Synthesis of the complex fluoride LiBaF3 and optical spectroscopy properties of LiBaF3 : M(M = Eu,Ce) through a solvothermal process

The complex fluoride LiBaF3 and LiBaF3:M(M = Eu, Ce) is solvothermally synthesized at 180 degreesC and characterized by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. In the solvothermal process, the solvents, molar ratios of initial mixtures and reaction temperature play important roles in the formation of products. The excitation and emission spectra of the LiBaF3:M(M= Eu,Ce) have been measured by fluorescence spectrophotometer. In the LiBaF3: Eu emission spectra, there is one sharp line emission located at 360 nm arising from f --> f transition of Eu2+ in the host lattice, and typical doublet 5d-4f emission of Ce3+ in LiBaF3 powder is shown.

VUV and Eu-L-3 edge XANES spectra of europium-doped strontium tetraborate prepared in air

VUV-UV and Eu-L-3 edge XANES spectra were measured for europium-doped strontium tetraborate prepared by solid state reaction at high temperature in air. The VUV-UV spectra show that the host absorption band of (SrBO7)-O-4 appears below 170 nm. The charge transfer band of Eu3+ doped in SrB4O7 is peaked at 272 nm. The 4f-5d transitions of Eu2+ consist of a band peaked at 310 nm with a shoulder at 280 nm and also include the bands peaked at 238 (weak) and 203 (strong) nm. The result of XANES spectrum at Eu-L3 edge of the synthesized sample indicates that Eu3+ and Eu2+ coexist in SrB4O7:Eu prepared in air, which is consistent with the results of the VUV-UV spectra.

XAFS at Eu-L-3 edge and UV-VUV excited luminescence of europium doped strontium borophosphate prepared in air

The local structure and the valences of europium in SrBPO5:Eu prepared in air were checked by means of XAFS at Eu-L-3 edge. From the EXAFS results, it was discovered that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.42 Angstrom in the host. From the XANES data, it was found that the divalent and trivalent europium coexisted in the matrix. The emission spectra excited by VUV or UV exhibited a prominent broad band due to the 4f(6)5d-4f(7) transition of Eu2+ ions, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Sr]" formed by aliovalent substitution between Sr2+ and Eu3+ ions. The VUV excitation spectra in 100-200 nm range showed that the matrix had absorption bands with the maxima at about 130 and 150 nm, respectively.

VUV excited luminescence of europium activated calcium borophosphate prepared in air

XAFS (EXAFS and XANES) at Eu-L-3 edge were used to determine the local structure and the valences of europium in CaBPO5:Eu prepared in air. The results of EXAFS showed that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.39 Angstrom in the host lattice. XANES at Eu-L-3 edge exhibited that Eu2+ and Eu3+ coexisted in the matrix. The luminescent spectrum of the material excited by VUV at 147 nm presented a similar spectrum with that excited by f-f transition of Eu2+ at 396 nm and f-d transition of Eu2+ at 312 nm. The broad emission band due to both 4f(6)5d - 4f(7) transition of EU2+ and f - f transition of Eu3+ could be observed in emission spectra, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Cn]" formed by aliovalent substitution between Ca2+ and Eu3+ ions. The UV excitation spectrum showed the typical f-f transition of Eu3+ and f-d transition of Eu2+. The bands with the maxima at about 113 and 158 nm in VUV excitation spectrum were assigned to originate from the absorption of the host lattice.

Eu~(2+),Dy~(3+)共掺杂硼铝锶长余辉玻璃陶瓷

首次介绍了一种新型长余辉材料 :Eu2 + ,Dy3 + 共掺杂硼铝锶长余辉玻璃陶瓷 ,该玻璃陶瓷用紫外灯、日光、荧光灯均可激发 ,发射黄绿色余辉 ,余辉的发射峰位于 5 16nm ,来自于Eu2 + 的 5d→ 8S7/ 2 跃迁。用12 0 0 0lx的荧光灯激发样品 2 0分钟 ,停止激发后 10秒时 ,该玻璃陶瓷的余辉亮度为 3 5 3cd/m2 ,色坐标为 :x =0 2 84 2 ,y =0 5 772 ;停止激发后 5小时 5 5分钟 ,该玻璃陶瓷的余辉亮度为 0 0 1cd/m2 ;停止激发 30小时后 ,余辉在黑暗中仍肉眼可见。文中对该玻璃陶瓷的相关性质进行了表征 ,并提出了可能的长余辉机理

M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性的研究

采用高温固相反应法合成了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)中荧光体,测量了荧光体的真空紫外激发光谱,研究了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性,观察到基质吸收带位于120～200 nm区域,Eu~(2+)离子的5d能级劈裂随着M~(2+)的半径的增加而减小,同时也观察到基质与稀土离子之间存在的能量传递。

Formation of mesophase mono-domains and micro-structures in thin films of a series of copolyethers containing both odd-numbered methylene units

The structural and morphological evolution of mono-domains in thin films has been investigated for a series of liquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4 ' -biphenylyl)-2-(4-hydroxyl-phenyl)propane (TPP) with 1,7-dibromoheptane and 1,11-undecane at different compositions (coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneous molecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase (Phi '). Similar to the nucleation process in polymer crystallization, transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing, where molecules form a uniaxial in-plane chain orientation. With increasing annealing time, the molecular orientation gradually became tilted with respect to the substrate surface, and finally, a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time. The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape, indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.

