Optically and thermally stimulated luminescence of KMgF3:Ce3 and NaMgF3:Ce3+

The potentialities of optically stimulated luminescence (OSL) for personal dosimetry of ionising radiation have stimulated the search for new synthetic materials with good dosimetric properties. The sensitivity of two new OSL materials KMgF3 and NaMgF3 doped with Ce3+ ions has been evaluated and found to be of the same order of magnitude as that of Al2O3:C. Several other characteristics have also been investigated. Promising results for KMgF3:Ce are the high sensitivity and the low fading. However, this material suffers from a high self-dose due to the presence of 40K. NaMgF5:Ce is sensitive as well but shows strong fading. Interesting information on the mechanism has been obtained by correlating the signals of OSL and TL. Furthermore, the different bleachabilities under blue LED illumination of the strongly overlapping glow peaks allowed the extraction of one single peak for KMgF3:Ce3+. The results demonstrate new possibilities offered by the combination of TL and OSL.     

Mg-Zn-Al-CO3 and Zn-Cu-Al-CO3 hydrotalcite-like compounds: Preparation and characterization

A series ofM-Zn-Al (M=Mg, Cu) double hydroxide phases with carbonate anion were prepared by coprecipitation of 333 K, from the corresponding nitrate solution and sodium carbonate aqueous solution at pH 10. The characterization and properties of the products were investigated. It seems that reactivity of aluminium ions into the host layer depends on the identity of coexistent divalent cations (magnesium or copper), and the thermal properties of this layer at relatively high temperatures also depend on the nature of divalent cations.     

NaYF4:Er3+和NaYF4:Yb3+/Er3+上转换荧光纳米晶的制备与表征

以EDTA为螯合剂,采用络合共沉淀法合成了NaYF4:Er3+和NaYF4:Yb3+/Er3+纳米晶.分别采用XRD、SEM、荧光分光光度计对合成的样品进行了结构、形貌和上转换荧光分析.XRD结果表明,制备的NaYF4:Er3+和NaYF4:Yb3+/Er3+均为纯立方相;SEM结果显示,制备的NaYF4:Er3+和NaYF4: Yb3+/Er3+晶粒粒径都在100nm左右,与NaYF4:Er3+相比,NaYF4:Yb3+/Er3+晶粒尺寸分布更均匀,分散性更好,符合作为荧光标记材料的要求;上转换荧光分析表明,在980nm激光器激发下,NaYF4:Yb3+/Er3+的发光强度比NaYF4:Er3+提高了1个数量级.     

Electronic structure and magnetism in superconductor ZnNNi3: A comparative study with ZnCNi3 and ZnNi3

We have investigated the structural, electronic, and magnetic properties of a newly discovered antiperovskite superconductor ZnNNi₃ and related compounds ZnCNi₃ and ZnNi₃ by using full-potential linearized augmented plane-wave method with the generalized gradient approximation (GGA). It is found that the electronic structures of ZnNNi₃ and ZnCNi₃ are very similar, existing a characteristic density of states (DOS) peak just below the Fermi level, which is dominated by Ni d bands with a small contribution from N/C p states. Contrarily, the band structure and Fermi surface in ZnNi₃ is changed considerably. Based on the free electron model, the Sommerfeld coefficients and the molar Pauli paramagnetic susceptibility for these compounds are evaluated. The spin-polarized calculations and the fixed spin-moment calculations indicate that both ZnNNi₃ and ZnCNi₃ are not near magnetism, while ZnNi₃ shows a typically ferromagnetic behavior. Furthermore, we also investigated the influence of N/C-defect on the electronic and magnetic properties. We found that ZnCNi₃ is more sensitive to the defect than ZnNNi₃, which well explains the fact why superconductivity has not yet been observed in ZnCNi₃.     

Synthesis and characterization of rod-like Y2O3 and Y2O3:Eu3+

Y₂O₃ rods 100 to 200 nm in diameter and 10 to 20 m in length are accessible via polyol-mediated synthesis of a precursor material with similar shape. By heating of Y(CH₃COO)₃ · xH₂O and a defined amount of water at 190°C in diethylene glycol, the rod-like precursor material is formed. Infrared spectroscopy (IR), differential thermal analysis (DTA) and thermal gravimetry (TG) evidence that this precursor material still contains acetate. However, the precursor material can be transformed to Y₂O₃ by sintering at 600°C without destruction of the rod-like shape. According to X-ray powder diffraction analysis, the rods are well crystallized. They can be assumed to be with [100] orientation. By doping with Eu³⁺ (5 mol%), red emitting phosphor rods can be realized. With optical spectroscopy the typical line emission of Eu³⁺ is observed. Diffuse reflectance of Y₂O₃:Eu³⁺ rods is determined to be higher than 95% in the visible. While exciting at 254 nm (Hg-discharge), a quantum efficiency of 38.5% is proven for the prepared Y₂O₃:Eu³⁺ rods.     

