Green photoluminescence of Tb3+ and Ce3+ doped mullite nanoparticles

Mullite have been actively surveyed, but as luminescent host materials, lanthanide doped mullite receive little attention. In this work, terbium and cerium co-doped mullite nanoparticles have been synthesized by co-precipitation process. These as-prepared mullite nanocrystals were characterized by transmission electron microscopy. The results showed that these nanoparticles are roughly spherical in shape and vary in size from 30 to 45 nm. The phase structures of these nanoparticles were investigated by X-ray diffraction. The results indicated that these nanoparticles crystallized well, and the peak positions and intensities agree well with the data for bulk mullite. Their fluorescence properties have been explored in detail and the resulting Al₆Si₂O₁₃: 8%Tb,0.1%Ce nanoparticles showed the typical emission bands centered at 490, 542 and 590 nm.     

In-situ crystal growth and photoluminescence properties of YBO3: Tb3+ microstructures

Three-dimensional (3D) YBO₃:Tb³⁺ flower-like and dense flower-like hierarchitecture constituted of nanoflakes are solvothermally synthesized in the presence of polyborate precursors in the mixture of ethanol and water. The growth process of the YBO₃:Tb³⁺ flowers and dense flowers was explored based on the time-dependent experiment and the results showed that the growth mechanism follows an in situ growth rather than self-assembly process as reported previously. YBO₃:Tb³⁺ morphologies composed of nanoflakes are achieved by controlling the concentration of ethanol and dependence of photoluminescence on morphology was studied. Remarkable photoluminescence enhancement was observed for YBO₃:Tb³⁺ with flower-like morphology demonstrating the potential of the microstructure in future applications as a green phosphor. Such a synthetic method and growth mechanism may be applied to fabricate complex 3D architectures of other materials.     

Electrospinning preparation of LaOBr:Tb3+ nanostructures and their photoluminescence properties

Tb³⁺-doped LaOBr nanostructures including nanofibers, nanobelts, and hollow nanofibers were synthesized for the first time via calcinating the electrospun polyvinyl pyrrolidone/[La(NO₃)₃ + Tb(NO₃)₃ + NH₄Br] composites. X-ray diffraction analysis revealed that LaOBr:Tb³⁺ nanostructures are tetragonal in structure with space group of P4/nmm. The morphologies and sizes of LaOBr:Tb³⁺ nanostructures were investigated using scanning electron microscope and transmission electron microscope. Under the excitation of 254-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emissions of predominant peak at 543 nm, which is ascribed to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. It is found that the optimum doping concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanofibers is 3 %. Interestingly, we found that the luminescence intensity of hollow nanofibers is obviously greater than that of nanofibers and nanobelts for LaOBr:Tb³⁺ under the same measuring conditions. Moreover, the luminescence of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The formation mechanisms of LaOBr:Tb³⁺ nanofibers, nanobelts, and hollow nanofibers were also proposed. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

Investigations of Ce3+ co-doped SbPO4:Tb3+ nano-ribbons and nanoparticles by vibrational and photoluminescence spectroscopy

Nano-ribbons and very small nanoparticles (size 2-5 nm) of SbPO4 doped with lanthanide ions (Ce3+ and Tb3+) are prepared at a relatively low temperature of 120 degrees C based on a solution method. Detailed vibrational and luminescence studies on these samples establish that these lanthanide ions are incorporated at Sb3+ site of the SbPO4 lattice. The excitation spectrum corresponding to the Tb3+ emission and the excited state lifetime of the 5D4 level of Tb3+ ions in the sample confirm the energy transfer from Ce3+ to Tb3+ ions in the SbPO4 host. The extent of energy transfer from Ce3+ to Tb3+ in these samples is found to be around 60%. Dispersion of these nanomaterials in silica matrix effectively shields the lanthanide ions at the surface of the nano-ribbons/nanoparticles from the stabilizing ligands resulting in the reduction in the vibronic quenching of the excited state. Our results show significant reduction in the surface contribution in the decay curve corresponding to the 5D4 level of the Tb3+ ions after incorporating the nano-ribbons/nanoparticles in silica. These nanomaterials incorporated in silica matrix can have potential applications in bio-assays and bio-imaging.     

