Red-orange phosphors Gd1-xPO4:Eux 3+ (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized with changing the concentration of Eu3+ 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 Eu3+ ionincreases. As for the PL properties, all of the ceramic phosphors, irrespective of Eu3+ 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 Eu3+ ion concentration, just like the grain size. An orange color stronger than the red means that 5D0→ 7F1 (magnetic dipole transition) is dominant over the 5D0→ 7F2 (electric dipole transition), and Eu3+ is located at the center of the inversion symmetry. These properties contrasted with those of a red phosphor Y1-xPO4:Eux 3+, which has a tetragonal system. Therefore, we confirm that the crystal structure of the host material has a major effect on the resulting color