White-light-emitting diodes using red-emitting LiEu(WO4)2-x(MoO4)x phosphors

The fundamental luminescence and chromaticity properties of a class of red-emitting phosphors LiEu(WO4)(2-x)(MoO4)(x) under near-UV excitation have been investigated. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra reveal that the absorption is mainly attributed to O -> Mo(W) charge transfer at 300 nm and the Eu3+ transitions in near-UV and visible regions, and red emissions are assigned to intraconfigurational 4f-4f transitions of Eu3+. Both PL and PLE intensity were found to increase with increasing doped Mo content. The intensity of the D-5(0) -> F-7(2) emission of Eu3+ activated at 394 nm was found to reach a maximum when the relative ratio of Mo/W was 2:0. The CIE chromaticity coordinates were found to be (0.66, 0.33) for LiEu(MoO4)(2) and it reached the same level as the commodity phosphor Y2O2S:Eu3+. A white-light-emitting diode fabricated using the composition-optimized LiEu(MoO4)(2) and the matching green- and blue-emitting phosphors shows that the quality of red color reproduction based on LiEu(MoO4)(2) was found to be much higher and improved than that using La2O2S:Eu3+. (C) 2007 The Electrochemical Society.