Search

Let G be a finite group and H a subgroup of G. We say that H is s-semipermutable in G if $$HG_{p}=G_{p}H$$ for any Sylow p-subgroup $$G_{p}$$ of G with $$(p,|H|)=1$$ . In this paper, we consider the s-semipermutability of prime-power order subgroups and prove the following result which generalizes some known results concerning s-semipermutable subgroups. Theorem: Suppose that p is a prime dividing the order of a finite group G and E is a normal subgroup of G. Then, $$E\le Z_{{\mathcal {U}}_p}(G)$$ , if there exists a normal subgroup X of G, such that $$F_p^*(E)\le X\le E$$ , and a Sylow p-subgroup P of X satisfies: Finally, we also prove a partially generalized version of this theorem, which extends some results in [Y. Berkovich and I.M. Isaacs, p-supersolvability, and actions on p-groups stabilizing certain subgroups, J. Algebra 414 (2014) 82–94.] and [L. Miao, A. Ballester-Bolinches, R. Esteban-Romero, and Y. Li, On the supersoluble hypercentre of a finite group, Monatsh.Math. 184 (2017), no. 4, 641–648].

To explore the role of microRNA-203 in laryngeal cancer and its underlying mechanism in regulating cell invasion and apoptosis.MicroRNA-203 expression in laryngeal cancer tissues and paracancerous tissues was detected by quantitative real time-polymerase chain reaction (qRT-PCR). The regulatory effects of microRNA-203 on the invasion and apoptosis of laryngeal cancer cells were detected by transwell assay and flow cytometry, respectively. Dual-Luciferase reporter gene assay was performed to access the binding condition of microRNA-203 and LASP1. Both mRNA and protein levels of LASP1 in laryngeal cancer cells were detected after transfection with microRNA-203 mimic or microRNA-203 inhibitor by qRT-PCR and Western blot, respectively. Rescue experiments were finally performed to detect whether microRNA-203 regulates laryngeal cancer development via targeting LASP1.MicroRNA-203 was lowly expressed in laryngeal cancer tissues and cell lines. MicroRNA-203 knockdown in Hep-2 cells can promote the invasion and inhibit the apoptosis of laryngeal cancer cells. Subsequently, LASP1 was predicted to be the target gene of microRNA-203, which was further verified by the Dual-Luciferase reporter gene assay. LASP1 expression was negatively regulated by microRNA-203. Furthermore, rescue experiments showed that the regulatory effects of microRNA-203 on the invasion and apoptosis of laryngeal cancer cells were reversed by LASP1.We showed that lowly expressed microRNA-203 could promote the invasion and inhibit apoptosis of laryngeal cancer cells via inhibiting LASP1.

With the aim to get optimised resistive switching properties, the influence of oxygen vacancy concentration of Nb:SrTiO3 (NSTO) on the resistive switching properties of Ag/NSTO/Ti structure was studied. To obtain the NSTO with different oxygen vacancy concentrations, the substrates had been annealed in different atmospheres and temperatures before they were used to fabricate Ag/NSTO/Ti structure. The resistive switching properties were investigated by measuring I–V characteristics, endurance ability and resistance distribution at room temperature. The results show that both annealing in oxygen atmosphere and vacuum atmosphere degraded the switching properties. In our case, the device annealed in air at 700°C displayed the best resistive switching behaviour. After analysis, we suggest that both Schottky barrier height and barrier width, which can be tuned by changing the oxygen vacancy concentration, play important roles in getting high quality resistive switching property.

Au/Nb:SrTiO3/Ti structures were fabricated by depositing Au and Ti electrodes on a single crystal 0.5 wt% Nb:SrTiO3 (NSTO) using rf-magnetron sputtering technique. Resistive switching properties at different temperature were investigated. The Ti/NSTO interface was ohmic contact, which indicated that the resistive switching behavior was attributed to Au/NSTO interface. The resistive switching behavior happened only at the temperature above 180 K, which was possibly caused by the increase of Schottky barrier height with the increase of temperature. The structure showed a semiconductor behavior at high-resistance state (HRS) and a metallic behavior at low-resistance state (LRS). The switching conduction mechanism of Au/NSTO/Ti device is primarily described as space-charge-limited conduction (SCLC) according to the electrical transport properties measurement.

