【作者】 赵军伟；

【导师】 孔祥贵； 张宏；

【作者基本信息】 中国科学院研究生院（长春光学精密机械与物理研究所） ， 凝聚态物理， 2010， 博士

【摘要】 近年来,随着纳米科学与技术的发展,稀土掺杂的荧光纳米粒子以其独特的发光特性在光学、电子学、信息学和生物学等领域表现出潜在的应用价值。自上个世纪50年代人们发现上转换这一现象以来,上转换发光材料研究一直是材料科学领域的研究热点之一。稀土掺杂的上转换发光纳米材料在生物标记、荧光在体成像、激光和光纤通信等领域有着广泛的应用。上转换发光材料与其他荧光材料相比,具有发射谱线窄,发光性质稳定,无光漂白现象,荧光信噪比高等优点,因此在生物医学领域有重要的潜在应用价值。最近,研究人员已经将上转换发光材料成功应用于细胞成像、免疫分析和DNA检测等。为了实现其在生物医学领域的广泛应用,人们希望制备出发光效率更高,尺寸更小,分散性更好的上转换发光材料。本论文主要围绕稀土掺杂的上转换发光纳米晶的合成与生物应用展开一系列研究工作,并得到了一些创新性结果,主要内容如下:1.采用柠檬酸钠作为螯合剂结合水热反应过程合成出不同尺寸与形貌的立方与六角结构的NaYF₄:Yb³⁺, Er³⁺纳米晶。对Fˉ离子的量、柠檬酸的量、水热反应温度和水热时间等参数对纳米晶的形貌、尺寸、结构以及上转换发光性质的影响进行了分析,并对NaYF₄:Yb³⁺, Er³⁺纳米晶的上转换发光性质进行了研究。研究发现,过量的Fˉ离子能够有效地降低样品的结晶温度,在相对较低的水热温度下,就能获得结晶性较好的纳米晶;通过调节柠檬酸钠的量能够有效控制样品的尺寸、形貌和晶格结构,柠檬酸分子与稀土阳离子强的螯合能力能有效地控制NaYF₄:Yb³⁺, Er³⁺纳米晶的生长速度,相变时间,其与六角相NaYF₄晶核的{0001}晶面的选择性吸附作用,使晶体在生长过程中,在六个对称的方向:±[101₀],±[011₀]和±[11₀0]的生长速率相对较快,最终形成了六角形的NaYF₄亚微米片。在980 nm激光激发下,观察到了立方相纳米粒子和六角相亚微米片的上转换发光,其绿光与红光上转换发光过程均属于双光子发光过程。相对与绿光发射,样品的红光上转换发射相对较强。实验证明,样品表面的柠檬酸分子上的高能有机振动基团引起的多声子驰豫过程和Er³⁺离子之间的交叉驰豫相互作用是样品红色上转换发射较强的主要原因。2.以聚乙烯亚胺（PEI）作为表面活性剂,采用水热合成法,首次合成出了多孔结构的六角相NaYF₄:Yb³⁺, Er³⁺空心纳米球。氮气吸附/脱附曲线证明了样品的多孔特性。通过对PEI浓度、水热反应温度和水热反应时间等参数对样品的形貌、尺寸和结构等的影响,讨论了六角相NaYF₄:Yb³⁺, Er³⁺空心纳米球的生长机理和上转换发光性质。实验结果发现,适当的PEI浓度和水热反应条件是六角相NaYF₄:Yb³⁺, Er³⁺空心纳米球形成的关键因素。对不同水热时间制备的样品进行表征分析发现,样品经历了从立方相NaYF₄:Yb³⁺, Er³⁺纳米晶到六角相NaYF₄:Yb³⁺, Er³⁺自组装纳米线,再到六角相NaYF₄:Yb³⁺, Er³⁺空心纳米球的相变和形貌演变过程,PEI诱导的Ostwald熟化过程是样品形成的主要机理。在980 nm光激发下,粒子显示出较强的上转换发光。由于掺杂离子浓度较高,相邻的Er³⁺离子之间有较强的交叉驰豫,加上样品表面高能的有机振动基团引起的多声子驰豫过程的影响,样品显示出红色上转换发射相对较强的特点。3.以不同分子量的PEI聚合物为表面活性剂,水/醇溶液为溶剂,利用水热/热溶剂法合成出尺寸可控的水溶性的NaYF₄:Yb³⁺, Er³⁺纳米粒子。实验发现,在相同的水热条件下,用高分子量的聚合物（HPEI）合成的样品比用低分子量的聚合物（LPEI）合成的样品的尺寸要小。值得注意的是,在相同功率的980 nm激光激发下,小尺寸的样品的上转换发光比同条件下大尺寸的样品的上转换发光强。结合晶体生长理论,我们认为,结晶性的差别是样品上转换发光强度不同的原因,高分子量的聚合物能够降低粒子的生长速率,有利于小尺寸、结晶性好的粒子生成。细胞毒性实验和荧光免疫分析实验证明所制备的样品具有很好的生物相容性。更多还原

