【作者】 李玲；

【导师】 唐睿康； 徐铸德；

【作者基本信息】 浙江大学 ， 物理化学， 2008， 博士

【摘要】 稀土元素具有独特的电子层结构,因而被广泛应用为荧光（发光）材料。稀土发光材料的优点在于其吸收能力强,转换率高,特别是在可见光区域具有很强的发射能力,且物理化学性质稳定,稀土磷酸盐是其中的一个重要的研究体系并已经应用于照明工业。本论文首先综述了稀土磷酸盐荧光材料的性质和常见合成方法,同时也概括性地讨论了纳米荧光材料的主要种类、特点、制备方法以及改进的主要途径。然后,围绕着怎样进一步增强稀土磷酸盐的荧光强度、降低其生产成本、研制荧光可调节的材料,并拓展稀土磷酸盐在生物医学领域的应用范围等几个重要主题来介绍我们的工作。具体来说可分为以下几个部分:（1）选用LnPO₄（LnPO₄=LaPO₄:Ce,Tb）作为研究体系探索了增强纳米稀土磷酸盐的发光强度的新方法。实验结果表明,纳米颗粒通过自组装可以大幅度地提高其荧光效率。与分散存在的纳米颗粒相比,一维线性自组装体的量子荧光产率从组装前的21%上升到了组装后的80%,这一数值已经很接近于体相材料的相应数值。同时材料的发光寿命也得到了相应的延长。一般来讲,由于存在着大量的表面态物质,纳米荧光材料的发光性能往往弱于相应的体相材料,从而限制了纳米荧光体的发展,而此定向自组装方法能够既简便又有效地增强纳米稀土磷酸盐的发光强度。（2）利用发光照明行业中最常用的两种发光材料——绿色的LnPO₄（LnPO₄=LaPO₄:Ce,Tb）和红色的Y₂O₃:Eu,设计合成了新型的发光可调的Y₂O₃:Eu—LnPO₄核—壳结构。通过调节核层和壳层的相对厚度比例,我们可以方便地调节核-壳结构颗粒在受到紫外激发时所发射出复合光的颜色,而且每个单一的核—壳结构颗粒都能够相对均一地发出可调的复合色光,这一特征已通过光致发光激发、荧光光谱、激光共聚焦等多种实验手段来共同确定。我们认为,新型的核—壳结构可以为设计和制造发光可调的荧光体提供一种全新的途径。（3）在核—壳结构的基础上,进一步探索降低稀土磷酸盐荧光材料生产成本的新途径。LnPO₄较高的生产成本主要是由生产原料中氧化铽的价格高昂所致。通过异相成核的均相沉淀法,以价格低廉但无荧光特性的LAPO₄微米颗粒作为内核通过定点结晶诱导形成LnPO₄作为外壳,最终得到了LaPO₄—LnPO₄核—壳结构颗粒。通过高温灼烧,颗粒表面更加光滑,壳层的结晶度得到了提高,此核—壳结构颗粒的发光性能可以得到进一步的提高,其亮度可与市售优质商用绿色荧光粉LnPO₄前驱体发光亮度基本相当。实验中还同时对最佳实验条件进行了初步探讨。这种方法成本低廉,制备简单,可望大大降低商用绿色荧光粉LnPO₄的工业成本,对于发光照明产业具有重要的实用价值。（4）探讨稀土磷酸盐在生物医学领域作为生物探针应用的可行性。羟基磷灰石（HAP,骨和牙的主要无机成份）虽然具有优良的生物兼容性和生物活性,但其本身并不具有发光特性,所以对无机物生物作用的跟踪一直以来是生物矿化研究的难点之一。我们通过对20 nm HAP颗粒进行表面掺杂,用具有良好荧光特性,而又与Ca²⁺性质相似的稀土离子Tb³⁺部分取代了HAP颗粒表面的Ca²⁺。经表面修饰后的Tb-HAP具有了相应的荧光特性,其最大发射峰值在544nm,而且可以被可见光波段（488 nm）激发。而表面掺杂的过程并没有改变HAP原有的形貌和生物活性。这种20 nm的Tb-HAP颗粒能够很容易地进入细胞并被激光共聚焦显微镜清楚地观察到。这说明通过稀土掺杂技术可以实现HAP颗粒的功能化处理,得到了具有良好生物兼容性的无机纳米探针。更多还原

