Synthesis and Upconversion Luminescence in LaF3:Yb3+, Ho3+, GdF3: Yb3+, Tm3+ and YF3:Yb3+, Er3+ obtained from Sulfide Precursors

Rare earth fluorides are mainly obtained from aqueous solutions of oxygen‐containing precursors. Probably, this method is simple and efficient, however, oxygen may partially be retained in the fluoride structure. We offer an alternative method: obtaining fluorides and solid solutions based on them from an oxygen‐free precursor. As starting materials, we choose sulfides of rare‐earth elements and solid solutions based on them. The fluorination is carried out by exposure to hydrofluoric acid of various concentrations. The transmission electron microscopy images revealed the different morphologies of the products, which depend on the concentration of the fluorinating component (HF) and the host element. The solid solution particle size varied from 30–35 nm in the case of GdF₃:Yb³⁺, Tm³⁺ (4 % HF) to larger structures with dimensions exceeding 200 nm, such as that for LaF₃:Yb³⁺, Ho³⁺ (40 % HF). The thermal characteristics, such as the temperatures of the transitions and melting and enthalpies, were determined for the solid solutions and simple fluorides. Applicability of the materials obtained as biological luminescent markers was tested on the example of upconversion luminescence, and good upconversion properties were detected.     

Cu3SbSe3: Synthese und Kristallstruktur

The Crystal Structure of Cu₃SbSe₃ The hitherto unknown crystal structure of Cu₃SbSe₃ has been determined from single crystals. The compound crystallizes in the orthorhombic system, space group Pnma (No. 62), with a = 7.9865(8), b = 10.6138(9) and c = 6.8372(7) Å, V = 579.6(1) ų, Z = 4. Most remarkable feature of the structure are groups of three cis-edge-sharing tetrahedra [Cu₃Se₈] which are interlinked to a threedimensional arrangement by SbSe₃-units. In contrast to Cu₃SbS₃ in the temperature range from ?180 to 25°C no hints for a phase transition could be detected by means of X-ray- and thermoanalytical methods.     

BiScO3: centrosymmetric BiMnO3-type oxide

With neutron powder diffraction, electron diffraction, and second-harmonic generation, we have shown that BiScO3 has a structure closely related to that of multiferroic BiMnO3, but BiScO3 crystallizes in the centrosymmetric space group of C2/c. These results bring up a question about the origin of ferroelectricity in BiMnO3. BiScO3 may serve as a model system to understand the role of Mn3+ ions in the ferroelectricity of BiMnO3.     

GdPO4:Eu3+和GdBO3:Eu3+中"Gd-Eu"间的能量传递

利用同步辐射光源(德国HASYLAB实验室的SUPERLUMI实验站)对高温固相法制备的GdPO4 Eu3+和GdBO3Eu3+的发射谱与激发谱进行了研究, 并从量子剪裁的角度对"Gd3+-Eu3+"之间的能量传递作了讨论. 在两种样品监测Eu3+红光发射的激发谱上, 都显著观察到了对应Gd3+离子4f-4f跃迁的谱线, 说明从基质中Gd3+离子向掺杂的Eu3+离子之间存在非常有效的能量传递, 这有利于量子剪裁的发生. 在激发谱上还观察到了对应Eu3+-O2-电荷迁移态的宽激发带(180～270 nm), 而对应Gd3+离子8S7/2→6GJ跃迁的谱线(196 nm, 203 nm)叠加在这个宽带之上, 微弱可辨, 这不利于Gd3+-Eu3+间交叉弛豫的能量传递过程, 从而不利于量子剪裁的发生. 结合Eu3+-O2-电荷迁移态位置变化的规律, 提出了如何避开其干扰以增强量子剪裁效应的材料设计方案.     

