Journal of Physical Chemistry Letters, Sep 6, 2020
Relatively weak red photoluminescence of carbon dots (CDots) is a major challenge on the way to t... more Relatively weak red photoluminescence of carbon dots (CDots) is a major challenge on the way to their successful implementation in biological and optoelectronic devises. We present a theoretical analysis of the interaction among the surface emission centers of CDots, showing that it may determine efficiency of the red photoluminescence of CDots. Based on the previous experimental studies, it is assumed that the optical response of the CDots is determined by the molecule-like subunits of polycyclic aromatic hydrocarbons (PAHs) attached to the CDots' surface. Three characteristic types of coupling of these PAH subunits are considered: noninteracting monomers, noncovalently bound dimers, and covalently bound dimers with two, three, or four carbon linkers. We demonstrate that the CDots' photoluminescence broadens, redshifts, and weakens by two orders of magnitude when the free monomers are substituted by the covalently bridged centers. These and other results of our study show that the realization of CDots with many weakly interacting surface emission centers may constitute an efficient way to achieve their efficient red photoluminescence, which is highly desirable for biological and optoelectronic applications.
PbS quantum dots (QDs) are a promising material for designing of modern solar energy convertors. ... more PbS quantum dots (QDs) are a promising material for designing of modern solar energy convertors. Yet, their reproducible synthesis is still intractable, since typical methods do not allow controlling the growth of PbS nanocrystals due to the high reaction rates. Here we propose the two-step synthetic procedure, which allows controlling precisely nanocrystal growth on the second stage. The first step allows obtaining small PbS QDs by the standard hot injection method, which are then slowly grown to a desired size on the second stage. By use of this method, we were able to obtain gram-scale batches of PbS QDs with high reproducibility of the photoluminescence properties of the synthesis product.
ABSTRACT New biocompatible complexes based on manganese-doped core/shell ZnS/ZnS quantum dots (Zn... more ABSTRACT New biocompatible complexes based on manganese-doped core/shell ZnS/ZnS quantum dots (ZnS:Mn2+/ZnS) and drug "Photoditazin" were formed and compared to traditional complexes with CdSe/ZnS quantum dots. Complexes with ZnS:Mn/ZnS quantum dots show some advantages in their photophysical properties. At the same time they demonstrate evident difference in their photophysical properties that may be associated with various location of trap states in places where drug molecule bounds with quantum dot.
Here we report our investigations of the formation conditions and photophysical properties of com... more Here we report our investigations of the formation conditions and photophysical properties of complexes between luminescent semiconducting nanoparticles (quantum dots, QDs) and the photosensitizer chlorin e6, which is widely used for the photodynamic therapy. In our complexes, bovine serum albumin (BSA), the most abundant protein in blood serum, was used as a linker between QDs and chlorin e6 molecules. The influence of BSA on the optical properties of Ce6 and QDs in complexes was properly examined using spectral-luminescent methods. It was found that BSA passivated QD surface and substantially QD quantum yield of luminescence was increased. In addition, BSA prevented the aggregation of chlorin e6 molecules in complexes with QDs. We demonstrated that the use of BSA as a linker allows to create functional QD-chlorin e6 complexes with effective photoexcitation energy transfer from QDs to the molecules.
A morphology and photoinduced changes of luminescence properties of two types of hybrid structure... more A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based on TiO2 nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir- Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of structure formation. A photodegradation of luminescence properties of the structures is associated with the formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the structure formation and the concentration of TiO2 nanoparticles. A decay of luminescence of QD aggregates in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform QD surface concentration by visible light resulted in a photopassivation of their surface, which is accompanied by significant increase of luminescence quantum yield of QDs.
Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been cre... more Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been created. It has been established by optical spectroscopy that effective energy transfer (~35%) from quantum dots to chlorin e6 is observed in the resulting conjugates.
Magnetic circular dichroism (MCD) spectra were measured for colloidal CdSe/CdS core-wing nanoplat... more Magnetic circular dichroism (MCD) spectra were measured for colloidal CdSe/CdS core-wing nanoplatelets (NPLs). MCD spectra of CdSe cores demonstrate well resolved features which could be attributed to excitonic transitions from heavy hole, light hole and split-off sublevels. A1/D0, B0/D0 MCD characteristic terms were determined. The values of A1/D0, B0/D0 terms have no dependence on NPL thickness and are very close to the corresponding values in organic molecules.
