Energy Level Scheme Research Articles

Calculations of the electronic levels, spin-Hamiltonian parameters and vibrational spectra for the CrCl3 layered crystals

Calculations of the Cr3+ energy levels, spin-Hamiltonian parameters and vibrational spectra for the layered CrCl3 crystals are reported for the first time. The crystal field parameters and the energy level scheme were calculated in the framework of the Exchange Charge Model of crystal field. The spin-Hamiltonian parameters (zero-field splitting parameter D and g-factors) for Cr3+ ion in CrCl3 crystals were obtained using two independent techniques: i) semi-empirical crystal field theory and ii) density functional theory (DFT)-based model. In the first approach, the spin-Hamiltonian parameters were calculated from the perturbation theory method and the complete diagonalization (of energy matrix) method. The infrared (IR) and Raman frequencies were calculated for both experimental and fully optimized geometry of the crystal structure, using CRYSTAL09 software. The obtained results are discussed and compared with the experimental available data.

Luminescence and energy-transfer properties of color-tunable Ca2Mg0.25Al1.5Si1.25O7:Ce(3+)/Eu(2+)/Tb(3+) phosphors for ultraviolet light-emitting diodes.

A series of Ca2Mg0.25Al1.5Si1.25O7:Ce(3+)/Eu(2+)/Tb(3+) phosphors was been prepared via a conventional high temperature solid-state reaction and their luminescence properties were studied. The emission spectra of Ca2Mg0.25Al1.5Si1.25O7:Ce(3+),Eu(2+) and Ca2Mg0.25Al1.5Si1.25O7:Ce(3+),Tb(3+) phosphors show not only a band due to Ce(3+) ions (409 nm) but also as a band due to Eu(2+) (520 nm) and Tb(3+) (542 nm) ions. More importantly, the effective energy transfer from Ce(3+) to Eu(2+) and Tb(3+) ions was confirmed and investigated by emission/excitation spectra and luminescent decay behaviors. Furthermore, the energy level scheme and energy transfer mechanism were investigated and were demonstrated to be of resonant type via dipole-dipole (Ce(3+) to Eu(2+)) and dipole-quadrupole (Ce(3+) to Tb(3+)) reactions, respectively. Under excitation at 350 nm, the emitting color could be changed from blue to green by adjusting the relative doping concentration of Ce(3+) and Eu(2+) ions as well as Ce(3+) and Tb(3+) ions. The above results indicate that Ca2Mg0.25Al1.5Si1.25O7:Ce(3+),Eu(2+)/Tb(3+) are promising single-phase blue-to-green phosphors for application in phosphor conversion white-light-emitting diodes.

Energy transfer upconversion dynamics in YVO4:Yb3+,Er3+

A new approach to calculate the effective Ln–Ln energy transfer rates in a doped crystal matrices was proposed and successfully applied to the YVO4:Yb3+,Er3+ upconversion system. This approach is based on the known set of Ln–Ln distances obtained from the crystal structure of the matrix and the probabilities of their occurrence. The non-radiative energy transfer rates were calculated in the intermediate coupling scheme taking into account the shielding of the 4f electrons. The required partial (that is, forced electric dipole-only, lacking the dynamic coupling contribution) Judd–Ofelt Ωλ parameters were calculated using the Simple Overlap Model (SOM). The spectral overlap factor F was estimated from optical absorption measurements. A simplified “one level-one manifold” energy level scheme was applied. The F7/24,H11/22andS3/24 states of Er3+ were treated as an effective level. The set of rate equations containing radiative, non-radiative and energy transfer processes was solved numerically using fourth-order Runge–Kutta method. Both continuous and pulsed excitation modes were simulated. The dependence of the upconversion intensity upon the pump power was found. The simulations resulted in good agreement with the experimental results and provided new insights into the dynamics of the upconversion process and a connection between the macroscopic properties and the microscopic description.

