Crystal structure and charge transfer energy of the vaterite-type orthoborate YBO3:Eu

Ligand-to-metal charge transfer energies of YBO3:Eu have been investigated from the chemical bond viewpoint. The chemical bond parameters, such as the covalency, the polarizability of the chemical bond volume, and the presented charge of the ligands in the chemical bond have been quantitatively determined based on the dielectric theory of complex crystal. We calculated the environmental factor (h(e)), which is the major factor influencing the charge transfer energy in the compounds. The calculated results show that the suitable group space of YBO3 is C2/c. The method provides us with a supplementary tool to judge the proper structure when the structure of the crystal has many uncertain space groups.

Monodisperse and core-shell-structured SiO2@YBO3 : Eu3+ spherical particles: Synthesis and characterization

Y0.9Eu0.1BO3 phosphor layers were deposited on monodisperse SiO2 particles of different sizes (300, 570, 900, and 1200 nm) via a sol-gel process, resulting in the formation of core-shell-structured SiO2@Y0.9Eu0.1BO3 particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL) spectra as well as lifetimes were employed to characterize the resulting composite particles. The results of XRD, FE-SEM, and TEM indicate that the 800 degrees C annealed sample consists of crystalline YBO3 shells and amorphous SiO2 cores, in spherical shape with a narrow size distribution. Under UV (240 nm) and VUV (172 nm) light or electron beam (1-6 kV) excitation, these particles show the characteristic D-5(0)-F-7(1-4) orange-red emission lines of Eu3+ with a quantum yield ranging from 36% (one-layer Y0.9Eu0.1BO3 on SiO2) to 54% (four-layer Y0.9Eu0.1BO3 on SiO2).

Vaterite-type YBO3 : Eu3+ crystals: hydrothermal synthesis, morphology and photoluminescence properties

Vaterite-type YBO3:Eu3+ crystals with interesting flower and hedgehog fungus-like structures composed of nanosheets were obtained by controlled crystallization of Y2O3 and Eu2O3 in H3BO3 solutions under acidic hydrothermal (HT) conditions. Nanosheets of uniform thicknesses were formed by preferential crystal growth along the (100) crystallographic plane and specific three-dimensional structures were further developed through a homocentric growth mechanism. Optical emission measurements showed that the HT-grown nanosheet crystals exhibited a higher ratio of the emitted red-to-orange light ratio than crystals grown from solid-state reactions. The photoluminescence intensity and emission lifetimes were also studied as a function of the Eu3+ dopant concentration and the HT synthesis temperature. The effect of some additives: a chelating ligand, a surfactant and a polymer, on the YBO3:Eu3+ crystals morphology was also investigated.

稀土离子的电荷迁移带与化学键性质研究

本论文主要研究的是掺杂在无机材料中的稀土离子的电荷迁移带，利用复杂晶体化学键的介电理论对晶体的化学键性质进行计算和分析，阐明了稀土离子的电荷迁移带与基质的化学键性质之间的规律，揭示了宏观电荷迁移带的微观机制，进而丰富和发展了稀土发光材料的理论知识。 根据大量掺杂稀土离子的化合物的电荷迁移带数据，利用复杂晶体的介电理论计算和分析出化合物的共价性、键体积极化率、配体在晶体中所呈现的电荷及配位数，进而得到由这四个参数定义的环境因子he。发现环境因子he能够有效地描述电荷迁移带的变化趋势,可以揭示电荷迁移的微观机制。具体获得了Eu3+、Sm3+和Yb3+在不同基质中的电荷迁移能与环境因子之间的定量关系。通过这些定量关系式，我们能够利用复杂晶体的介电理论来估算各种复杂晶体中稀土离子的电荷迁移带位置，为电荷迁移带方面的研究工作提供了理论依据。反过来，利用这一关系我们也可以从实验上测得的电荷迁移能数据来判断晶体结构的正确性。在此基础上，我们从化学键和YBO3：Eu的电荷迁移带的角度出发，研究了YBO3的结构，从而确定它的空间群为C2/c，排除了其他的可能性。 考虑到Eu3+的电荷迁移能随着基质平均能隙的增大而增大，而且利用复杂晶体化学键的介电理论可以估算化学键的平均能隙，我们研究了Eu3+在不同基质中的电荷迁移能与相应的化学键的平均能隙之间的关系，发现它们之间符合定量的线性关系。通过这一线性关系估算出的电荷迁移能与实验值一致，说明利用化学键的平均能隙来估算电荷迁移能的可靠性。在此基础上，我们预测了发光材料Gd4GdO(BO3)3:Eu的电荷迁移带位置，计算的结果与实验值相吻合；探索复杂化合物Li2Lu5O4(BO3)3:Eu中Eu3+取代的阳离子的格位，计算结果表明能量最低的电荷迁移带来源于Eu3+取代五种Lu中的Lu1格位，电荷迁移能的计算值与实验值一致。块状和纳米的Sr2CeO4分别通过高温固相法和溶胶凝胶法获得，根据电荷迁移能随平均能隙的增大而增大的规律，可以将激发光谱中出现的三个峰分别归属为：能量最高的激发峰来源于从O1到Ce的电荷迁移，能量最低的激发峰来源于从O2到Ce的电荷迁移，中间的峰是前面两种峰的叠加。

