Luminescence Properties of Dual Valence Eu Doped Nano-crystalline BaF2 Embedded Glass-ceramics and Observation of Eu2+ → Eu3+ Energy Transfer

Europium doped glass-ceramics containing BaF₂ nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF₂ nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm⁻¹ has been demonstrated from the emission spectra of Eu³⁺ ions showing the transitions from upper excitation states ⁵D_J (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu³⁺) ions to divalent (Eu²⁺) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu²⁺ to Eu³⁺ ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu³⁺ to Eu²⁺ under normal air atmospheric condition has been observed in a BaF₂ containing oxyfluoride glass-ceramics system.     

LnPO4: RE3+ (La = La, Gd; RE = Eu, Tb) nanocrystals: solvo-thermal synthesis, microstructure and photoluminescence

Through altering the solvents, we have obtained the Eu³⁺/Tb³⁺ ions-doped LnPO₄ (Ln = La, Gd) phosphors with different particle sizes, microstructures and morphologies via a facile solvo-thermal technology. X-ray powder diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscope (SEM) have shown that the products using different solvents have various structures and morphologies. With the increase of DMA/water volume ratio, the microstructure has changed from hexagonal phase to monoclinic one, and the morphology from nanorod to nanoparticle, revealing the decreased oriented growth. The presence of DMA is an important factor in guiding the anisotropic growth of hexagonal lanthanide phosphates. Besides, N-methyl-2-pyrrolidone has been used as solvent to induce the Eu³⁺/Tb³⁺ ions-doped LnPO₄ (Ln = La, Gd) phosphors with different morphologies and structures. Finally, the photoluminescence behaviors of these nanocrystals have been investigated, which are dependent on their microstructures and morphologies.     

微波热效应合成(Y,Gd)BO3:Eu3+荧光体

本文首次报道用微波热效应法合成(Y,Gd)BO3:EU3+荧光体粉晶材料,X射线粉末衍射确认为六方晶系,晶胞参数a=0.3796nm,c=0.8835nm;在589nm和613.0nm监测下,其激发光谱峰是239.0nm和240.0nm,半高宽40nm.在240.0nm激发下,589nm和612-626nm的荧光强度比为1.9/1.     

Ce3+和Tb3+, Eu3+在六方NaLnF4(Ln=La,Gd或Y)中的发光和能量传递

本文报道Ce3+掺杂和Ce3+—Tb3+、Ce3+—Eu3+共掺杂的六方NaLnF4(Ln=La,Gd或Y)发光体的研究结果:氟配位环境使Ce3+在300nm附近发射并有很低的猝灭浓度;阳离子缺陷发光中心可能形成于NaGdF4基质中并被Ce3+—Gd3+共同敏化;Ce3+的发光可以因Tb3+掺杂而增强,反过来Ce3+亦会使Tb3+的5D3/5D4发射强度比减小;Ce3+含量增加使Eu3+的5D2/5D1及5D2/5D0发射强度比减小,这与Ce3+的2F5/2→2F7/2跃迁和Eu3+的5D2→D1跃迁能级差匹配而产生共振能量传递有关。     

(Y,Gd)BO3:Tb3+的真空紫外及紫外激发光谱特性

采用传统的高温固相反应法合成出（Y,Gd）BO3：Tb荧光体,对所制得的荧光体进行了晶体结构分析,分析结果表明结晶良好。（Y,Gd）BO3：Tb在147nm真空紫外光激发下的发射主峰在544nm（Tb^3＋的^5D4→^7F5跃迁）,是一种绿色发光材料。样品的真空紫外激发光谱及紫外激发光谱表明,（Y,Gd）BO3：Tb的基质吸收带位于150nm附近。Gd^3＋离子对真空紫外区的光吸收有增强作用,存在着Gd^3＋→Tb^3＋的能量传递。测量了荧光粉在室温下的荧光衰减特性,其余辉时间约为8ms,能够满足显示显像技术的要求。因此,（Y,Gd）-BO3：Tb是一种有前景的PDP用绿色发光材料。     