Sensitization of ZnO by Light-Harvesting Antennas Composed of Multiple Stacked Dyes Grown by Liquid-Phase Molecular Layer Deposition

Light-harvesting antennas in the photosynthesis systems of plants are known to be high-efficiency photon collectors. Here we use light-harvesting antennas in dye-sensitized solar cells.1 The concept of spectral sensitization of ZnO by light-harvesting antennas composed of multiple stacked dyes is shown in Fig. 1. Dyes with different energy gaps are stacked in a designated sequence so that a wide range of wavelengths are absorbed. The resulting broad absorption spectrum is a superposition of the narrow absorption bands of the individual dye molecules. This energy scheme is expected to decrease the heat generation caused by excess photon energy in the light absorption process.2 We have previously sensitized ZnO using two-dye stacked structures consisting of a p-type dye and an n-type dye to widen the photocurrent spectral width.2 In the present work, we investigate sensitization of ZnO using three-dye stacked light-harvesting antennas grown by liquid-phase molecular layer deposition (LP-MLD)2-4using n- and p-type dye molecules. Meier5reported that p-type dyes such as rose bengal (RB), eosin (EO) and fluorescein (FL) tend to have negative charge because they accept electrons, while n-type dyes like crystal violet (CV) and brilliant green (BG) typically have positive charge as they donate electrons. Because ZnO is an n-type material, as shown in Fig. 2, three-dye stacked structures can be grown using a single dye in each step by providing source molecules with a sequence of p-, n-, and p-type. Here, the LP-MLD process was achieved by electrostatic force. Namely, the attraction between p–n and repulsion between p–p and n–n molecules resulted in self-limiting growth, allowing us to construct structures of [n-type ZnO/p-type dye/n-type dye/p-type dye]. Samples for photocurrent measurements were prepared as follows. In step 1, after a ZnO powder layer (~5 μm thick) was formed on a glass substrate with a slit-type indium tin oxide (ITO) electrode (slit width of 60 μm), the layer was immersed in an isopropyl alcohol (IPA) solution of the first p-type dye (p1). In step 2, the layer was rinsed with IPA, and immersed in an IPA solution of n-type dye (n1) before the layer was dried. In step 3, the layer was immersed in an IPA solution of the second p-type dye (p2) in the same manner. This procedure gave three-dye stacked light-harvesting antennas with a structure of [ZnO/p1/n1/p2]. Photocurrent spectra were then measured by applying a 3-V potential across the slit-type ITO electrodes over a wavelength range of 400–700 nm. Fig. 3 shows reflection spectra of ZnO powder layers with adsorbed RB, EO, FL, CV, and BG dyes. By stacking these five dyes, photocurrent spectra were widened to cover the wavelength range from ~450 to 700 nm. In Fig. 4(a), photocurrent spectra measured following each growth step are shown for a light-harvesting antenna of [ZnO/EO/CV/RB]. When EO was deposited on a ZnO surface during Step 1, large photocurrents were generated over the wavelength region from ~500 to ~550 nm. When CV was deposited on EO in Step 2, photocurrents caused by CV were generated in the wavelength region longer than ~550 nm in addition to the photocurrent from EO absorption. When RB was deposited on CV during Step 3, photocurrents caused by RB were observed around ~570 nm. These results suggest that the multi-dye stacked light-harvesting antenna is effective to widen the wavelength region for sensitization of ZnO. It is important to arrange the dye molecules so that an energy-level scheme with a gradual energy slope similar to that of light-harvesting antennas in plants is formed. This facilitates electron transfer from the multi-dye stacked structure to the semiconductor to achieve high-efficiency sensitization. Fig. 4(b) shows an energy-level scheme determined from photoemission yield spectroscopy in air (PYSA)6measurements for [ZnO/EO/CV/RB]. The direction of the energy slope is opposite to the preferred direction. As a future challenge, to further improve sensitization efficiency, the energy-level scheme of the dye molecules should be optimized. References 1 B. O’Regan and M. Gratzel, Nature 353, 737 (1991). 2 T. Yoshimura, H. Watanabe, and C. Yoshino, J. Electrochem. Soc., 58, 51 (2011). 3T. Yoshimura, Japanese Patent, Tokukai Hei3-60487 (1991) [in Japanese]. 4T. Yoshimura, Japanese Patent, Tokukai 2009-60487 (2009) [in Japanese]. 5 H. Meier, J. Phys. Chem. 69, 719 (1965). 6 Y. Nakajima, D. Yamashita, A. Ishizaki, B. Pellissier, and M. Uda, Mater.Res. Symp. Proc. 1029, 1029-F04-02 (2008). Figure 1

Concentration Dependency of Eu2+ Doped La4-XCaxSi12O3+XN18-X Phosphors and the Energy Levels of the Rare-Earth Ions

