Here we report on the effect of potassium or yttrium on the luminescence spectroscopic properties of Yb 3+-doped germano-gallate glasses as well as the ability to shape them into optical fibers with the objective of using such glasses to produce near-infrared optical gain medium. Two ytterbium-doped germano-gallate glass systems, (100-x) (28Ga 2 O 3-37GeO 2-23BaO-12K 2 O)-xYb 2 O 3 (x = 0, 0.5 and 3 mol.%) and 29.6Ga 2 O 3-39.1GeO 2-24.3BaO-7 (yY 2 O 3-zYb 2 O 3) (y = 6.5, 4, 0 and z = 0.5, 3, 7 mol% respectively) have been prepared and the systematic investigation of their thermal, structural, optical and spectroscopic properties have been carried out. The increase in ytterbium oxide content leads to an increase of the glass transition temperature, crystallization temperature and the density of the glasses, as well as induces a red-shift of the cutoff wavelength. Raman spectroscopy analysis shows that both ytterbium oxide addition and potassium substitution by yttrium modify the 3D interconnected germano-gallate glass network. Lifetime diminishes with the increase of Yb 3+ concentration but remains higher in the yttrium-containing glasses. We demonstrate that the production of crystal-free light guiding fibers via the preform-to-fiber approach becomes possible only in the yttrium-containing glass system. Cutback optical attenuation measurements of the produced fibers show minimum losses of 3.3 dB/m at 1310 nm.Read less <