NaGd(MoO_(4))_(2)∶Er^(3+),Yb^(3+)发光粉的合成与上转换发光性质

采用水热法合成了系列NaGd(MoO_(4))_(2)∶Er^(3+),Yb^(3+)上转换发光粉。利用X射线衍射仪、扫描电子显微镜和上转换发光光谱仪等对样品的结构、形貌和发光性能进行表征。结果显示,合成的样品均具有四方晶系NaGd(MoO_(4))_(2)结构;pH对样品的形貌有影响;980nm红外光激发下,NaGd(MoO_(4))_(2)∶Er^(3+),Yb^(3+)上转换发光粉显示来自于Er^(3+)的^(2)H_(11/2)→^(4)I_(15)和^(4)S_(3/2)→^(4)I_(15/2)跃迁产生的绿光发射和4I 9/2→4I 15/2跃迁产生的红光发射。比较各样品的发光强度和绿光/红光相对积分强度比,结果显示上转换发光强度和绿光/红光相对积分强度比与晶粒尺寸、晶粒表面形貌,以及Er^(3+)和Yb^(3+)掺杂浓度有关。讨论了可能的上转换发光过程,并计算了样品的色坐标。

动态缺陷导致Na_(3)Sc_(2)(PO_(4))_(3):Yb^(3+),Er^(3+)材料上转换和下转移发光不同热猝灭行为研究

掺Eu^(2+)的离子导体Na_(3)Sc_(2)(PO_(4))_(3)具有优异的抗热猝灭性能,是一种很有前景的大功率照明用发光材料。然而,其负热猝灭机理仍有待深入研究。本文以Yb^(3+)/Er^(3+)的f-f跃迁上转换和下转移窄带发射而非更易受干扰的Eu^(2+)d-f跃迁发射为研究对象,旨在获得更清晰的机理。结果表明,热致缺陷/离子的动态迁移能促进高温下辐射跃迁和抑制非辐射跃迁,导致上转换发光具有显著的负热猝灭,下转移发光热猝灭较小。其中,布居速率较慢的上转换过程更容易受到时间尺度与之相当的Na^(+)/空位迁移过程的影响。本研究可为理解发光材料热猝灭机制提供另一种视角。

NaY(MoO_(4))_(2):Sm^(3+)荧光材料的制备及其发光性能的研究

采用传统水热反应一步合成出一系列与基质同相的Sm^(3+)离子掺杂NaY(MoO_(4))_(2)荧光粉。XRD、SEM、粒度分布和发光光谱等测试结果表明,所得产物为具有四方白钨矿结构的微米颗粒,且当更多Sm^(3+)取代Y^(3+)离子后,会引起晶胞常数增大。此外,当引入EDTA-2Na后,其颗粒尺寸在减小的同时,形貌亦由八面体演变至长方体,这是EDTA-2Na控制颗粒生长以及对{001}晶面的优先作用吸附所致。最后,在814 nm近红外光激发下,可观察到565 nm绿光、600 nm橙光以及647 nm与706 nm处的红光发射,其中绿光发射源自Sm^(3+)的^(4)G_(5/2)→^(6)H_(5/2)跃迁,橙光由Sm^(3+)的^(4)G_(5/2)→^(6)H_(7/2)跃迁产生,而红光则分别归属于^(4)G_(5/2)→^(6)H_(9/2)和^(4)G_(5/2)→^(6)H_(11/2)跃迁。

