Sol-Gel Synthesis of Zn Doped MgO Nanoparticles and Their Applications

Abstract

The physicochemical properties of metal oxide nanoparticles can be significantly improved by doping. MgO and Zn²⁺ doped MgO (Zn:MgO) offers potential applications in photonic devices falling in the UV and visible region. In the present paper, sol gel method was employed to synthesize pure and Zn²⁺ doped MgO nanoparticles. XRD pattern inferred the crystalline nature of material and also the slight change in peak due to the dopant. FESEM showed the formation of nanoparticles with almost same shapes and dimensions with little agglomeration. Optical properties were studied by using UV-Vis and PL techniques. Doping of Zn²⁺ in MgO nanoparticles was verified by EDS.     

Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors

Photoluminescence and photocurrent characteristics of Eu^{2 +} activated MAl₂O₄ (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy^{3 +} as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested. The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl₂O₄ with only Eu^{2 +} as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl₂O₄ showed a good proportional relationship to UV and visible light intensity. Especially, SrAl₂O₄ showed an excellent linearity within 1–5 mW/cm², but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Spectroscopy of Pure and Eu 3+ Doped ZnO

Pure and Eu 3+ doped ZnO piezoelectric ceramics and thin films were prepared via solid state chemical reaction and by sol-gel method, respectively. Strong green emission band were observed from all samples. Both broad band emission from ZnO and line emission from Eu 3+ were observed in the sample ZnO doped with Eu 2 O 3 . In contrast to the report in the literature, excitation spectrum showed that energy transfer from ZnO host to Eu ions in these samples was very weak and the transfer was through Eu 3+ absorption of the green emission of ZnO.     

灯用荧光粉的燃烧合成法

近年来，燃烧反应被用为合成荧光粉的新方法，这种方法是通过作为氧化剂的金属硝酸盐和作为燃料（还原剂）的有机化合物之间的放热氧化－还原反应所释放的大量热能而进行的。本文对这种方法过去的发展历史、反应机理作了简要概述，并对其工艺要求和特点以及在灯用荧光粉方面的实际应用进行了较详尽的介绍，最后指出了今后的研究方向。     

灯用荧光粉的燃烧合成法(续上期)

近年来，燃烧反应被用为合成荧光粉的新方法，这种方法是通过作为氧化剂的金属硝酸盐和作为燃烧(还原剂)的有机化合物之间的放热氧化—还原反应所释放的大量热能而进行的。本文对这种方法过去的发展历史、反应机理作了简要慨述，并对其工艺要求和特点以及在灯用荧光粉方面的实际应用进行了较详尽的介绍，最后指出了今后的研究方向。     

Luminescence of YAl3 (BO3)4: Eu2+, Dy3+ phosphor and its luminescence decay characteristics

Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors are synthesized by sol-gel method. The phosphors show prominent blue luminescence due to the 4f⁷–4f⁶5d transition of Eu²⁺. The emission intensity is greatly improved when Dy³⁺ is doped into the YAl₃ (BO₃)₄:Eu²⁺ system. The 1% Dy³⁺ in Eu²⁺, Dy³⁺ co-doped YAl₃ (BO₃)₄ phosphors is the optimum doping concentration. The luminescence decay characteristics of the samples have also been investigated, exhibiting the decay times of approximately 0.1 μs, which is much shorter compare to other Eu²⁺ doped phosphors.     

Mechanoluminescence of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor by Impulsive Deformation

Di-calcium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using solid state reaction technique under a reducing atmosphere. Prepared sample suffered an impulsive deformation with an impact of a piston for mechanoluminescence (ML) investigations. A temporal characteristic of ML of the phosphor was observed, which expressed single sharp peak with a long decaying section. In order to investigate about the luminescence centre responsible for ML peak, ML spectrum of the same phosphor was also observed. ML spectrum recorded shown similarity in shape as well as peak wavelength with Photoluminescence (PL) spectrum that verifies the existence of single emission centre due to the transition of Eu²⁺ ions i.e. transitions from any of the sublevels of 4f⁶5d¹ configuration to ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve fitting technique. Time of ML peak and rate of decay did not change largely with respect to increasing impact velocity of the load and peak ML intensity varied linearly. Increasing impact velocity causes more number of Eu²⁺ ions to get excited to the higher energy level, subsequently de-excitation of more Eu²⁺ ions occurs. This gives rise to increase in ML intensity.     