Over the last decades, rare-earth doped silicon nitride and silicon oxynitride based materials have received considerable attention in luminescence research due to their wide range of possible structures, good luminescent properties, high thermal stability and chemical inertness. Examples hereof are Sr2Si5N8:Eu2+, CaAlSiN3:Eu2+ and α-sialon:Eu2+, which have shown to be good conversion phosphors for LEDs. The silicon nitride based luminescent materials are also considered for other applications like solar cells or as persistent luminescence materials. In order to find new nitridosilicate phosphors, a single-particle-diagnosis approach [1] has been developed in our group, based on single-particle spectroscopy techniques. One of the phosphors that has been found via this method is Eu2+ doped La4-xCaxSi12O3+xN18-x; a phosphor that was also found independently by Park et al. via a combi-chem approach [2]. The material has a strong 5d-4f emission band in the 450 to 650 nm range after 4f-5d excitation with UV or blue light, making it an interesting phosphor for LED applications. For this study, La4-xCaxSi12O3+xN4-x powders doped with rare-earths have been prepared via a solid-state reaction synthesis. The luminescence properties of the phosphors doped with Eu2+ have been studied as a function of the dopant concentration. An unusually large shift to longer wavelengths of the position of the emission band was observed with increasing Eu concentration, as is shown in Figure 1a. The shift can be attributed to a change in distribution of the Eu ions over the two different crystallographic sites, together with energy transfer between these sites. The effect of Eu concentration on the distribution and energy transfer, and with it the effects on the luminescence properties, have been investigated in detail by analyzing the luminescence decay time and temperature dependency of the luminescence as a function of the Eu concentration. Doping with Ce also gave rise to 4f-5d absorption bands, that resulted in blue 5d-4f emission after excitation with UV light. The results with Ce doping were compared with the results with Eu doping, regarding the distribution of the lanthanides over the two crystallographic sites. The information on the 4f-5d transitions of Eu and Ce, together with the thermal quenching data has been used to construct an energy level scheme (Figure 1b), showing the energy level positions of all lanthanides in La4-xCaxSi12O3+xN18-x relative to the valence and conduction band. With such a scheme the optical properties of all other lanthanides in the same host can be predicted and understood. [3] The scheme could be used to explain the absorption and emission spectra of samples doped with samarium and ytterbium, with regards to the positions of the charge transfer bands, the valence of the dopants and the thermal quenching behavior. [1] N. Hirosaki, T. Takeda, S. Funahashi, R.J. Xie; Chem. Mater. 26 (2014) 4280-4288. [2] W.B. Park, N. Shin, K.P. Hong, M. Pyo, K.S. Sohn; Adv. Funct. Mater. 22 (2012) 2258-2266. [3] P. Dorenbos; J. Alloys Compd. 488 (2009) 568. Figure 1

Sensitization of ZnO in Stacked Structures Containing Multiple Dyes Grown Using Liquid Phase Molecular Layer Deposition

