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...
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...
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
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,
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
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.
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...
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...
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
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,
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
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.
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