We present calculation results of multi-color spontaneous emission from quantum-dot-quantum-well semiconductor heteronanocrystals. Our theoretical results explain experimental results of onion-like spherical system similar to: CdSe (core), ZnS (shell), CdSe (shell) spherical quantum dots surrounded by ZnS. We demonstrate influence of shell thickness to exciton localization in distinct layers of heteronanocrystals. Multi-color emission of such heterosystem is determined by l=0, n=1 state localization in CdSe core and by l=0, n=2 state localization in CdSe shell.
Binding energy of a hydrogenic impurity located at the center of the CdTe/ZnTe spherical quantum dot has been calculated under the effective mass approximation by solving Schrödinger equation analytically. Eigen energies are expressed in terms of the Whittaker function and Coulomb wave function. The results show that impurity binding energy strongly depends on QD size if it is around one effective Bohr radius.
The theoretical investigation of the electron and hole spectra in a quantum dot with a linearly graded composition within the effective mass approximation is presented. The particular example is β-HgS surrounded by CdS. β-HgS core of radius r_C is surrounded by concentric spherical layers each of Hg_{1-x}Cd_{x}S composition (x is function of r) and finally, form radius r_S by CdS. The existence of these intermediate layers, as model of graded composition, influences rapidly electron and hole spectra.
The energy spectra of an electron in open spherical quantum dot (QD) within the effective mass approximation (EMA) and rectangular potential model is presented. Energy structure of quantum dots is important because of their possible applications in electronic and optoelectronic devices. For proper description and interpretation of tunneling processes knowledge of resonant states of quantum dots is necessary. Energy values depend on parameter like size of system and spatial composition. The lifetimes of the quasistationary states are computed within the framework of the scattering S-matrix method. It is shown how core radius and barrier thickness for the CdTe/ZnTe/CdTe example influence electron states and their lifetimes.
In this paper we present Raman scattering and photoluminescence spectra measured on CdTe/ZnTe self assembled quantum dots. The photoluminescence spectrum has shown two main emission peaks, both connected with existing of quantum dots. One presents direct deexcitation to ground state and the other is optical phonon (οmega = 207.3 cm^{-1})-assisted deexcitation. The registered multiphonon emission process depends on temperature. At low temperature phonon spectra shows line at 450 cm^{-1} (TA + 2LO in ZnTe) and 595 cm^{-1} (2LO + TO(Γ) in ZnTe).
We present far-infrared reflection spectra of Pb_{0.95}Mn_{0.05}Te single crystal doped with gallium between 10 and 300 K. The analysis of the far-infrared reflection spectra was made by a fitting procedure based on the model of coupled oscillators. Together with the strong plasmon-phonon coupling we obtain three local modes of gallium at about 122 cm^{-1}, 166 cm^{-1}, and 192 cm^{-1}. The position of these modes depends on impurity center charge, and their intensity depends on temperature.
In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1× 10^{19} at./cm^{3}. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm^{-1}. The modes at 126 and 143 cm^{-1}, which are also observed in other telluride compounds, originate from vibrations in TeO_2. We assume that the mode at about 181 cm^{-1} is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni^{3+} state). Modes at about 362 cm^{-1} and 724 cm^{-1} are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
Far-infrared and magnetic properties of Ni doped PbTe (Z_Ni = 1× 10^{19} at./cm^{3}) single crystal are investigated in a broad range of temperature and magnetic fields. Far-infrared reflection spectra were analyzed using a fitting procedure based on the modified plasmon-two phonon interaction model. Together with the strong plasmon-two longitudinal optical phonon coupling we obtained a local mode of Ni at about 180 cm^{-1}. This mode intensity depends on temperature. Magnetic measurements shows that PbTe alloys doped with Ni reveals weak ferromagnetic interaction between magnetic ions.
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