【作者】 刘宁；

【导师】 秦伟平；

【作者基本信息】 吉林大学 ， 物理电子学， 2011， 博士

【摘要】 随着纳米技术的发展,稀土掺杂纳米发光材料在荧光体、三维显示、光学器件、生物标记以及医学治疗等诸多领域有着巨大的应用前景。在众多的稀土掺杂纳米发光材料中,氟化物由于其声子能量低的特点,使得掺杂在其中的稀土离子具有更高的荧光量子效率,因此成为人们关注的热点。同时,以硼酸盐为基质的稀土掺杂纳米发光材料亦具有优异的化学稳定性、热稳定性、无毒性以及色纯度,是制备等离子显示器红粉的理想材料。众所周知,稀土掺杂纳米发光材料的形貌和尺寸与其发光性质有着密切的联系。因此,在过去几十年里,人们利用各种办法对其形貌尺寸进行控制,以获得优异的光学性质。其中,利用表面修饰来改善纳米粒子形貌并减少其表面猝灭中心,进而提高其发光效率是非常有效的方法。最近两年,人们开始利用贵金属来修饰纳米发光材料,通过贵金属的表面等离子共振效应来提高纳米发光材料的发光效率,并取得了良好的效果,成为纳米发光材料制备领域中又一个研究的焦点。本文首先综述了稀土掺杂氟化物和硼酸盐纳米材料的研究现状,概括总结了近年来稀土掺杂氟化物和硼酸盐纳米材料的制备和性质研究中所取得的成果,并针对目前制备纳米材料中存在的形貌不均一、分散性不好、生物兼容性差以及发光效率不高等问题,对今后的研究工作进行了制定和展望。在此基础上,我们利用不同表面修饰的方法,制备了多种具有不同形貌及发光性质的稀土掺杂纳米晶。并通过X射线衍射(XRD)、高分辨场发射扫描电镜(FE-SEM)、透射电镜(TEM)、红外光谱测试(FT-IR)、吸收谱(Abs)、光致发光光谱(PL)以及发光动力学测试等手段分析了各种可控合成条件及性质研究,获得了一定创新性研究成果,主要的研究内容如下：(1)我们采用油酸作为表面修饰剂,水热法首次成功合成Ba-B-O:Eu3+纳米棒、纳米线以及花瓣状自组装体。通过调节油酸的修饰量、反应时间以及pH值,详细的讨论了可控合成各个形貌纳米晶的最佳条件以及生长机理。确定1wt%油酸修饰的Ba-B-O:Eu3+纳米棒、纳米线以及花瓣状自组装体最佳的pH值分别为7.5、9和6。同时,我们发现这种Ba-B-O:Eu3+纳米材料具有很高的色纯度,不同形貌Ba-B-O:Eu3+样品都具有很强的5D0→7F2电偶极跃迁,发红光为主,它们的R/O值分别为2.01、1.85和2.29。三种形貌的纳米晶中花瓣状自组装体的I(5D0→7F2)/I(5D0→7F1)的荧光强度比是最大的,说明其色纯度是最好的。(2)我们采用油酸作为表面修饰剂,原位修饰一步可控合成BaF2：Eu3+纳米立方体。得到的固体在烘箱中80℃烘干6h并将其研磨。通过调节油酸的修饰量,很好的控制了样品的形貌及尺寸,并发现适量的油酸修饰可以改善纳米粒子表面的缺陷进而提高样品的发光强度。最终确定油酸的修饰量为1wt%时BaF2:Eu3+纳米立方体的尺寸最小,发光性质最好。(3)我们以柠檬酸钠为表面修饰剂,水热法制备了NaYF4:Yb3+,Tm3+(Er3+)上转换荧光纳米晶。XRD和TEM分析表明,所得上转换纳米晶为纯六角相,尺寸在150nm左右,分散性好。通过调节反应时间和柠檬酸钠的量来控制纳米晶的相、尺寸及形貌。最终确定最佳的反应条件为添加4 mmol柠檬酸钠反应12h。并讨论了Tm3+(Er3+)的掺杂浓度对上转换发射强度的影响,确定Tm3+离子最佳掺杂浓度为0.5%,Er3+离子最佳掺杂浓度为1.5%。(4)我们利用柠檬酸钠作为还原剂和连接剂在99℃条件下,液相反应制备了Au@NaYF4:Yb,Tm(Er)复合纳米晶并发现其具有优异的上转换发光效率和低的泵浦阈值。首先通过XRD、电镜以及吸收谱都很好的证明了我们合成出Au纳米粒子修饰的NaYF4:Yb.Tm(Er)上转换复合纳米晶,复合纳米晶直径在160nm左右,Au纳米粒子的直径大约为10nm左右。在980nm激发下,与NaYF4:Yb,Tm纳米晶相比,Au@NaYF4:Yb.Tm复合纳米晶从红外到紫外的发射强度都有明显的增加。尤其5光子过程的345nm发射强度增加了109倍,说明我们合成的复合纳米晶是优异的上转换发光材料,其中紫外上转换发射尤其显著。与NaYF4:Yb,Er纳米晶相比,Au@NaYF4:Yb,Er复合纳米晶从红外到紫外的发射强度都有明显的增加。最大的增强因子可达到几百倍。此外,Au@NaYF4:Yb,Tm和Au@NaYF4:Yb,Er复合纳米晶中Yb3+、Tm3+和Er3+离子寿命的增长为我们用表面等离子场增强效应来解释上转换发光增强提供了新的有力证据。这种复合上转换纳米晶优异的发光效率将在光学、医学、治疗学和生物医学等方面都具有巨大的应用潜力。此外,我们还初步研究了Au@SiO2@NaYF4:Yb,Tm纳米晶的上转换发射,发现加入0.3 ml正硅酸乙酯的上转换纳米晶用Au纳米粒子修饰后,其紫外上转换发射是最强的。更多还原

