用3种方法合成Y_3Al_5O_(12)∶RE~(3 )(RE=Eu,Dy)发光粉的对比研究

以金属硝酸盐为反应原料 ,分别采用柠檬酸 凝胶法、共沉淀法和固相法制备了YAG和YAG∶RE3 (RE =Eu ,Dy) (1% ,摩尔分数 )发光粉 ,并通过XRD ,TG DTA和发光光谱对样品进行了表征。柠檬酸 凝胶法、共沉淀法和固相法制备的YAG和YAG∶Eu的晶相形成温度分别是 80 0和 90 0℃。Eu3 在非晶态和晶态YAG中其激发和发射光谱有明显差异 ,在一定温度范围内 ,发光强度随烧结温度的升高而增强。由于碳杂质的存在 ,90 0和 10 0 0℃下柠檬酸 凝胶法制备样品的发射强度较其他两种方法低。     

R3GeVO9（R=Y，La）：Eu^3＋（或Dy^3＋）的合成及其发光性质

采用高温固相法台成了稀土复合钒锗酸盐R3GeVO9(R=Y,La)体系，并以此为基质研究了Eu^3 和Dy^3 在其中的发光性质，以Eu^3 为结构探针探讨了En^3 在R3GeVO9(R=Y,La)中的格位情况。同时，还研究了被取代离子R^3 Z／r对Eu^3 的红橙比和Dy^3 的黄蓝比的影响以及浓度、温度和Bi^3 对它们发光强度的影响。     

助熔剂对Y3Al5O12：Ce荧光粉性能的影响

在还原气氛下采用高温固相反应法合成了白光LED用黄色荧光粉Y3Al5O12:Ce(YAG:Ce)研究了助熔剂对YAG：Ce荧光粉发光特性的影响，。XRD的测量结果表明加入合适的助熔剂有利于YAG:Ce荧光粉的晶化，并且不引入杂相，选择BaF2和H3BO3同时使用效果要好于单独使用一种助熔剂，助熔剂的加入可增大YAG：Ce荧光粉的激发和发射光谱强度，并能有效降低荧光粉的中心粒径（D50）控制粉体的粒径分布，适用于白光LED的制造。     

La2O3：Sm发光粉的合成与发光性质的研究

以La2O3和Sm2O3为原料，用碳酸盐沉淀法制备了La2O3:Sm^3 发光粉，并分别用XRD，SEM和发光光谱及寿命进行了表征，La2O3晶相的形成温度为800℃，其发光强度随温度升高而增强，La2O3基质中Sm^3 的最佳掺杂浓度为1．5％（摩尔分数）。     

Ca2Y8（SiO4）6O2：RE（RE=Eu,Tb）发光薄膜的制备及发光性能的研究

采用溶胶－凝胶法制备了稀土离子掺杂（Eu^3 ,Tb^3 )的氧磷灰石三元稀土硅酸盐Ca2Y8(SiO4)6O2发光薄膜。通过X射线衍射（XRD）,红外光谱（IR）,扫描电镜（SEM）等方法对薄膜的组成、结构、颗粒尺寸、形貌及厚度进行了研究,通过发光光谱对薄膜的发光性质进行了分析。XRD结果表明700℃时薄膜尚处于非晶态,800℃时已开始有Ca2Y8(SiO4)6O2的物相形成,1000℃时结晶已完全。这一点和红外光谱的结果相符。发光光谱测试表明Ca2Y8(SiO4)6O2:Eu^3 薄膜显示了很强的红光发射,并以Eu^3＋的^5D0-^7F2(616nm)超灵敏跃迁为最强一组。Ca2Y8(SiO4)6O2:Tb^3 的发射光谱由蓝光发射和绿光发射两部分组成,前者对应于^5D3-^7FJ,后者对应于^5D4-^7FJ(J=6,5,4,3),且以^5D4-^7F5(544nm)绿光发射为最强。     

Ca1—xZnxTiO3：Pr^3＋,R^＋（R^＋=Li^＋,Na^＋,K^＋,Rb^＋,Cs^＋,Ag^＋）的合成和发光性质

采用X射线衍射、荧光光谱和热释发光研究了Ca1-xZnxTiO 3∶Pr3+, R+的物相组成和发光性质. Pr3+取代Ca2+形成PrCa ·正电性缺陷发光中心. 激发光谱是峰值位于330 nm附近的宽带谱, 发射光谱是峰值在613 nm半宽度为20 nm的带谱, 对应Pr3+的1D2-3H4跃迁发射. 发光强度和余辉随基质组分Zn/Ca摩尔比和合成温度而变化. Zn2+的最佳含量在10%～20%. X射线衍射研究表明掺入适量的Zn2+物相组成为CaTiO3, Ca2 Zn4Ti15O36和Zn2TiO4. 热释发光曲线表明掺入Zn2+离子后体系中形成了新的缺陷ZnTi″, 且ZnTi″的缺陷陷阱深度大于RCa′.     