Cu3SbS3: Zur Kristallstruktur und Polymorphie

Cu₃SbS₃: Crystal Structure and Polymorphism The hitherto unknown crystal structure of β-Cu₃SbS₃ at room temperature could be determined from a twinned crystal. The compound crystallizes in the monoclinic system, space group P2₁/c (No. 14), with a = 7.808(1), b = 10.233(2) and c = 13.268(2) Å, β = 90.31(1)°, V = 1 060.1(2) ų, Z = 8. An Extended-Hückel-Calculation shows weak bonding interactions between copper atoms which are coordinated trigonal planar. At ?9°C a first order phase transition occurs and the crystals disintegrate. The low-temperature modification (γ) crystallizes in the orthorhombic system with a = 7.884(2), b = 10.219(2) and c = 6.623(2) Å, V = 533.6(2) ų (?100°C). At 121°C a phase transition of higher order is observed. The high-temperature polymorph (α) of Cu₃SbS₃ is orthorhombic again. From high-temperature precession photographs the space groups Pnma (No. 62) or Pna2₁ (No. 33) can be derived. The lattice constants at 200°C are a = 7.828(3), b = 10.276(4) and c = 6.604(3) Å, V = 531.2(2) ų.     

Nd3+:LaCl3中的上转换发光研究

当用582.6 nm的黄色激光激发Nd3+:LaCl3的2G7/2+4G5/2能级时,观察到了4D3/2和2G9/2能级的兰光和紫外发射.研究表明,2D3/2上转换的机理是能量传递和激发态吸收,而2G9/2则是由于4G5/2+4Gs/2→2G9/2+4F7/2交叉驰豫过程.通过对12K下4D3/2→4I11/2荧光衰减曲线的分析,得出能量传递几率为wt1＝1468 s-1.测量和讨论了Nd3+:LaCl3和NdCl3主要发光能级室温和12K下的寿命.     

NaTaO3及NaTaO3∶Bi3+光催化剂的光致发光光谱研究

采用光致发光光谱技术对一系列不同条件下制备的NaTaO3及不同掺杂量的NaTaO3∶Bi3+进行了研究. 结果表明, NaTaO3的发光性质与其制备条件密切相关: 在钠离子不足的条件下合成的样品, 其发光带主要位于515和745 nm左右; 而在钠离子充足条件下合成的样品, 其发光带位于460 nm左右, 随着n(Na)/n(Ta)的降低, 发光带向长波长方向移动; 掺入Bi3+之后, 其发光峰由515 nm移至455 nm, 随着Bi3+掺入量的增加, 455 nm的发光带强度减弱. 515 nm的发光带与替位缺陷TaNa....相关; 745 nm的发光带与VNa`缺陷相关; 而460 nm的发光带与本征TaO6基团相关. 将Bi3+掺入到钽酸钠样品, TaNa....由BiNa..替代, 相应的发光带向高的n(Na)/n(Ta)方向移动, 从而呈现出本征TaO6基团的发光带.     

GdF3∶Eu3+/NaGdF4∶Eu3+纳米晶的水热合成及发光性质

采用水热法,以聚乙二醇(400)为分散剂,以NaOH和HNO3溶液调节初始溶液pH值,合成GdF3∶Eu3+和NaGdF4∶Eu3+纳米晶。XRD和SEM结果表明:在酸性溶液(pH=3,5)、中性溶液(pH=7)和碱性溶液(pH=9)中,分别获得具有正交结构的GdF3∶Eu3+纳米晶,GdF3∶Eu3+和NaGdF4∶Eu3+混合晶,六方结构NaGdF4∶Eu3+棒状微米晶。根据Scherrer公式估算pH=3和pH=5时制备纳米晶的一次性粒径分别为49和28 nm。样品的发射光谱结果表明:特征发射峰来自于5D2、5D1、5D0到7FJ跃迁。在主晶相为GdF3样品中,主发射峰来自于Eu3+的5D0→7F1的磁偶极跃迁;晶相为NaGdF4样品的主发射峰来自于Eu3+的5D0→7F2电偶极跃迁。5D0→7F1和5D0→7F2跃迁发射相对强度比值显示:Eu3+在NaGdF4晶体中的格位对称性下降。激发光谱显示出Gd3+和Eu3+具有较好的能量传递。     

Comparative Structural,Optical, and Photoluminescence Studies of YF3:Pr,YF3:Pr@LaF3, and YF3:Pr@LaF3@SiO2 Core–Shell Nanocrystals

