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Sub-monolayer quantities of Mg are introduced in multilayer stacked ZnMgTe quantum dots (QDs) embedded in ZnSe barriers in order to reduce the hole confinement energy by controlling the bandgaps and band-offsets of ZnTe/ZnSe system having type-II band alignment. The photoluminescence (PL) emission from such ZnMgTe/ZnSe QD structure is found to be a broad band centered at 2.35 eV. The higher energy side of the PL band shows a larger blue-shift with increasing excitation intensity and a faster life-time decay due to a greater contribution of the emission from the smaller size dots and the isoelectronic bound excitons. It is found that the characteristic decay time of the PL evolves along the band with a value of 129 ns at 2.18 eV to 19 ns at 2.53 eV. The temperature dependent PL emission is controlled by two thermally activated processes: ionization of electrons away from QD state to the barrier (EA1 ∼ 3 meV) by breaking the type-II excitons and thermal escape of the holes from the ground state to the barrier (EA2 ∼ 114-116 meV). We propose a modified band diagram and energy levels for this ZnMgTe/ZnSe multilayer QD system by determining the composition of Mg inside the QDs and solving the 1-D Schrodinger's equation and show that Mg incorporation lowers the hole activation energy via modification of the valence band offset without changing the barrier significantly. [ABSTRACT FROM AUTHOR]

A systematic analysis of the S1-trans (A1Au) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm-1. Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm-1. Its 13C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S1-cis isomer (A1A2). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)] of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the 13C isotope shift of the 46 175 cm-1 level (assigned here as cis-3161). The S1-cis zero-point level is deduced to lie near 44 900 cm-1, and the ν6 vibrational frequency of the S1-cis well is found to be roughly 565 cm-1; these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm-1 vibrational level is found to have a 3.9 cm-1 staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene that was previously thought to be unobservable, as well as the first high resolution spectroscopic results describing cis-trans isomerization. [ABSTRACT FROM AUTHOR]

We have studied the dynamics of strong radiative shocks generated with the high-energy subnanosecond iodine laser at Prague Asterix Laser System facility (Prague) over long time scales, up to 100 ns. These shock waves are characterized by a developed radiative precursor, a radiation driven ionization wave in front of the density jump of the shock. Electronic density profiles are measured at different times after the laser pulse and at different distances from the axis of the shock tube. A new feature, described as a split precursor, has been observed. Comparisons with two-dimensional computations are shown. [ABSTRACT FROM AUTHOR]

We present a nonperturbative time-dependent quantum mechanical theory of the laser catalysis and control of a bifurcating A+BC↔hω0ABC*(v)↔hω0AB+C reaction, with ABC*(v) denoting an intermediate, electronically excited, complex of ABC in the vth vibrational state. We apply this theory to the low collision energy fermion-boson light-induced exchange reaction, 6Li(2S)+7Li2(3Σu+)↔hω0(6Li7Li7Li)*↔hω06Li7Li(3Σ+)+7Li(2S). We show that at very low collision energies and energetically narrow (∼0.01 cm-1) initial reactant wave packets, it is possible to tune the yield of the exchange reaction from 0 to near-unity (yield >=99%) values. Controllability is somewhat reduced at collisions involving energetically wider (∼1 cm-1) initial reactant wave packets. At these energetic bandwidths, the radiative reactive control, although still impressive, is limited to the 0%–76% reactive-probabilities range. [ABSTRACT FROM AUTHOR]