In this study, complexes of CdSe/ZnS quantum dots and quantum rods with sulfophthalocyanine molec... more In this study, complexes of CdSe/ZnS quantum dots and quantum rods with sulfophthalocyanine molecules have been formed. Analysis of spectral and luminescent properties of solutions of the complexes has revealed that an increase in the number of molecules per one nanocrystal in a mixed solution results in a noticeable decrease in the intensity of the luminescence of the quantum dots and quantum rods. In addition, it has been found that, upon an increase in the concentration of sulfophthalocyanine molecules, the absorption spectra of the samples in the region of their first absorption band have signs of formation of nonluminiscent aggregates of sulfophthalocyanine molecules. Analysis of the absorption spectra of the mixed solutions has made it possible to demonstrate that the complexes with the quantum rods have a content of the sulfophthalocyanine aggregates significantly lower than the complexes with the quantum dots.
On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature l... more On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots
Energy transfer in hybrid structures based on colloidal quantum dots of CdSe/ZnS and molecules of... more Energy transfer in hybrid structures based on colloidal quantum dots of CdSe/ZnS and molecules of tetra(p-trimethylamino)phenylporphin formed in polyethylene terephthalate track membranes is considered. A physical model for the formation of these hybrid structures is proposed, and the distribution of structure components in the near-surface layer of track membrane pores is estimated.
In this work, we present a comprehensive theoretical modelling of a chiral dimer made of two pero... more In this work, we present a comprehensive theoretical modelling of a chiral dimer made of two perovskite quantum dots (QDs). Taking into account the bright triplet exciton of QDs, we calculate the energies of the dimer’s quantum states and analyze the dependence of these energies on the dimer geometry. We also compute the circular dichroism (CD) spectra of the dimer and establish the optimal dimer parameters for maximizing its CD response. Our results show that the perovskite QD dimers feature a strong and tunable chiroptical response, making these superstructures attractive for chiral application.
Intraband optical transitions in the complex valence band of spherical nanocrystals based on semi... more Intraband optical transitions in the complex valence band of spherical nanocrystals based on semiconductors with Td and Oh symmetries have been studied. The energy spectrum of the holes is calculated, using k·p perturbation theory. Analytical expressions are obtained for the hole–photon-interaction matrix elements. It is shown that the size dependence of these matrix elements is determined by the states that participate in the transitions. The selection rules obtained here permit transitions between a large number of states with various symmetries that are forbidden in the conduction zone. The radiative lifetime of the states in the valence band are computed as a function of the radius of the nanocrystal, and it is shown that it can vary in a wide range from 10−12 to 10−3 s.
The photoluminescence (PL) kinetics of heterostructures with InP self-assembled quantum dots are ... more The photoluminescence (PL) kinetics of heterostructures with InP self-assembled quantum dots are studied under quasi-resonant pulse excitation in the presence of an external electric field. An oscillatory behavior of the PL kinetics is shown to arise due to quantum beats of the radiative states. A model of the coherent excitation of nonresonant PL is proposed.
In recent years, carbon dots have attracted much scientific attention due to their unique propert... more In recent years, carbon dots have attracted much scientific attention due to their unique properties, which can find applications in many fields. We have developed synthesis protocols of carbon dots with different structure and optical properties using o-phenylenediamine. The change in absorption and luminescence spectra of carbon dots were studied in detail. The obtained samples show intensive luminescence at 350 nm and 450 or 550 nm dependent on synthesis parameters.
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.
Journal of the Optical Society of America, Sep 29, 2017
We study the propagation of real-argument Laguerre-Gaussian beams beyond the paraxial approximati... more We study the propagation of real-argument Laguerre-Gaussian beams beyond the paraxial approximation using the perturbation corrections to the complex-argument Laguerre-Gaussian beams derived earlier by Takenaka et al. [J. Opt. Soc. Am. A 2, 826 (1985)]. Each higher-order correction to the amplitude of the real-argument beam (l , m) is represented as a superposition of the same-order corrections to the amplitudes of the complexargument beams (l , q) with q 0;1;2;…;m. We derive explicit expressions for the electric and magnetic fields of transversely and longitudinally polarized real-argument beams and calculate the chirality densities of these beams up to the fourth order of the smallness parameter. For the first time to the best of our knowledge, we show that essentially achiral Gaussian beams (corresponding to l m 0) possess nonzero chirality density due to the wavefront curvature. The obtained corrections to the paraxial beams may prove useful for precise laser beam shaping and in studies of optomechanical forces.
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.
