Energy Sublevels Research Articles

Synthesis of Tetragonal Phase LiYF4: Yb and Tm Microcrystals with Strong UV Upconversion Fluorescence

In this work, we synthesized pure tetragonal phase LiYF4 microcrystals by a hydrothermal method. In the reaction, sodium ions acted as an intermedium species. The long axis of the quasi-octahedron crystals was about 5 to 20 micrometers. Strong UV 1I6 → 3H6 (~291 nm), 1I6 → 3F4 (~346 nm), and 1D2 → 3H6 (~362 nm) and blue emissions 1D2 → 3F4 (~450 nm) and 1G4 → 3H6 (~475 nm) could be observed in our samples. We could see blue luminescence from the microcrystals by our naked eyes in the daylight even if the pump power of the 980 nm laser diode was less than 10 mW. Obvious energy level splitting was also observed, which indicated that Tm3+ ions were embedded into the crystal lattice very well. The 1G4 energy level split into four subenergy levels owing to the effect of crystal field. The upconversion mechanisms were discussed in detail.

High responsivity, self-powered carbon–zinc oxide hybrid thin film based photodetector

A self-powered n-Si/C–ZnO/SiO2/p-Si heterojunction photodetector (PD) which comprises of carbon (C) and zinc oxide (ZnO) nanostructures on a n-type silicon (n-Si) substrate was prepared via vapor phase transport method. Excellent photodetection under 468 nm light illumination for powers ranging from 2.78 to 2910 µW delivered a quick response of about 9.5 µs. A high photoresponsivity of 2.082/AW and external quantum efficiency about 551% were obtained. The mechanism involved for the generation of a photocurrent at a zero bias voltage was discussed for future energy efficient optoelectronics devices. The morphology and composition of C, Zn and O were confirmed by field emission scanning electron microscope, energy dispersive X-ray and Raman scattering analysis. The formation of ZnO nanowires range from 10 to 100 nm, aided by the photoconduction mechanism. The Raman E2high mode of 437/cm of ZnO and the presence of D and G bands show the formation of a hybrid C–ZnO thin film. The calculated rectifying ratio is found to shift as the direct current bias voltage and light power increased. The deposition of C particles on the ZnO surface creates point defects and sub-energy levels in the ZnO bandgap which favour fast responsivity in the PD.

Residual degeneracy from non-degenerate Landau levels of ultracold atoms in light-induced gauge potentials

We study non-degenerate Landau levels of ultracold trapped atoms in two dimensions, subject to an U(1)×U(1) Abelian gauge field and a lateral confining potential along a specific direction. The Landau-level degeneracy is removed due to the presence of the lateral confining potential that makes the single-particle energy spectrum explicitly dependent on the transverse momentum. The effect of the finite size of the atomic cloud on the energy spectrum is to split each Landau level into a set of sub-levels, once the transverse momentum becomes quantized. We show that under appropriate conditions some energy sub-levels overlap leading to a residual degeneracy of the system. Through numerical calculations, we map the residual degeneracy as a function of the effective magnetic field strength. Finally, we briefly discuss future studies on the transport properties of this atomic system that can be considered an optically induced atomic waveguide.

Energy spectrum and specific heat of two-dimensional electron systems with spin-orbit interaction in a magnetic field parallel to the conducting layer

The energy spectrum of a quasi-two-dimensional electron gas in an in-plane magnetic field is studied using the perturbation theory and quasiclassical approach in the presence of the Rashba and Dresselhaus spin-orbit coupling. The existence of the intersection of energy sublevels in electron spectrum is demonstrated. The reciprocal mass tensor of electrons is analyzed. The heat capacity of the degenerate electron gas is examined, and its relations with the key features of the spectrum are shown.

Electron paramagnetic resonance study of theCe3+pair centers inYAlO3:Ce scintillator crystals

