M. Vasilevskiy | Universidade do Minho (original) (raw)

Papers by M. Vasilevskiy

Research paper thumbnail of Resonant Raman scattering in spherical quantum dots: II-VI versus III-V semiconductor nanocrystals

physica status solidi (b), 2010

Resonant Raman scattering (RRS) in nearly-spherical nanocrystal (NC) quantum dots (QDs) is discus... more Resonant Raman scattering (RRS) in nearly-spherical nanocrystal (NC) quantum dots (QDs) is discussed with respect to the underlying (Fröhlich-type and optical deformation potential, ODP) mechanisms of the exciton-phonon interaction. Their relative contribution for different QD materials, both II-VI and III-V is compared. It is shown that the (usually overlooked) ODP interaction is entirely responsible for an additional peak in the RRS spectra, situated near the transverseoptical (TO) phonon frequency, which has been observed for InP, InAs and, recently, CdTe QDs. RRS spectra calculated using continuum models for confined phonons and excitons and taking into account both interaction mechanisms are in excellent agreement with these experimental data.

Research paper thumbnail of Anomalous first-order Raman scattering in III-V quantum dots: Optical deformation potential interaction

Research paper thumbnail of Absorption and Photoluminescence Study of Cds Quantum Dots: The Role of Host Matrix and Nanocrystal Size and Density

MRS Proceedings, 1999

ABSTRACTIn this paper we present results of the absorption and photoluminescence (PL) of CdSdoped... more ABSTRACTIn this paper we present results of the absorption and photoluminescence (PL) of CdSdoped Si02 films fabricated by RF co-sputtering (semiconductor volume fraction f=1–15%, nano-crystallite's mean size 5–7nm) and matrix-free films of close-packed CdS nanocrystallites (f∼30%, size 2–5nm) produced by an original chemical method. The absorption spectra have been modelled using the modified Maxwell-Garnett model. This gives the e-h pair state energies and evidence of a strong absorption in the glass matrix containing CdS. The temperature dependence of the spectral position and broadening of the PL peak is analysed. It is concluded that a photo-generated hole is captured on an acceptor-type trap before the radiative recombination with a confined electron. The excitation of this ‘band-edge’ PL occurs through some states in the matrix and directly in the CdS crystallites for the two kinds of samples, respectively. The temperature coefficients of the optical transition energies f...

Research paper thumbnail of Resonance energy transfer in self-organized organic/inorganic dendrite structures

Nanoscale, 2013

Förster-type coupling is demonstrated for self-assembled dendrite structures consisting of J-aggr... more Förster-type coupling is demonstrated for self-assembled dendrite structures consisting of J-aggregates and QDs, with energy fluxes directed towards structures' center.

Research paper thumbnail of Cascade upconversion of photoluminescence in ensembles of II-VI semiconductor nanocrystals

physica status solidi (c), 2010

We present the theory of the thermally activated photoluminescence upconversion, also known as an... more We present the theory of the thermally activated photoluminescence upconversion, also known as anti-Stokes photoluminescence (ASPL), based on the quantum dot (QD) polaron effect and explaining all the principal features of the ASPL in colloidal solutions of chemically grown nanocrystals (NCs). The results obtained by Monte-Carlo simulations reproduce all the experimentally observed ASPL trends in colloidal NC solutions and are being extended to dense QD systems, such as films composed by layers of closely packed NCs.

Research paper thumbnail of Modelling of Environment Sensors Based on the Surface Plasmon Resonance Effect

Surface plasmons (SPs) are collective excitations of free electrons in a conducting medium bounde... more Surface plasmons (SPs) are collective excitations of free electrons in a conducting medium bounded by a surface or interface with a dielectric. They can originate surface plasmon-polaritons (SPPs), which are evanescent waves involving electron density oscillations and the associated electromagnetic (EM) field whose amplitude decays exponentially with distance from the surface. SPPs are characterised by a dispersion curve (frequency vs wavevector along the interface) that lies outside of the light cone, so they cannot be excited directly by propagating light; however, it is possible to excite them using the Attenuated Total internal Reflection (ATR) method or a periodic grating. SPs in a confined geometry such as a metallic sphere are localised in space and characterised by discrete frequencies (a single one in the case of sphere, two or three in the case of an ellipsoid). They can be excited directly by propagating light if its frequency coincides with the localised SP frequency, gi...

