Rapid Microwave-Assisted Synthesis of Morphology-Controlled Luminescent Lanthanide-Doped Gd2O2S Nanostructures

Abstract

Gadolinium oxysulfide (Gd₂O₂S) is an attractive material of demonstrated suitability for a variety of imaging applications, leveraging its magnetic, scintillating, and luminescent properties, particularly when doped with optically active lanthanide ions (Ln³⁺). For many of these applications, control over size and morphology at the nanoscale are crucial. This study demonstrates the rapid microwave-assisted synthesis of colloidal Ln₂O₂S (Ln = Gd and dopants Yb, Er, Tb) nanostructures in as little as 20 min. Structural characterization using X-ray diffraction analysis (XRD), Raman spectroscopy, as well as transmission electron microscopy (TEM), including elemental mapping via energy dispersive X-ray spectroscopy (EDS), unveiled the key role of elemental sulphur (S₈) in the reaction mixtures for materials growth. By systematically varying the Ln-to-S ratio from 1:0.5 to 1:15, controlled morphologies ranging from triangular nanoplatelets to berry- and flower-like shapes were achieved. Doping with Er³⁺/Yb³⁺ endowed the nano-triangles with upconverting and near-infrared emitting properties. Tb³⁺-doped Gd₂O₂S exhibited the characteristic green Tb³⁺ emission under UV excitation, while also showing X-ray excited optical luminescence (XEOL), rendering the material interesting as potential nano-scintillator.