Ag/0.7 wt% Nb-doped SrTiO3 (Nb:STO)/Ti structure was prepared by sputtering Ag and Ti electrodes on a Nb:STO single crystal substrate and the resistance switching (RS) properties were investigated. Reversible multilevel resistance switching behavior was obtained by applying different voltages. The resistance switching (RS) effect comes from the Schottky barrier existed between Ag and Nb:STO interface. The multilevel switching mechanism may be related to the different number of electrons trapped or detrapped by oxygen vacancies (Vo 2+) at the Ag/Nb:STO interface, which can change the width of depletion layer. The temperature dependence on resistance of Ag/Nb:STO/Ti suggests that both high resistance state (HRS) and low resistance state (LRS) are of semiconductor behavior. Substrate annealing in vacuum degrades the RS properties of Ag/Nb:STO/Ti structure due to the increase of Vo 2+ in Nb:STO.

To investigate the relationship between the preoperative coronal intervertebral angle changes and postoperative trunk shift (TS) in patients who received congenital scoliosis correction.The data of 921 patients with congenital scoliosis, who received posterior congenital scoliosis correction and internal fixation, was retrospectively analyzed. Anteroposterior (AP) whole spine standing radiographs and right and left lateral bending radiographs were taken preoperatively, and AP whole spine standing radiographs were obtained postoperatively and at the final follow-up. TS was measured in the coronal plane, and intervertebral angle change was the sum of the absolute values of L4-S1 intervertebral angle changes in the coronal plane, and was determined before surgery, postoperatively, and at final follow-up.A total of 38 patients with a mean age of 16.42±8.36 years old and a mean follow-up of 12.4 months (range, 6 to 36 months) were included. A median negative correlation were found between TS at the final follow-up and total variance of bending (r=-0.51, P=0.001). Groups were defined by two methods: coronal intervertebral angle changes ≥10° or10°, and final follow-up TS20 mm or ≥ 20 mm. TS at the final follow-up was significantly greater in the10° group than the ≥10° group (32.45 vs 12.44 mm, P=0.001), and coronal intervertebral angle changes was significantly greater in the TS20 mm group than the ≥ 20 mm group (14.2° vs 6°, P=0.001).Postoperative TS which will not compensate spontaneously can be predicted by measurement of the preoperative intervertebral interspace angle in the congenital scoliosis lumbosacral region.

Recently, the application of surface-mounted magnet brushless machines to EVs/HEVs is extensively researched. In this paper, the performance of such kind of brushless motor which has a trapezoidal back-emf waveform when operated in BLDC and BLAC modes is evaluated, in both constant torque and flux-weakening regions, assuming (a) the same torque, (b) the same peak current, and (c) the same rms current. It is shown that although the motor has an essentially trapezoidal back-emf waveform, the output power and torque when operated in the BLAC mode in the flux-weakening region are significantly higher than that can be achieved when operated in the BLDC mode due to the influence of the winding inductance and back-emf harmonics.

The exciton dynamics in InxGa1−xAs/GaAs quantum wells grown on (111)B and (100) GaAs substrates were studied by time-resolved photoluminescence (PL) under magnetic fields in a Faraday configuration. We have found that the piezoelectric fields in (111)B samples affect the transient behavior of the PL spectra. Compared with the reference (100) sample, we have found that the strong piezoelectric fields, as well as the magnetic fields, cause a slower spin–flip process in (111)B strained quantum wells.

Radiative and non-radiative recombination processes of excitons in quantum dots of diluted magnetic semiconductors were studied in magnetic fields. The Cd1−xMnxSe quantum dots fabricated by the self-organized mode on ZnSe showed marked increases of the photoluminescence intensity and the decay time in the magnetic field. These phenomena are related to the magnetic field induced shrinkage of the exciton Bohr radius.