Synthesis and temperature-dependent optical properties of Eu3+-doped NaYSiO4 red-emitting phosphors

Abstract

Novel Eu³⁺-activated orthosilicate NaYSiO₄:xEu³⁺ (x?=?0.02, 0.05, and 0.20) red-emitting phosphors were developed for white light emitting diode applications. The X-ray diffraction (XRD), photoluminescence excitation and emission spectra, temperature-dependent curves were applied to characterize the samples. The red emission of the NaYSiO₄:Eu³⁺ phosphor corresponding to ⁵D₀→⁷F₂ (614?nm) transition was observed under the excitation of 394?nm wavelength, which is suitable for UV LED chip. The quenching temperature for NaYSiO₄:0.05Eu³⁺ was found to be over 500 K. The CIE chromaticity coordinates of NaYSiO₄:0.05Eu³⁺ are very close to the National Television System Committee (NTSC) standard red.     

Structural and Optical Properties of Size and Morphology Controllable Nanoscale SrAl2O4: Eu2+, Dy3+

Abstract

Nanoscale SrAl₂O₄: Eu²⁺, Dy³⁺ with controllable size and morphology was synthesized by sol-gel auto-combustion method. The surface morphology and structural characterization were carried out with TEM and XRD. Optical properties were analyzed by comparing excitation spectra, emission spectra and afterglow decay of the nanoscale phosphor with that of the bulk phosphor. The results showed that citric acid acted as a soft template in the reaction system. The morphology and size changed clearly with pH value and sintering temperature. The crystallinity was affected by the quantity of citric acid. Both the nanoscale phosphors with different particle size and the bulk one have the strongest emission at 525?nm. But their strongest peaks in excitation spectra are very different from each other. The phosphorescence of nanoscale phosphor decays more rapidly than that of the bulk phosphor.     

溶胶凝胶-燃烧法合成La0.7Sr0.3MnO3阴极材料及其性能

低温合成钙钛矿单相La0.7Sr0.3MnO3粉体,以降低粒度、提高活性,已成为本领域研究的一个新方向。采用溶胶凝胶-燃烧法合成La0.7Sr0.3MnO3粉体,讨论了溶胶体系pH值和柠檬酸用量对燃烧程度及相组成的影响。利用络合理论,计算了溶胶体系的pH值对于络合物的影响。实验结果表明,当pH<3时,溶胶凝胶体系稳定存在;而当pH达到3有白色沉淀出现。燃烧完全程度随着pH值的增加和柠檬酸用量的减少而提高。晶相合成程度以柠檬酸/硝酸盐比值(j)=0.5时最为完全,随着j提高,生成微量第二相。1300℃烧结试样以j=1.5最为致密,电导率峰值达150S/cm。综合考虑相组成和性能两因素,运用此法制备La0.7Sr0.3MnO3粉体时,j以1.5为宜。     

Synthesis of superconducting Bi2Sr2CaCu2O8+δ single crystals using alumina crucibles with different purities

A self‐flux method is the simplest technique for synthesizing Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) superconducting single crystals. However, the crystals are inevitably contaminated because of the Bi‐2212 stoichiometric melt reacting with the crucible material. In this paper, we investigate the nonsuperconducting subproduct that forms during heating in the self‐flux method for synthesizing Bi‐2212. This subproduct was identified as BiSr₂CaAl₃O₉ by X‐ray diffraction. Bi‐2212 crystal growth was performed using A1₂O₃ crucibles with three different purities (nominally 97, 99.7, and 99.9%). For both the 97 and 99.7% purity crucibles, the subproduct was observed in all five samples out of five, whereas for the 99.9% purity crucible, it was observed in only two samples out of five. Furthermore, the 99.9% purity crucible gave a much lower subproduct volume than the 97% purity crucible. The average superconducting critical temperature (T_c,zero) varied depending on the crucible purity; it was 89.6, 90.8, and 91.8 K for the 97, 99.7, and 99.9% purity crucibles, respectively. Finally, we fabricated Bi‐2212 stacked devices with intrinsic Josephson junctions (Bi‐2212 stack) using as‐grown crystals from the 97 and 99.9% purity crucibles. The Bi‐2212 stacks exhibited a highly hysteretic current–voltage characteristic even at liquid N₂ temperature and they had identical quality parameters for Josephson junctions (i.e., I_r/I_c and voltage jump V_j). We conclude that the subproduct formation has little effect on the electrical characteristics of a Josephson junction device at 77 K. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