Nd^3＋：Gd3Ga5O12透明陶瓷纳米粉体的制备及光谱性能的研究

采用溶胶-凝胶法合成了用于Nd：Gd3Ga5O12（GGG）透明激光陶瓷的多晶纳米粉体，并利用XRD、SEM、荧光光谱分析对所得的GGG纳米粉体进行了分析。XRD分析结果表明：样品属于体心立方的晶体结构，随着温度的升高，粉体的晶化程度也相应提高，衍射峰强度增强，宽度减小，说明粉体粒径逐渐长大；SEM观察发现，获得了单分散、形状规则、似球形的GGG纳米粉体，且随着烧结温度的提高前驱粉体粒度不断增加。1000℃，12h是形成Nd：GGG纯相的较好的温度和烧结时间；荧光发射的最强峰位于1．06μm处，是Nd^3＋的^4I3/2→^4I11/2能级跃迁导致的荧光发射。溶胶-凝胶法制得的Nd：GGG粉体是比较均匀的，粒度较小的，纳米级的晶粒，有利于透明的陶瓷烧强，因此是比较合适的透明陶瓷前驱原料。     

YAG：Ce^3＋荧光粉的合成及α-Al2O3籽晶对相形成的促进作用

用聚丙烯酰胺凝胶法来合成YAG：Ge^3＋荧光粉，用XRD对煅烧过程粉体的结构进行了跟踪测定。结果发现，当直接煅烧凝胶时，可观察到θ-Al2O3，YAM和YAP等中间相的形成，而当煅烧含有α-Al2O3，YAM和YAP的形成，加速其与Y203的反应而在较低温度下直接生成YAG相。合成YAG：Ce^3＋荧光粉的发射峰为处于550nm的宽峰，其激发光谱有两个主要的吸收峰，主峰位于460nm，可以与GaN LED的蓝色发射相匹配而用于白光LED的组装。一些助熔剂可以提高荧光粉的光致发光特性，这归因于助熔剂对YAG结晶过程的改进作用和对YAG：Ce^3＋中三价铈离子的稳定作用。     

Tb4O7纯度对Tb3Al5O12发光性质的影响

采用溶胶－凝胶法用不同纯度的Tb4O7在非还原气氛下合成了Tb3Al5O12，并研究了最佳合成条件，电子能谱以及发光性质，结果表明：Tb3Al5O12最佳合成时间应不超过3h，最佳合成温度不超过900℃，提高Tb4O7的纯度，Tb3Al5O12中Tb^3 的发光明显增强。     

（ZnBaLa）BO3：Eu^3＋的合成与发光的研究

高温固相扩散法合成了发光材料Zn1．5xBa1．5yLa1-x-y-z)BO3∶Eu3+z(x+y+z＜0．4)．对样品进行了XRD和IR分析,结果表明：在空气中900 ℃条件下,合成了荧光体样品,LaBO3中La3+离子被部分Zn2+和Ba2+离子取代使晶系发生了变化,LaBO3属于正交晶系,而(Zn0．27Ba0．24La0．61)BO3∶Eu3+0．05经过XRD属于立方晶系,a=0.639 7,V=0.261 8 nm3．扫描电镜测其晶貌,平均粒度为22 μm左右．样品的激发光谱和发射光谱显示：在基质BO3结构中O2—Eu3+的CT带位于295 nm,Eu3+的强发射来自5D0→7F1和5D0→7F2跃迁,存在磁偶极和电偶极两种跃迁．     

High-temperature X-ray diffraction and specific heat studies on GdAlO3, Gd3Al5O12 and Gd4Al2O9

