Sonochemical synthesis of highly luminescent Ln₂O₃:Eu³⁺ (Y, La, Gd) nanocrystals

Sonication of Ln(CH₃COO)₃·H₂O, Eu(CH₃COO)₃·H₂O and NaOH dissolved in the ionic liquid-butyl-3-methylimidazolium bis(trifluoromethane)sulfonylamide lead to Ln(OH)₃:Eu (Ln: Gd, La, Y) nanoparticles. Subsequent calcination at 800 °C for 3 h allowed to obtain Ln₂O₃:Eu nanopowders. Gd₂O₃ and Y₂O₃ were obtained in the C-type lanthanide sequioxide structure, whereas La₂O₃ crystallized in the A-type. Structure, morphology, and luminescent properties of the nano-oxides were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), dispersive X-ray (EDX), and photoluminescence (PL). SEM studies revealed that the synthesized Gd₂O₃:Eu, La₂O₃:Eu, and Y₂O₃:Eu formed nano-spindle, -sheets, and -rods in shape, respectively. The nanoscale materials show very efficient red emission due to the intraconfigurational f–f transitions of Eu³⁺. The quantum yields for Ln₂O₃:Eu (5%) were determined to be 4.2% for Ln=Gd, 13.8% for Ln=Y and 5.2% for Ln=La. The asymmetric ratio I₀₂/I₀₁ of Eu³⁺ varies from 5.3 for Gd₂O₃, to 5.6 for Y₂O₃ to 6.5 for La₂O₃, which increased the color chromaticity. - Highlights: Ln₂O₃:Eu (Ln: Gd, La, Y) nanoparticles have been obtained by sonicating a solution of rare earth acetates and NaOH in the ionic liquid [C₄mim][Tf₂N] and subsequent calcination of the material at 800 °C for 3 h. This method, in general, is simple, novel, feasible, templateless, and surfactant-free. Raising the Eu³⁺ concentration from 5% to 15% causes a decrease in the emission intensity in the 450–550 nm spectral range together with a decrease in lifetimes from 1.06 to 0.69 ms and quantum yield from 4.24% to 0.48%. Furthermore, using different host materials when the concentration of activator is kept unchanged (Eu³⁺ 5%) leads to variations in the asymmetric ratio from 6.5 La₂O₃:Eu (5%) (A type) to 5.6 for Y₂O₃:Eu (5%) and 5.3 for Gd₂O₃ (C type) and increased color chromaticity for the C-type materials. Quantum yields (QY) range from 4.24% for Gd₂O₃:Eu (5%) to 0.48% for Gd₂O₃:Eu (15%), and are 14% for Y₂O₃: Eu³⁺ (5%), and 5.17% for La₂O₃:Eu³⁺ (5%).