Abstract. The X-ray luminescence and photoluminescence of the ultradispersed Gd2O3 powders with different purity were investigated in 90-360 K temperature range. Both impurity and intrinsic optical active centers were detected. The effect of energy transfer from Gd 3+ to RE 3+ ions was observed. IntroductionGadolinium oxide is of interest as a wide-band gap insulator (Eg = 5.6 eV) for optoelectronics, photonics, fluorescence sensing, etc., because of its optical and chemical properties, in particular, the ability of being easily doped with rare-earth (RE) ions in a wide concentrations range. The trivalent RE ions doping such as Pr, Dy, Tb ions or Yb-Er, Yb-Ho, Yb-Tm pairs determines prospects of Gd2O3 as down-and up-conversion material for energy transformation devices, including solar cells [1]. Energy and quantum efficiency of oxide matrixes doped with RE 3+ is mainly determined by dynamic of excitation states of material electronic subsystem [2]. Processes of charge carrier transport, especially the probabilities of non-radiative relaxations, depend on crystal structure and defectiveness of the host lattice. In general, the low-symmetric modifications of host matrixes along with the intrinsic and impurity-related defects lead to the creation of additional luminescence quenching channels [2,3]. On the other hand, there is information about enhancement the luminescence efficiency of RE-doped phosphors after co-doping that distorts the stoichiometry of lattice [4]. Thus, the investigation of matrix role in the spectral-optical properties of RE-doped materials will make it possible to find ways for improving of their functional characteristics.In the present work we have studied the features of different excitation channels of RE luminescence in ultradispersed Gd2O3 powders and revealed the influence of intrinsic defects on energy transfer processes.