Polyethylene glycol assisted facile sol-gel synthesis of lanthanum oxide nanoparticles: structural characterisation and photoluminescence studies

In this study, lanthanum oxide nanoparticles (La₂O₃ NPs) synthesised via the facile sol-gel method, using a solution of micro-sized lanthanum oxide powders containing 20% nitric acid and high molecular weight polyethylene glycol (PEG). The as synthesised La₂O₃ NPs were then characterized using X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), energy-dispersive X-ray (EDS) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy. Our findings indicated that the concentration of PEG strongly influences the particle size and the lattice strain of the La₂O₃ NPs. A single phase hexagonal crystal structure was confirmed via XRD studies with lattice constants, a = b = 0.3973 nm and c = 0.6129 nm. The average crystallite size and lattice strains estimated were in the range of approximately 25–28 nm and 0.0050–0.0055 respectively. The incremental nature of the crystallinity and lattice strains of the NPs was observed with the subsequent enhancement of PEG-contents, while the average particle size was reduced. The average particle size of La₂O₃ NPs estimated from ESEM imaging was consistent with that obtained from the XRD data. The photoluminescence spectra revealed a strong emission band located at a wavelength of 365 nm (typical green band) for all La₂O₃NPsamples. This is ascribed to the recombination of delocalized electrons around the conduction band with a single charged state of a surface oxygen vacancy.