Measurements of the key thermo-optical properties of Yb3+ in sesquioxides ceramics Y2O3, Sc2O3 and Lu2O3 are done at room and cryogenic temperatures. We show that laser performances are improved at low temperatures. We obtain a maximum output energy of 570 mJ, corresponding to a slope efficiency of nearly 40%, in free running regime at 1 Hz with a 10 at. % Yb:Y2O3 ceramic at 77 K. Temperature effects on the emitted wavelength are also investigated. Room temperature measurements, using both "laser flash" and "hot disk" methods, lead to thermal conductivity values of
ytterbium doped Y2O3 ceramics of 6.3 W/m.K and 5.3 W/m.K respectively. We also show that the thermal expansion
coefficients of a 10 at. % Yb:Y2O3 and a 20 at. % Yb:YAG are divided by a factor two between 293 K and 130 K.
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