LaF_3∶Eu^(3+)纳米粒子的水热法制备及发光性质研究

用水热法制备了LaF3及Eu3+掺杂的LaF3纳米粒子,通过X射线粉末衍射(XRD)、透射电子显微镜(TEM)和荧光光谱(FS)对样品进行了表征。结果表明:所得的纳米粒子粒度均匀、结晶完好,呈规则的六边形形状;研究了反应温度和时间对LaF3纳米粒子形成的影响,初步探讨了纳米粒子的生长机制。研究了掺杂Eu3+后的发光性质,发现纳米粒子经高温煅烧后,荧光强度有明显下降,适宜的煅烧条件为600℃/6 h,Eu3+的掺杂量在5%(摩尔分数)时,纳米粒子的荧光强度最强,更高的掺杂浓度将导致荧光猝灭。

室温下简易合成LaF_3纳米粒子

以十六烷基三甲基溴化铵(CTAB)作表面活性剂,室温下直接沉淀反应制备LaF3纳米粒子,并用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和荧光分光光度计进行了结构和光谱表征.结果表明,LaF3纳米粒子呈片状,直径40nm左右,结晶性能良好.

LaF_3对激光原位合成TiC/Ni涂层耐蚀性的影响

以Ni60、Ti、石墨、Mo及LaF3为原料,在闸板表面激光熔覆原位合成了TiC/Ni复合涂层。利用SEM、电化学腐蚀系统对涂层组织和耐蚀性能进行分析。结果表明,未添加LaF3和添加3%LaF3的熔覆层中存在异质相,自腐蚀电流升高,腐蚀电位降低,耐蚀性下降;添加2%LaF3的熔覆层中异质相消失,腐蚀电流密度降低,腐蚀电位升高,钝化区宽度增加,耐蚀性提高。

纳米LaF_3块体材料常温离子电导率的研究

采用水溶液直接沉淀法成功制备了LaF3纳米粉体.用透射电子显微镜（TEM）观察了粒子形貌及粒度,粒子呈球形,粒径范围在10～20 nm之间,粉体单分散性良好.用X射线衍射（XRD）分析得到的平均粒径16.7 nm.采用真空高压固结法在真空度10^-4 Pa条件下常温加压至1GPa制备了纳米LaF3块体材料.采用交流阻抗谱研究了纳米LaF3的室温离子电导率,发现纳米LaF3的室温离子电导率（10^-5 S·cm^-1）和单晶LaF3的室温离子电导率（10^-6 S·cm^-1）相比有明显提高.观察到由于纳米材料的弛豫引起电导率随测试次数增大的现象.

Dy^(3+)/Tb^(3+)共掺杂LaF_3微纳米球的水热合成及其发光性质

采用水热法制备了稀土离子掺杂LaF_3:Ln^(3+)(Ln=Tb^(3+),Dy^(3+)和Dy^(3+)/Tb^(3+))荧光材料,通过XRD、SEM、FL分别对样品的结构、形貌和荧光性能进行表征.实验结果表明样品为纯六方晶系LaF_3纳米微球.研究了不同的pH值、Tb^(3+)不同摩尔掺杂浓度对LaF_3:Tb^(3+)发光性质的影响.结果显示在水热为160℃,24h,pH=3条件下制备的LaF_3:7.5%Tb^(3+)荧光强度最强(Tb^(3+)的特征发射峰位于489 nm、543 nm、585 nm和621 nm处),当Tb^(3+)的摩尔掺杂浓度大于7.5%时,将导致荧光猝灭.研究了Dy^(3+)/Tb^(3+)共掺杂La F3的光谱性质,结果表明,Dy^(3+)作为敏化剂,能有效敏化Tb^(3+)的特征发光,其能量传递方式为非辐射共振传递.少量的Dy^(3+)掺入到LaF_3:Tb^(3+)中,可使其543nm处的Tb^(3+)荧光强度显著增强.

LaF_3对激光原位合成TiC组织与性能影响

利用激光熔覆技术原位合成添加稀土LaF3的TiC/Ni复合涂层.借助于电子探针(EPMA)、透射电镜(TEM)、扫描电镜(SEM)、显微硬度计、M—2000摩擦磨损试验机、M398电化学腐蚀系统对涂层组织结构、元素分布、硬度及耐磨、耐蚀性能进行了分析.结果表明,添加适量稀土LaF3,可改善组织均匀性,细化晶粒,TiC颗粒偏聚减轻,异质相含量降低,LaF3含量为1%时熔覆层硬度最高,LaF3含量为2%时熔覆层耐磨及耐蚀性较高.添加过量稀土LaF3后,异质相含量增加,TiC颗粒偏聚,熔覆层硬度降低,使耐磨性和耐蚀性降低.

Photoluminescence properties of LaF_3:Eu^(3+) nanoparticles prepared by refluxing method

The europium-doped LaF3 nanoparticles were prepared by refluxing method in glycerol/water mixture and characterized with X-ray diffraction（XRD）, field emission scanning electron microscopy（FE-SEM）, UV-vis diffuse reflectance spectrum, and photoluminescence spectra.The results of XRD indicated that the obtained LaF3：Eu^3＋ nanoparticles were well crystallized with a hexagonal structure.The FE-SEM image illustrated that the LaF3：Eu^3＋ nanoparticles were spherical with an average size around 30 nm.Under irradiation of UV light, the emission spectrum of LaF3：Eu^3＋ nanoparticles exhibited the characteristic line emissions arising from the 5D0→7FJ（J=1, 2, 3, 4） transitions of the Eu3＋ ions, with the dominating emission centered at 590 nm.In addition, the emissions from the 5D1 level could be clearly observed due to the low phonon energies（-350 cm^-1） of LaF3 matrix.The optimum doping concentration for LaF3：Eu3＋ nanoparticles was determined to be 20mol.%.

