氟化物发光材料的离子液体辅助水热法制备与荧光性质研究
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摘要
上转换发光在全固态紧凑型激光器件(紫、蓝、绿区域)、上转换荧光粉、红外量子计数器、三维立体显示、温度探测器和生物分子的荧光探针等领域有较好的应用前景,一直是发光材料的一个研究热点。氟化物材料是一类重要的上转换发光基质材料,具有较低的声子能量、较高的发光效率等优点。在众多氟化物中,LaF3纳米晶体具有良好的热稳定性和环境稳定性、低的声子能量(低于350 cm-1)、容易掺杂稀土离子等优点。所以研究LaF3发光材料具有重要的意义。
传统制备纳米材料的方法中多用到各种有机溶剂或模板,这对反应条件的要求相当苛刻,所以找到一种简便、有效、绿色的合成方法已成为人们追求的目标。室温离子液体具有绿色环保,良好的热稳定性,较宽液程等优点,可以作为一种良好的反应介质满足无机材料合成的要求。水热法则是一种有效的合成无机材料的方法,具有以下优点：合成的颗粒纯度高、分散性好,晶形好且可控制、可通过对反应条件的选择控制产物的尺寸和形貌,且生产成本低。本文采用离子液体辅助水热法成功制备了氟化物发光材料,并研究了其结构和荧光性质。
本文的研究内容如下：
1、结合离子液体和水热法的优点,得到了一种简便、绿色的合成稀土氟化物发光材料的方法,即离子液体辅助水热法。在合成过程中,离子液体[bmim]BF4起到共溶剂和提供氟源的作用,在温度高于120℃时会水解产生F-离子,它与加入的稀土硝酸盐在180℃生成稀土氟化物发光材料。
2、通过XRD, FE-SEM对制备的LaF3:RE样品进行了结构表征,测试结果表明样品的颗粒大小为60 nm。LaF3:Er的样品在980 nm红外光激发下,发射出较强的绿光,通过功率关系得出其绿光和红光发射均为双光子过程,并讨论了其发光机制。LaF3:Eu(5%)和LaF3:Ce(15%),Tb(5%)样品在紫外光的激发下分别能观察到红光和绿光发射。和商业绿粉对比,通过测试计算出LaF3:Ce(15%),Tb(5%)样品的荧光量子效率是34%。结果表明LaF3:RE纳米颗粒在高分辨显示器、放大器和荧光粉等领域有潜在的应用。
3、通过离子液体辅助水热法制备了LaF3:Ce,Tb样品,并加入EDTA-2Na控制样品的形貌和大小。TEM数据和XRD估算表明,样品是直径为25 nm、厚度为5 nm的圆盘结构。在实验过程中EDTA-2Na在控制形貌和粒径大小方面起到了重要作用。系统研究了LaF3:Ce,Tb样品在254 nm紫外光激发下的荧光性质。结果表明LaF3:Ce,Tb颗粒可以应用于生物标记等领域。
4、通过离子液体辅助水热法制备了CaF2:RE纳米颗粒,TEM和SEM结果显示样品是球状结构,直径大约为150 nm。测试和研究了在254 nm激发下,CaF2:Ce,Tb样品的荧光性质；在397nm激发下,CaF2:Eu样品的荧光性质；在980 nm激发下,CaF2:Er样品的上转换发光性质。结果表明红光和绿光的发射均为双光子过程,紫光的发射为三光子过程。
The synthesis and luminescent characterization of rare earth ions (REI) doped fluoride nanocrystals have aroused material scientists' great interest due to their potential application in phosphors, high resolution displays, electroluminescent devices, optical amplifiers, and fluorescent labels for biomolecules. Among the fluorides, LaF3 nanocrystals have received particular attention because of the outstanding physical and chemical properties of this material:excellent thermal and environ-mental stability, low phonon energy (as low as 350 cm-1), the capability of being easily doped with rare earth ions, and so on.
Tradition synthetic methods for fluoride nanocrystals are complicated and organic solvent or template always be used in process. Therefore, scientists expect to find green, facile and general method to prepare fluoride nanocrystals. Recently, ionic liquids (ILs) have attracted considerable interest owing to their exceptional features such as wide liquid range, thermal stability, non-coordinating properties, electrochemical stability, and adjustable solvent polarity. On the other hand, hydrothermal synthesis is considered as one of the useful and powerful pathways to prepare novel nanocrystals owing to high productivity, high purity, good dispersity, and so on.
