【作者】 刘娟；

【导师】 张治国；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2010， 硕士

【摘要】 羟基磷灰石(HA)的成分和结构与人体中骨骼和牙齿的无机成分很相近,所以具有良好的生物活性以及生物相容性,因而成为骨替代材料的研究热点。稀土离子上转换发光材料是一种很有发展前景的新型荧光探针,而且它具有很多吸引人的特性:激发光在红外区域,组织穿透深度大,能实现零背景探测等,因此备受人们关注。如果在羟基磷灰石内掺杂稀土离子,不仅羟基磷灰石可以应用于生物医学领域,而且可以通过上转换荧光标记法很方便的对其骨修复情况进行探测。基于此本论文首次合成了稀土掺杂羟基磷灰石双功能材料,并对F-离子以及Li+离子增强上转换发光特性进行了研究。采用溶胶凝胶法成功合成了均匀性比较好的HA:Er3+,Yb3+材料、在974nm二极管激光器(LD)的激发下,得到发射峰在522nm和551nm的绿光发射(4S3/2/2H11/2→4I15/2)和峰值在662nm的红光发射(4F9/2→4I15/2)。绿光布居为纯双光子过程,红光的布居为具有一定饱和程度的双光子过程。研究表明材料中掺杂高浓度的敏化离子Yb3+后,Er3+离子和Yb3+离子间存在着比较强的耦合作用,所以反向能量传递过程发生概率很大,从而造成4I13/2能级的饱和。结合速率方程的求解计算,本文从理论上论证了Er3+离子的上转换机制。在HA:Er3+,Yb3+材料中,采用F-离子替代羟基的办法可以增强上转换发光。F-离子替代羟基后,发现羟基的振动吸收峰消失,这意味着氟羟基磷灰石(FA)材料声子能量相对HA材料大大降低。基质HA材料声子能量的降低可显著增长Er3+离子各激发态能级寿命,这将非常有利于上转换发光的进行。因为红绿色上转换荧光光强和Er3+离子各能级寿命成正比或平方关系,所以寿命越大,上转换荧光强度越强。另外本文对于速率方程的求解也从理论上验证了本论文之前的分析。在FA:Er3+,Yb3+体系中引入Li+离子后,Er3+离子的绿色以及红色上转换荧光强度也明显增强。Li+离子的加入没有引起FA材料晶相的改变,但是会使其晶胞参数发生变化。Li+离子对FA材料的晶胞参数的影响会改变Er3+离子周围的晶体场环境,从而导致Er3+离子的各激发态能级的寿命大大增长,这极大的促进了Er3+离子的上转换发光。随着Li+离子掺杂浓度的变大,Er3+离子各激发态能级寿命也随之变长,Er3+离子的绿色以及红色上转换发光也越强。另外,Li+离子的加入使Er3+离子红色上转换荧光的布居由单光子和双光子过程的混合,向纯单光子过程逐渐转化,这种变化源于Li+掺杂导致Er3+离子各激发态能级寿命增长,4I11/2能级向下无辐射弛豫的概率降低,从而切断红光的双光子布居过程。更多还原

【Abstract】 Hydroxyapatite （HA） has attracted widespread interest for bone substitute materials due to its excellent bioactivity and biocompatibility coming from the analogy to the mineral components and structure of natural bones and teeth. Rare earth doped upconversion （UP） material is a new kind of promising fluorescent label materials, and is especially attractive due to its desirable properties, such as easily excited by near-infrared （NIR） region, high tissues Penetration, achieving zero background detect. If rare earth ions can be doped into hydroxyapatite materials, not only hydroxyapatite can be applied in the biomedical field, but also we can conveniently detect the bone repair situation with the help of upconversion fluorescent label. Thus, in the thesis, samples of HA: E1³⁺, yb³⁺ were synthesized by the sol-gel method at the first time. Furthermore, the upconversion properties of HA: E1³⁺, yb³⁺codoped with F- and Li⁺ ions is studied under 980nm diode laser excitation.Well-proportioned samples of HA: E1³⁺, yb³⁺ were successfully synthesized by the sol-gel method at the first time and excited by 974nm diode lasers, Two distinct UC emission bands centered around 522 nm, 551 nm and 660 nm, assigned to (⁴S_3/2/²H_11/2)→⁴I_15/2 and 4F_9/2→⁴I_15/2 transitions were obtained. The green UC emissions state level are completely populated by two-photon process, while the population of the red UC emission arise from a combining effect of the one-photon and two-photon process. At high yb³⁺ ions concentrations, the strong coupling between E1³⁺ ions and yb³⁺ ions causes a large possibility of energy back transfer process, which will leads to the saturation of the 4I13/2 level. The upconversion mechanism was discussed and substantiated by steady-state rate equations theory.In HA:E1³⁺,yb³⁺ series,substitution of （OH）- by F- ions can results in the dramatically enhancement of upconversion intensity. After the replacement of （OH）- by F- ions, the vibration absorption peaks of hydroxyl disappear, which means the greatly reduction of the phonon energy of HA materials. As we know, the significantly decrease of the phonon energy in matrix materials will result in the distinct lengthening of the lifetimes of E1³⁺ ions’metastable states which greatly benefited E1³⁺ ions’upconversion radiations. As the green and red upconversion intensity is proportional or square to the lifetime of E1³⁺ ions’excited states, therefore, the greater of the level’s lifetime, the stronger of the fluorescence intensity. In addition, theoretical investigations based on the steady-state rate equations demonstrate the correctness of the previous analysis. In FA:Er³⁺,Yb³⁺ series, it was observed that further doping with Li+ ions could obviously enhance Er³⁺ ions’green and red UC radiations. The changes of cell parameters of the same hexahedron HA lattice induced by Li+ ions doping were discovered, which indicate the change of Er³⁺ ions’local environment. Tailoring Er³⁺ ions’local environment will leads to the increment of the lifetimes of Er³⁺ ions’excited states, which can significantly favor the UC output. With more Li ions introduced, the lifetime of the Er ions’excited state become longer, so the green and red UC radiation become stronger. Additionally,the multiphoton processes of Er³⁺ ions’red upconversion radiations gradually changed from a combination of the one-photon and two-photon processes to a completely one-photon process after Li+ doping. These changes originated from that, the Li+ ions will leads to the dramatically increment of the Er³⁺ ions’excite state lifetime, which will greatly reduce the probability of non-radiative relaxation of the 4I11/2 level, so the two- phonon process for red UC emission is cut off.更多还原