Assignment Of Energy Levels Research Articles

Post-deposition annealing process as a defect-driven tool for tuning the chemical and electron properties of sol–gel spin-coated aluminium oxide thin layers

Within current work we present the impact of annealing temperature on the chemical and electron properties of alumina thin layered samples prepared by sol–gel method followed by spin-coating deposition. The determination of the impact was based on the comprehensive photoelectron spectroscopies investigations in X and UV range. Examinations were supported by the simulated density of states spectra that served also as a support for defect energy level assignment in the valence band region from X-ray photoelectron spectroscopy data. Moreover, the quality of the layers was additionally monitored with atomic force microscopy. We demonstrate that our technology results in continuous, homogenous and smooth layers of controlled stoichiometry. Our approach allows direct control of the chemical and electronic structure (e.g. work function, Wf, ionization energy, IE) with post-deposition temperature processing. We show that oxygen vacancies induced by temperature treatment are the main driving force changing the electronic structure. The control of the Wf and IE is possible in annealing conditions above 800 °C. Finally, we analyse carbon contamination impact on the obtained layers’ structure. Our findings may have a direct impact on the engineering of modern oxide-based electronics enabling cost reduction and more precise control of aluminium oxide layers–based devices.

Phosphate Functionalized Ionic Liquid: An Efficient Li+ Migration Inhibitor and Hole Extraction Accelerator for Perovskite Solar Cells

AbstractLithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI) doped 2,2′,7,7′ ‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) is employed as one of the most common hole transport layer. However, the Li+ in Li‐TFSI is easy to migrate from Spiro‐OMeTAD to perovskite and SnO2, left the voids/pinholes in perovskite film to accelerate the invasion of oxygen and moisture, and lead to the device degradation. Here, the 1‐butyl‐3‐methyl imidazolium phosphate dibutyl ester ([Bmim]+[DBP]−) ionic liquid (IL) is prepared and used to modify the perovskite/Spiro‐OMeTAD interface in the perovskite solar cells. The coordination interaction between P  O in [Bmim]+[DBP]− IL and Pb2+ can improve the morphology of perovskite film by passivating the uncoordinated Pb2+ defects. The interaction between P  O and Li+ can suppress the undesired Li+ migration. The regulated energy level assignment and ion nature of [Bmim]+[DBP]− IL can accelerate the carrier extraction at perovskite/Spiro‐OMeTAD interface. The device based on the [Bmim]+[DBP]− IL interface modification yields a highly efficient photoelectric conversion efficiency of 21.16% and improved stability, outperforming that of control (19.31%) devices under the illumination of 100 mW cm−2 (AM 1.5 G).

Ro-vibrational levels and their (e-f) splitting of acetylene molecule calculated from new potential energy surfaces

Ro-vibrational energy levels of acetylene are reported using variational nuclear motion calculations from new ab initio and empirically optimized full six-dimensional potential energy surfaces in the ground electronic state of the acetylene molecule. The calculations account for the triple, quadruple and quintuple excitations as well as relativistic and diagonal Born-Oppenheimer corrections. Variational nuclear motion calculations were performed using the exact kinetic energy operator in orthogonal coordinates. The convergence of energy levels calculations versus the size of the vibrational basis set functions was verified. Our best ab initio potential energy surface that includes the above-mentioned contributions provides the RMS (obs.-calc.) errors of 0.95 cm−1 for five fundamental energy levels. The largest contribution to the RMS error is caused primarily by a significant deviation of the ν4 fundamental frequency. Experimental values of 120 vibrational band origins were used to empirically adjust few lower-order parameters of the potential energy surface. The average error drops down to 0.45 cm−1 or 0.25 cm−1 for empirically optimized potential energy function with two or seven adjusted parameters corresponding to quadratic force field terms and one third order term. The splitting of (e – f) rovibrational doublets and their J dependence were calculated with high accuracy due to the full account of Coriolis interactions. Computed (e – f) splittings allow one to check the correctness of the assignment of empirical energy levels. The estimation of the accuracy for the calculated vibrational levels in an extended range up to 9500 cm−1 shows that the set of ab initio vibrational levels can be used for future assignments of empirically not observed ro-vibrational energy levels. The comparison of the calculated and experimental ro-vibrational energy levels of the C2D2 and 13C2H2 isotopologues is also reported.

