Microwave-induced plasma vaporization for manufacturing PbO–metal nanocomposites with metal-dependent optical functionality at sub-percent metal loadings

Metal–oxide nanocomposites capable of exhibiting strong optical functionality at ultralow metal loadings are attractive for energy harvesting, photonic, and optoelectronic applications. Here, we report the single-step fabrication of ligand-free PbO–metal nanocomposites by microwave-induced plasma vaporization (MIPV) in ambient air. The resulting nanocomposites exhibit metal-dependent optical properties. The process employs Pb-sheathed core–shell metallic precursors with Au, Ag, or Cu cores. A self-sustained plasma–surface feedback mechanism enables multicomponent plasma-assisted vaporization of Pb and the core metal within a common discharge region, despite their markedly different vaporization characteristics. Subsequent gas-phase oxidation and rapid non-equilibrium condensation produce PbO–M (M = Au, Ag, or Cu) nanocomposites with mean primary-particle sizes of 3.4–4.5 nm. Combined structural and compositional characterization, together with Pb–O thermodynamic data, supports a core–shell model for the PbO–M nanoparticles. This model comprises a crystalline β-PbO core associated with metallic nanodomains and a more oxidized, Pb⁴⁺-rich outer region. Despite extremely low metal contents (0.27–0.68 at%), the nanocomposites form macroscopically uniform coatings on quartz with pronounced metal-dependent colours and optical responses, without spectrally resolved localized surface plasmon resonance (LSPR) maxima. PbO–Au containing only 0.68 at% Au displays the largest apparent band-gap increase (+0.29 eV) and the strongest chromaticity shift (ΔE = 59), although Au remains undetectable by XPS and XRD. Across the three PbO–M compositions, the metal-dependent optical changes and structural evidence of intimate metal–oxide contact are consistent with a contribution from interfacial electronic interactions to the optical response. The results establish a single-step synthesis route toward optically functional oxide–metal nanocomposites, demonstrating that strong optical functionality can be achieved at metal concentrations below 1 at%. More broadly, MIPV provides a basis for developing scalable production of functional nanostructured materials under ambient-air conditions with reduced metal consumption.