合成工艺对Fe3O4纳米颗粒结构特性、光学特性和磁性的影响

分别采用共沉淀法和燃烧法制备了Fe3O4纳米颗粒,并利用X射线衍射仪、扫描电子显微镜、透射电子显微镜、紫外一可见分光光度计和振动样品磁强计研究了Fe3O4纳米颗粒的特性。结果表明：合成工艺对Fe3O4纳米颗粒结构特性、光学特性和磁性均存在一定的影响。采用燃烧法制备的Fe3O4纳米颗粒更具有纳米晶体特性,其粒径小,带隙大;两种颗粒均具有较好的超顺磁特性,而共沉淀法制备的Fe3O4纳米颗粒具有更高的饱和磁化强度值。     

红色荧光粉LiW_2O_8:Eu的制备及其发光性质

采用高温固相反应法制备了Li(4-3x)W2O8:Eux系列钨酸盐红色荧光粉,探讨了其合成工艺条件,确定了Eu3+的最佳含量为x=1,试样的最佳反应温度为850℃。该荧光粉具有较宽的激发光谱,适合与近紫外、蓝光芯片配合使用。其发射光谱主峰位于615nm,色坐标位于(X=0.666,Y=0.331)左右,具有较高的色纯度。因此,这种荧光粉是一种可能应用在白光LED上的红色荧光粉材料。     

2,7-双(4-氨基-2-三氟甲基苯氧基) 萘及其聚酰亚胺的合成与性能研究

2-氯-5-硝基三氟甲苯与2,7-二羟基萘经亲核取代反应得到2,7-双(4-硝基-2-三氟甲基苯氧基)萘(Ⅰ),然后在Pd/C和水合肼作用下发生还原反应得到2,7-双(4-氨基-2-三氟甲基苯氧基)萘(Ⅱ).该二胺单体分别与均苯四甲酸二酐(PMDA)、3,3’,4,4’-联苯四酸二酐(BPDA)、3,3’,4,4’-二...     

Synthesis of pure powder of La0.9Sr0.1Ga0.8Mg0.2O2.825 by microwave-induced solution combustion method

Solid oxide fuel cell(SOFC)has recently captured great con-cern for its characteristics such as environment-friendly,high effi-ciency,good fuel adaptability andlownoise·Sr and Mg doped La-GaO3(LSGM)as electrolytesin SOFCexhibits higher oxygenionicconduct…     

电池级K2FeO4的制备及其电化学性能

在浓NaOH溶液中电解铁电极所得Na2FeO4阳极液制备出电池级的K2FeO4,在一次性Al/KOH/K2FeO4实验电池中,K2FeO4的放电容量可达215mAh/g,利用率可达53%.0.0～0.8V(vs.Hg/HgO)范围内的循环伏安实验结果表明:K2FeO4的充放循环次数可达300～600次.高铁正极的容量利用率及自放电率与K2FeO4的纯度关系密切.     

掺硅Fe3O4磁粉磁性能的研究

Ｆｅ３Ｏ４磁粉掺硅后矫顽力大幅度提高,硅的加入导致Ｆｅ２Ｏ３磁粉内应力的产一,内应力是提高磁粉矫顽力的不可忽视的重要因素之一。     

尖晶石型ZnMn2O4的合成及其电化学行为

主要报道尖晶石型ZnMn2 O4的合成及其在非水介质中的电化学行为。实验表明 ,以醋酸锰、醋酸锌、碳酸锰和碳酸锌为原料 ,在 90 0℃左右合成的ZnMn2 O4具有尖晶石结构 ,初始容量达到 14 0mAh/ g ,且具有良好的可逆性 ,在Zn| 1mol/LZn(ClO4) 2 +PC|ZnMn2 O4模拟电池体系中 ,循环 2 0 0多次后容量衰减到 12 5mAh/ g。     

稀土Dy~(3+)掺杂Fe_3O_4纳米颗粒的合成与磁性

以二价、三价硫酸铁和硝酸镝、氢氧化钠为原料,合成出Dy掺杂铁氧体纳米颗粒,并用月桂酸进行了表面修饰。用透射电镜(TEM)、X射线衍射仪(XRD)对颗粒的形貌、晶型结构进行了表征,用振动样品磁强计(VSM)测量其磁性能。XRD测试结果表明产物的结构为面心立方尖晶石型;TEM照片表明产物的成球性好,且大部分颗粒的粒径在13~15nm左右;室温下的磁化曲线表明产物无剩磁和矫顽力,具有超顺磁性。并且发现,与相同工艺、相同条件下合成的未掺杂Fe3O4纳米颗粒相比,Dy掺杂铁氧体纳米颗粒的磁性能显著提高。