Controlling the activator site to tune europium valence in oxyfluoride phosphors

Kuan Wei Huang, Wei Ting Chen, Cheng I. Chu, Shu Fen Hu, Hwo Shuenn Sheu, Bing Ming Cheng, Jin Ming Chen, Ru Shi Liu

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130 Citations (Scopus)

Abstract

A new Eu 3+-activated oxyfluoride phosphor Ca 12Al 14O 32F 2:Eu 3+ (CAOF:Eu 3+) was synthesized by a solid state reaction. Commonly red line emission was detected in the range of 570-700 nm. To achieve the requirement of illumination, this study revealed a crystal chemistry approach to reduce Eu ions from 3+ to 2+ in the lattice. Replacing Al 3+-F - by the appreciate dopant Si 4+-O 2- is adopted to enlarge the activator site that enables Eu 3+ to be reduced. The crystallization of samples was examined by powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Photoluminescence results indicated that as-synthesized phosphors Ca 12Al 14-zSi zO 32+zF 2-z:Eu (z = 0-0.5, CASOF:Eu) display an intense blue emission peaking at 440 nm that was produced by 4f-5d transition of Eu 2+, along with the intrinsic emission of Eu 3+ under UV excitation. Moreover, the effect of Si 4+-O 2- substitution involved in the coordination environment of the activator site was investigated by further crystallographic data from Rietveld refinements. The 19F solid-state nuclear magnetic resonance (NMR) data were in agreement with refinement and photoluminescence results. Furthermore, the valence states of Eu in the samples were analyzed with the X-ray absorption near edge structure (XANES). The quantity of substituted Si 4+-O 2- tunes chromaticity coordinates of Ca 12Al 14-zSi zO 32+zF 2-z:Eu phosphors from (0.6101, 0.3513) for z = 0 to (0.1629, 0.0649) for z = 0.5, suggesting the potential for developing phosphors for white light emitting diodes (WLEDs). Using an activator that is valence tunable by controlling the size of the activator site represents a hitherto unreported structural motif for designing phosphors in phosphor converted light emitting diodes (pc-LEDs).

Original languageEnglish
Pages (from-to)2220-2227
Number of pages8
JournalChemistry of Materials
Volume24
Issue number11
DOIs
Publication statusPublished - 2012 Jun 12

Keywords

  • Rietveld refinement
  • XANES
  • crystal chemistry
  • mixed valence
  • phosphor
  • solid-state NMR

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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  • Cite this

    Huang, K. W., Chen, W. T., Chu, C. I., Hu, S. F., Sheu, H. S., Cheng, B. M., Chen, J. M., & Liu, R. S. (2012). Controlling the activator site to tune europium valence in oxyfluoride phosphors. Chemistry of Materials, 24(11), 2220-2227. https://doi.org/10.1021/cm3011327