Praseodymium (Pr³⁺)‐doped YF₃ (core) and LaF₃ ‐covered YF₃ :Pr (core–shell) nanocrystals (NCs ) were prepared successfully by an ecofriendly, polyol‐based, co‐precipitation process, which were then coated with a silica shell by using a sol–gel‐based Stober method. X‐ray diffraction (XRD), transmission electron microscopy (TEM ), thermal analysis, Fourier transform infrared (FTIR) , UV /vis, energy bandgap, and photoluminescence studies were used to analyze the crystal structure, morphology, and optical properties of the nanomaterial. XRD and TEM results show that the grain size increases after sequential growth of crystalline LaF₃ and the silica shell. The silica surface modification enhances the solubility and colloidal stability of the core–shell‐SiO₂ NCs . The results indicate that the surface coating affects the optical properties because of the alteration in crystalline size of the materials. The emission intensity of silica‐modified NCs was significantly enhanced compared to that of core and core–shell NCs . These results are attributed to the formation of chemical bonds between core–shell and noncrystalline SiO₂ shell via La–O–Si bridges, which activate the “dormant” Pr³⁺ ions on the surfaces of the nanoparticles. The luminescence efficiency of the as‐prepared core, core–shell, and core–shell‐SiO₂ NCs are comparatively analyzed, and the observed differences are justified on the basis of the surface modification surrounding the luminescent seed core NCs .     

Aromaten-Komplexe mit Halbsandwich-Struktur: Die 1:1-Komplexe des Mesitylens mit SbCl3, SbBr3, BiCl3 und BiBr3

Arene Complexes with a Half-Sandwich Structure: The 1:1 Complexes of Mesitylene with SbCl₃, SbBr₃, BiCl₃, and BiBr₃ 1,3,5-Trimethylbenzene forms stable 1:1 complexes with SbCl₃, SbBr₃, BiCl₃, and BiBr₃ of the stoichiometry C₆H₃Me₃·EX₃ ( 1 – 4 ). According to the results of X-ray structure analyses of compounds 2 and 3 , one arene molecule is coordinated to each antimony or bismuth atom characterizing these adducts as half-sandwich species. To a good approximation the mesitylene molecules are centered over the metal atoms, but deviations from strict η⁶-hapticity are larger for antimony than for bismuth. – Despite some obvious analogies in many features of the structures, 2 and 3 are not isostructural. Differences appear with regard to the halogen bridging between the EX₃ moieties giving rise to the formation of two-dimensional networks (EX₃)_n covered above and below by mesitylene molecules. The structural and sequential principles of the layers differ in a characteristic way for 2 and 3 .     

Preparation and Luminescence Behavior of CaSiO3:Eu3+(Bi3+)

CaSiO3:Eu3 0.08Bi3 0.002 with a monoclinic perovskite structure was synthesized by using sol-gel method, and its luminescence characteristics were investigated. From the excitation spectrum, it can be seen that the main peaks located at238, 396, 415, 437 and 359 nm correspond to the charge-transfer band of Eu3 -O2- , the absorption transitions of 7F0,1→5 L6,7F0→5D3,7F1→5D3 of Eu3 ions, and 3P1→1S0 of Bi3 ions, respectively. When the samples were excited with a light of wavelength 359 or 395 nm, it can be seen from the emission spectrum that the electronic dipole transition located at 609 nm corresponding to 5D0 →7F2 of Eu3 ions was stronger than the magnetic dipole transition located at 587 nm corresponding to 5D0→7F1 of Eu3 ions, which shows that more Eu3 ions were located in nonreversion center lattices. The energy transfer from Bi3 ions to Eu3 ions in the phosphor was also discussed. The results show that Eu3 ions could be well sensitized by Bi3 ions, and the energy-transfer pattern between Bi3 ions and Eu3 ions was resonance energy transfer.     

Li3BS3 und LiSrBS3: Neue Orthothioborate mit trigonal-planar koordiniertem Bor

Li₃BS₃ and LiSrBS₃: New Orthothioborates with Trigonal Planar Boron Coordination We report on the two new orthothioborates Li₃BS₃ (Pnma; a = 8.144(1) Å, b = 10.063(2) Å, 6.161(1) Å; Z = 4) and LiSrBS₃ (Pnma; a = 7.557(1) Å, b = 9.083(2) Å, c = 7.049(1) Å: Z = 4). The two new phases were prepared by reaction of the metal sulfides, amorphous boron, and sulfur at 700°C. Both compounds contain isolated, planar [BS₃]^3?-anions. The lithium ions have fourfold (Li₃BS₃) and sixfold (LiSrBS₃) sulfur coordination, the strontium ion shows an eightfold sulfur coordination. The two compounds represent new A₃BX₃ resp. AA′BX₃ structure types.