Using the pulsed excitation with a femtosecond laser and streak-camera detection we have studied the processes of spin relaxation in the system of localized excitons in low dimensional superlattices formed by the insertion of CdSe submonolayers into the ZnSe matrices. Polarization of exciton luminescence in the magnetic field arises due to the thermal redistribution of population in the system of splitted exciton spin sublevels. The distribution of polarization across the PL band countour is governed by the complicated interplay of energy and spin relaxation processes. The study of PL decay kinetics in polarized light allows us to determine with the help of a simple two-level model the times of exciton spin relaxation. Spin relaxation times strongly decrease with the increase of magnetic field indicating the phonon assisted mechanism of spin relaxation. The detailed analysis of the dependence of spin relaxation times on the exciton localization energy is not possible with the model used due to the complicated character of exciton population kinetics for deeply localized states. Deeply localized states are to a great extent populated through the tunnelling relaxation of excitons with higher energies. The transfer of polarization in the processes of exciton energy relaxation has been clearly observed in the study of spectrally resolved decay kinetics in polarized light.

We report an experimental evidence of the existence of free excitonic magnetic polaron (FEMP) states from the study of the dynamics of free and bound excitons in Cd 1−x Mn x Te (x=0.03) by time-resolved photoluminescence measurements. We found, for the first time, that FEMP are more stable than the polarons formed from bound excitons. The polaron binding energy for the free excitons is evaluated to be 4 meV , which is considerably larger than that of 1 meV found for the magnetic polarons of the bound excitons; these values were determined from the suppression of the excitonic energy relaxation in high magnetic fields. As a consequence, the peak energies of the optical emissions of free excitons and donor-bound excitons cross in the time-resolved photoluminescence spectra.

Optical pump-probe experiments were carried out in Cd1−xMnxTe/ZnTe multiple quantum wells to study the dynamics of the excitons and the exciton magnetic polarons in these materials. In the pump-probe spectra, three signals were detected. The main signal is negative and monitors the energy relaxation of the excitons created by the pump pulse. The two other pump-probe signals are positive and their intensity grows during the time when the excitons created by the pump pulse recombine. The low-energy positive pump-probe signal is found to track the average Mn spin polarization in the sample. Experiments performed with circular polarization show that long-range order is induced by a sufficiently intense pump beam. But in our samples, the spins of the excitons are found to be oriented mainly antiparallel to the long-range magnetization generated after the pump excitation. Furthermore, we found that, at high excitation densities, the excitons couple antiferromagnetically to the long-range ‘background’ magnetization of the Mn spins.

The formation of a spin superlattice structure was realized in Cd0.95Mn0.05Te/Cd0.95Mg0.05Te under a magnetic field. The experimental evidence of the spin superlattice structure was found from time-resolved polarized magneto-photoluminescence measurements, in the Zeeman splittings and the exciton magnetic polaron formation. The Zeeman splitting directly indicates the spatial separation of spin-up and spin-down electrons and heavy holes, which are localized in the Cd0.95Mg0.05Te and Cd0.95Mn0.05Te layers, respectively. The formation of exciton magnetic polarons under a magnetic field can be attributed to the spin-dependent confinement where a large polaron binding energy of 3.5 meV has been observed in 2.5 T to be enhanced by the field-induced localization of the excitons.

We carried out time-resolved magneto-photoluminescence experiments in diluted magnetic semiconducting Cd1−xMnxTe MBE grown epilayers to study the excitonic localization mechanisms. We found that, for samples with a high non-radiative recombination rate, the luminescence intensity and the decay time decrease significantly under a magnetic field. This shows that the magnetic localization dominates over the non-magnetic localization when magnetic polarons are formed.

We present optical pump–probe experiments carried out in Cd1—xMnxTe/ZnTe multiple quantum wells to study the dynamics of excitons, exchange-coupled to Mn spins in the form of magnetic polarons. From the analysis of the transient absorption spectra, we found that the magnetic polaron formation a) suppresses the formation of biexcitons (this simplifies the lineshape analysis of the pump–probe spectra) and b) retards the energy relaxation of the excitons by 14 ps in these semimagnetic structures.