The random first-order transition theory of the dynamics of supercooled liquids is extended to treat aging phenomena in nonequilibrium structural glasses. A reformulation of the idea of “entropic droplets” in terms of libraries of local energy landscapes is introduced which treats in a uniform way the supercooled liquid (reproducing earlier results) and glassy regimes. The resulting microscopic theory of aging makes contact with the Nayaranaswamy-Moynihan-Tool nonlinear relaxation formalism and the Hodge-Scherer extrapolation of the Adam-Gibbs formula, but deviations from both approaches are predicted and shown to be consistent with experiment. The nonlinearity of glassy relaxation is shown to quantitatively correlate with liquid fragility. The residual non-Arrhenius temperature dependence of relaxation observed in quenched glasses is explained. The broadening of relaxation spectra in the nonequilibrium glass with decreasing temperature is quantitatively predicted. The theory leads to the prediction of spatially fluctuating fictive temperatures in the long-aged glassy state, which have non-Gaussian statistics. This can give rise to “ultraslow” relaxations in systems after deep quenches. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A spectroscopic analysis is performed on Er[sup 3+] (4f[sup 11]) ions doped in NaBi(WO[sub 4])[sub 2] (NBWO) in order to assess this material for its potential as a near-infrared laser. The Judd–Ofelt model is applied to the room-temperature absorption intensities of Er[sup 3+] (4f[sup 11]) in NBWO to obtain the three phenomenological intensity parameters: Ω[sub 2]=5.50×10[sup -20] cm[sup 2], Ω[sub 4]=1.00×10[sup -20] cm[sup 2], and Ω[sub 6]=0.71×10[sup -20] cm[sup 2]. The intensity parameters are then used to determine the radiative decay rates (emission probabilities), radiative lifetimes, and branching ratios for the Er[sup 3+] transitions from the excited state multiplet manifolds to the lower lying manifold states. Using the radiative decay rates for the Er[sup 3+] (4f[sup 11]) transitions between the corresponding excited states and the lower lying states, the radiative lifetimes of eight excited states of Er[sup 3+] are determined in this host. Using the measured room temperature fluorescence lifetime of approximately 4.75 ms and the radiative lifetime of 5.63 ms as predicted by the Judd–Ofelt model for the [sup 4]I[sub 13/2]→[sup 4]I[sub 15/2] (1.52 μm) transition of Er[sup 3+] in NBWO the quantum efficiency is determined to be approximately 84% for this laser material. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the measurements of x-ray power, spatial and spectral distributions from transition radiators whose spectra are narrowed by the foil material's K-shell photoabsorption edge. Peak and total power density of the zinc radiator; Discussion on how transition radiation is produced; Factors that determine the energy of the x-rays.

In this Comment I discuss two incorrect statements which were made in the paper “Silver nanoparticle array structures that produce remarkably narrow plasmon line shapes” [J. Chem. Phys.130, 10871 (2004)] by Zou, Janel, and Schatz (ZJS). The first statement is about the use of quasistatic approximation in my earlier work on the similar subject, and the second statement concerns the possibility of exact cancellation of radiative relaxation in periodical chains of nanoparticles. The relationship between the quasistatic approximation, the dipole approximation, and the approximation due to Doyle [Phys. Rev. B39, 9852 (1989)] which was used by ZJS is clarified. It is shown that the exact cancellation of radiative relaxation cannot take place in the particular geometry considered by ZJS. [ABSTRACT FROM AUTHOR]

The radiative transitions in P- and B-doped Si nanocrystals are investigated by means of first-principle calculations. Using a three-level model, we show that the radiative lifetimes and oscillator strengths of the transitions between the conduction and the impurity bands, as well as the transitions between the impurity and the valence bands are strongly affected by the impurity position. On the other hand, the direct conduction-to-valence band decay is practically unchanged due to the presence of the impurity. In addition, the emission intensity of P(B)-doped nanocrystals with impurities positioned in the surface (anywhere) is higher (lower) than for pure nanocrystals. [ABSTRACT FROM AUTHOR]

The authors generated high-order harmonics by using the two-component laser-ablation plumes, which were irradiated by a femtosecond laser pulse. The harmonic spectra from double-target schemes comprised those obtained from separate targets. For indium/chromium plumes, the enhancement of two harmonics (13th and 29th orders) was obtained at the wavelengths of 61.15 and 27.41 nm, respectively. The conversion efficiencies of these two harmonics were estimated to be 10-5. The authors attribute the enhancement of 13th and 29th harmonics to the multiphoton resonances with the strong radiative transitions of ions in indium and chromium plumes, respectively. [ABSTRACT FROM AUTHOR]

Intersubband transitions in GaN/AlN short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of 1.35–2.90 μm for samples cut into 45° waveguides with GaN quantum well thicknesses ranging between 1.70 and 2.41 nm. The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method. [ABSTRACT FROM AUTHOR]

Using quantum-mechanical analysis, a strain-balanced stack of coupled GaN/AlGaN quantum wells has been engineered for bandwidth-optimized all-optical switching at low switching powers. Intersubband transitions between three conduction subbands provide the basis for the large, fast, nonlinear optical response. Optimized performance for a given symbol rate is obtained by engineering the response time and nonlinear phase shift. [ABSTRACT FROM AUTHOR]