新型白光LED用硅酸盐荧光材料的合成及性质研究

近年来，白光LED作为一种新型的固态光源激发了广大研究者的热情，其主要原因是白光LED具备节能、可再生、使用寿命长以及环境友好等诸多优点。通常情况下，LED芯片结合荧光材料是实现白光发射的主要方式。所以，荧光材料的品质对白光LED的性能比如器件色温（CCT）、显色指数（CRI）等方面有重要影响。因此，研究和开发具有高品质的新型荧光材料对LED的发展具有重大意义。本论文的工作重点集中在研究新型的硅酸盐基荧光材料，目前取得的主要成果如下： 1. 采用高温固相法合成了Eu2+离子单掺和Eu2+/Mn2+离子共掺的Ba1.3Ca0.7SiO4荧光材料。利用X射线衍射对样品的结构进行表征。在390 nm的激发条件下，Eu2+离子单掺的样品表现出主峰位于500 nm的宽带发射，这是Eu2+离子的f-d跃迁导致的。Eu2+/Mn2+离子共掺的样品除了表现出Eu2+离子的发光，还有主峰位于600 nm的红光发射，这个新增的发射来自于Mn2+离子的4T1(4G) →6A1(6S)跃迁。通过调节Mn2+离子的掺杂浓度，共掺样品的发光颜色可以从蓝光递变到红光。我们对Mn2+离子光谱的红移（593 ~ 620 nm）原因也进行了详细的讨论。 2. 合成了一系列以磷灰石结构的NaY9(SiO4)6O2作为基质，以Ce3+, Tb3+, Eu3+, Mn2+作为发光离子的单掺杂和共掺杂的荧光材料，详细研究了其晶体结构和发光性质，单掺杂的样品表现出发光离子的特征发射峰。Ce3+/Mn2+以及Ce3+/ Tb3+共掺杂的样品中，Ce3+离子的敏化作用表现显著，且能量传递效率的最大值分别为57.9%和47.6%。研究表明利用能量传递机理，通过改变掺杂方式，该类荧光材料可以实现多色发射。 3. 单一基质光色可调白光荧光材料Ca3Si2O7:Ce3+,Eu2+在200 ~ 400 nm表现出有效的吸收带。通过调控Ce3+和Eu2+ 的比例，此材料的色调可以实现从蓝光到红橙光的完整递变。用光谱重叠法计算得到Ce3+和Eu2+之间通过电偶极-电偶极相互作用进行能量传递，且Ce3+和Eu2+之间的临界距离为13.7?。 4. 首次合成出单一基质紫外光激发光色可调的枪晶石结构的白光荧光材料NaCa2LuSi2O7F2:Ce3+,Mn2+。利用Rietveld方法对样品的结构进行了精修。Ce3+离子的光谱性质分析表明其占据了基质中的Lu3+离子格位，通过高斯分解进行了完整解析。NaCa2LuSi2O7F2:Ce3+,Mn2+表现出位于410 nm的蓝光发射以及600 nm的红光发射。Ce3+-Mn2+之间的能量传递机制为电偶极-电四极相互作用。粗合成的样品的量子效率的最大值为66.5%。 5. 采用高温固相法首次合成了一种绿色荧光材料Ca8Mg3Al2Si7O28:Eu2+。用Rietveld法对样品的晶体结构进行了表征，该荧光材料在230 ~ 450 nm范围内有较强吸收。在420 nm的激发条件下，样品表现出主峰位于535 nm明亮的绿色宽带长波发射。对引起长波发射的原因进行了讨论。基于Dexter理论依据以及Inokuti-Hirayama 模型，对Eu2+离子之间的能量传递机理也做了详细研究。 6. 首次合成了一种新型蓝光激发的绿色荧光材料K2Ba7Si16O40:Eu2+。结构研究表明：其结构是由平行于（201）面SiO4四面体构成的平面层和分布在层与层之间的空隙中的K+，Ba2+组成的。其最强激发波长与现阶段440 nm蓝光芯片吻合，表现出最大发射波长位于500 nm的宽带发射。对Eu2+离子的浓度猝灭机制进行了讨论，且Eu-Eu之间的临界距离为16.57 ?。实验阶段的样品表现出极佳的热稳定性和较高的量子效率。 7. 采用高温固相法成功的合成了适用于紫外光激发的单一基质光色可调的白光荧光材料Na2Ca4Mg2Si4O15:Eu2+,Mn2+。其表现出位于480 nm的蓝光发射以及645 nm的红光发射。Eu-Mn之间的能量传递导致共掺样品中Mn2+离子的发光大大增强，并表现出光色可调的发射。我们基于其发射光谱和Eu2+离子的荧光衰减曲线，对Eu-Mn之间的能量传递机制进行了讨论。 8. 采用高温固相法合成了Si2O7以及SiO4基团共存的的光色可调的新型硅酸盐荧光材料Na2Ba6(Si2O7)(SiO4)2:Ce3+,Mn2+。X射线粉末衍射的Rietveld精修结果表明样品为纯相。在UV激发条件下，单掺Ce3+离子的样品表现出350 ~ 600 nm的宽带发射。Ce3+离子的低温光谱（5K）劈裂为主峰位于375 nm、420 nm、451 nm的三个独立光谱，这种结果与基质内占据阳离子格位一致。Na2Ba6(Si2O7)(SiO4)2:Ce3+,Mn2+样品表现出蓝光和橙光发射，其CIE色坐标表现出从蓝光到白光的递变。此外，粗合成的材料显示了极高的热稳定性。 关键词：硅酸盐，荧光材料，能量传递，光谱调控，稀土离子Recently, white light emitting diodes (WLEDs) are arousing more and more enthusiasm of researchers as solid-state light sources. The main reason of this phenomenon is their significantly reducing the use of fossil fuels，good reliability, long lifetime, and environmentally friendly. The most common way to realize white light emitting is the combination of LED chips with phosphors. As a result, phosphors as the key component have an important effect on the performance of the white LEDs, reflecting in the aspect of correlated color temperature (CCT) and color rendering index (CRI). Therefore, it is essential to design novel phosphors with high quality for the development of LEDs technology. Inspired by the above idea, we have synthesized a series of phosphors after many failure attempts in silicate compounds. The main contexts are listed as following: 1) Eu2+ doped and Eu2+/Mn2+ codoped Ba1.3Ca0.7SiO4 phosphors have been synthesized