【Abstract】 With the development of nanotechnology, rare-earth doped luminescent nanomaterials have been widely used in many applications, such as phosphors, three-dimensional displays, optical devices, biolabeling and therapeutics. Among various rare-earth doped luminescent nanomaterials. fluorides have received great attention due to their lower phonon energy, which leads to smaller relaxation rates and higher fluorescence quantum yields. Meanwhile, rare-earth doped borates are also ideal nanomaterials owning to their high chemical stability, thermal stability, non-toxic, and excellent color purity. As is well-known, the sizes and morphologies of rare-earth doped luminescent nanomaterials have much to do with their luminescent properties. In the past decades, much efforts have been made to control the size and morphology to obtain excellent luminescent properties. And the surface chemical modification is an efficient method to obtain high luminescence efficiency by improving the appearances and reducing the surface quenching centers of nanomaterials. Very recently, the incorporation of noble metal NCs with nanomaterials has received great attention because of the plasmon-enhanced luminescence properties.In this paper, the present status of lanthanide-doped fluoride and borate nanomaterials are reviewed for their preparation methods and property investigation. Due to problems of nonuniform morphologies, poor dispersion, poor biocompatibility and low luminescence efficiency, we prospect the research work in the near future. Here. lanthanide-doped fluoride and borate nanomaterials with various morphologies have been synthesized by different surface modifications. The preparation conditions and luminescent properties have been characterized by XRD, FE-SEM. TEM. FT-IR. Abs and PL analyses. The main contents are as follows:(1) Uniform and morphology controllable Ba-B-O:Eu3+ nanorods. nanowires. and flowerlike assemblies have been successfully synthesized via a hydrothermal method for the first time. Many factors, including the amount of OA. reaction time, and pH values, influenced the formation and growth of the Eu3+-doped Ba-B-O NCs. Based on the experimental results, we conclude that OA is a crucial factor acting as a capping reagent which has a effect on the growth of the NCs. By adjusting pH. we have controlled the absorptions of OA on the surfaces of NCs and modulated the growth rates along different crystallographic directions. The anisotropic growth and the process of Ostwald ripening determined the morphologies of the NCs. Furthermore, the I(5D0→7F2)/I(5D0→7F1) is about 2.01.1.89. and 2.29, respectively. The luminescent investigation indicates that the Ba-B-O:Eu3+ nanocrystals. especially the flower-like assemblies, can emit intense fluorescence with excellent color purity, which will promise the efficient photoluminescence in applications of displays and nanodevices.(2) Europium (Eu3+) doped BaF2 nanocubes have been synthesized successfully through one-step precipitation reaction, using OA as a capping agent. XRD analysis indicated that the products were cubic BaF2, SEM analysis indicated that the products exhibited nanocubic morphology with a side length of～150 nm. Furthermore, the luminescent investigation indicates that the emission intensity of the BaF2:Eu3+ nanocubes have been enhanced greatly after modified with proper amount of OA. which is promising for new optical technologies in the future.(3) NaYF4:Yb3+,Tm3+(Er3+) nanocrystals (NCs) have been synthesized by a hydrothermal method using trisodium citrate as a surfactant. XRD and TEM indicate that we have obtained well-dispersedβ-NaYF4: Yb3+,Tm3+(Er3+) NCs with the diameter of about 150 nm. Many factors, including the amount of trisodium citrate and reaction time influenced the formation and growth of theβ-NaYF4: Yb3+,Tm3+(Er3+) NCs. The optimal reaction condition is 4 mmol of trisodium citrate, 12 h. The influence of the concentration of dopants inβ-NaYF4 NCs on the upconversion emission intensities has been discussed, and 0.5% Tm3+ and 1.5% Er3+ and were chosen as the optimal condition.(4) we synthesized Au@β-NaYF4:Yb,Tm(Er) hybrid nanostructures and achieved enhanced multicolour UC emissions and decreased pumping threshold. Under low NIR pumping power of～50 mW. the enhancement for 5-photon UC emissions located at 291 and 345 nm have been enhanced most suggests that ANNCs are excellent UC nanomaterials especially for high-order photon UC. The prolonged lifetimes of Yb3+,Tm3+ and Er3+excited states suggest a new evidence that the enhanced UC emissions are induced by the plasmon field enhancement of attached Au NCs. This work provides a novel strategy to study how Au NCs improved efficiency for UC emissions and indicates the Au@β-NaYF4:Yb,Tm(Er) hybrid nanostructures exhibit great potential in a broad range of photonic, medical, therapeutic, and biological applications. In addition, we initially investigated the UC emissions of Au@SiO2@NaYF4:Yb,Tm NCs, and found that the UV UC emissions were enhanced most when 0.3 ml tetraethyl orthosilicate was added.更多还原