发光纳米晶NaYF_4：Ln（Yb，Er，Tm，Eu）的合成和聚丙烯酸（PAA）修饰研究
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摘要
稀土纳米材料,综合了稀土材料的光学特性和纳米材料的小尺寸效应,在生物标记领域有广阔的应用前景。六方晶型NaYF_4为基质,稀土共掺杂的荧光材料是发光效率最高的荧光材料之一。但NaYF_4本身水溶性不高,而合成过程中使用的表面活性剂等物质更使其难溶于极性溶剂,阻碍了其生物应用,所以对NaYF_4进行表面修饰十分重要。在本文中,首先低温油相合成了NaYF_4基质材料并进行稀土掺杂,然后选用聚丙烯酸(PAA)对其进行表面修饰,制备NaYF_4:Ln/PAA复合粒子。此外,为消除有机配体带来的荧光猝灭,合成了综合性能更佳的NaYF_4:Ln/NaYF_4/PAA纳米复合材料。本课题按照如下几个方面展开:
首先,采用反胶束法在常温下制备了几乎纯六方晶型的基质材料NaYF_4纳米粒子,在此基础上掺杂稀土离子,制备了上转换发光的NaYF_4:Yb,Er(Tm)和下转换发光的NaYF_4:Eu。对稀土发光材料用X射线衍射(X-ray diffraction analysis,XRD),透射电子显微镜(transmissionelectron microscopy,TEM),傅里叶变换红外光谱(fourier transformspectroscopy,FTIR)和荧光光度计(fluorescence spectroscopy)进行表征。结果表明:NaYF_4基质材料是粒径在8 nm左右六方晶形纳米晶,稀土掺杂后荧光性能良好,但是纳米粒子外部被表面活性剂油酸钠所包裹,有进一步表面修饰的必要。
其次,采用三种不同的方法进行表面修饰研究:①用配位交换法对NaYF_4:Ln进行表面修饰,该方法反应条件温和,过程简单,合成的NaYF_4:Ln/PAA复合粒子直径小,平均直径10 nm,但复合粒子的分散性欠佳,而且大幅降低材料的荧光性能;②用微乳液法对NaYF_4:Ln进行表面修饰,合成的NaYF_4:Ln/PAA复合粒子的分散性较好,平均直径15 nm,对上转换发光性能影响不大,但是降低下转换发光性能,反应过程复杂,能耗大;③用原位聚合法对NaYF_4:Ln进行表面修饰,形成了分散性良好的NaYF_4:Ln/PAA复合纳米微球,荧光性能佳,但是纳米粒子直径较大,平均100 nm左右,最小也有50 nm。综合来看,经过原位聚合法的到的复合粒子除了粒径较大外,综合性能最佳,最接近生物应用的要求。
最后,为了减少聚合物带来的荧光猝灭,在表面修饰前,先用反胶束法合成NaYF_4:Ln/NaYF_4核壳粒子,NaYF_4壳消除了内部发光核NaYF_4:Ln的表面缺陷,使晶型更加完整。然后通过配位交换法来制备NaYF_4:Ln/NaYF_4/PAA纳米复合材料。荧光测试结果表明,NaYF_4:Ln/NaYF_4/PAA的荧光强度比NaYF_4:Ln/PAA明显增强。此外,重点探究了稀土掺杂量对复合材料荧光性能的影响。在上转换材料NaYF_4:Yb,Er(Tm)/NaYF_4/PAA中,改变敏化剂Yb~(3+)和激活剂Er~(3+)(Tm~(3+))的配合掺杂比,能够改变发光的颜色。在下转换材料中,Eu~(3+)直接被激发,通过改变Eu~(3+)浓度,找到荧光强度最强的掺杂量。
Rare-earth nano-materials can be applied in biological labeling field due to their distinguished optical property from rare-earth elements and small size effect from their nano-scale. As is known to all, lanthanide(Ln) co-doped hexagonal sodium yttrium fluoride (NaYF_4:Ln) is one of the most efficient fluorescent materials. However, NaYF_4 itself is poorly water-soluble, and the frequently used surfactants during the synthetic process make it more difficult to dissolve in polar solvents, which is unfavourable for the biological application. Therefore, it is necessary to carry out the surface modification of NaYF_4. In this paper, the co-doped NaYF_4 nanoparticles were produced initially and then modified by polyacrylic acid (PAA) to improve surface properties. Additionally, due to the significant role of the outside NaYF_4 layer, the nanocomposites NaYF_4:Ln/NaYF_4/PAA with better comprehensive performance were also synthesized to eliminate the fluorescence quenching effect mainly from organic ligands. The details are showed in the following parts.