In this thesis, the main contents are as follows:
1. Combining the advantages of Ionic liquids and hydrothermal method, a novel and easy synthesis-ionic liquids assisted hydrothermal process is reported. Here. Ionic liquid ([bmim]BF4) acts as both a co-solvent and a reactant. When [bmim]BF4 exceeds its boiling temperature as a result of superheating, it decomposes. The BF4-anions undergo fast hydrolysis at temperature higher than 120℃. The fluoride ion reacts with the REI and REI-doped fluoride nanocrystals formed.
2. Highly luminescent, water-soluble LaF3:RE are prepared by ionic liquids assisted hydrothermal process. XRD, TEM and FE-SEM are used to characterize the structural properties of the LaF3:RE nanocrystals. The crystallite sizes of LaF3 nanocrystals are about 60 nm. Excited by 980 nm laser, intense green upconversion emissions are observed for LaF3:Er(1%) samples in the solid state and dispersion in solution. The quantum efficiency of LaF3:Ce(15%),Tb(5%) nanocrystals is about 34 %. The photoluminescent properties indicate that rare-earth ion-doped LaF3 nanocrystals may be applied as phosphors for high-resolution displays.
3. A novel and easy synthesis of highly luminescent, water-soluble LaF3:Ce,Tb nanodiskettes by an ionic liquids-based hydrothermal process is reported. XRD patterns and TEM images show that highly monodisperse LaF3:Ce,Tb nanodiskettes with mean diameter of about 25nm and mean thickness of about 5 nm are elaborated. EDTA-2Na is found to play dual roles as achelating ligand and shape modifier for the formation of green LaF3:Ce,Tb nanodiskettes. The photoluminescent properties indicate that LaF3:Ce,Tb nanocrystals may be applied as phosphors for high-resolution displays and fluorescent labels for biomolecules.
4. RE3+ ions doped CaF2 nanocrystals have been successfully synthesized by ionic liquids assisted hydrothermal process. The structural properties of samples are investigated by XRD, FE-SEM, TEM respectively. The luminescent properties of CaF2:Eu and CaF2:Ce,Tb are evaluated under ultraviolet excition.(397nm for Eu3+and 254nm for Ce3+, Tb3+). Under 980 nm laser excitation, weak blue (404-420 nm), green (513-564 nm) and red (643-676 nm) upconversion emissions have been observed in CaF2:Er,Yb. The laser power dependence of the upconverted emissions confirms that three-photon process for blue emission and two-photon process for green and red emission.
传统制备纳米材料的方法中多用到各种有机溶剂或模板,这对反应条件的要求相当苛刻,所以找到一种简便、有效、绿色的合成方法已成为人们追求的目标。室温离子液体具有绿色环保,良好的热稳定性,较宽液程等优点,可以作为一种良好的反应介质满足无机材料合成的要求。水热法则是一种有效的合成无机材料的方法,具有以下优点：合成的颗粒纯度高、分散性好,晶形好且可控制、可通过对反应条件的选择控制产物的尺寸和形貌,且生产成本低。本文采用离子液体辅助水热法成功制备了氟化物发光材料,并研究了其结构和荧光性质。
本文的研究内容如下：
1、结合离子液体和水热法的优点,得到了一种简便、绿色的合成稀土氟化物发光材料的方法,即离子液体辅助水热法。在合成过程中,离子液体[bmim]BF4起到共溶剂和提供氟源的作用,在温度高于120℃时会水解产生F-离子,它与加入的稀土硝酸盐在180℃生成稀土氟化物发光材料。
2、通过XRD, FE-SEM对制备的LaF3:RE样品进行了结构表征,测试结果表明样品的颗粒大小为60 nm。LaF3:Er的样品在980 nm红外光激发下,发射出较强的绿光,通过功率关系得出其绿光和红光发射均为双光子过程,并讨论了其发光机制。LaF3:Eu(5%)和LaF3:Ce(15%),Tb(5%)样品在紫外光的激发下分别能观察到红光和绿光发射。和商业绿粉对比,通过测试计算出LaF3:Ce(15%),Tb(5%)样品的荧光量子效率是34%。结果表明LaF3:RE纳米颗粒在高分辨显示器、放大器和荧光粉等领域有潜在的应用。
3、通过离子液体辅助水热法制备了LaF3:Ce,Tb样品,并加入EDTA-2Na控制样品的形貌和大小。TEM数据和XRD估算表明,样品是直径为25 nm、厚度为5 nm的圆盘结构。在实验过程中EDTA-2Na在控制形貌和粒径大小方面起到了重要作用。系统研究了LaF3:Ce,Tb样品在254 nm紫外光激发下的荧光性质。结果表明LaF3:Ce,Tb颗粒可以应用于生物标记等领域。
4、通过离子液体辅助水热法制备了CaF2:RE纳米颗粒,TEM和SEM结果显示样品是球状结构,直径大约为150 nm。测试和研究了在254 nm激发下,CaF2:Ce,Tb样品的荧光性质；在397nm激发下,CaF2:Eu样品的荧光性质；在980 nm激发下,CaF2:Er样品的上转换发光性质。结果表明红光和绿光的发射均为双光子过程,紫光的发射为三光子过程。