Facile template-free fabrication of olive-like ZnO nanoparticles and their photoluminescence properties

A facile template-free solvothermal approach was applied to synthesize olive-like ZnO nanoparticles with an average diameter of about 300 nm and an average length of about 600 nm. XRD, TEM, SEM, SAED, EDX and PL spectra were employed to characterize the crystal phase, morphologies, the chemical compositions, and optical properties of the ZnO nanostructure. The experimental results showed the as-obtained ZnO was single-crystalline nanostructure and the concentration of CH₃COO⁻ solution played a key role in controlling the morphology of ZnO. The growth mechanism of ZnO was tentatively investigated. Besides, the olive-like ZnO nanoparticles exhibit a very strong ultraviolet emission centered at 383 nm and a weak green luminescence emission at around 522 nm.     

Preparation and the luminescent properties of Tb3+-doped Gd2O3 fluorescent nanofibers via electrospinning

Tb(3+)-doped Gd(2)O(3) (Gd(2)O(3):Tb(3+)) nanofibers were prepared via a simple electrospinning technique using poly(ethylene oxide) (PEO) and rare-earth acetate tetrahydrates (Ln(CH(3)COO)(3)·4H(2)O (Ln = Gd, Tb)) as precursors. The obtained nanofibers have an average diameter of about 80 nm and are composed of pure cubic Gd(2)O(3) phase. A possible formation mechanism for the nanofibers is proposed on the basis of the experimental results, which reveals that PEO acts as the structure directing template during the whole electrospinning and subsequent calcination process. The luminescent properties of the nanofibers were investigated in detail. The nanofibers exhibit a favorable fluorescent property symbolized by the characteristic green emission (545 nm) resulting from the 5D4-->7F5 transition of Tb(3+). Concentration quenching occurs when the Tb(3+) concentration is 3 at.%, indicating that the Gd(2)O(3):Tb(3+) nanofibers have an optimum luminescent intensity under such a doping concentration.     

Facile fabrication of CdTe/montmorillonite nanocomposite films with stable photoluminescence properties

We report herein the facile synthesis of CdTe/montmorillonite (MMT) nanocomposite films via charge-charge interactions between the CdTe quantum dots (QDs) and MMT platelets. Firstly, negatively charged CdTe QDs were prepared with the use of thioglycolic acid (TGA) as ligand. Then hybrid of the as-prepared TGA-stabilized CdTe QDs with sodium montmorillonite (Na-MMT) and cetyltrimethylammonium-modified montmorillonite (CTA-MMT), respectively, afforded novel CdTe/MMT nanocomposite films. The structure and optical properties of CdTe/MMT nanocomposite films were thoroughly investigated by scanning electron microscope (SEM), ultraviolet transmittance reflection and photoluminescence (PL) measurements. Results showed that CdTe/(CTA-MMT) nanocomposite films exhibited highly enhanced PL intensity compared with CdTe/(Na-MMT) nanocomposite films. More importantly, CdTe QDs in CdTe/(CTA-MMT) nanocomposite films well maintained PL properties even after thermal annealing at 100 °C for 10 h.     

Sol-gel fabrication and photoluminescence properties of SiO2 @ Gd2O3:Eu3+ core-shell particles

A uniform nanolayer of europium-doped Gd2O3 was coated on the surface of preformed submicron silica spheres by a Pechini sol-gel process. The resulted SiO2 @ Gd2O3:Eu3+ core-shell structured phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays. The XRD results show that the Gd2O3:Eu3+ layers start to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. The core-shell phosphors possess perfect spherical shape with narrow size distribution (average size: 640 nm) and non-agglomeration. The thickness of the Gd2O3:Eu3+ shells on the SiO2 cores can be adjusted by changing the deposition cycles (70 nm for three deposition cycles). Under short UV excitation, the obtained SiO2@Gd2O3:Eu3+ particles show a strong red emission with 5D0-7F2 (610 nm) of Eu3+ as the most prominent group. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.     

Study on UV excitation properties of Y2O3:Ln3+ (Ln = Eu3+ or Tb3+) luminescent nanomaterials

Y2O3:Ln3+ (Ln = Eu or Tb) nanocrystals with different Ln3+ doping concentrations and average sizes were prepared by chemical self-combustion. The corresponding bulk materials with various doping concentrations were obtained by annealing the nanomaterials at high temperature. The emission spectra, excitation spectra, and X-ray diffraction spectra were used in this study. It was found that the charge transfer band of Y2O3:Eu3+ red-shifted as particle size decreased, and the charge transfer band in the 5-nm particles obviously broadened toward the long wavelength. It was also found that the profile of excitation spectra corresponding to the 4f5d (4f8 --> 4f(7)5d1) transition changed a lot with the variation of the particle size. The dependence of the excitation spectra of Y2O3:Ln3+ on particle size was investigated.     

