Luminescence Properties of Gd-2(MoO4)(3) Modified with Sm(III) and Tb(III) for Potential LED Applications

Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97-y SmyTb0.03(MoO4)(3) (y = 0.01-0.11, step 0.02) and Gd1.95-xSm0.05Tbx(MoO4)(3) (x = 0.01-0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd1.97-ySmyTb0.03(MoO4)(3) and Gd1.95-xSm0.05Tbx(MoO4)(3) changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 mu m. Based on a Williamson-Hall plot, the size of the crystallites was determined to be in the range of 42-60 nm for modified and pure Gd-2(MoO4)(3) samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd-2(MoO4)(3) emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors.