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Zhou Z.,Central South University | Wang F.,Central South University | Huang K.,Central South University | Liu S.,Central South University | And 2 more authors.
Asian Journal of Chemistry | Year: 2012

Europium-doped barium magnesium aluminate was double-coated with silicon dioxide and alumina by a sol-gel method. X-ray diffraction patterns show no phase change for coated phosphors. The scanning electron microscope and energy dispersive X-ray spectrophotometer result that the single coated material was uniform silicon dioxide thin film and the double coated surface was consisted of silicon dioxide and alumina hybrid films. The transmission electron microscope images revealed that the thickness of the first layer and the second layer was 60 and 15 nm, respectively. The results of thermal stability test indicated that relative-brightness loss of un-coated, single coated and double coated phosphors was 18.29, 6.83 and 2.76 %, respectively. Colour coordinate shift (Δx, Δy) of these samples was (0.0003, 0.0082), (0.0001, 0.0042) and (0.0001, 0.0028), respectively. Barium magnesium aluminate phosphor's colour coordinate shift was reduced while thermal stability was improved by double coating, which was better than that of single coated sample, because the double coating method overcame the problem of luminescence intensity decline in the process of thickening the single coated layer. Source


Wang F.,Central South University | Zhou Z.,Central South University | Liu S.,Central South University | Zeng S.,Hunan Steady New Material Company | Jiang K.,Hunan Steady New Material Company
Asian Journal of Chemistry | Year: 2012

A highly efficient white light emitting diodes phosphor BaMgAl 10O 17: Eu 2+, Mn 2+ coating with MgF2 layer was prepared and characterized. The phosphor consisted of a host material BaMgAl 10O 17 doped with 0.05 mol % Eu 2+ and co-doped 0.05 mol % Mn 2+. The mechanism of energy transfer between Eu 2+ and Mn 2+ is dipole-quadrupole. The phosphor coated with MgF2 reveals that the durability is greatly enhanced 9.8 % comparison with uncoated phosphor after thermal degradation tests. The CIE chromaticity coordinates (0.335, 0.330) of the phosphor fabricated light-emitting diodes has a very close to that of the standard white light point of (0.333, 0.333). And the colour rendering index increases from 79 to 85 after the BaMgAl 10O 17: Eu 2+ phosphor co-doped with Mn 2+. All the result could conclude that co-doped and surface coated were two promises approaches for improving the colour rendering index of the near UV light-emitting diode and the stability of BaMgAl 10O 17: Eu 2+, Mn 2+ phosphor. Source


Fang D.,Wuhan University of Technology | Zhang M.,Wuhan University of Technology | Luo Z.,Fayetteville State University | Cao T.,Wuhan University of Technology | And 4 more authors.
Optical Materials | Year: 2014

In this study, CeO2 nanofibers and that doped with Eu3+ were prepared via a facile electrospinning route and annealed at different temperatures ranging from 500 to 900 °C. Their structures were investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoluminescence properties of the nanofibers were studied in detail. It was found that the nanofibers with Eu% concentration of 0.67 mol.% and annealed at 700 °C exhibited the highest intensities of the luminescence peaks between 550 and 650 nm. © 2014 Elsevier B.V. All rights reserved. Source


Zhou Z.,Central South University | Wang F.,Central South University | Liu S.,Central South University | Huang K.,Central South University | And 3 more authors.
Journal of the Electrochemical Society | Year: 2011

A novel broadband emission phosphor Ba3LiMgV3O 12: Eu3+ is synthesized by a solid-state reaction method. The X-ray diffraction analysis indicate that Ba3LiMgV 3O12 single phase obtained at 800C show the same crystal structure with Ba3V2O8. The excitation and emission spectra exhibit that the excitation band distributes between 260 nm and 395 nm and peaks at 343 nm, emission band covers from 400 nm to 600 nm and centers at 500 nm, respectively. The emission band peaks at 613 nm originated from charge transfer transitions from Ba3LiMgV3O 12 host to doped Eu3+ ions can be observed when the Eu3+ ions doped into the host. White light can be obtained with coordinate of (0.312, 0.321) from the fabricated light emitting diodes (LEDs) with the doped content of Eu3+ ions at 5.0 mol, which shows that the phosphor is a promising single-phase phosphor for near ultraviolet (NUV) LEDs. © 2011 The Electrochemical Society. Source

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