Publications de Victoria Ciulin

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Time-resolved fluorescence spectra for C60 mols. embedded in Ne and Ar matrixes and C70 in Ne matrixes were recorded using a synchroscan streak camera. In the case of C60, the decay times of the S1 state are identical for all fluorescence bands confirming that it is a state of mixed T1g, T2g, and Gg characters. Its lifetime is detd. by the intersystem crossing rate to the triplet manifold which increases in going from Ar to Ne matrixes. This is attributed to a change of the dominant symmetry character of S1

Photoluminescence of p-type modulation doped (Cd,Mn)Te quantum wells is studied with carrier density up to 5 X 10(11) cm(-2) at various spin splittings. This splitting can be made larger than the characteristic energies of the system thanks to the giant Zeeman effect. At small spin splitting and regardless of the carrier density, the photoluminescence exhibits a single line, which corresponds to the charged exciton in the singlet state. Above a certain spin splitting, the charged exciton is destabilized in

We have studied experimentally the radiative lifetimes of negatively charged excitons (X-) and neutral excitons (X) in GaAs and CdTe quantum wells. Despite the different optical properties (e.g. trion binding energies) and the different quantum well structures of the studied samples, we find quite similar X- lifetimes in the range of 45 to 60 ps. On the other side, the X lifetimes are very different and influenced by the material. For relatively low electron concentrations, the X- lifetime is found to be co

We present a systematic study of the oscillator strength of the positively charged excitons (X+) in Cd1-xMnxTe quantum wells. CW-absorption and time-resolved photoluminescence measurements were combined as two approaches for the determination of the oscillator strength. By varying (in a small magnetic field) the spin subband hole distribution at constant total concentration, we observe an increase of the oscillator strength in absorption, proportional to the hole concentration in one spin subband (the one w

Using reflectivity and picosecond time-resolved photoluminescence, we have studied the intrinsic optical properties of negatively charged excitons in modulation doped CdTe quantum wells. In emission, we observe simultaneously a low energy exponential tail in the charged exciton spectral line and a linear increase of its radiative lifetime with temperature. In absorption, we find a consistent decrease of the charged exciton oscillator strength with temperature. For low electron concentrations these observati

Interactions among excitons, trions, and electrons are studied in CdTe modulation-doped quantum wells. These many-body interactions are investigated through the nonlinear dynamical properties in the excitonic complexes using time and spectrally resolved pump and probe techniques. This study is performed as a function of temperature and densities of excitons, trions, and electrons. The results reveal that the nonlinearities induced by trions differ from those induced by excitons and moreover they are mutuall

We have observed marked oscillations in the time-resolved photoluminescence of a semiconductor microcavity under non-resonant excitation conditions. Hot excitons, created with an ultrashort light pulse, rapidly relax into polaritons in the cavity with a large in-plane momentum K. Shortly after illumination, above a certain excitation power, the polaritons accumulate into an energy trap at the bottom of the dispersion and the light emission, governed by final-state stimulated scattering, starts at K similar

We report on the nonlinear optical dynamical properties of excitonic complexes in CdTe modulation-doped quantum wells, due to many-body interactions among excitons, trions, and electrons. These were studied by time and spectrally resolved pump-probe experiments. The results reveal that the nonlinearities induced by trions differ from those induced by excitons, and in addition they are mutually correlated. We propose that the main source of these subtle differences comes from the Pauli exclusion-principle th

Using time-resolved photoluminescence, we have investigated the radiative behavior of neutral and negatively charged excitons in CdTe-based quantum wells. We find that the photoluminescence of negatively charged excitons can be well reproduced by a model of delocalized and thermalized three-particle complexes. A large radiative zone in k-space results from the transfer of the charged exciton momentum to the remaining electron (recoil effect). On the other hand, the photoluminescence decay of excitons is not

We study the dynamics of the charged and neutral excitons in a modulation-doped GaAs quantum well by time-resolved photoluminescence under a resonant excitation. The radiative lifetime of the charged exciton is found to be surprisingly short, 60 ps. This time is temperature independent between 2 and 10 K, and increases by a factor of 2 at 6 T. We discuss our findings in view of present theories of exciton radiative decay. [S0163-1829(98)03143-9].

We report on time-resolved photoluminescence studies of charged and neutral excitons in a modulation doped GaAs quantum well under resonant excitation and high magnetic field. The radiative lifetime of the charged exciton is rather short, 60 ps at zero held, and is found to increase by a factor of similar to 2 up to 7 T. The short lifetimes suggest that, under magnetic field, the exciton bound in the trion is delocalized. (C) 1998 Elsevier Science B.V. All rights reserved.