First, well-dispersed hexagonal NaYF_4 fluorescent matrix nanocrystals were synthesized by reversed micelle method, and then doped with lanthanide elements. NaYF_4 nanocrystals doped with Yb, Er (Tm) are up-converting phospors while doped with Eu are down-converting. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), fourier transform spectroscopy (FTIR), and fluorescence spectroscopy were used to characterize the luminescent nanocrystals. The results indicated that NaYF_4 nanoparticles were hexaganol crystals with an average size of 8 nm. After doping with lanthanide elements, the materials performed good fluorescent property. However, the nanoparticles were proved to be capped with sodium oleate and need to be modified.
Next part is relative to the study of surface modification. Three modifying methods were used:①Modifying NaYF_4:Ln by ligand exchange is a mild and simple reaction method. The synthesized NaYF_4:Ln /PAA composites were small, with an average size of 10 nm. But the dispersion and fluorescent property of the composites were in poor performance;②Then the NaYF_4:Ln nanoparticles were modified by microemulsion method. The synthesized NaYF_4:Ln/PAA composites with an average size of 15 nm were well-dispersed in aqueous such as water and alcohol. The surface modification almost had no influence on up-converting property but greatly reduced the down-converting luminescence. The reaction process is complex and high-energy-consumed;③In-situ polymerization is the third modification method. The products were well-dispersed NaYF_4:Ln/PAA nanospheres with an excellent fluorescence property. But these nanospheres were big, and the minimum was also about 50 nm. In a word, except the shortcoming of size, the composites synthesized by in-situ polymerization performed the best comprehensive property and were closest to the requirement of biological application among all the three methods.
To reduce the fluorescence quenching effect caused by polymer, NaYF_4:Ln/NaYF_4 core-shell particles were finally synthesized through the reverse micelle method. NaYF_4 shell eliminated the surface defects of the internal light-emitting nuclear NaYF_4:Ln, thus perfecting its nanocrystal. Then NaYF_4:Ln/NaYF_4/PAA nanocomposites were produced by ligand exchange method. Fluorescence test results proved that the fluorescence intensity of NaYF_4:Ln/NaYF_4/PAA was higher than that of NaYF_4:Ln/PAA. In addition, the influence of rare-earth doping ratio on fluorescense property was explored in detail. For up-converting property, the change of the doping ratio between Yb~(3+) sensitizer and Er~(3+) (Tm~(3+)) activator altered the color of emission light. For down-converting property, Eu~(3+) was directly stimulated. The strongest fluorescence was found by regulating the concentration of Eu~(3+)
首先,采用反胶束法在常温下制备了几乎纯六方晶型的基质材料NaYF_4纳米粒子,在此基础上掺杂稀土离子,制备了上转换发光的NaYF_4:Yb,Er(Tm)和下转换发光的NaYF_4:Eu。对稀土发光材料用X射线衍射(X-ray diffraction analysis,XRD),透射电子显微镜(transmissionelectron microscopy,TEM),傅里叶变换红外光谱(fourier transformspectroscopy,FTIR)和荧光光度计(fluorescence spectroscopy)进行表征。结果表明:NaYF_4基质材料是粒径在8 nm左右六方晶形纳米晶,稀土掺杂后荧光性能良好,但是纳米粒子外部被表面活性剂油酸钠所包裹,有进一步表面修饰的必要。
其次,采用三种不同的方法进行表面修饰研究:①用配位交换法对NaYF_4:Ln进行表面修饰,该方法反应条件温和,过程简单,合成的NaYF_4:Ln/PAA复合粒子直径小,平均直径10 nm,但复合粒子的分散性欠佳,而且大幅降低材料的荧光性能;②用微乳液法对NaYF_4:Ln进行表面修饰,合成的NaYF_4:Ln/PAA复合粒子的分散性较好,平均直径15 nm,对上转换发光性能影响不大,但是降低下转换发光性能,反应过程复杂,能耗大;③用原位聚合法对NaYF_4:Ln进行表面修饰,形成了分散性良好的NaYF_4:Ln/PAA复合纳米微球,荧光性能佳,但是纳米粒子直径较大,平均100 nm左右,最小也有50 nm。综合来看,经过原位聚合法的到的复合粒子除了粒径较大外,综合性能最佳,最接近生物应用的要求。
最后,为了减少聚合物带来的荧光猝灭,在表面修饰前,先用反胶束法合成NaYF_4:Ln/NaYF_4核壳粒子,NaYF_4壳消除了内部发光核NaYF_4:Ln的表面缺陷,使晶型更加完整。然后通过配位交换法来制备NaYF_4:Ln/NaYF_4/PAA纳米复合材料。荧光测试结果表明,NaYF_4:Ln/NaYF_4/PAA的荧光强度比NaYF_4:Ln/PAA明显增强。此外,重点探究了稀土掺杂量对复合材料荧光性能的影响。在上转换材料NaYF_4:Yb,Er(Tm)/NaYF_4/PAA中,改变敏化剂Yb~(3+)和激活剂Er~(3+)(Tm~(3+))的配合掺杂比,能够改变发光的颜色。在下转换材料中,Eu~(3+)直接被激发,通过改变Eu~(3+)浓度,找到荧光强度最强的掺杂量。