纳米／微米结构氧化物材料的水热合成、形貌与发光性质研究

采用水热法结合后续热处理制备了一系列纯的和稀土离子（Eu3＋，Dy3＋）掺杂的黔具有纳米／微米结构的无机氧化物材料，包括YB03、姚03、Ga203和硅基MCM一攀41介孔分子筛体系。研究了这些体系的水热产物的晶体形貌、结构以及它们的生乖～一＿长机理，并通过进一步热处理得到了保持水热产物纳米／微米结构形貌的发光材料，报道了以上各个体系材料的光致发光性能。一把姚03和Eu203粉末直接加入H3Bo3水溶液中，调节pH一1一4，在180一270夸＿少℃水热处理得到了具有vaterite结构的YBo3：Eu3＋晶体。xRD和FEsEM结果证明一扭03：E矿"晶体是由厚度小于50nm的纳米晶片构成的花状和猴头菇状的微米级晶丫体。水热温度提高时纳米晶片的厚度没有增加，形貌也不变，但是结晶度和发光一强度有所提高。pH值对纳米晶片之间的距离、角度和晶片数量有影响。pH低时，纳米晶片更多且包裹得更紧，形成了猴头菇状；而pH高时，晶片分得更开一些呈花朵状。这与pH值低时结晶成核较快较多有关。YB03：E矿＋水热和固相法样品在24Onm激发下的发光谱峰位相同。但水热样品比固相法样品具有较高的红橙比［Eu3＋：I（，D。一7F2）／I（SD。一7FI）］，增加了12一37％。在24oC下制备的花03：Eu3＋水热样品具有最大的结晶度和发光强度。报道了三种晶形调节剂对水热晶体形貌的影响结果。硝酸钻水溶液用氨水调节至pH一8一n，200oC下水热处理24小时，产物经xRD确定是单斜晶系的碱式硝酸盐叽O（0H）9困03）。FEsEM观察发现产物是一种具有几＿三叶形截面的棱柱。改变合成条件可以调节三叶形棱柱的尺寸。增加氨水量时，PH从8调到n后，棱柱直径可从微米级调节到亚微米级，即从3一5林m左右下降到200一300纳米，同时长径比也有所增加，从pH一8的5增加到pH＝n的10。调节机制可解释为较高的pH条件下结晶成核作用进行较快，形成了更多的晶核。三叶形棱柱的生长机理是、O（OH）9困03）的晶核依靠内在的趋势长成棒状纳米粒子；并通过一种直接的聚集生长，这些起始的纳米棒沿着它们横截面的径向方向快速自堆积成一种Y型结构的棒束；然后沿着棱柱轴向和平行于棱柱叶片方向的晶面同时优先生长，而垂直于叶片方向上的晶面生长得相对缓慢，导致三叶形棱I、－纳米／微米结构氧化物材料的水热合成、形貌与发光性质研究柱的形成。、经过高温相转变得到了姚03三叶形棱柱。采用同样方法可以制得姚03：E矿＋的三叶形棱柱发光粉，其光谱与固相法样品的一致。将Gacl3一HZO一NaOH体系在pH＝6一8时于180℃下水热处理得到了正交晶系的Gao0H晶体，其形貌分别是宽度在200一30Onm之间长径比约1：7的四方棱柱（pH＝6）和长径比约1：3纺锤状的纳米棒束（pH＝8）。使用HZO／DEG混合溶剂可以增加棱柱的长径比，1：Ivol时增加到1：15；1：Zvol时获得的是长达几十微米的四方棱柱纳米线6Go0OH纳米棒是从最初的胶状沉淀中成核后沿着c轴优先生长而成的。pH值的高低可导致Ga0OH晶体从四方棱柱到纳米棒束的不同形貌。DEG的存在对晶体的生长可能有两点作用：一是抑制晶核形成；二是降低晶体沿着横截面晶面的生长速度。经过高温锻烧的产物是保持着前驱体形貌的p一GaZO3晶体。254nm激发下p一GaZO3纳米棒的发射谱是从300nm到600nln的宽峰，最大值在455nln。发光的平均寿命是64ns。其蓝光发射起源于氧空位给体提供的电子和来自受体嫁空位或者嫁氧空位对的空穴之间的复合。采用相似方法制备了p一GaZO3：Dy纳米棒束，并与固相法样品对比了光谱性质的异同。将三种5102基材料：MCM一41型分子筛（直接分子筛CMS和萃取分子筛EMS）、无规颗粒（ASP）和干凝胶（SG）进行从室温到1000℃的不同温度不同时间热处理。254nm激发下，MCM一41没有发光现象。而ASP和SG系列样品随着热处理温度不同而显示不同的PL。说明ASP和SG与MCM一41有着不同的发光机理。排除了ASP和SG样品的发光中心是来自5102网络本身的结构缺陷，认为是其中所含有机物在热处理中产生的碳杂质引起。结果也表明MCM41中模板剂在热处理的碳化产物并没有引起MCM一41的PL。在365nm激发下，MCM一41与ASP、SG的PL现象大致相同。表明所有系列的样品的发光机理相同。CMS和EMS两个系列在300℃以上处理的样品的PL相似，说明模板剂的存在及其碳化并没有影响MCM一41的PL。所有系列样品在365nm激发下的PL认为是起源于5102网络中与氧相关的结构缺陷三Si一0．，而不是碳掺杂作用引起的。