Lu_(2)(MoO_(4))_(3):Eu^(3+)荧光粉的制备及热增强发光

采用固相法制备了Lu_(2)(MoO_(4))_(3):Eu^(3+)系列红色荧光粉,利用X射线粉末衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、能谱仪(EDS)和荧光光谱(PL)仪对制备荧光粉的结构、形貌、元素组成及光致发光性能进行表征与分析。实验结果表明Eu^(3+)成功掺入基质晶格中并得到Lu_(2)(MoO_(4))_(3):Eu^(3+)纯相样品,荧光粉颗粒大小在2μm左右。制备温度依赖样品光致发光结果表明1000℃下制备Lu_(2)(MoO_(4))_(3):Eu^(3+)样品发光性能最好。煅烧时间依赖样品光致发光结果表明1000℃下煅烧时间为6 h时样品发光效果最好。反常于荧光粉发光热猝灭现象,Lu_(2)(MoO_(4))_(3):Eu^(3+)样品在外界测试温度为250℃左右时出现热增强发光现象,与Lu_(2)(MoO_(4))_(3)负热膨胀特性有关。

一种白色发光二极管用Ag_(2)Sr(MoO_(4))_(2)∶xSm^(3+)红色荧光粉发光性能的研究

采用水热制备系列Ag_(2)Sr(MoO_(4))_(2)∶xSm^(3+)红色荧光粉,并对其进行X射线衍射、扫描电镜和荧光光谱测试。结果表明,Sm^(3+)的掺入不影响Ag_(2)Sr(MoO_(4))_(2)∶xSm^(3+)晶相的形成,合成的荧光粉体晶粒较小,粒度分布均匀。在紫外灯照射下,Ag_(2)Sr(MoO_(4))_(2)∶0.08Sm^(3+)荧光粉发出更亮的红光,而且具有良好的发光性能。

掺Er^(3+)离子Sr_3Y_2(BO_3)_4晶体光谱性能的研究

研究了提拉法生长的掺Er^(3=)的Sr_3Y_2(BO_3)_4晶体的吸收光谱和荧光光谱。应用J-O理论分析并计算了光谱参数,得到唯象参数Ω_2、Ω_4和Ω_6分别为11.90×10^(-20)cm^2、3.44×10^(-20)cm^2和1.92×10^(-20)cm^2。在Er^(3+)∶Sr_3Y_2(BO_3)_4晶体中,Er^(3+)在1533 nm波长的发射截面为1.00×10^(-20)cm^2,~4I_(13/2)→I_(15/2)能级跃迁的荧光寿命和辐射寿命分别为0.58 ms和4.10 ms,良好的光谱性能表明Er^(3+)∶Sr_3Y_2(BO_3)_4晶体可能成为潜在的1.55μm波段的一种激光材料。

Er^(3+)/Yb^(3+):KY(WO_4)_2晶体光学性质研究

以Er3+/Yb3+:KY(WO4)2晶体为基质,研究了铒激光器,提出了采用有顶部籽晶提拉法生长KYW晶体的方法.实验表明,当掺入Yb3+离子作为敏化剂时,其能量转移约为53%,同时,由实验中的Er3+/Yb3+:KY(WO4)2晶体吸收和发射截面图可以看出,1610nm波长是一个好选择,可避开Er的吸收峰,达到提高输出效率的目的.最后分析了激光器调Q器件的选择,提出采用了U2+:CaF2或者Co2+:Al2O3可作为被动Q开关,为今后发展人眼安全激光器的研究打下了良好的基础.

碱土金属离子对掺杂NaY(MoO_(4))_(2):Sm^(3+)上转换发光的影响

采用水热法合成了不同种类的二价碱土金属离子Re2+(Mg2+、Ba2+、Sr2+、Ca2+)掺杂NaY(MoO4)2:Sm3+上转换荧光材料,通过X射线粉末衍射、扫描电子显微镜、发射光谱,对合成样品的晶型结构、形貌和上转换发光性能进行研究。结果表明:碱土金属的掺杂可以通过Y3+格位和占据晶格间隙的方式进入基质晶格;在814nm近红外光上转换激发下,观察到NaY(MoO4)2:Sm3+565 nm处4G5/2→6H5/2能级跃迁的绿光发射峰,600 nm处4G5/2→6H7/2能级跃迁的橙光发射峰以及647nm处4G5/2→6H9/2能级跃迁的红光发射峰。掺杂碱土金属离子后的Re2+@NaY(MoO4)2:Sm3+晶型均与NaY(MoO4)2标准卡一致,颗粒更加均匀。掺杂Re2+(Mg2+、Ba2+、Sr2+、Ca2+)后,上转换发光强度增强,分别可提高60%、70%、45%、60%,这是因为掺杂的Re2+离子替换了Y3+离子产生O2-空位,空位在电荷迁移耦合作用下作为敏化剂,向激活离子传递上转换能量。

