Yb-doped Lu2O3 crystals of very high optical quality have been grown by the heat exchanger method from a Re-crucible using high-purity raw materials and an improved crystal growth technique. The composition of the grown crystals has been determined by microprobe analysis. The fluorescence lifetime, measured by the pinhole method, revealed no concentration quenching up the maximum grown doping concentration of 10 at%. Laser operation of these high-purity samples was studied in a nearly concentric resonator under Ti:sapphire pumping. Compared to previous results the cw laser efficiency of Yb:Lu2O3 could be increased considerably to a maximum slope efficiency of ηs=86% and 76% at a laser wavelength of 1034 and 1080 nm, respectively.