Optical Spectra and Energy Levels Analysis of the 4fNIons Doped into Ba2YCl7

Absorption emission and excitation spectra are measured and analyzed to achieve assignments of energy levels for 4f(N) ions in Ba(2)YCl(7):RE(3+) (RE = Pr, Nd, Tb, Dy, Ho, Er, and Tm) crystals. The experimental energy levels were analyzed in terms of the usual free-ion parameters and the crystal field (CF) ones, B(kq), in the Wybourne notation. The orthorhombic C(2v) symmetry is shown to be a good approximation of the actual triclinic C(1) site symmetry at the metal center. The starting values of the CF parameters B(kq) used for fittings for the studied crystals were obtained from superposition model analysis. A good agreement between the calculated and experimental energy levels was obtained with rms deviations in the range from 6.8 cm(-1) (for Ho(3+)) to 14.1 cm(-1) (for Pr(3+)). The fitted sets of B(kq) parameters are, in general, consistent across the 4f(N) series. This study has enabled determination and discussion of the trends in variation of the free-ion parameters and CF ones across the 4f(N) series. The CF parameter set and energy level structure obtained for Nd(3+) ion in Ba(2)YCl(7) crystal are consistent with those for Nd(3+) in structurally related RbY(2)Cl(7) crystal. This systematic analysis of CF parameters is one of only few such studies encompassing nearly whole series of RE(3+) ions.

Crystal-field analysis for RE 3+ ions in laser materials: II. Absorption spectra and energy levels calculations for Nd 3+ ions doped into SrLaGa 3O 7 and BaLaGa 3O 7 crystals and Tm 3+ ions in SrGdGa 3O 7

Low temperature polarized absorption spectra are analyzed to achieve assignments of energy levels for Nd 3+ and Tm 3+ ions at monoclinic C s site symmetry in ABC 3O 7 crystals. Based on the concept of average optical center, the experimental energy levels for single crystals of SrLaGa 3O 7:Nd 3+ (SLG:Nd), BaLaGa 3O 7:Nd 3+ (BLG:Nd), and SrGdGa 3O 7:Tm 3+ (SGG:Tm) were analyzed in terms of the free-ion parameters and the crystal field (CF) ones, B kq . Assignments of the energy levels resolved in the spectra were done in stages applying the ascent/descent in symmetry method in CF analysis. The actual monoclinic C s site symmetry at the metal centers in ABC 3O 7 crystals and the approximated orthorhombic C 2v and tetragonal C 4v symmetry were considered. The starting values of B kq ’s for SLG:Nd and BLG:Nd crystals were obtained from superposition model (SPM) analysis. The final fitted crystal field parameters show high compatibility with the existing data for structurally similar ion-host systems. The obtained values of the intrinsic parameters provide basis for SPM analysis of CF parameters for rare earth ions in other similar systems, especially those exhibiting low-symmetry sites. The SPM parameters derived for SLG:Nd are used for simulation and assignment of the energy levels involved in the potential laser transitions at about 1800 nm due to Tm 3+ ions in SGG crystals. The evaluated emission cross-section is about two times lower than that obtained previously.

Crystal-field analysis for RE 3+ ions in laser materials: I. Absorption spectra and energy levels calculations for Nd 3+ and Pr 3+ ions in ABCO 4 crystals

Low temperature polarized absorption spectra are analyzed to achieve assignments of energy levels for Nd 3+ ions at tetragonal C 4v symmetry sites in SrLaAlO 4:Nd 3+, SrLaGaO 4:Nd 3+, and CaNdAlO 4 as well as Pr 3+ ions at C 4v sites in SrLaAlO 4:Pr 3+ crystals. The C 4v selection rules for polarized electric dipole transitions are strictly obeyed for Pr 3+ ion doped into SrLaAlO 4. However, for Nd 3+ ions in the same crystal neither the C 4v polarization rules nor the C 4 ones are strictly confirmed. This is explained in terms of structural disorder. The experimental energy levels for Pr 3+ and Nd 3+ ions in these crystals were analyzed in terms of the free-ion parameters and the crystal field (CF) ones, B kq , assuming C 4v site symmetry and using the starting values of B kq ’s obtained from superposition model (SPM) analysis. A good agreement between the calculated and experimental energy levels was obtained with rms deviations in the range from 20.5 to 23.6 cm −1 for Nd 3+-doped crystals and 19.8 cm −1 for SrLaAlO 4:Pr 3+. Using the CF parameters B kq optimized in fittings of the calculated and experimental energy levels, the model parameters, i.e. the intrinsic parameters B ¯ k and the power law exponents t k , were determined and compared with those for other similar systems hitherto studied. The obtained values of the intrinsic parameters may serve as a starting point for SPM analysis of CF parameters for other systems, particularly those exhibiting low symmetry of metal centers. As an example of such systems, we consider Nd 3+ ions at triclinic C 1 symmetry sites in BaLaAlO 4:Nd 3+ crystals. Low temperature polarized absorption spectra for this system is also analyzed yielding assignments of energy levels. The results of preliminary low symmetry CF analysis carried out for BaLaAlO 4:Nd 3+ are presented.

