EPR study of quasi-one-dimensional complex oxides A3n + 3mA′nMn3m + nO9m + 6n (A-Sr, Ba; A′-Mg, Zn, Cu)

Exchange interactions in the quasi-one-dimensional complex oxides Sr₄MgMn₂O₉, Ba₆MgMn₄O₁₅, Ba₈MgMn₆O₂₁, and Ba₉ M ₂Mn₅O₂₁ (M-Cu, Zn, Mg) have been studied by electron paramagnetic resonance. The temperature dependence of the spectral parameters showed that the exchange interaction is antiferromagnetic and occurs mainly inside the manganese-containing groups and to a lesser extent between them.     

蓝色荧光粉Sr2B5O9Cl:Eu2+发光特性的研究

采用高温固相法合成了近紫外光激发的蓝色荧光粉Sr₂B₅O₉Cl:Eu²⁺,研究了SrCl₂ ·6H₂O用量和Eu²⁺浓度对其结构和发光性能的影响.随着Eu²⁺浓度的增加,其结构无明显变化,发光强度先增强后减弱,当其浓度为8mol%时,荧光粉的发光强度最大;当用Ca取代Sr时,荧光粉的发射峰从425 nm红移到453 nm. 适当过量 关键词： 氯硼酸盐 蓝色荧光粉 LED     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.     

Ionic conductivity in the single crystals of non-stoichiometric fluorite phases M1−xRxF2+x (M=Ca,Sr, Ba; R=Y,La-Lu)

The ionic conductivity has been measured of single crystals of rare earth fluoride solid solutions in Ca, Sr and Ba fluorides described by the formula M_1?xR_xF_2+x (M=Ca, Sr, Ba; R=Y, La-Lu). The measurements have been done using dc and ac within the temperature range 300–850 K. With the increase of RF₃ concentration up to x=0.05–0.15 (in different systems) conductivity steeply increases. With the further concentration growth the conductivity increases only slightly, reaching saturation value for the solid solution Ba_1?xR_xF_2+x. The dependence of solid solution conductivity on the chemical composition has been studied for isoconcentrates M_0.9R_0.1F_2.1. It has been established that in CaF_2- based series the crystals with R=Gd, Tb possess maximum conductivity and minimum activation energy. For SrF₂ and BaF₂-based series the highest conductivity was observed for crystals containing LaF₃. It has been established that for all the crystals, independent of the chemical composition and defect concentration, the conductivity logarithm at definite temperature linearly depends on the activation energy. Within the investigated class of substances the optimum composition for solid electrolytes is Sr_0.69La_0.31F_2.31.     

Theoretical design on a new double functional device of 2,2′‐bipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5

Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza‐crown ether (2,2′‐dipyridine‐embedded N‐(9‐anthraceneyl(pyrenyl)methyl)aza‐15‐crown‐5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) were investigated. The fully optimized geometry structures of the free ligands ( L _1, L ₂) and their metal cation complexes ( L ₁/M²⁺, L ₂/M²⁺) were calculated with the B3LYP/6‐31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L ₁/M²⁺, L ₂/M²⁺ molecules. The absorption spectra of L _1, L ₂, L ₁/M²⁺, and L ₂/M²⁺, and their excited states were studied by time‐dependent density functional theory. A new type molecular device L ₂(2,2′‐dipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5) is designed, which not only has the selectivity for Sr²⁺, and construct allosteric switch, but also has fluorescent sensor performance.     

The Field Effect in a Metal–Ferroelectric–Semiconductor System of Multilayer Ferroelectric Films with Various Structure Types

The ability to grow the interfacial defect-poor Sr_0.5Ba_0.5Nb₂O₆ + Ba_0.2Sr_0.8TiO₃ and Ba_0.8Sr_0.2TiO₃ + Ba_0.4Sr_0.6TiO₃ ferroelectric films onto the doped silicon substrates is discussed. A study of piezo-response via the quasi-static method (using the electrode area of 0.07 mm²) reveals that heterostructures possess an initial polarized ferroelectric state with a spontaneous polarization vector perpendicular to the substrate at any type of Si conductivity. The polarized state is established to refer to two-dimension stresses in the ferroelectric, which is tunable through a preprepared Ba_xSr_{1 – x}TiO₃ onto a sublayer substrate as well as to a thickness of this sublayer. Polarization switching in Sr_0.5Ba_0.5Nb₂O₆/Si and Ba_0.8Sr_0.2TiO₃/Si heterostructures under the external field arises at only using the barium–strontium titanate sublayer predeposited onto silicon. A 15% decrease in switching polarization in Ba_0.8Sr_0.2TiO₃/Ba_0.4Sr_0.6TiO₃/Si structures is observed after 500 h.     