LnAlO3中Ce3+,Tb3+,Dy3+的发光及Ce-Tb,Ce-Dy的敏化发光(Ln=La,Gd,Y)

本文采用BaF2作为助熔剂和抑制剂经固相反应合成了一系列以LnAlO3(Ln=La,Gd,Y)为基质的磷光体,系统地研究了LnAlO3中Ce3+,Tb3+,Dy3+的发光及Ce-Tb,Ce-Dy的敏化发光,发现随Ln的不同,LnAlO3作为基质对激活剂的发光性质的影响也不同,本文得到一些规律性结果,并作了讨论。     

Eu3+:Ln2O2S(Ln=Lu,Y,Gd,La)晶体的角重迭参数计算

本文使用角重迭模型(AOM),针对Eu3+:Ln2O2S(Ln=Lu,Y,Gd,La)晶体系列,在考虑硫和氧两种不同格位的情况下,对f电子的全部四个角重迭参数eσ、eπ、eδ和eφ进行了计算,得到了一些基本规律,即中心离子与配位体之间的共价性大小次序为Lu～Y>Gd>La,并且Ln-O键的共价性要强于Ln-S键.     

(Y,Gd)Al3(BO3)4:Tb的真空紫外光谱特性

(Y,Gd)Al3(BO3)4属于三角晶系,具有R32的空间群,掺入Ce3 ,Tb3 杂质后,其晶格结构没有变化。(Y,Gd)Al3(BO3)4:Tb随着Gd3 摩尔浓度增大,基质吸收带红移。Gd3 和Tb3 之间存在着很有效的能量传递。Gd3 摩尔浓度在一定范围内(0~0·75mol)增大时,样品在120~300nm光谱范围内的激发强度均是增强的;但是,Gd3 浓度过高造成Gd3 的发射增强,GdAl3(BO3)4:Tb在120~240nm光谱范围内激发强度很明显下降。(Y,Gd)Al3(BO3)4:Ce,Tb在真空紫外激发下,发现Tb3 的发光明显的被Ce3 猝灭。     

Tb3+离子在固溶体(Y0.9Gd0.1)2O2S和(Gd0.9La0.1)2O2S中的发光

用稀土氧化物硫化法合成了固溶体发光材料(Y0.9Gd0.1)2O2S:Tb和(Gd0.9La0.1)2O2S:Tb,并且用阴极射线和254nm紫外线两种激发方式测试了它们的发光性能.研究了固溶体(Y0.9Gd0.1)2O2S:Tb和(Gd0.9La0.1)2O2S:Tb中Tb3+离子5D3——7FJ和5D4——7FJ的能级跃迁强度随Tb3+离子浓度而变化的关系,以及它们的发光色度随激活剂Tb3+离子浓度的变化,探讨了Tb3+离子的浓度猝灭机理.     

(REO)3BO3(RE=La、Gd、Y)中Pr3+的光致发光

研究了紫外光激发下,（ＲＥＯ）３ＢＯ３（ＲＥ＝Ｌa、Ｇd、Ｙ）基质中Ｐr＾３＋的光 谱性质;探讨了基质晶格、阳离子半径、Ｐr＾３＋－Ｏ＾２－键的共价性等因素对光谱性 质的影响;分析了Ｐr＾３＋的发光强度随组成变化的规律性及Ｐr＾３＋的＾３Ｐ１→＾３Ｆ２跃迁发射的自身浓度猝灭机理。     