Fabrication and luminescence of YF3:Tb3+ hollow nanofibers

YF₃:Tb³⁺ hollow nanofibers were successfully fabricated via fluorination of the relevant Y₂O₃:Tb³⁺ hollow nanofibers which were obtained by calcining the electrospun PVP/[Y(NO₃)₃ + Tb(NO₃)₃] composite nanofibers. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope, transmission electron microscope, and fluorescence spectrometer. YF₃:Tb³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 148 ± 23 nm. Fluorescence emission peaks of Tb³⁺ in the YF₃:Tb³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) (490, 543, 588, and 620 nm) of Tb³⁺ ions, and the ⁵D₄ → ⁷F₅ hypersensitive transition at 543 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Tb³⁺ hollow nanofibers were located in the green region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Tb³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Tb³⁺ ions and reached a maximum at 7 mol% of Tb³⁺. The possible formation mechanism of YF₃:Tb³⁺ hollow nanofibers was also discussed. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.     

Photoluminescence and energy storage traps in CaTiO3:Pr3+

Red-emitting CaTiO₃:Pr³⁺ phosphors are fabricated using a solid state method and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. The optical properties are investigated using photoluminescence emission, excitation, photoluminescence decay curves, diffused reflectance and thermoluminescence spectra, and persistent phosphorescence decay curves. The optimal fabrication temperatures for photoluminescence and persistent phosphorescence are found at 1200–1300 °C for photoluminescence and 1400 °C for persistent phosphorescence. The energy storage traps for persistent phosphorescence in the system are analyzed based on the dependence of photoluminescence and persistent phosphorescence on sintering temperature. The distribution of energy storage traps is further characterized by thermoluminescence spectra and the parameters of the traps are calculated. Oxygen vacancies as the main trapping centers play the key role for persistent phosphorescence in CaTiO₃:Pr³⁺.     

花球状YBO3:Eu3+的水热合成与表征

采用水热法制备了均匀分散、具有花球形貌的YBO3:Eu3+. 利用X射线衍射仪、X射线能量仪、高分辨透射电镜、扫描电镜等手段对其结构、形貌进行了研究,发现其为六方球霰石晶相,仅含有Y、O、B、Eu元素,微球直径约1～2μm,组装成花球的薄片厚度约100nm. 提出了其形成机理:在水热过程中生成的YBO3晶核在六亚甲基四胺(HMT)的调节下各向异性生长为二维薄片,并最终组装成为花球状结构. 研究发现得到的YBO3:Eu3+在612nm表现出显著的红光发射,并且由于Eu3+附近晶体场对称性降低,样品表现出较高的红光/橙光(R/O)比率.     

Infrared Luminescence of Y2O2S:Er3+ and Y2O3:Er3+

The diffuse reflectance and luminescence spectra of Y₂O₂S:Er³⁺ and Y₂O₃:Er³⁺ are studied under selective and polarized laser excitation. The results indicate that the Er³⁺ luminescence bands of yttrium oxysulfide in the 1.54-m region are one order of magnitude stronger and broader than those of yttria. Y₂O₂S:Er³⁺ is shown to contain two types of Er-related emission centers differing in the anion environment of the Er³⁺ ion.     

3D UV-microforming: principles and applications

A low-cost surface micromachining technology is described and examples provided of its application to microsensor and microactuator fabrication. The new technology 3D UV-macroforming, combines depth ultraviolet (UV) lithographic patterning of very thick photoresists and electrodeposition of structural materials into the patterned resist moulds. Neither UV lithography nor electrodeposition needs expensive or special equipment. Micromechanical components with high structures can be directly manufactured onto the system surface. Movable three-dimensional (3D) microstructures with a high aspect ratio can be obtained by combining the 3D UV-microforming process with a sacrificial layer technique. As an example of an advanced application in microsystem technology, the fabrication of triaxial accelerometers is presented, using titanium as a sacrificial layer and nickel as the structural material     

Y2O3:Eu3+ core-in-multi-hollow microspheres: facile synthesis and luminescence properties

Y2O3:Eu3+ core-in-multi-hollow microspheres were synthesized via a facile hydrothermal method in the presence of glucose followed by a subsequent heat-treatment process. X-ray diffraction (XRD) pattern shows that the as-obtained hollow spheres are cubic phase of Y2O3. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images indicate that the samples are three layer hollow spheres with a diameter of 2-4 microm and the outermost wall thickness of 100 nm, the size of the inner core is about 300-400 nm, and the sub-outer wall thickness is about 100 nm. X-ray energy dispersive spectrum (EDS) shows that the samples are composed of Y, Eu and O. Photoluminescence spectra show that the hollow spheres have a strong characteristic red emission corresponding to the 5D0 - 7F2 transition of Eu3+ ions under ultraviolet excitation. This method can be used to synthesize other rare earth oxide hollow luminescent materials.     

BaSrTiCeO3: growth and crystal structure

Ce doped barium strontium titanate single crystals have been grown by high temperature solution growth technique with different concentrations of Cerium. The structure of the crystals has been solved by single crystal X-ray diffraction. The structural properties, filling coefficients and the thermal properties are presented.     