In the 1970’s, Kiyota et al. developed a sensitization method for ZnO photoreceptors in electrophotography using two-dye stacked structures of p-type dye/n-type dye on ZnO. This was an effective method to widen the photocurrent spectra.1 Two-dye sensitization can be applied to dye-sensitized solar cells as shown in Fig. 1. In the n/p/n structure of n-type ZnO/p-type dye/n-type dye, electrons excited in the p-type dye are directly injected into ZnO, and electrons excited in the n-type dye are also injected into ZnO through the p-type dye. Consequently, the photocurrent spectrum arising from the p-type dye and that of the n-type dye can be superimposed to widen the photocurrent spectra. P-type dyes such as fluorescein (FL), eosine (EO) and rose bengal (RB), which can accept electrons, and n-type dyes such as crystal violet (CV) and brilliant green (BG), which can donate electrons,2 have absorption peaks at 510, 540, 570, 600, 660 nm, respectively. By stacking these five dyes, the photocurrent spectra can be widened, covering a wavelength range from ~450 nm to 700 nm. However, to date, sensitization has been carried out by combining only two dyes, limiting the degree of the spectral widening. In the present work, stacked structures containing three or four kinds of dyes were constructed for further spectral widening. The structures were fabricated using liquid-phase molecular layer deposition (LP-MLD)3-5 using the electrostatic force between molecules. The p-n attraction and the p-p and n-n repulsion enable self-limiting growth to construct the n/p/n structures with strong connections. Fig. 2 shows an example of the LP-MLD process for growth of a four-dye stacked structure on ZnO. In step 1, p-type dyes of p 1 and p 2 are deposited on a ZnO surface to form a monomolecular layer of p 1+p 2. Once the surface is covered with p 1 and p 2, the dye molecule deposition is automatically terminated because p-type dye molecules cannot be connected to other p-type dye molecules. After removing p 1 and p 2, n 1 and n 2 are deposited in step 2 to connect them to p 1 or p 2, resulting in four types of stacked structures: p 1-n 1, p 1-n 2, p 2-n 1, and p 2-n 2. Fig. 3(a) shows a schematic illustration of an energy level scheme for the sensitization of ZnO using the four-dye containing stacked structure. This structure resulted in a broad photocurrent spectrum of a superposition of photocurrents generated by the four kinds of dyes. The spectrum is shown in Fig. 3(b). Photocurrents were measured by applying a 3 V potential across slit-type ITO electrodes with a slit gap of 60 μm on glass substrates. Approximately ~5-μm-thick ZnO powder layers were formed on the substrates. Fig. 4(a) shows the photoluminescence (PL) spectrum of ZnO powder layers with the added dyes. The two-dye stacked structure of ZnO/RB/CV exhibits a broad PL spectrum compared with the single dye structure of ZnO/RB. The four-dye stacked structure of ZnO/RB+EO/CV+BG exhibits a broader spectrum than ZnO/RB/CV as expected. Fig. 4(b) shows the photocurrent spectra. In ZnO/EO, photocurrents were generated between ~450 nm and ~550 nm. The ZnO/EO/CV+BG stack was prepared after depositing EO on ZnO in step 1, and then CV and BG in step 2. This stack had a broad photocurrent spectrum extending to the long wavelength region beyond 600 nm and covered almost the whole visible region from 450 nm to 700 nm. The photocurrents generated in the wavelength region from ~550 nm to ~700 nm were attributed to CV and BG which have strong absorption in the long wavelength region. This result suggests that the three-dye stacked structure provides effective sensitization. In the case of the two-dye stacked structure containing four kinds of dyes of ZnO/RB+EO/CV+BG, a strong sensitization was observed in the long wavelength region extending beyond 700 nm. However, the photocurrent decreased in the short wavelength region. The reason for this has not been determined, and is being investigated at present by considering the energy levels determined using photoemission yield spectroscopy in air (PYSA).6 References 1 K. Kiyota, T. Yoshimura, and M. Tanaka, Photogr. Sci. Eng. 25, 76 (1981). 2 H. Meier: J. Phys. Chem. 69, 719 (1965). 3 T. Yoshimura, H. Watanabe, and C. Yoshino, J. Electrochem. Soc., 58, 51(2011). 4 T. Yoshimura, Japanese Patent, Tokukai Hei3-60487 (1991) [in Japanese]. 5 T. Yoshimura, Japanese Patent, Tokukai 2009-60487 (2009) [in Japanese]. 6 Y. Nakajima, D. Yamashita, A. Ishizaki, B. Pellissier, and M. Uda, Mater.Res. Symp. Proc. 1029, 1029-F04-02 (2008). Figure 1

3d and 4f Ions in Solids: Description and Understanding of Optical Properties

An overview of recent results on modeling of properties of optical materials doped with transition metal and rare earth ions is given. Studies of various groups of materials – pyrochlores, perovskites, garnets, spinels – are presented. Applications of several different approaches (e.g. crystal field theory, DFT-based computational techniques, configurational coordinate model etc) are discussed in details. Special attention is given to the positioning of impurity ions energy levels in the host band gap. It is shown that through the combination of the crystal field theory and ab initio methods of electronic structure calculations it is possible to build up the complete energy level scheme of a doped crystal, which includes the host’s electronic band structure and impurity ion energy levels superimposed onto it. A new model that links together the energies of the spin-forbidden transitions of transition metal ions (Mn4+, Cr3+, Ni2+) with the covalent effects experienced by those ions is also outlined. Several recommendations on how to tune the emission wavelengths of the Mn4+ 2Eg – 4A2g transition are outlined. All shown examples are compared with the corresponding experimental results (whenever possible). Predictive potential of the presented models is discussed.

