Core level excitation spectra of La and Mn ions in LaMnO3

Manganese-based perovskite is popular for research on ferromagnetic materials,and its spectroscopic studies are essential for understanding its electronic structure,dielectric,electrical,and magnetic properties.In this paper,the M-edge spectra of La ions and the M-edge,L-edge,and K-edge spectra of Mn ions in LaMnO3 are calculated by considering both the free-ion multiplet calculation and the crystal field effects.We analyze spectral shapes,identify peak origins,and estimate the oxidation states of La and Mn ions in LaMnO3 theoretically.It is concluded that La ions in LaMnO3 predominantly exist in the trivalent state,while Mn ions exist primarily in the trivalent state with a minor presence of tetravalent ions.Furthermore,the calculated spectra are in better conformity with the experimental spectra when the proportion of Mn3+is 90%and Mn4+is 10%.This article enhances our comprehension of the oxidation states of La and Mn within the crystal and also provides a valuable guidance for spectroscopic investigations of other manganates.

Theoretical Analyses of 4f^11→4f^105d Excitation Spectra of Er^3＋ Doped in LiYF4

Spectral terms and J-spectral multiplet of low-spin 4f105d configuration of Er3+ were obtained with the method of ligand field theory. According to the selection rules for dipole transitions, the excitation spectra of Er3+ doped in LiYF4 in vacuum ultraviolet region (120～160 nm) of the spectrum were theoretically interpreted by applying the crystal field model, and the six bands were assigned to the spin-allowed transitions from the ground state (4I15/2) to J-spectral multiplet of low-spin 4f105d configuration of Er3+ion.

Co-Precipitation Synthesis and Spectral Characteristics of Long Afterglow Phosphor Y_2O_2S:Sm^(3+), Mg^(2+), Ti^(4+)

Y2O2S：Sm^3＋, Mg^2＋, Ti^4＋ phosphor was synthesized by co-precipitation method. The crystalline structure of all synthesized phosphors was investigated by XRD. The result showed that all synthesized phosphors had a hexagonal crystal structure, which was the same as Y2O2S. The emission spectrum and excitation spectrum were measured, and the effect of Sm^3 ＋ molar ratio on the spectra was discussed. The emission spectra of the phosphors showed three emission peaks due to typical transitions of Sm^3 ＋ （4G5/2→6HJ ,J = 5/2, 7/2, 9/2）, and the emission peaks at 606 nm was stronger than others. With the increase of Sm^3 ＋ molar ratio, the emission intensity was strengthened. The excitation peaks were ascribed to the representative energy transition 4f→4f of Ti^4＋ phosphor prepared by co-precipitation method was Sm^3＋ ions. The results indicated that the Y2O2S ： Sm^3＋ , Mg^2＋ , an efficient long afterglow phosphor.

Charge Transfer Spectra (CTS) in CaS:Ce^(3+) Phosphors

This paper describes the excitation spectra nearby 220hm of CaS:Ce^(3+),Na^+ and CaS:Ce^(3+),X^-(X=F,Cl or Br).It is considered that the charge transfer excitation is caused by electron transfer of S^(2-)on 3p^6 to the 4f shell of Ce^(3+).It has been discussed that,when halogen ions act as coactivators,this excitation band shifts to low- er wavenumber.

Redshift of Excitation Wavelength Caused by the Concentration of L-Tryptophan in Water: A Theoretical and Experimental Study

A redshift in the wavelength of excitation spectra is experimentally measured as a function of the concentration parameter for tryptophan solutions in water. To understand the microscopic causes of this behavior, theoretical calculations obtained from four model clusters are carried out: (Trp)1 - (H2O)9, (Trp)2 - (H2O)18, (Trp)3 - (H2O)27 and (Trp)4 - (H2O)36, where there are interactions among 1, 2, 3 and 4 molecules of tryptophan. According to the literature, each interaction occurred with nine molecules of water to stabilize its expected zwitterionic form. In these models, the molecules of tryptophan appear at an adjacent distance among them to generate an analogous behavior when there is an experimental increase in the concentration. It is evident that the distance between adjacent molecules of tryptophan decreases as their concentration increases. The optical properties of these clusters are obtained by studying the corresponding excited states and the molecular orbitals involved, showing charge transfers by using time-dependent density functional theory (TD-DFT) methods. The experimental spectroscopic data are obtained by using the clusters proposed, and good agreement is found by drawing a comparison with the theoretical data.