Er^(3+)/Yb^(3+):KY(WO_4)_2晶体光谱的各向异性分析

在室温下测量和分析Er3+/Yb3+:KY(WO4)2晶体三个折射率主轴方向上的吸收光谱和荧光光谱,其吸收光谱和荧光光谱谱带强度明显呈现各向异性;用修正的Judd-Ofelt理论计算Er3+/Yb3+:KY(WO4)2晶体中Er3+在三个折射率主轴方向上的强度参量Ωt(t=2,4,6)和各吸收谱带的电偶极跃迁振子强度,同时计算了Yb3+在三个轴向上980nm波长处的积分吸收截面。结果表明:Er3+/Yb3+:KY(WO4)2晶体吸收光谱和荧光光谱存在各向异性,Np轴为Er3+/Yb3+:KY(WO4)2激光晶体的最佳泵浦轴向。

基于能量传递的 Ba_(3)Y_(2)(BO_(3))_(4):Yb^(3+)/Er^(3+)颜色可调上转换发光研究

采用高温固相法合成了不同Yb^(3+)掺杂量的新型Ba_(3)Y_(2)(BO_(3))_(4):Yb^(3+)/Er^(3+)上转换荧光粉。借助XRD、SEM、荧光光谱等表征方法研究了Yb^(3+)掺杂量对材料晶体结构、上转换发光性能的影响,探讨了材料的上转换发光机制。结果表明,Yb^(3+)、Er^(3+)的掺杂未引入杂相,由于Yb^(3+)、Er^(3+)与Y^(3+)离子半径相近,随着Yb^(3+)掺杂量增加,晶胞参数呈现微弱的减小趋势。Yb^(3+)掺杂量0.05时,荧光粉具有最大发光强度。调控Yb^(3+)掺杂量,增强了Yb^(3+)与Er^(3+)间的能量传递,实现了样品发光颜色由绿色→黄色→红色的转变。在980 nm激光激发下,Er^(3+)的绿光和红光发射均为双光子过程。

Ce_(2)(MoO_(4))_(3) as an efficient catalyst for aerobic oxidative desulfurization of fuels

Ce_(2)(MoO_(4))_(3)was synthesized by a simple reflux method using cerium nitrate hexahydrate and ammonium molybdate as reactants.The as-prepared Ce_(2)(MoO_(4))_(3)was characterized by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),Scanning electron microscope(SEM),and X-ray photoelectron spectroscopy(XPS).The removal of dibenzothiophene(DBT)in model oil was studied using Ce_(2)(MoO_(4))_(3)as catalyst and oxygen as oxidant.The reaction factors such as reaction temperature,amount of catalyst,and sulfide type on sulfur removal were researched.The results prove that both Ce3+and MoO42-play significant role in the conversion from DBT to DBTO2.The Ce_(2)(MoO_(4))_(3)catalyst has an excellent performance for the sulfur removal of DBT.Under the optimum reaction conditions,sulfur removal of 99.6%was obtained.After recycling five times,no significant loss in catalyst activity of Ce_(2)(MoO_(4))_(3).Mechanism of aerobic oxidative desulfurization was proposed based on the experiment of free radical capture and infrared characterization.