Study of energy transfer in KMgF3 : Eu-X (X = Gd, Cr, Ce) by the decay model of P-6(7/2) exited state of Eu2+

Energy transfer processes between Eu2+ and Gd3+, Cr3+, Ce3+ ions in KMgF3, which are difficult to study spectroscopically, have been investigated by using the proposed four-level decay model of the P-6(7/2) excited state of the Eu2+ ion. Gd3+ and Ce3+ transfer its energy to the vibronic transition of the P-6(7/2) --> S-8(7/2) transition of Eu2+, whereas Cr3+ receive energy from Eu2+ via the d-d interaction. The energy transfer from the Eu2+ 4f(6)5d level to the Ce3+ 4f5d state is observed spectroscopically, and the energy transfer mechanism is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

稀土离子的高能光谱

讨论了稀土离子在能量高于 5 0 0 0 0cm- 1 (波长短于 2 0 0nm)的光谱 ,包括 4f 4f跃迁 ,4f 5d跃迁 ,4f 6s跃迁 ,基质吸收和电荷迁移带。利用Dorenbos提出的公式 :E(Ln ,A ) =493 40 -D(A) +ΔELn ,Ce,指认了Sm3+ 离子在我们合成的Ba3BP3O1 2 中的 4f 5d跃迁的能量值为 170nm。利用我们提出的稀土离子光学电负性 χM与标准还原电位E0Ln的关系式 :E0Ln(Lnn + →Ln(n - 1 ) ) =4 2 73 χM-7 776(其中n =3或 4) ,从稀土离子的光学电负性 χM 与J rgensen提出的公式Ect=[χX-χM]× 3 0 0 0 0cm - 1 ,估算出Er3+和Eu3+离子在含氧杂质的LiYF4 ∶Er和LiYF4 ∶Eu3+中Er O和Eu3+ O的电荷迁移带的能量 ,以及LiYF4 ∶Eu3+ 中Eu3+ F的电荷迁移带的能量 ,估算值与文献报道的实验值基本相符。

BaLaB_9O_(16)∶Eu,Tb的真空紫外光谱特性

采用高温固相反应法合成了 BaLaB9O1 6 ∶RE (RE =Eu ,Tb)等离子荧光体 ,测量了它们的真空紫外激发光谱和 14 7nm激发下的发射光谱。结果表明 ,硼氧阴离子基团基质吸收带位于 15 0nm附近 ,Eu3+ 电荷迁移带位移 2 5 0nm附近 ,Tb3+ 的 4f 5d吸收位于 15 0～ 2 60nm的区域内 ,相关数据表明 ,基质与稀土离子之间存在能量传递。

掺Eu~(3+)、Tb~(3+)或Ce~(3+)的InBO_3的合成与光谱

采用固相反应法合成了InBO_3:Re(Re=Eu,Tb,Ce),研究了InBO_3基质中稀土离子的光谱特性,观察到电荷迁移带位于255 nm附近,Eu~(3+)离子在InBO_3 中产生极强的~5D_0→~7F_1 的跃迁表明Eu~(3+)离子在该基质中占据对称性格位。Tb~(3+)的4f-5d 允许跃迁位于240 nm附近,而4f-5d 禁戒跃迁位于267 nm附近,Tb~(3+)离子呈现出极强的~5D_4→~7F_5 发射。Ce~(3+)离子在InBO_3 中不发光。

Luminescence of RE2+ (RE = Sm, Yb) in barium octoborate

The reduction process from trivalent to divalent state for Sm3+ and Yb3+ ions in barium berates (BaB8O13) prepared in air was observed. The luminescence properties of these divalent rare-earth ions were studied. Yb2+ shows an f-d broad emission band, due to the 4f(14) --> 4f(13)5d transition, while the Sm2+ ion shows an f --> f transition. From the spectra of Yb2+, and using the D-5(0) --> F-7(0) transition of Sm2+ as a structural probe, two crystallographic sites were found to be available for the cations in the host. Vibronic transitions of Sm2+ were observed at low temperature. BaB8O13 was found to be a good host for reducing the trivalent rare-earth ions to divalent state and to exhibit interesting spectroscopic properties,

Phase identification in a series of liquid crystalline TPP polyethers and copolyethers having highly ordered mesophase structures. 7. Phase structures in a series of copolyethers containing odd and even numbers of methylene units of different compositions