Journal of Physical Chemistry Letters, Sep 6, 2020
Relatively weak red photoluminescence of carbon dots (CDots) is a major challenge on the way to t... more Relatively weak red photoluminescence of carbon dots (CDots) is a major challenge on the way to their successful implementation in biological and optoelectronic devises. We present a theoretical analysis of the interaction among the surface emission centers of CDots, showing that it may determine efficiency of the red photoluminescence of CDots. Based on the previous experimental studies, it is assumed that the optical response of the CDots is determined by the molecule-like subunits of polycyclic aromatic hydrocarbons (PAHs) attached to the CDots' surface. Three characteristic types of coupling of these PAH subunits are considered: noninteracting monomers, noncovalently bound dimers, and covalently bound dimers with two, three, or four carbon linkers. We demonstrate that the CDots' photoluminescence broadens, redshifts, and weakens by two orders of magnitude when the free monomers are substituted by the covalently bridged centers. These and other results of our study show that the realization of CDots with many weakly interacting surface emission centers may constitute an efficient way to achieve their efficient red photoluminescence, which is highly desirable for biological and optoelectronic applications.
PbS quantum dots (QDs) are a promising material for designing of modern solar energy convertors. ... more PbS quantum dots (QDs) are a promising material for designing of modern solar energy convertors. Yet, their reproducible synthesis is still intractable, since typical methods do not allow controlling the growth of PbS nanocrystals due to the high reaction rates. Here we propose the two-step synthetic procedure, which allows controlling precisely nanocrystal growth on the second stage. The first step allows obtaining small PbS QDs by the standard hot injection method, which are then slowly grown to a desired size on the second stage. By use of this method, we were able to obtain gram-scale batches of PbS QDs with high reproducibility of the photoluminescence properties of the synthesis product.
ABSTRACT New biocompatible complexes based on manganese-doped core/shell ZnS/ZnS quantum dots (Zn... more ABSTRACT New biocompatible complexes based on manganese-doped core/shell ZnS/ZnS quantum dots (ZnS:Mn2+/ZnS) and drug "Photoditazin" were formed and compared to traditional complexes with CdSe/ZnS quantum dots. Complexes with ZnS:Mn/ZnS quantum dots show some advantages in their photophysical properties. At the same time they demonstrate evident difference in their photophysical properties that may be associated with various location of trap states in places where drug molecule bounds with quantum dot.
Here we report our investigations of the formation conditions and photophysical properties of com... more Here we report our investigations of the formation conditions and photophysical properties of complexes between luminescent semiconducting nanoparticles (quantum dots, QDs) and the photosensitizer chlorin e6, which is widely used for the photodynamic therapy. In our complexes, bovine serum albumin (BSA), the most abundant protein in blood serum, was used as a linker between QDs and chlorin e6 molecules. The influence of BSA on the optical properties of Ce6 and QDs in complexes was properly examined using spectral-luminescent methods. It was found that BSA passivated QD surface and substantially QD quantum yield of luminescence was increased. In addition, BSA prevented the aggregation of chlorin e6 molecules in complexes with QDs. We demonstrated that the use of BSA as a linker allows to create functional QD-chlorin e6 complexes with effective photoexcitation energy transfer from QDs to the molecules.
A morphology and photoinduced changes of luminescence properties of two types of hybrid structure... more A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based on TiO2 nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir- Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of structure formation. A photodegradation of luminescence properties of the structures is associated with the formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the structure formation and the concentration of TiO2 nanoparticles. A decay of luminescence of QD aggregates in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform QD surface concentration by visible light resulted in a photopassivation of their surface, which is accompanied by significant increase of luminescence quantum yield of QDs.
Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been cre... more Water-soluble conjugates based on semiconductor quantum dots ZnS:Mn with chlorin e6 have been created. It has been established by optical spectroscopy that effective energy transfer (~35%) from quantum dots to chlorin e6 is observed in the resulting conjugates.
Magnetic circular dichroism (MCD) spectra were measured for colloidal CdSe/CdS core-wing nanoplat... more Magnetic circular dichroism (MCD) spectra were measured for colloidal CdSe/CdS core-wing nanoplatelets (NPLs). MCD spectra of CdSe cores demonstrate well resolved features which could be attributed to excitonic transitions from heavy hole, light hole and split-off sublevels. A1/D0, B0/D0 MCD characteristic terms were determined. The values of A1/D0, B0/D0 terms have no dependence on NPL thickness and are very close to the corresponding values in organic molecules.
