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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 8
BKCSDE 33(8)
August 20, 2012 

Highly Luminescent (Zn0.6Sr0.3Mg0.1)2Ga2S5:Eu2+ Green Phosphors for a White Light-Emitting Diode
Yong-Kwang Jeong, Dong-Hee Cho, Kwang-Bok Kim, Jun-Gill Kang*
Two-component green luminescence, Donor-Acceptor recombination, MgO coating, White LED
Green phosphors (Zn1-a-bMaM’b)xGaySx+3y/2:Eu2+ (M, M’ = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, SrCO3, Ga2O3, Eu2O3, and S with a flux NH4F using a conventional solidstate reaction. A phosphor with the composition of (Zn0.6Sr0.3Mg0.1)2Ga2S5:Eu2+ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the ZnS:Eu2+ component on excitation at 460 nm was attributed to the donor-acceptor ( ) recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.
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