Sol-gel prepared Yb3+/Er3+ co-doped RE2O3 (REÂ =Â La, Gd, Lu) nanocrystals: Structural characterization and temperature-dependent upconversion behavior

RE2O3 (RE = La, Gd, Lu) co-doped with Yb3+ and Er3+ nanocrystals were synthesized by sol-gel method. Phase evolutions upon the calcination temperature were studied. The structural parameters of the RE2O3 systems were refined by the Rietveld method based on the powder XRD data. Upconversion (UC) properties with 980-nm NIR excitation as well as the mechanism were investigated. The temperature dependent UC behaviors and the optical temperature sensing properties based on the fluorescence intensity ratio (FIR) of the Er3+ green UC emissions were studied comparatively. Result reveals that the Lu2O3 system exhibits the strongest UC luminescence while the La2O3 system exhibits the highest temperature sensitivity among the three nanocrystals, and the Gd2O3 system exhibits an intermediate performance among the three systems. However, taking into account of the preparation, emission intensity, and sensor sensitivity, the Gd2O3 system in between should be the optimum candidate for optical temperature sensing application among the three systems.