Uniform Lu2O3 hollow microspheres: template-directed synthesis and bright white up-conversion luminescence properties

Abstract

Well-dispersed, uniform Lu₂O₃ hollow microspheres have been successfully fabricated via a urea-based precipitation method in the presence of colloidal PS microspheres as templates, followed by subsequent heat treatment. The structure, morphology, formation process, and fluorescent properties are well investigated using various techniques. The results indicate that the hollow microspheres can be well indexed to the cubic Lu₂O₃ phase. The hollow Lu₂O₃ microspheres with a uniform diameter of about 2.2 μm maintain the spherical morphology and good dispersion of the PS spheres template. The shell of the hollow microspheres consists of numerous nanocrystals with the thickness of approximately 20 nm. Moreover, the possible formation mechanism of evolution from the PS spheres to the amorphous precursor and to the final hollow Lu₂O₃ microspheres has also been proposed. Under 980 nm laser diode excitation, Lu₂O₃:Yb³⁺/Tm³⁺, Lu₂O₃:Er³⁺ and Lu₂O₃:Yb³⁺/Er³⁺ products are mainly dominated by blue, green and red light emissions, respectively. The ratio of the intensity of green luminescence to that of red luminescence decreases with an increase of the concentration of Yb³⁺ in Lu₂O₃:Er³⁺ samples. Furthermore, the UC white light was successfully obtained in the Lu₂O₃:Yb³⁺/Er³⁺/Tm³⁺ system by adjusting the relative doping concentration of Yb³⁺, Er³⁺ and Tm³⁺. The obtained UC white light has CIE-x = 0.3478 and CIE-y = 0.3143, which are very close to the standard equal energy white light illuminate (x = 0.33, y = 0.33). Because of abundant luminescent colors from RGB to white in Lu₂O₃:Yb³⁺/Er³⁺/Tm³⁺ samples under 980 nm laser diode (LD) excitation, they can potentially be used as fluorophores in the fields of color displays, backlights, UC lasers, photonics, and biomedicine.