Synthesis of colloidal LaF_3: 0.04Yb^(3+), 0.01Er^(3+) nanocrystals with green upconversion luminescence

A synthesis of LaF3：0.04Yb^3＋,0.01Er^3＋ nanocrystals with oleic acid as a capping ligand was presemed. The X-Ray Diffraction （XRD） pattern indicated that the power was a single hexagonal phase. Transmission Electron Microscopy （TEM） demonstrated that the average size of the nanocrystals was less than 10 nm, with a narrow size distribution. The nanocrystals were dispersible in nonpolar solvents and form a fully transparent colloidal solution, and the solution was stable for several months without any aggregates. The Yb^3＋-Er^3＋ codoped nanocrystal colloidal solution exhibited a bright green upconversion fluorescence under 980 nm excitation from a diode laser. The nanocrystals were potentially applicable in biolabeling and bioimaging.

Synthesis and Upconversion Luminescence of LaF_3:Yb^(3+),Er^(3+)/SiO_2 Core/Shell Microcrystals

LaF3：Yb^3＋ , Er^＋ microcrystals were synthesized by a hydrothermal method, and then, the LaF3： Yb^3＋ , Er^＋ microcrystals were coated with silica. Phase identification of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 was performed via XRD. The TEM image showed that the size of LaF3： Yb^3＋ , Er^＋ was 150 nm and LaF3： Yb^3＋ , Er^＋/SiO2 presented clearly a core/shell structure with 20 nm shell thickness. The upconversion spectra of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 in solid state and in ethanol were studied with a 980 nm diode laser as the excitation source. The upconversion spectra showed that the silica shell had little effect on the properties of fluorescence of the LaF3：Yb^3＋ , Er^＋ microcrystals. At the same time, the green luminescence photo of LaF3： Yb3＋, Er3＋/SiO2 in the PBS buffer was obtained, which indicated that the LaF3： Yb^3＋ , Er^＋/SiO2 could be used in biological applications.

Hydrothermal Preparation and Luminescence of LaF_3∶Eu^(3+) Nanoparticle

Pure andEu^3＋-doped LaF3 nanoparticle were prepared by a hydrothermal process at a low temperature and characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and fluorescence spectra. Well-dispersed nanopartiele with an average size of 30 nm and a hexagonal shape were synthesized. The effects of temperature and reaction time on the preparation of nanoparticle were investigated, and the growth mechanism of nanoparticle was briefly discussed. The effects of Eu^3＋-doped concentration, the calcination time and temperature were also investigated. An optimal Eu^3 ＋-doped concentration of 5% is found. Calcination temperature and prolonged of the nanoparticle at high time greatly reduce the fluorescence intensity. The sample calcinated at 600 ℃ for 6 h emits the strongest fluorescence.

Ionic Conductivity of Nano-LaF_3 Bulk Material at Room Temperature

Nanocrystalline powder of LaF3 was synthesized by a method of direct precipitation from water solution. Particle size and shape of LaF3 nanocrystalline powder was analysed with TEM. Particles were mainly spherical with narrow particle size distribution （10 20 nm）. The average particle size analysed with XRD is 16.7 nm. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and a vacuum of 10^-4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material （1 × 10^-5 S·cm^-1 ） at room temperature is significantly increased compared to that of single crystal LaF3 （1 × 10^-6 S·cm^-1）. A special phenomenon was observed firstly time that the ionic conductivity increased gradually with multiple testing in result of relaxation.

LaF_3-LiF-La_2O_3系熔盐密度的研究

根据阿基米德定律,测定了La F3-Li F-La2O3熔盐电解质体系的密度,研究了温度、La F3的含量、La2O3加入量对体系密度的影响。结果表明：密度随着温度的升高呈明显线性降低的趋势,而随着La F3含量的增加而增大。在温度为1050℃时,La F3摩尔含量为20%~35%的该熔盐电解质体系的密度随着La2O3加入量的增加先增加后降低,在La2O3的饱和溶解度（1.5%~3%）附近达到最大值。

沉淀转化法制备多孔片状纳米LaF_3

采用实验中所合成的LaPO4纳米棒为前驱体,通过沉淀的转化作用,大面积地制备了单分散的片状纳米LaF3。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、BET(Brunauer-Emmett-Teller)测试对片状纳米LaF3的形貌、结构、相组成及表面性质进行了分析。片状纳米LaF3底边长约为40 nm,片的厚度约为35 nm,大小均一,具有多孔结构。通过改变反应溶剂,可以控制LaF3粒子的成核、生长和团聚,从而有效地调控多孔片状纳米LaF3的颗粒尺寸和分散性。对多孔片状纳米LaF3的生长机制进行了研究,结果表明LaPO4和LaF3的溶度积常数差导致了片状纳米LaF3的生成;体系中自身存在的Ostwald ripening作用使片状纳米LaF3出现了多孔结构。

LaF_3:Ce^(3+)纳米晶的制备及荧光性质

采用水热法制备了掺杂Ce3+的LaF3的纳米粒子,分别用X射线粉末衍射(XRD)和荧光光谱(PL)对样品的结构和性质进行了表征。XRD的结果表明:LaF3∶Ce3+纳米晶标准卡为JCPDS73-2192,且颗粒平均尺寸为18.7nm,掺入Ce3+杂质后晶格结构没有变化。荧光光谱结果表明:Ce3+呈现其宽带发射,激发峰在245nm处,发射峰在444nm处,随着Ce3+的摩尔浓度比的增加,样品的荧光强度先增大后减小,且Ce3+的掺杂量为4%(摩尔比)时,纳米粒子的荧光强度最强,但更高的掺杂浓度将导致荧光猝灭。