Luminescent properties of R 2(MoO 4) 3:Eu 3+ (R=La, Y, Gd) phosphors prepared by sol–gel process

Abstract

A series of red phosphors R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) have been synthesized by sol–gel method. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry–differential thermal analysis (TG–DTA), and the properties of these resulting phosphors have also been characterized by photoluminescence (PL) spectra and reflectance spectra. Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and the size of the samples. The results of TG–DTA and XRD indicated that all of the R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) phosphors crystallized completely at 650 °C. Y 0.8Eu 1.2(MoO 4) 3 and Gd 0.8Eu 1.2(MoO 4) 3 have two structures, monoclinic and orthorhombic, while La 0.8Eu 1.2(MoO 4) 3 only adopts monoclinic structure. The luminescent properties of phosphors R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) are dependent on their structures to some extent. The orthorhombic Y 0.8Eu 1.2(MoO 4) 3 and Gd 0.8Eu 1.2(MoO 4) 3 phosphors show very similar luminescent properties, which differ from those of phosphors with monoclinic structure. For all of R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) phosphors, intense red emission is obtained by exciting at ∼394 and ∼465 nm which are owing to the sharp 7F 0→ 5L 6 and 7F 0→ 5D 2 lines of Eu 3+. Two strongest lines at 394 and 465 nm in excitation spectra of these phosphors match well with the two popular emissions from near-UV and blue GaN-based LEDs, so they could be used as red components for white light-emitting diodes.