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Magnetophotoluminescence properties of Zn0.88Mn0.12Se thin films grown by metal-organic chemical vapor deposition on GaAs substrates are investigated in fields up to 10 T. The linewidth of the excitonic luminescence peaks decreases with the increasing magnetic field (<1 T), but the peak energy is almost unchanged. There is a crossover of the photoluminescence intensities between interband and bound excitonic transitions as the magnetic field is increased to about 1 T. These behaviors are interpreted by the strong tuning of the local alloy disorder potential by the applied magnetic field. In addition, the magnetic field-induced suppression of the energy transfers from excitons to Mn2+ ions is also observed. [ABSTRACT FROM AUTHOR]

We have studied the temperature-dependent carrier transfer processes in InGaN/GaN multi-quantum-well light-emitting devices using various optical techniques such as photoluminescence, electroluminescence, and photoluminescence excitation spectra. The role of the defects in the GaN barrier neighboring to the InGaN region was demonstrated clearly in capturing carriers only at low temperatures. The physical origin of the defects was most possibly attributed to the stacking faults at the interface according to the high-resolution transmission electron spectroscopy pictures. [ABSTRACT FROM AUTHOR]

Optical and electrical characterization of the ZnS self-organized quantum dots (QDs) embedded in ZnS by molecular beam epitaxy have been investigated using photoluminescence (PL), capacitance–voltage (C-V), and deep level transient Fourier spectroscopy (DLTFS) techniques. The temperature dependence of the free exciton emission was employed to clarify the mechanism of the PL thermal quenching processes in the ZnSe QDs. The PL experimental data are well explained by a two-step quenching process. The C-V and DLTFS techniques were used to obtain the quantitative information on the electron thermal emission from the ZnSe QDs. The correlation between the measured electron emission from the ZnSe QDs in the DLTFS and the observed electron accumulation in the C-V measurements was clearly demonstrated. The emission energy for the ground state of the ZnSe QDs was determined to be at about 120 meV below the conduction band edge of the ZnS barrier, which is in good agreement with the thermal activation energy, 130 meV, obtained by fitting the thermal quenching process of the free exciton PL peak. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ab initio quadratic CI calculation method and the effective-core-potential basis set have been used to calculate the equilibrium geometries, potential energy curves, dissociation energies of the ground state, and low-lying electronic states of Lu[sub 2] for the first time. The symmetries of these states are determined by analyzing the potential energy curves and optimization calculations at the same time. The analytical potential energy functions of these states have been fitted with the Murrell–Sorbie potential energy function from the calculated values with the ab initio method. The spectroscopic parameters of each state are calculated through the relationship equations between analytical potential energy function and spectroscopic parameters, and are compared with some other theoretical and experimental data available from the experiment at present. For the ground state, we obtain the symmetry is X [sup 3]Σ[sub g], ω[sub e]=113.3 cm[sup -1] with ω[sub e]χ[sub e]=0.16 cm[sup -1], leading to a spectroscopic dissociation energy of 1.79 eV. They are in agreement with the recent experiments. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optical properties of ZnO quantum dots (QDs) capped with polyvinyl pyrrolidone (PVP) molecules have been investigated. It is demonstrated that surface modification by PVP can dramatically change the emission spectra of the ZnO QDs. At the optimized condition with a PVP/Zn[sup 2+] ratio of 3:5, the photoluminescence (PL) spectrum of ZnO QDs shows a strong ultraviolet (UV) emission while the low energy green emission is fully quenched. This is a result of the surface passivation of the ZnO QDs by the PVP molecules. The origin of the green emission is attributed to the surface states associated with oxygen vacancies. Temperature and excitation power dependent PL studies suggest that the UV emission is associated with localized states. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We observed a violation of the normal Raman selection rule in the resonant Raman spectra of interface (IF) phonon modes of the ultrathin (GaAs)[sub 4]/(AlAs)[sub 2] superlattice. Contrary to the prediction of conventional theories, all four IF modes were observed in both (XX) and (XY) geometries. The result can be interpreted as a consequence of the deep penetration of the electron wave function in the GaAs wells into the AlAs barriers and a lack of definite parity of the electron wave function. Furthermore, our result indicates that conventional theory for bulk (thicker) systems may need to be modified and further developed to be applicable to ultrathin systems. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In their natural habitats and application environments, lactic acid bacteria are often exposed to osmotic changes. At metabolic level, bacteria are able to de novo synthesize or uptake specific solutes from environment to maintain constant turgor pressure. In the work, the 1H nuclear magnetic resonance (NMR) spectroscopy based on intracellular metabolites profiles of Lactobacillus salivarius under hyperosmotic growth conditions was characterized. New characteristic peaks of compatible compounds, such as betaine, carnitine, choline and/or their derivatives were detected. Especially, the cytoplasmic concentrations of proline increased dramatically when the osmolarity was raised from about 0.40 to 1.84 osmol/kg by adding 0.8 mol/l NaCl to the medium. Comparative analysis of the metabolites of L. salivarius FDB89 grown under aerobic and anaerobic conditions with NaCl stress revealed an overlap of up-regulated compounds of more than 50%. 2-aminobutyrate, pyruvate, glycine, trimethylamine-N-oxide, and acetylcholine were detected only under anaerobic condition, and 2-oxoglutarate, tyrosine, glutamine and glutamate were detected only under aerobic condition, which suggested oxygen also has a nonnegligible effect on osmotic response in L. salivarius FDB89. [ABSTRACT FROM AUTHOR]

The symmetry-adapted-cluster (SAC)/symmetry-adapted-cluster configuration interaction (SAC-CI) method has been applied to study the ground and low-lying excited states properties of F2BO and H2BO free radicals. The geometry of the ground states for F2BO and H2BO are optimized by SAC method with the different basis sets and the results show that the SAC/D95** and SAC/6-311G(df) levels are in excellent agreement with the available experimental and existing theoretical data. Based on SAC-CI/D95** and SAC-CI/6-311G(df) levels, the vertical excitation energies, transition dipole moments and oscillation strengths of F2BO and H2BO in the low-lying excited states are calculated. Besides, the optimized geometries, adiabatic excitation energies, and rotational constants of low-lying excited states of F2BO and H2BO are also obtained. We hope that the calculated results can provide the useful data for the studies of the excited state properties for F2BO, H2BO, and similar free radicals. [ABSTRACT FROM AUTHOR]

Presents a study which examined the systematic variation of anomalous praseodymium (Pr) antiferromagnetic ordering temperature for two-CuO[sub2]-layer cuprate systems. Details of the experimental techniques used; Discussion on the systematic of anomalous Pr ordering.

Examines the phase compositions of rapidly quenched Nd[sub4]Fe[sub77.5]B[sub18.5] alloys annealed under different conditions. Preparation of the samples; Data on the spin-echo nuclear magnetic resonance spectra and Mössbauer spectra for the alloys.