We demonstrate a new technique to grow high-quality CdSe quantum films and islands with a very small sulfur contamination by using a cadmium sulfide compound source as Cd supply and additional Se flux. By monitoring the lattice constant with reflection high-energy electron diffraction, it is shown that the sulfur is almost completely substituted by Se and CdSe with a contamination below 5% sulfur is formed. The quantum structures obtained by the new method are generally of higher quality than those obtained by more conventional growth methods using elemental sources, even if migration enhanced methods were employed. With a brief growth interruption or post-growth annealing step the initially smooth CdSe layer can be reorganized into islands. The duration of this step as well as the initial amount of deposition allows a rather good control over the island formation. A strongly enhanced growth rate is observed for the first few monolayers of the ZnSe capping layer, which indicates a partial dissolution of the islands in the ZnSe growth front and Cd segregation.

Nanometer-scale structures of II-VI diluted magnetic semiconductors were synthesized by the microfabrication techniques. Quantum dots of Cd 1 -x Mn x Se (x = 0.03) with diameters of 9.0-9.4 nm were grown by the self-organized mode in the molecular beam epitaxy. Quantum wires of Cd 1 -x Mn x Se (x = 0.08) were synthesized with the width of 60-125 nm from the two-dimensional quantum wells by the electron beam lithography and chemical etching. The optical properties and the exciton dynamics of these quantum structures were studied by the transient photoluminescence spectroscopy. The magneto-optical properties of the confined excitons in the quantum dots, the wires and the wells are discussed.

Optical pump–probe experiments were carried out in Cd 1− x Mn x Te/ZnTe multiple-quantum wells to study the carrier dynamics and the exciton formation in these materials. Starting from 15 ps after the pump excitation, the bleaching of the absorption of the heavy-hole excitons in the wells yields a strong negative pump–probe signal. But before this occurs, the pump–probe signal has a completely different lineshape resembling a lying `S'. The time evolution of the pump–probe signal is understood to have arisen from a coexistence of carriers and excitons. We treated the excitons in the wells as Mahan excitons and obtained a good fit to the experimental data. The cooling of the carriers after the pump excitation can be monitored as an increasing Fermi energy of the `cold’ carriers at the band edge. The Fermi sea is then depleted starting from 15 ps after the pump excitation due to the formation of excitons.

Time-resolved photoluminescence has been studied on molecular beam epitaxy grown Cd 1− x Mn x Te epilayers and Cd 1− x Mn x Te/Cd 1− y Mg y Te single- and multiple-quantum wells. The formation of exciton magnetic polarons is detected in the single-quantum wells of various well widths. The transient photoluminescence of magnetic polarons is significantly affected by the external field. The photoluminescence intensity of the exciton is found to show two-exponential decay characteristics. The magnetic field dependence of the two decay times is attributed to the conversion of the dark excitons to the bright excitons by a spin-flip process. The temperature dependence of exciton decay times is interpreted as the thermal activation process in the multiple-quantum well.

We report on a field-dependent photoluminescence (PL) emission rate for the transitions between band states in modulation-doped CdTe/Cd1−xMgxTe single quantum wells in the integer quantum Hall region. The recombination time observed for the magneto-PL spectra varies in concomitance with the integer quantum Hall plateaus. Furthermore, different PL decay times were observed for the two circular polarizations, i.e. for the transitions between the Zeeman split subbands of the Landau levels. We analyzed the data in comparison with the experimentally determined spin polarization of the conduction electrons and the Zeeman splitting of the valence band. Furthermore, we discuss the relevance of the spin polarization of the conduction electrons, the electron–hole exchange interaction and the spin-flip processes of the hole states for the PL decay time.

We present a study of the exciton dynamics in modulation doped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}$ heterojunctions and GaAs epilayers. The comparison permits to identify the features characteristic for the heterojunctions. In particular, we analyze the rise time of the transient photoluminescence (PL) intensity. In general, we find a longer PL rise time for the lower-energy excitons indicating that the time required for the energy relaxation process increases with increasing binding energy of the excitons. Moreover, the rise time of the free excitons turns out to be conspicuously longer in heterojunctions than in epilayers although the time integrated PL spectra of the two systems are similar. From our analysis we conclude that the long rise time observed in the heterojunctions is closely connected with the vertical drift of the photoexcited carriers driven by the interface potential. In fact, we find that the carriers (i.e., holes in n-doped samples) photoexcited in the heterojunctions drift vertically from the heterointerface to the flat band region, where they finally recombine after forming excitons (bimolecular formation) with oppositely charged and locally excited carriers (i.e., electrons in n-doped samples).

