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Qiu K.,Tianjin University of Technology | Tian H.,Tianjin University of Technology | Song J.,Tianjin University of Technology | Mao Z.,CAS Shanghai Institute of Ceramics | And 3 more authors.
Journal of Rare Earths | Year: 2012

Europium-doped borosilicate glasses were prepared by melt-quenching procedure in the air. The mixed valence of Eu 2+ and Eu 3+ was identified by photo luminescence spectrum and electron paramagnetic resonance (EPR). The existence of mixed valence was observed owing to the unequivalent substitution and de-polymerization network of the as-prepared borosilicate glasses. The variation of the glass composition in B 2O 3/BaO ratios changed the stability of the Eu 3+ ions distinctly. In particular, as-prepared borosilicate glasses exhibited a tri-wavelength light excitable spectra centered at 397, 466 and 534 nm to give the broadened orange-red emission at around 592 and 617 nm, due to supersensitive transitions of Eu 3+ ions. This simultaneous tri-wavelength excitation happened to correspond with the emitting wavelength from near ultraviolet, blue AlInGaN chips and that from YAG:Ce 3+. The total quantum yield (QY) of the Eu-doped glasses under 466 nm excitation was evaluated to be 10, potentially providing a versatile combination with the europium-doped borosilicate glasses for red component addition to improve the quality of white light. © 2012 The Chinese Society of Rare Earths. Source


Lu Q.-F.,Tianjin University of Technology | Li J.,Tianjin University of Technology | Wang D.-J.,Tianjin University of Technology | Wang D.-J.,Tianjin Key Laboratory for Photoelectronic Materials and Devices
ECS Solid State Letters | Year: 2012

Intensification of the photosynthetic action spectrum (PAS) of Ba 3MgSi2O8:Eu2+, Mn2+ (BMS-EM) with a simultaneous emission peaked at 620 nm and 430 nm is investigated via template-free spray pyrolysis (SP) followed by post-annealing. The cage-like sphere of phase-pure BMS-EM with a nano-porous shell composed of building blocks of nanocrytals, exhibits a high harvesting of incident photonic energy as verified with Diffuse Reflection Spectra (DRS) and microscopic observation, respectively. The enhanced emission of BMS-EM, which is related to the light-trapping effect, shows great promise to improve the eco-lighting devices currently used for plant cultivations. © 2012 The Electrochemical Society. Source


Wang P.,Tianjin University of Technology | Wang D.-J.,Tianjin University of Technology | Wang D.-J.,Tianjin Key Laboratory for Photoelectronic Materials and Devices | Song J.,Tianjin University of Technology | And 3 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2012

The role of Si 4+ in the valence state of Ce and phase control in YAG:Ce phosphors was investigated upon incorporation of Si-O in the form of SiO 2. By varying the amount of SiO 2 addition, the valence state of tetravalent and trivalent Ce ions was identified distinctly by X-ray photoelectron spectroscopy and the phase purity of YAG host phase was examined by X-ray diffraction patterns. The self-reduction phenomena from Ce 4+ to Ce 3+ in YAG:Ce samples was observed to be featured in a typical 5d → 4f yellow-green transition of Ce 3+ ion upon firing in air, driven by charge compensation for imbalance substitution of Ce 4+ for Y 3+. The addition of SiO 2 promotes further reduction of Ce 4+ to Ce 3+ in an amount up to 7.0 wt%, owing to spontaneous charge compensation, and suppresses the formation of YAP (yttrium aluminate perovskite, YAlO 3) and YAM (yttrium aluminate monoclinic, Y 4Al 2O 9). The results reveal the role of SiO 2 addition in a proper amount to be able to achieve desired luminous center of Ce 3+ and phase-pure YAG for a series of YAG hosted luminescence materials such as blue-excitable YAG phosphor or laser-pumped YAG-based transparent ceramics or glass ceramics for lighting and display purposes. © Springer Science+Business Media, LLC 2012. Source


Tian H.,Tianjin University | Tian H.,Tianjin University of Technology | Tian H.,Tianjin Key Laboratory for Photoelectronic Materials and Devices | Wang D.-J.,Tianjin University of Technology | And 4 more authors.
Faguang Xuebao/Chinese Journal of Luminescence | Year: 2011

Calcium silicate glass-ceramic phosphor with green emission was evaluated. The effect of crystals precipitation microstructure on spectral properties was investigated by changing the holding time at melting temperature. With the in crease of holding duration, the amount ratio of luminous β-Ca 2SiO 4:Eu 2+ crystalline phase to glassy phase tended to be decreased, leading to a red-shift of the emission band and exhibiting more transparent of the glass-ceramic phosphor. The precipitation of SiO 2 crystals in priority was proposed. The broad excitation band of the green-emitting glass-ceramic phosphors covers the wavelength from 270 to 440 nm, showing the potential for the high-power phosphor-converted LED. Source


Lu Q.-F.,Tianjin University of Technology | Lu Q.-F.,Tianjin Key Laboratory for Photoelectronic Materials and Devices | Li J.,Tianjin University of Technology | Wang D.-J.,Tianjin University of Technology | Wang D.-J.,Tianjin Key Laboratory for Photoelectronic Materials and Devices
Current Applied Physics | Year: 2013

A single-phased (Ba,Sr)3MgSi2O8:Eu 2+, Mn2+ phosphor with 660 nm-featured dual band-emission is investigated upon optimizing composition to simulate the artificial photosynthetic action spectrum (PAS) for near-ultraviolet (NUV) biological light-emitting diodes (bio-LEDs). A specific composition range in Ba -Sr binary solid solution of (Ba,Sr)3MgSi2O8 is found to be capable of obtaining single-phased host in the absence of an easily formed orthosilicate impurity, leading to a 660 nm-featured red band emission of Mn2+ induced by an efficient energy transfer from a co-doped blue-emitting Eu2+ sensitizer. This dual broad band emission phosphor has a 72 nm full width at half maximum (FWHM) for red band that covers fairly well to the absorption spectrum of chlorophyll and PAS for most plants, enabling a flexible option in the application of bio-illumination for artificial photosynthesis. © 2013 Elsevier B.V. All rights reserved. Source

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