Research paper thumbnail of Optical bistability of graphene in the terahertz range

Research paper thumbnail of Electron-phonon interaction effects in semiconductor quantum dots:A nonperturabative approach

Research paper thumbnail of Anti-Stokes cooling in semiconductor nanocrystal quantum dots: A feasibility study

physica status solidi (a), 2009

In this review, we discuss the feasibility of laser cooling of semiconductor nanocrystal quantum ... more In this review, we discuss the feasibility of laser cooling of semiconductor nanocrystal quantum dots by phonon-assisted anti-Stokes photoluminescence. Taking into account recent experimental advances, in particular, the development of semiconductor nanocrystals with very high quantum yield, we analyze in detail how the various physical processes in nanocrystals might help or hinder the cooling process. Possible experimental approaches to achieve efficient optical cooling are also discussed.

Research paper thumbnail of A many body study of the SASER dynamics

Microelectronic Engineering, 1998

Research paper thumbnail of Further insight into the temperature quenching of photoluminescence from InAs∕GaAs self-assembled quantum dots

Journal of Applied Physics, 2008

ABSTRACT

Research paper thumbnail of Polaron effect in semiconductor quantum dots: Impact on the optical absorption, up-converted photoluminescence and raman scattering

AIP Conference Proceedings, 2005

Multi-phonon processes in a model quantum dot (QD) containing a small number of most important el... more Multi-phonon processes in a model quantum dot (QD) containing a small number of most important electronic states and several optical phonon modes are considered exactly, taking into account both intra- and inter-level interactions. The calculated optical spectra allow for explanation of several previously published experimental results obtained for spherical and self-assembled QD's, such as enhanced 2LO phonon replicas in the

Research paper thumbnail of Graphene and polarisable nanoparticles: Looking good together?

2016 18th International Conference on Transparent Optical Networks (ICTON), 2016

Several potentially interesting plasmonic effects can arise from combining graphene with polarisa... more Several potentially interesting plasmonic effects can arise from combining graphene with polarisable nanoparticles (NPs), such as metallic or dielectric spheres, related to surface plasmon-polaritons (SPPs) supported by the latter in the terahertz (THz) spectral range. Owing to the electromagnetic coupling between the graphene SPPs and dipole moments of polarisable (nano-) particles deposited on top of it, the optical properties of such a composite system have some new features as compared to its constituents. First, the NP's polarizability is renormalized due to the electromagnetic back action of SPPs which are excited in graphene when an external propagating electromagnetic wave impinges on the particle. The coupling also results in a considerable enhancement of the THz radiation absorption in graphene, while the reflection drops to zero. This effect can be potentially interesting e.g. for cloaking in a certain THz frequency range.

Research paper thumbnail of Dipole-active vibrations confined in InP quantum dots

Physica B: Condensed Matter, 2002

Dipole-active optical phonons confined in nearly spherical InP quantum dots (QDs) were studied th... more Dipole-active optical phonons confined in nearly spherical InP quantum dots (QDs) were studied theoretically and experimentally. Spatial quantization of the phonon modes in an InP QD was considered theoretically by solving the coupled continuous equation of motion and Poisson equation. It is shown that, when the Fröhlich frequency falls into the gap between the bulk LO and TO phonon bands,

Research paper thumbnail of Renormalization of nanoparticle polarizability in the vicinity of a graphene-covered interface