by high temperature solid state reaction method. The single phase purity was checked by means of X?ray diffraction. Under the excitation at 390 nm, the emission spectra of the Eu2+ doped phosphors exhibit a broadband emission centered at 500 nm caused by the electric dipole allowed transition of the Eu2+ ions. The emission spectra of codoped phosphors show one more broad emission centered at 600 nm attributable to the transitions from the 4T1(4G) →6A1(6S) of Mn2+ ions. The luminescent color of the codoped phosphors can be easily adjusted from blue to red with variation of Mn2+ content. Additionally, a great red shift from 593 nm to 620 nm has been observed following the increase of Mn2+ content, and the phenomenon has been discussed. 2) We have synthesized a series of (Ce3+, Tb3+, Eu3+) singly doped & (Ce3+/Tb3+, Ce3+/Mn2+) codoped NaY9(SiO4)6O2 phosphors with apatite structure via high temperature solid state reaction and investigated their crystal structures and luminescent properties in detail. The singly doped phosphors exhibit the characteristic emission of activators under UV excitation, respectively. On the basis of the photoluminescence emission spectra of codoped NaY9(SiO4)6O2 samples, we clearly observed the sensitizing effects from the Ce3+ ions to the Tb3+ or Mn2+ ions and coarsely calculated the energy transfer efficiency. Furthermore, the tunable color tune of these codoped NaY9(SiO4)6O2 phosphors can be easily obtained by adjusting the relative content between the Ce3+ and Tb3+/Mn2+. 3) Single-phased Ca3Si2O7:Ce3+,Eu2+ phosphor shows efficient excitation bands from 200 to 400 nm and adjustable emission bands through the energy transfer from the Ce3+ to Eu2+ ions. The color hues can change from blue towards white ultimately to orange by adjusting the percentage content of doping ions. The investigation reveals that an electric dipole-dipole intereaction mechanism should be responsible for the energy transfer from the Ce3+ to Eu2+ ions. The critical distance was obtained to be about 13.7 ? from the spectral overlap in terms of Dexter’s theory. 4) NaCa2LuSi2O7F2:Ce3+,Mn2+ phosphors have been firstly prepared by a high-temperature solid-state reaction technique. The Rietveld refinement result confirmed that the obtained phosphors have a pure crystalline phase with cuspidine-group structure. The luminescent properties of the singly-doped samples reveal that the Ce3+ ions occupy two different Lu3+ sites in the host lattice, which has been studied on the basis of Gaussian function. NaCa2LuSi2O7F2:xCe3+,Mn2+ phosphors could be efficiently excited by the UV light and show two broad band emissions at 410 and 600 nm. The energy transfer from the Ce3+ to Mn2+ ions was observed and investigated systematically by the luminescence spectra, the energy transfer efficiency, and the decay curves of the phosphors. And its mechanism was a resonant type via a nonradiative dipole-quadrupole interaction. The maximum quantum efficiency of coarsely samples is about 66.5%. 5) A novel green phosphor Ca8M

