White-Light-Emitting Diodes Using Red-Emitting LiEu(WO[sub 4])[sub 2−x](MoO[sub 4])[sub x] Phosphors

The fundamental luminescence and chromaticity properties of a class of red-emitting phosphors Li Eu ( W O 4 ) 2 − x ( Mo O 4 ) 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 Eu 3 + transitions in near-UV and visible regions, and red emissions are assigned to intraconfigurational 4f-4f transitions of Eu 3 + . Both PL and PLE intensity were found to increase with increasing doped Mo content. The intensity of the D 0 5 → F 2 7 emission of Eu 3 + 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 Li Eu ( Mo O 4 ) 2 and it reached the same level as the commodity phosphor Y 2 O 2 S : Eu 3 + . A white-light-emitting diode fabricated using the composition-optimized Li Eu ( Mo O 4 ) 2 and the matching green- and blue-emitting phosphors shows that the quality of red color reproduction based on Li Eu ( Mo O 4 ) 2 was found to be much higher and improved than that using La 2 O 2 S : Eu 3 + .