【Abstract】 Rare earth elements are used widely as fluorescent（luminescent） materials because of their characteristic electron structures.The rare earth fluorescent materials have many advantages such as high absorption ability,high transformation ratio,strong emission ability（especially at visible light regions）,and stable physicochemical properties.The rare earth phosphates are one of the most important parts in the rare earth phosphors as they have been applied widely in illumination industry.In this dissertation,we review the properties and the synthetic methods of the rare earth phosphates in the first chapter.The main types,characteristics,preparation,and improvement of nano phosphors are also discussed.Our experimental work consists of four parts:improvement of nano phosphors by self-assembly,design and synthesis of a novel color-tunable particle by core-shell structure,reduction manufacture cost of phosphor by core-shell complex,and development of biological probe of rare earthdoped nanoparticles.The above-mentioned studies can be summarized as followings.（1） LnPO₄（LnPO₄=LaPO₄:Ce,Tb） system is used as a model system to explore a new strategy to improve the luminescence of nano phosphors.The results indicate that the luminescent efficiency of the nano phosphors can be enhanced significantly by 1D ordered aggregation.Compared with the individual nanoparticles,the quantum efficiency of the 1D linear assemblies can increase from 21%to 80%.This value is even close to that of the corresponding bulk ones.It is also found that the fluorescent life is also increased by the oriented assembly.Generally,nano phosphors are featured by the relatively low luminescence,which limits their industrial application.We suggest that the assembly of nano phosphors can be used as an easy but effective pathway to improve the luminescent intensities of these materials.（2） A novel color tunable phosphor with core-shell structure is designed and synthesized using two materials,LnPO₄（LnPO₄=LaPO₄:Ce,Tb ）（green phosphor） and Y₂O₃:Eu（red phosphor）,which are widely used in industry.By adjusting the proportion of core and shell,the fluorescence colors of the phosphor complex can be tuned conveniently.It is important that the individual core-shell structured particle can emit the similar lights even at micron scale.This interesting result is well confirmed by photoluminescence examination,fluorescence spectrum,and confocal laser scanning microscopy.It is suggested that the core-shell structure can provide a new method to design and fabricate color-tunable phosphors. （3） The core-shell structure can also be used to reduce the manufacture cost of the rare earth phosphors.The relative high price of LnPO₄ is attributed to the expensive Tb₃O₄.We use the cheap LaPO₄ micron particle as the core to induce heterogeneous precipitation of LnPO₄ to form the LaPO₄-LnPO₄ core-shell complex. After calcination,the surface of resulted particles become smooth and the crystallinity is also improved.The luminescence of the core-shell particles is examined and the brightness is almost as same as the commercial LnPO₄ precursor.The optimum synthesis condition for this novel structure is also summarized.This method is easy but can greatly reduce the industrial cost in the production of LnPO₄ phosphors.（4） The incorporation of rare earth ions into biominerals is developed as a new approach to the biological probes.As the main inorganic component of biological bone and tooth enamel,hydroxyapatite（HAP） is featured by its excellent biocompatibility and bioactivity.But the particle itself is a non-luminescent material.The in situ studies of the biological function of this important mineral in living organisms is one of the unsolved issues in biomineralization.By partially replacing the calcium ions on the surfaces of 20 nm HAP particles with Tb³⁺,the Tb-HAP nanoparticles can be obtained readily.After such a treatment,the HAP nanoparticles become luminescent and their maximum emission intensity is observed at 544 nm under an excitation of 488 nm visible light.The experiment also confirms that the surface doping do not change the original morphology and biological activity of HAP particles.The observations of biological transmission electron microscopy and the confocal laser scanning microscopy confirm that these Tb-HAP nanoparticles can be internalized by the rabbit mesenchymal stem cells readily and their luminescence in the cells can be detected clearly under a fluorescent microscope.Therefore,the surface modification of rare earth doped nanoparticles can be developed as a functional treatment to design the new biological probes.更多还原