Electroluminescence of Y2O3:Eu and Y2O3:Sm films

Electroluminescence of Y₂O₃:Eu and Y₂O₃:Sm films, as well as the films coactivated with Eu and Sm, is studied. The electroluminescence spectra are measured. The physical mechanism of electroluminescence is analyzed It is shown that the increase in the heat treatment temperature and the content of doping impurities of the films enhances the intensity of electroluminescence. Additional doping of Y₂O₃:EuF₃ films by the SmF₃ impurity, practically does not influence the emission spectrum.     

LiNbO3:Pr3+: A Multipiezo Material with Simultaneous Piezoelectricity and Sensitive Piezoluminescence

Red‐emitting piezoluminescence (elasticoluminescence) is achieved by doping rare earth Pr³⁺ into the well‐known piezoelectric matrix, LiNbO₃. By precisely tuning the Li/Nb ratio in nonstoichiometric Li _x NbO₃:Pr³⁺, a material that exhibits an unusually high piezoluminescence intensity, which far exceeds that of any well‐known piezoelectric material, is produced. Li _x NbO₃:Pr³⁺ shows excellent strain sensitivity at the lowest strain level, with no threshold for stress sensing. These multipiezo properties of sensitive piezoluminescence in a piezoelectric matrix are ideal for microstress sensing, damage diagnosis, electro‐mechano‐optical energy conversion, and multifunctional control in optoelectronics.     

Hole burning in YSZ:Pr3+ and YSZ:Eu3+ with various Y2O3 concentration

We have measured the hole spectra in YSZ:Pr³⁺ and YSZ:Eu³⁺ with various Y₂O₃ concentrations at low temperature. The temperature dependence of the hole width which obtained from the hole spectra in YSZ:Pr³⁺ and YSZ:Eu³⁺ was similar to that for disordered materials.

However, the Y₂O₃ concentration dependence of the hole width in YSZ:Pr³⁺ was contrary to that for YSZ:Eu³⁺ at low temperature. The hole width was the widest in the case of YSZ:Pr³⁺ at 10 mol% Y₂O₃. On the contrary, it was the narrowest in the case of YSZ:Eu³⁺ at the same concentration of Y₂O₃. It was found that there are two states in YSZ, in which the degree of ordered differs from each other. Additionally, the Y₂O₃ concentration dependence of the hole width at low temperature has reflected the ionic conductivity of YSZ at high temperature. It is suggested that the ordering of local structure is responsible for the ionic conduction in YSZ.

© 2003 Elsevier Science Ltd. All rights reserved.     

Two new cerium-doped mixed-anion elpasolite scintillators: Cs2NaYBr3I3 and Cs2NaLaBr3I3

We recently discovered that mixed-anion Br–I elpasolite scintillators, Cs₂NaYBr₃I₃: Ce and Cs₂NaLaBr₃I₃: Ce, have promising performance. Ce concentration of these compounds was optimized in terms of light yield. Cs₂NaLaBr₃I₃ with 5% Ce (by mole) has a light yield of 58,000 ph/MeV, and excellent energy resolution of 2.9% at 662 keV. It is better than both endpoint compounds of the Br–I solid solution. Cs₂NaYBr₃I₃ with 2% Ce doping shows energy resolution of 3.3% at 662 keV, despite a relatively modest light yield of 43,000 ph/MeV. Non-proportionality of the mixed Br–I compounds was measured using gamma ray sources ranging in energy from 14 keV to 835 keV.The electronic band gaps of undoped Cs₂NaLaBr₃I₃ and Cs₂NaYBr₃I₃ were determined from optical transmittance and absorbance measurements. The band gaps of the compounds are 4.4 ± 0.1 eV, and 4.3 ± 0.1 eV, respectively.The crystal structures of Cs₂NaLaBr₃I₃: Ce and Cs₂NaYBr₃I₃: Ce are tetragonal and cubic respectively. The high symmetry leads to fewer cracks during crystal growth and minimizes light scattering at grain boundaries. The ease of crystal growth is promising for the scale-up of the growth process to larger sizes.     

BaZrO3 and BaHfO3: preparation,properties and compatibility with YBa2Cu3O7-x

Single-phase BaZrO₃ and BaHfO₃ polycrystalline powders were prepared by solid-state reaction and by spray-drying methods. BaHfO₃ ceramic was fabricated at 1300°C for 24 h after pre-sintering HfO₂ and BaCO₃ powders at 1040°C for 4 h. Homogeneous powders of BaZrO₃ and BaHfO₃ were also prepared by a spray-drying route. The interaction between YBa₂Cu₃O_7-x (YBCO) and BaHfO₃ and BaZrO₃ was investigated in the temperature range 900–1060°C using heat-treatment cycles appropriate to composite reaction processing and melt-texturing. The results indicate that neither compound reacts significantly with YBCO at 950°C, and BaHfO₃ is still unreactive up to 1000°C. Both of them are also very stable during the melting-texture process. BaHfO₃ and BaZrO₃ are thus very promising substrate materials and buffer layers for the deposition of thin and thick films and as container materials for bulk YBCO superconductors; BaHfO₃ seems to be a more stable material than BaZrO₃.