Rapid progress in nanotechnology and biomedicine led to the high demand for accurate and contactless thermal sensing in real time. To address this issue, dual-doped Gd2O3:Tb3+,Eu3+ nanopowders were suggested as ratiometric thermometers within a fairly wide temperature range of 123–473 K. Here, we studied calcination temperature effect on structure, morphology, luminescence and thermometric properties. Luminescence intensity ratios between the Tb3+ and Eu3+ transitions were successfully utilized as temperature dependent parameters. Relative thermal sensitivities of synthesized samples were found to be in the middle range (0.49–0.82% K-1) at room temperature, while their values strongly increased at moderately high temperatures. All regarded thermometers could provide sub-degree sensing based on LIR1 monitoring. The growth of the calcination temperature results in an enhancement of thermometric performances. The best thermometer Gd2O3:Tb3+,Eu3+ 1100 oC displayed a sensitivity of 5.04% K-1@473 K and 0.3 K resolution. The obtained results can be used for the construction of thermal sensors with improved thermometric characteristics at moderately high temperatures.