Single crystals of $\mathrm{YAl}{\mathrm{O}}_{3}$ doped with Ce have been studied by electron paramagnetic resonance (EPR) at the 9.4 and 34 GHz microwave bands. Besides the single-ion $\mathrm{C}{\mathrm{e}}^{3+}$ spectrum, measurements have revealed many satellite lines which belong to the $\mathrm{C}{\mathrm{e}}^{3+}\text{\ensuremath{-}}\mathrm{C}{\mathrm{e}}^{3+}$ pair centers. Their spectra have been fitted by a general effective spin Hamiltonian describing two interacting particles with the spin $S=1/2$. Corresponding $g$ factors and spin-spin coupling constants have been determined. The spin-spin coupling constants are in the range from 0.1 up to $0.65\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ for the nearest and next-nearest neighbors depending on the distance between Ce ions and their position. The exchange interaction between next-nearest neighbors (NNNs) is comparable to or even bigger than that between nearest neighbors (NNs), being in the range $0.4\ensuremath{-}0.6\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. For a single $\mathrm{C}{\mathrm{e}}^{3+}$ ion, crystal field parameters, energy sublevels of the ${}^{2}{F}_{5/2}$ and ${}^{2}{F}_{7/2}$ multiplets and principal $g$ tensor components were obtained from the density functional theory calculation. They are in satisfactory agreement with those determined experimentally. The principal $g$ tensor components of $\mathrm{C}{\mathrm{e}}^{3+}$ pair centers are also calculated. Nevertheless, it was impossible to assign each of the satellite lines to actual positions of the six NN and 12 NNN Ce pairs in the lattice due to lack of valid information on the sign of the exchange interactions. The influence of $\mathrm{C}{\mathrm{e}}^{3+}$ pairs on the luminescence efficiency is discussed as well.

Energy levels of magneto-optical polaron in spherical quantum dot — Part 1: Strong coupling

We investigate the influence of a magnetic field on the ground state energy of a polaron in a spherical semiconductor quantum dot (QD) using the modified LLP method. The ground state energy is split into sub-energy levels and there is a degeneracy of energy levels. It is also observed that the degenerate energy increase with the electron–phonon coupling constant and decrease with the magnetic field. The numerical results show that, under the influence of magnetic field and the interaction with the total momentum along the z-direction, the split energy increases and decreases with the longitudinal and the transverse confinement length, respectively.

Particle visualization in high-power impulse magnetron sputtering. II. Absolute density dynamics

Time-resolved characterization of an Ar-Ti high-power impulse magnetron sputtering discharge has been performed. The present, second, paper of the study is related to the discharge characterization in terms of the absolute density of species using resonant absorption spectroscopy. The results on the time-resolved density evolution of the neutral and singly-ionized Ti ground state atoms as well as the metastable Ti and Ar atoms during the discharge on- and off-time are presented. Among the others, the questions related to the inversion of population of the Ti energy sublevels, as well as to re-normalization of the two-dimensional density maps in terms of the absolute density of species, are stressed.

Energy Levels of Weak Coupling Magneto-Optical Polaron and Temperature Effect in Spherical Quantum Dot

In this paper, we investigate the influence of the magnetic field and the temperature on the ground state energy of a weak coupling polaron in a spherical semiconductor quantum dot (QD) using the modified LLP method. The ground state energy of a weak coupling magneto-optical polaron is split into sub-energy levels and there is the degeneracy of the energy levels. It is also seen that the split energies are increasing functions of the electron-phonon coupling constant and decreasing functions of the magnetic field while the temperature is an increasing function of the cyclotron frequency for very low values of the longitudinal confinement length.

Thomas-Fermi method for computing the electron spectrum and wave functions of highly doped quantum wires in n-Si

The application of the Thomas-Fermi method to calculate the electron spectrum in quantum wells formed by highly doped n-Si quantum wires is presented under finite temperatures where the many-body effects, like exchange, are taken into account. The electron potential energy is calculated initially from a single equation. Then the electron energy sub-levels and the wave functions within the potential well are simulated from the Schr?dinger equation. For axially symmetric wave functions the shooting method has been used. Two methods have been applied to solve the Schr?dinger equation in the case of the anisotropic effective electron mass, the variation method and the iteration procedure for the eigenvectors of the Hamiltonian matrix.

MAGNETIC DIAGRAM FOR THE TEACHING OF QUANTIC NUMBERS AND ELECTRONIC ARRANGEMENT

This paper describes the construction of a magnetic diagram, for the purpose of teaching quantic numbers and for conventional electronic arrangement, at the level of the medium teaching. The use of small pieces of magnet allows the representation of electrons, which enables us to work all the chemical elements of the periodic table, making a clear display easier, and improving the student’s understanding, about electronic arrangement in each atom in a dynamic way. The brief visualization of each electron enables us to work the atomic number (Z), the period and family of each element, as well as the energy level and sub-level.

