Enhanced luminescence of gadolinium niobates by Bi3+ doping for field emission displays

Blue emitting GdNbO4: Bi3+ powder phosphors for field emission displays were prepared by a solid state reaction. Both photoluminescence and cathodoluminescence properties of the materials were investigated. GdNbO4 itself shows only a very weak luminescence in the blue spectral region. By doping Bi3+ in GdNbO4, the luminescence intensity was improved greatly. The emission spectrum of the GdNbO4: Bi3+ consists of a broad band with maximum at 445 nm (lifetime = 0.74 mu s; CIE chromaticity coordinates: x = 0.1519 and y = 0. 1196) for both UV and low voltage (1-7 kV) cathode ray excitation. In GdNbO4:Bi3+ phosphors, the energy transfer from NbO43- to activator Bi3+ occurred.

Sol-gel deposition and luminescence properties of LiYF4 : Tb3+ thin films

Tb3+-doped LiYF4 films were deposited on quartz glass by a simple sol-gel method. X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), photoluminescence spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 300 degrees C and fully crystallized at 400 degrees C. AFM and FESEM images of singly coated LiY0.95Tb0.05F4 annealed at 400 degrees C indicated that the film is uniform and crack-free films with average grain size of 90 nm, root mean square roughness of 11 nm and thickness of 120 nm. The doped Tb3+ ions showed its characteristic emission in crystalline LiYF4 films, i.e., D-5(3), F--7(4)J (J = 6, 5, 4, 3) emissions. The optimum doping concentration of the Tb3+ was determined to be 5.0 mol% of Y3+ in LiYF4 films.

The luminescence of CaYBO4 : RE3+ (RE=Eu, Gd, Tb, Ce) in VUV-visible region

Phosphors CaYBO4:RE3+ (RE = Eu, Gd, Tb, Ce) were synthesized with the method of solid-state reaction at high temperature, and their vacuum ultraviolet (VUV)-visible luminescent properties in VUV-visible region were studied at 20 K. In CaYBO4, it is confirmed that there are two types of lattice sites that can be substituted by rare-earth ions. The host excitation and emission peaks of undoped CaYBO4 are very weak, which locate at about 175 and 350-360nm, respectively. The existence of Gd3+ can efficiently enhance the utilization of host absorption energy and result in a strong emission line at 314 nm. In CaYBO4, Eu3+ has typical red emission with the strongest peak at 610 nm; Tb3+ shows characteristic green emission, of which the maximum emission peak is located at 542 nm. The charge transfer band of CaYBO4:Eu3+ was observed at 228 nm; the co-doping of Gd3+ and Eu3+ can obviously sensitize the red emission of Eu3+. The fluorescent spectra of CaYBO4:Ce3+ is very weak due to photoionization; the co-addition of Ce3+-Tb3+ can obviously quench the luminescence of Tb3+.

Synthesis and luminescence properties of nanocrystalline Gd2O3 : Eu3+ by combustion process

The nanocrystalline Gd2O3:Eu3+ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 45, and 23 run for the precursor and samples annealed at 600, 700 and 800 degrees C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O-2-Eu3+ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu3+ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu3+, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu3+ ions.

Mn~(2+)-NaY型分子筛作为口服胃肠道MRI造影剂的研究

用离子交换法制备了Mn2+交换的NaY分子筛MnNaY,用红外光谱(IR)和X射线粉末衍射(XRD)等方法进行了表征.研究了Mn2+含量为3.2%的样品在酸性水溶液中的稳定性和离子交换选择性.弛豫时间测量和体内磁共振成像实验表明其弛豫效率变化范围为4.9～9.7mmol·L·s-1,高于目前临床所用造影剂Gd-DTPA,对胃部MRI信号具有良好的增强效果.它是比较好的潜在口服胃肠道造影剂.

Mn(II)-monosubstituted polyoxometalates as candidates for contrast agents in magnetic resonance imaging

Two mono-substituted manganese polyoxometalates, K6MnSiW11O39 (MnSiW11) and K8MnP2W17O61 (MnP2W17), have been evaluated by in vivo and in vitro experiments as the candidates of potential tissue-specific contrast agents for magnetic resonance imaging (MRI). T-1-relaxivities of 12.1 mM(-1) s(-1) for MnSiW11 and 4.7 mM(-1) s(-1) for MnP2W17 (400 MHz, 25 degrees C) were higher than or similar to that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in BSA and hTf solutions were also reported. After administration of MnSiW11 and MnP2W17 to Wistar rats, MR imaging showed longer and remarkable enhancement in rat liver and favorable renal excretion capability. The signal intensity increased by 74.0 +/- 4.9% for the liver during the whole imaging period (90 min) and by 67.2 +/- 5.3% for kidney within 20-70 min after injection at 40 +/- 3 mu mol kg(-1) dose for MnSiW11. MnP2W17 induced 71.5 +/- 15.1%. enhancement for the liver in 10-45 min range and 73.1 +/- 3.2% enhancement for kidney within 5-40 min after injection at 39 +/- 3 mu mol kg(-1) dose. In vitro and in vivo study showed MnSiW11 and MnP2W17 being favorable candidates as the tissue-specific contrast agents for MRI.

Silica-coated Y2O3 : Eu nanoparticles and their luminescence properties

Crystalline Y2O3:Eu is of paramount significance in rare earth materials and research on luminescence spectra. In this work, the nanocrystalline Y2O3:Eu was coated with silica by a facile solid state reaction method at room temperature. The transmission electron microscope (TEM) photographs showed that the prepared Y2O3:Eu particle is polycrystalline with the size of 20 nm, the size of silica-coated particle is about 25 nm. The XPS spectra indicated that the silica layer is likely to interact with Y2O3:Eu by a Si-O-Y chemical bond. The luminescence spectra showed that the intensity of ground samples is lower than that of unground ones, the intensity of silica-coated phosphors is higher than that of the ground samples, while almost the same as that of the unground ones. Therefore, the silica coating decreases the surface defects of nanoparticles of the nanocrystalline Y2O3:Eu, thus increasing their luminescent intensity.

Sonochemical synthesis and luminescence properties of single-crystalline BaF2:Eu3+ nanospheres

BaF2 nanocrystals doped with 5.0 mol% Eu3+ has been successfully synthesized via a facile, quick and efficient ultrasonic solution route employing the reactions between Ba(NO3)(2), Eu(NO3)(3) and KBF4 under ambient conditions. The product was characterized via X-ray powder diffraction (XRD), scanning electron micrographs (SEM), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra. The ultrasonic irradiation has a strong effect on the morphology of the BaF2:Eu3+ particles. The caddice-sphere-like particles with an average diameter of 250 nm could be obtained with ultrasonic irradiation, whereas only olive-like particles were produced without ultrasonic irradiation. The results of XRD indicate that the obtained BaF2:Eu3+ nanospheres crystallized well with a cubic structure. The PL spectrum shows that the BaF2:Eu3+ nanospheres has the characteristic emission of Eu3+ D-5(0)-F-7(J) (J = 1-4) transitions, with the magnetic dipole D-5(0)-F-7(1) allowed transition (590 nm) being the most prominent emission line.

Hydrothermal synthesis of Fe and Mn doped SnO2 and its magnetic structures

The dilute magnetic semiconductor of Sn1-x-yMnxFeyO2 (0 <= x <= 0.10, 0 <= y <= 0.10) Were syhthesized with the hydrothermal method using SnCl4, Mn(CH3COO)(2) center dot 4H(2)O and FeCl3 center dot 6H(2)O as the raw materials. The structure, morphologies and magnetic properties of the sample were characterized via X-ray powder diffractometer(XRD), transmission electron microscopy(TEM), Raman spectrum and superconducting and quantum interference device(SQUIT), and Mossbeaur spectrum. No secondary phase was found in the XRD spectrum. The morphology of the samples is affected by the kind or the mount of transition metal. The local vibrating model-of Mn Positioned SnO2 sites was found in Raman spectrum. The measured magnetic results indicate that when x = 0.10, y = 0, the sample exhibits strong magnetization in low-temperature (5 K), but the magnetization decrease rapidly at room. temperature; In contrast, when x = 0, y = 0.1, the sample's magnetization and coercivity are both small, but being temperature independent. Mossbeaur spectra indicates that part of the Fe is ferromagnetic coupled, and the simulating results indicate that the ferromagnetic character is intrinsic.

