Nanostructured Yb3+/Er(3+)co-doped La2O3 with intense green-light emission has been successfully synthesized by solvothermal method with further calcination. The prepared La2O3: Yb3+, Er3+ are composed of approximate spherical nanoparticles with the size of about 50 nm. Optical temperature sensing performances depended on the thermally coupled levels of Er3+ are evaluated by analyzing temperature-dependent up-conversion luminescence (UCL) spectra, and the maximum sensitivity is 0.0040 K-1 at 315 K in the physiological working temperature range (295 K-315 K). Furthermore, the heating effect is also investigated, which causes the temperature of the samples to increase from 300 to 341 K with the variation of power density from 7.08 to 26.19 W/cm(2). In addition, cell toxicity experiment shows that the La2O3 has low cell cytotoxicity, and the confocal images of samples in HeLa cells are also obtained. All the results indicate that the nanostructured La2O3: Yb3+/Er3+ also may be used as fluorescent bio-imaging. (C) 2017 Elsevier Ltd. All rights reserved.