共查询到20条相似文献,搜索用时 46 毫秒
1.
棒状LaF3∶Eu3+纳米晶的制备与发光性能 总被引:1,自引:0,他引:1
采用一种简单的液相反应法在室温下合成了棒状的LaF3∶Eu3+纳米晶, 对其结构和发光性能进行了表征. XRD分析结果表明, 室温下即可得到结晶良好的六方晶相的LaF3, 灼烧之后样品的衍射峰增强, 没有杂相产生. TEM照片表明, 棒状LaF3∶Eu3+纳米材料的直径为8 nm左右, 长度达到50 nm. 荧光光谱表明, 室温下合成的棒状LaF3∶Eu3+纳米晶的最强发射峰位于589 nm, 对应于Eu3+的5D0-7F1跃迁发射, 说明Eu3+占据LaF3基质中La3+晶格点的C2对称格位上. 同时Eu3+的猝灭摩尔分数为5%, 荧光寿命随着灼烧温度的升高而延长. 相似文献
2.
Sun X Zhang YW Du YP Yan ZG Si R You LP Yan CH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(8):2320-2332
We report the first systematic synthesis of monodisperse rare-earth (RE=La to Lu, Y) fluoride and oxyfluoride nanocrystals with diverse shapes (trigonal REF3 triangular, truncated-triangular, hexagonal, and polygonal nanoplates; orthorhombic REF3 quadrilateral and zigzag-shaped nanoplates; cubic REOF nanopolyhedra and nanorods) from single-source precursors (SSP) of [RE(CF(3)COO)(3)] through controlled fluorination in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE). To selectively obtain REF3 or REOF nanocrystals, the fluorination of the RE-O bond to the RE-F bond at the nucleation stage was controlled by finely tuning the ratio of OA/ODE or OA/OM, and the reaction temperature. For phase-pure REF3 or REOF naocrystals, their shape-selective syntheses could be realized by further modifying the reaction conditions. The two-dimensional growth of the REF3 nanoplates and the one-dimensional growth of the REOF nanorods were likely due to the selective adsorption of the capping ligands on specific crystal planes of the nanocrystals. Those well-shaped nanocrystals with diverse geometric symmetries (such as D(3h), D(6h), C(2h), O(h), and D(nh)) displayed a remarkable capability to form self-assembled superlattices. By manipulating the solvent-substrate combination, the plate-shaped REF3 nanocrystals could form highly ordered nanoarrays by means of either the face-to-face formation or the edge-to-edge formation. By using this SSP strategy, we also obtained high-quality LaF3:Eu and LaF3:Eu/LaF3 triangular nanoplates that showed photoluminescent red emissions of Eu3+ ions sensitive to the surface effect. 相似文献
3.
Meng JX Zhang MF Liu YL Man SQ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,66(1):81-85
LaF3:Eu3+ nanoparticles were prepared by a simple hydrothermal process at low temperature and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectrum. Well-dispersed nanoparticles with an average size of 30 nm and a hexagonal shape were obtained. The influences of reaction temperature and time on the preparation and luminescence of LaF3:Eu3+ nanoparticles were investigated. Luminescent quenching occurred at a much higher concentration ( approximately 25mol%) and stronger luminescent intensity than in bulk LaF3:Eu3+. Fluorescence intensity of the LaF3:Eu3+ nanoparticles varied remarkably with calcination temperatures. It was found that samples without any further calcinations can emit quite strong fluorescence. 相似文献
4.
Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba(2)LaF(7) nanocrystals with the size of sub-10nm through a solvothermal method. We found the dopants of Ho(3+), Er(3+), or Yb(3+) facilitated the growth of Ba(2)LaF(7) nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF(3) nanocrystals. We find that Ln(3+) (e.g., Ho(3+), Er(3+), or Yb(3+)) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba(2)LaF(7) nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln(3+)-doped Ba(2)LaF(7) nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba(2)LaF(7):Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than α-NaYF(4):Yb/Er (20/1 mol%) nanocrystals under the same conditions. 相似文献
5.
采用简单的液相法合成了SiO2/LaF3:Eu3+核壳结构发光粒子, 并对其结构及发光性能进行了表征. XRD分析表明包覆层LaF3:Eu3+为立方晶相结构, 红外光谱表明SiO2颗粒表面有柠檬酸的修饰, 电镜照片表明合成了球形的核-壳结构的复合粒子, 包覆层厚度为10~20 nm, 光谱测试表明核-壳复合粒子与纯的LaF3:Eu3+具有相同的发光性能, 均以589 nm附近的5D0—7F1磁偶极跃迁为最强发射峰, 说明Eu3+在LaF3基质中占据的格位相同. 相似文献
6.