In this study, complexes of CdSe/ZnS quantum dots and quantum rods with sulfophthalocyanine molec... more In this study, complexes of CdSe/ZnS quantum dots and quantum rods with sulfophthalocyanine molecules have been formed. Analysis of spectral and luminescent properties of solutions of the complexes has revealed that an increase in the number of molecules per one nanocrystal in a mixed solution results in a noticeable decrease in the intensity of the luminescence of the quantum dots and quantum rods. In addition, it has been found that, upon an increase in the concentration of sulfophthalocyanine molecules, the absorption spectra of the samples in the region of their first absorption band have signs of formation of nonluminiscent aggregates of sulfophthalocyanine molecules. Analysis of the absorption spectra of the mixed solutions has made it possible to demonstrate that the complexes with the quantum rods have a content of the sulfophthalocyanine aggregates significantly lower than the complexes with the quantum dots.
On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature l... more On the origin of stretched exponential (Kohlrausch) relaxation kinetics in the room temperature luminescence decay of colloidal quantum dots
Energy transfer in hybrid structures based on colloidal quantum dots of CdSe/ZnS and molecules of... more Energy transfer in hybrid structures based on colloidal quantum dots of CdSe/ZnS and molecules of tetra(p-trimethylamino)phenylporphin formed in polyethylene terephthalate track membranes is considered. A physical model for the formation of these hybrid structures is proposed, and the distribution of structure components in the near-surface layer of track membrane pores is estimated.
In this work, we present a comprehensive theoretical modelling of a chiral dimer made of two pero... more In this work, we present a comprehensive theoretical modelling of a chiral dimer made of two perovskite quantum dots (QDs). Taking into account the bright triplet exciton of QDs, we calculate the energies of the dimer’s quantum states and analyze the dependence of these energies on the dimer geometry. We also compute the circular dichroism (CD) spectra of the dimer and establish the optimal dimer parameters for maximizing its CD response. Our results show that the perovskite QD dimers feature a strong and tunable chiroptical response, making these superstructures attractive for chiral application.
Intraband optical transitions in the complex valence band of spherical nanocrystals based on semi... more Intraband optical transitions in the complex valence band of spherical nanocrystals based on semiconductors with Td and Oh symmetries have been studied. The energy spectrum of the holes is calculated, using k·p perturbation theory. Analytical expressions are obtained for the hole–photon-interaction matrix elements. It is shown that the size dependence of these matrix elements is determined by the states that participate in the transitions. The selection rules obtained here permit transitions between a large number of states with various symmetries that are forbidden in the conduction zone. The radiative lifetime of the states in the valence band are computed as a function of the radius of the nanocrystal, and it is shown that it can vary in a wide range from 10−12 to 10−3 s.
The photoluminescence (PL) kinetics of heterostructures with InP self-assembled quantum dots are ... more The photoluminescence (PL) kinetics of heterostructures with InP self-assembled quantum dots are studied under quasi-resonant pulse excitation in the presence of an external electric field. An oscillatory behavior of the PL kinetics is shown to arise due to quantum beats of the radiative states. A model of the coherent excitation of nonresonant PL is proposed.
In recent years, carbon dots have attracted much scientific attention due to their unique propert... more In recent years, carbon dots have attracted much scientific attention due to their unique properties, which can find applications in many fields. We have developed synthesis protocols of carbon dots with different structure and optical properties using o-phenylenediamine. The change in absorption and luminescence spectra of carbon dots were studied in detail. The obtained samples show intensive luminescence at 350 nm and 450 or 550 nm dependent on synthesis parameters.
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.
Journal of the Optical Society of America, Sep 29, 2017
We study the propagation of real-argument Laguerre-Gaussian beams beyond the paraxial approximati... more We study the propagation of real-argument Laguerre-Gaussian beams beyond the paraxial approximation using the perturbation corrections to the complex-argument Laguerre-Gaussian beams derived earlier by Takenaka et al. [J. Opt. Soc. Am. A 2, 826 (1985)]. Each higher-order correction to the amplitude of the real-argument beam (l , m) is represented as a superposition of the same-order corrections to the amplitudes of the complexargument beams (l , q) with q 0;1;2;…;m. We derive explicit expressions for the electric and magnetic fields of transversely and longitudinally polarized real-argument beams and calculate the chirality densities of these beams up to the fourth order of the smallness parameter. For the first time to the best of our knowledge, we show that essentially achiral Gaussian beams (corresponding to l m 0) possess nonzero chirality density due to the wavefront curvature. The obtained corrections to the paraxial beams may prove useful for precise laser beam shaping and in studies of optomechanical forces.
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.
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Papers by Anatoly Fedorov