Excited-state absorption of excitons confined in CuCl quantum dots (original) (raw)
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EXTREMELY-NARROW LINEWIDTH OF THE CONFINED EXCITONS IN CuCl QUANTUM DOTS
1998
Homogeneous linewidth of the excitons confined in CuCl quantum dots embedded in a NaCl crystal was studied by heterodyne-detected accumulated photon echo technique. At 2K, photon echo signal shows an exponential decay with a decay time of 160ps except for a slow rise. The homogeneous linewidth calculated from the dephasing time was found to be much smaller than that reported previously by the other methods. At 1.5K, we observed the linewidth of 1.6μeV. As far as we know, this is the narrowest exciton linewidth in quantum dots.
Biexciton and Triexciton States in Quantum Dots in the Weak Confinement Regime
Physical Review Letters, 1997
Biexciton and triexciton states in CuCl quantum dots were studied by means of time-resolved size-selective pump-and-probe technique. A clear induced absorption band is observed on the highenergy side of the excitation photon energy. The new induced absorption is assigned to the transition from the exciton ground state to one of the weakly correlated exciton pair states which were theoretically predicted to exist and to play an important role in nonlinear optical processes. Its pump energy dependence and temporal evolution strongly support this assignment. Under high-density or two-color excitation condition, a triexciton state in quantum dots is observed for the first time.
Exciton States Spectroscopy in Quasi - Zero - Dimensional Nanostruсtures: Theory
Optics, 2014
The theory of exciton states in a quantum dot under conditions of dominating polarization interaction of an electron and a hole with a spherical (quantum dot-dielectric matrix) interface is developed. An shown, that the energy spectrum of heavy hole in the valence band quantum dot is equivalent to the spectrum of hole carrying out oscillator vibrations in the adiabatic electron potential. In the framework of the dipole approximation studied interband absorption of light in a quasi-zero-dimensional nanosystems. We show that the absorption and emission edge of quantum dots is formed by two transitions of comparable intensity from different hole size-quantization levels and into a lower electron sizequantization level. Propose a theoretical prospect of using hole transitions between equidistant series of quantum levels observed in nanocrystals for desining a nanolaser.
Exciton Spectroscopy of Spatially Separated Electrons and Holes in the Dielectric Quantum Dots
Crystals
It is shown that in the potential energy of an exciton of spatially separated electrons and holes (hole moves in the amount of quantum dots (QDs), and the electron is localized on a spherical surface section (QD-dielectric matrix)) taking into account centrifugal energy gives rise band of the quasi-stationary surface exciton states that with the increase of the radius of QD becomes stationary state. The mechanisms of formation of the spectra of interband and intraband absorption (emission) of light in nanosystems containing aluminum oxide QDs, placed in the matrix of vacuum oil, are presented. It is shown that the electron transitions in the area of the surface exciton states cause significant absorption in the visible and near infrared wavelengths, and cause the experimentally observed significant blurring of the absorption edge.
SOP Transactions on Theoretical Physics, 2014
The theory of an exciton formed from spatially separated electron and hole (the hole is in the quantum dot volume, and the electron is localized at the outer spherical quantum dotdielectric matrix interface) is developed within the modified effective mass method. The effect of significantly increasing the exciton binding energy in quantum dots of zinc selenide, synthesized in a borosilicate glass matrix, relative to that in a zinc selenide single crystal is revealed. It was shown that the short-wavelength shift of the peak of the low-temperature luminescence spectrum of samples containing zinc-selenide quantum dots, observed under the experimental conditions, is caused by quantum confinement of the ground-state energy of the exciton with a spatially separated electron and hole.
Stochastic treatment of the dynamics of excitons and excitonic molecules in CuCl nanocrystals
Physical Review B, 1996
Dynamics of excitons and excitonic molecules in CuCl nanocrystals were investigated by means of both picosecond time-resolved luminescence and femtosecond transient absorption. Stochastic as well as rateequation treatments are made to explain the temporal changes of both luminescence and absorption. In the stochastic treatment, a Monte Carlo simulation is made for 10 5 nanocrystals with the initial condition that the exciton number distribution follows the Poisson distribution. The stochastic treatment satisfactorily explains all the experimental results, while the rate-equation treatment does not. Success of the stochastic treatment shows the unique property of the dynamics of excitons and excitonic molecules in quantum dots arising from discreteness of the exciton number. ͓S0163-1829͑96͒04120-3͔
Absorption spectra of small semiconductor quantum dots
1999
The density matrix approach has been employed to analyze the pump-probe spectroscopic absorption spectra of small semiconductor nanocrystals popularly known as quantum dots (QDs) under the strong confinement regime (SCR) with sizes smaller than the bulk exciton Bohr radius such that the Coulombic interaction energy becomes negligible in comparison with the confinement energy. The average time rate of absorption has been obtained by incorporating the radiative and nonradiative decay processes as well as the inhomogeneous broadening arising due to nonuniform QD sizes. The analytical results are obtained for QDs duly irradiated by a strong near-resonant pump and a broadband weak probe. Numerical estimations have been made for: (i) isolated QDs and (ii) QD-arrays of GaAs and CdS. The results agree very well with the available experimental observations in CdS QDs. The results in the case of GaAs QDs can lead one to experimentally estimate absorption/gain spectra in the important III-V semiconducting microscopic structures.
Size Selective Excitonic Transition Energies in Strongly Confined CdSe Quantum Dots
Journal of Nanoscience and Nanotechnology, 2011
We report on the synthesis of CdSe nanocrystal quantum dots (QDs) of different radii (R). Size dependent optical properties like increase in the confinement energy with decreasing radius for different excitonic transitions are studied. Different excitonic transitions are calculated from the second derivative of UV-vis absorption spectra of as synthesized CdSe QDs. The transitions are assigned to specific states by calculating the transition energies using effective mass approximation. A close matching of the transition energies with the experiment suggesting that the second derivative of the absorption spectra could provide a direct knowledge of the electronic transition for the direct band gap semiconductor quantum dots.