MoO_3微纳米片的简单制备及其光致发光性能

采用简单热氧化蒸发沉积法在ITO玻璃基片上制备了大面积MoO3微纳米片。制备出的微纳米片具有良好晶体结构,其长度、宽度和片层厚度分别可达100,1~5μm和约100nm;微纳米片沿[001]方向生长,这是因为晶体各方向键合能的不同而具有不同的生长速度,其形成过程遵循气-固生长机制。光致发光谱显示室温下MoO3微纳米片同时具有紫光发射峰、蓝光发射峰和绿光发光带,发射光强度随氧化沉积温度升高而增大,这是由于温度升高,微纳米片缺陷增加导致的。     

Facile synthesis of Gd2O2SO4:Tb and Gd2O2S:Tb green phosphor nanopowders of unimodal size distribution and photoluminescence

Suppressing the crystallization and plate-like crystallite growth of RE₂(OH)₄SO₄·2H₂O compound by low-temperature (~4 °C) precipitation produced an amorphous RE₂(OH)_3.3(CO₃)_0.35SO₄·2H₂O precursor (RE = Gd_1-xTb_x) that can be decomposed to Gd₂O₂SO₄:Tb and Gd₂O₂S:Tb green phosphor nanopowders of unimodal size distributions upon calcination in air at 1000 °C (average particle size ~156.9 nm) and in hydrogen at 800 °C (average particle size ~130.2 nm), respectively. The optimal RE³⁺ concentration for precursor synthesis was determined to be ~0.10 mol/L. Through detailed characterization by XRD, FTIR, DTA/TG, FE-SEM, TEM and particle sizing, the courses of phase/morphology evolution were clarified. Photoluminescence study found that the (Gd_0.99Tb_0.01)₂O₂SO₄ and (Gd_0.98Tb_0.02)₂O₂S representative phosphors have quantum efficiencies of ~16.8% (λ_ex = 275 nm) and 38.5% (λ_ex = 286 nm), fluorescence lifetimes of ~3.70 and 1.75 ms and activation energies for thermal quenching of ~0.552 and 0.385 eV, respectively. The values are remarkably larger than those reported for Gd₂O₂S:Tb, which are considered to be due to higher purity, better crystallization and fewer luminescence-quenching defects of the product. Particularly, the (Gd_0.99Tb_0.01)₂O₂SO₄ phosphor has negative thermal quenching up to ~150 °C and can retain over 85% of its room temperature emission intensity at 250 °C, which may enlighten its application in high-power LEDs.     

准一维纳米材料的研究现状

自从碳纳米管被发现以后,一维纳米材料作为纳电子器件的重要组成部分,其合成、材料物性以及应用已经引起了人们的广泛重视.本文从一维纳米材料的制备入手,讨论了一维纳米材料的的制备方法及其各自特点,分析了一维纳米材料形成机制,并对其表征方法做了简单的介绍,根据其特殊性能分析其潜在应用.     

一维纳米结构材料研究进展

一维纳米材料在纳米电子学、纳米光电子学、超高密度存储和扫描探针显微镜等领域具有潜在的应用前景,已成为21世纪材料领域研究的热点.本文介绍了一维纳米材料的特性和制备方法,并阐述了一维纳米材料的应用状况和前景,以及国内外在一维纳米材料方面的研究进展.     

