spectra of the chiral-shape nanocrystal consists only of the electric dipole allowed transitions. Taking into account the splitting of the valence band, one can interpret experimental circular dichroism spectra using just a few fitting parameters. The results of our study may prove useful for various branches of nanophotonics, chiral chemistry, and biomedicine.
Abstract : The novel technique of coherent control of quantum states in semiconductor nanostructu... more Abstract : The novel technique of coherent control of quantum states in semiconductor nanostructures was applied to the inhomogeneously broadened ensemble of quantum dots. By taking an advantage of the interaction between electronic states in quantum dots and phonons in the host matrix the inhomogeneous broadening was effectively eliminated. The coherence decay rate was measured.
Covalently bonded complexes based on CdSe/ZnS quantum dots and chlorin e6 have been formed, and t... more Covalently bonded complexes based on CdSe/ZnS quantum dots and chlorin e6 have been formed, and their spectroluminescence properties have been investigated. It is established that the resulting complexes exhibit efficient (about 40%) energy transport from the quantum dots to the chlorin e6, with insignificant variation of its luminescence quantum yield.
Complexes of semiconductor CdSe/ZnS quantum dots and molecules of chlorin e6 in dimethyl sulfoxid... more Complexes of semiconductor CdSe/ZnS quantum dots and molecules of chlorin e6 in dimethyl sulfoxide have been formed. Conditions of formation and spectral and luminescent properties of the complexes have been studied. The quantum yield of luminescence of chlorin e6 in the complexes has been found to correspond to that of its monomer form. It has been shown that the complexes have energy transfer from the quantum dots to the molecules of chlorin e6 being observed, with its effectiveness being about 25%.
Lead chalcogenide nanocrystals (NCs) are an emerging class of photoactive materials that have bec... more Lead chalcogenide nanocrystals (NCs) are an emerging class of photoactive materials that have become a versatile tool for fabricating new generation photonics devices operating in the near-IR spectral range. NCs are presented in a wide variety of forms and sizes, each of which has its own unique features. Here, we discuss colloidal lead chalcogenide NCs in which one dimension is much smaller than the others, i.e., two-dimensional (2D) NCs. The purpose of this review is to present a complete picture of today’s progress on such materials. The topic is quite complicated, as a variety of synthetic approaches result in NCs with different thicknesses and lateral sizes, which dramatically change the NCs photophysical properties. The recent advances highlighted in this review demonstrate lead chalcogenide 2D NCs as promising materials for breakthrough developments. We summarized and organized the known data, including theoretical works, to highlight the most important 2D NC features and giv...
In this Letter, we analyze circular dichroism (CD) enhancement of a helical semiconductor nanorib... more In this Letter, we analyze circular dichroism (CD) enhancement of a helical semiconductor nanoribbon exposed to a weak homogenous electric field. By creating a periodic superlattice for the confined electrons, the electric field splits the electronic sub-bands into minibands and gives rise to critical points in the electronic density of states. We show that the modification of the electronic energy spectrum results in the appearance of new optically active transitions in the CD and absorption spectra, and that the CD signal of the nanoribbon is significantly enhanced at the critical points. The ability to dynamically control the chiroptical response of semiconductor nanoribbons by an external electric field makes them promising for the next-generation nanophotonic devices.
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Papers by Anatoly Fedorov