Theoretical Study of the Crystal-Field Energy Levels and Two-Photon Absorption Intensities of Tb3+ in Cubic Host Lattices

Published two photon excitation (TPE) intensities for the cubic elpasolite systems Cs(2)NaTbX(6) (X = Cl, F) have been simulated by a calculation of two photon absorption (TPA) intensities which takes into account electric dipole transitions involving the detailed crystal-field structure of 4f(7)5d intermediate states, as well as the interactions of the 4f(7) core with the d-electron. The intensity calculation employed parameters from an energy level calculation which not only presented an accurate fit, but also yielded parameters consistent with those from other lanthanide ions. The calculated intensities were used to confirm or adjust the previous assignments of energy levels, resulting in some minor revisions. Generally, the TPA intensity simulations were in better agreement with experimental data for the fluoride, rather than the chloride, system and possible reasons for this are given.

Prediction and assignment of site occupation and energy levels for Pb 2+ ions in crystal hosts

The environmental factor h e of the host was calculated quantitatively in Pb 2+-doped 23 compounds based on the dielectric theory of chemical bond for complex crystals. The relationship between the A band energy E A of Pb 2+ and the environmental factor h e was intensively studied. The results indicate that E A of Pb 2+ decreases linearly with increasing of h e . A linear model was proposed which allows us to correctly predict and assign the site occupations and the position of A band for Pb 2+-doped compounds if the crystal structure and the refraction index were known. Applied to SrGa 2O 4:Pb 2+, CaAl 2B 2O 7:Pb 2+ and SrAl 2B 2O 7:Pb 2+, the theoretical predictions are in very good agreement with the experimental data. In SrGa 2O 4:Pb 2+, the excitation spectrum of Pb 2+ from two different cation sites was identified: the higher energy band of A (265 nm) from the site of Sr2, and the lower ones (280 nm) from the site of Sr1.

On meeting lifetime goals and providing constant application quality

Most work in sensor networks tries to maximize network lifetime. However, for many applications the required lifetime is known in advance. Therefore, application quality should rather be maximized for that given time. Levels , the approach presented in this article, is a programming abstraction for energy-aware sensor network applications that helps to meet such a user-defined lifetime goal by deactivating optional functionality. With this programming abstraction, the application developer defines so-called energy levels . Functionality in energy levels is deactivated if the required lifetime cannot be met otherwise. The runtime system uses data about the energy consumption of different levels to compute an optimal level assignment that maximizes each node's quality for the time remaining. As described in this paper, Levels includes a completely distributed coordination algorithm that balances energy level assignments and keeps the application quality of the network roughly constant over time. In this approach, each node computes its schedule based on those of its neighbors. As the evaluation shows, applications using Levels can accurately meet given lifetime goals with only small fluctuations in application quality. In addition, the runtime overhead both for computation and for communication is negligible.

Coupled translation-rotation eigenstates of H2 in C60 and C70 on the spectroscopically optimized interaction potential: Effects of cage anisotropy on the energy level structure and assignments

We have developed a quantitatively accurate pairwise additive five-dimensional (5D) potential energy surface (PES) for H(2) in C(60) through fitting to the recently published infrared (IR) spectroscopic measurements of this system for H(2) in the vibrationally excited nu=1 state. The PES is based on the three-site H(2)-C pair potential introduced in this work, which in addition to the usual Lennard-Jones (LJ) interaction sites on each H atom of H(2) has the third LJ interaction site located at the midpoint of the H-H bond. For the optimal values of the three adjustable parameters of the potential model, the fully coupled quantum 5D calculations on this additive PES reproduce the six translation-rotation (T-R) energy levels observed so far in the IR spectra of H(2)@C(60) to within 0.6%. This is due in large part to the greatly improved description of the angular anisotropy of the H(2)-fullerene interaction afforded by the three-site H(2)-C pair potential. The same H(2)-C pair potential spectroscopically optimized for H(2)@C(60) was also used to construct the pairwise additive 5D PES of H(2) (nu=1) in C(70). This PES, because of the lower symmetry of C(70) (D(5h)) relative to that of C(60) (I(h)), exhibits pronounced anisotropy with respect to the direction of the translational motion of H(2) away from the cage center, unlike that of H(2) in C(60). As a result, the T-R energy level structure of H(2) in C(70) from the quantum 5D calculations on the optimized PES, the quantum numbers required for its assignment, and the degeneracy patterns which arise from the T-R coupling for translationally excited H(2) are all qualitatively different from those determined previously for H(2)@C(60) [M. Xu et al., J. Chem. Phys. 128, 011101 (2008).