Upconversion luminescence and temperature sensing performance of Er^(3+) ions doped self-activated KYb(MoO_(4))_(2) phosphors

In this work,a series of self-activated KYb(MoO_(4))_(2) phosphors with various x at% Er^(3+) doping concentrations(x=0.5,1,3,5,8,10,15) was synthesized by the solid-state reaction method.The phase structure of the as-prepared samples was analyzed by X-ray diffraction(XRD),XRD Rietveld refinement and Fourier transform infrared(FT-IR) spectroscopy.The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er^(3+) doping concentration up to 15 at%.High-purity upconversion(UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er^(3+) ions in the self-activated KYb(MoO_(4))_(2) host is revealed as 3 at%.The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra.In addition,the fluorescence intensity ratios(FIRs) of the two thermally-coupled energy levels,namely ^(2)H_(11/2) and ^(4)S_(3/2).of Er^(3+) ions were investigated in the temperature region 300-570 K to evaluate the optical temperature sensor behavior of the sample.The maximum relative sensitivity(S_(R)) is determined to be 0.0069 K^(-1) at300 K and the absolute sensitivity(S_(A)) is determined to be 0.0126 K^(-1) at 300 K.The S_(A) of self-activated KYb(MoO_(4))2:Er^(3+)is almost twice that of traditional KY(MoO_(4))2:Er^(3+)/Yb^(3+)codoping phosphor.The results demonstrate that Er^(3+) ions doped self-activated KYb(MoO_(4))2 phosphor has promising application in visible display,trademark security and optical temperature sensors.

Li_(0.5)Bi_(0.5)MoO_(4)对Li_(2)Zn_(2)(MoO_(4))_(3)陶瓷的微波介电性能影响

采用传统固相反应法制备了xLi_(0.5)Bi_(0.5)MoO_(4)-(1-x)Li_(2)Zn_(2)(MoO_(4))_(3)[xLBM-(1-x)LZM]复合陶瓷,研究添加不同质量分数(x=25%,30%,35%,40%和45%)的LBM对LZM陶瓷的烧结特性、物相组成、微观结构以及微波介电性能的影响。结果表明:添加一定量的LBM不仅能将LZM的谐振频率温度系数(τf)调节近零,还能降低LZM的烧结致密化温度;LBM可与LZM共存,且不发生化学反应生成其他新相。随着LBM添加量增加,复合陶瓷的烧结致密化温度逐渐降低、体积密度先增大后减小、介电常数(εr)与τf逐渐增大而品质因数(Q×f)逐渐减小。当LBM添加量为40%时,LZM-LBM复合陶瓷在600℃烧结2 h获得最大体积密度为4.41 g/cm^(3),以及优异的微波介电性能:ε_(r)为13.8,Q×f为28 581 GHz,τ_(f)为-4×10^(-6)/℃。

水热法合成不同形貌NaGd(WO_(4))_(2)∶Eu^(3+)及其荧光性能

以氧化钆(Gd_(2)O_(3))、氧化铕(Eu_(2)O_(3))、钨酸钠(Na_(2)WO_(4)·2H_(2)O)为原料,EDTA-2Na为辅助剂,水热合成了不同形貌的NaGd(WO_(4))_(2)∶Eu^(3+)荧光材料,利用XRD、SEM以及UV-Vis对产物的结构、形貌及其发光性能进行表征。探讨了辅助剂用量、Eu^(3+)离子掺杂量等因素对NaGd(WO_(4))_(2)∶Eu^(3+)荧光材料的结构、形貌以及荧光性能影响。结果表明:合成样品均为四方晶系白钨矿结构NaGd(WO_(4))_(2);水热条件下,辅助剂EDTA-2Na用量的不同,NaGd(WO_(4))_(2)的形貌也发生了明显变化:从不规则颗粒状,演变成多面体颗粒,以及纳米片自组装花状颗粒,再演变成大脑状形貌。NaGd(WO_(4))_(2)晶体在激活离子Eu^(3+)掺杂浓度较低的情况下,没有出现浓度猝灭效应。

Crystal structure,chemical bond characteristics,infrared reflection spectrum,and microwave dielectric properties of Nd_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9) ceramics