The synthesis and luminescent characterization of rare earth ions (REI) doped fluoride nanocrystals have aroused material scientists' great interest due to their potential application in phosphors, high resolution displays, electroluminescent devices, optical amplifiers, and fluorescent labels for biomolecules. Among the fluorides, LaF3 nanocrystals have received particular attention because of the outstanding physical and chemical properties of this material:excellent thermal and environ-mental stability, low phonon energy (as low as 350 cm-1), the capability of being easily doped with rare earth ions, and so on.
Tradition synthetic methods for fluoride nanocrystals are complicated and organic solvent or template always be used in process. Therefore, scientists expect to find green, facile and general method to prepare fluoride nanocrystals. Recently, ionic liquids (ILs) have attracted considerable interest owing to their exceptional features such as wide liquid range, thermal stability, non-coordinating properties, electrochemical stability, and adjustable solvent polarity. On the other hand, hydrothermal synthesis is considered as one of the useful and powerful pathways to prepare novel nanocrystals owing to high productivity, high purity, good dispersity, and so on.
In this thesis, the main contents are as follows:
1. Combining the advantages of Ionic liquids and hydrothermal method, a novel and easy synthesis-ionic liquids assisted hydrothermal process is reported. Here. Ionic liquid ([bmim]BF4) acts as both a co-solvent and a reactant. When [bmim]BF4 exceeds its boiling temperature as a result of superheating, it decomposes. The BF4-anions undergo fast hydrolysis at temperature higher than 120℃. The fluoride ion reacts with the REI and REI-doped fluoride nanocrystals formed.
2. Highly luminescent, water-soluble LaF3:RE are prepared by ionic liquids assisted hydrothermal process. XRD, TEM and FE-SEM are used to characterize the structural properties of the LaF3:RE nanocrystals. The crystallite sizes of LaF3 nanocrystals are about 60 nm. Excited by 980 nm laser, intense green upconversion emissions are observed for LaF3:Er(1%) samples in the solid state and dispersion in solution. The quantum efficiency of LaF3:Ce(15%),Tb(5%) nanocrystals is about 34 %. The photoluminescent properties indicate that rare-earth ion-doped LaF3 nanocrystals may be applied as phosphors for high-resolution displays.
3. A novel and easy synthesis of highly luminescent, water-soluble LaF3:Ce,Tb nanodiskettes by an ionic liquids-based hydrothermal process is reported. XRD patterns and TEM images show that highly monodisperse LaF3:Ce,Tb nanodiskettes with mean diameter of about 25nm and mean thickness of about 5 nm are elaborated. EDTA-2Na is found to play dual roles as achelating ligand and shape modifier for the formation of green LaF3:Ce,Tb nanodiskettes. The photoluminescent properties indicate that LaF3:Ce,Tb nanocrystals may be applied as phosphors for high-resolution displays and fluorescent labels for biomolecules.
4. RE3+ ions doped CaF2 nanocrystals have been successfully synthesized by ionic liquids assisted hydrothermal process. The structural properties of samples are investigated by XRD, FE-SEM, TEM respectively. The luminescent properties of CaF2:Eu and CaF2:Ce,Tb are evaluated under ultraviolet excition.(397nm for Eu3+and 254nm for Ce3+, Tb3+). Under 980 nm laser excitation, weak blue (404-420 nm), green (513-564 nm) and red (643-676 nm) upconversion emissions have been observed in CaF2:Er,Yb. The laser power dependence of the upconverted emissions confirms that three-photon process for blue emission and two-photon process for green and red emission.
引文
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