Physical Review B, 2014

We study the electromagnetic properties of a metamaterial consisting of polarizable (nano)particl... more We study the electromagnetic properties of a metamaterial consisting of polarizable (nano)particles and a single graphene sheet placed at the interface between two dielectrics. We show that the particle's polarizability is renormalized because of the electromagnetic coupling to surface plasmons supported by graphene, which results in a dispersive behavior, different for the polarizability components corresponding to the induced dipole moment, parallel and perpendicular to the graphene sheet. In particular, this effect is predicted to take place for a metallic particle whose bare polarizability in the terahertz (THz) region is practically equal to the cube of its radius (times 4πε0). This opens the possibility to excite surface plasmons in graphene and enhance its absorption in the THz range by simply using a monolayer of metallic particles randomly deposited on top of it, as we show by explicit calculations.

Research paper thumbnail of Polaron effect in semiconductor quantum dots: Impact on the optical absorption, up-converted photoluminescence and raman scattering

AIP Conference Proceedings, 2005

Multi-phonon processes in a model quantum dot (QD) containing a small number of most important el... more Multi-phonon processes in a model quantum dot (QD) containing a small number of most important electronic states and several optical phonon modes are considered exactly, taking into account both intra- and inter-level interactions. The calculated optical spectra allow for explanation of several previously published experimental results obtained for spherical and self-assembled QD's, such as enhanced 2LO phonon replicas in the

Research paper thumbnail of Optical Phonons in CdS Nanocrystals: Effects of Size, Shape and Packing Density

Research paper thumbnail of Third-Order Optical Nonlinearities in Thin Films of CdS Nanocrystals

physica status solidi (b), 2001

The non-resonant nonlinear optical properties of CdS nanocrystals (NCs) embedded in silica (i) an... more The non-resonant nonlinear optical properties of CdS nanocrystals (NCs) embedded in silica (i) and forming matrix-free (MF) almost close-packed films (ii) were studied using the Z-scan technique. Among the group (i), samples containing NCs covered with a HgS and CuS shell were investigated. The highest value of the nonlinear refractive index n2 ¼ 1.85  10––6 cm2/W was measured for the MF films. This number exceeds by far the value typical for bulk CdS and cannot be explained in terms of thermally induced nonlinearity. Strong enhancement of local fluctuations of the electro-magnetic field in MF films where NCs form aggregates or clusters is suggested to explain this result. Within the group (ii), an enhancement of the nonlinearity was observed under pulsed irradiation for both CdS/HgS and CdS/CuS nanoparticles, compared to CdS NCs without a shell.

Research paper thumbnail of Probing the exciton density of states in semiconductor nanocrystals using integrated photoluminescence spectroscopy

Monatshefte für Chemie …, 2002

We present the results of a comparative analysis of the absorption and photoluminescence excitati... more We present the results of a comparative analysis of the absorption and photoluminescence excitation (PLE) spectra vs. integrated photoluminescence (IPL) measured as a function of the excitation wavelength for a number of samples containing II±VI semiconductor nanocrystals (NCs) produced by different techniques. The structure of the absorption and PL spectra due to excitons con®ned in NCs and dif®culties with the correct interpretation of the transmittance and PLE results are discussed. It is shown that, compared to the conventional PLE, the IPL intensity plotted against the excitation wavelength (IPLE spectra) reproduce better the structure of the absorption spectra. Therefore, IPLE spectroscopy can be successfully used for probing the quantized electron-hole (e-h) transitions in semiconductor nanocrystals.

Research paper thumbnail of Optical bistability of graphene in the terahertz range

Physical Review B, 2014

We use an exact solution of the relaxation-time Boltzmann equation in an uniform AC electric fiel... more We use an exact solution of the relaxation-time Boltzmann equation in an uniform AC electric field to describe the nonlinear optical response of graphene in the terahertz (THz). The cases of monolayer, bilayer and ABA-stacked trilayer graphene are considered, and the monolayer species is shown to be the most appropriate one to exploit the nonlinear free electron response. We find that a single layer of graphene shows optical bistability in the THz range, within the electromagnetic power range attainable in practice. The current associated with the third harmonic generation is also computed.