A structurally simple perylene dye with ethynylbenzothiadiazole-benzoic acid as the electron acceptor achieves an over 10% power conversion efficiency

On the basis of the N-annulated perylene electron donor and the ethynylbenzothiadiazole-benzoic acid electron acceptor, we herein report on synthesizing a structurally simple donor-acceptor (D-A) perylene dye C272. Without the use of any coadsorbate, we have achieved an impressive power conversion efficiency of 10.4% at air mass global (AM1.5G) conditions, which is comparable to that of the well-known zinc porphyrin dye YD2-o-C8

Pd(II)-Catalyzed Enantioselective Synthesis of P-Stereogenic Phosphinamides via Desymmetric C-H Arylation

We present the enantioselective synthesis of P-stereogenic phosphinamides through Pd-catalyzed desymmetric ortho C-H arylation of diarylphosphinamides with boronic esters. The method represents the first example of the synthesis of P-stereogenic phosphorus compounds via the desymmetric C-H functionalization strategy. The reaction proceeded efficiently with a wide array of reaction partners to afford the P-stereogenic phosphinamides in up to 74% yield and 98% ee. The efficiency was further demonstrated by gram scale syntheses. Moreover, the flexible conversion of the P-stereogenic phosphinamides into various types of P-stereogenic phosphorus derivatives was also elaborated. Thus, the protocol provides a novel tool for the efficient and versatile synthesis of P-stereogenic compounds

Improved Thermal Stability of Polymer Solar Cells by Incorporating Porphyrins

Thermal stability has been the important issue in organic solar cell, especially for the large scale fabrication and application in the future. In this work, a new strategy involving the introduction of porphyrin compound (BL) is proposed to prevent the [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) aggregation. The supramolecular interactions between PC61BM and BL are first demonstrated in PC61BM:BL binary blend, and then the effect of BL on P3HT:PC61BM blend is qualitatively and quantitatively studied by differential scanning calorimetry, UV-vis absorption spectroscopy, atomic force microscopy, optical microscopy, and fluorescence techniques. It is found that the BL addition not only stabilizes the morphology of P3HT:PC61BM blend films, but also shows a good ability to maintain the electron mobility by depressing the PC61BM crystallization. And the thermal stability of the devices based on P3HT:PC61BM:BL ternary blend films is therefore greatly improved. For example, 8 wt% BL doping drops the power conversion efficiency by 10.5% relative to its peak value after 48 h of annealing at 130 degrees C, while 71.5% of decrease is obtained for the device without BL after only 3 h of annealing. This strategy is preliminarily proved to be universal and will show great potentials in future commercialization of polymer solar cells

Aptamer-based colorimetric biosensing of abrin using catalytic gold nanoparticles

In this study we propose a simple and sensitive colorimetric aptasensor for the quantitative analysis of abrin by using catalytic AuNPs for the first time. AuNPs possess the peroxidase-like activity that can catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, leading to color change of the solution. It is interesting to find that the peroxidase-like activity of AuNPs can be improved by surface activation with a target-specific aptamer. However, with a target molecule, the aptamer is desorbed from the AuNPs surface, resulting in a decrease of the catalytic abilities of AuNPs. The color change of the solution is relevant to the target concentration, and this can be judged by the naked eye and monitored by using a UV-vis spectrometer. The linear range for the current analytical system was from 0.2 nM to 17.5 nM. The corresponding limit of detection (LOD) was 0.05 nM. Some other proteins such as thrombin (Th), glucose oxidase (GOx), and bovine serum albumin (BSA) all had a negligible effect on the determination of abrin. Furthermore, several practical samples spiked with abrin were analyzed using the proposed method with excellent recoveries. This aptamer-based colorimetric biosensor is superior to other conventional methods owing to its simplicity, low cost, and high sensitivity

High performance ethanol/air biofuel cells with both the visible-light driven anode and cathode