Y(BO3,PO4):Ce,Tb,Gd的发光特性研究

用ＢＰＯ４和稀土氧化为原料,通过单片灼烧,首次合成了铈、铽、钆共激活的硼磷钇绿色荧光粉,利用发射光谱和激发光谱研究了基质中Ｃｅ＾３＋、Ｔｂ＾３＋、Ｇｄ＾３＋的发光以及它们之间的相互作用结果表明在铈、铽或钆、铽的双掺杂体系中存在Ｃｅ＾３＋→Ｔｂ＾３＋、Ｇｄ＾３＋→Ｔｂ＾３＋的能量传递,而在铈、钆双掺杂的体系中却观察到了Ｃｅ＾３＋和Ｇｄ＾３＋离子之间的竞争吸收和独自发射。在铈、铽共激活的硼磷民体系中掺     

纳米发光材料LnVO4:Eu(Ln=La,Gd,Y)的光谱研究

采用络合溶胶 凝胶法制备了系列纳米发光材料LnVO4:Eu(Ln =La ,Gd ,Y) ,并采用X射线衍射(XRD)、红外光谱 (FTIR)、荧光光谱以及紫外 可见光谱 (UV Vis)对三种发光材料的结构以及发光性质进行研究。结果表明 :YVO4与GdVO4具有相同的结构 ,均属于四方晶系 ,二者具有相似的光谱性质 ;而LaVO4属于单斜晶系 ,受对称性的影响其光谱也相应的发生了变化 ,红外光谱和发射光谱的特征峰发生明显的宽化 ,紫外光谱峰的数目增多     

均一球形PDP用荧光粉(Y,Gd)BO3:Eu的合成

利用共沉淀法通过控制稀土离子浓度、沉淀温度等得到稀土氧化物前驱体沉淀,再将其和H3BO3按化学计量比混合煅烧制备出了平均粒径在0．5～1．0μm的球形、粒径分布较小和无团聚的(Y,Gd)BO3：Eu荧光粉,其性能在一些方面优于商用荧光粉。利用X射线衍射、SEN、粒度分析仪和PL光谱进行表征。研究了不同的煅烧温度对荧光粉性能的影响,结果发现用本实验方法在800℃煅烧即可得到纯相的(Y,Gd)BO3：Eu。而传统固相合成纯相的(Y,Gd)BO3：Eu反应温度高达1200℃。因本方法工艺较易控制,适于在工业生产上推广。     

均一球形PDP用荧光粉(Y,Gd)BO_3∶Eu的合成

利用共沉淀法通过控制稀土离子浓度、沉淀温度等得到稀土氧化物前驱体沉淀,再将其和H3BO3 按化学计量比混合煅烧制备出了平均粒径在 0. 5~1. 0μm的球形、粒径分布较小和无团聚的 (Y,Gd)BO3∶Eu荧光粉,其性能在一些方面优于商用荧光粉。利用X射线衍射、SEM、粒度分析仪和PL光谱进行表征。研究了不同的煅烧温度对荧光粉性能的影响,结果发现用本实验方法在 800 ℃煅烧即可得到纯相的(Y,Gd)BO3∶Eu。而传统固相合成纯相的(Y,Gd)BO3∶Eu反应温度高达 1 200℃。因本方法工艺较易控制,适于在工业生产上推广。     

Photophysical Properties of Ternary RE3+ (RE = Eu, Tb, Sm) Hybrids with β-Diketone Functionalized Linkages and 4-(4-nitrostyryl)pyridine Though Coordination Bonding

In this paper, the organic ligands TTA and TAA are grafted onto the coupling agent to achieve the organic precursors (TTA-Si, TAA-Si) as first ligand and the organic 4-(4-nitrostyryl)pyridine (Nspy) is synthesized as the second ligand. Both of them are coordinated to the rare ions with the carbonyl group and nitrogen atom respectively. After the hydrolysis and copolycondensation between the teraethoxysilane (TEOS) and the ternary rare earth organic complex via the sol–gel process, the chemical bonded hybrid materials are constructed and characterized in detail. The obtained hybrid materials present superior thermal stabilities and regular and homogenous square blocks microstructure. Among the hybrids Eu(TTA-Si)₃Nspy shows a more strong characteristic emission and longer lifetime than the hybrids Eu(TAA-Si)₃Nspy, while hybrids Tb(TAA-Si)₃Nspy exhibits the stronger characteristic emission and longer lifetime than the hybrids Tb(TTA-Si)₃Nspy. For Sm³⁺ hybrid materials, the photoluminescence of Sm(TAA-Si)₃Nspy is too weak to find in the characteristic emission spectra, meanwhile, Sm(TTA-Si)₃Nspy has the excellent luminescent intensity.     