Improvement in the luminescence properties and processability of LaF3/Ln and LaPO4/Ln nanoparticles by surface modification 总被引:2,自引:0,他引:2
Stouwdam JW van Veggel FC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11763-11771
The surface of lanthanide(III)-doped LaPO4 nanoparticles was modified by reaction with an alcohol, leading to a covalent bond between the ligand and the particle surface. The surface of lanthanide(III)-doped LaF3 nanoparticles was modified to alter the solubility of the nanoparticles and study the influence of surface effects on the luminescence of lanthanide ions doped in the nanoparticles. The coordinated organic ligands can be modified by a quantitative exchange reaction in solution or by using functionalized ligands during the synthesis. Variation of the ratio of ligand to core reagents had a significant influence on the size of the nanoparticles. Smaller nanoparticles were formed with a higher ligand ratio. The optical properties of these nanoparticles show a strong dependence on nanoparticle size, indicating the influence of quenching probably by CH and OH groups at or near the surface of the nanoparticle cores. The luminescence lifetime of LaF3/Eu nanoparticles varied from 6.5 to 7.4 ms for nanoparticles with an average size of 7.1 to 8.4 nm. A significant reduction of the quenching from the surface of the nanoparticles was obtained by the synthesis of core-shell nanoparticles, in which a shell of LaF3 was grown epitaxially around the doped core nanoparticles. This leads to an increase in the luminescence lifetime of the Eu3+ ion and the observation of emissions from the 5D2 energy level, in addition to emissions from the 5D1 and 5D0 levels. The quantum yield of LaF3/Ce,Tb nanoparticles could be increased from 24 to 54% by the growth of a LaF3 shell around the nanoparticles. 相似文献
7.
Pi D Wang F Fan X Wang M Zhang Y 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(11-12):2455-2459
Europium-doped LaF3 nanoparticles have been prepared by the ionic reaction in the ethanol at 60 degrees C. From the XRD pattern of nanoparticles and the emission spectra of Eu3+ ions, it has been concluded that the Eu3+ ions could easily substitute the La3+ sites and the solid solution La(1-x)Eu(x)F3 can be synthesized. Due to very low phonon energies of LaF3 matrix, the 5D1 emission of Eu3+ ions in La(1-x)Eu(x)F3 nanoparticles can be observed at room temperature when doping concentration of Eu3+ ions is lower than 30 mol%. The quenching process of 5D1 emission can be attributed to cross-relaxation. Since clusters of Eu3+ ions and resonance energy transfer only occurs within one particle due to the hindrance by the particle boundary, the concentration quenching resulted from resonance energy transfer between neighboring Eu3+ ions occurs at higher Eu3+ concentrations in the Eu3+ doped LaF3 nanoparticles. 相似文献
8.
Selinsky RS Han JH Morales Pérez EA Guzei IA Jin S 《Journal of the American Chemical Society》2010,132(45):15997-16005
EuS nanocrystals (NCs) were doped with Gd resulting in an enhancement of their magnetic properties. New EuS and GdS single source precursors (SSPs) were synthesized, characterized, and employed to synthesize Eu(1-x)Gd(x)S NCs by decomposition in oleylamine and trioctylphosphine at 290 °C. The doped NCs were characterized using X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy, which support the uniform distribution of Gd dopants through electron energy loss spectroscopy (EELS) mapping. X-ray absorption spectroscopy (XAS) revealed the dopant ions in Eu(1-x)Gd(x)S NCs to be predominantly Gd(3+). NCs with a variety of doping ratios of Gd (0 ≤ x < 1) were systematically studied using vibrating sample magnetometry and the observed magnetic properties were correlated with the Gd doping levels (x) as quantified with ICP-AES. Enhancement of the Curie temperature (T(C)) was observed for samples with low Gd concentrations (x ≤ 10%) with a maximum T(C) of 29.4 K observed for NCs containing 5.3% Gd. Overall, the observed T(C), Weiss temperature (θ), and hysteretic behavior correspond directly to the doping level in Eu(1-x)Gd(x)S NCs and the trends qualitatively follow those previously reported for bulk and thin film samples. 相似文献
9.
10.
11.
12.
Rieter WJ Taylor KM An H Lin W Lin W 《Journal of the American Chemical Society》2006,128(28):9024-9025
Nanoscale metal-organic frameworks (NMOFs) based on Gd3+ centers and benzenedicarboxylate and benzenetricarboxylate bridging ligands were synthesized using reverse microemulsions and characterized using SEM, PXRD, and TGA. These NMOFs exhibit extraordinarily large R1 and R2 relaxivities because of the presence of up to tens of millions of Gd3+ centers in each nanoparticle and are thus efficient T1 and T2 contrast agents for MRI. The NMOFs can also be made highly luminescent by doping with Eu3+ or Tb3+ centers. The results from this work suggest that NMOFs can be used as potential contrast agents for multimodal imaging. 相似文献
13.