Emission spectra of lanthanide ions in hexafluoroelpasolite lattices excited by synchrotron radiation

Emission spectra at 10 K employing synchrotron radiation have been recorded for the tripositive lanthanide ions, Ln = Sm, Gd, Tb, Ho, and Er situated at octahedral (or nearly octahedral) site symmetry in hexafluoroelpasolite Cs 2NaMF 6 (M = Y, Sc, or Ga) lattices. Interconfigurational 5d → 4f transitions are only observed for Er 3+, and the intensity ratio of 4f 105d → 4f 11 emission, compared with 4f 11 → 4f 11 emission, with excitation into 5d levels, is greater for M = Ga than M = Sc. The highest energy intraconfigurational emission is from 4G 5/2 (Sm 3+), 6P 7/2 (Gd 3+), 5D 3 (Tb 3+), 5G 4 (Ho 3+), and 2F(2) 7/2 (Er 3+). Detailed energy level assignments have been given for Ln = Sm, Gd, and the remaining spectra are assigned as multiplet–multiplet transitions.

Infrared and visible spectroscopic studies of the ytterbium doped borate Li 6Y(BO 3) 3

The spectroscopic study of trivalent ytterbium doped Li 6Y(BO 3) 3 is conducted in the UV–visible and infrared range. An excitation in the charge transfer band of ytterbium has been selected in order to reduce the reabsorption effect on the IR emission intensity. The maximum of the emission is located at 972 nm for an excitation at 230 nm. The energy level assignment has been successfully conducted using vibrational spectroscopy to distinguish the pure electronic transitions from the phonon-assisted ones. The splitting of the 2F 5/2 and 2F 7/2 components is equal to 523 cm −1 and 676 cm −1, respectively. The decay time dependence as a function of the concentration is also reported. The calculated value τ rad is about (1.03 ± 0.01) ms for the 1% doped material. For the highest concentration, an IR excitation gives rise to the observation of a blue-green luminescence caused by two mechanisms: an erbium emission at 550 nm after upconversion and a cooperative luminescence of ytterbium ions.

Simulation of two-photon absorption spectra of [formula omitted] by direct calculation

Two-photon absorption (TPA) line strengths for transitions within the 4 f 7 configuration of Gd 3 + have been successfully calculated with several different time-independent perturbation methods. However, attempts to use similar methods to predict TPA line strengths for transitions within the 4 f 7 configuration of Eu 2 + have been much less successful, due to the fact that the low-lying 4 f 6 5 d excited states make straight-forward application of perturbation theory unreliable. In this work we carry out a direct calculation of TPA line strengths that take into account the major interactions for 4 f 7 and 4 f 6 5 d configurations nonpertubatively. We also calculate the linewidths of TPA peaks due to nonradiative relaxation to 4 f 6 5 d energy levels by considering the odd parity vibrations responsible for nonradiative relaxation. Comparisons of calculated TPA line strengths and linewidths with experimental spectra allow improved energy-level assignments. The calculated TPA spectra give a good reproduction of the experimental line strengths, polarization dependences, and linewidths.

Yb3+-doped Gd3Ga5O12 garnet single crystals grown by the micro-pulling down technique for laser application. Part I: Spectroscopic properties and assignment of energy levels

Abstract Spectroscopic characterization were carried out to identify Stark’s levels of Yb 3+ transitions in the Gd 3+ dodecahedral S 4 crystallographic site in Gd 3 Ga 5 O 12 garnet crystals which are grown by the micro-pulling down technique. Yb 3+ concentration dependence of the 2 F 5/2 excited level experimental decay time was analyzed in order to understand involved concentration quenching mechanisms.

Growth of Yb3+-doped YLiF4 laser crystal by the Czochralski method. Attempt of Yb3+ energy level assignment and estimation of the laser potentiality

YLiF4 (YLF) single crystals undoped and Yb3+-doped with different concentrations were grown by the Czochralski technique under CF4 atmosphere. Detailed analysis of Yb3+-doped YLF spectroscopy were made to contribute to the determination of energy levels in this host. We are dealing with temperature and concentration dependences of both π and σ polarizations of the infrared (IR) absorption and emission spectra. Raman spectra were also used to give an attempt of interpretation of electronic and vibronic levels. The radiative energy transfer (self-trapping) and strong phonon–electron coupling make the assignment of Yb3+ energy levels difficult. Evaluation of the laser potentiality of this fluoride host is also presented.