Gadolinium aluminates, GdAlO₃, Gd₃Al₅O₁₂ and Gd₄Al₂O₉ were synthesized by the solution combustion method. Very fine particles in the nanoparticle range of ∼10-20 nm could be prepared by this method as evidenced by surface area measurement by multipoint BET method. Thermal studies on these compounds were carried out using high-temperature X-ray diffraction (HT-XRD) and differential scanning calorimetry (DSC) methods. The thermal expansion coefficients of GdAlO₃, Gd₃Al₅O₁₂ and Gd₄Al₂O₉ were calculated from the lattice parameter data and specific heats were calculated from DSC data. The lattice parameters of GdAlO₃ and Gd₃Al₅O₁₂ were found to increase linearly with temperature whereas Gd₄Al₂O₉ did not show a linear trend. The specific heats of these compounds show an increasing trend with increase in aluminum atom fraction. Based on the thermodynamic data available in the literature and the specific heat data obtained in this study, oxygen potential diagram was constructed at 1000 K.     

Quantum efficiency of double activated Tb3Al5O12:Ce, Eu

The quantum efficiency and luminescence properties of double activated terbium aluminum garnet samples were investigated in the present study. A mathematical procedure and PL measurement system are developed for express analysis of quantum efficiency of luminescent materials. The energy-level diagram was proposed to explain the luminescence mechanism. Application of TAG:Ce,Eu with improved CIE and CRI in LED device is demonstrated.     

Application of TiO2/Er3+:Y3Al5O12 composite to photo-degrade acid red B dye under sun light irradiation

In this work, an upconversion luminescence agent, Er³⁺:Y₃Al₅O₁₂, was synthesized and its absorption and fluorescent spectra was determined. By calculation, the upconversion efficiency of the emission peak at 320 nm was estimated to be about 3.4%. And then, TiO₂/Er³⁺:Y₃Al₅O¹² composite was prepared by simple ultrasonic dispersion and liquids boil methods. The obtained composite was characterized by X-ray diffrac-tion. The effect of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite with different Er³⁺:Y₃Al₅O₁₂ doping amount, heat-treated temperature and heat-treated time on photodegradation of acid red B under sun light was investigated in detail. It was found that the photocatalytic activity of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite was much higher than that for the similar system with only TiO₂ powder. These results support the usefulness of TiO₂/Er³⁺:Y₃Al₅O₁₂ composite in the process of photodegrading dye wastewater and using the sun light.     

Dilatometric studies of Y2W3O12 with added Al2O3

Y₂W₃O₁₂ exhibits negative thermal expansion along the three crystallographic directions due to the transverse thermal vibrations perpendicular to the Y-O-W linkage. It is highly hygroscopic and forms a trihydrate structure at room temperature. Dilatometric studies of Y₂W₃O₁₂ show large thermal expansion hysteresis due to large grain size and a large initial positive thermal expansion due to the removal of water molecules. Al₂O₃ has been added to Y₂W₃O₁₂ upto 10 wt% in an attempt to overcome the hygroscopicity and reduce the particle size and thereby the thermal expansion hysteresis. Thermo gravimetric, dilatometric and electron microscopic studies are presented to support these observations. Dedicated to Professor C N R Rao on his 70th birthday     

Polymorphism in yttrium molybdate Y2Mo3O12

Yttrium molybdate (Y₂Mo₃O₁₂) has been prepared by non-hydrolytic sol–gel chemistry. The phase evolution upon heating was investigated using in situ and ex situ heat treatments combined with powder X-ray diffraction. This method has led to the isolation of two orthorhombic phases with different atomic connectivity. Yttrium adopts 6- and 7-coordinate sites in the Pbcn and Pba2 structures, respectively. Cocrystallization of both phases was observed in a narrow temperature range, suggesting that crystallization kinetics play a major role in phase formation. It was found that the Pba2 phase is the stable polymorph below 550 °C, and converts to Pbcn at higher temperatures.     

Standard free energy of formation of YFeO3, Y3Fe5O12, and a new compound YFe2O4 in the FeFe2O3Y2O3 system at 1200°C

The phase equilibria in the FeFe₂O₃Y₂O₃ system have been established at 1200°C. The following phases were stable: yttria, hematite, magnetite, wüstite, metallic iron, yttrium-iron perovskite, yttrium-iron garnet, and a new phase YFe₂O₄, belonging to a rhombohedral crystal system. The YFe₂O₄ compound has a solid solution from YFe₂O_3.905 to YFe₂O_4.000. The standard free energies of formation of YFe₂O_3.905, YFeO₃, and Y₃Fe₅O₁₂ have been determined to be ?96 800 ± 200 cal, ?59 800 ± 200 cal, and ?143 700 ± 600 cal, respectively, from metallic iron, Y₂O₃, and oxygen.     