A membrane-less ethanol/air biofuel cell (BIC) with both the anode and cathode driven by visible light has been assembled. Simply upon a light source illumination, the BFC generates the maximum power density of 0.27 mW cm(-2) with an open circuit voltage of 1.13 V, realizing the dual route energy conversion of light energy and chemical energy to electricity, improving the energy utilization efficiency. (C) 2014 Elsevier Ltd. All rights reserved

Structurally Ordered Pt3Cr as Oxygen Reduction Electrocatalyst: Ordering Control and Origin of Enhanced Stability

Ordered intermetallic phases provide predictable control over structure and electronic effects, not afforded by the widely studied alloys. However, because of the lack of a unifying principle or model for controlling the ordering and particle size, it is still a great challenge to synthesize the desired ordered phase (5 nm and smaller). Here, we employ Pt3Cr as a typical ordered intermetallic phase to comprehensively study the factors that control both the ordering and particle size. Ordered Pt3Cr intermetallic nanopartides (similar to 5 nm) are successfully synthesized using a KCl-matrix method in combination with adjusting annealing conditions. Such structurally ordered Pt3Cr/C exhibits superior kinetics toward the oxygen reduction reaction (ORR), relative to disordered PtCr alloy phases and commercial Pt/C. More importantly, the ordered Pt3Cr intermetallic catalyst shows a minimal loss of activity after 5000 potential cycles (14.7%) and a minimal Cr leaching loss after 4 weeks of testing (13.5%). The mechanism for the enhanced stability of ordered phases is discussed and elucidated. The high stability and activity of ordered Pt3Cr/C make it very promising for application as cathode catalysts for fuel cells. This work provides a guide to optimizing the synthesis of ordered intermetallic catalysts and improving their catalytic performance

Ultrasonic synthesis of highly dispersed Au nanoparticles supported on Ti-based metal-organic frameworks for electrocatalytic oxidation of hydrazine

In this work, Au nanoparticles supported on amino-functionalized Ti-benzenedicarboxylate metal-organic frameworks (Au/NH2-MIL-125(Ti)) were prepared by a facile ultrasonic method. The complex was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy and electrochemical methods. The obtained nanocomposites exhibit excellent electrocatalytic activity toward hydrazine oxidation, which is attributed to their large specific surface area and good conductivity. In addition, we found that solution pH has an obvious effect on the electrocatalytic activity of Au/NH2-MIL-125(Ti) toward hydrazine oxidation. On this basis, we constructed a simple, sensitive, selective and inexpensive electrochemical method to detect hydrazine. A linear dynamic range of 10 nM to 100 mu M with a detection limit of 0.5 nM was obtained. It was demonstrated that the fabrication of Au NPs on amino-functionalized Ti-based MOFs could be promising for the sensing of hydrazine. Our results imply the potential application of metal nanoparticle/MOF nanocomposites in the field of electroanalytical chemistry

Hydrothermal route to crystallization of FeOOH nanorods via FeCl3 center dot 6H(2)O: effect of Fe3+ concentration on pseudocapacitance of iron-based materials

In this work, we studied the crystallization of FeOOH nanorods via hydrolysis of FeCl3 center dot 6H(2)O solution under a low-temperature hydrothermal route (100 degrees C). The effect of Fe3+ concentration and solution pH on the crystallized morphology and size of FeOOH nanorods was systematically studied based on the chemical reaction and crystallization process. The electrochemical performance of the as-obtained FeOOH materials as supercapacitors is evaluated and the effect of Fe3+ concentration on the pseudo-capacitance of iron-based materials is also discussed. FeOOH electrode materials obtained in 0.2 M FeCl3 center dot 6H(2)O solution display the highest specific capacitance of 714.8 F g(-1), which is higher than reported values for FeOOH electrode materials. The present work demonstrates a simple hydrolysis route to synthesize high capacitance electrode materials

EGFP-Based Protein Nanoparticles with Cell-Penetrating Peptide for Efficient siRNA Delivery

Development of an innovative nucleic acid nanocarriers still represents a challenge. In this study, we develop a protein nanoparticle (H6-TatEGFP) and examine its siRNA condensing activity. Gel retardation assay show that protein nanoparticle can condense siRNA into stable nanoparticle/siRNA complexes. UsingCy3-labelled siRNA, we also evaluate siRNA transport characteristic of protein nanoparticles in tumor cells, the results indicate that H6-TatEGFP nanoparticle may be a potential nanocarrier for siRNA in tumor cells