Microwave dielectric ceramics(MWDCs)with low dielectric constant and low dielectric loss are desired in contemporary society,where the communication frequency is developing to high frequency(sub-6G).Herein,Nd_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)(NZ_(1−x)T_(x)M,x=0.02-0.10)ceramics were prepared through a solid-phase process.According to X-ray diffraction(XRD)patterns,the ceramics could form a pure crystal structure with the R3c(167)space group.The internal parameters affecting the properties of the ceramics were calculated and analyzed by employing Clausius-Mossotti relationship,Shannon’s rule,and Phillips-van Vechten-Levine(P-V-L)theory.Furthermore,theoretical dielectric loss of the ceramics was measured and analyzed by a Fourier transform infrared(IR)radiation spectrometer.Notably,when x=0.08 and sintered at 700℃,optimal microwave dielectric properties of the ceramics were obtained,including a dielectric constant(ε_(r))=10.94,Q·f=82,525 GHz(at 9.62 GHz),and near-zero resonant frequency temperature coefficient(τ_(f))=−12.99 ppm/℃.This study not only obtained an MWDC with excellent properties but also deeply analyzed the effects of Ti^(4+)on the microwave dielectric properties and chemical bond characteristics of Nd_(2)Zr_(3)(MoO_(4))_(9)(NZM),which laid a solid foundation for the development of rare-earth molybdate MWDC system.

Structure characteristics and microwave dielectric properties of Pr_(2)(Zr_(1-x)Ti_(x))_(3)(MoO_(4))_(9) solid solution ceramic with a stable temperature coefficient

Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)(x=0.1-1.0)ceramics were prepared via a conventional solid-state method,the dependence of crystal structure and bond characteristics on microwave dielectric properties was investigated systemically.The X-ray diffraction patterns indicated that the single-phase Pr_(2)Zr_(3)(MoO_(4))_(9)structure was formed in all the specimens.As the Ti^(4+)content increased,the lattice volume gradually decreased,which was ascribed to the fact that the ionic radius of Ti^(4+)was smaller than that of Zr^(4+).Notably,outstanding microwave dielectric properties withεr of 10.73-16.35,Q·f values of 80,696-18,726 GHz and minorτ_(f) values−14.1-−2.6 ppm/℃were achieved in Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)ceramics.Theε_(r) increased with the rising x values,which was associated with the increase ofα/Vm values.The decreasing Q·f was affected by the decline of lattice energy of[Zr/TiO_(6)]octahedral.Theτf value was dominated by[Zr/TiO_(6)]octahedral distortion,Mo-O bond energy,bond strength and B-site bond valence.Furthermore,infrared reflection spectra suggested that the properties were mainly caused by the absorption of phonon,and the dielectric loss could be further reduced by optimizing the experimental process.

Crystal structure and enhanced microwave dielectric properties of the Ce_(2)[Zr_(1−x)(Al_(1/2)Ta_(1/2))_(x)]_(3)(MoO_(4))_(9) ceramics at microwave frequency

Dense microwave dielectric ceramics of Ce_(2)[Zr_(1−x)(Al_(1/2)Ta_(1/2))_(x)]_(3)(MoO_(4))_(9)(CZMAT) (x = 0.02–0.10) were prepared by the conventional solid-state route. The effects of (Al1/2Ta1/2)^(4+) on their microstructures, sintering behaviors, and microwave dielectric properties were systematically investigated. On the basis of the X-ray diffraction (XRD) results, all the samples were matched well with Pr_(2)Zr_(3)(MoO_(4))_(9) structures, which belonged to the space group R3¯c. The lattice parameters were obtained using the Rietveld refinement method. The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by using the Phillips—Van Vechten—Levine (P—V—L) theory. Excellent dielectric properties of Ce_(2)[Zr_(0.94)(Al_(1/2)Ta_(1/2))_(0.06)]_(3)(MoO_(4))_(9) with a relative permittivity (ε_(r)) of 10.46, quality factor (Q × f) of 83,796 GHz, and temperature coefficient of resonant frequency (τ_(f)) of −11.50 ppm/℃ were achieved at 850 ℃.

