稀土掺杂氟化物纳米材料的制备及多色上转换发光研究
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摘要
稀土掺杂荧光纳米晶独特的光学特性引起了人们广泛的研究兴趣。由于外层5s和5p轨道的有效屏蔽,稀土离子内层4f电子能级间跃迁产生的吸收和发射谱线具有高量子产率、长寿命和高稳定性。此外,稀土离子梯状的能级分布特征使它能在红外激光器激发下吸收两个或多个低能长波光子然后将其转换成高能短波光子。因此,稀土掺杂纳米晶在全固态激光器、红外探测、三维立体显示特别是生物荧光标签等方面有着广泛的应用价值。近年来,随着生物科技和纳米技术的发展,高强度蓝、紫、紫外以及多色彩(含白光)上转换荧光纳米晶由于其在光动力学治疗、可调紫外激光器、纳米光源器件以及同步多通道探测、分子荧光探测等领域的潜在应用价值逐渐成为了人们竞相追逐的热点。本文在课题组前几年工作的基础之上,通过调节基质材料组分和稀土离子组合,在蓝、紫、紫外和多色上转换荧光发射研究上取得了一些重要结果。主要内容如下:
1.采用水热法使用不同比例的油酸和氢氧化钠分别制备了不同比表面积的Yb3+/Tm3+共掺杂单一六角相NaYF4纳米晶。在980 nm激光器激发下,通过改变激光器激发功率,在强蓝光和红外光发射的Yb3+/Tm3+共掺杂β-NaYF4纳米棒材料中,我们观察到了800 nm、475 nm和450 nm发射波段可控的荧光转变。
2.通过引入Gd3+离子,采用水热法制备了Yb3+/Tm3+/Gd3+三掺杂NaYF4纳米棒。XRD测试结果表明改变Gd3+离子浓度可以有效调节纳米晶的尺寸。在980 nm激光的激发下,除了观察到Tm3+离子从紫外光、蓝光、红光到红外光的上转换发射以外,还观察到了Gd3+离子深紫外270～330 nm波段发射。光谱分析结果表明深紫外上转换发射是通过Yb3+到Tm3+然后再到Gd3+的高效的能量传递实现的。
3.采用水热法制备了不同稀土离子掺杂的直径约为12 nm的立方相KGdF4纳米晶。在980 nm激光的激发下,Yb3+/Er3+、Yb3+/Ho3+和Yb3+/Tm3+双掺杂KGdF4纳米晶发出肉眼可见明亮的红色、黄色和蓝色上转换荧光。透射电镜(TEM)、上转换光谱和X射线衍射(XRD)研究表明,样品经过低温热处理后发光强度得到显著的增强,且不会导致晶粒尺寸明显增大。通过调节Yb3+/Ho3+/Tm3+掺杂浓度控制红、绿、蓝三基色荧光强度实现了白色上转换荧光输出。考虑到Gd3+离子常用于磁共振成像,我们的结果表明KGdF4荧光纳米晶在生物医学,防伪和光磁多功能纳米探针等方面有很好的应用前景。
The interest in lanthanide (Ln3+)-doped nanocrystals have renewed by their unique optical properties at the end of the 20th century. These nanomaterials have sharp absorption and emission lines arising from the intra 4f transitions with high quantum yields, long lifetimes, and superior photostability, due to the effective shielding of the 4f orbitals by the higher lying 5s and 5p orbitals, thereby minimizing the effect of the outer ligand field. In particular, owing to the ladder-like arranged energy levels of Ln3+ ions, high efficiency of the photon upconversion (UC) that absorb one or more low-energy near-infrared (NIR) photons and subsequently convert them to high-energy emissions can be obtained under the excitation of infrared lasers with moderate excitation densities. Therefore, the Ln3+ doped nanocrystals are envisioned to have extensively potential applications in solid-state lasers, infrared detection, multicolor three dimensional displays,and especially biological fluorescent labels. In recent years, obtaining highly efficient and strong blue, purple, ultraviolet (UV) and multicolor (including white light) nanocrystals become a research focus. The former can especially be used to produce singlet oxygen for photodynamic therapies in the field of biomedicine and develop solution-based scintillator materials besides tunable UV laser, while the latter can especially serve as lighting sources in nano-optics devices and fluorescent biolabels offering more simultaneous detection channels or allowing molecular fluorescence detection independent of the color of solution. On the basis of our group’s previous studies, we achieved some important conclusions on blue, purple, UV and multicolor UC luminescence by changing matrix and rare-earth ions. The major contents of our study as follows:
1. Yb3+/Tm3+ codoped hexagonal NaYF4 nanocrystals were fabricated via changing dosage of oleic acid and sodium hydroxide using a facile hydrothermal method. Intense infrared-to-visible UC emissions were obtained in these nanocrystals under excitation at 980 nm. Especially, luminescent switching among different UC emissions wavelengths at 800, 475 and 450 nm were observed by adjusting excitation powers.