Structure–Property Relationship of Amplified Spontaneous Emission in Organic Semiconductor Materials: TPD, DPABP, and NPB

N,N'-Diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) was demonstrated to be suitable for stimulated emission in doping and nondoping planar waveguide structure, but the mechanism for its lasing is of ambiguity. With the aim of providing a microsscopic picture for its lasing, we performed a combined experimental and theortical investigation of the absorption, photoluminescence (PL), and stimulated emission of TPD and other two similar molecules: 1,4-bis (diphenylamino)biphenyl (DPABP) and N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4″-diamine (NPB). It was found that DPABP shows the same amplified spontaneous emission (ASE) characteristics as TPD, but NPB did not. In theory, density functional theory (DFT) and Franck-Condon Principle were used to analyze the molecular geometry in the electronic ground state as well as the optically excited state and the vibrational levels in electronic ground state, respectively. The calculation results show that for TPD and DPABP, several strongly elongated high-frequency modes (1199-1664 cm(-1)) in the carbon rings contribute to the distinct first vibronic sideband in the PL spectra, which form an effective four-level system for lasing. For NPB, when the peripheral toluene or benzene is replaced with naphthyl, a number of strongly elongated low-frequency modes (11-689 cm(-1)) deriving from naphthyl leads to a series of energy sublevels, which destroys the four-level system. Our results provided a new insight and better understanding into the lasing of organic molecules.

Random polarization dynamics in a resonant optical medium

Random optical-pulse polarization switching along an active optical medium in the Λ configuration with spatially disordered occupation numbers of its lower energy sublevel pair is described using the idealized integrable Maxwell-Bloch model. Analytical results describing the light polarization-switching statistics for the single self-induced transparency pulse are compared with statistics obtained from direct Monte Carlo numerical simulations.

Electron spectrum of δ-doped quantum wells by the Thomas–Fermi method at finite temperatures

The electron spectrum of δ-doped quantum wells i n n-GaAs is investigated by means of the Thomas–Fermi (TF) method at finite temperatures. This method shows rapid convergence and good accuracy. Under two-dimensional (2D) doping concentrations 10 13…2×10 13 cm −2, the simplest TF method ( T=0 K) can be used to calculate the profiles of the potential well up to T≈200 K. The simplest TF method yields correct results for the electron concentrations and the differences of the electron energy sublevels in the quantum well up to room temperature ( T∼300 K).

Direct Evidence for Nitrogen Ligation to the High Stability Semiquinone Intermediate in Escherichia coli Nitrate Reductase A

The membrane-bound heterotrimeric nitrate reductase A (NarGHI) catalyzes the oxidation of quinols in the cytoplasmic membrane of Escherichia coli and reduces nitrate to nitrite in the cytoplasm. The enzyme strongly stabilizes a menasemiquinone intermediate at a quinol oxidation site (Q(D)) located in the vicinity of the distal heme b(D). Here molecular details of the interaction between the semiquinone radical and the protein environment have been provided using advanced multifrequency pulsed EPR methods. (14)N and (15)N ESEEM and HYSCORE measurements carried out at X-band ( approximately 9.7 GHz) on the wild-type enzyme or the enzyme uniformly labeled with (15)N nuclei reveal an interaction between the semiquinone and a single nitrogen nucleus. The isotropic hyperfine coupling constant A(iso)((14)N) approximately 0.8 MHz shows that it occurs via an H-bond to one of the quinone carbonyl group. Using (14)N ESEEM and HYSCORE spectroscopies at a lower frequency (S-band, approximately 3.4 GHz), the (14)N nuclear quadrupolar parameters of the interacting nitrogen nucleus (kappa = 0.49, eta = 0.50) were determined and correspond to those of a histidine N(delta), assigned to the heme b(D) ligand His-66 residue. Moreover S-band (15)N ESEEM spectra enabled us to directly measure the anisotropic part of the nitrogen hyperfine interaction (T((15)N) = 0.16 MHz). A distance of approximately 2.2 Abetween the carbonyl oxygen and the nitrogen could then be calculated. Mechanistic implications of these results are discussed in the context of the peculiar properties of the menasemiquinone intermediate stabilized at the Q(D) site of NarGHI.

Radioluminescence in ZnO

ZnO powders were obtained by proteic sol–gel process using zinc sulfate as the precursor. They have an energy gap of 3.3 eV and display a radioluminescence signal centered in 550 nm, which corresponds to 2.6 eV. This signal has appeared due to defects in the gap (energy sublevels) caused by the distortions in its crystalline structure, which result from the loss of sulfur at high temperature. These powders were characterized by radioluminescence, XRD, SEM, EDS and DTA/TG.