A new family of chloroborate compounds, which was investigated from the viewpoint of rare earth ion activated phosphor materials, have been synthesized by a conventional high temperature solid-state reaction. The crystal structure and thermally stable luminescence of chloroborate phosphors Ba(2)Ln(BO(3))(2)Cl:Eu(2+) (Ln = Y, Gd, and Lu) have been reported in this paper. X-ray diffraction studies verify the successful isomorphic substitution for Ln(3+) sites in Ba(2)Ln(BO(3))(2)Cl by other smaller trivalent rare earth ions, such as Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. The detailed structure information for Ba(2)Ln(BO(3))(2)Cl (Ln = Y, Gd, and Lu) by Rietveld analysis reveals that they all crystallize in a monoclinic P2(1)/m space group. These compounds display interesting and tunable photoluminescence (PL) properties after Eu(2+)-doping. Ba(2)Ln(BO(3))(2)Cl:Eu(2+) phosphors exhibit bluish-green/greenish-yellow light with peak wavelengths at 526, 548, and 511 nm under 365 UV light excitation for Ba(2)Y(BO(3))(2)Cl:Eu(2+), Ba(2)Gd(BO(3))(2)Cl:Eu(2+), and Ba(2)Lu(BO(3))(2)Cl:Eu(2+), respectively. Furthermore, they possess a high thermal quenching temperature. With the increase of temperature, the emission bands show blue shifts with broadening bandwidths and slightly decreasing emission intensities. It is expected that this series of chloroborate phosphors can be used in white-light UV-LEDs as a good wavelength-conversion phosphor. 相似文献
14.
A new self-assembled gadolinium(III)-aluminum(III) complex (Gd(3)Al) was synthesized and characterized. The efficacy of this Gd(3)Al complex as a potential bimodal magnetic resonance imaging (MRI)/optical imaging agent has been evaluated. Relaxivity studies showed that the Gd(3)Al complex has higher relaxation efficiency (7.18 mM(-1) s(-1)) compared with the clinically used complex gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA, 3.9 mM(-1) s(-1)) at 400 MHz and 25 °C. In vitro T(1)-MR images on a 0.5 T magnetic field exhibited a remarkable enhancement of signal contrast for Gd(3)Al compared to Gd-DTPA. Furthermore, the Gd(3)Al complex exhibits bright-green luminescence with the emission spectrum centred at 510 nm. Live-cell fluorescence imaging reveals that the Gd(3)Al complex is permeable to cells and localizes to the cytoplasm. In view of the relaxometric and luminescent properties, this Gd(3)Al complex could serve as a potential bimodal MRI/optical imaging agent. 相似文献
15.
W Xu K Kattel JY Park Y Chang TJ Kim GH Lee 《Physical chemistry chemical physics : PCCP》2012,14(37):12687-12700
There is no doubt that magnetic resonance imaging contrast agents (MRI CAs) can play a vital role in diagnosing diseases. Therefore, demand for new MRI CAs with an enhanced sensitivity and advanced functionalities is very high. Here, paramagnetic nanoparticles (NPs) are reviewed as new potential candidates for either T(1) or T(2) MRI CAs or both. These include surface coated lanthanide (Ln) oxide NPs (Ln = Gd, Dy, and Ho) and manganese oxide NPs. Surface coating materials should be biocompatible and hydrophilic. Compared to conventional large NPs, these surface coated paramagnetic NPs can be made ultrasmall with core particle diameter ranging from 1 to 3 nm, but their magnetic properties are still sufficient for MRI CAs. At this particle diameter, they can be easily excreted from the body through the renal system, which is prerequisite for in vivo applications. Mixed lanthanide oxide NPs into which a fluorescent Ln material is incorporated will be valuable as multiple imaging agents for both MRI-fluorescent imaging (FI) and MRI-cellular imaging (CL). These paramagnetic NPs can be further functionalized towards target-specific imaging, multiplex imaging, and drug delivery. 相似文献
16.
以尿素为燃烧剂,乙二醇为分散剂采用燃烧法制备了Gd3Ga5O12∶Eu3+纳米晶。利用X射线衍射、电镜和荧光光谱对前驱体和热处理后样品的结构、形貌和发光性能进行了表征。XRD结果表明:700℃热处理2 h即可获得立方结构Gd3Ga5O12∶Eu3+纳米晶。根据Scherrer公式估算经700℃和900℃热处理2 h获得的纳米晶的一次性粒径分别为28 nm和42 nm。发射光谱和激发光谱的结果表明:特征发射峰来自于5D0-7FJ跃迁,而来自于Eu3+的5D0→7F1的磁偶极跃迁发射最强;宽激发带主要来自于Eu-O电荷迁移带和Gd3Ga5O12基质吸收。发射强度和激发强度随热处理温度的提高而增强。 相似文献
17.