Exciton dynamics has been studied in quantum wells, quantum dots and quantum wires of diluted magnetic semiconductors by time-resolved photoluminescence spectroscopy. The transient exciton photoluminescence with resonant excitation in Cd 1− x Mn x Te/ZnTe ( x =0.1) multiple quantum wells shows the formation of magnetic polarons in the quantum well excitons. Free and localized states of the excitonic magnetic polarons are distinguished from the difference of the lifetimes and the binding energies. The magnetic polaron formation accompanied with emission or absorption of LO phonons was also observed. Quantum dots of Cd 1− x Mn x Se grown by the self-organization mode showed the luminescence of confined excitons in the dots. The Mn ions in the quantum dots induce large Zeeman shifts and the excitonic magnetic polaron formation in the dots. Quantum wires of Cd 1− x Mn x Se showed polarized exciton emissions parallel to the wires. The polarization was decreased by the external magnetic field perpendicular to the wires. The excitonic magnetic polaron states in the quantum wires are also discussed.

The exciton dynamics in In 0.15 Ga 0.85 As/GaAs quantum wells grown on (111)B and (100) GaAs substrates are studied by the time-resolved photoluminescence (PL). We have found that the piezoelectric fields in (111)B samples affect the transient behavior of PL spectra. Compared with the reference (100) samples, we have confirmed that the piezoelectric effect induces slower exciton relaxation in (111)B strained quantum wells.

Employing two different growth methods: standard molecular beam epitaxy (MBE) and low-temperature atomic layer epitaxy (ALE) with subsequent annealing, we have obtained high-quality quantum dot structures consisting of CdSe embedded in ZnSe. Single dot emission lines are observed in micro-luminescence. The samples have been investigated by further optical methods including time-resolved photoluminescence under resonant excitation at 4.2 K. Distinct properties of systems with three-dimensional confinement are observed such as the suppression of the interaction between isolated quantum dots (QDs). In standard quantum wells tunneling/hopping processes generally lead to a pronounced red shift of the luminescence over time due to a lateral localization of excitons in potential fluctuations. A much less pronounced red shift is observed for the QDs reflecting only the different lifetimes of single dots and higher excited states. The red shift completely vanishes under resonant excitation that selectively excites only a few QDs of the ensemble in the layer. Typical behaviour is also observed from the halfwidth of the quantum dot emission.

The exciton dynamics in Ga1 − xInxAs/GaAs self-organized quantum dots grown on GaAs (111)B substrates are studied by the time-resolved photoluminescence (PL). We have found the intra-dot exciton relaxation by the reduction of the linewidth and peak energy and also by the energy-dependent PL rise time in the transient PL spectra. Compared with the energy relaxation in the reference quantum wells, we have confirmed that the exciton relaxation in three-dimensionally confined quantum dots is slower than in the quantum wells.

Excitonic lifetimes in Cd1 − xMnUe2Te, Cd1 − xMgxTe epilayers and CdTe/Cd1 − xMnxTe, Cd1 − xMnxTe/Cd1 − vMgyTe single quantum wells with different well widths and Mn, Mg compositions are investigated. The excitonic lifetimes are found to reduce drastically by applying external magnetic fields to samples with giant Zeeman splittings. The observed phenomenon is interpreted in terms of the PL decay time contribution from the long-life dark excitons which can convert to excitons for recombinations by a spin-flip process. We attribute the lifetime reduction to the depletion of dark excitons due to their crossing over the exciton energies for dipole allowed transitions in magnetic fields.

Nanostructures of diluted magnetic semiconductors show varieties of optical phenomena caused by the interaction of electrons and holes with magnetic ions in the confined electronic states. We present giant magneto-optical effects and ultrafast exciton dynamics in two-dimensional quantum wells of the Cd 1− x Mn x Te/ZnTe system and quantum dots of Cd 1− x Mn x Se.