Negatively charged Pb− ion produced by electrolytical colouration of KCl crystalscontaining Li+, Na+ and Rb+ ions

Electrolytic colouration has been undertaken for not only a KCl crystal containingPb2+ ions but also KCl crystals containing alkali impurity ions (Li+, Na+ and Rb+)besides Pb2 + ions. Absorption spectra of these electrolytically coloured crystalshave been studied, together with the emission spectra. Similar spectra wereobserved among these crystals. Eight weak absorption bands are observed in the290–700 nm region, while five intense bands are observed in the 200–290 nmregion. It is suggested that these bands arise from Pb− ions with tetragonal crystalfield symmetry. The energy-level assignment for these absorption bands is madeusing the energy-level diagram of the isoelectronic Bi0 atom with C4vcrystal field symmetry. It is suggested that an off-centre position effect of the Li+ion is observed in the KCl crystal codoped with Li+ ions. Broad emission bands at1530 and 1580 nm have been observed in electrolytically coloured KClcontaining Pb2 + ions and KCl containing Li+ and Pb2 + ions, respectively.

Energy levels and optical properties of neodymium-doped barium fluorapatite

Energy levels of the 4f3 electronic configuration of Nd3+ in barium fluorapatite, Ba5(PO4)3F(B-FAP) have been determined from polarized absorption and fluorescence spectra using crystals at 8 K. Experimental energy-level assignments were made initially by comparing the crystal spectra energy levels with those obtained from those previously reported for Nd3+ in strontium fluorapatite and fluorapatite. The initial crystal-field parameters were calculated by using lattice summation techniques. The crystal-field parameters were varied to obtain a best fit between experimental and theoretical energies and the final values give a root-mean-square deviation of 7.1 cm−1. The odd-fold crystal-field components are used to calculate the emission intensities and lifetimes of the Nd3+ ions in B-FAP. These calculations yield results in good agreement with the experimental measurements of the absorption and emission cross sections and lifetimes.

Spectroscopic and optical properties of the rare earth-doped liquid PBr 3/AlBr 3/SbBr 3

A complete spectroscopic evaluation of rare earth-doped PBr 3/AlBr 3/SbBr 3 has been carried out for several of the lanthanides. A comprehensive assignment of 4f energy levels has been made and absorption and fluorescence spectra have been used in evaluating the Judd–Ofelt parameters for most of the rare earths studied. The stimulated emission cross sections for the 4F 3/2– 4I 11/2 transition in the neodymium-doped solution was found to be σ Nd=6.8 × 10 −20 cm 2, and for the 4I 13/2– 4I 15/2 transition in the erbium-doped solution σ Er=6.2 × 10 −21 cm 2. Non-radiative relaxation rates and stimulated emission cross sections have also been evaluated for potential laser transitions in the 3–5 μm spectral region.

Optically Pumped FIR Laser Lines from CH3OH: New Laser Lines, Frequency Measurements, and Assignments

We report the identification and characterization of eight new FIR laser lines from methanol (CH3OH) in the range 48.4 to 453.7 μm pumped by sequence and hot bands of a cw CO2laser. Frequency measurements for most of the new FIR laser lines and from previously reported ones were obtained in the range 0.6–6.8 THz with a one-sigma reproducibility of two parts in 107. We propose an assignment of energy levels for two of the new laser lines and for five pumped by 10R(46) previously reported. The high frequency lines with absorption centers outside of the tuning range of the CO2laser pump showed doublets. These were used to evaluate the offsets of the CO2absorption transitions.

Theoretical studies of the optical spectra and their pressure dependence for ZnS : Ni 2+ crystal

In this paper, the optical spectra and their pressure dependence for ZnS : Ni 2+ crystal have been calculated by diagonalizing the energy matrixes (including the spin–orbit coupling coefficient) based on a modified crystal-field theory, in which the normalization parameters N t , N e for describing covalency and the spin–orbit coupling coefficients ζ tt , ζ te are obtained from a cluster approach. The calculated optical spectra and their pressure dependence show good agreement with the experimental values given by Schotz et al. (J. Phys.: Condens. Matter. 7 (1995) 795). The assignments of energy levels A 1- 1A 1( 1G) and T 2- 1T 2( 1G) are opposite to those obtained from the conventional crystal-field theory in the paper of Schotz et al. The difficulty in explaining the pressure dependence of the two energy levels is therefore removed.