Liu J Bu W Zhang S Chen F Xing H Pan L Zhou L Peng W Shi J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2335-2341
Here we report the design and controlled synthesis of monodisperse and precisely size-controllable UCNP@mSiO(2) nanocomposites smaller than 50?nm by directly coating a mesoporous silica shell (mSiO(2)) on upconversion nanocrystals NaYF(4):Tm/Yb/Gd (UCNPs), which can be used as near-infrared fluorescence and magnetic resonance imaging (MRI) agents and a platform for drug delivery as well. Some key steps such as transferring hydrophobic UCNPs to the water phase by using cetyltrimethylammonium bromide (CTAB), removal of the excess amount of CTAB, and temperature-controlled ultrasonication treatment should be adopted and carefully monitored to obtain uniform upconversion core/mesoporous silica shell nanocomposites. The excellent performance of the core-shell-structured nanocomposite in near-infrared fluorescence and magnetic resonance imaging was also demonstrated. 相似文献
18.
Three nonequivalent centers of Cs (A, B, and C) in monoclinic phase and C2 and S6 centers in cubic phase were identified in the Gd2O3:Eu3+ nanocrystals with spectral techniques. Size dependence in the spectra indicated that the excitations from both host and charge-transfer band (CTB) for the 5D0 --> 7F2 transition of Eu3+ ions were nearly equal for a larger size of 135 nm of the cubic phase; however, with decreasing the size to or less than 23 nm, the excitations by the CTB dominated. The variation of excitation leading to the symmetry and energy change in the C2 and S6 sites was also observed for larger particle sizes. The Judd-Ofelt intensity parameters Omega(lambda) (lambda = 2, 4) for Gd2O3:Eu3+ nanoparticles were experimentally determined. The parameters Omega(lambda) were found to significantly change with the sizes of Gd2O3:Eu3+ from nanoparticles to bulk material. With decreasing the size from 135 to 15 nm, the quantum efficiencies for 5D0 reduced from 23.6% to 4.6% due to the increasing ratio of surface to volume. 相似文献
19.
GdF3∶Eu3+/NaGdF4∶Eu3+纳米晶的水热合成及发光性质 总被引:1,自引:0,他引:1
采用水热法,以聚乙二醇(400)为分散剂,以NaOH和HNO3溶液调节初始溶液pH值,合成GdF3∶Eu3+和NaGdF4∶Eu3+纳米晶。XRD和SEM结果表明:在酸性溶液(pH=3,5)、中性溶液(pH=7)和碱性溶液(pH=9)中,分别获得具有正交结构的GdF3∶Eu3+纳米晶,GdF3∶Eu3+和NaGdF4∶Eu3+混合晶,六方结构NaGdF4∶Eu3+棒状微米晶。根据Scherrer公式估算pH=3和pH=5时制备纳米晶的一次性粒径分别为49和28 nm。样品的发射光谱结果表明:特征发射峰来自于5D2、5D1、5D0到7FJ跃迁。在主晶相为GdF3样品中,主发射峰来自于Eu3+的5D0→7F1的磁偶极跃迁;晶相为NaGdF4样品的主发射峰来自于Eu3+的5D0→7F2电偶极跃迁。5D0→7F1和5D0→7F2跃迁发射相对强度比值显示:Eu3+在NaGdF4晶体中的格位对称性下降。激发光谱显示出Gd3+和Eu3+具有较好的能量传递。 相似文献
20.
Fan X Wang J Qiao X Wang M Adam JL Zhang X 《The journal of physical chemistry. B》2006,110(12):5950-5954
The preparation process and upconversion luminescence of the Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals were investigated. The formation of Ba(2)LaF(7) nanocrystals in the glass ceramics was confirmed by X-ray diffraction. Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals exhibited highly efficient upconversion luminescence in comparison with glasses. With the increase of heat treatment temperature the upconversion luminescence intensity increased gradually. The composition of glasses was also found to have significant influence on the crystallization process of glass ceramics. The mixture of Ba(2)LaF(7) and La(2)O(3) nanocrystals and the mixture of La(2)F(3) and La(2)O(3) nanocrystals in the glass ceramics could be obtained by controlling different compositions of glasses. The upconversion luminescence intensity also varied significantly with different nanocrystals in the glass ceramics. 相似文献