This study examines the binaural and frequency representation in the primary auditory cortex (AC) of the big brown bat, Eptesicus fuscus, by using an ear-phone stimulation system. All 306 cortical neurons studied were excited by contralateral sound stimulation but they were either excited, inhibited or not affected by ipsilateral sound stimulation. These cortical neurons were columnarly organized according to their binaural and frequency-tuning properties. The excitation-excitation columns which occupy about 15% of the AC are mainly aggregated within an oval-shaped area of the central AC. The excitation-inhibition neurons and binaural neurons with mixed properties are distributed in the remaining 85% of the surrounding primary AC. Although the best frequency (BF) of these neurons shows a tendency to decrease from high to low along the anteroposterior axis of the primary AC, systematic variation in BF is not always consistent across the entire mapping area. In particular, BFs of cortical neurons isolated in the anterior AC vary quite unsystematically such that neurons with similar BFs are aggregated in isolated patches. Isofrequency and binaural columns are segregated into bands that intersect each other.

IES LM-80-08/Energy Star, as an accepted method for LED life testing, requires LED be operated under three temperatures for at least 6000 hours to claim the lifetime of LED by using B50L70, meaning that 50% (B50) of LED's lumen output is less than 70% (L70) of initial value. However, it is not acceptable for manufacturers to wait for 6000-hour testing data for lifetime prediction before product launch, as being shortened product design cycle. Therefore, an effective qualification testing is necessary to build for assisting designer in the preliminary verification to eliminate failures and make improvement before product release. This paper demonstrates the trend of lumen maintenance in Wet high temperature operation test (WHTOL) testing, indicating that a prediction method for LED lumen maintenance could be initiated with rather short testing time, which is obviously becoming important for LED release with shortened design cycle.

The potential of stem cells in regenerative medicine, developmental biology, and drug discovery has been well documented. For example, stem cells have the extraordinary ability of self-renewal, and also give rise to many specialized cells. It is clear that stem cell technology has revolutionized our understanding of modern biology and medicine and provided new insights into the mechanisms controlling basic cell biology and various diseases. Nicotinic acetylcholine receptors (nAChRs) are prototypical members of the ligand-gated ion channel super family of neurotransmitter receptors that play many critical roles in brain and body function. It has been demonstrated that in addition to mediation of classical excitatory neurotransmission at some loci and modulation of release of neurotransmitters in some cases, nAChRs also play important roles in influencing synaptic architecture and plasticity as well as neuronal survival/death. Recently, emerging lines of evidence have suggested that nAChRs express on stem cells, where they likely mediate crucial effects of cholinergic signaling on stem cell survival/apoptosis, proliferation, differentiation and maturation. In this review, we summarize current development in cholinergic modulations of stem cell survival/apoptosis, proliferation and differentiation in order to evaluate the impact of nAChRs in stem cell biology and pathology.

We present a study of the dynamics of the excitonic magnetic polarons in Cd1−xMnxTe epilayers. The transient photoluminescence measured by a streak camera under resonant excitation is analyzed with a special attention devoted to line shape of the emission signal. A nonradiative spectral region is observed in zero field and is strongly suppressed in a field of 6 T. This observation is understood to be directly related to the alignment of the Mn2+ spins and is therefore closely related to the formation of magnetic polarons. A few Mn spins are found to be aligned already within 10 ps, but the total Mn spin polarization in the sample is found to increase exponentially with a rise time of 37 ps in Cd0.73Mn0.27Te epilayers. Furthermore, the values of 19.2 and 12.4 meV were determined for the energies of the excitonic magnetic polarons in Cd0.73Mn0.27Te and Cd0.79Mn0.21Te epilayers, respectively.

We report optical properties of quantum dots and quantum wires of diluted magnetic semiconductors. The quantum dots of Cd1−xMnxSe (x=0.03) show the exciton luminescence at around 2.4 eV, which indicates a strong confinement effect of the exciton energy corresponding to the dot size of 4–6 nm. The Zeeman shift of the exciton luminescence was observed with an effective g value of 91, showing a significant exchange interaction of the excitons with the Mn ions in the dots. The exciton luminescence from the quantum wires of Cd1−xMnxSe (x=0.08) shifts by 5.2 meV to the higher energy side with decreasing the wire width from 126 to 26 nm. The high energy shift in the narrow wires indicates the influence of the one-dimensional quantum confinement effect for the exciton states. The effective g value of the exciton in these quantum wires is 100–150. The exciton luminescence from the wires is linearly polarized (up to 80%) parallel to the wire direction at zero field, which indicates one-dimensional properties of the...