Synthesis, structure and photoluminescence of (PLAGH)2[ZnCl4] and comparative analysis of photoluminescence properties with tris(2,2′-bipyridine)ruthenium(II)

The first compound of zinc(II) containing pyridoxalaminoguanidine has been synthesized and characterized by elemental analysis, infrared spectra, conductometric measurements and X-ray crystallography. Single crystals of the compound were obtained in the reaction of methanolic solution of zinc(II) chloride and pyridoxalaminoguanidine hydrochloride. In this compound the coordination of chelate ligand is absent and tetrachlorido complex of zinc(II) with pyridoxalaminuguanidinium cation as contraion is obtained. Photoluminescence spectra were measured. Lorentzian multipeak technique was used to determine peak wavelengths and their intensities. Photoluminescence spectroscopy upon 325, 488 and 514nm laser excitation light was used to obtain results. This novel compound of zinc(II) was compared to the well-known organic light emitting diode material—ruthenium(II) complex with bypiridine i.e., tris(2,2′-bipyridine)ruthenium(II), under the same circumstances and the identical experimental setup. A scheme of energy levels and transitions is proposed to explain the obtained experimental results.

Estudo das propriedades ópticas de vidros borosilicatos dopados com íons de Itérbio em função da concentração

Rare Earth elements have been studied for different scientific areas due to its excellent spectroscopic and magnetic properties with possible application for construction of different optical and electric devices (MARTINS, 2005; LOURENCO et al., 2011). In this work, it is studied the optical properties of Ytterbium (Yb 3+ ) ions embedded in a lead-borosilicate glass matrix synthesized by the melting method, using the optical absorption and photoluminescence techniques. The Yb 3+ ions were chosen to dope the glass matrix because it has an energy level scheme more simplified compared with other Rare-Earth ions, with only two energy levels, making it very attractive for the construction of high efficiency optical devices. Increasing the annealing temperature as well as the ion concentration in the matrix leads to a shift of the optical band gap of the matrix to higher energies. We believe that this shift (blue-shift) can be associated with the nanocrystallization process of the glass matrix SBP (SiO 2 , B 2 O 3 , PbO 2 ). The reduction of radiative lifetime with increasing ion concentration in matrix was studied using the Stokowski empirical relation, in which, it studies processes of energy transfer as a function of Rare-Earth concentration.

Photoluminescence and resonant energy transfer from Tb3+ to Eu3+ in Tb3Ga5O12:Eu3+ garnet phosphor

Eu3+-activated Tb3Ga5O12 (TGG) phosphor was synthesized by metal-organic deposition and its luminescence properties were reported in detail. The (Tb1−xEux)3Ga5O12 phosphor was synthesized from a mixture of organic gallium solution and acetic acid dissolved with TbCl3/Eu2O3. The X-ray diffraction analysis indicated that the synthesized phosphor was cubic garnet structure. The luminescence properties of the TGG:Eu3+ phosphor were investigated using photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and PL decay measurement. The effects of Eu3+ concentration on the PL properties were studied between x=0 and 0.14, and the strongest PL emission was observed at x~0.002. The PLE and PL decay characteristics showed the occurrence of an efficient energy transfer from the host (Tb3+) to Eu3+ in the TGG:Eu3+ phosphor. The increase in the PL intensity with increasing temperature was observed and analyzed on the basis of a simplified charge transfer along with the inclusion of conventional thermal quenching. The detailed energy-level scheme for the Tb3+ and Eu3+ ions in the TGG host was also determined from these PL and PLE spectra.

Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compoundCeAuAl3

We have investigated the noncentrosymmetric tetragonal heavy fermion compound $\mathrm{CeAuA}{\mathrm{l}}_{3}$ using muon spin rotation $(\ensuremath{\mu}\mathrm{SR})$, neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp $\ensuremath{\lambda}$-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector $\mathbf{k}=(0,0,0.52(1))$ and a spiral structure of Ce moments coupled ferromagnetically within the $ab$ plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of $\mathrm{CeAuA}{\mathrm{l}}_{3}$ that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a $4{f}^{1}$ electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of ${T}_{\mathrm{K}}=3.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural $\mathrm{CeCuA}{\mathrm{l}}_{3}$ The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in $\mathrm{CeAuA}{\mathrm{l}}_{3}$.