Research paper thumbnail of Resonant Raman scattering in spherical quantum dots: II-VI versus III-V semiconductor nanocrystals

physica status solidi (b), 2010

Resonant Raman scattering (RRS) in nearly-spherical nanocrystal (NC) quantum dots (QDs) is discus... more Resonant Raman scattering (RRS) in nearly-spherical nanocrystal (NC) quantum dots (QDs) is discussed with respect to the underlying (Fröhlich-type and optical deformation potential, ODP) mechanisms of the exciton-phonon interaction. Their relative contribution for different QD materials, both II-VI and III-V is compared. It is shown that the (usually overlooked) ODP interaction is entirely responsible for an additional peak in the RRS spectra, situated near the transverseoptical (TO) phonon frequency, which has been observed for InP, InAs and, recently, CdTe QDs. RRS spectra calculated using continuum models for confined phonons and excitons and taking into account both interaction mechanisms are in excellent agreement with these experimental data.

Research paper thumbnail of Anomalous first-order Raman scattering in III-V quantum dots: Optical deformation potential interaction

Research paper thumbnail of Absorption and Photoluminescence Study of Cds Quantum Dots: The Role of Host Matrix and Nanocrystal Size and Density

MRS Proceedings, 1999

ABSTRACTIn this paper we present results of the absorption and photoluminescence (PL) of CdSdoped... more ABSTRACTIn this paper we present results of the absorption and photoluminescence (PL) of CdSdoped Si02 films fabricated by RF co-sputtering (semiconductor volume fraction f=1–15%, nano-crystallite's mean size 5–7nm) and matrix-free films of close-packed CdS nanocrystallites (f∼30%, size 2–5nm) produced by an original chemical method. The absorption spectra have been modelled using the modified Maxwell-Garnett model. This gives the e-h pair state energies and evidence of a strong absorption in the glass matrix containing CdS. The temperature dependence of the spectral position and broadening of the PL peak is analysed. It is concluded that a photo-generated hole is captured on an acceptor-type trap before the radiative recombination with a confined electron. The excitation of this ‘band-edge’ PL occurs through some states in the matrix and directly in the CdS crystallites for the two kinds of samples, respectively. The temperature coefficients of the optical transition energies f...

Research paper thumbnail of Resonance energy transfer in self-organized organic/inorganic dendrite structures

Nanoscale, 2013

Förster-type coupling is demonstrated for self-assembled dendrite structures consisting of J-aggr... more Förster-type coupling is demonstrated for self-assembled dendrite structures consisting of J-aggregates and QDs, with energy fluxes directed towards structures' center.

Research paper thumbnail of Cascade upconversion of photoluminescence in ensembles of II-VI semiconductor nanocrystals

physica status solidi (c), 2010

We present the theory of the thermally activated photoluminescence upconversion, also known as an... more We present the theory of the thermally activated photoluminescence upconversion, also known as anti-Stokes photoluminescence (ASPL), based on the quantum dot (QD) polaron effect and explaining all the principal features of the ASPL in colloidal solutions of chemically grown nanocrystals (NCs). The results obtained by Monte-Carlo simulations reproduce all the experimentally observed ASPL trends in colloidal NC solutions and are being extended to dense QD systems, such as films composed by layers of closely packed NCs.

Research paper thumbnail of Modelling of Environment Sensors Based on the Surface Plasmon Resonance Effect

Surface plasmons (SPs) are collective excitations of free electrons in a conducting medium bounde... more Surface plasmons (SPs) are collective excitations of free electrons in a conducting medium bounded by a surface or interface with a dielectric. They can originate surface plasmon-polaritons (SPPs), which are evanescent waves involving electron density oscillations and the associated electromagnetic (EM) field whose amplitude decays exponentially with distance from the surface. SPPs are characterised by a dispersion curve (frequency vs wavevector along the interface) that lies outside of the light cone, so they cannot be excited directly by propagating light; however, it is possible to excite them using the Attenuated Total internal Reflection (ATR) method or a periodic grating. SPs in a confined geometry such as a metallic sphere are localised in space and characterised by discrete frequencies (a single one in the case of sphere, two or three in the case of an ellipsoid). They can be excited directly by propagating light if its frequency coincides with the localised SP frequency, gi...