Luminescence properties of Eu2+ in M2MgSi2O7 (M=Ca, Sr, and Ba) phosphors

The photoluminescence properties of alkali-earth magnesium silicates (M₂MgSi₂O₇, M=Ca, Sr, and Ba) doped with Eu²⁺ were investigated. Solid solutions of Ba _x Sr_2−x Si₂O₇, Ca₂MgSi₂O₇, and Sr₂MgSi₂O₇ were prepared. Ba _x Sr_2−x Si₂O₇ retained a tetragonal crystal structure similar to the structure of the other compounds up to a stoichiometry of x=1.6, which enabled a systematic study of the common structure. Monoclinic Ba₂MgSi₂O₇ was prepared, and the luminescence properties were compared with those of other samples. The emission and excitation spectra of tetragonal M₂MgSi₂O₇ (M=Ca, Sr, and Ba) changed as a function of the covalency, site symmetry, and crystal field strength. The luminescence properties showed excellent agreement with theoretical predictions based on these factors. The Stokes shift differentiated the emission behaviors of the tetragonal and monoclinic structures.     

Synthesis and Luminescent Properties of M<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu (M=Sr,Ba) Nanophosphors

A solution combustion route for the synthesis of Eu³⁺-activated M₂V₂O₇ (M = Sr, Ba) and their luminescent properties have been investigated. Structure and luminescent characteristics of Sr₂V₂O₇:Eu³⁺ and Ba₂V₂O₇:Eu³⁺ nanophosphors have been studied by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, fluorescence spectrometry and Fourier transform infra-red spectroscopy. The incorporation of Eu³⁺ activator in these nanoparticles has been checked by luminescence characteristics. These nanoparticles have displayed red color under a UV source which is due to characteristics transition of Eu³⁺ from ⁵D₀ → ⁷F₂ at 613 nm in both Sr₂V₂O₇:Eu³⁺ and Ba₂V₂O₇:Eu³⁺ nanophosphors. In addition, the optimal Eu³⁺ - doped contents of Sr_2(1-x)Eu_2xV₂O₇ and Ba_2(1-x)Eu_2xV₂O₇ nanophosphors for both were 4 mol%.     

Highly Efficient pc-LED Phosphors Sr1-xBaxSi2O2N2:Eu2+ (0 x 1) - Crystal Structures and Luminescence Properties Revisited

Due to their excellent luminescence properties in the blue-green to green-yellow spectral region, oxonitridosilicates Sr_1-xBa_xSi₂O₂N₂:Eu²⁺ (0 x 1) are promising conversion materials for application in phosphor-converted high-power LED devices. In order to understand the properties and thus to fully exploit the potential of these materials, detailed knowledge of corresponding (local) crystal structures is indispensable. Detailed insights into real structures have been achieved by combining X-ray diffraction and electron-microscopy methods. A major reason for the excellent luminescence properties of the phases Sr_1-xBa_xSi₂O₂N₂:Eu²⁺ (0 x 1) is the rigid silicate substructure built up of two-dimensionally condensed SiON₃ tetrahedra. The general topology of these layers is analogous for all members. However, there is no complete solid-solution series. Crystal-structure determination was frequently not straightforward because several real-structure effects had to be considered. The relative orientation of the silicate layers and the metal-atom layers inserted between them can differ without changing the chemical composition. As a consequence, polytypes are formed. The differentiation between such closely related structures was only possible by a thorough analysis of crystallographic data. The same applies for phases which differ in their composition as all Sr_1-xBa_xSi₂O₂N₂:Eu²⁺ (0 x 1) phases are very similar. The literature on these compounds is critically discussed with respect to phase analysis and structure determination. Different synthesis routes are reviewed and the results of luminescence investigations are discussed in this contribution. Beyond thermal as well as chemical stability and high transparency, electron-phonon coupling is effectively suppressed in Sr_1-xBa_xSi₂O₂N₂:Eu²⁺ (0 x 1) phases. Therefore, primary UV to blue light (GaN based semiconductor LEDs) is efficiently converted into visible components of the spectrum. Sr_1-xBa_xSi₂O₂N₂:Eu²⁺ (0 x 1) phases are therefore promising oxonitridosilicate phosphors for application in LED industry.     

Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca²⁺, Sr²⁺ and Ba²⁺. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl₂]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca²⁺, Sr²⁺ and Ba²⁺. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr²⁺ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [ SrCl₂]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.     