Electronic structure and energy level schemes of RE3+:LaSi3N5 and RE2+:LaSi3N5−xOx phosphors (RE=Ce, Pr, ND, Pm, Sm, Eu) from first principles

First principles calculations of rare earth (RE)-doped LaSi3N5 host lattice are performed to obtain the electronic structure, the band gap (BG), and the character of electronic transitions. Doping with both trivalent and bivalent RE cations is inspected. RE 4f states form two bands of occupied and unoccupied states separated by ~5eV. In RE3+-doped compounds 4f states are shifted by ~6eV to more negative energies compared with RE2+-compounds. This stabilization causes that RE3+ 4f bands are in a different position relative to the valence band and the conduction band than RE2+ 4f bands and therefore different electronic transitions apply. BG of RE3+-compounds decreases from ~4.6eV (Ce) to ~1.5eV (Eu). Except for Ce3+, exhibiting the 4f→5d transition, other RE3+-compounds show the charge transfer of the p→4f character. BG of RE2+-compounds increases from ~0.80eV (Ce, Pr) to ~0.95eV (Nd, Pm), ~1.43eV (Sm), and ~3.28eV (Eu) and the electronic transition is of the 4f→5d character. The energy level scheme constructed from ab initio calculated electronic structures agrees well with the experimental energy level diagram. The agreement demonstrates the reliability of the hybrid functional HSE06 to describe correctly bands of nonbonding RE 4f electrons.

Collective excitations in the transitional nucleiRe163andRe165

Excited states in the neutron-deficient nuclei 75163Re88 and 75165Re90 were populated in the 106Cd(60Ni,p2nγ) and 92Mo(78Kr, 3p2nγ) fusion-evaporation reactions at bombarding energies of 270 and 380 MeV, respectively. γ rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated in-flight by the RITU gas-filled recoil separator and implanted in the GREAT spectrometer. The energy level schemes for Re163 and Re165 were identified using recoil-decay correlation techniques. At low spin, the yrast bands of these isotopes consist of signature partner bands based on a single πh11/2 quasiproton configuration. The bands display large energy splitting consistent with the soft triaxial shape typical of transitional nuclei above N=82. The configurations of the excited states are proposed within the framework of the cranked shell model.3 MoreReceived 22 December 2014DOI:https://doi.org/10.1103/PhysRevC.91.034319©2015 American Physical Society

Shannon Entropy as a Measurement of the Information in a Multiconfiguration Dirac—Fock Wavefunction

Discrete Shannon entropy is applied to describe the information in a multiconfiguration Dirac—Fock wavefunction. The dependence of Shannon entropy is shown as enlarging the configuration space and it can reach saturation when there are enough configuration state wavefunctions to obtain the convergent energy levels; that is, the calculation procedure in multiconfiguration Dirac—Fock method is an entropy saturation process. At the same accuracy level, the basis sets for the smallest entropy are best able to describe the energy state. Additionally, a connection between the sudden change of Shannon information entropies and energy level crossings along with isoelectronic sequence can be set up, which is helpful to find the energy level crossings of interest in interpreting and foreseeing the inversion scheme of energy levels for an x-ray laser.

Energy level modeling of lanthanide materials: review and uncertainty analysis.

Energy level schemes are an essential tool for the description and interpretation of atomic spectra. During the last 40 years, several empirical methods and relationships were devised for constructing energy level schemes of lanthanide defects in wide band gap solids, culminating in the chemical shift model by Thiel and Dorenbos. This model allows us to calculate the electronic and optical properties of the considered materials. However, an unbiased assessment of the accuracy of the obtained values of the calculated parameters is still lacking to a large extent. In this paper, error margins for calculated electronic and optical properties are deduced. It is found that optical transitions can be predicted within an acceptable error margin, while the description of phenomena involving conduction band states is limited to qualitative interpretation due to the large error margins for physical observables such as thermal quenching temperature, corresponding to standard deviations in the range 0.3-0.5 eV for the relevant energy differences. As an example, the electronic structure of lanthanide doped calcium thiogallate (CaGa2S4) is determined, taking the experimental spectra of CaGa2S4:Ln(Q+) (Ln(Q+) = Ce(3+), Eu(2+), Tm(3+)) as input. Two different approaches to obtain the shape of the zig-zag curves connecting the 4f levels of the different lanthanides are explored and compared.

