The steady-state luminescence thermometry analysis was performed on thin-films of undoped Gd2O3 and Gd2O3 doped with Ho3+, Eu3+ and Er3+, created by the plasma electrolytic oxidation process. The experimental setup for luminescent measurements closely resembles the practical luminescent fiber-optic thermometer. The visible PL from Gd3+ was utilized for the luminescence intensity ratio method, exceling over the traditional method by using the thermally coupled levels, as it is superior by either better sensitivities, widened temperature range or improved temperature resolution. The relative uncertainty by our method is ~300 times lower @ 300 K for Gd2O3:Eu3+. The maximum relative sensitivities by the luminescence intensity ratio (LIR) of Gd2O3:Ho3+, Gd2O3:Eu3+ and Gd2O3:Er3+ are 0.12% @ 295 K, 0.44% @ 580 K and 1.1% @ 290 K, respectively. Line-shift showed a significant change solely for Eu3+ doped sample, by 0.076 cm−1 K−1. The full-width-half-maximum (FWHM) changes of undoped Gd2O3 and doped by Eu3+ at the high rate of 0.3 cm−1 K−1 @ 573 K and 0.53 cm−1 K−1 @ 300 K, respectively, but was marked impractical for other samples. Display omitted