Influence of a chelating agent on optical and morphological properties of YAG: Tb3+ phosphors prepared by the sol-gel process

Chemical modifications are widely used in sol-gel method in order to control the mechanisms involved during hydrolysis-condensation and polymerization processes. In this paper, the influence of acetylaceton (acac) used as a chelating agent in the synthesis of undoped and Tb³⁺-doped Y₃Al₅O₁₂ (YAG) powders and sols, has been investigated. Its effects on samples crystallization and morphology have been studied by means of high-temperature X-ray diffraction (HTXRD), thermal analysis (DTA-TG), infrared (IR) and Raman spectroscopies, transmission electron microscopy (TEM) and laser granulometry. It was shown that acetylaceton enhances the structural organization of YAG compound. Moreover, acac-modified powders exhibit much smaller particles than unmodified ones. Optical study has also been achieved on doped samples. Laser induced luminescence spectra and fluorescence decays of Tb³⁺ ions show that acac affects the optical properties of YAG: Tb³⁺ for any types of samples (sol, xerogel or crystallized powder). Powders demonstrate a better luminescence yield without acetylaceton, whereas stabilized sols are more efficient than unstabilized ones.     

Deep hydration of an Li7–3xLa3Zr2MIIIxO12 solid-state electrolyte material: a case study on Al- and Ga-stabilized LLZO

Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li₇La₃Zr₂O₁₂ (LLZO), have been analysed using single-crystal X-ray diffraction to determine the pristine structural state immediately after synthesis via ceramic sintering techniques. Hydrothermal treatment at 150 °C for 28 d induces a phase transition in the Al-stabilized compound from the commonly observed cubic Iad structure to the acentric I3d subtype. Li^I ions at the interstitial octahedrally (4 + 2-fold) coordinated 48e site are most easily extracted and Al^III ions order onto the tetrahedral 12a site. Deep hydration induces a distinct depletion of Li^I at this site, while the second tetrahedral site, 12b, suffers only minor Li^I loss. Charge balance is maintained by the incorporation of H^I, which is bonded to an O atom. Hydration of Ga-stabilized LLZO induces similar effects, with complete depletion of Li^I at the 48e site. The Li^I/H^I exchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.     

Synthesis and Structure of Europium Aluminium Garnet (EAG)

Europium aluminium garnet (Eu₃Al₅O₁₂, EAG) was synthesized by an aqueous sol‐gel process and subsequent thermal annealing at 800 – 850 °C. Eu₃Al₅O₁₂ crystallizes cubic ( and its crystal structure was refined from X‐ray powder data. The refined oxygen position in the structure of EAG yields four shorter and four longer distances between europium and the eight surrounding oxygen atoms, forming a distorted dodecahedron. Pure Eu₃Al₅O₁₂ can be treated at temperatures around 1000 °C before it converts into perovskite‐like EAP near 1300 °C.     

Al掺杂Sm_3Fe_5O_(12)的合成、结构及热致变色性能

采用高温固相法合成了一系列热致变色材料Sm_3Fe_(5-x_Al_xO_(12)(x=0,0.1,0.3,0.5),通过粉末X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱,X射线光电子能谱(XPS)和固体紫外光谱(UV)对产物进行了表征.结果表明,样品在Al掺杂量(x)为0~0.5范围内均能得到纯相,材料中的Fe—O键为主要发色基团,随着温度的升高,样品颜色由黄绿色逐渐变为棕红色,变色区间为室温到240℃.     

An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field

The superexchange interaction on a magnetic ion may be represented by an effective field H_m = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$H_e with $\chi$ being the magnetic susceptibility and H_e being the applied field. The variation of the equivalent $\lambda_{\chi}$with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f⁷5d¹ of the Tb³⁺ ion are calculated in the Tb₃Ga₅O₁₂. By means of the effective field H_m and the applied field H_e, the Faraday rotation of Tb₃Ga₅O₁₂ at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data.     

Eu2+掺杂MgY2Al3Si2O11N青光荧光粉的制备和发光性能

采用高温固相法合成了一系列Eu²⁺掺杂的Mg Y₂Al₃Si₂O₁₁N(MYASON)青光荧光粉。详细探讨了不同制备方法对荧光粉的物相结构和发光强度的影响,利用X射线衍射精修和X射线光电子能谱实验证明Si⁴⁺-N^3-离子对成功掺入石榴石晶格中。通过荧光光谱、寿命衰减曲线和变温光谱研究了发光性能,研究结果表明,用365 nm紫外光激发MYASON∶Eu²⁺荧光粉时,在青光区域呈现不对称宽带发射,峰值为490 nm,可以为紫外芯片激发的白光发光二极管有效提供青光成分。     

Damage processes in Fe 3 O 4 magnetic insulator irradiated by swift heavy ions. Experimental results and modelisation

The behavior of the magnetic properties of magnetite Fe₃O₄ irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y₃Fe₅O₁₂. Received 18 April 2001 and Received in final form 24 July 2001     

Structure dependence of magnetic properties in yttrium iron garnet by metal-organic decomposition method

The yttrium iron garnet(YIG) samples are prepared at different temperatures from 900?C to 1300?C by the metalorganic decomposition(MOD) method. The chemical composition and crystal structure of the samples are studied by scanning electron microscope(SEM), XRD, and M ¨ossbauer spectrometer. It is shown that the ratio of ferric ions on two types of sites, the octahedral and the tetrahedral, is increased with the sintering temperature. At 1300?C, the pure garnet phase has been obtained, in which the ferric ions ratio is 2:3 leading to the minimum magnetic coercivity and maximum saturation magnetization. These results provide a route to synthesize pure YIG materials as the basic materials used in various spintronics applications.     

Influence of deviations from stoichiometry on the ir spectra of yttrium-iron garnet crystals

We have measured the absorption coefficients in the IR range as well as the cathodoluminescence spectra and also evaluated the content of the basic (Y, Fe, O) and impurity (Ba, Mn, Pt, Bi, Sm, V, Pb) elements of yttrium-iron garnet Y₃Fe₅O₁₂ (YIG) cut along different crystallographic planes. We show that Ba ions, as the main uncontrolled impurity, replace Y ions in varying degrees, thus exerting an inadequate influence on the absorption coefficients α (λ=1.3 μm) for samples of sections (110) and (111). It is established that Ba impurity in the concentration range 0.8 to 1.5 wt.% reduces α to a minimum, which is apparently due to suppression of the process of generation of dislocations. The quality of the YIG crystals is most fully characterized by the ratio of the sum of the masses of cations to the sum of anions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 217–222, March–April, 2000.     

氨水反滴共沉淀法制备Nd:YAG透明陶瓷粉体

以氨水为沉淀剂,硝酸盐为初始原料,采用反向滴定共沉淀法制备Nd∶YAG前驱体,将前驱体在不同温度下进行煅烧。采用XRD、IR、TG/DS等测试手段对样品进行表征,结果表明:前驱体在900℃下煅烧2 h就完全生成纯YAG相,没有中间相出现。最终得到分散性较好,平均尺寸在60 nm左右的粉体。