Self-assembled 3D Architectures of LuBO3 : Eu3+: Phase-selective synthesis, growth mechanism, and tunable luminescent properties

Rhombohedral-calcite and hexagonal-vaterite types of LuBO:Eu3+ microparticles with various complex self-assembled 3D architectures have been prepared selectively by an efficient surfactant- and template-free hydrothermal process for the first time. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, photoluminescence, and cathodoluminescence spectra as well as kinetic decays were used to characterize the samples.

喷雾热解法制备YBO_3∶Eu球形发光粉

用喷雾热解两段法制备了 YBO3∶ Eu荧光粉 .其粒径分布窄 (1～ 2 μm) ,为规则的球形 ,且在高温下不会团聚 .考察了 PEG浓度 (聚乙二醇 ,分子量为 1 0 0 0 0 )对发光粉形貌和发光强度的影响、温度对结晶性和发光强度的影响、前躯体溶液的浓度对粒径大小的影响以及掺杂浓度对发光强度的影响 .当 PEG的浓度为 0 .0 0 4mol/L时 ,得到实心球形的发光粉 ,PEG的浓度过高或过低都会使小球产生破裂和空心 ,从而降低发光粉的发光强度 ;样品在 70 0℃时开始结晶 ,1 1 0 0℃时结晶性最好 ,相应的发光强度也最强 ;通过改变前驱体溶液的浓度 ,可以很容易地调控发光粉小球的粒径 ,控制前驱体溶液的浓度在 0 .0 7mol/L,可以得到粒径为 1～ 2 μm的球形发光粉 ;Eu3+在 YBO3基质中的最佳掺杂摩尔分数为 1 0 %.

Dependence of charge transfer energy on crystal structure and composition in Eu3+-doped compounds

We report a method for estimating the positions of charge transfer (CT) bands in Eu3+-doped complex crystals. The environmental factor ( he) influencing the CT energy is presented. he consists of four chemical bond parameters: the covalency, the bond volume polarization, the presented charge of the ligand in the chemical bond, and the coordination number of the central ion. These parameters are calculated with the dielectric theory of complex crystals. The relationship between the experimental CT energies and calculated environmental factors was established by an empirical formula. The calculated values are in good agreement with the experimental results. Such a relationship was confirmed by detailed analysis. In addition, our method is also useful to predict the charge-transfer position of any other rare earth ion.

Photoluminescent properties of sol-gel derived (La, Gd)MgB5O10 : Ce3+/Tb3+ nanocrystalline thin films

Ce3+ and/or Tb3+-doped (La,Gd)MgB5O10 nanocrystalline thin films were deposited on silica glass substrates by a sol-gel dip-coating process using triethyl borate B(OC2H5)(3) as the boron source. The results of XRD indicated that the films have fully crystallized after annealing at 800 degrees C. The films are transparent, uniform and crack free with a thickness of about 300 nm, consisting of particles with an average grain size of 50 nm. The luminescence and energy transfer properties of Ce3+ and Tb3+ have been studied in the films. It is confirmed that the excitation energy of Ce3+ transfers to the Gd3+, migrates over the Gd3+ sublattices, trapped by the Tb3+ and resulted in its characteristic green emission (D-5(4)-F-7(5) at 543 nm) in GdMgB5O10 nanocrystalline films as in the powder phosphors.