Synthesis of Y₂O₃:Bi³⁺,Yb³⁺ nanosheets from layered yttrium hydroxide precursor and their photoluminescence properties

Y₂O₃:Bi³⁺,Yb³⁺ fluorescent nanosheets were prepared through calcining solvothermally synthesized layered yttrium hydroxide precursors at 600-1200 °C. X-ray diffraction (XRD) and transmission electron microscope (TEM) images confirmed that the nanosheets were polycrystalline with uniform crystallographic orientation. TEM images also confirmed that the nanosheet structure was maintained after calcination at temperatures up to 1000 °C. Atomic force microscope (AFM) images revealed that the Y₂O₃:Bi³⁺,Yb³⁺ nanosheets had thicknesses of 10-30 nm. The photoluminescence excitation (PLE) spectrum featured a broad band at 332 nm corresponding to the ¹S₀ → ³P₁ transition of Bi³⁺. The emission spectrum featured a peak at 976 nm corresponding to the ²F_5/2 → ²F_7/2 transition of Yb³⁺. The photoluminescence (PL) intensity and PL lifetime increased with increasing calcination temperature, because of the improved crystallinity of Y₂O₃:Bi³⁺,Yb³⁺. The photostability of the nanosheets was evaluated by measuring the change in PL intensity under continuous irradiation by near-ultraviolet light for 2 h. The PL intensity of the nanosheets increased therein, possibly because of photooxidation by ambient oxygen of bismuth or ytterbium ions that were reduced during the solvothermal reaction.