Time-resolved photoluminescence (PL) and optical pump–probe experiments were carried out in Cd1−xMnxTe/ZnTe multiple quantum wells to study the dynamics of the exciton magnetic polaron in this material. In the pump–probe data, three signals were detected. The main signal is negative and monitors the energy relaxation of the excitons created by the pump pulse. The other two pump–probe signals are positive and their intensity grows while the excitons created by the pump pulse recombine. The low-energy positive pump–probe signal is found to track the average Mn spin polarization in the sample. On the contrary, the high-energy positive peak indicates the enhancement of the density of states due to correlation effects.

Exciton localization is studied with time-resolved photoluminescence (PL) in Cd 1− x Mg x Te epilayers. The energy relaxation rate of excitons is found to be energy dependent and reduces drastically below an effective excitonic mobility edge. This particular property results in the saturation of the PL intensity rise time below the mobility edge and a two-exponential decay for the PL intensity and the energy relaxation of the excitons.

The lifetime of excitons in Cd1−xMnxTe/Cd1−yMgyTe single quantum wells was investigated by time-resolved photoluminescence spectroscopy. Spin-flips between dark and bright excitons remarkably change the excitonic lifetime yielding a two-exponential decay in the photoluminescence intensity. The temperature dependence of the two decay times shows that the spin-flip rate depends strongly on the formation of excitonic magnetic polarons. By forming polarons, the spin-flip rate from dark excitons to bright excitons is reduced effectively by the spin- barriers of the polarized Mn ions, which extends significantly the luminescence decay time.

Luminescence of excitons has been studied in quantum nanostructures of Cd1−xMnxSe by time-resolved spectroscopy with femtosecond pulse lasers. Self-organized quantum dots show luminescence of quantum-confined excitons. Quantum wires show the exciton luminescence polarized parallel to the wires. Large Zeeman effects and the excitonic magnetic polaron formation are observed in these quantum structures.

The decay properties of excitons in Cd 1− x Mn x Te/Cd 1− y Mg y Te single and multiple quantum wells are investigated by the time-resolved photoluminescence measurements. We observed the conversion of the dark excitons to the bright excitons by a spin-flip process. This yields a two-exponential decay of the photoluminescence intensity. The magnetic field dependence of the two-exponential decay is discussed in the frame of the spin-flip scattering and the giant Zeeman splitting in single quantum wells. The temperature dependence of exciton decays is interpreted by the increase of exciton scattering rate due to thermal activation in multiple quantum well.

Electron spin polarization is studied on n-type modulation doped Cd1−xMnxTe/Cd1−x−yMnxMgyTe single quantum wells. The influence of the electron–electron exchange interaction on the electron spin polarization is discussed. In magnetic fields, the electronic states undergo an initial giant splitting due to the s–d and p–d exchange interactions with localized magnetic moments. Such a giant Zeeman splitting creates an initial spin polarization which will be further enlarged due to the many-body effects of the electron self-energy corrections.

Time-resolved photoluminescence has been measured on molecular beam epitaxy grown Cd1−xMnxTe epilayer samples. The photoluminescence intensity of magnetic polarons exhibits a very long emission tail. The observed phenomenon is attributed to the conversion of the dark excitons to dipole allowed transitions by a spin-flip process. The magnetic field dependence of the two-exponential decay property is discussed within the frame of giant Zeeman splitting, the spin-flip scattering, and the formation of the magnetic polarons.

Optical pump-probe experiments were performed in Cd0.9Mn0.1Te/ZnTe multiple quantum wells to study the dynamics of the exciton magnetic polaron in this material. Two transient absorptions of opposite sign were observed. The first signal is negative and indicates the decrease of optical absorption, as the excitons are approaching saturation. The second signal is positive and is interpreted as the absorption of “new excitons” after the initial excitons created by the pump pulse have decayed leaving behind a magnetic polarized Mn environment. The spin relaxation time of the Mn ions has been determined to be 601 ps. Finally, we discuss the effect of the polaron–polaron interaction, relevant in our experiment because we saturate the excitons in the quantum wells.