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

Highlights: • Yb³⁺/Er³⁺ co-doped sesquioxides RE₂O₃ (RE = La, Gd, Lu) nanocrystals are prepared by so-gel method. • Power and temperature dependent upconversion properties have been comparatively evaluated. • The nanocrystalline systems can be used for optical thermometry in high temperature environment. 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.