Research paper thumbnail of Optical bistability of graphene in the terahertz range

Research paper thumbnail of Electron-phonon interaction effects in semiconductor quantum dots:A nonperturabative approach

Research paper thumbnail of Anti-Stokes cooling in semiconductor nanocrystal quantum dots: A feasibility study

physica status solidi (a), 2009

In this review, we discuss the feasibility of laser cooling of semiconductor nanocrystal quantum ... more In this review, we discuss the feasibility of laser cooling of semiconductor nanocrystal quantum dots by phonon-assisted anti-Stokes photoluminescence. Taking into account recent experimental advances, in particular, the development of semiconductor nanocrystals with very high quantum yield, we analyze in detail how the various physical processes in nanocrystals might help or hinder the cooling process. Possible experimental approaches to achieve efficient optical cooling are also discussed.

Research paper thumbnail of A many body study of the SASER dynamics

Microelectronic Engineering, 1998

Research paper thumbnail of Further insight into the temperature quenching of photoluminescence from InAs∕GaAs self-assembled quantum dots

Journal of Applied Physics, 2008

ABSTRACT

Research paper thumbnail of Polaron effect in semiconductor quantum dots: Impact on the optical absorption, up-converted photoluminescence and raman scattering

AIP Conference Proceedings, 2005

Multi-phonon processes in a model quantum dot (QD) containing a small number of most important el... more Multi-phonon processes in a model quantum dot (QD) containing a small number of most important electronic states and several optical phonon modes are considered exactly, taking into account both intra- and inter-level interactions. The calculated optical spectra allow for explanation of several previously published experimental results obtained for spherical and self-assembled QD's, such as enhanced 2LO phonon replicas in the

Research paper thumbnail of Graphene and polarisable nanoparticles: Looking good together?

2016 18th International Conference on Transparent Optical Networks (ICTON), 2016

Several potentially interesting plasmonic effects can arise from combining graphene with polarisa... more Several potentially interesting plasmonic effects can arise from combining graphene with polarisable nanoparticles (NPs), such as metallic or dielectric spheres, related to surface plasmon-polaritons (SPPs) supported by the latter in the terahertz (THz) spectral range. Owing to the electromagnetic coupling between the graphene SPPs and dipole moments of polarisable (nano-) particles deposited on top of it, the optical properties of such a composite system have some new features as compared to its constituents. First, the NP's polarizability is renormalized due to the electromagnetic back action of SPPs which are excited in graphene when an external propagating electromagnetic wave impinges on the particle. The coupling also results in a considerable enhancement of the THz radiation absorption in graphene, while the reflection drops to zero. This effect can be potentially interesting e.g. for cloaking in a certain THz frequency range.

Research paper thumbnail of Dipole-active vibrations confined in InP quantum dots

Physica B: Condensed Matter, 2002

Dipole-active optical phonons confined in nearly spherical InP quantum dots (QDs) were studied th... more Dipole-active optical phonons confined in nearly spherical InP quantum dots (QDs) were studied theoretically and experimentally. Spatial quantization of the phonon modes in an InP QD was considered theoretically by solving the coupled continuous equation of motion and Poisson equation. It is shown that, when the Fröhlich frequency falls into the gap between the bulk LO and TO phonon bands,

Research paper thumbnail of Renormalization of nanoparticle polarizability in the vicinity of a graphene-covered interface

