Synthesis, photoluminescence, and photostability of Y₂O₃:Bi³⁺,Eu³⁺ nanosheets

Y₂O₃:Bi³⁺,Eu³⁺ nanosheets are produced by calcinating hydrothermally synthesized precursor nanosheets. Transmission electron microscope observation confirms that the sheet-like morphology remains unchanged after calcination at either 600 or 800 °C for 2 h. The excitation spectrum monitored at 612 nm emission corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ has a broad band at 331 nm that is attributed to the 6s²→6s6p transition of Bi³⁺. The Y₂O₃:Bi³⁺,Eu³⁺ nanosheets therefore exhibit the red emission of Eu³⁺ through energy transfer from Bi³⁺ to Eu³⁺ following excitation of Bi³⁺. The photostability of Y₂O₃:Bi³⁺,Eu³⁺ nanosheets is evaluated from their change in photoluminescence intensity during continuous excitation. The photoluminescence intensity of Y₂O₃:Bi³⁺,Eu³⁺ nanosheets decreases to more than 90% of the initial intensity soon after irradiation begins, and then the photoluminescence intensity gradually recovers. In contrast, the photoluminescence intensity of YVO₄:Bi³⁺,Eu³⁺ nanoparticles decreases to 53.6% of the initial intensity during excitation. These results indicate that Y₂O₃:Bi³⁺,Eu³⁺ nanosheets have higher photostability than YVO₄:Bi³⁺,Eu³⁺ nanoparticles.