Er$^{3+}$and Yb$^{3+}$ co-doped Gd$_{(0.85-x)}$AlO$_{3}$:Yb$_{0.15}^{3+}$, Er$_{x}^{3+}$ ($x$ = 0.06, 0.09, 0.12 and 0.15) polycrystalline powders have been prepared by using a solid-state reaction method. The crystallinity of the powders shows a polycrystalline orthorhombic system. For the down-conversion photoluminescence, through the direct excitation of Er$^{3+}$ ions using a wide emission spectrum in the range of 420 ~ 500 nm from the host crystal and 520 ~ 570 nm from the Er$^{3+}$ ions has been observed. The up-conversion photoluminescence properties of Gd$_{(0.85-x)}$AlO$_{3}$:Yb$_{0.15}^{3+}$, Er$_{x}^{3+}$ phosphors were investigated in detail. The green and the red up-conversion emissions from the phosphors were observed under an excitation at 980 nm by using a semiconductor laser. The powders exhibited strong green and weak red up-conversion emission peaks at 545 and 657 nm, respectively. The luminescence intensity showed the different Er$^{3+}$ concentration dependencies for the up- and down-conversion luminescence behaviors due to the difference in their luminescence mechanisms. The maximum intensities for the up- and down-conversion luminescence occurred at Er$^{3+}$ ions 0.12 and 0.09 mol, respectively.

Keywords: GdAlO$_{3}$, Yb$^{3+}$/Er$^{3+}$-doped, Phosphors, Down-conversion, Up-conversion