Oscillator strengths, transition probabilities and state lifetimes of on- and off-center donor impurities in quantum dots: off-center displacement, quantum size and potential-shape effects

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Non-relativistic energy levels, binding energies and oscillator strengths of CdSe⁄ZnT e core/shell spherical quantum dots with or without impurities submitted to an external magnetic ﬁeld have been investigated by using a B-spline based variational method, within the framework of the eﬀective mass approximation. In the case where the system contains hydrogenic impurity, the eﬀects of its oﬀ-center displacement combined to the height of the conﬁning potential have also been studied. The dielectric constant as well as the eﬀective mass are considered to be dependent on the radius. The modiﬁcations occurring due to the presence of the magnetic ﬁeld have been analyzed. We have found that the electronic and optical properties are strongly aﬀected by the magnetic ﬁeld strength, the spatial conﬁnement and the oﬀ-center displacement. The oscillator strengths and the binding energies increase with the magnetic ﬁeld, but its eﬀect on the binding energies (both ground and excited states) is dimmed by the reduction of the core-to-shell radii ratio and the increase of the oﬀ-center displacement to the vicinity of the shell. However, the oscillator strengths increase with the magnetic ﬁeld when the oﬀ-center displacement increases towards the shell.

Section: Energy Levels and Binding Energiesmentioning

confidence: 64%

Binding energies, oscillator strengths of core/shell spherical quantum dots with or without on- or off-center donor impurities under an external magnetic field

Aboulaï¹,

Melono²,

Doba³

et al. 2022

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“…^where τ is the relaxation lifetime. M , i j k k represents the dipole transition matrix elements which depends on the polarization direction [46][47][48]. In case of parallel polarization [46],…”

Section: Third Order Nonlinear Optical Susceptibility (Tonos)mentioning

confidence: 99%

Effects of the magnetic field and the off-center displacement on the third-order nonlinear optical susceptibility of inverted core/shell spherical one-electron quantum dots

Negoukoumé Abdoulaï,

Melingui Melono,

Motapon

2023

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The third order nonlinear optical susceptibility (TONOS) of an inverted ZnS/CdSe core–shell spherical quantum dot embedded in SiO 2-matrix with or without impurity, and subjected to an external magnetic field is investigated. Within the framework of effective mass approximation and using B-splines basis functions, the energy levels, the dipole matrix elements and the TONOS are computed. The dielectric mismatch in the interface dots as well as the effective mass dependence on the core and shell regions are taken into account. It is revealed that, simultaneously the shell size, magnetic field and off-center displacement have a noticeable effect on the positions and the heights of the peaks of the TONOS. Moreover, we have shown that, due to the magnetic field and the off-center displacement effects, the TONOS takes different profiles associated with the polarization direction (parallel and perpendicular). In the perpendicular polarization, two peaks of the nonlinear optical properties appear for each off-center displacement value corresponding to the two transversal allowed transitions. The shift towards higher energies of the peak position and the reduction of the intensity of the peak when the magnetic field increases are recorded in the transversal transition case. Furthermore, in the longitudinal transition, as increasing the magnetic field strength, the intensity of the peak of the TONOS grows and the position of the peak is shifted towards lower frequencies. The dielectric constant, effective mass and conduction band offset of the materials that constitute the core and shell are equally found to modify significantly the main features of the susceptibility.

“…The electric dipole polarizability, due to its usefulness in the testing of the accuracy of the wave functions and energies on the one hand, and on the other hand, in the understanding of the electron cloud configuration, is also investigated. The specificity of this study is also found on the consideration of a form of the confining potential which has appropriate parameters whose definition allows to configure the quantum dot shape [8,23]. The effect of changing the material properties, such as effective mass and permittivity of the medium is also analyzed.…”

Section: Introductionmentioning

confidence: 99%

Shape and quantum size effects on the electronic structure, oscillator strengths and state lifetimes of helium-like quantum dots

Doba,

Melingui Melono,

Motapon

2023

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Transition energies, electric static polarizability, oscillator strengths and state lifetimes of helium-like quantum dots are determined as a function of their shape and size. A configuration interaction approach based on B-spline functions is used. We found that, the oscillator strengths present an extremum around a low value of the dot radius whatever the shape of the confining potential. This extremum is due to the pressure on the energy levels in such a way that for a particular value of the dot radius, the second electron in the excited one-electron state reaches the borders of the confinement potential. The extremum position depends on the impurity charge and the oscillator strength value at this point changes with the potential well shape. As well, the increase of the effective mass involves the shift of the position of the oscillator strength extremum towards weak radius values. The first excited state lifetime globally increases with the dot radius and the reduction of the nuclear charge but presents a shoulder for a certain low value of the dot radius mostly marked for a triangular form of the confining potential.