Effects of Eu^(3+) Concentration on the Photoluminescence Properties of Red-orange Phosphor Gd_(1-x)PO_4:Eu_x^(3+)

Abstract

Red-orange phosphors <TEX>$Gd_{1-x}PO_4:{Eu_x}^{3+}$</TEX> (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized with changing the concentration of <TEX>$Eu^{3+}$</TEX> ions using a solid-state reaction method. The crystal structures, surface morphology, and optical properties of the ceramic phosphors were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectrophotometry. The XRD results were in accordance with JCPDS (32-0386), and the crystal structures of all the red-orange phosphors were found to be a monoclinic system. The SEM results showed that the size of grains increases and then decreases as the concentration of <TEX>$Eu^{3+}$</TEX> ionincreases. As for the PL properties, all of the ceramic phosphors, irrespective of <TEX>$Eu^{3+}$</TEX> ion concentration, had orange and red emissions peaks at 594 nm and 613 nm, respectively. The maximum excitation and emission spectra were observed at 0.10 mol of <TEX>$Eu^{3+}$</TEX> ion concentration, just like the grain size. An orange color stronger than the red means that <TEX>$^5D_0{\rightarrow}^7F_1$</TEX> (magnetic dipole transition) is dominant over the <TEX>$^5D_0{\rightarrow}^7F_2$</TEX> (electric dipole transition), and <TEX>$Eu^{3+}$</TEX> is located at the center of the inversion symmetry. These properties contrasted with those of a red phosphor <TEX>$Y_{1-x}PO_4:{Eu_x}^{3+}$</TEX>, which has a tetragonal system. Therefore, we confirm that the crystal structure of the host material has a major effect on the resulting color.