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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 9
BKCSDE 34(9)
September 20, 2013 

Pycnometric and Spectroscopic Studies of Red Phosphors Ca(1– 1.5x)2+ WO4:Eux3+ and Ca(1– 2x)2+ WO4:Eux3+,Nax+
Seon-Woog Cho
Scheelite, Ca(1– 1.5x)Eux3+ WO4, Ca(1−2x)Eux3+Nax+ WO4, Gas pycnometer, Raman and FT-IR
Red phosphors Ca(1−1.5x)EuxWO4 and Ca(1−2x)EuxNaxWO4 were synthesized with various concentrations x of Eu3+ ions by using a solid-state reaction method. The crystal structure of the red phosphors were found to be a tetragonal scheelite structure with space group I41/a. X-ray diffraction (XRD) results show the (112) main diffraction peak centered at 2θ = 28.71o, and indicate that there is no basic structural deformation caused by the vacancies VCa'' or the Eu3+ (and Na+) ions in the host crystals. Densities of Ca(1−1.5x)EuxWO4 were measured on a (helium) gas pycnometer. Comparative results between the experimental and theoretical densities reveal that Eu3+ (and Na+) ions replace the Ca2+ ions in the host CaWO4. Also, the photoluminescence (PL) emission and photoluminescence excitation (PLE) spectra show the optical properties of trivalent Eu3+ ions, not of divalent Eu2+. Raman spectra exhibit that, without showing any difference before and after the doping of activators to the host material CaWO4, all the gerade normal modes occur at the identical frequencies with the same shapes and weaker intensities after the substitution. However, the FT-IR spectra show that some of the ungerade normal modes have shifted positions and different shapes, caused by different masses of Eu3+ ions (or Na+ ions, or VCa'' vacancies) from Ca2+.
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