发光二极管用红色荧光粉Sr0.8-xBaxEu0.2WO4的制备和性质研究

采用化学共沉淀法制备了不同Ba²⁺掺杂浓度、 不同煅烧温度的Sr_0.8-xBa_xEu_0.2WO₄红色荧光粉. 研究了样品的晶体取向和晶格 畸变对发光性质的影响, 实验结果表明: 合成的Sr_0.8-xBa_xEu_0.2WO₄红色荧光粉为四方相, 样品中Eu³⁺的⁵D₀–⁷F₂跃迁的红光能被近紫外光和蓝光有效激发. 适量的Ba²⁺离子取代部分的Sr²⁺提高了Sr_0.8Eu_0.2WO₄荧光粉的发光强度, Ba²⁺掺杂浓度的改变对基质的晶格参数、晶体对称性和发光性能影响较大, Ba²⁺的最佳掺杂量为30%.     

The ac conductivity and complex impedance of CuO-doped (Ba0.5Sr0.5)TiO3 ceramic

The AC conductivity and complex impedance spectroscopy of CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramic were investigated. X-ray diffraction analysis showed that CuO-doped (Ba_0.5Sr_0.5)TiO₃ has a perovskite structure without any pyrochlore phase. Frequency dependent dielectric permittivity was discussed at a different temperature range. The activation energy was calculated and discussed through the Arrehnius equation from the ac conductivity with different frequency plots. CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramics have a negative temperature coefficient of resistivity. Dependence of impedance spectroscopy on frequency and temperature showed that the conduction process in the CuO-doped (Ba_0.5Sr_0.5)TiO₃ ceramic follows the thermally activated conduction mechanism.     

Effect of Sr2+-doping on structure and luminescence properties of BaAl2Si2O8:Eu2+ phosphors

Sr²⁺ doped BaAl₂Si₂O₈:Eu²⁺ phosphor was synthesized by chemical co-precipitation method. With the increase of Sr²⁺ concentration, the phase structure of (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ changes from hexagonal phase to monoclinic phase owing to large activation energy in SrAl₂Si₂O₈ system. (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ phosphor exhibits a broad blue band peaking at 425 nm due to the 4f⁶5d–4f⁷(⁸S_7/2) transition of Eu²⁺ ions. The emission intensity increases, accompanied by the blue shift of emission maximum from 459 to 417 nm with the Sr²⁺ doping concentration increasing. The optimal concentration of Sr²⁺ ion is 40%, and the phosphor shows high color stability in CIE chromaticity diagram. The result indicates that Sr²⁺ doped phosphor not only can enhance the relative intensity but also can adjust the chromaticity coordinate.     

Growth of BaxSr1−xSO4 nano-steps on barite (0 0 1) face

Crystal growth has been promoted in the fluid cell of an Atomic Force Microscope (AFM) by passing Ba-Sr-SO₄ aqueous solutions over barite (0 0 1) cleavage surfaces. Steps advance in structural continuity with the original barite (0 0 1) surfaces and two-dimensional nucleation occurs preferentially on the newly-formed terraces. The terraces are, on average, 7.5% lower than pure barite terraces. Since the ionic radius of Sr²⁺ is smaller that the ionic radius of Ba²⁺, the reduction of terrace height is consistent with an extensive incorporation of Sr²⁺ into the barite structure. Therefore, it can be considered that the newly-formed terraces have compositions corresponding to terms of the Ba_xSr_1−xSO₄ solid solution. A non-linear dependence of step rate on [SrSO₄] concentration in the solution (and therefore on supersaturation) has been found. The growth behaviour has been discussed by considering both the physicochemical properties of the Ba_xSr_1−xSO₄ solid solution-aqueous solution (SS-AS) system and a kinetic-based step growth model.     

Adsorption of formaldehyde on the Fe site of clean and M (Ca, Sr and Ba) doped LaFeO3 (0 1 0) surface

The adsorption of formaldehyde (H₂CO) on the Fe site of clean and M²⁺ (Ca²⁺, Sr²⁺ and Ba²⁺) doped LaFeO₃ (0 1 0) surface have been investigated using the density functional theory (DFT) method. Calculation results show that the oxygen atom of the H₂CO molecule prefers to be adsorbed on the Fe site of the clean LaFeO₃ (0 1 0) surface. The adsorption of H₂CO could change the electronic properties of the LaFeO₃, indicating that the LaFeO₃ could be used as gas sensing material to detect the H₂CO gas. The analysis results of the DOS suggest that the bonding mechanism between the H₂CO molecule and the Fe site is mainly from the interaction between the Fe 3d and H₂CO 2p orbital. Comparing with the binding energy and the net charge-transfer, we find that the M²⁺ (Ca²⁺, Sr²⁺ and Ba²⁺) doping cannot improve the sensitivity of the LaFeO₃ to the H₂CO gas.     

