General synthesis route to fabricate uniform upconversion luminescent gadolinium oxide hollow spheres

Uniform upconversion luminescent gadolinium oxide hollow spheres were successfully synthesized via a homogeneous precipitation method with carbon spheres as template followed by a calcination process. During the annealing process, the carbon spheres template can be effectively removed and the amorphous precursor has converted to crystalline Gd2O3, which can be confirmed by the XRD and TG-DSC analysis. SEM and TEM images indicate that the Gd2O3 hollow spheres with diameters of 300-400 nm are uniform in size and distribution. The rare earth activator ions Ln3+-doped Gd2O3 hollow spheres exhibit intense upconversion luminescence with different colors under 980 nm light excitation, which may find potential applications in the fields such as drug delivery or biological labeling. Moreover, the upconversion luminescent mechanisms of the hollow spherical phosphors were investigated in detail.