We report on optical investigation of phosphate glasses doped with Yb2O3. UV-Vis and FT-NIR optical absorption, photoluminescence, time-resolved photoluminescence and refractometry techniques are used. Cluster formation of Yb3+ was not observed as well as, no evidence of cooperative luminescence among Yb3+. An exponential decay of the F-2(5/2) -> F-2(7/2) lifetime of ytterbium was found when the interionic distance decreases. The quantum efficiency and laser performance were also investigated. Relatively high figure of merit was found, 0.33 x 10(-20) cm(2) ms. The values of the minimum fraction of Yb3+ for minimum laser gain, pump saturation intensity and minimum absorbed pumping intensity were estimated. (C) 2013 Elsevier B.V. All rights reserved.