【Abstract】 In the recent years, with the development of nanoscience and nanotechnology, fluorescent nanocrystals have attracted much attention due to their unique optical properties. There has been considerable research on upconverting phosphors since initial interest in the late 1950s. Rare-earth-doped upconverting materials have wide potential applications in many fields, including phosphors, display monitor, lasers and amplify for fiber-optic communications. Compared with other fluorescent materials, such as organic dye, the upconverting materials have several advantages in optical properties of narrow band emissions, high photostability, low background light, nonfading, and no significant influence of environment under near infrared radiation, so they can be used as biological labels materials. Rare-earth-doped upconverting nanocrystals have been reported to be used for the cell imaging, detection of nucleic acid and immunoassay. The nanocrystals should be highly efficient emission, size-controlled and monodisperse for biological applications. So developing synthetic technologies and researching the quenching mechanisms of luminescence are very important to both fundamental research and practical application. Surrounding the rare-earth doped fluoride nanocrystals, this dissertation presents a systematic research about preparation, characterization and biomedical application of nanoparticles. Now, some original results are obtained from our experiments, the main results are outlined as followings:1. Develop a simple hydrothermal method for synthesis of different sizes and morphology of cubic and hexagonal structure of NaYF₄: Yb³⁺, Er³⁺ nanocrystals using sodium citrate as a chelating agent. The effects of the amount of Fˉions and citrate as well as the hydrothermal temperature and hydrothermal time on the nano-crystalline morphology, size, structure, and up-conversion luminescence properties were analyzed in detail. The upconversion luminescence properties of the NaYF₄: Yb³⁺, Er³⁺ nanocrystals were also studied. It is found that excessive levels of Fˉion can effectively reduce the crystallization temperature of the sample, at a relatively low hydrothermal temperature, you can get nanocrystals with better crystallization; the size, morphology and crystal structure of the samples can be effectively controlled by adjusting the amount of sodium citrate; the strong chelating ability between rare earth cation and citric acid molecules can be able to effectively control the growth rate, phase-change time of NaYF₄: Yb³⁺, Er³⁺ nanocrystals; due to the selective coordination role of citrate with the {0001} crystal plane of the hexagonal NaYF₄ nuclei, during the crystal growth process, the growth rate of crystal relatively fast in the six symmetric directions:±[101₀],±[011₀] and±[11₀0] and the hexagonal NaYF₄ sub-micron plates eventually formed. In the 980 nm laser excitation, the upconversion luminescence of cubic phase nanoparticles and hexagonal sub-micron plates is observed and its green and red upconversion luminescence process belongs to the two-photon process. Relative to green emission, the red up-conversion emission of samples is relatively strong. Experiments show that the multi-phonon relaxation induced by the high energy vibration groups of the citrate adsorbed on the sample surface and the cross-relaxation interaction between Er³⁺ ions in the samples are the main reasons for a strong red up-conversion emission.2. The hexagonal-phase NaYF₄:Yb³⁺, Er³⁺ hollow nanospheres have been successfully prepared for the first time via a hydrothermal route with the aid of polyethylenimine （PEI） as a surfactant. The nitrogen adsorption/desorption isotherms demonstrated the porous nature of the NaYF₄ hollow nanospheres. Through discussing the effects of the PEI concentration, hydrothermal temperature and hydrothermal time on the morphology, size and structure of samples, the growth mechanism of hollow nanospheres was proposed. It was found that the appropriate PEI concentration and hydrothermal reaction conditions are the key factors to form hexagonal NaYF₄: Yb³⁺, Er³⁺ hollow nanospheres. By analysing the character of the samples prepared in different hydrothermal time, it was revealed that the samples suffered morphology evolution and the phase transition from the cubic phase NaYF₄: Yb³⁺, Er³⁺ nanocrystals to the hexagonal phase NaYF₄: Yb³⁺, Er³⁺ self-assembled nanowires, to the hexagonal phase NaYF₄: Yb³⁺, Er³⁺ hollow nanospheres; PEI-induced Ostwald ripening process is the main mechanism of the formation of the sample. In the 980 nm light excitation, the particles showed strong up-conversion luminescence emission. As the strong cross-relaxation process exist among neighboring Er³⁺ ions due to the relatively higher doping concentration and the multi-phonon relaxation induced by the organic high-energy vibration of the sample surface, the samples showed relatively strong red upconversion emission.3. The effect of branched polyethylenimine with different chain lengths, used as the surfactants in the preparation of water-soluble NaYF₄:Yb³⁺, Er³⁺ nanocrystals following solvothermal approach, on the infrared （IR） to visible photon upconversion has been studied. It was found that under the same hydrothermal conditions, the size of the sample synthesized with high molecular weight polymer （HPEI） is smaller than those with low molecular weight polymer （LPEI）. Interestingly, in the same power 980 nm laser excitation, the upconversion luminescence intensity of the sample with small size is stronger than that of the samples with large size. Combining the crystal growth theory, we believe that the difference in the sample crystallinity is the main reason for the different up-conversion luminescence intensity. High molecular weight polymer can reduce the particle growth rate and favor the formation of nanoparticles with small size and good crystallinity. Cytotoxicity test and fluorescent immunoassay results show the obtained nanoparticles have good biocompatibility.更多还原