2. Deep UV UC emissions in the region of 270~330 nm of Gd3+ under the excitation of 980 nm laser diode in hexagonal Yb3+/Tm3+/Gd3+ triply doped NaYF4 nanorods synthesized using hydrothermal method were studied. Spectral analyses indicate that the UV UC emissions originate from highly efficient energy-transfer from Yb3+ to Tm3+, then to Gd3+ ions, and the intensity of the emission as well as the ratios of the emission peaks are strongly dependent on the doping concentrations and pump power. XRD results indicate that crystallite size can be controlled by changing concentration of Gd3+.
3. Ln3+ doped cubic KGdF4 (Ln= Yb, Er, Ho, Tm) nanocrystals, approximately 12 nm in diameter, synthesized via a hydrothermal method with multicolor UC emissions including red, yellow, blue and white, under the excitation of a 980 nm diode laser was studied. The transmission electron microscopy (TEM),X-ray diffraction (XRD) and UC spectra results indicated that the UC fluorescence intensity is remarkably enhanced after low-temperature heat treatment, but the gain size dose not increased obviously. The calculated color coordinate demonstrated that white UC emission including nearly standard white light (CIE-X=0.351, CIE-Y=0.346) can be tuned through controlling the intensities of red, green and blue emissions by adjusting the dopant concentration in Yb3+/Ho3+/Tm3+ triply doped nanocrystals. Keeping in mind that the Gd3+ ion is a paramagnetic relaxation agent extensively used in magnetic resonance imaging, our results suggest that these Ln3+ doped KGdF4 nanocrystals have promising applications in optical and magnetic dual modal nanoprobes for biomedicine besides anti-counterfeiting, color displays and back light sources.
1.采用水热法使用不同比例的油酸和氢氧化钠分别制备了不同比表面积的Yb3+/Tm3+共掺杂单一六角相NaYF4纳米晶。在980 nm激光器激发下,通过改变激光器激发功率,在强蓝光和红外光发射的Yb3+/Tm3+共掺杂β-NaYF4纳米棒材料中,我们观察到了800 nm、475 nm和450 nm发射波段可控的荧光转变。
2.通过引入Gd3+离子,采用水热法制备了Yb3+/Tm3+/Gd3+三掺杂NaYF4纳米棒。XRD测试结果表明改变Gd3+离子浓度可以有效调节纳米晶的尺寸。在980 nm激光的激发下,除了观察到Tm3+离子从紫外光、蓝光、红光到红外光的上转换发射以外,还观察到了Gd3+离子深紫外270～330 nm波段发射。光谱分析结果表明深紫外上转换发射是通过Yb3+到Tm3+然后再到Gd3+的高效的能量传递实现的。
3.采用水热法制备了不同稀土离子掺杂的直径约为12 nm的立方相KGdF4纳米晶。在980 nm激光的激发下,Yb3+/Er3+、Yb3+/Ho3+和Yb3+/Tm3+双掺杂KGdF4纳米晶发出肉眼可见明亮的红色、黄色和蓝色上转换荧光。透射电镜(TEM)、上转换光谱和X射线衍射(XRD)研究表明,样品经过低温热处理后发光强度得到显著的增强,且不会导致晶粒尺寸明显增大。通过调节Yb3+/Ho3+/Tm3+掺杂浓度控制红、绿、蓝三基色荧光强度实现了白色上转换荧光输出。考虑到Gd3+离子常用于磁共振成像,我们的结果表明KGdF4荧光纳米晶在生物医学,防伪和光磁多功能纳米探针等方面有很好的应用前景。
The interest in lanthanide (Ln3+)-doped nanocrystals have renewed by their unique optical properties at the end of the 20th century. These nanomaterials have sharp absorption and emission lines arising from the intra 4f transitions with high quantum yields, long lifetimes, and superior photostability, due to the effective shielding of the 4f orbitals by the higher lying 5s and 5p orbitals, thereby minimizing the effect of the outer ligand field. In particular, owing to the ladder-like arranged energy levels of Ln3+ ions, high efficiency of the photon upconversion (UC) that absorb one or more low-energy near-infrared (NIR) photons and subsequently convert them to high-energy emissions can be obtained under the excitation of infrared lasers with moderate excitation densities. Therefore, the Ln3+ doped nanocrystals are envisioned to have extensively potential applications in solid-state lasers, infrared detection, multicolor three dimensional displays,and especially biological fluorescent labels. In recent years, obtaining highly efficient and strong blue, purple, ultraviolet (UV) and multicolor (including white light) nanocrystals become a research focus. The former can especially be used to produce singlet oxygen for photodynamic therapies in the field of biomedicine and develop solution-based scintillator materials besides tunable UV laser, while the latter can especially serve as lighting sources in nano-optics devices and fluorescent biolabels offering more simultaneous detection channels or allowing molecular fluorescence detection independent of the color of solution. On the basis of our group’s previous studies, we achieved some important conclusions on blue, purple, UV and multicolor UC luminescence by changing matrix and rare-earth ions. The major contents of our study as follows:
1. Yb3+/Tm3+ codoped hexagonal NaYF4 nanocrystals were fabricated via changing dosage of oleic acid and sodium hydroxide using a facile hydrothermal method. Intense infrared-to-visible UC emissions were obtained in these nanocrystals under excitation at 980 nm. Especially, luminescent switching among different UC emissions wavelengths at 800, 475 and 450 nm were observed by adjusting excitation powers.
2. Deep UV UC emissions in the region of 270~330 nm of Gd3+ under the excitation of 980 nm laser diode in hexagonal Yb3+/Tm3+/Gd3+ triply doped NaYF4 nanorods synthesized using hydrothermal method were studied. Spectral analyses indicate that the UV UC emissions originate from highly efficient energy-transfer from Yb3+ to Tm3+, then to Gd3+ ions, and the intensity of the emission as well as the ratios of the emission peaks are strongly dependent on the doping concentrations and pump power. XRD results indicate that crystallite size can be controlled by changing concentration of Gd3+.
3. Ln3+ doped cubic KGdF4 (Ln= Yb, Er, Ho, Tm) nanocrystals, approximately 12 nm in diameter, synthesized via a hydrothermal method with multicolor UC emissions including red, yellow, blue and white, under the excitation of a 980 nm diode laser was studied. The transmission electron microscopy (TEM),X-ray diffraction (XRD) and UC spectra results indicated that the UC fluorescence intensity is remarkably enhanced after low-temperature heat treatment, but the gain size dose not increased obviously. The calculated color coordinate demonstrated that white UC emission including nearly standard white light (CIE-X=0.351, CIE-Y=0.346) can be tuned through controlling the intensities of red, green and blue emissions by adjusting the dopant concentration in Yb3+/Ho3+/Tm3+ triply doped nanocrystals. Keeping in mind that the Gd3+ ion is a paramagnetic relaxation agent extensively used in magnetic resonance imaging, our results suggest that these Ln3+ doped KGdF4 nanocrystals have promising applications in optical and magnetic dual modal nanoprobes for biomedicine besides anti-counterfeiting, color displays and back light sources.
引文
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