A series of liquid crystalline copolyethers have been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane with 1,7-dibromoheptane and 1,12-dibromododecene [coTPPs(7/12)], which represents copolyethers containing both odd and even numbers of methylene units. The molar ratio of odd to even methylene units in this series ranges from 1/9 to 9/1. The coTPPs(7/12) exhibit multiple phase transitions during cooling and heating in differential scanning calorimetry experiments. For all these thermal transitions, a small undercooling and superheating dependence is observed upon cooling and heating at different rates. Three types of phase behaviors can be classified in coTPPs(7/12) on the basis of the structural analyses by wide-angle X-ray diffraction on powder and fiber samples and by electron diffraction experiments in transmission electron microscopy. At room temperature, highly ordered smectic and smectic crystal (SC) phases are identified in coTPPs(7/12: 1/9 and 2/8), which is similar to the homopolymer TPP(m = 12). The coTPPs(7/12: 3/7, 4/6, and 5/5) possess a hexagonal columnar (Phi(H)) phase in which the molecular and columnar axes are parallel to the fiber direction and perpendicular to the hexagonal lateral packing. The coTPPs(7/12: 6/4, 7/3, and 8/2) possess a tilted hexagonal columnar (Phi(TH)) phase with a single tilt angle which increases with the increasing composition of the seven-numbered methylene units. However, in coTPP(7/12: 9/1), a Phi(TH) phase with multiple tilt angles is found. Upon heating, phase structures in most coTPPs(7/12) involving the columnar phases enter directly into the nematic (N) phase, while the coTPP(7/12: 1/9) exhibits a highly ordered smectic F (S-F) phase before it reaches the N phase. One exception is found in coTPP(7/12: 2/8), wherein the transformation from the S-F to Phi(H) occurs prior to the N phase. Combining the copolymer phase behaviors observed with the corresponding homopolymers TPP(n = 7) and TPP(m = 12), a phase diagram describing transition temperatures with respect to the composition can be constructed.

Phase identification in a series of liquid crystalline TPP polyethers and copolyethers having highly ordered mesophase structures. 6. Structure changes from smectic to columnar phases in a series of copolyethers containing odd and even numbers of methylene units in equal molar composition

A series of liquid crystalline copolyethers has been synthesized from 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)propane and different alpha,omega-dibromoalkanes [coTPP(n/m)]. In this report, coTPPs having n = 5, 7, 9, 11 and m = 12 are studied, which represent copolyethers having both varying odd number and a fixed even number of methylene units. The compositions were fixed at an equal molar ratio (50/50). These coTPPs(nlm) show multiple phase transitions during cooling and heating in differential scanning calorimetry experiments. The undercooling dependence of these transitions is found to be small, indicating that these transitions are close to equilibrium, Although the coTPPs possess a high-temperature nematic (N) phase, the periodicity order along the chain direction is increasingly disturbed when the length of the odd-numbered methylene units decreases from n 11 to 5. in the coTPPs(5/12, 7/12, and 9/12), wide-angle X-ray diffraction experiments at different temperatures show that, shortly after the N phase formation during cooling, the lateral molecular packing improves toward a hexagonal lattice, as evidenced by a gradual narrowing of the scattering halo. This process represents the possible existence of an exotic N phase, which serves as a precursor to the columnar (Phi(H)) phase. A further decrease in temperature leads to a (PH phase having a long-range ordered, two-dimensional hexagonal lattice. In coTPP(11/12), the phase structures are categorized as highly ordered and tilted, smectic and smectic crystal phases, similar to homoTPPs, such as the smectic F (S-F) and smectic crystal G (SCG) phases. An interesting observation is found for coTPP(9/12), wherein a structural change from the high-temperature Phi(H) phase to the low-temperature S-F phase occurs. It can be proven that, upon heating, the well-defined layer structure disappears and the lateral packing remains hexagonal. The overall structural differences in this series of coTPPs between those of the columnar and highly ordered smectic phases are related to the disorders introduced into the layer structure by the dissimilarity of the methylene unit lengths in the comonomers.

Luminescent properties of divalent samarium-doped strontium hexaborate

The valence change of samarium from trivalent to divalent in strontium hexaborate (SrB6O10) prepared in air is observed. The temperature dependence of the luminescence and vibronic transitions of Sm2+ are studied. The Sm2+ ions occupy three crystallographic sites. With increasing temperature, the D-5(0)-->F-7(0) transition line exhibits red shifts, and the half-width increases. At room temperature, due to the thermal population through the 4f(5)5d channel, the D-5(1)-->F-7(J) transitions are observed even though the vibrational energy is very close to the energy gap between the D-5(1) and D-5(0) levels in the host. A coupled phonon energy of about 108 cm(-1) is determined from the vibronic transitions of Sm2+ in the host.