Gd2O3:Yb3+ phosphor has been synthesized by the solid state reaction method with boric acid used as a flux. The resulting Gd2O3:Yb3+ phosphor was characterized by X-ray diffraction (XRD) technique, Fourier transmission infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM), and photoluminescence and thermoluminescence. The results of the XRD show that obtained Gd2O3:Yb3+ phosphor has a cubic structure. The average crystallite sizes could be calculated as 42.9？nm, confirmed by the TEM results. The study suggested that Yb3+ doped phosphors are potential luminescence material for IR laser diode pumping. 1. Introduction Luminescent materials in various forms such as colloidal, bulk, nano, crystals, and nanocrystals are of interest not only for basic research, but also for interesting application [1–3]. Rare earth activated phosphors have attracted great interest because of their marked improvements in lumen output, color rendering index, and energy efficiency, and greater radiation stability Lanthanum oxide (La2O3) is recognized as an excellent host material for rare earth (RE) with luminescence applications with a relatively low cost. These phosphors have been recognized to hold tremendous potential in the field of photonic applications. The doping concentration is controlled over a broad range without the host structure influence. The luminescent properties of RE in La2O3 nanocrystalline powders using different synthesis methods have been recently reported [4, 5]. Gd2O3 is an Ln2O3-type oxide. The Ln2O3 (Ln = Gd, Y, Sc, Lu, Dy, etc.) oxides have been extensively studied because of their optoelectronic and display applications. Gadolinium oxide (Gd2O3) has been studied widely as the host matrix for downconversion [6–8] processes because of its interesting physical properties, such as high melting point (2320°C), chemical durability, thermal stability, and low phonon energy (~600？cm？1). Gd2O3 hosts have smaller phonon energies compared to hosts such as YAG or YAP; smaller phonon energies lead to a reduction in nonradiative losses and hence lead to increases in the luminescence efficiency [9, 10]. The Yb3+ ion has several advantages compared with other rare earth ions due to its very simple energy level scheme, constituting of only two 2F5/2 and 2F7/2 levels. There is no excited state absorption, no cross-relaxation process, and no more upconversion internal mechanism able to reduce the effective laser cross section and, in addition, the intense and broad Yb3+ absorption lines are well suited for IR laser
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