Abstract:Lutetium oxide nanocrystals codoped with Tm³⁺ and Yb³⁺ were synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitant. Effects of the Tm³⁺, Yb³⁺ molar fractions and calcination temperature on the structural and upconversion luminescent properties of the Lu₂O₃ nanocrystals were investigated. The XRD results show that all the prepared nanocrystals can be readily indexed to pure cubic phase of Lu₂O₃ and indicate good crystallinity. The experimental results show that concentration quenching occurs when the mole fraction of Tm³⁺ is above 0.2%. The optimal Tm³⁺ and Yb³⁺ doped molar fractions are 0.2% and 2%, respectively. The strong blue (490 nm) and the weak red (653 nm) emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the ¹G₄→³H₆ and ¹G₄→³F₄ transitions of Tm³⁺, respectively. Power-dependent study reveals that the ¹G₄ levels of Tm³⁺ can be populated by three-step energy transfer process. The upconversion emission intensities of 490 nm and 653 nm increase gradually with the increase of calcination temperature. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing number of OH⁻ groups and the enlarged nanocrystal size.

Key words: Lu₂O₃:Yb³⁺,Tm³⁺ nanocrystal; co-precipitation method; upconversion luminescence