Synthesis of Y2O3:Bi3+,Eu3+ nanosheets from layered yttrium hydroxide precursor and their photoluminescence properties

Abstract

We produced Y₂O₃:Bi³⁺,Eu³⁺ nanosheets by calcining layered yttrium hydroxide (LYH) precursor nanosheets at 800 °C for 2 h. The precursor nanosheets were synthesized from metallic chlorides dissolved in methanol, via a solvothermal reaction at 200 °C for 2.5 h. X-ray diffraction and transmission electron microscopy revealed that the LYH nanosheets were composed of crystallites with a uniform crystallographic orientation. Their sheet-like morphology and single-crystal nature remained after calcination, while the thickness of the nanosheets decreased. Their excitation spectrum was monitored at the 612 nm emission wavelength, corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺, and featured a broad band at 332 nm that was attributed to the 6s² → 6s6p transition of Bi³⁺. The Y₂O₃:Bi³⁺,Eu³⁺ nanosheets therefore exhibited red emission from Eu³⁺ via energy transfer from Bi³⁺ to Eu³⁺ following near-UV excitation of Bi³⁺. The photoluminescence (PL) properties of the calcined samples were investigated with various concentrations of Bi³⁺ in Y₂O₃ nanosheets codoped with 2 at% Eu³⁺. The highest PL quantum yield was 23% at a Bi³⁺ concentration of 0.2 at%. The PL lifetimes of the calcined samples decreased with increasing Bi³⁺ concentration due to concentration quenching. The PL intensity increased over time under continuous excitation, which might be attributable to the photooxidation of Bi following its reduction by polyethyleneimine or methanol during the LYH synthesis.