Facile fabrication and photoluminescence properties of rare-earth-doped Gd2O3 hollow spheres via a sacrificial template method

Rare-earth-doped gadolinium oxide (Gd2O3) hollow spheres were successfully fabricated on a large scale by using PS spheres as sacrificed templates and urea as a precipitating agent, which involved the deposition of an inorganic coating Gd(OH)CO3 on the surface of PS spheres and subsequent calcination in the air. Various approaches including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), as well as photoluminescence spectroscopies were used to characterize the samples. The results indicate that the sample is composed of uniform hollow Gd2O3 spheres with a mean particle size of about 2.3 mu m and these hollow spheres have the mesoporous shell that are composed of a large amount of nanoparticles. The possible mechanism of evolution from PS spheres to the amorphous precursor and to the final hollow Gd2O3 spheres have been proposed. The as-obtained samples show strong light emission with different colors corresponding to different Ln(3+) ions under ultraviolet-visible light and electron-beam excitation. Under 980 nm NIR irradiation, Gd2O3:Ln(3+) (Ln(3+) = Yb3+/Er3+, Yb3+/Tm3+ and Yb3+/Ho3+) exhibit characteristic up-conversion (UC) emissions of red (Er3+, H-2(11/2), S-4(3/2), F-4(9/2) -> I-4(15/2)), blue (Tm3+, (1)G(4) -> H-3(6)) and green (Ho3+, F-5(4), S-5(2) -> I-5(8)), respectively. These merits of multi-color emissions in the visible region endow these kinds of materials with potential applications in the field of light display systems, lasers, optoelectronic devices, and MRI contrast agents.