Inelastic Neutron Scattering Studies on the Crystal Field Excitations in Superconducting NdFeAsO0.85F0.15

Inelastic neutron scattering experiments were performed on polycrystalline samples of NdFeAsO0.85F0.15over a wide temperature range (3 K–250 K). Based on the analysis of the experimental data, a Nd3+CF energy level scheme is proposed to give a consistent explanation about the observed CF transitions. The observed extra ground-state CF transitions could not be simply explained by the transitions between five Kramers doublets split from the Nd3+ 4I9/2ground state in theC4vpoint symmetry. A reliable explanation would be a superposition of crystal fields due to different local symmetries around the Nd3+ions induced by the fluorine doping.

Photoluminescence properties of Ce^3+and Tb^3+-activated Ba_2Mg(PO_4)_2

The luminescence and energy transfer of cerium and terbium codoped Ba2Mg(PO4)2 were investigated. The phosphor was prepared by a solid-state reaction at high temperature. The photoluminescence properties were investigated under UV excitation. From a powder X-ray diffraction analysis, the formation of single-phased Ba2Mg(PO4)2 with a monoclinic structure was confirmed. The photoluminescence excitation spectrum of Ba2Mg(PO4)2:Ce3+ shows that the excitation band from 220 to 350 nm and the broad-band UV-blue emission are attributed to the allowed 4f ↔ 5d transitions of Ce3+. Upon excitation of Ce3+ band, Ba2Mg(PO4)2:Ce3+,Tb3+ phosphors exhibit both Ce3+ emission band the characteristic Tb3+ emission lines. Also, efficient energy transfer from Ce3+ to Tb3+ in Ba2Mg(PO4)2 was verified by observing the excitation spectra of Ba2Mg(PO4)2:Ce3+,Tb3+. An energy level scheme is constructed to depict the energy transfer process.

First observation of the rotational spectrum of the HD–CO weakly bound complex

In this Note we present the first observation of the rotational spectrum of the HD–CO van der Waals complex. Three b-type transitions, namely R(1), R(2) and R(3) corresponding to the rotation of the CO subunit within the complex, were measured in the millimeter-wave region using the orotron jet spectrometer. An approximate low energy level scheme for the HD–CO complex was built on the basis of the previous investigations of the paraH2–CO and orthoD2–CO complexes and the presented measurements.

Ab initio study on the effect of structural relaxation on the electronic and optical properties of P-doped Si nanocrystals

In contrast to the conventional doping of bulk silicon (Si), the doping of Si nanocrystals (NCs) that are often smaller than 5 nm in diameter may lead to serious structural changes. Since the electronic and optical properties of Si NCs are intimately associated with their structures, it is critical to understand how doping impacts the structures of Si NCs. By means of ab initio calculation we now compare 1.4 nm phosphorus (P)-doped Si NCs without structural relaxation and those with structural relaxation. Structural changes induced by structural relaxation are manifested by the stretching and compressing of bonds and apparent variations in bond angles. With the increase of the concentration of P structural changes induced by structural relaxation become more serious. It is found that structural relaxation makes differences in the energy-level schemes of P-doped Si NCs. Structural relaxation also causes the binding energy of an electron in a P-doped Si NC to more significantly increase as the concentration of P increases. With the increase of the concentration of P structural relaxation leads to more pronounced changes in the optical absorption of P-doped Si NCs.

Hydrogen Evolution Using Palladium Sulfide (PdS) Nanocorals as Photoanodes in Aqueous Solution

Palladium sulfide (PdS) nanostructures are proposed to be used as photoanodes in photoelectrochemical cells (PECs) for hydrogen evolution due to their adequate transport and optical properties shown in previous works. Here, a complete morphological and electrochemical characterization of PdS films has been performed by different techniques. PdS flatband potential (Vfb=-0.65±0.05 V vs NHE) was determined by electrochemical impedance spectroscopy measurements in aqueous Na2SO3 electrolyte, providing a description of the energy levels scheme at the electrolyte-semiconductor interface. This energy levels scheme confirms PdS as a compound able to photogenerate hydrogen in a PEC. At last, photogenerated hydrogen rates are measured continuously by mass spectrometry as a function of the external bias potential under illumination, reaching values up to 4.4 μmolH2/h at 0.3 V vs Ag/AgCl.