稀土掺杂Lu3Al5O12荧光粉的发光特性及能量传递

采用高温固相法制备了Ce、Sm共掺Lu_3Al_5O_(12)荧光粉。通过X射线衍射分析、荧光光谱分析研究了样品的结构、发光特性,并通过理论计算研究了能量传递效率、能量传递的临界距离以及能量传递方式。X射线衍射分析表明所制备的荧光粉具有单一的石榴石结构;荧光光谱分析表明,在464 nm蓝光激发下,Sm~(3+)的引入可增加Lu_3Al_5O_(12)∶Ce,Sm发射光谱中红光成分,并且随着Sm~(3+)浓度的增加,Ce~(3+)发光强度逐渐减弱。计算出Ce~(3+)、Sm~(3+)之间的能量传递效率高达77.42%,确定了Ce~(3+)、Sm~(3+)之间的能量传递机制为偶极-偶极相互作用。     

稀土掺杂Lu3Al5O12荧光粉的发光特性及能量传递

采用高温固相法制备了Ce、Sm共掺Lu₃Al₅O₁₂荧光粉。通过X射线衍射分析、荧光光谱分析研究了样品的结构、发光特性,并通过理论计算研究了能量传递效率、能量传递的临界距离以及能量传递方式。X射线衍射分析表明所制备的荧光粉具有单一的石榴石结构;荧光光谱分析表明,在464 nm蓝光激发下,Sm³⁺的引入可增加Lu₃Al₅O₁₂：Ce,Sm发射光谱中红光成分,并且随着Sm³⁺浓度的增加,Ce³⁺发光强度逐渐减弱。计算出Ce³⁺、Sm³⁺之间的能量传递效率高达77.42%,确定了Ce³⁺、Sm³⁺之间的能量传递机制为偶极-偶极相互作用。     

Cr3+在不同基质Y3Ga5O12或Ga2O3中的荧光特性

以Ga_2O_3、Y_2O_3、Cr(NO_3)_3·9H_2O为原料,柠檬酸为配位剂,通过溶胶-凝胶高温固相合成法制备出Ga_(2-2x)O_3∶2xCr~(3+)(Ga_2O_3∶xCr)与Y_3Ga_(5-5x)O_(12)∶5xCr~(3+)(YGG∶xCr)2种多晶粉体(x=0.01,0.03,0.05,0.07)。并采用X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)、荧光光谱(PL)对样品的结构、组成、形貌和荧光性能进行测试分析。XRD和IR分析结果显示在900℃煅烧后Ga_2O_3∶xCr和YGG∶xCr两种样品均成相。SEM照片显示Ga_2O_3∶xCr样品形貌为柱形多面体,YGG∶xCr为短棒状。PL结果显示Cr~(3+)在Ga_2O_3和YGG两种基质中的最强荧光发射峰分别位于742和740 nm,均属于Cr~(3+)的~2E-~4A_2跃迁,对比发现Cr~(3+)在YGG基质中的荧光发射强度更强,在远红光区的荧光性能更好,能满足温室照明中植物光合作用的需求。     

Structure and properties of Y5Mo2O12 and Gd5Mo2O12: Mixed valence oxides with structurally equivalent molybdenum atoms

Crystals of Ln₅Mo₂O₁₂ (Ln = Y, Gd) were grown by electrochemical reduction of alkali-molybdate/rare-earth oxide melts at 1075–1100°C. A single crystal of Y₅Mo₂O₁₂, used for structure determination, was found to be monoclinic with a = 12.2376(7) Å, b = 5.7177(8) Å, c = 7.4835(5) Å, β = 108.034(5)°, and Z = 2. Although the structure was refined in space group C2/m, the true space group appears to be P2₁/m. In Y₅Mo₂O₁₂, rutile-like sheets of edge-shared MoO₆ chains linked by YO₆ octahedra are interconnected with YO₇ monocapped trigonal prisms. The Mo atoms in the chains have alternating distances of 2.496 and 3.221 Å and in that respect are similar to MoO₂. However, in contrast to metallic MoO₂ both the Y and Gd compounds are n-type semiconductors with room temperature resistivities of the order of 10³ ohm-cm. Magnetic susceptibility measurements confirm the presence of one unpaired electron per Mo₂ unit. The semiconducting behavior can be explained in terms of an unfavorable bridging oxygen coordination which prevents electron delocalization through metal-oxygen pi bonding as in MoO₂.