Gd3+-Tb3+能量转移与Tb3+自敏化效应对重金属锗酸盐玻璃发光性能的影响

研究了一组Tb^3 掺杂重金属锗酸盐玻璃的发光特性。玻璃样品的X射线激发发射光谱结果显示,玻璃基质中由Gd^3 离子向发光中心Tb^3 的能量转移机制以及在一定浓度范围内Tb^3 之间的交叉弛豫过程对玻璃的发光性能有重要影响。前者表现在Gd^3 紫外发射光的减弱及Tb^3 绿发射光的增强,后者则显示Tb^3 在一定浓度范围内所特有的自敏化效应,使其蓝发射光减弱、绿发射光增强。第3种稀土离子La^3 的引入对发光中心Tb^3 离子具有分离效应,使Tb^3 之间的交叉弛豫概率降低,蓝发射光增强。     

Converted growth mechanism and photoluminescence of Tb3+ doped YBO3 micropancakes and NaYF4 nanorods synthesized from the identical precursor

YBO3 micropancakes and NaYF4 nanorods were synthesized through a two-step hydrothermal chemical conversion route. The uniform sheetlike yttrium precursor was first hydrothermally prepared. Well-crystallized YBO3 and NaYF4 were then obtained at the expense of the precursor. The two steps were both carried out in aqueous conditions without any template, surfactant, or catalyst. The formation mechanisms of our samples are both governed by the dissolution-recrystallization. During the recrystallization, oriented attachment attributes most to the final morphology of our products. We have investigated the relation between their growth habits and inherent crystal structures in detail for the first time and the results afford some guidance for the green synthesis of other inorganic nano-/micro-materials with specific morphology. We have also investigated the luminescence properties of Tb3+ doped YBO3 and NaYF4, which preserved the same morphology as the undoped samples.     

Fabrication and luminescence of YF3:Tb3+ hollow nanofibers

YF₃:Tb³⁺ hollow nanofibers were successfully fabricated via fluorination of the relevant Y₂O₃:Tb³⁺ hollow nanofibers which were obtained by calcining the electrospun PVP/[Y(NO₃)₃ + Tb(NO₃)₃] composite nanofibers. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope, transmission electron microscope, and fluorescence spectrometer. YF₃:Tb³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 148 ± 23 nm. Fluorescence emission peaks of Tb³⁺ in the YF₃:Tb³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) (490, 543, 588, and 620 nm) of Tb³⁺ ions, and the ⁵D₄ → ⁷F₅ hypersensitive transition at 543 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Tb³⁺ hollow nanofibers were located in the green region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Tb³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Tb³⁺ ions and reached a maximum at 7 mol% of Tb³⁺. The possible formation mechanism of YF₃:Tb³⁺ hollow nanofibers was also discussed. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.     

ZnO一维纳米材料的制备与表征

首先以乙醇为溶剂,乙酸锌为前驱体,油酸钠为表面修饰剂,采用溶液化学法,制得ZnO纳米粒子。以自制ZnO纳米粒子为基体,通过煅烧方法制备针状ZnO纳米线束。通过紫外-可见吸收光谱(UVVis)、荧光光谱(FL)、透射电子显微镜(TEM)、X射线衍射(XRD)和扫描电子显微镜(SEM)等方法对合成的样品进行表征。结果表明,所合成ZnO纳米粒子样品UV-Vis吸收光谱在355nm给出ZnO纳米粒子的特征吸收峰,FL光谱显示在400和550nm处产生荧光发射。ZnO纳米粒子尺寸约为5nm且粒径分布较窄。自制ZnO纳米粒子样品经500℃煅烧后可得到针状ZnO纳米线束。纳米线为六方晶系纤锌矿结构ZnO单晶纳米线,长度约为10μm,直径约为100nm,长径比约为100,且具有良好的紫外发光性能。     

Mechanical force-induced assembly of one-dimensional nanomaterials

There have been intensive and continuous research efforts in large-scale controlled assembly of one-dimensional (1D) nanomaterials, since this is the most effective and promising route toward advanced functional systems including integrated nano-circuits and flexible electronic devices. To date, numerous assembly approaches have been reported, showing considerable progresses in developing a variety of 1D nanomaterial assemblies and integrated systems with outstanding performance. However, obstacles and challenges remain ahead. Here, in this review, we summarize most widely studied assembly approaches such as Langmuir-Blodgett technique, substrate release/stretching, substrate rubbing and blown bubble films, depending on three types of external forces: compressive, tensile and shear forces. We highlight the important roles of these mechanical forces in aligning 1D nanomaterials such as semiconducting nanowires and carbon nanotubes, and discuss each approach on their effectiveness in achieving high-degree alignment, distinct characteristics and major limitations. Finally, we point out possible research directions in this field including rational control on the orientation, density and registration, toward scale-up and cost-effective manufacturing, as well as novel assembled systems based on 1D heterojunctions and hybrid structures.