Blue-shift of Nano-Y_2O_3 : Eu^(3+) Emission Spectra Excited by X-ray

Nano-Y_2O_3:Eu^(3+) powder was prepared by the homogeneous precipitation. With controlling the conditions of the reaction, nano powders with different grain size were obtained. It is found that the blue-shift phenomena exist in the nano-Y2O3:Eu3+ emission spectra excited by X-ray. The wave lengths of the peak (5D0→7F2) are related with the grain size of the powder

First-Principles Study of Ca3Sc2Si3O12： Ce3＋ Phosphors

Charge compensation plays a very important role in modifying the local atomic structure and moreover the spectroscopic property of an isolated luminescent center, and so has been widely adopted in phosphor designs. In this work, we carry out first-principles calculations on various cases of Ce3＋ centers in Ca3Sc2Si3O12 by considering the effects of the charge com- pensations related to N3-, Sc3＋, Mn2＋, Mg2＋, and Na＋. Firstly, the local structures around Ce3＋ are optimized by using density functional theory calculations with supercell model. The 4f→5d transition energies of Ce3＋ are then obtained from the CASSCF/CASPT2/RASSI-SO calculations performed on Ce3＋-centered embedded clusters. The calculated energies support the previous assignments of the experimental spectra. Especially, a previously unclear peak is identified to be caused by Sc3＋ substituting Si4＋. The results show that the first-principles calculations can be used as an effective tool for predicting and interpreting spectroscopic properties of the phosphors.

Theoretical Investigations of Nonlinear Optical Properties of Transition Metal Cluster Anions

In the framework of density functional theory （DFT）, the electronic excitations and nonlinear optical （NLO） properties of six binuclear transition metal cluster anions with the formula of [Ch2M-（μ-Ch）2-M＇CN]^2- （M = Mo, W; Ch = S, Se; M＇ = Cu, Ag） have been systemically investigated at both cases of gas phase and DMF solution. The obtained electronic absorption spectra reveal that the element replacements of metals M and ligands Ch have significant influence on the absorptions, especially on the low-lying ones. In addition, the transitions of μ-Ch→M are dominant for the low-lying excitations, whereas the transitions of M＇→M as well as Ch→M are mainly responsible for the higher excitations. The calculated molecular first and second hyperpolarizabilities present the remarkable element substitution and solvent effects. The analyses show that the transitions involving μ-Ch→M charge transfer make the critical contributions to the first hyperpolarizability t, and that the charge transfers from the moieties of MCh4 to M＇CN as well as those of μ-Ch→M and M＇→M are responsible for the second hyperpolarizability y. Moreover, the introduction of solvent leads to the results that the transitions within the moieties of MCh4 and M＇CN make larger contributions to the hyperpolarizability, especially to γ.

Dynamical quantum phase transition in XY chains with the Dzyaloshinskii-Moriya and XZY-YZX three-site interactions

We study the dynamical quantum phase transitions(DQPTs)in the XY chains with the Dzyaloshinskii-Moriya interaction and the XZY-YZX type of three-site interaction after a sudden quench.Both the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form■where the quasiparticle excitation spectraεkmay be smaller than 0 for some k and are asymmetrical■It is found that the factors of Loschmidt echo equal 1 for some k corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfyingε_(k)·ε_(-k)<0,when the quench is from the gapless phase.By considering the quench from different ground states,we obtain the conditions for the occurrence of DQPTs for the general XY chains with gapless phase,and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless phase.This is different from the DQPTs in the case of quench from the gapped phase to gapped phase,in which the DQPTs will always appear.Moreover,we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped phase.The conclusion can also be extended to the general quantum spin chains.