Energy level splitting of CdS nanocrystals

CdS nanocrystals have been fabricated using mercaptopropionic acid (MPA) as the stabilizing agentand Na2S as a sulfur source. The structure and morphology of the CdS nanocrystals have beenmeasured by x-ray diffraction (XRD) and high resolution transmission electron microscopy(HRTEM). Energy level splitting was observed in the UV–VIS optical absorption spectrumof small CdS nanocrystals; the main absorption peak splits into three separate peaks, whichare considered to be three discrete sub-energy levels of the 1S electronic state of the CdSnanocrystals.

ESTIMATES AND COMPUTATIONS IN RABINOWITZ–FLOER HOMOLOGY

The Rabinowitz–Floer homology of a Liouville domain W is the Floer homology of the Rabinowitz free period Hamiltonian action functional associated to a Hamiltonian whose zero energy level is the boundary of W. This invariant has been introduced by K. Cieliebak and U. Frauenfelder and has already found several applications in symplectic topology and in Hamiltonian dynamics. Together with A. Oancea, the same authors have recently computed the Rabinowitz–Floer homology of the cotangent disk bundle D* M of a closed Riemannian manifold M, by means of an exact sequence relating the Rabinowitz–Floer homology of D* M with its symplectic homology and cohomology. The first aim of this paper is to present a chain level construction of this exact sequence. In fact, we show that this sequence is the long homology sequence induced by a short exact sequence of chain complexes, which involves the Morse chain complex and the Morse differential complex of the energy functional for closed geodesics on M. These chain maps are defined by considering spaces of solutions of the Rabinowitz–Floer equation on half-cylinders, with suitable boundary conditions which couple them with the negative gradient flow of the geodesic energy functional. The second aim is to generalize this construction to the case of a fiberwise uniformly convex compact subset W of T* M whose interior part contains a Lagrangian graph. Equivalently, W is the energy sublevel associated to an arbitrary Tonelli Lagrangian L on TM and to any energy level which is larger than the strict Mañé critical value of L. In this case, the energy functional for closed geodesics is replaced by the free period Lagrangian action functional associated to a suitable calibration of L. An important issue in our analysis is to extend the uniform estimates for the solutions of the Rabinowitz–Floer equation — both on cylinders and on half-cylinders — to Hamiltonians which have quadratic growth in the momenta. These uniform estimates are obtained by the Aleksandrov integral version of the maximum principle. In the case of half-cylinders, they are obtained by an Aleksandrov-type maximum principle with Neumann conditions on part of the boundary.

Rotational Sublevels of an Ortho-Hydrogen Molecule Encapsulated in an IsotropicC60Cage

From specific heat measurements in high quality H2@C60 samples performed over a broad temperature range, we obtain the smallest yet observed splitting of rotational energy sublevels of encapsulated single H2 molecules, 0.1-0.2 meV, in the nearly spherical potential well provided by highly isotropic C60 cages. Additionally, we find evidence of the quantized oscillation state of isolated H2 in the C60 cage. The minuscule splitting indicates that H2@C60 provides unprecedented opportunities to study free-molecule quantum dynamic properties.

Energy levels of Nd3+ ions in GaN

AbstractWe report the Stark energy sublevels of Nd3+ ions in GaN grown by plasma‐assisted molecular beam epitaxy as determined by luminescence spectra. The photoluminescence spectra is correlated with transitions from the 4F3/2 doublet state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). A splitting of the 4F3/2 excited state is determined to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sub‐levels of the excited states 4F5/2, 2H9/2, 4F7/2, 4S3/2, 2G7/2, and 4G5/2. Photoluminescence excitation spectra exhibit an optimal excitation energy of 1.48 eV (836 nm). Site‐selective spectroscopy studies using combined excitation‐emission spectroscopy with confocal microscopy imply enhanced substantial doping at the Ga site. In addition, optical loss and gain measurements of a GaN:Nd waveguide excited above bandgap indicate an internal loss coefficient of ∼6.5 +/– 2 cm–1 and a net gain of ∼ –2 +/– 2 cm–1. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal-field split levels of Nd3+ ions in GaN measured by luminescence spectroscopy

We present the Stark energy sublevels of Nd3+ ions in GaN grown by plasma-assisted molecular beam epitaxy as determined by luminescence spectra. We correlate the photoluminescence spectra with transitions from the F43/2 excited state to the I49/2, I411/2, and I413/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). We determine a splitting of the F43/2 excited state to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sublevels of the upper states F45/2, H29/2, F47/2, S43/2, G27/2, and G45/2. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). Site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site.