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Preparation and Photoluminescence of Green-Emitting Phosphors SrGa<sub>2</sub>S<sub>4</sub>:Eu
Preparation and Photoluminescence of Green-Emitting Phosphors SrGa2S4:Eu
Bulletin of the Korean Chemical Society. 2013. Dec, 34(12): 3919-3922
Copyright © 2013, Korea Chemical Society
  • Received : September 03, 2013
  • Accepted : September 28, 2013
  • Published : December 20, 2013
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About the Authors
Sang-Hee Na
Young-Sik Cho
Young Rag Do
Department of Chemistry, Kookmin University, Seoul 136-702, Korea
Young-Duk Huh

Abstract
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Experimental Section
SrS (99.9%, Strem Chemicals), Ga 2 S 3 (99.99%, Alfa Aesar), S (99.98%, Aldrich), Eu(NO 3 ) 3 ·5H 2 O (99.9%, Aldrich), Ga(NO3)3·xH 2 O (99.9%, Aldrich), tetramethyl ammonium chloride (Me 4 NCl, 98%, Aldrich), and dimethyldithiocarbamic acid sodium salt dihydrate (NaMe 2 dtc·2H 2 O, 98%, TCI) were used as received, without any further purification. A europium complex, (Me 4 N)Eu(Me 2 dtc) 4 , was precipitated by mixing of 10 mL of 0.25 M Me 4 NCl, 10 mL of 0.25 M Eu(NO 3 ) 3 ·6H 2 O, and 10 mL of 1.0 M NaMe 2 dtc·2H 2 O aqueous solutions at room temperature. A gallium complex, Ga(Me 2 dtc) 3 , was precipitated by mixing 10 mL of 0.25 M Ga(NO 3 ) 3 ·xH 2 O and 10 mL of 0.75 M NaMe 2 dtc·2H 2 O aqueous solutions at room temperature. The (Me 4 N)Eu(Me 2 dtc) 4 and Ga(Me 2 dtc) 3 products were filtered, and dried under vacuum at room temperature.
SrGa 2 S 4 :Eu phosphors were prepared by a solid-state reaction, with a double crucible configuration system. One crucible was nestled in the other, with activated carbon as a reduction atmosphere in between. The starting materials were SrS, Ga 2 S 3 , (Me 4 N)Eu(Me 2 dtc) 4 , S, and a flux. One of Li 2 CO 3 , Na 2 CO 3 , KBr, KI, or NaCl was used as the flux. The 0.20 mmol of flux and 50 mol of S were used, respectively. For the typical preparation of Sr 0.96 Ga 2 S 4 :0.04Eu phosphor, the mixture of 3.84 mmol of SrS, 4.0 mmol of Ga 2 S 3 , 0.16 mmol of (Me 4 N)Eu(Me 2 dtc) 4 , 50 mol S, and 0.20 mmol Li 2 CO 3 was fired at 850 ℃ for 1.5 h in a box furnace. In this SrGa 2 S 4 :Eu phosphor, the atomic molar ratio of Sr:Ga:Eu was 0.96:2:0.04. Thus, the phosphor of Sr 0.96 Ga 2 S 4 :0.04Eu formula was formed. To investigate the emission spectra dependence on the reaction temperature as one of the synthetic conditions, we used various reaction temperatures (550 ℃, 650 ℃, 750℃, 850 ℃, and 950 ℃), with the other synthetic conditions kept the same. Similarly, we also examined the various synthetic conditions (reaction time, choice of flux, and amount of activator), with the other synthetic conditions kept the same. The commercial SrGa 2 S 4 :Eu phosphor was obtained from Phosphor Tech. Ltd.
Excitation and emission spectra of the SrGa 2 S 4 :Eu phosphors were obtained by using a spectrum analyzer (DARSA, PSI). The excitation spectra were obtained by fixing the emission wavelength (λ em ) of 535 nm. Similarly, the emission spectra were obtained by fixing the excitation wavelength (λ ex ) of 465 nm, which was the wavelength of the commercial blue InGaN LED chip. The crystal structures of the SrGa 2 S 4 :Eu phosphors were analyzed by using powder Xray diffraction (XRD, Rigaku DMAX-3A) with Cu Kα radiation. The morphologies of the SrGa2S4:Eu phosphors were examined with scanning electron microscopy (SEM, Hitachi S-4300).
Acknowledgements
This work was supported by the GRRC program of Gyeonggi province (GRRC-Dankook- 2011-B02).
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