Transport effects in La0.67−x R x Sr0.33MnO3 (R=Eu, Gd)

An experimental study is reported on the temperature dependences of the magnetic susceptibility, electrical resistivity, magnetoresistance, thermo-and magnetothermopower, and on the Hall effect of the polycrystalline lanthanum manganites La_0.67?x R _x Sr_0.33MnO₃ (x=0 and 0.07, R=Eu, Gd) within the 77-to 430-K temperature range. Replacement of a small amount of lanthanum by europium or gadolinium was found to result in a considerable decrease in the resistivity and in a change in the pattern of its temperature dependence. The temperature dependence of both the ordinary and anomalous Hall coefficients near the Curie temperature is shown to be determined by the change in the number of carriers in delocalized states. A method is proposed for separation of the hole and electronic contributions to thermopower in the ferromagnetic region. The conduction mechanisms are discussed in terms of the concept of mobility edge motion.     

Luminescence and recombination processes in bulky Li6Gd x Y1 − x (BO3)3:Eu crystals

The luminescence and recombination processes in crystals of lithium borates Li₆Gd _x Y_{1 − x} (BO₃)₃:Eu have been investigated. The steady-state X-ray luminescence (XRL) spectra, the temperature dependences of the XRL intensity, and the thermally stimulated luminescence (TSL) spectra have been measured for the Li₆Gd(BO₃)₃, Li₆Eu(BO₃)₃, Li₆Y_0.5Gd_0.5(BO₃)₃:Eu, and Li₆Gd(BO₃)₃:Eu compounds in the temperature range of 90–500 K. It is established that the band at 312 nm, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ ions and the group of lines at 580–700 nm, which are due to the ⁵ D ₀ → ⁷ F _J (J = 0 … 4) transitions in Eu³⁺ ions dominate in the XRL spectra. The XRL intensity in these bands increases several times with a change in temperature from 100 to 400 K for undoped crystals. The likely mechanisms of the observed temperature dependence of the XRL intensity and their relationship with the features of electronic-excitation energy transfer in these crystals are discussed. The spectra of all crystals under study exhibit a dominant composite TSL peak with a maximum at 110–160 K and a series of weaker peaks, the composition and structure of which depend on the crystal type. The nature of the shallow traps, which are responsible for the TSL at temperatures below room, and their relationship with the defects of lithium cation sublattice are discussed.     

Luminescence Spectra of YGG：RE^3＋, Bi^3＋ （RE = Eu and Tb） and Energy Transfer from Bi^3＋ to RE^3＋

We investigate the luminescence properties of Bi^3＋ and RE^3＋ （RE = Tb or Eu） in a Y3Ga5O12 （YGG） host system. The additional doping of Bi^3＋ can enhance the luminescence of Th^3＋ or Eu^3＋ in this host. Energy transfer from Bi^3＋ to Tb^3＋ and Eu^3＋ is observed and the mechanism of energy transfer is investigated. Mechanism of energy transfer can be explained as electric multipole interaction since the Bi^3＋ emission band and Tb^3＋ or Eu^3＋ excitation band overlaps and the Bi^3＋ emission intensity decreases while the intensity of Tb^3＋ or Eu^3＋ increases with the increase of Tb^3＋ or Eu^3＋ concentration. Therefore, Bi^3＋ ion is a kind of efficient sensitizer to the Tb^3＋ and Eu^3＋ activators in the Y3Ga5O12 host.