Rare-earth nano-materials can be applied in biological labeling field due to their distinguished optical property from rare-earth elements and small size effect from their nano-scale. As is known to all, lanthanide(Ln) co-doped hexagonal sodium yttrium fluoride (NaYF_4:Ln) is one of the most efficient fluorescent materials. However, NaYF_4 itself is poorly water-soluble, and the frequently used surfactants during the synthetic process make it more difficult to dissolve in polar solvents, which is unfavourable for the biological application. Therefore, it is necessary to carry out the surface modification of NaYF_4. In this paper, the co-doped NaYF_4 nanoparticles were produced initially and then modified by polyacrylic acid (PAA) to improve surface properties. Additionally, due to the significant role of the outside NaYF_4 layer, the nanocomposites NaYF_4:Ln/NaYF_4/PAA with better comprehensive performance were also synthesized to eliminate the fluorescence quenching effect mainly from organic ligands. The details are showed in the following parts.
First, well-dispersed hexagonal NaYF_4 fluorescent matrix nanocrystals were synthesized by reversed micelle method, and then doped with lanthanide elements. NaYF_4 nanocrystals doped with Yb, Er (Tm) are up-converting phospors while doped with Eu are down-converting. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), fourier transform spectroscopy (FTIR), and fluorescence spectroscopy were used to characterize the luminescent nanocrystals. The results indicated that NaYF_4 nanoparticles were hexaganol crystals with an average size of 8 nm. After doping with lanthanide elements, the materials performed good fluorescent property. However, the nanoparticles were proved to be capped with sodium oleate and need to be modified.
Next part is relative to the study of surface modification. Three modifying methods were used:①Modifying NaYF_4:Ln by ligand exchange is a mild and simple reaction method. The synthesized NaYF_4:Ln /PAA composites were small, with an average size of 10 nm. But the dispersion and fluorescent property of the composites were in poor performance;②Then the NaYF_4:Ln nanoparticles were modified by microemulsion method. The synthesized NaYF_4:Ln/PAA composites with an average size of 15 nm were well-dispersed in aqueous such as water and alcohol. The surface modification almost had no influence on up-converting property but greatly reduced the down-converting luminescence. The reaction process is complex and high-energy-consumed;③In-situ polymerization is the third modification method. The products were well-dispersed NaYF_4:Ln/PAA nanospheres with an excellent fluorescence property. But these nanospheres were big, and the minimum was also about 50 nm. In a word, except the shortcoming of size, the composites synthesized by in-situ polymerization performed the best comprehensive property and were closest to the requirement of biological application among all the three methods.
To reduce the fluorescence quenching effect caused by polymer, NaYF_4:Ln/NaYF_4 core-shell particles were finally synthesized through the reverse micelle method. NaYF_4 shell eliminated the surface defects of the internal light-emitting nuclear NaYF_4:Ln, thus perfecting its nanocrystal. Then NaYF_4:Ln/NaYF_4/PAA nanocomposites were produced by ligand exchange method. Fluorescence test results proved that the fluorescence intensity of NaYF_4:Ln/NaYF_4/PAA was higher than that of NaYF_4:Ln/PAA. In addition, the influence of rare-earth doping ratio on fluorescense property was explored in detail. For up-converting property, the change of the doping ratio between Yb~(3+) sensitizer and Er~(3+) (Tm~(3+)) activator altered the color of emission light. For down-converting property, Eu~(3+) was directly stimulated. The strongest fluorescence was found by regulating the concentration of Eu~(3+)
引文
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