Oriented growth and luminescence of ZnO : Eu films prepared by sol-gel process

A series of Eu3+-doped ZnO films have been prepared by a sol-gel method. These films were characterized by X-ray diffraction (XRD) and photoluminecent spectra (PL). Effects of synthetic parameters, such as annealing atmosphere, temperature and concentration of doped ions, on the highly oriented crystal growth were studied in detail. The crystalline structures of films annealed in vacuum have a wurtzite symmetry with highly c-axis orientation. A characteristic D-5(0) -> F-7(J)(J = 1, 2, 3 and 4) red emission is observed due to energy transfer from the ZnO host to the doped Eu3+ in the c-oriented ZnO films.

White electroluminescence from a single polymer system: Improved performance by means of enhanced efficiency and red-shifted luminescence of the blue-light-emitting species

High-efficiency white electrolurninescence from a single polymer is achieved by enhancing the electroluminescence efficiency and effecting a red-shift in the emission spectrum of the blue emissive species. A single-layer device of the resultant polymer exhibits a higher luminous efficiency than the nonmodified species (12.8 cd A(-1), see figure) and an external quantum efficiency of 5.4 % with CIE coordinates of (0.31,0.36), exemplifying the success of the reported methodology.

Synthesis, structure and luminescence properties of zinc (II) complexes with terpyridine derivatives as ligands

Five zinc (II) complexes (1-5) with 4 '-phenyl-2,2 ':6 ',2 ''-terpyridine (ptpy) derivatives as ligands have been synthesized and fully characterized. The para-position of phenyl in ptpy is substituted by the group (R), i.e. tert-butyl (t-Bu), hexyloxy (OHex), carbazole-9-yl (Cz), naphthalen-1-yl-phenyl-amine-N-yl (NPA) and diphenyl amine-N-yl (DPA), with different electron-donating ability. With increasing donor ability of the R, the emission color of the complexes in film was modulated from violet (392 nm) to reddish orange (604 nm). The photoexcited luminescence exhibits significant solvatochromism because the emission of the complexes involves the intra-ligand charge transfer (ILCT) excited state. The electrochemical investigations show that the complexes with stronger electro-donating substituent have lower oxidation potential and then higher HOMO level. The electroluminescence (EL) properties of these zinc (II) complexes were studied with the device structure of ITO/PEDOT/Zn (II) complex: PBD:PMMA/BCP/AlQ/ LiF/Al. Complexes 3, 4 and 5 exhibit EL wavelength at 552, 600 and 609 nm with maximum current efficiency of 5.28, 2.83 and 2.00 cd/A, respectively.

Electrogenerated chemi luminescence from Ru(BPY)(3)(2+) ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films.

Synthesis and luminescence properties of Gd2O3 : Eu3+ phosphors

Gd2O3: EU3+ phosphors were prepared by urea homogeneous precipitation with different surfactant and sol-gel method. XRD patterns show that all the obtained samples are in cubic Gd2O3, and the results of FTIR and fluorescent spectra conformed that OP is a good surfactant for preparing the Gd2O3: Eu3+ phosphors. The SEM photographs show that the particles prepared by urea homogeneous precipitation method are all spherical and well-dispersed, and grain morphology can be controlled by different surfactant. XRD and SEM indicate that the particle sizes prepared by sol-gel method are in the range of 5 similar to 30 nm, and the grain sizes increase with increasing of heated temperatures. Luminescence spectra indication that the main emission peaks of all samples are at 610 nm, the intensities are different from samples prepared with different surfactant and the luminescence intensities increase with increasing of annealed temperatures.