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