Morphology-dependent electrocatalytic performance of Fe_(2)(MoO_(4))_(3) for electro-oxidation of methanol in alkaline medium

Electrochemically synthesized nanosphere,nanorod and nanotube Fe_(2)(MoO_(4))_(3) at optimized temperature and current density are characterized with XRD,SEM,TEM,XPS.Crystal lattices of the three types Fe_(2)(MoO_(4))_(3) detected by HRTEM are well matched with the simulation analysis results from Materials Studio 6.0 based on the inorganic crystal structure database(ICSD)data and the modified XRD lattice parameters.The ratios of Fe/Mo on the surface resulted from XPS analysis are 1.47,1.63 and 2.22 respectively for nanosphere,nanorod and nanotube.The mixture of Fe_(2)(MoO_(4))_(3) with polytetrafluoroethylene dispersion are coated on glass carbon substrate as electrode for electrocatalytic performance test by cyclic voltammetries in 0.1 mol/L KOH and 1 mol/L methanol electrolyte.Methanol oxidation peak current density of the Nanotube-Fe_(2)(MoO_(4))_(3)/GCEs electrode is 3.27 mA/cm^(2) higher than 2.8 mA/cm^(2) of platinum foil electrode,which shows enhanced catalytic activity of Nanotube-Fe_(2)(MoO_(4))_(3)/GCEs.The cyclic stability in terms of peak current retention are 91%,92%and 88%respectively for Nanosphere-Fe_(2)(MoO_(4))_(3)/GCE,Nanorod-Fe_(2)(MoO_(4))_(3)/GCE and Nanotube-Fe_(2)(MoO_(4))_(3)/GCE electrode after 220 cycles.It is concluded that nanosized Fe_(2)(MoO_(4))_(3) could be promising alternative non-noble electro-catalysts for electro-oxidation of methanol in alkaline medium.

Keggin-type polycationic AlO_(4)Al_(12)(OH)_(24)H_(2)O_(12)^(7+)intercalated MoO_(3)composites for methyl orange adsorption

Molybdenum trioxide(MoO_(3))can be employed as an excellent host for intercalation due to its 2D lay-ered structure that connected by van der Waals interactions.Herein,a series of polyoxometalate-based MoO_(3) composites(Al_(13)@MoO_(3))were successfully prepared by interpolating the Keggin-type polycationic AlO_(4)Al_(12)(OH)_(24)H_(2)O_(12)^(7+)(Al_(13))into MoO_(3)gallery.These composites can be applied to rapidly adsorb the anionic dye methyl orange(MO)through strong electrostatic interactions lead to compact and sta-ble gathering in the surrounding of the numerous charged Al_(13).Adsorption behaviors of composites with the different amount of Al_(13) were determined,these results revealed that Al_(13)-3.34%@MoO_(3)exhibited the most remarkable adsorption capacity.More importantly,the composite maintains superior adsorption capacity for five consecutive adsorption/desorption cycles,suggesting that Al_(13)@MoO_(3)can be an efficient and durable adsorbent.

掺铕钼酸钆发光材料的制备及性质研究

以氧化钆(Gd_(2)O_(3))、氧化铕(Eu_(2)O_(3))、钼酸铵(H_(8)MoN_(2)O_(4))、柠檬酸(C_(6)H_(8)O_(7))为原料,采用超声波辅助溶胶-凝胶法成功制备了Gd_(2)(MoO_(4))_(3):Eu^(3+)荧光粉发光材料。讨论了Eu离子掺杂浓度和前驱体是否煅烧对荧光材料性能的影响,利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、荧光光谱仪(LS)对材料进行表征和分析。结果表明:在403 nm最优激发波长激发下,材料的发射峰位于470~530nm之间,Eu离子掺杂浓度及是否煅烧都会对材料的形貌和发光性能产生影响。