Fluorescence Properties of Eu^(3+) :Y_2SiO_5 Single Crystal

Fluorescence properties of Eu 3+ :Y 2SiO 5 have been investigated. Transitions between 5D and 7Fwere were studied with transmission spectra, fluorescence spectra, photoluminescence excitation ( or absorption ) spectra and site selective fluorescence spectra. The X ray powder diffraction pattern of Eu 3+ :Y 2SiO 5 shows that the crystal belong to monoclinic, and lattice's constants a, b, c and β are obtained by a simulation with the measured diffraction angles.

Investigation of the Spin Crossover Complex [Fe(bapbpy)(NCS)_2 ] in Its Low-spin and Highspin State by DFT/TD-DFT/BS-DFT Calculations

The spin crossover（SCO） compound [Fe（bapbpy）（NCS）2],where bapbpy contains two fused N,N-bis（2-pyridyl）amines,has been studied by DFT/TD-DFT/BS-DFT methods.Several density functionals and basis sets were used in the calculation to obtain optimized geometries of the compound in the low-（LS） and high-spin（HS） states.The vibrational modes and IR spectra,spin splitting energies,excited states and UV/Vis absorption spectra were obtained.The structural parameters of the calculated isolated complex are in good agreement with the X-ray data.We investigate three dimers of [Fe（bapbpy）（NCS）2] complex for their magnetic properties.It has been found that the complex（1,3） has ferromagnetic character while the others are antiferromagnetic in nature by using a broken symmetry approach in the DFT framework（BS-DFT） with support from the coupling constant values（J） and spin density plots.

Studies on NaLn(WO_4)_2 Single Crystals(Ln=La,Pr,Nd)

The crystals of NaLn(WO4)_2(Ln=La,Pr,Nd)are grown from a melt of LiCl-Na_2WO_4 flux by slow cooling method.The chemical analysis data show that the crystals are NaLa(WO_4)_2,NaPr(WO4)_2 and NaNd(WO_4)_2 respectively.The structures of the crystals are ascertained that they belong to scheelite structure of the tetragonal system with a space group of 14_1/a.The lattice parameters of the crystals have been calculated.It is found that the cell volume of NaLn(WO_4)_2 crystals decrease with a decrease of Ln^(3+)radius. The bond distances and their angles in NaLa(WO_4)_2 and NaNd(WO_4)_2 are given.It is found that in accordance with the decrease of ionic radii of Ln^(3+)due to increase of atomic number,the bond distances between Ln-O,Ln-Ln and W-O decrease regularly.The infrared spectra of NaLn(WO_4)_2 are measured.The tetrahedra characteristic absorptions of WO_4^(2-)are shown.The sensitization of host lattice is observed from the excitation and fluorescent spectra of NaLa(WO_4)_2 and NaPr(WO_4)_2.

Luminescence of Eu(MBA)_2NO_3Phen Complexes

At 77 K excitation spectra,luminescence and time-resolved spectra of Eu(o-MBA)2NO3 Phen and Eu(m-MBA)2NO3 Phen (MBA:methylbenzoate,Phen 1,10-phenanthroline) complexes were measured. Spectral data show that because of steric effect of ortho-methyl substituent there occur two Eu3+ sites with slightly different chemical environment in the Eu(o-MBA)2NO3Phen complex.The local symmetnes for the central metal ions are C2v and C1,C2 or Cs,respectively.However,there is only one Eu3+ site in the Eut(m-MBA)2NO3Phen complex which is similar to the C2v Eu3+ site of the previous complex.This demonstrates that the Eu3+ ion can be used as a conformational probe in the solid state compounds.

Study on the Phase Diagram of CsCl-CeCl_3-HCl(11%)-H_2O System and the Properties of the Compounds

The equilibrium solubility of CsCl CeCl 3 HCl(11%) H 2O quaternary system at 25 ℃ has been determined by the physic chemical analysis method, and the phase diagram was plotted. Two new double salts 3CsCl·CeCl 3·3H 2O and CsCl·CeCl 3·4H 2O obtained from the complicated system were identified and characterized by XRD, TG DTA, DSC, UV and fluorescence spectroscopy. Studies on the fluorescence excitation and emission show that 3CsCl·CeCl 3·3H 2O and CsCl·CeCl 3·4H 2O have upconversion luminescence of infrared visible range, and the upconversion emission intensity increases with the increase of ratio of CeCl 3 in CsCl.