Size-dependent upconversion luminescence and temperature sensing behavior of spherical Gd2O3:Yb3+/Er3+ phosphor

Yb3+/Er3+ codoped spherical Gd2O3 phosphors with different particle sizes were prepared via a urea-assisted homogeneous precipitation process by adjusting the molar ratio of rare earth ions and urea followed by annealing at high temperature. The phases, morphologies, and luminescence properties of the as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and upconversion luminescence (UCL) spectra, respectively. The spherical Gd2O3:Yb3+/Er3+ phosphors showed size-dependent upconversion luminescence properties under the excitation of 980 nm-laser. The temperature sensing behavior of spherical Gd2O3:Yb3+/Er3+ phosphors with different particle sizes was studied based on the change of emission intensities from two thermally coupled H-2(11/2) and S-4(3/2) levels. It is interesting to observe that the sensing sensitivity of the sample increases with decreasing particle size and a sensitivity of 84 x 10(-4) K-1 was obtained for the sample with a particle size of 45 nm. Finally, Judd-Ofelt theory was used for explaining and predicting the effect of particle size on sensing sensitivity.