Sr和Ba替代对Eu掺杂Ca2.955Si2O7的结构和发光特性的影响研究

利用固相反应法制备了Sr和Ba替代的Ca_2.955-xM_xSi₂O₇: 0.045Eu²⁺ (M= Sr, Ba, x= 0.1-0.5)系列荧光粉, 利用较大离子半径的Sr和Ba元素替代Eu掺杂Ca_2.955-xM_xSi₂O₇ 中的Ca元素,研究Sr和Ba替代对样品结构和发光特性的影响. X射线衍射测试结果表明,少量Sr和Ba替代不会改变基质的晶体结构, 样品仍然为单斜晶系.未替代前, Ca_2.955Si₂O₇: 0.045Eu²⁺ 样品的发射峰在574 nm左右,随着Sr含量的增加,样品的发射峰发生蓝移; 而Ba含量在x= 0.1-0.4时不会引起发射峰位置的移动, 但x= 0.5样品的发射峰发生蓝移.同等含量的Sr和Ba部分替代样品中的Ca元素, Ba替代样品的光谱强度较强.     

Mössbauer study of fluorides: Ba2MFeF9 and NaBaFe2F9

The Mössbauer spectra of the compounds Ba₂NiFeF₉, Ba₂FeCrF₉ and NaBaFe₂F₉ have been studied as a function of temperature. Values of the Néel temperature are obtained and the effects of cationic inversion between the two sites of M^II and M^III in compounds Ni^IIFe^III and Fe^IICr^III are observed. In the latter compound, we observe broad lines at all temperatures and a smearing of the magnetic ordering temperature. However, the Fe^IIFe^III compound shows strict structural order. The two sites of Fe^III in NaBaFe₂F₉ have not been resolved.     

Crystal structure and photoluminescence of (Ba1−x−ySryEux)9Sc2Si6O24

Divalent europium-doped alkaline earth metal silicate phosphors, (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (x=0.005–0.1, y=0–0.95), have been successfully prepared by solid-state reaction at 1350 °C. The analysis of X-ray diffraction shows that the compounds are in a single phase at the proper concentration of Sr²⁺. At room temperature, the Eu²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor exhibits a single emission band peaking at about 506 nm. With the increasing content of Sr²⁺, the luminescent intensity of (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ weakens, and the emission peak shifts towards red. Luminescence concentration quenching occurs when Eu²⁺ content x is more than 1 mol% in (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (y=0/0.2). At low temperatures (Ba_0.9?ySr_yEu_0.1)₉Sc₂Si₆O₂₄ (y=0/0.2) phosphors have two emission bands corresponding to different Eu²⁺ crystallographic sites. The high energy peak (P₁) is quenched at room temperature, while the low energy peak (P₂) weakens much more slowly owing to the energy transfer from P₁ to P₂.     

Luminescence characteristics of Eu2+ activated Ca2SiO4 Sr2SiO4 and Ba2SiO4 phosphorsfor white LEDs

<正>This paper investigates the luminescence characteristics of Eu²⁺ activated Ca₂SiO₄,Sr₂SiO₄ and Ba₂SiO₄ phosphors. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices,and show different emission colour variation caused by substituting M²⁺ cations for smaller cations.This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence.These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes（LEDs） based on ultraviolet chip/phosphor technology.     

Characteristics of Ba xSr 1–xTiO 3 thin films grown by pulsed laser ablation of rotating split targets of BaTiO 3 and SrTiO 3

We have grown heterostructures of Ba_xSr_1-xTiO₃(BST)/La_0.7Sr_0.3MnO₃(LSMO) on LaAlO₃(LAO) substrates by the pulsed laser deposition method. BST films with x=0.2,0.5,0.7 and 0.8 have been prepared using a novel rotating split-target arrangement. The lattice constant of the BST films is found to vary linearly with Ba/Sr ratio. An excellent cube-on-cube epitaxial relationship of (100)_BST||(100)_LSMO||(100)_LAO has also been obtained. Scanning electron microscopy studies have revealed smooth and crack-free BST films with a uniform grain size of about 100 nm. Dielectric measurements, made with patterned Au top electrodes and conducting LSMO bottom layers, have shown a maximum permittivity of approximately 280 at 5 kHz in BST films with x=0.7. P–E loop analyses of the Ba_0.7Sr_0.3TiO₃ and Ba_0.8Sr_0.2TiO₃ films have yielded remnant polarization values of 1.66 and 1.81C/cm², respectively. PACS 81.15Fg; 68.55Jk; 77.55+f