Sonochemical synthesis of luminescent Nd2O3 nanoparticles and optimization of NIR luminescence through precursor selection and annealing process

Abstract

A novel approach to synthesize neodymium oxide nanoparticles with enhanced emission at 1056 nm, utilizing a bioreduction-sonochemical process using tannic acid is presented. The precursors and postprocessing techniques were systematically investigated to improve light emission due to transitions among the inter-electronic energy levels associated with Nd³⁺. An extensive analysis was performed on the characteristics presented by the phosphors obtained using various precursor reactives including Nd(NO₃)₃, NdCl₃, NaOH, KOH, and different annealing treatments. TEM micrographs revealed finely tuned nanoparticles, in the range of 5–60 nm in diameter, enveloped in tannic acid residues; consequently, agglomerations of nanoparticles between 60 and 170 nm were self-assembled measured by DLS. PXRD and Raman spectroscopy confirmed the formation of Nd₂O₃, along with subproducts such as NaNO₃, KNO₃, NaCl, KCl, and distinctive surface groups, depending on the specific synthesis process studied. Significantly, luminescence measurements demonstrated a remarkable enhancement in signal intensity and quality. To avoid luminescence quench, anneal treatment was used; however, the optimization of the annealing processes was achieved through TGA studies. A self-assembly mechanism is proposed to elucidate the formation process of these neodymium oxide nanoparticles.