Physical Review B, 2014

We study the electromagnetic properties of a metamaterial consisting of polarizable (nano)particl... more We study the electromagnetic properties of a metamaterial consisting of polarizable (nano)particles and a single graphene sheet placed at the interface between two dielectrics. We show that the particle's polarizability is renormalized because of the electromagnetic coupling to surface plasmons supported by graphene, which results in a dispersive behavior, different for the polarizability components corresponding to the induced dipole moment, parallel and perpendicular to the graphene sheet. In particular, this effect is predicted to take place for a metallic particle whose bare polarizability in the terahertz (THz) region is practically equal to the cube of its radius (times 4πε0). This opens the possibility to excite surface plasmons in graphene and enhance its absorption in the THz range by simply using a monolayer of metallic particles randomly deposited on top of it, as we show by explicit calculations.

Research paper thumbnail of Polaron effect in semiconductor quantum dots: Impact on the optical absorption, up-converted photoluminescence and raman scattering

AIP Conference Proceedings, 2005

Multi-phonon processes in a model quantum dot (QD) containing a small number of most important el... more Multi-phonon processes in a model quantum dot (QD) containing a small number of most important electronic states and several optical phonon modes are considered exactly, taking into account both intra- and inter-level interactions. The calculated optical spectra allow for explanation of several previously published experimental results obtained for spherical and self-assembled QD's, such as enhanced 2LO phonon replicas in the

Research paper thumbnail of Optical Phonons in CdS Nanocrystals: Effects of Size, Shape and Packing Density

Research paper thumbnail of Third-Order Optical Nonlinearities in Thin Films of CdS Nanocrystals

physica status solidi (b), 2001

The non-resonant nonlinear optical properties of CdS nanocrystals (NCs) embedded in silica (i) an... more The non-resonant nonlinear optical properties of CdS nanocrystals (NCs) embedded in silica (i) and forming matrix-free (MF) almost close-packed films (ii) were studied using the Z-scan technique. Among the group (i), samples containing NCs covered with a HgS and CuS shell were investigated. The highest value of the nonlinear refractive index n2 ¼ 1.85  10––6 cm2/W was measured for the MF films. This number exceeds by far the value typical for bulk CdS and cannot be explained in terms of thermally induced nonlinearity. Strong enhancement of local fluctuations of the electro-magnetic field in MF films where NCs form aggregates or clusters is suggested to explain this result. Within the group (ii), an enhancement of the nonlinearity was observed under pulsed irradiation for both CdS/HgS and CdS/CuS nanoparticles, compared to CdS NCs without a shell.

Research paper thumbnail of Probing the exciton density of states in semiconductor nanocrystals using integrated photoluminescence spectroscopy

Monatshefte für Chemie …, 2002

We present the results of a comparative analysis of the absorption and photoluminescence excitati... more We present the results of a comparative analysis of the absorption and photoluminescence excitation (PLE) spectra vs. integrated photoluminescence (IPL) measured as a function of the excitation wavelength for a number of samples containing II±VI semiconductor nanocrystals (NCs) produced by different techniques. The structure of the absorption and PL spectra due to excitons con®ned in NCs and dif®culties with the correct interpretation of the transmittance and PLE results are discussed. It is shown that, compared to the conventional PLE, the IPL intensity plotted against the excitation wavelength (IPLE spectra) reproduce better the structure of the absorption spectra. Therefore, IPLE spectroscopy can be successfully used for probing the quantized electron-hole (e-h) transitions in semiconductor nanocrystals.

Research paper thumbnail of Optical bistability of graphene in the terahertz range

Physical Review B, 2014

We use an exact solution of the relaxation-time Boltzmann equation in an uniform AC electric fiel... more We use an exact solution of the relaxation-time Boltzmann equation in an uniform AC electric field to describe the nonlinear optical response of graphene in the terahertz (THz). The cases of monolayer, bilayer and ABA-stacked trilayer graphene are considered, and the monolayer species is shown to be the most appropriate one to exploit the nonlinear free electron response. We find that a single layer of graphene shows optical bistability in the THz range, within the electromagnetic power range attainable in practice. The current associated with the third harmonic generation is also computed.