Synthesis, optical characterization, and antimicrobial applications of gold-coated Gd₂O₃:Eu³⁺ nanostructures

This study reports the synthesis and characterization of Eu³⁺-doped gadolinium oxide (Gd₂O₃:Eu³⁺) nanomaterials and their surface-modified counterparts coated with gold nanoparticles (Au NPs). A comprehensive suite of techniques, including thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), UV-Vis absorption spectroscopy, zeta potential measurements, X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence were used to analysis and evaluate the synthesized samples. The SEM, TEM and XRD results revealed the successful formation of cubic-phase Gd₂O₃:Eu³⁺ with uniform spherical morphology (∼80 nm) and the homogeneous deposition of sub 10 nm Au NPs on their surfaces. The photoluminescence spectra clearly displayed the characteristic Eu³⁺ emission transitions (⁵D₀ → ⁷F _j , j = 0-4), confirming effective doping. The introduction of Au NPs induced a surface plasmon resonance effect, which significantly enhanced the antibacterial efficacy of the nanocomposite. This was quantitatively demonstrated against a panel of clinically relevant Gram-negative and Gram-positive bacterial strains, as well as the fungal pathogen Candida albicans (Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Klebsiella pneumoniae ATCC 70060, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 14053). The Au-coated Gd₂O₃:Eu³⁺ samples exhibited significantly enhanced bactericidal efficiency compared to the uncoated ones. Our findings underscore the strategic advantages of coupling lanthanide luminescence with noble metal plasmonics, paving the way for a novel class of multifunctional nanomaterials with potent applications in antimicrobial therapy and biomedical diagnostics.