The formation dynamics of charged excitons is studied in CdTe-based quantum wells by picosecond time-resolved photoluminescence. The formation time is obtained by an analysis of temporal behavior of photoluminescence signal after excitation in resonance with either neutral or charged exciton. It is shown that the formation time varies strongly when changing the electron concentration. We also demonstrate that the localization of neutral excitons has strong impact on the formation time of charged exciton and

We present the results of a study of the dynamics of trions and excitons in a CdTe modulationdoped quantum well as a function of temperature in the low-density regime. Using three-pulse four-wave mixing technique, we show that, at low temperature, these quasi-particles are inhomo-geneously broadened and localized due to disorder effects. At higher temperatures, trions and excitons are mobile and their homogeneous broadening is largely increased as a result of acoustic phonon scattering. Consistently, time-r

We investigate the spin relaxation of negatively charged excitons in modulation-doped CdTe quantum wells by time-resolved photoluminescence. The charged exciton spin flip process is found to be very sensitive to the excitation energy but not to a change of electron concentration. We exclude the Bir-Aronov-Pikus mechanism, which is based on the exchange interaction, as responsible for the X- spin flip.

The intramol. energy relaxation processes of UV-excited C60 mols. embedded in Ar crystals were studied by picosecond fluorescence studies and femtosecond pump-probe absorption spectroscopy. The various internal energy relaxation steps are clearly identified. The importance of intramol. energy relaxation processes in solid C60 films is underlined. [on SciFinder (R)]

Excitons and trions in a CdTe modulation-doped quantum well are investigated by picosecond three-pulse four-wave mixing experiments as a function of temperature in the low-density regime. We show that trions are mobile for high enough temperatures. The diffusivity of trions and excitons increases with temperature but, like their mobilities, is limited by acoustic-phonon scattering. Consistently, studying the decay of the interband coherence reveals an increase of the homogeneous broadening as the temperatur

A brief review is given of optical experiments related to the creation and recombination of charged excitons. The fundamental parameters of these states are discussed. This includes their energies, optical transition probabilities, and characteristic times of their formation, thermalisation, and decay. A model of free three-particle charged exciton is shown to describe correctly the results of many experiments. The applicability range of the model is limited by many body effects at higher carrier concentrat

We investigate the nonlinear optical dynamics of excitons and trions in CdTe modulation-doped quantum wells by time and spectrally resolved pump-probe experiments. We find that the nonlinearities induced by excitons are different from those due to the presence of the trions. From a comparison between the exciton and trion behaviours, we show that, at low temperature, trions are formed from excitons in about 10 picoseconds and, as the temperature is increased, a thermal equilibrium is reached between exciton

The dynamics of excitons and trions in CdTe modulation-doped quantum wells are studied as a function of temperature by three-pulse four-wave mixing experiments. It is shown that trions are localized by interface roughness scattering and/or by the remote ionized donor potential at low temperature in the low-density regime. The diffusivity of excitons and trions increases with temperature but their mobilities are limited by acoustical phonon scattering, The coherence study reveals that the system is inhomogen

Victoria Ciulin

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Picosecond studies of the intramolecular relaxation processes in isolated C60 and C70 molecules

Photoluminescence of p-doped quantum wells with strong spin splitting

Radiative lifetime of negative trions in GaAs and CdTe quantum wells

Oscillator strengths of charged excitons: combining magnetoabsorption and photoluminescence dynamics in semimagnetic quantum wells

Radiative behavior of negatively charged excitons in CdTe-based quantum wells: A spectral and temporal analysis

Many-body interaction evidenced through exciton-trion-electron correlated dynamics

Oscillatory behaviour in the nonlinear emission of semiconductor microcavities

Interacting many-body systems in quantum wells: Evidence for exciton-trion-electron correlations

Negatively charged excitons in CdTe-based quantum wells: A time-resolved study

Charged exciton dynamics in GaAs quantum wells

Dynamics of charged excitons in GaAs quantum wells under high magnetic field

Formation time of negatively charged excitons in CdTe-based quantum wells

Trions and excitons in CdTe quantum wells: Lifetimes, coherence, diffusion and localization

Spin relaxation of negatively charged excitons in CdTe quantum wells

Picosecond and femtosecond studies of the energy redistribution in matrix-isolated C60 molecules

Diffusion, localization, and dephasing of trions and excitons in CdTe quantum wells

Optical studies of charged excitons in II-VI semiconductor quantum wells

Picosecond dynamics of neutral and charged excitons in semiconductor quantum wells

Nonlinear optical dynamics of excitons and trions

Dynamics of excitons and trions in CdTe quantum wells: Direct observation of diffusion and localization