【作者】 陈冠英；

【导师】 张治国；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2009， 博士

【摘要】 连续光频率上转换在医学探测和编码、人体内部疾病光动力治疗、开发连续短波长激光器、立体成像、显示等方面都有美好的应用前景。然而,目前在上转换荧光发射方面还存在着诸如光光转换效率不高、光谱人工设计严重不足、紫外上转换发射很少被设计等问题,从而影响了上转换在医学和光子学方面的应用。本文以稀土氧化物和氟化物为研究对象,在上转换荧光光谱设计、荧光增强方法、紫外上转换荧光的获得,以及在医学中应用等方面开展了系统的研究。开展了氧化物单色和白光上转换发光的设计研究。通过调节Yb3+离子掺杂浓度,在980 nm激光激发下,获得了单红和单绿上转换荧光;通过激发光和荧光功率关系分析、荧光光谱分析,和速率方程理论分析,阐明了单色上转换发射机制;通过定义“抑制比”概念,提出了对单色上转换发射的评价标准;通过Er3+、Tm3+和Yb3+的合理配比,获得了在宽功率范围内的980 nm激光激发下纳米粒子的白光上转换发射;通过实验和理论分析,阐明了白光上转换发射机制。对氧化物上转换发光增强方法进行了研究。通过在稀土上转换纳米材料中,进一步引入Li+离子掺杂,获得了二个数量级增强的上转换发光。通过大量的实验和理论分析,提出了其增强机制:Li+离子的引入,使其在晶格中占位,从而修饰了晶格场,使稀土离子相关能级的寿命增加,从而实现了上转换发光增强。实验结果表明这种增强方法不仅适用于不同的稀土离子的上转换发光增强,而且适用于不同基质中稀土离子的上转换发光增强。证明了这种增强方法是普适的。对紫外上转换发光进行了研究。在Yb3+/Tm3+掺杂的氧化物中,在980 nm激光激发下观察到300 nm附近的紫外上转换发光,激发光和荧光功率关系表明其紫外辐射为五光子和六光子过程;提出了其上转换发光机制。提出并证实了Yb3+/Er3+掺杂的氧化物中蓝色和紫外上转换荧光的发光机制。观察到980 nm激光激发下240-490 nm波段的Yb3+/Ho3+掺杂的氟化物的上转换发射,提出并证实了其发光机制并解释了观察到的饱和现象。采用Ho3+离子敏化Gd3+离子设计获得NaGdF4:Yb3+/Ho3+纳米晶中Gd3+离子紫外上转换发光,并解释了其发光机制。观察到在氟化物中掺杂Er3+以及Er3+敏化Gd3+离子的近真空紫外上转换发光和超级饱和效应,提出并解释其发光机制。对医用纳米粒子制备、上转换发光和医学应用进行了研究。采用湿化学方法,探索出不同尺寸氟化物纳米粒子及其包壳的制备工艺,制备出可控尺寸和形貌的氟化物纳米材料和核壳结构的氟化物纳米材料。通过Ce3+、Yb3+离子掺杂浓度的调节,获得了氟化物纳米粒子在红外光激发下的红光上转换辐射,并阐明了其光谱调节机制。设计了核壳结构氟化物纳米粒子,获得了增强的上转换发光,提出并解释了上转换增强机制。利用制备的氟化物纳米材料,证明了在组织液成像中上转换发光成像在空间分辨率方面大大优于传统荧光标记的荧光成像。通过动物实验,证明了我们制备的氟化物纳米粒子能够做到无背景、多色、活体成像。更多还原

【Abstract】 Contiuous-wave-induced photon upconversion has prosmising applications in many fields, such as biomedical detection and encoding, photodynamic therapy of human diseases, continous-wave short-wavelength lasers, volumetric color imaging and displays, etc. Unfortunately, upconversion materials currently have several serious spectrocscopic problems, including low upconversion efficiency, unsatisfied emission spectra without design, and scarce realization of ultraviolet upconversion emissions, etc. These problems seriously limit their applications in photonics and biomedicine. Based on rare-earth-ion-doped oxide and fluoride materials, we have performed systematic investigations on upconversion emission spectral design, upconversion emission enhancement, ultraviolet upconversion emission realization, as well as practical applications of designed nanocrystals in biomedicine.Green, red and white color upconversion emissions were designed in rare-earth-ion-doped oxide nanocrystals. Single green and red colors were obtained in oxide nanocrystals through controlling the doped Yb3+ ion concentrations under the excitation of 980 nm diode laser. Their corresponding mechanisms were prosposed and verified based on systematic analyses of pump power dependence, fluorescence spectroscopy, and theoretical calculations. The parameter of“suppression ratio”was introduced, which can quantitatively define the monochromonity of upconversion biolabels. White color output was achieved in oxide nanocrystals by controlling appropriate ion concentrations of Er3+、Tm3+ and Yb3+. The mechanism for white upconversion was proposed based on experimental observations and theortical analysis.A general strategy for upconversion emission enhancement in oxide nanocrystals is proposed. Upconversion emissions in rare-earth-ion-doped oxide nanocrystal were increased by two orders of magnitude via introducing monovalent Li+ ions in the host lattice. Mechanisms for the enhancement were proposed and verified based on substantial experimental observations and theoretical analyses. Introducing Li+ ions in the host lattice can modify rare-earth ions’local crystal filed, lengthen the lifetime of energy levels involved, and finally lead to the significant increase in upconversion radiations. The proposed strategy not only can apply to nanocrystals of different oxide host lattices, but also can apply to diverse codoping and tridoping rare-earth ions. Hence, the proposed strategy has general validity in rare-earth-ion-doped oxide nanocrystals.Ultraviolet upconversion emissions were investigated. Ultraviolet upconversion emissions around 300 nm were observed in Yb3+/Tm3+-codoped oxide nanocrystals under diode laser excitation of 980 nm. Pump power dependence investigations indicate that they arise from five- and six-photon processes, which can be well explained by using the proposed upconversion mechanisms. Upconversion mechanisms for blue and ultraviolet emissions in Yb3+/Er3+ -codoped oxide nanocrystals were proposed and demonstrated. Ultraviolet upconversion emissions of 240-490 nm were observed in Yb3+/Ho3+-codoped fluoride materials. Their generation mechanisms and saturation effects were explained. Ho3+-sensitized ultraviolet upconversion of Gd3+ ions were designed in NaGdF4:Yb3+/Ho3+ nanocrystals. Near vaccum ultraviolet upconversion emission of Er3+ and Er3+-sensitized Gd3+ ions as well as their“super saturation effect”were experimentally observed in fluoride materials, which can be well explained by the proposed upconversion mechanisms.Synthesis, upconversion emission design, and biomedical applications of fluoride nanocrystals were performed. Size- and morphology-controllable fluoride nanocrystals and core/shell fluoride nanocrystals were prepared by wet chemical methods. Single red upconversion in fluoride nanocrystals were realized in nanocrystals NaYF4:Yb3+/Ho3+/Ce3+ and NaYF4:Yb3+/Er3+ by adjusting Ce3+ and Yb3+ contents, respectively. A novel core/shell structure was developed in fluoride nanocrystals, which can greatly increase the intensity of upconversion emission. The prepared fluoride nanocrystals were applied to optical tomorgraph in tissue, and it was found that upconversion fluoride nanocrystals can produce higher space resolution images than conventional fluorescent labels. Through animal experimentals, it is demonstrated that our designed fluoride nanocrystals can be successfully applied to autofluorescence-free in vivo multicolor imaging.更多还原